[Federal Register Volume 63, Number 68 (Thursday, April 9, 1998)]
[Proposed Rules]
[Pages 17492-17627]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-8756]



[[Page 17491]]

_______________________________________________________________________

Part II





Department of Labor





_______________________________________________________________________



Mine Safety and Health Administration



_______________________________________________________________________



30 CFR Parts 72 and 75



Diesel Particulate Matter Exposure of Underground Coal Miners; Proposed 
Rule

  Federal Register / Vol. 63, No. 68 / Thursday, April 9, 1998 / 
Proposed Rules  

[[Page 17492]]



DEPARTMENT OF LABOR

Mine Safety and Health Administration

30 CFR Parts 72 and 75

RIN 1219-AA74


Diesel Particulate Matter Exposure of Underground Coal Miners

AGENCY: Mine Safety and Health Administration (MSHA), Labor.

ACTION: Proposed rule.

-----------------------------------------------------------------------

SUMMARY: This proposed rule would establish new health standards for 
underground coal mines that use equipment powered by diesel engines.
    This proposal is designed to reduce the risks to underground coal 
miners of serious health hazards that are associated with exposure to 
high concentrations of diesel particulate matter (dpm). DPM is a very 
small particle in diesel exhaust. Underground miners are exposed to far 
higher concentrations of this fine particulate than any other group of 
workers. The best available evidence indicates that such high exposures 
put these miners at excess risk of a variety of adverse health effects, 
including lung cancer.
    The proposed rule for underground coal mines would require that 
mine operators install and maintain high-efficiency filtration systems 
on certain types of diesel-powered equipment. Underground coal mine 
operators would also be required to train miners about the hazards of 
dpm exposure.
    By separate notice, MSHA will soon propose a rule to reduce dpm 
exposures in underground metal and nonmetal mines.

DATES: Comments must be received on or before August 7, 1998. Submit 
written comments on the information collection requirements by August 
7, 1998.

ADDRESSES: Comments on the proposed rule may be transmitted by 
electronic mail, fax, or mail, or dropped off in person at any MSHA 
office. Comments by electronic mail must be clearly identified as such 
and sent to this e-mail address: [email protected]. Comments by fax 
must be clearly identified as such and sent to: MSHA, Office of 
Standards, Regulations, and Variances, 703-235-5551. Send mail comments 
to: MSHA, Office of Standards, Regulations, and Variances, Room 631, 
4015 Wilson Boulevard, Arlington, VA 22203-1984, or any MSHA district 
or field office. The Agency will have copies of the proposal available 
for review by the mining community at each district and field office 
location, at the National Mine Safety and Health Academy, and at each 
technical support center. The document will also be available for loan 
to interested members of the public on an as needed basis. MSHA will 
also accept written comments from the mining community at the field and 
district offices, at the National Mine Safety and Health Academy, and 
at technical support centers. These comments will become a part of the 
official rulemaking record. Interested persons are encouraged to 
supplement written comments with computer files or disks; please 
contact the Agency with any questions about format.
    Written comments on the information collection requirements may be 
submitted directly to the Office of Information and Regulatory Affairs, 
New Executive Office Building, 725 17th Street, NW., Rm. 10235, 
Washington, D.C. 20503, Attn: Desk Officer for MSHA.

FOR FURTHER INFORMATION CONTACT: Patricia W. Silvey, Director; Office 
of Standards, Regulations, and Variances; MSHA; 703-235-1910.

SUPPLEMENTARY INFORMATION:

I. Questions and Answers About This Proposed Rule

(A) General Information of Interest to the Entire Mining Community

(1) What Actions Are Being Proposed?
    MSHA has determined that action is essential to reduce the exposure 
of miners to a harmful substance emitted from diesel engines--and that 
regulations are needed for this purpose in underground mines. This 
notice proposes requirements for underground coal mines; by separate 
notice, MSHA will soon propose a rule for underground metal and 
nonmetal mines.
    The harmful substance is known as diesel particulate matter (dpm). 
As shown in Figure I-1, average concentrations of dpm observed in 
dieselized underground mines are up to 200 times as high as average 
environmental exposures in the most heavily polluted urban areas and up 
to 10 times as high as median exposures estimated for the most heavily 
exposed workers in other occupational groups. The best available 
evidence indicates that exposure to such high concentrations of dpm 
puts miners at significantly increased risk of incurring serious health 
problems, including lung cancer.
    The goal of the proposed rule is to reduce underground miner 
exposures to attain the highest degree of safety and health protection 
that is feasible.

BILLING CODE 4510-43-P 

[[Page 17493]]

[GRAPHIC] [TIFF OMITTED] TP09AP98.000



BILLING CODE 4510-43-C

[[Page 17494]]

    In underground coal mines, MSHA's proposal would require the 
installation of high-efficiency filters on diesel-powered equipment to 
trap diesel particles before they enter the mine atmosphere. Following 
18 months of education and technical assistance by MSHA after the rule 
is issued, filters would first have to be installed on permissible 
diesel-powered equipment. By the end of the following year (i.e., 30 
months after the rule is issued), such filters would also have to be 
installed on any heavy-duty outby equipment. No specific concentration 
limit would be established in this sector; the proposed rule would 
require that filters be installed and properly maintained. Miner 
awareness training on the hazards of dpm would also be required.
    MSHA is not at this time proposing a rule applicable to surface 
mines. As illustrated in Figure I-1, in certain situations the 
concentrations of dpm at surface mines may exceed those to which rail, 
trucking and dock workers are exposed. Problem areas identified in this 
sector include production areas where miners work in the open air in 
close proximity to loader-haulers and trucks powered by older, out-of-
tune diesel engines, or other confined spaces where diesel engines are 
running. The Agency believes, however, that these problems are 
currently limited and readily controlled through education and 
technical assistance. Using tailpipe exhaust extenders, or directing 
the exhaust across the engine fan, can dilute the high concentrations 
of dpm that might otherwise occur in areas immediately adjacent to 
mining equipment. Surface mine operators using or planning to switch to 
environmentally conditioned cabs to reduce noise exposure to equipment 
operators might also be able to incorporate filtration features that 
would protect these miners from high dpm concentrations as well. 
Completing already planned purchases of new trucks containing cleaner 
engines may also help reduce the isolated instances of high dpm 
concentrations at such mines.
    The Agency would like to emphasize, however, that surface miners 
are entitled to the same level of protection as other miners, and that 
the Agency's risk assessment indicates that even short-term exposures 
to concentrations of dpm like those observed may result in serious 
health problems. Accordingly, in addition to providing education and 
technical assistance to surface mines, the Agency will also continue to 
evaluate the hazards of diesel particulate exposure at surface mines 
and will take any necessary action, including regulatory action if 
warranted, to help the mining community minimize any hazards.
(2) How Is This Notice of Proposed Rulemaking Organized?
    The proposed rule for underground coal mines can be found at the 
end of this Notice. The remainder of this preamble to the proposed rule 
(Supplementary Information) describes the Agency's rationale for what 
is being proposed.
    Part I consists of twelve ``Questions and Answers.'' The Agency 
hopes they will provide most of the information you will need to 
formulate your comments. The first ten of these (Section A) cover 
general topics. The last two (Section B) contain additional detail 
about the proposed rule for the underground coal sector, and a 
discussion of two alternatives on which the Agency would particularly 
like additional comment.
    Part II provides some background information on nine topics that 
are relevant to this rulemaking. In order, the topics covered are: (1) 
the role of diesel-powered equipment in mining; (2) the composition of 
diesel exhaust and diesel particulate; (3) measurement of diesel 
particulate; (4) reducing soot at the source--EPA regulation of diesel 
engine design; (5) limiting the public's exposure to soot--EPA ambient 
air quality standards; (6) controlling diesel particulate emissions in 
mining--a toolbox; (7) existing mining standards that limit miner 
exposure to occupational diesel particulate emissions; (8) how other 
jurisdictions are restricting occupational exposure to diesel soot; and 
(9) MSHA's initiative to limit miner exposure to diesel particulate--
the history of this rulemaking and related actions. Appended to the end 
of this document is a copy of an MSHA publication, ``Practical Ways to 
Reduce Exposure to Diesel Exhaust in Mining--A Toolbox,'' which 
includes additional information on methods for controlling dpm, and a 
glossary of terms.
    Part III is the Agency's risk assessment. The first section 
presents the Agency's data on current dpm exposure levels in each 
sector of the mining industry. The second section reviews the 
scientific evidence on the risks associated with exposure to dpm. The 
third section evaluates this evidence in light of the Mine Act's 
statutory criteria.
    Part IV is a detailed section-by-section explanation and discussion 
of the elements of the proposed rule.
    Part V is an analysis of whether the proposed rule meets the 
Agency's statutory obligation to attain the highest degree of safety or 
health protection for miners, with feasibility a consideration. This 
part begins with a review of the law and a profile of the coal 
industry's economic position. This next part explores the extent to 
which the proposed rule is expected to impact existing concentration 
levels, reviews significant alternatives that might provide more 
protection than the rule being proposed but which have not been adopted 
by the Agency due to feasibility concerns, and then discusses the 
feasibility of the rule being proposed. Part V draws upon a computer 
simulation of how the proposed rule in underground coal mines is 
expected to impact dpm concentrations; accordingly, an Appendix to this 
discussion provides information about the simulation methodology. The 
simulation method, which can be performed using a standard spreadsheet 
program, can be used to model conditions and control impacts in any 
underground mine; copies of this model are available to the mining 
community from MSHA.
    Part VI reviews several impact analyses which the Agency is 
required to provide in connection with a proposed rulemaking. This 
information summarizes a more complete discussion that can be found in 
the Agency's Preliminary Regulatory Economic Analysis (PREA). Copies of 
this document are available from the Agency and will be posted on the 
MSHA Web site (http://www.msha.gov).
    Part VII is a complete list of publications referenced by the 
Agency in the preamble.
(3) What Evidence Does MSHA Have That Current Underground 
Concentrations of DPM Need To Be Controlled?
    The best available evidence MSHA has at this time is that miners 
subjected to an occupational lifetime of dpm exposure at concentrations 
we presently find in underground mines face a significant risk of 
material impairment to their health.
    It has been recognized for some time that miners working in close 
contact with diesel emissions can suffer acute reactions--e.g., eye, 
nose and throat irritations--but questions have persisted as to what 
component of the emissions was causing these problems, whether exposure 
increased the risk of other adverse health effects, and the level of 
exposure creating health consequences.
    In recent years, there has been growing evidence that it is the 
very small respirable particles in diesel exhaust (dpm) that trigger a 
variety of

[[Page 17495]]

adverse health outcomes. These particles are generally less than one-
millionth of a meter in diameter (submicron), and so can readily 
penetrate into the deepest recesses of the lung. They consist of a core 
of the element carbon, with up to 1,800 different organic compounds 
adsorbed onto the core, and some sulfates as well. (A diagram of dpm 
can be found in part II of this preamble--see Figure II-3). The 
physiological mechanism by which dpm triggers particular health 
outcomes is not yet known. One or more of the organic substances 
adsorbed onto the surface of the core of the particles may be 
responsible for some health effects, since these include many known or 
suspected mutagens and carcinogens. But some or all of the health 
effects might also be triggered by the physical properties of these 
tiny particles, since some of the health effects are observed with high 
exposures to any ``fine particulate,'' whether the particle comes from 
diesel exhaust or another source.
    There is clear evidence that exposure to high concentrations of dpm 
can result in a variety of serious health effects. These health effects 
include: (i) sensory irritations and respiratory symptoms serious 
enough to distract or disable miners; (ii) death from cardiovascular, 
cardiopulmonary, or respiratory causes; and (iii) lung cancer.
    By way of example of the non-cancer effects, there is evidence that 
workers exposed to diesel exhaust during a single shift suffer material 
impairment of lung capacity. A control group of unexposed workers 
showed no such impairment, and workers exposed to filtered diesel 
exhaust (i.e., exhaust from which much of the dpm has been removed) 
experienced, on average, only about half as much impairment. Moreover, 
there are a number of studies quantifying significant adverse health 
effects--as measured by lost work days, hospitalization and increased 
mortality rates--suffered by the general public when exposed to 
concentrations of fine particulate matter like dpm far lower than 
concentrations to which some miners are exposed. The evidence from 
these fine particulate studies was the basis for recent rulemaking by 
the Environmental Protection Agency to further restrict the exposure of 
the general public to fine particulates, and the evidence was given 
very widespread and close scrutiny before that action was made final. 
Of particular interest to the mining community is that these fine 
particulate studies indicate that those who have pre-existing pulmonary 
problems are particularly at risk. Many individual miners in fact have 
such pulmonary problems, and the mining population as a whole is known 
to have such conditions at a higher rate than the general public.
    Although no epidemiological study is flawless, numerous 
epidemiological studies have shown that long term exposure to diesel 
exhaust in a variety of occupational circumstances is associated with 
an increased risk of lung cancer. With only rare exceptions, involving 
relatively few workers and/or observation periods too short to reliably 
detect excess cancer risk, the human studies have consistently shown a 
greater risk of lung cancer among workers exposed to dpm than among 
comparable unexposed workers. When results from the human studies are 
combined, the risk is estimated to be 30-40 percent greater among 
exposed workers, if all other factors (such as smoking habits) are held 
constant. The consistency of the human study results, supported by 
experimental data establishing the plausibility of a causal connection, 
provides strong evidence that chronic dpm exposure at high levels 
significantly increases the risk of lung cancer in humans.
    Moreover, all of the human occupational studies indicating an 
increased frequency of lung cancer among workers exposed to dpm 
involved average exposure levels estimated to be far below the levels 
observed in underground mines. As noted in Part III, MSHA views 
extrapolations from animal experiments as subordinate to results 
obtained from human studies. However, it is noteworthy that dpm 
exposure levels recorded in some underground mines have been within the 
exposure range that produced tumors in rats.
    Based on the scientific data available in 1988, the National 
Institute for Occupational Safety and Health (NIOSH) identified dpm as 
a probable or potential human carcinogen and recommended that it be 
controlled. Other organizations have made similar recommendations.
    MSHA carefully evaluated all the evidence available in light of the 
requirements of the Mine Act. Based on this evaluation, MSHA has 
reached several conclusions:
    (1) The best available evidence is that the health effects 
associated with exposure to dpm can materially impair miner health or 
functional capacity.
    (2) At levels of exposure currently observed in underground mining, 
many miners are presently at significant risk of incurring these 
material impairments over a working lifetime.
    (3) The reduction in dpm exposures that is expected to result from 
implementation of the proposed rule for underground coal mines would 
substantially reduce the significant risks currently faced by 
underground coal miners exposed to dpm.
    MSHA had its risk assessment independently peer reviewed. The risk 
assessment presented here incorporates revisions made in accordance 
with the reviewers recommendations. The reviewers stated that:

* * * principles for identifying evidence and characterizing risk 
are thoughtfully set out. The scope of the document is carefully 
described, addressing potential concerns about the scope of 
coverage. Reference citations are adequate and up to date. The 
document is written in a balanced fashion, addressing uncertainties 
and asking for additional information and comments as appropriate. 
(Samet and Burke, Nov. 1997).

    The proposed rule would reduce the concentration of one type of 
fine particulate in underground coal mines--that from diesel 
emissions--but would not explicitly control miner exposure to other 
fine airborne particulates present underground. In light of the 
evidence presented in the Agency's risk assessment on the risks that 
fine particulates in general may pose to the mining population, MSHA 
would welcome comments as to whether the Agency should also consider 
restricting the exposure of underground coal miners to all fine 
particulates, regardless of the source.
(4) Aren't NIOSH and the NCI Working on a Study That Will Provide 
Critical Information? Why Proceed Before the Evidence Is Complete?
    NIOSH and the National Cancer Institute (NCI) are collaborating on 
a cancer mortality study that will provide additional information about 
the relationship between dpm exposure levels and disease outcomes, and 
about which components of dpm may be responsible for the observed 
health effects. The study is projected to take about seven years. The 
protocol for the study was recently finalized.
    The information the study is expected to generate will be a 
valuable addition to the scientific evidence on this topic. But given 
its conclusions about currently available evidence, MSHA believes the 
Agency needs to take action now to protect miners' health. Moreover, as 
noted by the Supreme Court in an important case on risk involving the 
Occupational Safety and Health Administration, the need to evaluate 
risk does not mean an agency is placed into a ``mathematical 
straightjacket.'' Industrial Union Department, AFL-CIO v. American 
Petroleum Institute, 448 U.S. 607, 100 S.Ct. 2844 (1980). The Court 
noted that

[[Page 17496]]

when regulating on the edge of scientific knowledge, absolute 
scientific certainty may not be possible, and ``so long as they are 
supported by a body of reputable scientific thought, the Agency is free 
to use conservative assumptions in interpreting the data * * * risking 
error on the side of overprotection rather than underprotection.'' (Id. 
at 656). This advice has special significance for the mining community, 
because a singular historical factor behind the enactment of the 
current Mine Act was the slowness in coming to grips with the harmful 
effects of other respirable dust (coal dust).
    It is worth noting that while the cohort selected for the NIOSH/NCI 
study consists of underground miners (specifically, underground metal 
and nonmetal miners), this choice is in no way linked to MSHA's 
regulatory framework or to miners in particular. This cohort was 
selected for the study because it provides the best population for 
scientists to study. For example, one part of the study would compare 
the health experiences of miners who have worked underground in mines 
with long histories of diesel use with the health experiences of 
similar miners who work in surface areas where exposure is 
significantly lower. Since the general health of these two groups is 
very similar, this will help researchers to quantify the impacts of 
diesel exposure. No other population is as easy to study for this 
purpose. But as with any such epidemiological study, the insights 
gained are not limited to the specific population used in the study. 
Rather, the study will provide information about the relationship 
between exposure and health effects that will be useful in assessing 
the risks to any group of workers in a dieselized industry.
(5) What are the Impacts of the Proposed Rule?
    Costs. Tables I-1 and I-2 provide cost information. Some 
explanation is necessary.
    Costs consist of two components: ``initial'' costs (e.g., capital 
costs for equipment, or the one-time costs of developing a procedure), 
which are then amortized over a period of years in accordance with a 
standardized formula to provide an ``annualized'' cost; and ``annual'' 
costs that occur every year (e.g., maintenance or training costs). 
Adding together the ``annualized'' initial costs and the ``annual'' 
costs provides the per year costs for the rule.
    It should be noted that in amortizing the initial costs, a net 
present value factor was applied to certain costs: those associated 
with provisions where mine operators do not have to make capital 
expenditures until some period of time after the effective date. 
Detailed information on this point is contained in the Agency's 
Preliminary Regulatory Economic Analysis (PREA), as are the Agency's 
cost assumptions.
    The costs per year to the underground coal industry are about $10 
million. Diesel equipment manufacturers would have a yearly cost 
increase of about $14,000.
    The Agency spent considerable time developing its cost assumptions, 
which are discussed in detail in the Agency's PREA, and would encourage 
the mining community to provide detailed comments in this regard so as 
to ensure these cost estimates are as accurate as possible.

                                                 Table I-1.--Compliance Costs for Underground Coal Mines                                                
                                                                    [Dollars + 1,000]                                                                   
                                                                                                                                                        
                                                  Large mines (20)              Small mines (<20)                      Total mines           
                                             -----------------------------------------------------------------------------------------------------------
                   Detail                        Total                               Total                               Total                          
                                              [Col. B+C]  Annualized    Annual    [Col. E+F]  Annualized    Annual    [Col. H+I]  Annualized    Annual  
                                                     (A)         (B)         (C)         (D)         (E)         (F)         (G)         (H)         (I)
--------------------------------------------------------------------------------------------------------------------------------------------------------
75.1915.....................................          $9          $9          $0          $1          $1          $0         $10         $10          $0
72.500(a)...................................       4,910         457       4,453          95          22          73       5,005         479       4,526
72.500(b)...................................       4,768       1,335       3,433          22          12          10       4,790       1,347       3,443
72.510......................................         185           0         185           1           0           1         186           0         186
75.371qq and 75.370.........................           1           1           0           1           1           0           2           2           0
                                             -----------------------------------------------------------------------------------------------------------
    Total...................................       9,873       1,802       8,071         120          36          84       9,993       1,838       8,155
--------------------------------------------------------------------------------------------------------------------------------------------------------


             Table I-2.--Compliance Costs for Manufacturers             
                            [Dollars x 1,000]                           
------------------------------------------------------------------------
                                                   Manufacturers        
                                         -------------------------------
                 Detail                     Total                       
                                            [Col.   Annualized   Annual 
                                            B+C]                        
------------------------------------------------------------------------
                                              (A)         (B)         (C)
Part 36.................................      $14         $14        $0 
                                         -------------------------------
    Total...............................      $14         $14        $0 
------------------------------------------------------------------------

    As required by the Regulatory Flexibility Act, MSHA has performed a 
review of the effects of the proposed rule on ``small entities''. The 
results--including information about the average cost for mines in each 
sector with less than 500 employees and mines in each sector with less 
than 20 miners--are summarized in response to Question 7.

Paperwork

    Tables I-3 and I-4 show additional paperwork burden hours which the 
proposed rule would require. Only those existing or proposed regulatory 
requirements which would, as a result of this rulemaking, result in new 
burden hours, are noted. The costs for these paperwork burdens, a 
subset of the overall costs of the proposed rule, are specifically 
noted in part VII of the Agency's PREA. Each of these tables shows 
separately the burden hours on smaller mines--those with less than 20 
miners. Table I-3 shows additional paperwork burden hours for 
underground coal operators.

             Table I-3.--Underground Coal Mine Burden Hours             
------------------------------------------------------------------------
                    Detail                      Large    Small    Total 
------------------------------------------------------------------------
75.370.......................................       93        9      102
75.371.......................................      158        8      166
75.1915......................................       12        1       13
72.510.......................................      347        5      352
                                              --------------------------
    Total....................................      610       23      633
------------------------------------------------------------------------

    Table I-4 shows the additional burden hours for diesel equipment 
manufacturers. All of the manufacturer burden hours will occur once and 
not recur annually.

[[Page 17497]]



         Table I-4.--Diesel Equipment Manufacturers Burden Hours        
------------------------------------------------------------------------
                             Detail                               Total 
------------------------------------------------------------------------
Part 36........................................................      520
                                                                --------
    Total......................................................      520
------------------------------------------------------------------------

Benefits

    The proposed rule would reduce the exposure of underground miners 
to dpm, thereby reducing the risk of adverse health effects and their 
concomitant effects.
    The risks being addressed by this rulemaking arise because some 
miners are exposed to high concentrations of the very small particles 
produced by engines that burn diesel fuel. As discussed in part II of 
the preamble, diesel powered engines are used increasingly in 
underground mining operations because they permit the use of mobile 
equipment and provide a full range of power for both heavy-duty and 
light-duty operations (i.e., for production equipment and support 
equipment, respectively), while avoiding the explosive hazards 
associated with gasoline. But underground mines are confined spaces 
which, despite ventilation requirements, tend to accumulate significant 
concentrations of particles and gases--both those produced by the mine 
itself (e.g., methane gas and coal dust liberated by mining operations) 
and those produced by equipment used in the mine.
    As discussed in MSHA's risk assessment (part III of this preamble), 
the concentrations of diesel particulates to which some underground 
miners are currently exposed are significantly higher than the 
concentrations reported for other occupations involving the use of 
dieselized equipment; and at such concentrations, exposure to dpm by 
underground miners over a working lifetime is associated with an excess 
risk of a variety of adverse health effects.
    The nature of the adverse health effects associated with such 
exposures suggests the nature of the savings to be derived from 
controlling exposure. Acute reactions can result in lost production 
time for the operator and lost pay (and perhaps medical expenses) for 
the worker. Hospital care for acute breathing crises or cancer 
treatment can be expensive, result in lost income for the worker, lost 
income for family members who need to provide care and lost 
productivity for their employers, and may well involve government 
payments (e.g., Social Security disability and Medicare). Serious 
illness and death lead to long term income losses for the families 
involved, with the potential for costs from both employers (e.g., 
workers' compensation payouts, pension payouts) and society as a whole 
(e.g., government assisted aid programs).
    The information available to the Agency suggests that as exposure 
is reduced, so are the adverse health consequences. For example, data 
collected on the effects of environmental exposure to fine particulates 
suggest that reducing occupational dpm exposures by as little as 75 
g/m\3\ (roughly corresponding to a reduction of 25 g/
m\3\ in 24-hour ambient atmospheric concentration) could lead to 
significant reductions in the risk of various acute responses, 
including mortality. And chronic occupational exposure has been linked 
to an estimated 30 to 40 percent increase in the risk of lung cancer. 
All the quantitative risk models reviewed by NIOSH suggest excess risks 
of lung cancer of more than one per thousand for miners who have long-
term occupational exposures to dpm concentrations in excess of 1000 
g/m\3\, and the epidemiologically-based risk estimates suggest 
higher risks.
    Despite these quantitative indications, quantification of the 
benefits is difficult. Although increased risk of lung cancer has been 
shown to be associated with dpm exposure among exposed workers, a 
conclusive dose-response relationship upon which to base quantification 
of benefits has not been demonstrated. The Agency nevertheless intends, 
to the extent it can, to develop an appropriate analysis quantifying 
benefits in connection with the final rule.
    The Agency does not have much experience in quantifying benefits in 
the case of a proposed health standard (other than its recent proposal 
on controlling mining noise, where years of compliance data and hearing 
loss studies provide a much more complete quantitative picture than 
with dpm). MSHA therefore welcomes suggestions for the appropriate 
approach to use to quantify the benefits likely to be derived from this 
rulemaking. Please identify scientific studies, models, and/or 
assumptions suitable for estimating risk at different exposure levels, 
and data on numbers of miners exposed to different levels of dpm.
(6) Did MSHA Actively Consider Alternatives to What Is Being Proposed?
    Yes. Once MSHA determined that the evidence of risk required a 
regulatory action, the Agency considered a number of alternative 
approaches, the most significant of which are reviewed in part V of the 
preamble.
    The consideration of options proceeded in accordance with the 
requirements of section 101(a)(6)(A) of the Federal Mine Safety and 
Health Act of 1977 (the ``Mine Act''). In promulgating standards 
addressing toxic materials or harmful physical agents, the Secretary 
must promulgate standards which most adequately assure, on the basis of 
the best available evidence, that no miner will suffer material 
impairment of health over his/her working lifetime. In addition, the 
Mine Act requires that the Secretary, when promulgating mandatory 
standards pertaining to toxic materials or harmful physical agents, 
consider other factors, such as the latest scientific data in the 
field, the feasibility of the standard and experience gained under the 
Mine Act and other health and safety laws. Thus, the Mine Act requires 
that the Secretary, in promulgating a standard, attain the highest 
degree of health and safety protection for the miner, based on the 
``best available evidence,'' with feasibility a consideration.
    As a result, MSHA seriously considered a number of alternatives 
that would, if adopted as part of the proposed rule, have provided 
increased protection--and would also have significantly increased 
costs. For example, in underground coal mining, the Agency considered 
requiring filtration of all light-duty diesel-powered equipment as well 
as heavier equipment. The Agency concluded, however, that such an 
approach may not be feasible for the underground coal sector at this 
time, although it is asking for comment as to whether there are some 
types of light-duty equipment whose dpm emissions should, and could 
feasibly, be controlled.
    MSHA also considered alternatives that would have led to a 
significantly lower-cost proposal, e.g., increasing the time for mine 
operators to come into compliance. However, based on the current 
record, MSHA has tentatively concluded that such approaches would not 
be as protective as those being proposed, and that the approach 
proposed is both economically and technologically feasible. As a 
result, the Agency has not proposed to adopt these alternatives.
    MSHA also explored whether to permit the use of administrative 
controls (e.g., rotation of personnel) and personal protective 
equipment (e.g., respirators) to reduce the diesel particulate exposure 
of miners. It is generally accepted industrial hygiene practice, 
however, to eliminate or minimize hazards at the source before 
resorting to personal protective

[[Page 17498]]

equipment. Moreover, such a practice is generally not considered 
acceptable in the case of carcinogens since it merely places more 
workers at risk.
    Other alternatives the Agency considered include: establishing a 
concentration limit for dpm in this sector; requiring filters on some 
light-duty equipment; and looking at the filter and the engine as a 
package that has to meet a particular emission standard, instead of 
requiring that all engines be equipped with a high-efficiency filter. 
The Agency also spent a considerable amount of time studying whether it 
could simply propose a concentration limit for dpm in underground coal 
mines. Such an approach would provide underground coal mine operators 
with flexibility to elect any combination of engineering controls they 
wish as long as the concentration of dpm in the mine remains below a 
set level. At this point in the rulemaking process, however, the Agency 
is not confident that there is a measurement method for dpm that will 
provide accurate, consistent and verifiable results at lower 
concentration levels in underground coal mines. As discussed in detail 
in part II of this preamble, the problem arises because coal dust 
contains organic compounds that might be mistaken for dpm in the 
methods otherwise validated for use at lower dpm concentrations. The 
Agency is continuing to explore questions about the measurement of dpm 
in underground coal mines in consultation with NIOSH, and welcomes 
comment on this issue. However, at this point in the rulemaking 
process, the Agency believes that the best approach for the underground 
coal sector would be one which does not require measurement of ambient 
dpm levels to ascertain compliance or noncompliance.
    MSHA recognizes that a specification standard does not allow for 
the use of future alternative technologies that might provide the same 
or enhanced protection at the same or lower cost. MSHA welcomes comment 
as to whether and how the proposed rule can be modified to enhance its 
flexibility in this regard.
    MSHA did consider two alternative specification standards which 
would provide somewhat more flexibility for coal mine operators. 
Alternative 1 would treat the filter and engine as a package that has 
to meet a particular emission standard. Instead of requiring that all 
engines be equipped with a high-efficiency filter, this approach would 
provide some credit for the use of lower-polluting engines. Alternative 
2 would also provide credit for mine ventilation beyond that required. 
The Agency believes, however, that these alternatives may be less 
protective of miners than the alternative proposed, although it is 
seeking comment on them. More information on these two alternatives can 
be found in this part in response to Question 12.
(7) What Will the Impact Be on the Smallest Underground Coal Mines? 
What Consideration Did MSHA Give to Alternatives for the Smallest 
Mines?
    The Regulatory Flexibility Act requires MSHA and other regulatory 
agencies to conduct a review of the effects of proposed rules on small 
entities. That review is summarized here; a copy of the full review is 
included in part VI of this preamble, and in the Agency's PREA. The 
Agency encourages the mining community to provide comments on this 
analysis.
    The Small Business Administration generally considers a small 
mining entity to be one with less than 500 employees. MSHA has 
traditionally defined a small mine to be one with less than 20 miners, 
and has focused special attention on the problems experienced by such 
mines in implementing safety and health rules, e.g., the Small Mine 
Summit, held in 1996. Accordingly, MSHA has separately analyzed the 
impact of the proposed rule on mines with 500 employees or less, and 
those with less than 20 miners.
    Table I-5 summarizes MSHA's estimates of the average costs of the 
proposed rule to a small underground coal entity or small underground 
coal mine.

        Table I-5.--Average Cost per Small Underground Coal Mine        
------------------------------------------------------------------------
                                                     UG Coal    UG Coal 
                       Size                            <500       <20   
------------------------------------------------------------------------
Cost per mine.....................................    $58,000     $8,000
------------------------------------------------------------------------

    Pursuant to the Regulatory Flexibility Act, MSHA must determine 
whether the costs of the proposed rule constitute a ``significant 
impact on a substantial number of small entities.'' Pursuant to the 
Regulatory Flexibility Act, if an Agency determines that a proposed 
rule does not have such an impact, it must publish a ``certification'' 
to that effect. In such a case, no additional analysis is required (5 
U.S.C. 605).
    In evaluating whether certification is appropriate, MSHA utilized a 
``screening test,'' comparing the costs of the proposal to the revenues 
of the sector involved (only the revenues for underground coal mines 
are used in this calculation). For underground coal mines, the costs of 
the proposed rule appear to be significantly less than one percent of 
revenues--even for mines with less than 20 miners. As a result, MSHA is 
certifying that the proposed rule for underground coal mines does not 
have a ``significant impact on a substantial number of small 
entities,'' and has performed no further analyses.
    In promulgating standards, MSHA does not reduce protection for 
miners employed at small mines. But MSHA does consider the impact of 
its standards on even the smallest mines when it evaluates the 
feasibility of various alternatives. For example, a major reason why 
MSHA concluded it needed to stagger the effective dates of some of the 
requirements in the proposed rule is to ensure that it would be 
feasible for the smallest mines to have adequate time to come into 
compliance.
    Consistent with recent amendments to the Regulatory Flexibility Act 
under SBREFA (the Small Business Regulatory Enforcement Fairness Act), 
MSHA has already started considering actions it can take to minimize 
the anticipated compliance burdens of this proposed rule on smaller 
mines. For example, no equipment filtration would be required for 18 
months, and during that time, the Agency plans to provide extensive 
compliance assistance to the mining community. MSHA intends to focus 
its efforts on smaller operators in particular to provide training to 
them and technical assistance on available controls. The Agency will 
also issue a compliance guide, and continue its current efforts to 
disseminate educational materials and software. Comment is invited on 
whether compliance workshops or other such approaches would be 
valuable.
(8) Why Would the Proposed Rule Require Special Training for 
Underground Miners Exposed to Diesel Exhaust? And Why Does the Proposed 
Rule Not Address Medical Surveillance and Medical Removal Protection 
for Affected Miners?
    Training. Diesel particulate exposure has been linked to a number 
of serious health hazards, and the Agency's risk assessment indicates 
that the risks should be reduced as much as feasible. It has been the 
experience of the mining community that miners must be active and 
committed partners along with government and industry in successfully 
reducing these risks. Therefore, training miners as to workplace risks 
is a key component of mine safety and health programs. This rulemaking 
continues this approach.
    Specifically, pursuant to proposed Sec. 72.510, any underground 
coal miner ``who can reasonably be expected to be

[[Page 17499]]

exposed to diesel emissions'' would have to receive instruction in: (a) 
the health risks associated with dpm exposure; (b) in the methods used 
in the mine to control diesel particulate concentrations; (c) in 
identification of the personnel responsible for maintaining those 
controls; and (d) in actions miners must take to ensure the controls 
operate as intended. The training is to be provided annually in all 
mines using diesel-powered equipment, and is to be provided without 
charge to the miner.
    MSHA does not expect this training to be a significant new burden 
for mine operators. The training required can be provided at minimal 
cost and with minimal disruption. The proposal would not require any 
special qualifications for instructors, nor would it specify the 
minimum hours of instruction. The purpose of the proposed requirement 
is miner awareness, and MSHA believes this can be accomplished by 
operators in a variety of ways. In mines that have regular safety 
meetings before the shift begins, devoting one of those meetings to the 
topic of diesel particulate would probably be a very easy way to convey 
the necessary information. Mines not having such a regular meeting can 
schedule a ``toolbox'' talk for this purpose. MSHA will be developing 
an outline of educational material that can be used in these settings. 
Simply providing miners with a copy of MSHA's toolbox, and reviewing 
how to use it, can cover several of the training requirements.
    Operators may choose to include required dpm training under part 48 
training as an additional topic. Part 48 training plans, however, must 
be approved. There is no existing requirement that part 48 training 
include a discussion of the hazards and control of diesel emissions. 
While mine operators are free to cover additional topics during the 
part 48 training sessions, the topics that must be covered during the 
required time frame may make it impracticable to cover other matters 
within the prescribed time limits. Where the time is available in mines 
using diesel-powered equipment, operators should be free to include the 
dpm instruction in their proposed part 48 training plans. The Agency 
does not believe special language in the proposed rule is needed to 
permit this action under part 48, but welcomes comment in this regard.
    The proposal would not require the mine operator to separately 
certify the completion of the diesel particulate training, but some 
evidence that the training took place would have to be produced upon 
request. A serial log with the employee's signature is a perfectly 
acceptable practice in this regard.

Medical surveillance

    Another important source of information that miners and operators 
can use to protect health can come from medical surveillance programs. 
Such programs provide for medical evaluations or tests of miners 
exposed to particularly hazardous substances, at the operator's 
expense, so that a miner exhibiting symptoms or adverse test results 
can receive timely medical attention, ensure that personal exposure is 
reduced as appropriate and controls are reevaluated. Sometimes, to 
ensure that this source of information is effective, medical removal 
(transfer) protection must also be required. Medical transfer may 
address protection of a miner's employment, a miner's pay retention, a 
miner's compensation, and a miner's right to opt for medical removal.
    As a general rule, medical surveillance programs have been 
considered appropriate when the exposures are to potential carcinogens. 
MSHA has in fact been considering a generic requirement for medical 
surveillance as part of its air quality standards rulemaking. And MSHA 
recently proposed a medical surveillance program for hearing, as part 
of the Agency's proposed rule on noise exposure. (61 FR 66348).
    MSHA is not proposing such a program for dpm at this time because 
it is still gathering information on this issue. The Agency, however, 
welcomes comments regarding this issue and also, on medical removal.
    Specifically, the Agency would welcome comment on the following 
questions: (a) what kinds of examinations or tests would be appropriate 
to detect whether miners are suffering ill effects as a result of dpm 
exposure; (b) the qualifications of those who would have to perform 
such examinations or tests and their availability; (c) whether such 
examinations or tests need to be provided and how frequently once the 
provisions of the rule are in effect; and (d) whether medical removal 
protections should be a component of a medical surveillance program.
(9) What Are the Major Issues on Which MSHA Wants Comments?
    MSHA wants the benefit of your experience and expertise: whether as 
a miner or mine operator in any mining sector; a manufacturer of 
diesel-powered engines, equipment, or emission control devices; or as a 
scientist, doctor, engineer, or safety and health professional. MSHA 
intends to review and consider all comments submitted to the Agency.
    The following list reflects some topics on which the Agency would 
particularly like information; requests for information on other topics 
can be found throughout the preamble.
    (a) Assessment of Risk/Benefits of the Rule. Part III of this 
preamble reviews information that the Agency has been able to obtain to 
date on the risks of dpm exposure to miners. The Agency welcomes your 
comments on the significance of the material already in the record, and 
any information that can supplement the record. For example, additional 
information on existing and projected exposures to dpm and to other 
fine particulates in various mining environments would be useful in 
getting a more complete picture of the situation in various parts of 
the mining industry. Additional information on the health risks 
associated with exposure to dpm--especially observations by trained 
observers or studies of acute or chronic effects of exposure to known 
levels of dpm or fine particles in general, information about pre-
existing health conditions in individual miners or miners as a group 
that might affect their reactions to exposures to dpm or other fine 
particles, and information about how dpm affects human health--would 
help provide a more complete picture of the relationship between 
current exposures and the risk of health outcomes. Information on the 
costs to miners, their families and their employers of the various 
health problems linked to dpm exposure, and the prevalence thereof, 
would help provide a more complete picture of the benefits to be 
expected from reducing exposure. And as discussed in response to 
Question and Answer 5, the Agency would welcome advice about the 
assumptions and approach to use in quantifying the benefits to be 
derived from this rule.
    (b) Proposed Rule. Part IV of this preamble reviews each provision 
of the proposed rule, part V discusses the economic and technological 
feasibility of the proposed rule, and part VI reviews the projected 
impacts of the proposed rule. The Agency would welcome comments on each 
of these topics.
    The Agency would like your thoughts on the specific alternative 
approaches discussed in part V. The options discussed include: 
establishing a concentration limit for dpm in this sector; requiring 
filters on some light-duty equipment; and looking at the filter

[[Page 17500]]

and the engine as a package that has to meet a particular emission 
standard, instead of requiring that all engines be equipped with a 
high-efficiency filter.
    The Agency would also like your thoughts on more specific changes 
to the proposed rule that should be considered. The Agency is also 
interested in obtaining as many examples as possible as to the specific 
situation in individual mines: the composition of the diesel fleet, 
what controls cannot be utilized due to special conditions, and any 
studies of alternative controls using the computer spreadsheet 
described in the Appendix to part V of this preamble. (See Adequacy of 
Protection and the Feasibility of the Proposed Rule). Information about 
the availability and costs of various control technologies that are 
being developed (e.g., high-efficiency ceramic filters), experience 
with the use of available controls, and information that will help the 
Agency evaluate alternative approaches for underground coal mines would 
be most welcome. And the Agency would appreciate information about any 
unusual situations that might warrant the application of special 
provisions.
    (c) Compliance Guidance. The Agency welcomes comments on any topics 
on which initial guidance ought to be provided as well as any 
alternative practices which MSHA should accept for compliance before 
various provisions of the rule go into effect.
    (d) Minimizing Adverse Impact of the Proposed Rule. The Agency has 
set forth its assumptions about impacts (e.g., costs, paperwork, and 
impact on smaller mines in particular) in some detail in this preamble 
and in the PREA, and would welcome comments on the methodology. 
Information on current operator equipment replacement planning cycles, 
tax, State requirements, or other information that might be relevant to 
purchasing new engines or control technology would likewise be helpful.
    (10) When Will the Rule Become Effective? Will MSHA Provide 
Adequate Guidance Before Implementing the Rule?
    Some requirements of the proposed rule would go into effect 60 days 
after the date of promulgation: specifically, the requirement to 
provide basic hazard training to miners who are exposed underground to 
dpm.
    The next set of requirements would go into effect 18 months after 
the date the rule is promulgated. Underground coal mines would have to 
properly filter permissible diesel-powered equipment.
    A year later (30 months after the date of promulgation), 
underground coal mines would have to properly filter heavy-duty 
nonpermissible equipment.
    MSHA intends to provide considerable technical assistance and 
guidance to the mining community before the various requirements go 
into effect, and be sure MSHA personnel are fully trained in the 
requirements of the rule. A number of actions have already been taken 
toward this end. The Agency held workshops on this topic in 1995 which 
provided the mining community an opportunity to share advice on how to 
control dpm concentrations. The Agency has published a ``toolbox'' of 
methods available to mining operators to achieve reductions in dpm 
concentration (a copy is attached as an Appendix at the end of this 
document). The ``toolbox'' provides information on filter technology as 
well as on other actions mine operators can take to address dpm 
concentrations in their mines.
    The Agency is committed to issuing a compliance guide for mine 
operators providing additional advice on implementing the rule. MSHA 
would welcome suggestions on matters that should be discussed in such a 
guide. MSHA would also welcome comments on other actions it could take 
to facilitate implementation, and in particular whether a series of 
additional workshops would be useful.

(B) Additional Information About the Proposed Rule for Underground Coal 
Mines

(11) More Specifically, What Changes Does the Proposal Make to the 
Current Rules on the Use of Diesel-Powered Equipment in Underground 
Coal Mines?
    The proposal builds on the changes to part 75 recently adopted in 
MSHA's final rule ``Approval, Exhaust Gas Monitoring, and Safety 
Requirements for the Use of Diesel-Powered Equipment in Underground 
Coal Mines.'' (61 FR 55412). As a result of these changes, grounded in 
safety considerations, underground coal mines must already comply with 
certain rules that have the added benefit of reducing harmful dpm 
emissions from diesel-powered equipment. These include a requirement 
that only low-sulfur diesel fuel be used underground, restrictions on 
the idling of diesel-powered equipment, ensuring that maintenance of 
diesel-powered equipment is performed only by qualified personnel, 
weekly tailpipe tests to ensure the engines are operating in approved 
condition, and the requirement that the entire diesel fleet have 
approved engines before the year 2000.
    The proposed rule would require that all permissible and heavy-duty 
nonpermissible diesel-powered equipment be equipped with a filtration 
system that is capable of removing, on average, at least 95% by mass of 
the particulate emissions coming out of that equipment. These 
filtration systems must be properly maintained in accordance with 
manufacturer specifications (e.g., changing paper filters at the proper 
interval). The permissible equipment must be so equipped within 18 
months after the rule becomes final, and the heavy-duty nonpermissible 
equipment a year later. The mine's ventilation and dust control plan 
must contain a list of the diesel-powered equipment used in the mine 
and the filtration system installed on each. And finally, to ensure 
they can better contribute to dpm reduction efforts, underground coal 
miners who can reasonably be expected to be exposed to diesel emissions 
must be annually trained about the hazards associated with that 
exposure and in the controls being used by the operator to reduce dpm 
concentrations.
    The proposed rule would not require the filtration of light-duty 
outby diesel equipment. It would not establish a concentration limit 
for dpm in underground coal mines. And it would not require monitoring 
of dpm concentrations by either operators or MSHA in this sector. 
Enforcement of the proposed requirements would be through observation 
by MSHA inspectors who are at the mine on a regular basis.
    MSHA's decision to propose this approach for underground coal mines 
was driven by two interrelated considerations.
    First, the Agency is not confident that there is a measurement 
method for dpm that will provide accurate, consistent and verifiable 
results at lower concentration levels in underground coal mines. The 
available measurement methods for determining dpm concentrations in 
underground coal mines were carefully evaluated by the Agency, 
including field testing, before the Agency reached this conclusion. The 
problems are discussed in detail in part II of this preamble. 
Basically, coal dust contains compounds that could be mistaken for dpm 
in the methods that do not exclude organic materials. A size selective 
impactor minimizes this problem by screening out most of the coal dust 
before it can reach the filter medium, but doesn't eliminate it. 
Measuring only the elemental carbon in a sample does provide a way to 
distinguish dpm from coal dust, but there remain questions about 
whether a

[[Page 17501]]

measured amount of elemental carbon can be equated to a prescribed 
amount of whole diesel particulate under the variable engine conditions 
found in actual mining environments. The Agency is continuing to 
explore questions about the measurement of dpm in underground coal 
mines in consultation with NIOSH, and welcomes comment on this issue. 
If at some future time it can be established that a particular 
measurable component of dpm is responsible for the adverse health 
effects observed (e.g., the elemental carbon cores), the Agency would 
evaluate the question of measurement in that light.
    Second, filtration systems for the diesel equipment used in this 
sector are readily available, and if properly maintained can provide 
generally consistent, highly effective elimination of dpm from 
underground mine atmospheres.
    MSHA's analysis of dpm emissions in underground coal mines 
indicates that it is currently the permissible equipment used for face 
haulage that contributes most to high dpm levels, but heavy-duty outby 
equipment can also generate significant dpm emissions. On the 
permissible equipment, paper type filtration systems can be installed 
directly on the tailpipes; accordingly, the rule would require these 
filters to be installed within 18 months. In the case of outby 
equipment, scrubbers and cooling system upgrades will need to be added 
to cool the exhaust before the paper type filters can be installed, or 
a dry technology system would need to be utilized. The Agency is 
seeking information as to whether ceramic filters might achieve the 
required efficiency once a market develops; but at this time, the 
proposal would provide an additional year for the nonpermissible 
equipment to be converted and fitted with high efficiency filtration 
systems.
    The proposed rule specifies a laboratory method that equipment 
manufacturers can use to determine whether a particular filtration 
system meets the requirement that the system be at least 95% effective 
in removing dpm.
(12) Why not Consider a more Flexible Approach Under Which the Filter, 
the Engine, and the Available Ventilation is Viewed as a Single System 
that has to Meet a Defined Emission Limit?
    MSHA has considered some approaches along this line. The Agency 
welcomes comment on such ideas so it can better evaluate whether they 
provide more protection to underground coal miners.
    Alternative 1 would in essence provide some credit in filter 
selection to those operators who use less polluting engines. Under this 
approach, the engine and aftertreatment filter would be bench tested as 
a unit; and if the emissions from the unit are below a certain level 
per defined volume of air (e.g., 120DPM g/
m3), the package would be acceptable without regard to the 
efficiency of just the filter component. Alternative 2 would also 
provide credit in filter selection for extra ventilation used in an 
underground coal mine. If the bench test of the combined engine and 
filter package was conducted at the name plate ventilation, a mine's 
use of more than that level of ventilation would be factored into the 
calculation of what package would be acceptable.
    One practical effect of these alternatives would be to permit some 
operators to save the costs of installing heat exchangers or other 
exhaust-cooling devices on nonpermissible heavy-duty equipment. Such 
devices are necessary in order for this equipment to be fitted with 
paper filters--and as noted in response to the previous question, at 
the moment these are the only filters on the market capable of 
providing 95% and more filtration capability.
    The appropriateness of Alternative 1 is not clear. With the proper 
equipment to cool the exhaust, a 95% paper filter can be installed on 
any piece of heavy-duty equipment in coal mines--and of course directly 
on any permissible piece of equipment. And, as indicated herein, the 
Agency is tentatively concluding that such an approach is economically 
feasible as well. Installing a 95% efficient filter on an engine lowers 
the dpm concentration in the mine more than would installing a less 
efficient filter. Hence for engines whose emissions can, with a 95% 
filter, be reduced below 120DPM g/m3 or 
whatever other dpm limit is set under such an approach, the alternative 
approach may result in less miner protection.
    Moreover, it is not clear to MSHA that 95% filtration of the 
engines used on the majority of permissible machines in underground 
coal mines can meet an emissions limit of 120DPM g/
m3 using MSHA's name plate ventilation. These engines are of 
older design and produce higher concentrations of diesel particulate. 
Thus adopting a rule with such an emissions limit would in effect 
require these engines to be replaced with cleaner engines. Of course, 
it follows that such a rule would be more costly than the one proposed, 
because it would require the 95% filters plus the replacement of these 
engines.
    The second alternative appears to be less protective in all cases. 
To provide mines who need extra ventilation for other reasons (e.g., to 
keep methane in check) with a credit for this fact in determining the 
required filter efficiency would not reduce dpm concentrations as much 
as simply requiring a 95% filter.
    The Agency welcomes comments on these approaches and information 
that will help it assess them in light of the requirements of the Mine 
Act.

II. Background Information

    This part provides the context for this rulemaking. The nine topics 
covered are:
    (1) The role of diesel-powered equipment in mining;
    (2) Diesel exhaust and diesel particulate;
    (3) Methods available to measure DPM;
    (4) Reducing soot at the source--engine standards;
    (5) Limiting the public's exposure to soot -- ambient air quality 
standards;
    (6) Controlling diesel particulate emissions in mining--a toolbox;
    (7) Existing mining standards that limit miner exposure to 
occupational diesel particulate emissions;
    (8) How other jurisdictions are restricting occupational exposure 
to diesel soot; and
    (9) MSHA's initiative to limit miner exposure to diesel 
particulates--the history of this rulemaking and related actions.
    In addition, an Appendix at the end of this document reprints a 
recent MSHA publication, ``Practical Ways to Reduce Exposure to Diesel 
Exhaust in Mining--A Toolbox'', which contains considerable information 
of interest in this rulemaking.
    These topics will be of interest to the entire mining community, 
even though this rulemaking is specifically confined to the underground 
coal sector.
    (1) The Role of Diesel-Powered Equipment in Mining. Diesel engines 
now power a full range of mining equipment on the surface and 
underground, in both coal and in metal/nonmetal mining. Many in the 
mining industry believe that diesel-powered equipment has a number of 
productivity and safety advantages over electrically-powered equipment. 
Nevertheless, concern about miner safety and health has slowed the 
spread of this technology, and in certain states resulted in a complete 
ban on its use in underground coal mines. As the industry has moved to 
realize the advantages this equipment may provide, the Agency has 
endeavored to address

[[Page 17502]]

the miner safety and health issues presented.

Historical Patterns of Use

    The diesel engine was developed in 1892 by the German engineer 
Rudolph Diesel. It was originally intended to burn coal dust with high 
thermodynamic efficiency. Later, the diesel engine was modified to burn 
middle distillate petroleum (diesel fuel). In diesel engines, liquid 
fuel droplets are injected into a prechamber or directly into the 
cylinder of the engine. Due to compression of air in the cylinder the 
temperature rises high enough in the cylinder to ignite the fuel.
    The first diesel engines were not suited for many tasks because 
they were too large and heavy (weighing 450 lbs. per horsepower). It 
was not until the 1920's that the diesel engine became an efficient 
lightweight power unit. Since diesel engines were built ruggedly and 
had few operational failures, they were used in the military, railway, 
farm, construction, trucking, and busing industries. The U.S. mining 
industry was slow, however, to begin using these engines. Thus, when in 
1935 the former U.S. Bureau of Mines published a comprehensive overview 
on metal mine ventilation (McElroy, 1935), it did not even mention 
ventilation requirements for diesel-powered equipment. By contrast, the 
European mining community began using these engines in significant 
numbers, and various reports on the subject were published during the 
1930's. According to a 1936 summary of these reports (Rice, 1936), the 
diesel engine had been introduced into German mines by 1927. By 1936, 
diesel engines were used extensively in coal mines in Germany, France, 
Belgium and Great Britain. Diesel engines were also used in potash, 
iron and other mines in Europe. Their primary use was in locomotives 
for hauling material.
    It was not until 1939 that the first diesel engine was used in the 
United States mining industry, when a diesel haulage truck was used in 
a limestone mine in Pennsylvania, and not until 1946 was a diesel 
engine used in coal mines. Today, however, diesel engines are used to 
power a wide variety of equipment in all sectors of U.S. mining, such 
as: air compressor; ambulance; crane truck; ditch digger; foam machine; 
forklift; generator; grader; haul truck; load-haul-dump machine; 
longwall retriever; locomotive; lube unit; mine sealant machine; 
personnel car; hydraulic pump machine; rock dusting machine; roof/floor 
drill; shuttle car; tractor; utility truck; water spray unit and 
welder.

Estimates of Current Use

    Estimates of the current inventory of diesel engines in the mining 
industry are displayed in Table II-1. Not all of these engines are in 
actual use. Some may be retained rather than junked, and others are 
spares. MSHA has been careful to take this into account in developing 
cost estimates for this proposed rule; its assumptions in this regard 
are detailed in the Agency's PREA.

          Table II-1.--Diesel Equipment in Three Mining Sectors         
------------------------------------------------------------------------
                                                        No.             
                Mine type                     No.    Mines w/     No.   
                                             Mines    Diesel    Engines 
----------------------------------------------\2\-----------------------
Underground Coal.........................       971   \3\ 173  \4\ 2,950
    \1\ Small............................       426        15         50
    Large................................       545       158      2,900
Underground M/NM.........................       261   \5\ 203  \6\ 4,100
    \1\ Small............................       130        82        625
    Large................................       131       121      3,475
Surface Coal.............................     1,673  \7\ 1,67           
                                                            3  \8\ 22,00
                                                                       0
    \1\ Small............................     1,175     1,175      7,000
    Large................................       498       498     15,000
Surface M/NM.............................    10,474  \9\ 10,4           
                                                           74  \10\ 97,0
                                                                      00
------------------------------------------------------------------------
Notes on Table II-1:                                                    
\1\ A mine with less than 20 miners. MSHA traditionally regards mines   
  with less than 20 miners as ``small'' mines, and those with 20 or more
  miners as ``large'' mines based on differences in operation. However, 
  in examining the impact of the proposed regulations on the mining     
  community, MSHA, consistent with the Small Business Administration    
  definition for small mines, which refers to employers with 500        
  employees or less, has analyzed impact for this size. This is         
  discussed in the Agency's preliminary regulatory economic analysis for
  this proposed rule.                                                   
\2\ Preliminary 1996 MSHA data.                                         
\3\ Data from MSHA approval and certification center, Oct.95.           
\4\ Actual inventory, rounded to nearest 50.                            
\5\ Estimates are based on a January 1998 count, by MSHA inspectors, of 
  underground mines that use diesel powered equipment.                  
\6\ The estimates are based on a January 1998 count, by MSHA inspectors,
  of diesel powered equipment normally in use.                          
\7\ Based on assumption that all surface coal mines had some diesel     
  powered equipment.                                                    
\8\ Based on MSHA survey of 25% of surface coal mines.                  
\9\ MSHA assumes all surface M/NM mines use some diesel engines.        
\10\ Derived by applying ratios (engines per mine) from MSHA survey of  
  surface coal mines to M/NM mines.                                     

    As noted in Table II-1, nearly all underground metal and nonmetal 
mines, and all surface mines, use diesel-powered equipment. This is not 
true in underground coal mines--in no small measure because, as 
discussed later in this part, several key underground coal states have 
for many years banned the use of diesel-powered equipment in such 
mines.
    Neither the diesel engines nor the diesel-powered equipment are 
identical from sector to sector. This relates to the equipment needs in 
each sector. This is important information because the type of engine, 
and the type of equipment in which it is installed, can have important 
consequences for particulate production and control.
    As the horsepower size of the engine increases, the mass of dpm 
emissions produced per hour increases. (A smaller engine may produce 
the same or higher levels of particulate emissions per volume of 
exhaust as a large engine, due to the airflow, but the mass of 
particulate matter increases with the engine size.) Accordingly, as 
engine size increases, control of emissions may require additional 
efforts.
    Diesel engines in underground metal and nonmetal mines, and in 
surface coal mines, range up to 750 HP or greater; by contrast, in 
underground coal mines, the average engine size is less than 150 HP. 
The reason for this disparity is the nature of the equipment powered by 
diesel engines. In underground metal and nonmetal mines, and surface 
mines, diesel engines are widely used in all types of equipment--both 
the equipment used under the heavy stresses of production and the 
equipment used for support. By contrast, the great majority of the 
diesel usage in underground coal mines is in support equipment. For 
example, in underground metal and nonmetal mines, of the approximate 
4,100 pieces of diesel equipment normally in use, about 1,800 units are 
for loading and hauling. By contrast, of the approximate 3,000 pieces 
of diesel equipment in underground coal, MSHA estimates that less than 
50 pieces are for coal haulage. The largest diesel engines are used in 
surface operations; in underground metal and nonmetal mines, the size 
of the engine can be limited by the size of the shaft opening.
    The type of equipment in the sectors also varies in another way 
that can affect particulate control directly, as well as constrain 
engine size. In underground coal, equipment that is used in face 
(production) areas of the coal mine must be MSHA-approved part 36 
permissible equipment. These locations are the areas where methane gas 
is likely to accumulate in higher concentrations. This includes the in-
by section starting at the tailpiece (coal dump point) and all returns. 
Part 36 permissible equipment for coal requires the use of flame 
arresters on the intake and exhaust systems and surface temperature 
control to below 302 deg.F. As

[[Page 17503]]

discussed in more detail elsewhere in this notice, the cooler exhaust 
from these permissible pieces of equipment permits the direct 
installation of particulate filtration devices such as paper type 
filters that cannot be used directly on engines with hot exhaust. In 
addition, the permissibility requirements have had the effect of 
limiting engine size. This is because prior to MSHA's issuance of a 
diesel equipment rule in 1996, surface temperature control was done by 
water jacketing. This limited the horsepower range of the permissible 
engines because manufacturers have not expended resources to develop 
systems that could meet the 302 deg.F surface temperature limitation 
using a water jacketed turbocharger.
    In the future, larger engines may be used on permissible equipment, 
because the new diesel rule allows the use of new technologies in lieu 
of water jacketing. This new technology, plus the introduction of air-
charged aftercoolers on diesel engines, may lead to the application of 
larger size diesel engines for underground coal production units. 
Moreover, if manufacturers choose to develop this type of technology 
for underground coal production units, the number of diesel production 
machines may increase.
    There are also a few underground metal and nonmetal mines that are 
gassy, and these require the use of part 36 permissible equipment. 
Permissible equipment in metal and nonmetal mines must be able to 
control surface temperatures to 400 deg. F. MSHA estimates that there 
are currently less than 15 metal and nonmetal mines classified as gassy 
and which, therefore, must use part 36 permissible equipment if diesels 
are utilized in areas where permissible equipment is required. These 
gassy metal and nonmetal mines have been using the same permissible 
engines and power packages as those approved for underground coal 
mines. (MSHA has not certified a diesel engine exclusively for a part 
36 permissible machine for the metal and nonmetal sector since 1985 and 
has certified only one permissible power package; however, that engine 
model has been retired and is no longer available as a new purchase to 
the industry). As a result, these mines are in a similar situation as 
underground coal mines: engine size (and thus dpm production of each 
engine) is more limited, and the exhaust is cool enough to add the 
paper type of filtration device directly to the equipment.
    In nongassy underground metal and nonmetal mines, and in all 
surface mines, mine operators can use conventional construction 
equipment in their production sections without the need for 
modifications to the machines. Two examples are haulage vehicles and 
dump trucks. Some construction vehicles may be redesigned and 
articulated for sharper turns in underground mines; however, the 
engines are still the industrial type construction engines. As a 
result, these mines can and do use engines with larger horsepower. At 
the same time, since the exhaust is not cooled, paper-type filters 
cannot be added directly to this equipment without first adding a water 
scrubber, heat exchanger or other cooling device. The same is true for 
the equipment used in outby areas of coal mines, where the methane 
levels do not require the use of permissible equipment.

Future Demand and Emissions

    MSHA expects there will be more diesel-powered equipment added to 
the Nation's mines. While other types of power sources for mining 
equipment are available, many in the mining industry believe that 
diesel power provides both safety and economic advantages over 
alternative power sources available today. Not many studies have been 
done recently on these contentions, and the studies which have been 
reviewed by MSHA do not clearly support this hypothesis; but as long as 
this view remains prevalent, continued growth is likely.
    There are additional factors that could increase growth. As noted 
above, permissible equipment can now be designed in such a way to 
permit the use of larger engines, and in turn more use of diesel-
powered production equipment in underground coal and other gassy mines. 
Moreover, state laws banning the use of diesel engines in the 
underground coal sector are under attack. As noted in section 8 of this 
part, until recently, three major underground coal states, 
Pennsylvania, West Virginia, and Ohio, have prohibited the use of 
diesel engines in underground coal mines. In late 1996, Pennsylvania 
passed legislation (PA Senate Bill No. 1643) permitting such use under 
conditions defined in the statute. West Virginia passed legislation 
lifting its ban as of May, 1997 (WV House Bill 2890), subject to 
regulations to be developed by a joint labor-industry commission. This 
makes the need to address safety and health concerns about the use of 
such engines very pressing.
    In the long term, the mining industry's diesel fleet will become 
cleaner, even if the size of the fleet expands. This is because the old 
engines will eventually be replaced by new engines that will emit fewer 
particulates than they do at present. As discussed in section 4 of this 
part, EPA regulations limiting the emissions of particulates and 
various gasses from new diesel engines are already being implemented 
for some of the smaller engines used in mining. Under a defined 
schedule, these new standards will soon apply to other new engines, 
including the larger engines used in mining. Moreover, over time, the 
emission standards which new engines will have to pass will become more 
and more stringent. Under international accords, imported engines are 
also likely to be cleaner: European countries have already established 
more stringent emission requirements (Needham, 1993; Sauerteig, 1995).
    But MSHA believes that turnover of the mining fleet to these new, 
cleaner engines will take a very long time because the mining industry 
tends to purchase for mining use older equipment that is being 
discarded by other industries. In the meantime, the particulate burden 
on miners as a group is expected to remain at current levels or even 
grow.
    (2) Diesel Exhaust and Diesel Particulate. The emissions from 
diesel engines are actually a complex mixture of compounds, containing 
gaseous and particulate fractions. The specific composition of the 
diesel exhaust in a mine will vary with the type of engines being used 
and how they are used. Factors such as type of fuel, load cycle, engine 
maintenance, tuning, and exhaust treatment will affect the composition 
of both the gaseous and particulate fractions of the exhaust. This 
complexity is compounded by the multitude of environmental settings in 
which diesel-powered equipment is operated. Elevation, for example, is 
a factor. Nevertheless, there are a few basic facts about diesel 
emissions that are of general applicability.
    The gaseous constituents of diesel exhaust include oxides of 
carbon, nitrogen and sulfur, alkanes and alkenes (e.g., butadiene), 
aldehydes (e.g., formaldehyde), monocyclic aromatics (e.g., benzene, 
toluene), and polycyclic aromatic hydrocarbons (e.g., phenanthrene, 
fluoranthene). The oxides of nitrogen (NOX) are worth 
particular mention because in the atmosphere they can precipitate into 
particulate matter. Thus, controlling the emissions of NOX 
is one way that engine manufacturers can control particulate production 
indirectly. (See section 4 of this part).
    The particulate fraction of diesel exhaust--what is known as soot--
is made up of very small individual particles. Each particle consists 
of an insoluble, elemental carbon core and an

[[Page 17504]]

adsorbed, surface coating of relatively soluble organic carbon 
(hydrocarbon) compounds. There can be up to 1,800 different organic 
compounds adsorbed onto the elemental carbon core. A portion of this 
hydrocarbon material is the result of incomplete combustion of fuel; 
however, the majority is derived from the engine lube oil. In addition, 
the diesel particles contain a fraction of non-organic adsorbed 
materials.
    Diesel particles released to the atmosphere can be in the form of 
individual particles or chain aggregates (Vuk, Jones, and Johnson, 
1976). In underground coal mines, more than 90% of these particles and 
chain aggregates are submicrometer in size--i.e., less than 1 
micrometer (1 micron) in diameter. In underground metal and nonmetal 
mines, a greater portion of the aggregates may be larger than 1 micron 
in size because of the equipment used. Dust generated by mining and 
crushing of material--e.g., silica dust, coal dust, rock dust--is 
generally not submicrometer in size.
    Figure II-1 shows a typical size distribution of the particles 
found in the environment of a mine that uses equipment powered by 
diesel engines (Cantrell and Rubow, 1992). The vertical axis represents 
relative concentration, and the horizontal axis the particle diameter. 
As can be seen, the distribution is bimodal, with dpm generally being 
well less than 1 m in size and dust generated by the mining process 
being well greater than 1 m. Because of their small size, even when 
diesel particles are present in large quantities, the environment might 
not be perceived as ``dusty''. Rather, the perception might be 
primarily of a vaporous, dirty and smelly ``soot'' or ``smoke''.

[GRAPHIC] [TIFF OMITTED] TP09AP98.001


    The particulate nature of diesel soot has special significance for 
the mining community, which has a history of significant health and 
safety problems associated with dusts in the mining atmosphere. As a 
result of this long experience, the mining community is familiar with 
the standard techniques to control particulate concentrations. It knows 
how to use ventilation systems, for example, to reduce dust levels in 
underground mines. It knows how to water down particulates capable of 
being impacted by that approach, and to divert particulates away from 
where miners are actively working. Moreover, the mining community has 
long experience in the sampling and measurement of particulates--and in 
all the problems associated therewith. Miners and mine operators are 
very familiar with sampling devices that are worn by miners during 
normal work activities or placed in specific locations to collect dust. 
They understand the significance of sample integrity, the validity of 
laboratory analysis, and the concept of statistical error in individual 
samples. They know that weather and mine conditions can affect 
particulate production, as can changes in mine operations in an area of 
the mine. MSHA and the former Bureau of Mines have conducted 
considerable research into these topics. While the mining community has 
often argued over these points, and continues to do so, the 
sophistication of the arguments reflects the thorough familiarity of 
the mining community with particulate sampling and analysis techniques.
    (3) Methods Available to Measure DPM. There are a number of methods 
which can measure dpm concentrations with reasonable accuracy when it 
is at high concentrations and when the purpose is exposure assessment. 
Measurements for the purpose of compliance determinations must be more 
accurate, especially if they are to measure compliance with a dpm 
concentration as low as 200 g/m3 or lower. It is 
with these considerations in mind that MSHA has carefully analyzed

[[Page 17505]]

the available methods for measuring dpm.
    Comments. In its advanced notice of proposed rulemaking (ANPRM) in 
1992, MSHA sought information on whether there are methodologies 
available for assessing occupational exposures to diesel particulate.
    Some commenters argued that at that time there was no validated 
sampling method for diesel exhaust and there had been no valid 
analytical method developed to determine the concentration of diesel 
exhaust. According to the American Mining Congress, (AMC 1992), 
sampling methods commonly in use were prototypic in nature, were 
primarily being utilized by government agencies and were subject to 
interference. Commenters also stated that sampling instrumentation was 
not commercially available and that the analytical procedures could 
only be conducted in a limited number of laboratories. Several industry 
commenters submitted results of studies to support their position on 
problems with measuring diesel particulate in underground mines. A 
problem with sampler performance was noted in a study using prototype 
dichotomous sampling devices. Another commenter indicated that the 
prototype sampler developed by the former Bureau of Mines (discussed 
later in this section) for collecting the submicrometer respirable dust 
was difficult to assemble but easy to use, and that no problems were 
encountered. Problems associated with gravimetric analysis were also 
noted in assessing a short term exposure limit (STEL). Another 
commenter (Morton, 1992) indicated the cost of the sampling was 
prohibitive.
    Another issue addressed by commenters to the 1992 ANPRM was ``Are 
existing sampling and exposure monitoring methods sufficiently 
sensitive, accurate and reliable?'' If not, what methods would be more 
suitable? Some commenters indicated their views that sampling methods 
had not been validated at that time for compliance sampling. They 
asserted that, depending on the level of measurement, both the size 
selective and elemental carbon techniques have some utility. The 
measurement devices give a precise measurement; however, because of 
interferants, corrections may need to be made to obtain an accurate 
measurement. Commenters also expressed the view that all of the 
sampling devices are sophisticated and require some expertise to 
assemble and analyze the results, and that MSHA should rely on outside 
agencies to evaluate and validate the sampling methods. An on-board 
sampler being developed by Michigan Technological University was the 
only other emission measurement technology discussed in the comments. 
However, this device is still in the development stage. Another 
commenter indicated that the standard should be based on the hazard and 
that the standard would force the development of measurement 
technology.

Submicrometer Sampling

    The former Bureau of Mines (BOM) submitted information on the 
development of a prototype dichotomous impactor sampling device that 
separates and collects the submicrometer respirable particulate from 
the respirable dust sampled (See Figure II-2).

[GRAPHIC] [TIFF OMITTED] TP09AP98.002


    The sampling device was designed to help measure dpm in coal mine 
environments, where, as noted in the last section of this part, nearly 
all the dpm is submicrometer (less than 1 micron) in size. In its 
submission to MSHA, the former BOM noted it had redesigned a prototype 
and had verified the sampler's performance through laboratory and field 
tests.
    As used by the former BOM in its research, the submicrometer 
respirable particulate was collected on a pre-weighed filter. Post-
weighing of the filter provides a measure of the submicrometer 
respirable particulate. The relative insensitivity of the gravimetric 
method only allows for a lower limit of detection of approximately 200 
g/m3. Because submicrometer respirable particulate 
can contain particulate material other than diesel particulate, 
measurements can be subject to interference from other submicrometer 
particulate material.

[[Page 17506]]

NIOSH Method 5040

    In response to the ANPRM, NIOSH submitted information relative to 
the development of a sampling and analytical method to assess the 
diesel particulate concentration in an environment by measuring the 
amount of total carbon.
    As discussed earlier in this part, diesel particulate consists of a 
core of elemental carbon (EC), adsorbed organic carbon (OC) compounds, 
sulfates, vapor phase hydrocarbons and traces of other compounds. The 
method developed by NIOSH provides for the collection of a sample on a 
quartz fiber filter. The filter is mounted in an open face filter 
holder that allows for the sample to be uniformly deposited on the 
filter surface. After sampling, a section of the filter is analyzed 
using a thermal-optical technique (Birch and Cary, 1996). This 
technique allows the EC and OC species to be separately identified and 
quantified. Adding the EC and OC species together provides a measure of 
the total carbon concentration in the environment. This is indicated 
diagrammatically in Figure II-3.
    Studies have shown that the sum of the carbon (C) components (EC + 
OC) associated with dpm accounts for 80-85% of the total dpm 
concentration when low sulfur fuel is used (Birch and Cary, 1996). 
Since the TC:DPM relationship is consistent, it provides a method for 
determining the amount of dpm.
    The method can detect as little as 1 g/m3 of 
TC.

[GRAPHIC] [TIFF OMITTED] TP09AP98.003


    Moreover, NIOSH has investigated the method and found it to meet 
NIOSH's accuracy criterion (NIOSH, 1995); i.e., that measurements come 
within 25 percent of the true TC concentration at least 95 percent of 
the time.
    NIOSH Method 5040 is directly applicable for the determination of 
diesel particulate levels in underground metal and nonmetal mines. The 
only potential sources of carbon in such mines would be organic carbon 
from oil mist and cigarette smoke. Oil mist may occur when diesel 
equipment malfunctions or is in need of maintenance. MSHA, currently, 
has no data as to the frequency of occurrence or the magnitude of the 
potential interference from oil mist. However, during studies conducted 
by MSHA to evaluate different methods used to measure diesel 
particulate concentrations in underground mines, MSHA has not 
encountered situations where oil mist was found to be an interferant. 
Moreover, the Agency assumes that full operator implementation of 
maintenance standards to minimize dpm emissions (which are part of 
MSHA's proposed rule) will minimize any remaining potential for such 
interference. MSHA welcomes comments or data relative to oil mist 
interference. Cigarette smoke is under the control of operators, during 
sampling times in particular, and hence should not be a consideration.
    While samples in underground metal and nonmetal mines could be 
taken with a submicrometer impactor, this could lead to underestimating 
the total amount of dpm present. This is because the fraction of dpm 
particles greater than 1 micron in size in the environment of noncoal 
mines can be as great as 20% (Vuk, Jones, and Johnson, 1976).
    When sampling diesel particulate in coal mines, the NIOSH method 
recommends that a specialized impactor with a submicrometer cut point, 
such as the one developed by the former BOM, be used. Use of the 
submicron impactor minimizes the collection of coal particles, which 
have an organic carbon content. However, if 10% of coal particles are 
submicron, this means that up to 200 micrograms of submicrometer coal 
dust could be collected in face areas under current coal dust 
standards. Accordingly, for samples collected in underground coal 
mines, an adjustment may have to be made for interference from 
submicrometer coal dust; however, outby areas where little coal mine 
dust is present may not need such an adjustment.
    NIOSH further recommends that in using its method in coal mines, 
the sample only be analyzed for the EC component. Measuring only the EC 
component ensures that only diesel particulate material is being 
measured in such cases. However, there are no established relationships 
between the concentration of EC and total dpm under various operating 
conditions. (The organic carbon component of dpm can vary with engine 
type and duty cycle; hence, the amount of whole dpm present for a 
measured amount of EC may vary). The Agency welcomes data and 
suggestions that would help it ascertain if and how measurements of

[[Page 17507]]

submicrometer elemental carbon could realistically be used to measure 
dpm concentrations in underground coal mines.
    Although NIOSH Method 5040 requires no specialized equipment for 
collecting a dpm sample, the sample would most probably require 
analysis by a commercial laboratory. MSHA recognizes that the number of 
laboratories currently capable of analyzing samples using the thermal-
optical method is limited. However, there are numerous laboratories 
available that have the ability to perform a TC analysis without 
identifying the different species of carbon in the sample. Total carbon 
determinations using these laboratories would provide the mine with 
good information relative to the levels of dpm to which miners are 
potentially exposed. MSHA believes that once there is a need (e.g., as 
a result of the requirements of the proposed rule), more commercial 
laboratories will develop the capability to analyze dpm samples using 
the thermo-optical analytical method. Currently, the cost to analyze a 
submicrometer particulate sample for its TC content ranges from $30 to 
$50. This cost is consistent with costs associated with similar 
analysis of minerals such as quartz.

RCD Method

    Another method, referred to as the Respirable Combustible Dust 
Method (RCD), has been developed in Canada for measuring dpm 
concentrations in noncoal mines. Respirable dust is collected with a 
respirable dust sampler consisting of a 10 millimeter nylon cyclone and 
a filter capsule containing a preweighed, preconditioned silver 
membrane filter. Samples are collected at a flow rate of 1.7 liter per 
minute. The respirable sample collected includes both combustible and 
noncombustible particulate matter.
    Samples collected in accordance with the RCD method require 
analysis by a commercial laboratory. Total respirable dust is 
determined gravimetrically by weighing the filter after the sample is 
collected. After the sample has been subjected to a controlled 
combustion process at 400 deg.C for two hours, the remainder of the 
sample is weighed, and the amount of the particulate burned off 
determined by subtraction. This is the RCD. The combustible particulate 
matter consists of the soluble organic fraction, the EC core of the 
dpm, and any other combustible material collected. Thus, only a portion 
of the RCD is attributable to dpm. Oil mist and other combustible 
matter collected on the filter are interferants that can affect the 
accuracy of dpm concentration determination using this method. Because 
the mass of RCD is determined by weighing, the relative insensitivity 
of this method is similar to that obtained with the size selective 
gravimetric method (approximately 200 g/m3).
    One commenter (Inco Limited) indicated experience with this method 
for identifying diesel particulate in their mining operations and 
suggested that this technique may be appropriate for determining eight 
hour exposures. Although this method was commonly used by the commenter 
for assessing dpm levels, concerns for the efficiency of the cyclones 
used to sample the respirable fraction of the particulate along with 
interference from oil mist were expressed.
    Canada is now experimenting with the use of a submicron impactor 
with the RCD method.

Sampler Availability

    The components for conducting sampling according to the 
submicrometer and the RCD methods are commercially available, as are 
those for NIOSH Method 5040, without a submicrometer particulate 
separator (impactor).
    A reusable impactor can be manufactured by machine shops following 
the design specifications developed by the former U.S. Bureau of Mines 
(BOM IC 9324, 1992). The use of the size-selective samplers requires 
some training and laboratory time to prepare the impaction plate and 
assemble the unit. The cost to manufacture the size-selective units is 
approximately $35.
    In addition, MSHA has requested NIOSH to develop and provide a 
commercially available disposable submicrometer particulate separator 
that would be used with existing personal respirable dust sampling 
equipment. The commercially available separator will be manufactured 
according to design criteria specified by NIOSH. It is anticipated that 
other sampling instrument manufacturers will develop commercial units 
once there is an established need for such a sampling device.

Use of Alternative Surrogates to Assess DPM Concentrations

    A number of commenters on the ANPRM indicated that a number of 
surrogates were available to monitor diesel particulate. Of the 
surrogates suggested, the most desirable to use would be carbon dioxide 
because of its ease of measurement. In 1992 the former Bureau of Mines 
(BOM IC 9324, 1992) reported on research being conducted to investigate 
the use of CO2 as a surrogate to assess mine air quality 
where diesel equipment is utilized. However, because the relationship 
between CO2 and other exhaust components depends on the 
number, type and duty cycle of the engines in operation, no acceptable 
measurement method based on the use of CO2 has been 
developed.
    (4) Reducing Soot at the Source--Engine Standards. One way to limit 
diesel particulate emissions is to redesign diesel engines so they 
produce fewer pollutants. Engine manufacturers around the world are 
being pressed to do this pursuant to environmental regulations. These 
cleaner engine requirements are sometimes referred to as tailpipe 
standards because compliance is measured by checking for pollutants as 
the exhaust emerges from the engine's tailpipe--before any 
aftertreatment devices. This section reviews developments in this area, 
and explains the relationship between the environmental standards on 
new engines and MSHA engine ``approval'' requirements.

The Clean Air Act and Mobile Sources

    The Clean Air Act authorized the Federal Environmental Protection 
Agency (EPA) to establish nationwide standards for new mobile vehicles, 
including those powered by diesel engines. These standards are 
designed, over time, to reduce the volume of certain harmful 
atmospheric pollutants emanating from mobile sources: particulate 
matter, nitrogen oxides (which as previously noted, can result in the 
generation of particulates in the atmosphere), hydrocarbons and carbon 
monoxide.
    California has its own standards. New engines destined for use in 
California must meet standards under the law of that State. The 
standards are issued and administered by the California Air Resources 
Board (CARB). In recent years, EPA and CARB have worked together with 
industry in establishing their respective standards, so most of them 
are identical.
    Regulatory responsibility for implementation of the Clean Air Act 
is vested in the Office of Mobile Sources (OMS), part of the Office of 
Air and Radiation of the EPA. Some of the discussion which follows was 
derived from materials which can be accessed from the OMS home page on 
the World Wide Web at (http://www.epa.gov/docs/omswww/omshome.htm). 
Information about the CARB standards may be found at the home page of 
that agency at (http://www.arbis.arb.ca.gov/homepage.htm).
    Engines are generally divided into three broad categories for 
purposes of

[[Page 17508]]

environmental emissions standards, in accordance with the primary use 
for which the type of engine is designed: (1) cars and light duty 
trucks (i.e., to power passenger transport); (2) heavy duty trucks 
(i.e., to power over-the-road hauling); and (3) nonroad vehicles (i.e., 
to power small equipment, construction equipment, locomotives and other 
non-highway uses). Engines used in mining equipment are not regulated 
as a separate category in this regard, but engines in all three 
categories are engaged in mining work, from generator sets to pickup 
trucks to huge earth movers and haulers.

New vs. Used

    The environmental tailpipe requirements are applicable only to new 
engines. In the mining industry, used engines are often purchased; and, 
of course, the existing fleet consists of engines that are not new. 
Thus, although these tailpipe requirements will bring about gradual 
reduction in the overall contribution of diesel pollution to the 
atmosphere, the beneficial effects on mining atmospheres may require a 
longer timeframe, absent actions to accelerate the turnover of mining 
fleets to the cleaner engines.
    In underground coal mining, MSHA has already taken actions which 
will have such an effect on the fleet. The diesel equipment rule issued 
in late 1996 requires that by November 25, 1999, all diesel equipment 
used in underground coal mines use an approved engine and maintain that 
engine in approved condition. (30 CFR 75.1907.) MSHA expects this will 
result in the replacement of about 47 percent of the diesel engines now 
in the underground coal mine inventory with engines that emit fewer 
pollutants. The timeframe permitted for the turnover was based upon 
MSHA's estimates of the useful life in an underground mining 
environment of the ``outby'' equipment involved.

Technology-Forcing Schedule

    As noted above, the exact environmental tailpipe requirements which 
a new diesel engine must meet varies with the date of manufacture. The 
Clean Air Act, which was most recently amended in 1990, establishes a 
schedule for the reduction of particular pollutants from mobile 
sources. EPA and CARB, working closely with the diesel engine industry, 
have endeavored to turn this into a regulatory schedule that forces 
technology while taking into account certain technological realities 
(e.g., actions taken to reduce particulate emissions may increase NOx 
emissions, and vice versa). Existing EPA regulations for on-highway 
engines (both for light duty vehicles and heavy duty trucks) and non-
road engines schedule the tailpipe standards that must be met for the 
rest of this century. Agreements between EPA, CARB and the engine 
industry are now leading to proposed rules for engine standards to be 
met during the early part of the next century. These standards will be 
stricter and will lower the levels of diesel emissions.

Light-Duty Engines

    The current regulations on light duty vehicle engines (cars and 
passenger trucks) were set in 1991. (56 FR 25724). EPA is currently 
considering proposing new standards for this category. Pursuant to a 
specific requirement in the Clean Air Act Amendments of 1990, EPA is to 
study and report to Congress on whether further reductions in this 
category should be pursued. A public workshop was held in the Spring of 
1997. EPA plans provide for a draft report to be available for public 
comment by Spring of 1998, and a final report completed by July 1998, 
although a notice of citizen suit has been filed to speed the process. 
Up-to-date information about the progress of this initiative can be 
found at the home page for the study (http://www.epa.gov/omswww/
tr2home.htm).

On-Highway Heavy Duty Truck Engines

    The first phase of the on-highway standards for heavy duty diesel 
engines was applicable to engines manufactured in 1985. (40 CFR 86.085-
11.) For the first time, separate standards for NOX and 
hydrocarbons were established. The nitrogen oxides and hydrocarbons are 
precursors of ground level ozone, a major component of smog. A number 
of hydrocarbons are also toxic, while nitrogen oxides contribute to the 
formation of acid rain and can, as previously noted, precipitate into 
particulate matter. In 1988, a specific standard limiting particulate 
matter emitted from the heavy duty on-highway diesel engines went into 
effect. (40 CFR 86.088-11). The Clean Air Act Amendments and the 
regulations provided for phasing in even tighter controls on 
NOX and particulate matter through 1998. Reductions in 
NOX took place in 1990 and 1991 and are to occur again in 
1998, and reductions in PM took place in 1991 and 1994. Certain types 
of trucks in particularly polluted urban areas must reach even tighter 
requirements.
    On October 21, 1997, EPA issued a new rule for on-highway engines 
that will take effect for engine model years starting in 2004. (62 FR 
54693.) The rule establishes a combined requirement for NOX 
and HC. The combined standard is set at 2.5gm/bhp-hr, which includes a 
cap of 0.5gm/bhp-hr for HC. Prior to the rule, the EPA, CARB, and the 
engine manufacturers signed a Statement of Principles (SOP) that agreed 
on harmonization of the emission standards and the feasible levels that 
could be achieved. The rule allows manufacturers a choice of two 
combinations of NOX and HC, with a net expected reduction in 
NOX emissions of 50%. The rule does not require further 
reductions in tailpipe emissions of PM.

Non-road Engines

    Of particular interest to the mining community is the EPA's 
regulatory work on the standards that will be applicable to non-road 
engines, for these include the engines used in the heaviest mining 
equipment.
    The 1990 Clean Air Act Amendments specifically directed EPA to 
study the contribution of nonroad engines to air pollution, and 
regulate them if warranted. In 1991, EPA released a study that 
documented higher than expected emission levels across a broad spectrum 
of nonroad engines and equipment (EPA Fact Sheet, EPA420-F-96-009, 
1996). In response, EPA initiated several regulatory programs. One of 
these set emission standards for land-based nonroad engines greater 
than 50 horsepower (other than for rail use). Limits are established 
for tailpipe emissions of hydrocarbons, carbon monoxide, 
NOX, and dpm. The limits are phased in from 1996 to 2000: 
starting in 1996 with nonroad engines from 175 to 750 hp, then smaller 
engines, and by 2000 the larger nonroad engines. Moreover, in February 
1997, restrictions on nonroad engines for locomotives were proposed. 
(62 FR 6366.)
    In September 1996, EPA announced another Statement of Principles 
(SOP) with the engine industry and CARB on new rounds of restrictions 
for non-road engines to begin to take place in this century. This led 
in September 1997 to a proposed rule setting standards for almost all 
types of engines in this category manufactured after 1999-2006 (the 
actual year depends on the category). (62 FR 50151.) The applicable 
standards for an engine category would be gradually tightened through 
three tiers. They would set a cap on the combined NOX and HC 
(similar to the on-highway), set CO standards, and lower standards on 
PM. The implementation of the final tier of the proposed reductions is 
subject to a technology review in 2001 to ensure

[[Page 17509]]

that the appropriateness of the levels to be set is feasible.

Will the Diesel Engine Industry Meet Mining Industry Requirements?

    Concern has been expressed from time to time that the diesel 
industry might not be able to meet the ever tightening standards on 
tailpipe emissions, and might, therefore, stop producing certain 
engines needed by the mining community or other industries (Gushee, 
1995). To date, however, such concerns have not been realized. The fact 
that the most recent regulations have been developed through a 
consensus process with the engine industry, and that the non-road plan 
includes a scheduled technology review to ensure the proposed emission 
standards can really be achieved, suggests that although the EPA 
standards are technology forcing, diesel engines will continue to be 
available to meet the needs of the mining community for the foreseeable 
future. In addition, the nonroad engine agreement with the industry 
calls for development of a separate research agreement involving 
stakeholders in the exploration of technologies that can achieve very 
low emission levels of NOX and PM ``while preserving 
performance, reliability, durability, safety, efficiency, and 
compatibility with nonroad equipment'' (EPA420-F-96-015, September 
1996). Also, Vice President Gore has recently noted that the 
Administration is committed to emissions research that would clean up 
both the diesels currently on the road, as well as enabling these 
engines an opportunity to compete as a new generation of vehicles is 
developed that are far more efficient than today's vehicles (White 
House Press Release, July 23, 1997). It is always possible, of course, 
that some new technological problems could emerge that could impact 
diesel engine availability--e.g., confirmation that some of the newer 
engines produce high levels of ``nanoparticles'' particulates and that 
such emissions pose some sort of a health problem. Research of 
nanoparticles and their health effects is currently a topic of 
investigation (Bagley et al., 1996).
    A related question has been whether the costs of the ``high-tech'' 
diesel engines will make them unaffordable in practice to the mining 
community. MSHA believes the new engines will be affordable. The fact 
that the engine industry has agreed to the new standards, and has some 
assurance of what the applicable standards will be for the foreseeable 
future, should help keep costs in check.
    In theory, underground mines can control costs by purchasing 
certain types of new engines that do not have to meet the new EPA 
standards. The rules on heavy duty on-highway truck engines were not 
applied to engines intended to be used in underground coal mines (59 FR 
31336), and the new proposed rules on nonroad vehicles would likewise 
not be mandatory for engines intended for any underground mining use. 
In practice, however, it is not likely that engine manufacturers will 
produce special engines once they switch over their production lines to 
meet the new EPA standards, because there are few types and sizes of 
engines in production for which the mining community is the major 
market. Moreover, the larger engines (above 750 hp) are specifically 
covered by the EPA nonroad rules (Engine Manufacturers Assn. vs. EPA, 
88 F.3d 1075, 319 U.S. App.D.C. 12 (1996)).

MSHA Approved Engines

    Acting under its own authority to protect miner safety and health, 
MSHA requires that diesel engines used in certain types of mining 
operations be ``approved'' as meeting certain tailpipe standards.
    In some ways, the standards are akin to those of EPA and CARB. For 
example, MSHA, CARB and EPA generally use the same tests to check 
emissions. MSHA uses a steady state, 8-mode test cycle, the same as EPA 
and CARB use to test engines designed for use in off-road equipment; 
however, EPA uses a different, transient test for on-highway engines.
    But to be approved by MSHA, an engine does not have to be as clean 
as the newer diesel engines, every generation of which must meet ever 
tighter EPA and CARB tailpipe standards. Approval of an engine by MSHA 
merely ensures that the tailpipe emissions from that engine meet 
certain basic standards of cleanliness--cleaner than the engines which 
many mines continue to use.
    The MSHA approval rules were revised in 1996 (as part of the 1996 
rule on the use of diesel equipment in underground coal mines) to 
provide the mining community with additional information about the 
cleanliness of the emissions emerging from the tailpipe of various 
engines. Specifically, the agency now requires that a particulate index 
(PI) be reported as part of MSHA's engine approval. This index permits 
operators to evaluate the contribution of a proposed new addition to 
the fleet to the mine's particulate concentrations.
    There is no requirement that approved engines meet a particular PI; 
rather, the requirement is for information purposes only. In its 1996 
rulemaking, MSHA explicitly deferred until this rulemaking the question 
of whether to require engines used in mining environments to meet a 
particular PI. (61 FR 55420-21, 55437). The Agency has decided not to 
take that approach, for the reasons discussed in part V of this 
preamble.
    (5) Limiting the Public's Exposure to Soot--Ambient Air Quality 
Standards. Pursuant to the Clean Air Act, EPA is responsible for 
setting air pollution standards to protect the public from toxic air 
contaminants. These include standards to limit exposure to particulate 
matter. The pressures to comply with these limits have an impact upon 
the mining industry, which contributes various types of particulate 
matter into the environment during mining operations, and a special 
impact on the coal mining industry whose product is used extensively in 
emission-generating power facilities. But those standards hold interest 
for the mining community in other ways as well, for underlying some of 
them is a large body of evidence on the harmful effects of airborne 
particulate matter on human health. Increasingly, that evidence has 
pointed toward the risks of the smallest particulates--including the 
particles generated by diesel engines.
    This section provides an overview of EPA rulemaking on particulate 
matter. For more detailed information, commenters are referred to ``The 
Plain English Guide to the Clean Air Act,'' EPA 400-K-93-001, 1993, to 
the ``Review of the National Ambient Air Quality Standards for 
Particulate Matter: Policy Assessment of Scientific and Technical 
Information'', EPA-452/R-96-013, 1996; and, on the latest rule, to EPA 
Fact Sheets, July 17, 1997. These and other documents are available 
from EPA's Web site.

Background

    Air quality standards involve a two-step process: standard setting 
by EPA, and implementation by each State.
    Under the law, EPA is specifically responsible for reviewing the 
scientific literature concerning air pollutants, and establishing and 
revising National Ambient Air Quality Standards (NAAQS) to minimize the 
risks to health and the environment associated with such pollutants. It 
is supposed to do a review every five years. Feasibility of compliance 
by pollution sources is not supposed to be a factor in establishing 
NAAQS. Rather, EPA is required to set the level that provides ``an 
adequate margin of safety'' in protecting the health of the public.

[[Page 17510]]

    Implementation of each national standard is the responsibility of 
the states. Each must develop a state implementation plan that ensures 
air quality in the state consistent with the ambient air quality 
standard. Thus, each state has a great deal of flexibility in targeting 
particular modes of emission (e.g., mobile or stationary, specific 
industry or all, public sources of emissions vs. private-sector 
sources), and in what requirements to impose on polluters. However, EPA 
must approve the state plans pursuant to criteria it establishes, and 
then take pollution measurements to determine whether all counties 
within the state are meeting each ambient air quality standard. An area 
not meeting an NAAQS is known as a ``nonattainment area''.

TSP

    Particulate matter originates from all types of stationary, mobile 
and natural sources, and can also be created from the transformation of 
a variety of gaseous emissions from such sources. In the context of a 
global atmosphere, all these particles are mixed together, and both 
people and the environment are exposed to a ``particulate soup'' the 
chemical and physical properties of which vary greatly with time, 
region, meteorology, and source category.
    The first ambient air quality standards dealing with particulate 
matter did not distinguish among these particles. Rather, the EPA 
established a single NAAQS for ``total suspended particulates'', known 
as ``TSP.'' Under this approach, the states could come into compliance 
with the ambient air requirement by controlling any type or size of 
TSP. As long as the total TSP was under the NAAQS which was established 
based on the science available in the 1970s--the state met the 
requirement.

PM10

    When the EPA completed a new review of the scientific evidence in 
the mid-eighties, its conclusions led it to revise the particulate 
NAAQS to focus more narrowly on those particulates less than 10 microns 
in diameter, or PM10. The standard issued in 1987 contained 
two components: an annual average limit of 150 g/
m3, and a 24-hour limit of 50 g/m3. This 
new standard required the states to reevaluate their situations and, if 
they had areas that exceeded the new PM10 limit, to refocus 
their compliance plans on reducing those particulates smaller than 10 
microns in size. Sources of PM10 include power plants, iron 
and steel production, chemical and wood products manufacturing, wind-
blown and roadway fugitive dust, secondary aerosols and many natural 
sources.
    Some state implementation plans required surface mines to take 
actions to help the state meet the PM10 standard. In 
particular, some surface mines in Western states were required to 
control the coarser particles--e.g., by spraying water on roadways to 
limit dust. The mining industry has objected to such controls, arguing 
that the coarser particles do not adversely impact health, and has 
sought to have them excluded from the EPA ambient air standards (Shea, 
1995; comments of Newmont Gold Company, March 11, 1997, EPA docket 
number A-95-54, IV-D-2346).

PM2.5

    The next scientific review was completed in 1996, following suit by 
the American Lung Association and others. A proposed rule was published 
in November of 1996, and, after public hearings and review by the 
Office of the President, a final rule was promulgated on July 18, 1997. 
(62 FR 38651).
    The new rule further modifies the standard for particulate matter. 
Under the new rule, the existing national ambient air quality standard 
for PM10 remains basically the same--an annual average limit 
of 150 g/m\3\ (with some adjustment as to how this is measured 
for compliance purposes), and a 24-hour ceiling of 50 g/m\3\. 
In addition, however, a new NAAQS has now been established for ``fine 
particulate matter'' that is less than 2.5 microns in size. The 
PM2.5 annual limit is set at 15 g/m\3\, with a 24-
hour ceiling of 65 g/m\3\.
    The basis for the PM2.5 NAAQS is a new body of 
scientific data suggesting that particles in this size range are the 
ones responsible for the most serious health effects associated with 
particulate matter. The evidence was thoroughly reviewed by a number of 
scientific panels through an extended process. (A chart of the 
scientific review process is available on EPA's web site -- http://
ttnwww.rtpnc.epa.gov/naaqspro/pmnaaqs.gif). The proposed rule resulted 
in considerable press attention, and hearings by Congress, in which 
this scientific evidence was further discussed. Following a careful 
review, President Clinton announced his concurrence with the rulemaking 
in light of the scientific evidence of risk. However, the 
implementation schedule for the rule is long enough so that the next 
review of the science is scheduled to be completed before the states 
are required to meet the new NAAQS for PM2.5--hence, 
adjustment of the standard is still possible before implementation.

Implications for the Mining Community

    As noted earlier in this part, diesel particulate matter is mostly 
less than 1.0 micron in size. It is, therefore, a fine particulate. The 
body of evidence of human health risk from environmental exposure to 
fine particulates must, therefore, be considered in assessing the risk 
of harm to miners of occupational exposure to one type of fine 
particulate--diesel particulate. MSHA has accordingly done so in its 
risk assessment (see part III of this preamble).
    (6) Controlling Diesel Particulate Emissions in Mining--a Toolbox. 
Efforts to control diesel particulate emissions have been under review 
for some time within the mining community, and accordingly, there is 
considerable practical information available about controls--both in 
general terms, and with respect to specific mining situations.

Workshops

    In 1995, MSHA sponsored three workshops ``to bring together in a 
forum format the U.S. organizations who have a stake in limiting the 
exposure of miners to diesel particulate (including) mine operators, 
labor unions, trade organizations, engine manufacturers, fuel 
producers, exhaust aftertreatment manufacturers, and academia.'' 
(McAteer, 1995). The sessions provided an overview of the literature 
and of diesel particulate exposures in the mining industry, state-of-
the-art technologies available for reducing diesel particulate levels, 
presentations on engineering technologies toward that end, and 
identification of possible strategies whereby miners' exposure to 
diesel particulate matter can be limited both practically and 
effectively. One workshop was held in Beckley, West Virginia on 
September 12 and 13, and the other two were held on October 6, and 
October 12 and 13, 1995, in Mt Vernon, Illinois and Salt Lake City, 
Utah, respectively. A transcript was made. During a speech early the 
next year, the Deputy Assistant Secretary for MSHA characterized what 
took place at these workshops:

    The biggest debate at the workshops was whether or not diesel 
exhaust causes lung cancer and whether MSHA should move to regulate 
exposures. Despite this debate, what emerged at the workshops was a 
general recognition and agreement that a health problem seems to 
exist with the current high levels of diesel exhaust exposure in the 
mines. One could observe that while all the debate about the studies 
and the level of risk was going on, something else interesting was 
happening at the workshops: One by one miners, mining companies, and

[[Page 17511]]

manufacturers began describing efforts already underway to reduce 
exposures. Many are actively trying to solve what they clearly 
recognize is a problem. Some mine operators had switched to low 
sulfur fuel that reduces particulate levels. Some had increased mine 
ventilation. One company had tried a soy-based fuel and found it 
lowered particulate levels. Several were instituting better 
maintenance techniques for equipment. Another had hired extra diesel 
mechanics. Several companies had purchased electronically 
controlled, cleaner, engines. Another was testing a prototype of a 
new filter system. Yet another was using disposable diesel exhaust 
filters. These were not all flawless attempts, nor were they all 
inexpensive. But one presenter after another described examples of 
serious efforts currently underway to reduce diesel emissions. 
(Hricko, 1996).

Toolbox 

    In March of 1997, MSHA issued, in draft form, a publication 
entitled ``Practical Ways to Control Exposure to Diesel Exhaust in 
Mining--a Toolbox''. The draft publication was disseminated by MSHA to 
all underground mines known to use diesel equipment and posted on 
MSHA's Web site. Following comment, the toolbox was finalized in the 
Fall of 1997 and disseminated. For the convenience of the mining 
community, a copy is reprinted as an Appendix at the end of this 
document.
    The material on controls is organized as a ``toolbox'' so that mine 
operators have the option of choosing the control technology that is 
most applicable to their mining operation for reducing exposures to 
dpm. The Toolbox provides information about nine types of controls that 
can reduce dpm emissions or exposures: Low emission engines; fuels; 
aftertreatment devices; ventilation; enclosed cabs; engine maintenance; 
work practices and training; fleet management; and respiratory 
protective equipment.

The Estimator

    MSHA has developed a model that can help mine operators evaluate 
the effect of alternative controls on dpm concentrations. The model is 
in the form of a template that can be used on standard computer 
spreadsheet programs; as information about a new combination of 
controls is entered, the results are promptly displayed. A complete 
description of this model, referred to as ``the Estimator,'' and 
several examples, are presented in part V of this preamble. MSHA 
intends to make this model widely available to the mining community, 
and hopes to receive comments in connection with this rulemaking based 
on the results of estimates conducted with this model.

History of Diesel Aftertreatment Devices in Mining

    For many years, the majority of the experience has been with the 
use of oxidation catalytic converters (OCCs), but in more recent years 
both ceramic and paper filtration systems have also been used more 
widely.
    OCCs began to be used in underground mines in the 1960's to control 
carbon monoxide, hydrocarbons and odor (Haney, Saseen, Waytulonis, 
1997). That use has been widespread. It has been estimated that more 
than 10,000 OCCs have been put into the mining industry over the years 
(McKinnon, dpm Workshop, Beckley, WV, 1995).
    When such catalysts are used in conjunction with low sulfur fuel, 
there is a reduction of up to 90 percent of carbon monoxide, 
hydrocarbons and aldehyde emissions, and nitric oxide can be 
transformed to nitrogen dioxide. Moreover, there is also an 
approximately 20 percent reduction in diesel particulate mass. The 
diesel particulate reduction comes from the elimination of the soluble 
organic compounds that, when condensed through the cooling phase in the 
exhaust, will attach to the elemental carbon cores of diesel 
particulate. Unfortunately, this effect is lost if the fuel contains 
more than 0.05 percent sulfur. In such cases, sulfates can be produced 
which ``poison'' the catalyst, severely reducing its life. With the use 
of low sulfur fuel, some engine manufacturers have certified diesel 
engines with catalytic converter systems to meet EPA requirements for 
lower particulate levels (see section 4 of this part).
    The particulate trapping capabilities of some OCCs are even higher. 
In 1995, the EPA implemented standards requiring older buses in urban 
areas to reduce the dpm emissions from rebuilt bus engines. (40 CFR 
85.1403). Aftertreatment manufacturers developed catalytic converter 
systems capable of reducing dpm by 25%. Such systems are available for 
larger diesel engines common in the underground metal and nonmetal 
sector.
    Other types of aftertreatment devices capable of more significant 
reductions in particulate levels began to be developed for commercial 
applications following EPA rules in 1985 limiting diesel particulate 
emissions from heavy duty diesel engines. The wall flow type ceramic 
honeycomb diesel particulate filter system was initially the most 
promising approach (SAE, SP-735, 1988). However, due to the extensive 
work performed by the engine manufacturers on new technological designs 
of the diesel engine's combustion system, and the use of low sulfur 
fuel, particulate traps turned out to be unnecessary to comply with the 
EPA standards of the time.
    While this work was underway, efforts were also being made to 
transfer this aftertreatment technology to the mining industry. The 
former Bureau of Mines investigated the use of catalyzed diesel 
particulate filters in underground mines in the United States (BOM, RI-
9478, 1993). The investigation demonstrated that filters could work, 
but that there were problems associated with their use on individual 
unit installations, and the Bureau made recommendations for 
installation of ceramic filters on mining vehicles. But as noted by one 
commenter at one of the MSHA workshops in 1995, ``while ceramic filters 
give good results early in their life cycle, they have a relatively 
short life, are very expensive and unreliable.'' (Ellington, dpm 
Workshop, Salt Lake City, UT, 1995).
    Canadian mines also began to experiment with ceramic traps in the 
1980's with similar results (BOM, IC 9324, 1992). Work in Canada today 
continues under the auspices of the Diesel Emission Evaluation Program 
(DEEP), established by the Canadian Centre for Mineral and Energy 
Technology in 1996 (DEEP Plenary Proceedings, November 1996). The goals 
of DEEP are to: (1) Evaluate aerosol sampling and analytical methods 
for dpm; and (2) evaluate the in-mine performance and costs of various 
diesel exhaust control strategies.
    Work with ceramic filters in the last few years has led to the 
development of the ceramic fiber wound filter cartridge (SAE, SP-1073, 
1995). The ceramic fiber has been reported by the manufacturer to have 
dpm reduction efficiencies up to 80 percent. This system has been used 
on vehicles to comply with German requirements that all diesel engines 
used in confined areas be filtered. Other manufacturers have made the 
wall flow type ceramic honeycomb dpm filter system commercially 
available to meet the German standard. In the case of some engines, a 
choice of the two types is available; but depending upon horsepower, 
this may not always be the case.
    In the early 1990's, MSHA worked with the former Bureau of Mines 
and a filter manufacturer to successfully develop and test a pleated 
paper filter for wet water scrubber systems of permissible diesel 
powered equipment. The dpm reduction from these filters has been 
determined in the field by the former BOM to be up to 95% (BOM, IC

[[Page 17512]]

9324). The same type of filter has been used in recently developed dry 
systems for permissible machines, with reported laboratory reductions 
in dpm of 98% (Paas, dpm Workshop, Beckley WV, 1995).

ANPRM Comments

    The ANPRM requested information about several kinds of work 
practices that might be useful in reducing dpm concentrations. These 
comments were provided well before the workshops mentioned above, and 
before MSHA issued its diesel equipment standard for underground coal 
mines, and are thus somewhat dated. But, solely to illustrate the range 
of comments received, the following sections review the comments 
concerning certain work practices--fuel type, fuel additives, and 
maintenance practices.

Type of Diesel Fuel Required

    It has been well established that the quality of diesel fuel 
influences emissions. Sulfur content, cetane number, aromatic content, 
density, viscosity, and volatility are interrelated fuel properties 
which can influence emissions. Sulfur content can have a significant 
effect on diesel emissions.
    Use of low sulfur diesel fuel reduces the sulfate fraction of dpm 
matter emissions, reduces objectionable odors associated with diesel 
exhaust and allows oxidation catalysts to perform properly. The use of 
low sulfur fuel also reduces engine wear and maintenance costs. Fuel 
sulfur content is a particularly important parameter when the fuel is 
used in low emission diesel engines. Low sulfur diesel fuel is 
available nationwide due to EPA regulations. (40 CFR parts 80 and 86.) 
In MSHA's ANPRM, information was requested on what reduction in 
concentration of diesel particulate can be achieved through the use of 
low sulfur fuel. Information was also solicited as to whether the use 
of low sulfur fuel reduces the hazard associated with diesel emissions.
    Responses from commenters stated that there would be a positive 
reduction in particulate with the use of low sulfur fuel. One commenter 
stated that the brake specific exhaust emissions (grams/brake 
horsepower-hour) of particulate would decrease by about 0.06 g/bhp-hr 
for a fuel sulfur reduction of 0.25 weight percent sulfur. The 
particulate reduction effect is proportional to the change in sulfur 
content. Another commenter stated that a typical No. 2 diesel fuel 
containing 0.25 percent weight sulfur will include 1 to 1.6 grams of 
sulfate particulate per gallon of fuel consumed. A fuel containing 0.05 
percent weight sulfur will reduce sulfate particulate to 0.2-0.3 grams 
per gallon of fuel consumed, an 80 percent reduction.
    In responding to the question on whether reducing the sulfur 
content of the fuel will reduce the health hazard associated with 
diesel emissions, several commenters stated that they knew of no 
evidence that sulfur reduction reduces the hazard of the particulate. 
MSHA also is not aware of any data supporting the proposition that 
reducing the sulfur content of the fuel will reduce the health hazard 
associated with diesel emissions. However, in the preamble to the final 
rule for the EPA requirement for the use of low sulfur fuel, EPA stated 
that there were a number of benefits which could be attributed to 
lowering the sulfur content of diesel fuel. The first area was in 
exhaust aftertreatment technology. Reductions in fuel sulfur content 
will result in small reductions in sulfur compounds being emitted. This 
will cause the whole particulate concentration from the engine to be 
reduced. However, the number of carbon particles is not reduced, 
therefore, the total carbon concentration would be the same.
    The major benefit of using low sulfur fuel is that the reduction of 
sulfur allows for the use of some aftertreatment devices such as 
catalytic converters, and catalyzed particulate traps which were 
prohibited with fuels of high sulfur content (greater than 0.05 percent 
sulfur). The high sulfur content led to sulfate particulate that when 
passed through the catalytic converter or catalyzed traps was changed 
to sulfuric acid when the sulfates came in contact with water vapor. 
Using low sulfur fuel permits these devices to be used.
    The second area of benefits that the EPA noted was that of reduced 
engine wear with the use of low sulfur fuel. Reducing engine wear will 
help maintain engines in their near manufactured condition that would 
help limit increases in particulate matter due to lack of maintenance 
or age of the engine.
    Other questions posed in the ANPRM requested information concerning 
the differences in No. 1 and No. 2 diesel fuel regarding particulate 
formation; the current sulfur content of diesel fuel used in mines; and 
when would 0.05 percent sulfur fuel be available to the mining 
industry.
    In response to those questions, commenters stated that a difference 
in No. 1 and No. 2 fuel regarding particulate formation would be that 
No. 1 fuel typically has less sulfur than No. 2 fuel and would 
therefore be expected to produce less particulate. Also, the No. 1 fuel 
has a lower density, boiling range and aromatic content and a higher 
cetane number. All of these fuel property differences tend to cause 
lower particulate emissions.
    Commenters also stated that the sulfur content of fuels 
commercially available for diesel-powered equipment can vary from 
nearly zero to 1 percent. The national average sulfur content for 
commercial No. 2 diesel fuel is approximately 0.25 percent. One 
commenter stated that sulfur content varied from region to region and 
the National Institute of Petroleum and Energy Research survey could be 
used to get the answers for specific regions.
    Commenters noted that low sulfur fuel, less than 0.05 percent 
sulfur, would be available for on-highway use as mandated by the EPA by 
October 1993. Also, California requires the statewide availability of 
0.05 percent sulfur fuel for all diesel engine applications by the same 
date. Although the EPA mandate ensures that low sulfur fuel will be 
available throughout the nation, commenters indicated the availability 
for off-road and mining application was uncertain at that time.
    The ANPRM also requested information on the differences in the per 
gallon costs among No. 1, No. 2 and 0.05 percent sulfur fuel; how much 
fuel is used annually in the mining industry; and what would be the 
economic impact on mining of using 0.05 percent sulfur fuel. In 
response, commenters stated that No. 1 fuel typically costs the user 10 
to 20 percent more than does No. 2 fuel. They also stated that the 
price of 0.05 percent sulfur fuel will eventually be set by the 
competitive market conditions. No information was submitted for 
accurately estimating fuel usage costs to the industry. The economic 
impact on the mining industry of using 0.05 percent fuel will vary 
greatly from mine to mine. Factors influencing that cost are a mine's 
dependence on diesel powered equipment, the location of the mine and 
existing regulation. Mines relying heavily on diesel equipment will be 
most impacted.
    Another commenter stated that the price for 0.05 percent fuel is 
forecast to average about 2 cents per gallon higher than the price for 
typical current No. 2 fuel. Kerosene and No. 1 distillate are forecast 
as 2 to 4 cents per gallon above 0.05 percent fuel and 4 to 6 cents 
above current No. 2 fuel. A recent census of mining and manufacturing 
dated 1987 showed mining industry energy consumption from all sources 
to total 1968.4 trillion BTU per year. Coal mining alone used 9.96 
million barrels

[[Page 17513]]

annually of distillate, at a cost of 258.1 million dollars. Included in 
these quantities was diesel fuel for surface equipment and vehicles at 
or around the mine site. The commenter also stated that applying a cost 
increase of 2 cents per gallon to the total industry distillate 
consumption would increase annual fuel costs by $24.3 million. For coal 
mining only, the cost increase would be $8.4 million annually.
    While MSHA does not have an opinion on the accuracy of the 
information received in this regard, it is in any event dated. Since 
the time that the ANPRM was open, the availability of low sulfur fuel 
has become more common. Comments received at MSHA's Diesel Workshops 
indicate that low sulfur fuel is readily available and that all that is 
needed to obtain it is to specify the desired fuel quality on the 
purchase order. The differences in the fuel properties of No. 1 and No. 
2 fuel are consistent with specifications provided by ASTM and other 
literature information concerning fuel properties.

Fuel Additives

    Information relative to fuel additives was requested in MSHA's 
ANPRM. The ANPRM requested information on the availability of fuel 
additives that can reduce dpm or additives being developed; what diesel 
emissions reduction can be expected through the use of these fuel 
additives; the cost of additives and advantages to their use; and will 
these fuel additives introduce other health hazards. One commenter 
stated that cetane improvers and detergent additives can reduce dpm 
from 0 to 10 percent. The data, however, does not indicate consistent 
benefits as in the case with sulfur reduction. Oxygenate additives can 
give larger benefits, as with methanol, but then the oxygenate is not 
so much an additive as a fuel blend. Another commenter stated the cost 
depended on the price and concentration of the additive. This commenter 
estimated the cost to be between three and seven cents per gallon of 
fuel.
    Another commenter stated that some additives are used for reducing 
injector tip fouling, other alternative additives also are offered 
specifically for the purpose of reducing smoke or dpm such as 
organometallic compounds, i.e., copper, barium, calcium, iron or 
platinum; oxygenate supplements containing alcohols or peroxides; and 
other proprietary hydrocarbons. The commenter did not quantify the 
expected reductions in dpm.
    The former Bureau of Mines commented on an investigation of barium-
based, manganese based, and ferrocene fuel additives. Details of the 
investigation are found in the literature (BOM, IC 9238, 1990). In 
general, fuel additives are not widely used by the mining industry to 
reduce dpm or to reduce regeneration temperatures in ceramic 
particulate filters. Research has shown aerosol reductions of about 30 
percent without significant adverse impacts although new pollutants 
derived from the fuel additive remain a question.
    One commenter stated that a cetane improver and detergent additives 
should not exceed 1 cent per gallon at the treat rates likely to be 
used. The use of oxygenates depends on which one and how much but would 
be perhaps an order of magnitude higher than the use of a cetane 
improver. One commenter also added that any fuel economy advantages 
would be very small.
    In response to the creation of a health hazard when using 
additives, one commenter stated that excessive exposure to cetane 
improver (alkyl nitrates), which is hazardous to humans, requires 
special handling because of poor thermal stability. Detergent additives 
are similar to those used in gasoline and probably have similar safety 
and health issues. Except at low load operation, additives are not 
likely to result in any significant quantity in the exhaust. Another 
commenter stated that the effect on human health of new chemical 
exhaust species that may result from the use of some of these additives 
has not been determined. Engine manufacturers also are concerned about 
the use of such products because their effectiveness has not always 
been adequately demonstrated and, in many cases, the effect on engine 
durability has not been well-documented for different designs and 
operating conditions.
    MSHA agrees with the commenters that fuel additives can affect 
engine performance and exhaust emissions. MSHA's experience with 
additives has shown that they can enhance fuel quality by increasing 
the cetane number, depressing the cloud point, or in the case of a 
barium based additive, affect the combustion process resulting in a 
reduction of particulate output. MSHA's experience also has shown that 
in most cases the effects of an additive on engine performance or 
emissions cannot be adequately determined without extensive research. 
The additives listed on EPA's list of ``registered additives'' meet the 
requirements of EPA's standards in 40 CFR part 79.
    MSHA is concerned about the use of untested fuel additives. A large 
number of additives are currently being marketed to reduce emissions. 
These additives include cetane improvers that increase the cetane 
number of the fuel, which may reduce emissions and improve starting; 
detergents that are used primarily to keep the fuel injectors clean; 
dispersants or surfactants that prevent the formation of thicker 
compounds that can form deposits on the fuel injectors or plug filters. 
While the use of many of these additives will result in reduced 
particulate emission, some have been found to introduce harmful agents 
into the environment. For this reason, it is a good idea to limit the 
use of additives to those that have been registered by the EPA.

Maintenance Practices

    The ANPRM requested information concerning what maintenance 
procedures are effective in reducing diesel particulate emissions from 
existing diesel-powered equipment, and what additional maintenance 
procedures would be required in conjunction with anticipated 
developments of new diesel particulate reduction technology. 
Information was also requested about the amount of time to perform the 
maintenance procedures and if any, loss of production time.
    Commenters stated that some maintenance procedures have a very 
dramatic impact on particulate emissions, while other procedures that 
are equally important for other reasons have little or no impact at all 
on particulates. Another commenter stated that maintenance procedures 
are intended to ensure that the engine operates and will continue to 
operate as intended. Such procedures will not reduce diesel particulate 
below that of the new, original equipment. A commenter stated that the 
diesel engine industry experience has demonstrated that emissions 
deterioration over the useful life of an engine is minimal.
    Commenters stated that depending on the implied technology, the 
need for additional maintenance will be based on complexity of the 
control devices. Also, time for maintenance will be dependent on 
complexity of the control device. Some production loss will occur due 
to increased maintenance procedures.
    MSHA agrees with the commenters' view that maintenance does affect 
engine emissions, some more dramatically than others. Research has 
clearly shown that without engine maintenance, all engine emissions 
will increase greatly. For example, the former Bureau of Mines, in 
conjunction with Southwest Research, conducted extensive research on 
the effects of maintenance on diesel engines which indicated this 
result (BOM contract H-0292009, 1979). MSHA agrees that

[[Page 17514]]

emissions increase is minimal over the useful life of the engine only 
when proper maintenance is performed daily. However, MSHA believes that 
with the awareness of the increased maintenance, production may not be 
lost due to the increased time that the machines are able to operate 
without unwanted down time due to poor maintenance practices.
    MSHA's diesel ``toolbox'' includes an extensive discussion on the 
importance of maintenance. It reminds operators and diesel maintenance 
personnel of the basic systems on diesel engines that need to be 
maintained, and how to avoid various problems. It includes suggestions 
from others in the mining community, and information on their success 
or difficulties in this regard.
    (7) Existing Mining Standards that Limit Miner Exposure to 
Occupational Diesel Particulate Emissions. MSHA already has in place 
various requirements that help to control miner exposure to diesel 
emissions in underground mines--including exposure to diesel 
particulate. These include ventilation requirements, engine approval 
requirements, and explicit restrictions on the concentration of various 
gases in the mine environment.
    In addition, in 1996, MSHA promulgated a rule governing the use of 
diesel-powered equipment in underground coal mines. (61 FR 55412). 
While the primary focus of the rulemaking was to promote the safe use 
of diesel engines in the hazardous environment of underground coal 
mines, various parts of the rule will help to control exposure to 
harmful diesel emissions in those mines. The new rule revised and 
updated MSHA's diesel engine approval requirements and the ventilation 
requirements for underground coal mines using diesel equipment, and 
established requirements concerning diesel fuel sulfur content and the 
idling, maintenance and emissions testing of diesel engines in 
underground coal mines.

Background

    Beginning in the 1940s, mining regulations were promulgated to 
promote the safe and healthful use of diesel engines in underground 
mines. In 1944, part 31 established procedures for limiting the gaseous 
emissions and establishing the recommended dilution air quantity for 
mine locomotives that use diesel fuel. In 1949, part 32 established 
procedures for testing of mobile diesel-powered equipment for non-coal 
mines. In 1961, part 36 was added to provide requirements for the use 
of diesel equipment in gassy noncoal mines, in which engines must be 
temperature controlled to prevent explosive hazards. These rules 
responded to research conducted by the former Bureau of Mines.
    Continued research by the former Bureau of Mines in the 1950s and 
1960s led to refinements of its ventilation recommendations, 
particularly when multiple engines are in use. An airflow of 100 to 250 
cfm/bhp was recommended for engines that have a properly adjusted fuel 
to air ratio (Holtz, 1960). An additive ventilation requirement was 
recommended for operation of multiple diesel units, which could be 
relaxed based on the mine operating procedures. This approach was 
subsequently refined to become a 100-75-50 percent guideline (MSHA 
Policy Memorandum 81-19MM, 1981). Under this guideline, when multiple 
pieces of diesel equipment are operated, the required airflow on a 
split of air would be the sum of: (a) 100 percent of the nameplate 
quantity for the vehicle with the highest nameplate air quantity 
requirement; (b) 75 percent of the nameplate air quantity requirement 
of the vehicle with the next highest nameplate air quantity 
requirement; and (c) 50 percent of the nameplate airflow for each 
additional piece of diesel equipment.

Diesel Equipment Rule

    On October 6, 1987, MSHA published in the Federal Register (52 FR 
37381) a notice establishing a committee to advise the Secretary of 
Labor on health and safety standards related to the use of diesel-
powered equipment in underground coal mines. The ``Mine Safety and 
Health Advisory Committee on Standards and Regulations for Diesel-
Powered Equipment in Underground Coal Mines'' (the Advisory Committee) 
addressed three areas of concern: the approval of diesel-powered 
equipment, the safe use of diesel equipment in underground coal mines, 
and the protection of miners' health. The Advisory Committee submitted 
its recommendations in July 1988.
    With respect to the approval of diesel-powered equipment, the 
Advisory Committee recommended that all diesel equipment except for a 
limited class, be approved for use in underground coal mines. This 
approval would involve both safety (e.g., fire suppression systems) and 
health factors (e.g., maximum exhaust emissions).
    With respect to the safe use of diesel equipment in underground 
coal mines, the Advisory Committee recommended that standards be 
developed to address the safety aspects of the use of diesel equipment, 
including such concerns as equipment maintenance, training of 
mechanics, and the storage and transport of diesel fuel.
    The Advisory Committee also made recommendations concerning miner 
health, discussed later in this section.
    As a result of the Advisory Committee's recommendations on approval 
and safe use, MSHA developed and, on October 25, 1996, promulgated as a 
final rule, standards for the ``Approval, Exhaust Gas Monitoring, and 
Safety Requirements for the Use of Diesel-Powered Equipment in 
Underground Coal Mines.'' (61 FR 55412).
    The October 25, 1996 final rule on diesels focuses on the safe use 
of diesels in underground coal mines. Integrated requirements are 
established for the safe storage, handling, and transport of diesel 
fuel underground, training of mine personnel, minimum ventilating air 
quantities for diesel powered equipment, maintenance requirements, fire 
suppression, and design features for nonpermissible machines. While the 
focus was on safety, certain rules related to emissions are included in 
the final rule. For example, the final rule requires maintenance on 
diesel powered equipment. Regular maintenance on diesel powered 
equipment should keep the diesel engine and vehicle operation at its 
original or baseline condition. However, as a check that the 
maintenance is being performed, MSHA wrote a standard for checking the 
gaseous CO emission levels on permissible and heavy duty outby machines 
to determine the need for maintenance. The CO check requires that a 
regular repeatable loaded engine condition be run on a weekly basis and 
the CO measured. Carbon monoxide is a good indicator of engine 
condition. If the CO measurement increases to a higher concentration 
than what was normally measured during the past weekly checks, then a 
maintenance person would know that either the regular maintenance was 
missed or a problem has developed that is more significant than could 
be identified by a general daily maintenance program.
    Consistent with the Advisory Committee's recommendation, the final 
rule, among other things, requires that virtually all diesel-powered 
engines used in underground coal mines be approved by MSHA. (30 CFR 
part 7 (approval requirements), part 36 (permissible machines defined), 
and part 75 (use of such equipment in underground coal mines). The 
approval requirements, among other things, are designed to require 
clean-burning

[[Page 17515]]

engines in diesel-powered equipment. (61 FR 55417). In promulgating the 
final rule, MSHA recognized that clean-burning engines are ``critically 
important'' to reducing toxic gasses to levels that can be controlled 
through ventilation. (Id.). To achieve the objective of clean-burning 
engines, the rule sets performance standards which must be met for 
virtually all diesel-powered equipment in underground coal mines (30 
CFR part 7).
    Consistent with the recommendation of the Advisory Committee, the 
technical requirements for approved diesel engines include undiluted 
exhaust limits for carbon monoxide and oxides of nitrogen. (61 FR 
55419). As recommended by the Advisory Committee, the limits for these 
gasses are derived from existing 30 CFR part 36. (61 FR 55419). Also 
consistent with the recommendation of the Advisory Committee, the final 
rule requires that as part of the approval process, ventilating air 
quantities necessary to maintain the gaseous emissions of diesel 
engines within existing required ambient limits be set. (61 FR 55420). 
As recommended by the Advisory Committee, the ventilating air 
quantities are required to appear on the engine's approval plate. (61 
FR 55421).
    The final rule also implements the Advisory Committee's 
recommendation that a particulate index be set for diesel engines. (61 
FR 55421). Although, as discussed below, there is not yet a specific 
standard limiting miners' exposure to diesel particulate, the 
particulate index is nonetheless useful in providing information to the 
mining community so that operators can compare the particulate levels 
generated by different engines. (61 FR 55421).
    Also consistent with the recommendation of the Advisory Committee, 
the final rule addresses the monitoring and control of gaseous diesel 
exhaust emissions. (30 CFR part 70; 61 FR 55413). In this regard, the 
final rule requires that mine operators take samples of carbon monoxide 
and nitrogen dioxide. (61 FR 55413, 55430-55431). Samples exceeding an 
action level of 50 percent of the threshold limits set forth in 30 CFR 
75.322, trigger corrective action by the mine operator. (30 CFR part 
70, 61 FR 55413). Also consistent with the Advisory Committee's 
recommendation, the final rule requires that diesel-powered equipment 
be adequately maintained. (30 CFR 75.1914; 61 FR 55414). Among other 
things, as recommended by the Advisory Committee, the rule requires the 
weekly examination of diesel-powered equipment, including testing of 
undiluted exhaust emissions for certain types of equipment. (30 CFR 
75.1914(g)). In addition, consistent with the Advisory Committee's 
recommendation, operators are required to establish programs to ensure 
that those performing maintenance on diesel equipment are qualified. 
(61 FR 55414). As explained in the preamble, maintenance requirements 
were included because of MSHA's recognition that inadequate equipment 
maintenance can, among other things, result in increased levels of 
harmful gaseous and particulate components from diesel exhaust. (61 FR 
55413-55414).
    Consistent with the Advisory Committee's recommendation, the final 
rule also requires that underground coal mine operators use low sulfur 
diesel fuel. (30 CFR 75.1901; 61 FR 55413). The use of low sulfur fuel 
lowers not only the amount of gaseous emissions, but also the amount of 
diesel particulate emissions. (Id.). To further reduce miners' exposure 
to diesel exhaust, the final rule prohibits operators from 
unnecessarily idling diesel-powered equipment. (30 CFR 75.1916(d)).
    Also consistent with the recommendation of the Advisory Committee, 
the final rule establishes minimum air quantity requirements in areas 
of underground coal mines where diesel-powered equipment is operated. 
(30 CFR 75.325). As set forth in the preamble, MSHA believes that 
effective mine ventilation is a key component in the control of miners' 
exposure to gasses and particulate emissions generated by diesel 
equipment. (61 FR 55433). The final rule also requires generally that 
mine operators maintain the approval plate quantity minimum airflow in 
areas of underground coal mines where diesel-powered equipment is 
operated. (30 CFR 75.325 \2\).
---------------------------------------------------------------------------

    \2\ On December 23, 1997, the National Mining Association and 
Energy West Mining Company filed petitions for review of the final 
rule. National Mining Association versus Secretary of Labor, Nos. 
96-1489 and 96-1490. These cases were consolidated and held in 
abeyance pending discussions between the mining industry and the 
Secretary. On March 19, 1998, petitioners filed an Unopposed Joint 
Motion for Voluntary Dismissal. This motion is still pending before 
the Court.
---------------------------------------------------------------------------

    The diesel equipment rule will help the mining community use 
diesel-powered equipment more safely in underground coal mines. As 
discussed throughout this preamble, the diesel equipment rule has many 
features which, though it was not their primary purpose, will 
incidently reduce harmful diesel emissions in underground coal mines--
including the particulate component of these emissions. (The 
requirements of the diesel equipment rule are highlighted with a 
special typeface in MSHA's publication, ``Practical Ways to Control 
Exposure to Diesel Exhaust in Mining--a Toolbox'', reprinted as an 
Appendix at the end of this document. An example is the requirement in 
the diesel equipment rule that all engines used in underground coal 
mines be approved engines, and be maintained in approved condition --
thus reducing emissions at the source.
    In developing this safety rule, however, MSHA did not explicitly 
consider the risks to miners of a working lifetime of dpm exposure at 
very high levels, nor the actions that could be taken to specifically 
reduce those exposure levels in underground coal mines. Moreover, the 
rule does not apply to the remainder of the mining industry, where the 
use of diesel machinery is much more intense than in underground coal.

Gas Limits

    Various organizations have established or recommended limits for 
many of the gasses occurring in diesel exhaust. Some of these are 
listed in Table II-2, together with information about the limits 
currently enforced by MSHA. MSHA requires mine operators to comply with 
gas specific threshold limit values (TLV's) recommended by the American 
Conference of Governmental Industrial Hygienists (ACGIH) in 1972 (for 
coal mines) and in 1973 (for metal and nonmetal mines).

                                   Table II-2.--Gaseous Exposure Limits (PPM)                                   
----------------------------------------------------------------------------------------------------------------
                                                                                                                
----------------------------------------------------------------------------------------------------------------
                                                                                                                
(1)                                                                                                             
(1)MSHA limits                                                                                                  
                                                                                       -------------------------
                          Pollutant                                                                             
(1)Range of limits                                                                                              
                                                                                                                
(1)recommended                                                   Coal a       M/NM b                            
----------------------------------------------------------------------------------------------------------------
HCHO........................................................      c 0.016       d. 0.3            2            2

[[Page 17516]]

                                                                                                                
CO..........................................................         d 25           50           50           50
CO2.........................................................      c 5,000        5,000        5,000        5,000
NO2.........................................................     c d e 25           25           25           25
NO2.........................................................          f 1          d 3            5            5
SO2.........................................................        c d 2          e 5            2           5 
----------------------------------------------------------------------------------------------------------------
Table Notes:                                                                                                    
a ACGIH, 1972.                                                                                                  
b ACGIH, 1973.                                                                                                  
c NIOSH recommended exposure limit (REL), based on a 10-hour, time-weighted average.                            
d ACGIH, 1996.                                                                                                  
e OSHA permissible exposure limit (PEL).                                                                        
f NIOSH recommends only a 1-ppm, 15-minutes, short-term exposure limit (STEL).                                  

    In 1989, MSHA proposed changing some of these limits in the context 
of a proposed rule on air quality standards. (54 FR 35760). Following 
opportunity for comment and hearings, a portion of that proposed rule, 
concerning control of drill dust, has been promulgated, but the other 
components are still under review. To change a limit at this point in 
time requires a regulatory action; the rule does not provide for their 
automatic updating.
    (8) How Other Jurisdictions are Restricting Occupational Exposure 
to Diesel Soot. MSHA's proposed rule is the first effort by the Federal 
government to deal with the special risks faced by workers exposed to 
diesel exhaust on the job--because, as described in detail in the part 
III of this preamble, miner exposures are an order of magnitude above 
those of any other group of workers. But others have been looking at 
the problem of exposure to diesel soot.

States

    As noted in the first section of this part, few underground coal 
mines now use diesel engines. Several states have had bans on the use 
of such equipment: Pennsylvania, West Virginia, and Ohio.
    Recently, Pennsylvania has replaced its ban with a special law that 
permits the use of diesel-powered equipment in deep coal mines under 
certain circumstances. The Pennsylvania statute goes beyond MSHA's new 
regulation on the use of diesel-powered equipment in underground coal 
mines. Of particular interest is that it specifically addresses diesel 
particulate. The State did not set a limit on the exposure of miners to 
dpm, nor did it establish a limit on the concentration of dpm in deep 
coal mines. Rather, it approached the issue by imposing controls that 
will limit dpm emissions at the source.
    First, all diesel engines used in underground deep coal mines in 
Pennsylvania must be MSHA-approved engines with an ``exhaust emissions 
control and conditioning system'' that meets certain tests. (Article 
II-A, Section 203-A, Exhaust Emission Controls). Among these are dpm 
emissions from each engine no greater than ``an average concentration 
of 0.12 mg/m3 diluted by fifty percent of the MSHA approval 
plate ventilation for that diesel engine.'' In addition, any exhaust 
emissions control and conditioning system must include a ``Diesel 
Particulate Matter (DPM) filter capable of an average of ninety-five 
percent or greater reduction of dpm emissions.'' It also requires the 
use of an oxidation catalytic converter. Thus, the Pennsylvania statute 
requires the use of low-emitting engines, and then the use of 
aftertreatment devices that significantly reduce what particulates are 
emitted from these engines.
    The Pennsylvania law also has a number of other requirements for 
the safe use of diesel-powered equipment in the particularly hazardous 
environments of underground coal mines. Many of these parallel the 
requirements in MSHA's rule. Like MSHA's requirements, they too can 
result in reducing miner exposure to diesel particulate--e.g., regular 
maintenance of diesel engines by qualified personnel and equipment 
operator examinations. The requirements in the Pennsylvania law take 
into account the need to maintain the aftertreatment devices required 
to control diesel particulate (see, e.g., section 217-A(b)(6)).
    West Virginia has also lifted its ban, subject to rules to be 
developed by a joint labor-management commission. MSHA understands that 
pursuant to the West Virginia law lifting the ban, the Commission has 
only a limited time to determine the applicable rules, or the matter is 
to be referred to an arbitrator for resolution.

Other Countries

    Concerns about air pollution have been a major impetus for most 
countries' standards on vehicle emissions, including diesel 
particulate. Most industrialized nations recognize the fundamental 
principle that their citizens should be protected against recognized 
health risks from air pollution and that this requires the control of 
particulate such as diesel exhaust. In November of 1995, for example, 
the government of the United Kingdom recommended a limit on 
PM10, and noted it would be taking further actions to limit 
airborne particulate matter (including a special study of dust from 
surface minerals workings).
    Concerns about international trade have been another impetus. 
Diesel engines are sold to an international market to power many types 
of industrial and nonindustrial machinery and equipment. The European 
Union manufacturers exported more than 50 percent of their products, 
mainly to South Korea, Taiwan, China, Australia, New Zealand and the 
United States. Germany and the United Kingdom, two major producers, 
have pushed for harmonized world standards to level the playing field 
among the various countries' engine producers and to simplify the 
acceptance of their products by other countries (Financial Times, 
1996). This includes products that must be designed to meet pollution 
standards. The European Union (EU) is now considering a proposal to set 
an EU-wide standard for the control of the emission of pollutants from 
non-road mobile machinery (Official Journal of European Communities, 
1995). The proposal would largely track that of the U.S. Environmental 
Protection Agency's final rule on the Control of Air Pollution 
Determination of Significance for Nonroad Sources and Emission 
Standards for New Nonroad Compression-Ignition Engines at or above 37 
kilowatts (50 HP)p (discussed in section 3 of this part of the 
preamble).
    A third impetus to action has been the studies of the health 
effects of worker exposure to diesel exhaust--many of which have been 
epidemiological studies concerning workers in other countries. As noted 
in Part III of this preamble, the studies include cohorts of Swedish 
dock workers and bus garage workers, Canadian railway workers and

[[Page 17517]]

miners, French workers, London transport workers, and Danish chimney 
sweeps.
    Below, the agency summarizes some information obtained on exposure 
limits of other countries. Due to differences in regulatory schemes 
among nations considering the effects of diesel exhaust, countries 
which have addressed the issue are more likely to have issued 
recommendations rather than a mandatory maximum exposure limit. Some of 
these may have issued mandatory design features for diesel equipment to 
assist in achieving the recommended exposure level. Measurement systems 
also vary.

Germany

    German legislation on dangerous substances classifies diesel engine 
emissions as carcinogenic. Therefore, diesel engines must be designed 
and operated using the latest technology to cut emissions. This always 
requires an examination to determine whether the respective operations 
and activities may be carried out using other types of less polluting 
equipment. If, as a result of the examination, it is decided that the 
use of diesel engines is necessary measures must be instituted to 
reduce emissions. Such measures can include low-polluting diesel 
engines, low sulphur fuels, regular maintenance, and, where technology 
permits, the use of particulate traps. To reduce exposure levels 
further, diesel engine emissions may be regulated directly at the 
source; ventilation systems may be required to be installed.
    The use of diesel vehicles in a fully or partly enclosed working 
space--such as in an underground mine--may be restricted by the 
government, depending on the necessary engine power or load capacity 
and on whether the relevant operation could be accomplished using a 
non-polluting vehicle, e.g., an electrically powered vehicle. When 
determining whether alternate equipment is to be used, the burden to 
the operator to use such equipment is also considered.
    In April of 1997, the following permissible exposure limits (TRK 
\3\) for diesel engine emissions were instituted for workplaces in 
mining.
---------------------------------------------------------------------------

    \3\ TPK is the technical exposure limit of a hazardous material 
that defines the concentration of gas, vapour or airborne 
particulates which is the minimum possible with current technology 
and which serves as a guide for necessary protective measures and 
monitoring in the workplace.
    \4\ Colloid dust is defined as that part of total respirable 
dust in a workplace that passes the alveolar ducts of the worker.
---------------------------------------------------------------------------

    (1) Non-coal underground mining and construction work: TRK = 0.3 
mg/m\3\ of colloid dust.\4\
    (2) other: TRK = 0.1 mg/m\3\ of colloid dust.
    (3) The average concentration of diesel engine emissions within a 
period of 15 minutes should never be higher than four times the TRK 
value.
    The TRK is ascertained by determining the fraction of elemental 
carbon in the colloid (fine) dust by coulometric analysis. Determining 
the fraction of elemental carbon always involves the determination of 
total organic carbon in the course of analysis. If the workplace 
analysis shows that the fraction of elemental carbon in total carbon 
(elemental carbon plus organic carbon) is lower than 50%, or is subject 
to major fluctuations, then the TRK limits total carbon in such 
workplaces to 0.15 mg/m\3\.
    Irrespective of the TRK levels, the following additional measures 
are considered necessary once the concentration reaches 0.1 mg/m\3\ 
colloid dust:
    (1) Informing employees concerned;
    (2) Limited working hours for certain staff categories;
    (3) Special working hours; and
    (4) Medical checkups.
    If concentrations continue to fail to meet the TRK level, the 
employer must:
    (1) Provide appropriate, effective, hygienic breathing apparatus, 
and
    (2) Ensure that workers are not kept at the workplace for longer 
than absolutely necessary and that health regulations are observed.
    Workers must use the breathing apparatus if the TRK levels for 
diesel engine emissions at the work place are exceeded. Due to the 
interference of recognized analysis techniques in coal mining, it is 
currently impossible to ascertain exposure levels in the air in coal 
mines. As a consequence, the coal mining authorities require the use of 
special low-polluting engines in underground mining and impose special 
requirements on the supply of fresh air to the workplace.

European Standards

    On April 21, 1997, the draft of a European directive that applied 
to emissions from non-road mobile machinery was prepared. The directive 
proposed technical measures that would result in a reduction in 
emissions from internal-combustion engines (gasoline and diesel) 
installed in non-road mobile machinery, and type-approval procedures 
that would provide uniformity among the member nations for the approval 
of these engines.
    The directive proposed a two-stage process. Stage 1, proposed to 
begin December 31, 1997, was for three different engine categories:

--A: 130 kW <= P <= 560 kW,
--B: 75 kW <= P < 130. kW,
--C: 37 kW <= P < 75 kW.

    Stage 2, proposed to begin December 31, 1999, consisted of four 
engine categories being phased-in over a four-year period:

-- D: after December 31,1999 for engines of a power output of 18 kW <= 
P < 37 kW,
-- E: after December 31, 2000 for engines of a power output of 130 kW<= 
P <= 560 kW,
--F: after December 31, 2001 for engines of a power output of 75 kW<= P 
< 130 kW,
--G: after December 31, 2002 for engines of a power output of 37 kW<= P 
<=75 kW.

    The emissions shown in the following table for carbon monoxide, 
hydrocarbons, oxides of nitrogen and particulates are to be met for the 
respective engine categories described for stage I.

----------------------------------------------------------------------------------------------------------------
                                                                Carbon                  Oxides of               
                                                               monoxide   Hydrocarbon    nitrogen   Particulates
                     Net power (P) (kW)                        (P)  (g/   s (HC)  (g/   (NOX)  (g/    (PT)  (g/ 
                                                                 kWH)         kWh)         kWh)         kWh)    
----------------------------------------------------------------------------------------------------------------
130P<560........................................          5.0          1.3          9.2          0.54
75P<130.........................................          5.0          1.3          9.2          0.70
37P<75..........................................          6.5          1.3          9.2          0.85
----------------------------------------------------------------------------------------------------------------

    The engine emission limits that have to be achieved for stage II 
are shown in the following table. The emissions limits shown are 
engine-out limits and are to be achieved before any aftertreatment 
device is used.

[[Page 17518]]



----------------------------------------------------------------------------------------------------------------
                                                               Carbon                   Oxides of               
                                                              monoxide   Hydrocarbons    nitrogen   Particulates
                    Net power (P) (kW)                        (P)  (g/     (HC)  (g/    (NOX)  (g/    (PT)  (g/ 
                                                                kWH)         kWh)          kWh)         kWh)    
----------------------------------------------------------------------------------------------------------------
130P<560.......................................          3.5           1.0          6.0           0.2
75P<130........................................          5.0           1.0          6.0           0.3
37P<75.........................................          5.0           1.3          7.0           0.4
18P<37.........................................          5.5           1.5          8.0           0.8
----------------------------------------------------------------------------------------------------------------

Canada (Related Developments in Canada)

    The Mining and Minerals Research Laboratories (MMRL) of the Canada 
Centre for Mineral and Energy Technology (CANMET), an arm of the 
Federal Department of Natural Resources Canada (NRCAN), began work in 
the early 1970s to develop measurement tools and control technologies 
for diesel particulate matter (dpm). In 1978, I.W. French and Dr. Anne 
Mildon produced a CANMET-sponsored contract study entitled: ``Health 
Implications of Exposure of Underground Mine Workers to Diesel Exhaust 
Emissions.'' In this document, an Air Quality Index (AQI) was developed 
involving several major diesel contaminants (CO, NO, NO2, 
SO2 and RCD--respirable combustible dust which is mostly 
dpm). These concentrations were divided by their then current 
permissible exposure limits, and the sum of the several ratios 
indicates the level of pollution in the mine atmosphere. The maximum 
value for this Index was fixed at 3.0. This criterion was determined by 
the known health hazard associated with small particle inhalation, and 
the known chemical composition of dpm, among other matters.
    Subsequently, in 1986, the Canadian Ad hoc Diesel Committee was 
formed from all segments of the mining industry, including: mine 
operators, the labor force, equipment manufacturers, research agencies 
including CANMET, and Canadian regulatory bodies. The objective was the 
identification of major problems for research and development 
attention, the undertaking of the indicated studies, and the 
application of the results to reduce the impact of diesel machines on 
the health of underground miners.
    In 1990-91, CANMET developed an RCD mine sampling protocol on 
behalf of the Ad hoc Committee. Then current underground sampling 
studies indicated an average ratio of RCD to dpm of 1.5. This factor 
accounted for the presence of other airborne combustible liquids 
including fuel, lubrication and particularly drilling oils, in addition 
to the dpm.
    The original 1978 French-Mildon study was updated under a CANMET 
contract in 1990. It recommended that the dpm levels be reduced to 0.5 
mg/m3 (suggesting a corresponding RCD level of 0.75 mg/
m3).
    However, in 1991, the Ad hoc Committee decided to set an interim 
recommended RCD level of 1.5 mg/m3 (the equivalent 1.0 mg/
m3). This value matched the then recommended, but not 
promulgated, MSHA ``Ventilation Index'' value for dpm of 1.0 mg/
m3. Consequently, all of the North American mining industry 
then seemed to be accepting the same maximum levels of dpm.
    It should be noted that for coal mine environments or other 
environments where a non-diesel carbonaceous aerosol is present, RCD 
analysis is not an appropriate measure of dpm levels.
    Neither CANMET nor the Ad hoc Committee is a regulatory body. In 
Canada, mining is regulated by the individual provinces and 
territories. However, the federal laboratories provide: research and 
development facilities, advice based on research and development, and 
engine/machine certification services, in order to assist the provinces 
in their diesel-related mining regulatory functions.
    Prior to the 1991 recommendation of the Ad hoc Committee, Quebec 
enacted regulations requiring: ventilation, a maximum of 0.25% sulfur 
content in diesel fuel; a prohibition on black smoke; exhaust cooling 
to a maximum temperature of 85 deg.C; and the setting of maximum 
contaminant levels. Since 1997, new regulations add the CSA Standard 
for engine certification, a maximum RCD level of 1.5 mg/m3, 
and the application of an exhaust treatment system.
    Further, after the Ad hoc Committee recommendation was published in 
1991 (RCDmax = 1.5 mg/m3), various provinces took the 
following actions:
    (1) Five provinces--British Columbia, Ontario, Quebec, New 
Brunswick, and Nova Scotia, and the Northwest Territories, adopted an 
RCD limit of 1.5 mg/m3.
    (2) Two others, Manitoba and Newfoundland/Labrador, have been 
adopting the ACGIH TLVs.
    (3) Two provinces, Alberta and Saskatchewan, and the Yukon 
Territory, continue to have no dpm limit.
    Most Canadian Inspectorates accept the CSA Standard for diesel 
machine/engine certification. This Standard specifies the undiluted 
Exhaust Quality Index (EQI) criterion for calculation of the 
ventilation in cfm, required for each diesel engine/machine. Fuel 
sulfur content, type of aftertreatment device and rated engine load 
factor are on-site, variable factors which may alter the ventilation 
ultimately required. Diesel fuel may not exceed 0.50% sulfur, and must 
have a minimum flash point of 52 deg.C. However, most mines in Canada 
now use fuel containing less than 0.05% sulfur by weight.
    In addition to limiting the RCD concentration, Qntario, established 
rules in 1994 that required diesel equipment to meet the Canadian 
Standards Association ``Non-Rail-Bound Diesel-Powered Machines for use 
in Non-Gassy Underground Mines'' (CSA M424.2-M90) Standard, excepting 
the ventilation assessment clauses. As far as fuel sulfur and 
flashpoint are concerned, Ontario is intending to change to: Smax = 
0.05% from 0.25%, and maximum fuel flash point = 38 deg.C from 
52 deg.C.
    New Brunswick, in addition to limiting the RCD concentration, 
requires mine operators to submit an ambient air quality monitoring 
plan. Diesel engines above 100 horsepower must be certified, and there 
is a minimum ventilation requirement of 105 cfm/bhp.
    Since 1996, the Ad hoc organization and the industry consortium 
called the Diesel Emissions Evaluation Program (DEEP) have been 
cooperating in a research and development program designed to reduce 
dpm levels in mines.

World Health Organization (WHO)

    Environmental Health Criteria 171 on ``Diesel Fuel and Exhaust 
Emissions'' is a 1996 monograph published under joint sponsorship of 
the United Nations Environment Programme, the International Labour 
Organisation, and the World Health Organization. The monograph provides 
a comprehensive review of the literature and evaluates the risks for 
human health and the

[[Page 17519]]

environment from exposure to diesel fuel and exhaust emissions.
    The following tables compiled in the monograph show diesel engine 
exhaust limits for various exhaust components and illustrate that there 
is international concern about the amount of diesel exhaust being 
released into the environment.

                           Table II-3.--International Limit Values for Components of Diesel Exhaust Light-Duty Vehicles (g/km)                          
--------------------------------------------------------------------------------------------------------------------------------------------------------
           Region             Carbon monoxide   Nitrogen oxides    Hydrocarbons      Particulates                          Comments                     
--------------------------------------------------------------------------------------------------------------------------------------------------------
Austria.....................  2.1............  0.62............  0.25............  0.124...........  3.5t; since 1991; from 1995, adoption of
                                                                                                      European Union standards planned.                 
Canada......................  2.1............  0.62............  0.25............  0.12............  Since 1987.                                        
European Union..............  2.72...........  0.97 (with        ................  0.14............  Since 1992.                                        
                                                hydrocarbons).                                                                                          
                              1.0............  0.7.............  ................  0.08............  From 1996.                                         
Finland.....................  ...............  ................  ................  Since 1993......                                                     
Japan.......................  2.1............  0.7.............  0.62............  None............  Since 1986.                                        
                              2.1............  0.5.............  0.4.............  0.2.............  Since 1994.                                        
Sweden, Norway..............  2.1............  0.62 (city).....  0.25............  0.124...........  3.5t; from motor year 1992.             
                                               0.76 (highway)                                                                                           
Switzerland.................  2.1............  0.62 (city).....  0.25............  0.124...........  3.5t; since 1988; from 1995, adoption of
                                               0.76 (highway)                                         European Union standard planned.                  
USA (California)............  2.1-5.2........  0.2-0.6.........  0.2-0.3 (except   0.05 (up to       Depending on mileage.                              
                                                                  methane).         31000 km).                                                          
US Environmental Protection   2.1-2.6........  0.6-0.8.........  0.2.............  0.05-0.12.......  Depending on mileage.                              
 Agency.                                                                                                                                                
--------------------------------------------------------------------------------------------------------------------------------------------------------


                          Table II-4.--International Limit Values for Components of Diesel Exhaust Heavy-Duty Vehicles (g/kWh)                          
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                         Carbon      Nitrogen       Hydro                                                                               
               Region                   monoxide      oxides       carbons    Particulates                            Comments                          
--------------------------------------------------------------------------------------------------------------------------------------------------------
Austria.............................          4.9          9.0          1.23          0.4                                                               
Canada..............................         15.5          5.0          1.3           0.25  g/bhp-h.                                                    
                                             15.5          5.0          1.3           0.1   g/bhp-h; from 1995-97.                                      
European Union......................          4.5          8.0          1.1           0.36  Since 1992.                                                 
                                              4.0          7.0          1.1           0.15  From 1995-96.                                               
Japan...............................          7.4          5.0          2.9           0.7   Indirect injection engines.                                 
                                              7.4          6.0          2.9           0.7   Direct injection engines.                                   
Sweden..............................          4.9          9.0          1.23          0.4                                                               
USA.................................         15.5          5.0          1.3           0.07  g/bhp-h; bus.                                               
                                             15.5          4.0          1.3           0.1   g/bhp-h; truck.                                             
                                             15.5          5.0          1.3           0.05  g/bhp-h; bus; from 1998.                                    
                                             15.5          4.0          1.3           0.1   g/bhp-h; truck; from 1998.                                  
--------------------------------------------------------------------------------------------------------------------------------------------------------
Adapted from Mercedes-Benz AG (1994b).                                                                                                                  

    With respect to the protection of human health, the monograph 
states that the data reviewed supports the conclusion that inhalation 
of diesel exhaust is of concern with respect to both neoplastic and 
non-neoplastic diseases. The monograph found that diesel exhaust ``is 
probably carcinogenic to humans.'' It also states that the particulate 
phase appears to have the greatest effect on health, and both the 
particle core and the associated organic materials have biological 
activity, although the gas-phase components cannot be disregarded. The 
monograph recommends the following actions for the protection of human 
health:
    (1) Diesel exhaust emissions should be controlled as part of the 
overall control of atmospheric pollution, particularly in urban 
environments.
    (2) Emissions should be controlled strictly by regulatory 
inspections and prompt remedial actions.
    (3) Urgent efforts should be made to reduce emissions, specifically 
of particulates, by changing exhaust train techniques, engine design, 
and fuel consumption.
    (4) In the occupational environment, good work practices should be 
encouraged, and adequate ventilation must be provided to prevent 
excessive exposure.
    The monograph made no recommendations as to what constitutes 
excessive exposure.

International Agency for Research on Cancer (IARC)

    The carcinogenic risks for human beings were evaluated by a working 
group convened by the International Agency for Research on Cancer in 
1988 (International Agency for Research on Cancer, 1989b). The 
conclusions were:
    (1) There is sufficient evidence for the carcinogenicity in 
experimental animals of the whole diesel engine exhaust.
    (2) There is inadequate evidence for the carcinogenicity in animals 
of gas-phase diesel engine exhaust (with particles removed).
    (3) There is sufficient evidence for the carcinogenicity in 
experimental animals of extracts of diesel engine exhaust particles.
    (4) There is limited evidence for the carcinogenicity in humans of 
engine exhausts (unspecified as from diesel or gasoline engines).

[[Page 17520]]

Overall IARC Evaluation

    Diesel engine exhaust is probably carcinogenic to humans (Group 
2A).
    (9) MSHA's Initiative to Limit Miner Exposure to Diesel 
Particulate--a Brief History of this Rulemaking and Related Actions. As 
discussed in part III of this preamble, by the early 1980's, the 
evidence indicating that exposure to diesel exhaust might be harmful to 
miners, particularly in underground mines, had started to grow. As a 
result, formal agency actions were initiated to investigate this 
possibility and to determine what, if any, actions might be 
appropriate. These actions are summarized here in chronological 
sequence, without comment as to the basis of any action or conclusion.
    In 1984, in accordance with the Sec. 102(b) of the Mine Act, NIOSH 
established a standing Mine Health Research Advisory Committee to 
advise it on matters involving or related to mine health research. In 
turn, that group established a subgroup to determine if:

    * * * there is a scientific basis for developing a 
recommendation on the use of diesel equipment in underground mining 
operations and defining the limits of current knowledge, and 
recommending areas of research for NIOSH, if any, taking into 
account other investigators' ongoing and planned research. (49 FR 
37174).

    In 1985, MSHA established an Interagency Task Group with the 
National Institute for Occupational Safety and Health (NIOSH) and the 
former Bureau of Mines (BOM) to assess the health and safety 
implications of the use of diesel-powered equipment in underground coal 
mines. In part, as a result of the recommendation of the Task Group, 
MSHA, in April 1986, began drafting proposed regulations on the 
approval and use of diesel-powered equipment in underground coal mines. 
Also in 1986, the subgroup of the NIOSH advisory committee studying 
this issue summarized the evidence available at that time as follows:

    It is our opinion that although there are some data suggesting a 
small excess risk of adverse health effects associated with exposure 
to diesel exhaust, these data are not compelling enough to exclude 
diesels from underground mines. In cases where diesel equipment is 
used in mines, controls should be employed to minimize exposure to 
diesel exhaust. (Interagency Task Group Report, 1986).

    As noted previously in section 7 of this part, in discussing MSHA's 
diesel equipment rule, on October 6, 1987, pursuant to Section 102(c) 
of the Mine Act, 30 U.S.C. Sec. 812(c), MSHA appointed an advisory 
committee ``to provide advice on the complex issues concerning the use 
of diesel-powered equipment in underground coal mines.'' (52 FR 37381). 
MSHA appointed nine members to the Advisory Committee. As required by 
Section 101(a)(1), MSHA provided the Advisory Committee with draft 
regulations on the approval and use of diesel-powered equipment in 
underground coal mines. The draft regulations did not include standards 
setting specific limitations on diesel particulate, nor had MSHA at 
that time determined that such standards should be promulgated.
    In July 1988, the Advisory Committee completed its work with the 
issuance of a report entitled ``Report of the Mine Safety and Health 
Administration Advisory Committee on Standards and Regulations for 
Diesel-Powered Equipment in Underground Coal Mines.'' The Advisory 
Committee recommended that MSHA promulgate standards governing the 
approval and use of diesel-powered equipment in underground coal mines. 
The Advisory Committee recommended that MSHA promulgate standards 
limiting underground coal miners' exposure to diesel exhaust.
    With respect to diesel particulate, the Advisory Committee 
recommended that MSHA ``set in motion a mechanism whereby a diesel 
particulate standard can be set.'' (MSHA, 1988). In this regard, the 
Advisory Committee determined that because of inadequacies in the data 
on the health effects of diesel particulate matter and inadequacies in 
the technology for monitoring the amount of diesel particulate matter 
at that time, it could not recommend that MSHA promulgate a standard 
specifically limiting the level of diesel particulate matter. (Id. 64-
65). Instead, the Advisory Committee recommended that MSHA request 
NIOSH and the former BOM to prioritize research in the development of 
sampling methods and devices for diesel particulate. The Advisory 
Committee also recommended that MSHA request a study on the chronic and 
acute effects of diesel emissions (Id.). In addition, the Advisory 
Committee recommended that the control of diesel particulate ``be 
accomplished through a combination of measures including fuel 
requirements, equipment design, and in-mine controls such as the 
ventilation system and equipment maintenance in conjunction with 
undiluted exhaust measurements.'' The Advisory Committee further 
recommended that particulate emissions ``be evaluated in the equipment 
approval process and a particulate emission index reported.'' (Id. at 
9).
    In addition, the Advisory Committee recommended that ``the total 
respirable particulate, including diesel particulate, should not exceed 
the existing two milligrams per cubic meter respirable dust standard.'' 
(Id. at 9). Section 202(b)(2) of the Mine Act requires that coal mine 
operators maintain the average concentration of respirable dust at 
their mines at or below two milligrams per cubic meter which 
effectively prohibits diesel particulate matter in excess of two 
milligrams per cubic meter, 30 U.S.C. 842(b)(2).
    Also in 1988, NIOSH issued a Current Intelligence Bulletin 
recommending that whole diesel exhaust be regarded as a potential 
carcinogen and controlled to the lowest feasible exposure level (NIOSH, 
1988). In its bulletin, NIOSH concluded that although the excess risk 
of cancer in diesel exhaust exposed workers has not been quantitatively 
estimated, it is logical to assume that reductions in exposure to 
diesel exhaust in the workplace would reduce the excess risk. NIOSH 
stated that ``[g]iven what we currently know there is an urgent need 
for efforts to be made to reduce occupational exposures to DEP [dpm] in 
mines.''
    Consistent with the Advisory Committee's research recommendations, 
MSHA, in September 1988, formally requested NIOSH to perform a risk 
assessment for exposure to diesel particulate. (57 FR 500). MSHA also 
requested assistance from NIOSH and the former BOM in developing 
sampling and analytical methodologies for assessing exposure to diesel 
particulate in mining operations. (Id.). In part, as a result of the 
Advisory Committee's recommendation, MSHA also participated in studies 
on diesel particulate sampling methodologies and determination of 
underground occupational exposure to diesel particulate. A list of the 
studies requested and reports thereof is set forth in 57 FR 500-501.
    On October 4, 1989, MSHA published a Notice of Proposed Rulemaking 
on approval requirements, exposure monitoring, and safety requirements 
for the use of diesel-powered equipment in underground coal mines. (54 
FR 40950). The proposed rule, among other things, addressed, and in 
fact followed, the Advisory Committee's recommendation that MSHA 
promulgate regulations requiring the approval of diesel engines (54 FR 
40951), limiting gaseous pollutants from diesel equipment, (Id.), 
establishing ventilation requirements based on approval plate dilution 
air quantities (54 FR 40990), requiring equipment maintenance (54 FR 
40958), requiring that trained personnel work on diesel-powered 
equipment, (54 FR 40995), establishing fuel requirements,

[[Page 17521]]

(Id.), establishing gaseous contaminant monitoring (54 FR 40989), and 
requiring that a particulate index indicating the quantity of air 
needed to dilute particulate emissions from diesel engines be 
established. (54 FR 40953).
    On January 6, 1992, MSHA published an Advance Notice of Proposed 
Rulemaking (ANPRM) indicating that it was in the early stages of 
developing a rule specifically addressing miners' exposure to diesel 
particulate. (57 FR 500). In the ANPRM, MSHA, among other things, 
sought comment on specific reports on diesel particulate prepared by 
NIOSH and the former BOM. (Id.). MSHA also sought comment on reports on 
diesel particulate which were prepared by or in conjunction with MSHA. 
(57 FR 501). The ANPRM also sought comments on the health effects, 
technological and economic feasibility, and provisions which should be 
considered for inclusion in a diesel particulate rule. (57 FR 501). The 
notice also identified five specific areas where the agency was 
particularly interested in comments, and about which it asked a number 
of detailed questions: (1) exposure limits, including the basis 
therefore; (2) the validity of the NIOSH risk assessment model and the 
validity of various types of studies; (3) information about non-cancer 
risks, non-lung routes of entry, and the confounding effects of tobacco 
smoking; (4) the availability, accuracy and proper use of sampling and 
monitoring methods for diesel particulate; and (5) the technological 
and economic feasibility of various types of controls, including 
ventilation, diesel fuel, engine design, aftertreatment devices, and 
maintenance by mechanics with specialized training. The notice also 
solicited specific information from the mining community on ``the need 
for a medical surveillance or screening program and on the use of 
respiratory equipment.'' (57 FR 500). The comment period on the ANPRM 
closed on July 10, 1992.
    While MSHA was completing a ``comprehensive analysis of the 
comments and any other information received'' in response to the ANPRM 
(57 FR 501), it took several actions to encourage the mining community 
to begin to deal with this problem, and to provide the knowledge and 
equipment needed for this task. As described earlier in this part, the 
Agency held several workshops in 1995, published a ``toolbox'' of 
controls, and developed a spreadsheet template that allows mine 
operators to compare the impacts of various controls on dpm 
concentrations in individual mines.
    On October 25, 1996, MSHA published a final rule addressing 
approval, exhaust monitoring, and safety requirements for the use of 
diesel-powered equipment in underground coal mines. (61 FR 55412). The 
final rule addresses and in large part is consistent with the specific 
recommendations made by the Advisory Committee for limiting underground 
coal miners' exposure to diesel exhaust. (A further summary of this 
rule is contained in section 7 of this part).
    On February 26, 1997, the United Mine Workers of America petitioned 
the U.S. Court of Appeals for the D.C. Circuit to issue a writ of 
mandamus ordering the Secretary of Labor to promulgate a rule on diesel 
particulate. In Re: International Union, United Mine Workers of 
America, D.C. Cir. Ct. Appeals, No. 97-1109. The matter was scheduled 
for oral argument on September 12, 1997. On September 11, 1997, the 
Court granted the parties' joint motion to continue oral argument and 
hold the proceedings in abeyance. The Court directed the parties to 
file status reports or motions to govern future proceedings at 90-day 
intervals. Pursuant to that order, on March 10, 1998, the Secretary 
filed a status report.

III. Risk Assessment

Table of Contents

Introduction

1. Exposures of U.S. Miners
    a. Underground Coal Mines
    b. Underground Metal and Nonmetal Mines
    c. Surface Mines
    d. Comparison of Miner Exposures to Exposures of Other Groups
2. Health Effects Associated with DPM Exposures
    a. Relevancy Considerations
    i. Relevance of Health Effects Observed in Animals
    ii. Relevance of Health Effects that are Reversible
    iii. Relevance of Health Effects Associated with Fine 
Particulate Matter in Ambient Air
    b. Acute Health Effects
    i. Symptoms Reported by Exposed Miners
    ii. Studies Based on Exposures to Diesel Emissions
    iii. Studies Based on Exposures to Particulate Matter in Ambient 
Air
    c. Chronic Health Effects
    i. Studies Based on Exposures to Diesel Emissions
    A. Chronic Effects Other than Cancer
    B. Cancer
    i. Lung Cancer
    ii. Bladder Cancer
    ii. Studies Based on Exposures to Fine Particulate in Ambient 
Air
    d. Mechanisms of Toxicity
    i. Effects Other than Cancer
    ii. Lung Cancer
    A. Genotoxicological Evidence
    B. Evidence from Animal Studies
3. Characterization of Risk
    a. Material Impairments to Miner Health or Functional Capacity
    i. Sensory Irritations and Respiratory Symptoms
    ii. Excess Risk of Death from Cardiovascular, Cardiopulmonary, 
or Respiratory Causes
    iii. Lung Cancer
    b. Significance of the Risk of Material Impairment to Miners
    i. Definition of a Significant Risk
    ii. Evidence of Significant Risk at Current Exposure Levels
    c. Substantial Reduction of Risk by Proposed Rule
Conclusions

Introduction

    MSHA has reviewed the scientific literature to evaluate the 
potential health effects of diesel particulate at occupational 
exposures encountered in the mining industry. Based on its review of 
the currently available information, this part of the preamble assesses 
the risks associated with those exposures. Additional material 
submitted for the record will be considered by MSHA before final 
determinations are made.
    Agencies sometimes place risk assessments in the rulemaking record 
and provide only a summary in the preamble for a proposed rule. MSHA 
has decided that, in this case, it is important to disseminate a 
discussion of risk widely throughout the mining community. Therefore, 
the full assessment is being included as part of the preamble.
    The risk assessment begins with a discussion of dpm exposure levels 
observed in the mining industry. This is followed by a review of 
information available to MSHA on health effects that have been 
associated with diesel particulate exposure. Finally, in the section 
entitled ``Characterization of Risk,'' the Agency considers three 
questions that must be addressed for rulemaking under the Mine Act, and 
relates the available information about risks of dpm exposure at 
current levels to the regulatory requirements.
    A risk assessment must be technical enough to present the evidence 
and describe the main controversies surrounding it. At the same time, 
an overly technical presentation could cause stakeholders to lose sight 
of the main points. MSHA is guided by the first principle the National 
Research Council established for risk characterization: that the 
approach be--

    [a] decision driven activity, directed toward informing choices 
and solving problems * * * Oversimplifying the science or skewing 
the results through selectivity can lead to the inappropriate use of 
scientific information in risk management decisions,

[[Page 17522]]

but providing full information, if it does not address key concerns 
of the intended audience, can undermine that audience's trust in the 
risk analysis.

    MSHA intends this risk assessment to further the rulemaking 
process. The purpose of a proposed rulemaking is to advise the 
regulated community of what information the agency is evaluating, how 
the agency believes it should evaluate that information, and what 
tentative conclusions the agency has drawn. Comments and guidance from 
all interested members of the public are encouraged. The risk 
assessment presented here is meant to facilitate public comment, thus, 
helping to ensure that final rulemaking is based on as complete a 
record as possible--on both the evidence itself and the manner in which 
it is to be evaluated by the Agency. Those who want additional detail 
are welcome to examine the materials cited in this part, copies of 
which are included in MSHA's rulemaking record.
    While this rulemaking only covers the underground coal sector, this 
risk assessment was prepared so as to enable MSHA and to assess the 
risks throughout the mining industry. Accordingly, this information 
will be of interest to the entire mining community.
    MSHA had this risk assessment independently peer reviewed. The risk 
assessment presented here incorporates revisions made in accordance 
with the reviewers recommendations. The reviewers stated that:

    * * * principles for identifying evidence and characterizing 
risk are thoughtfully set out. The scope of the document is 
carefully described, addressing potential concerns about the scope 
of coverage. Reference citations are adequate and up to date. The 
document is written in a balanced fashion, addressing uncertainties 
and asking for additional information and comments as appropriate. 
(Samet and Burke, Nov. 1997).
III.1. Exposures of U.S. Miners
    Information about U.S. miner exposures comes from published studies 
and from additional mine surveys conducted by MSHA since 1993.\5\ 
Previously published studies of U.S. miner exposure to dpm are: Watts 
(1989, 1992), Cantrell (1992, 1993), Haney (1992), and Tomb and Haney 
(1995). MSHA has also conducted surveys subsequent to the period 
covered in Tomb and Haney (1995), and the previously unpublished data 
from those surveys are included here. Overall, the period covered in 
MSHA's surveys, on which this section is based, is late 1988 through 
mid 1997.
---------------------------------------------------------------------------

    \5\ MSHA has only limited information about miner exposures in 
other countries. Based on 223 personal and area samples, average 
exposures at 21 Canadian noncoal mines were reported to range from 
170 to 1300 g/m\3\ (respirable combustible dust), with 
maximum measurements ranging from 1020 to 3100 g/m\3\ 
(Gangel and Dainty, 1993). Among 622 full shift measurements 
collected since 1989 in German underground noncoal mines, 91 (15%) 
exceeded 400 g/m\3\ (total carbon) (Dahmann et al., 1996). 
As explained in Part II of this preamble, 400 g/m\3\ (total 
carbon) corresponds to approximately 500 g/m\3\ dpm.
---------------------------------------------------------------------------

    MSHA's field studies involved measuring dpm concentrations at a 
total of 48 mines: 25 underground metal and nonmetal (M/NM) mines, 12 
underground coal mines, and 11 surface mining operations (both coal and 
M/NM). At all surface mines and all underground coal mines, dpm 
measurements were made using the size-selective method, based on 
gravimetric determination of the amount of submicrometer dust collected 
with an impactor. With two exceptions, dpm measurements at underground 
M/NM mines were made using the RCD method (with no submicrometer 
impactor). Measurements at the two remaining underground M/NM mines 
were made using the size-selective method, as in coal and surface 
mines. The various methods of measuring dpm are explained in Part II of 
this preamble. Weighing errors inherent in the gravimetric analysis 
required for both size-selective and RCD methods become statistically 
insignificant at the relatively high dpm concentrations observed.
    Each underground study typically included personal dpm exposure 
measurements for approximately five production workers. Also, area 
samples were collected in return airways of underground mines to 
determine diesel particulate emission rates. Operational information 
such as the amount and type of equipment, airflow rates, fuel, and 
maintenance was also recorded. In general, MSHA's studies focused on 
face production areas of mines, where the highest concentrations of dpm 
could be expected; but, since some miners do not spend their time in 
face areas, studies were performed in other areas as well, to get a 
more complete picture of miner exposure. Because of potential 
interferences from tobacco smoke in underground M/NM mines, samples 
were not collected on or near smokers.
    Table III-1 summarizes key results from MSHA's studies.
    The higher concentrations in underground mines were typically found 
in the haulageways and face areas where numerous pieces of equipment 
were operating, or where insufficient air was available to ventilate 
the operation. In production areas and haulageways of underground mines 
where diesel powered equipment is used, the mean dpm concentration 
observed was 755 g/m\3\. By contrast, in travelways of 
underground mines where diesel powered equipment is used, the mean dpm 
concentration (based on 107 samples not included in Table III-1) was 
307 g/m\3\. In surface mines, the higher concentrations were 
generally associated with truck drivers and front-end loader operators. 
The mean dpm concentration observed was less than 200 g/m\3\ 
at all 11 of the surface mines in which measurements were made. More 
information about the dpm concentrations observed in each sector is 
presented in the material that follows.

 Table III-1.--Full-Diesel Particulate Matter Concentrations Observed in Production Areas and Haulageways of 48 
                       Dieselized U.S. Mines. Intake and Return Area Samples are Excluded.                      
----------------------------------------------------------------------------------------------------------------
                                                                              Mean exposure      Exposure range 
                       Mine type                         Number of samples   g/m\3\    g/m\3\ 
----------------------------------------------------------------------------------------------------------------
Surface................................................                 45                 88              9-380
Underground Coal.......................................                226                644            0-3,650
Underground Metal and Nonmetal.........................                331                830           10-5,570
----------------------------------------------------------------------------------------------------------------

III.1.a. Underground Coal Mines

    Approximately 170 out of the 971 existing underground coal mines 
currently utilize diesel powered equipment. Of these 170 mines, fewer 
than 20 currently use diesel equipment for face coal haulage. The 
remaining mines use diesel equipment for transportation, materials 
handling and other support operations. MSHA focused its efforts in 
measuring dpm concentrations in coal mines on mines that use diesel 
powered equipment for face coal haulage. Twelve mines using diesel-
powered face haulage were

[[Page 17523]]

sampled. Mines with diesel powered face haulage were selected because 
the face is an area with a high concentration of vehicles operating at 
a heavy duty cycle at the furthest end of the mine's ventilation 
system.
    Diesel particulate levels in underground mines depend on: (1) the 
amount, size, and workload of diesel equipment; (2) the rate of 
ventilation; and, (3) the effectiveness of whatever diesel particulate 
control technology may be in place. In the dieselized mines studied by 
MSHA, the sections used either two or three diesel coal haulage 
vehicles. In eastern mines the haulage vehicles were equipped with a 
nominal 100 horsepower engine. In western mines the haulage vehicles 
were equipped with a nominal 150 horsepower engine. Ventilation rates 
ranged from the nameplate requirement, based on the 100-75-50 percent 
rule (Holtz, 1960), to ten times the nameplate requirement. In most 
cases, the section airflow was approximately twice the name plate 
requirement. Control technology involved aftertreatment filters and 
fuel. Two types of aftertreatment filters were used. These filters 
included a disposable diesel emission filter (DDEF) and a Wire Mesh 
Filter (WMF). The DDEF is a commercially available product; the WMF was 
developed by and only used at one mine. Both low sulfur and high sulfur 
fuels were used.
    Figure III-1 displays the range of exposure measurements obtained 
by MSHA in the field studies it conducted in underground coal mines. A 
study normally consisted of collecting samples on the continuous miner 
operator and ramcar operators for two to three shifts, along with area 
samples in the haulageways. A total of 142 personal samples and 84 area 
samples were collected. No statistically significant difference was 
observed in mean dpm concentration between the personal and area 
samples.

[GRAPHIC] [TIFF OMITTED] TP09AP98.004


    In six mines, measurements were taken both with and without 
employment of disposable after treatment filters, so that a total of 
eighteen studies, carried out in twelve mines, are displayed. Without 
employment of after treatment filters, average observed dpm 
concentrations exceeded 500 g/m \3\ in eight of the twelve 
mines and exceeded 1000 g/m \3\ in four.\6\
---------------------------------------------------------------------------

    \6\ In coal mine E, the average as expressed by the mean 
exceeded 1000 g/m \3\, but the median did not.
---------------------------------------------------------------------------

    The highest dpm concentrations observed at coal mines were 
collected at Mine ``G.'' Eight of these samples were collected during 
employment of DDEF's, and eight were collected while filters were not 
being employed. Without filters, the mean dpm concentration observed at 
Mine ``G'' was 2052 g/m\3\

[[Page 17524]]

(median = 2100 g/m\3\). With disposable filters, the mean 
dropped to 1241 g/m\3\ (median = 1235 g/m\3\).
    Filters were employed in three of the four studies showing median 
dpm concentration at or below 200 g/m\3\. After adjusting for 
outby sources of dpm, exposures were found to be reduced by up to 95 
percent in mines using the DDEF and by up to 50 percent in the mine 
using the WMF. The higher dpm concentrations observed at the mine using 
the WMF are attributable partly to the lower section airflow. The only 
study without filters showing a median concentration at or below 200 
g/m\3\ was conducted in a mine (Mine ``A'') which had section 
airflow approximately ten times the nameplate requirement. The section 
airflow at the mine using the WMF was approximately the nameplate 
requirement.
    III.1.b. Underground Metal and Nonmetal Mines. Currently there are 
approximately 260 underground M/NM mines in the United States. Nearly 
all of these mines utilize diesel powered equipment, and twenty-five of 
those doing so were sampled by MSHA for dpm. The M/NM studies typically 
included measurements of dpm exposure for dieselized production 
equipment operators (such as truck drivers, roof bolters, haulage 
vehicles) on two to three shifts. A number of area samples were also 
collected. None of the M/NM mines studied were using diesel particulate 
afterfilters.
    Figure III-2 displays the range of dpm concentrations measured by 
MSHA in the twenty-five underground M/NM mines studied. A total of 254 
personal samples and 77 area samples were collected. No statistically 
significant difference was observed in mean dpm concentration between 
the personal and area samples. Personal exposures observed ranged from 
less than 100 g/m\3\ to more than 3500 g/m\3\. With 
the exception of Mine ``V'', personal exposures were for face workers. 
Mine ``V'' did not use dieselized face equipment.
    Average observed dpm concentrations exceeded 500 g/m\3\ in 
17 of the 25 M/NM mines and exceeded 1000 g/m\3\ in 12.\7\ The 
highest dpm concentrations observed at M/NM mines were collected at 
Mine ``E''. Based on 16 samples, the mean dpm concentration observed at 
Mine ``E'' was 2008 g/m\3\ (median = 1835 g/m\3\). 
Twenty-five percent of the dpm measurements at this mine exceeded 2400 
g/m\3\. All four of these were based on personal samples.

    \7\ At M/NM mines C, I, J, and P, the average as expressed by 
the mean exceeded 100 g/m\3\ but the median did not. At N/
NM mines H and S, the median exceeded 1000 g/m\3\ but the 
mean did not. At M/NM mine K, the mean exceeded 500 g/m\3\, 
but the median did not.
[GRAPHIC] [TIFF OMITTED] TP09AP98.005


    As with underground coal mines, dpm levels in underground M/NM 
mines are related to the amount and size of equipment, to the 
ventilation rate, and to the effectiveness of the diesel particulate 
control technology employed. In the dieselized M/NM mines studied by 
MSHA, front-end-loaders were used either to load ore

[[Page 17525]]

onto trucks or to haul and load ore onto belts. Additional pieces of 
diesel powered support equipment, such as bolters and mantrips, were 
also used at the mines. The typical piece of production equipment was 
rated at 150 to 350 horsepower. Ventilation rates in the M/NM mines 
studied mostly ranged from 100 to 200 cfm per horsepower of equipment. 
In only a few of the mines surveyed did ventilation exceed 200 cfm/hp. 
For single-level mines, working areas were ventilated in series, i.e., 
the exhaust air from one area became the intake for the next working 
area. For multi-level mines, each level typically had a separate fresh 
air supply. One or two working areas could be on a level. Control 
technology used to reduce diesel particulate emissions in mines 
surveyed included oxidation catalytic converters and engine maintenance 
programs. Both low sulfur and high sulfur fuel were used; some mines 
used aviation grade low sulfur fuel.
    III.1.c. Surface Mines. Currently, there are approximately 12,200 
surface mining operations in the United States. The total consists of 
approximately 1,700 coal mines and 10,500 M/NM mines. Virtually all of 
these mines utilize diesel powered equipment.
    MSHA conducted diesel particulate studies at eleven surface mining 
operations: eight coal mines and three M/NM mines. To help select those 
surface facilities likely to have significant dpm concentrations, MSHA 
first made a visual examination (based on blackness of the filter) of 
surface mine respirable dust samples collected during a November 1994 
study of surface coal mines. This preliminary screening of samples 
indicated that higher exposures to diesel particulate are typically 
associated with front-end-loader operators and haulage-truck operators; 
accordingly, sampling focused on these operations. A total of 45 
samples were collected.
    Figure III-3 displays the range of dpm concentrations measured at 
the eleven surface mines. The average dpm concentration observed was 
less than 200 g/m\3\ at all mines sampled. The maximum dpm 
concentration observed was less than or equal to 200 g/m\3\ in 
8 of the 11 mines (73%). The surface mine studies indicate that even 
when sampling is performed at the areas of surface mines believed most 
likely to have high exposures, dpm concentrations are generally less 
than 200 g/m\3\.

[GRAPHIC] [TIFF OMITTED] TP09AP98.006


    III.1.d. Comparison of Miner Exposures to Exposures of Other 
Groups. Occupational exposure to diesel particulate primarily 
originates from industrial operations employing equipment powered with 
diesel engines. Diesel engines are used to power ships, locomotives, 
heavy duty trucks, heavy machinery, as well as a small number of light-
duty passenger cars and trucks. NIOSH estimates that approximately 1.35 
million workers are occupationally exposed to the combustion products 
of diesel fuel in approximately 80,000 workplaces in the United States. 
Workers who are likely to be exposed to diesel emissions include: mine 
workers; bridge and tunnel workers; railroad workers; loading dock 
workers; truck drivers; fork-lift drivers; farm workers; and, auto, 
truck, and bus maintenance garage workers (NIOSH, 1988). Besides 
miners, groups for which occupational exposures have been reported and 
health effects have been studied include dock workers, truck drivers, 
and railroad workers.

[[Page 17526]]

    As estimated by geometric mean, median occupational exposures 
reported for dock workers either operating or otherwise exposed to 
diesel fork lift trucks have ranged from 23 to 55 g/m\3\, as 
measured by submicrometer elemental carbon (NIOSH, 1990; Zaebst et al., 
1991). Watts (1995) states that ``elemental carbon generally accounts 
for about 40% to 60% of diesel particulate mass.'' Assuming that, on 
average, the submicrometer elemental carbon constituted approximately 
50% by mass of the whole diesel particulate, this would correspond to a 
range of 46 to 110 g/m\3\ in median dpm concentrations at 
various docks.
    In a study of dpm exposures in the trucking industry, Zaebst et al. 
(1991) reported geometric mean concentrations of submicrometer carbon 
ranging from 2 to 7 g/m \3\ for drivers to 5 to 28 g/
m \3\ for mechanics, depending on weather conditions. Again assuming 
that, on average, the mass concentration of whole diesel particulate is 
about twice that of submicrometer elemental carbon, the corresponding 
range of median dpm concentrations would be 4 to 56 g/m \3\.
    Exposures of railroad workers to dpm were estimated by Woskie et 
al. (1988) and Schenker et al. (1990). As measured by total respirable 
particulate matter other than cigarette smoke, Woskie et al. reported 
geometric mean concentrations for various occupational categories of 
exposed railroad workers ranging from 49 to 191 g/
m3.
    Figure III-4 shows the range of median dpm concentrations observed 
for mine workers at different mines compared to the range of median 
concentrations estimated for dock workers (including forklift drivers 
at loading docks), truck drivers and mechanics, railroad workers, and 
urban ambient air. The range for ambient air, 1 to 10 g/
m3, was obtained from Cass and Gray (1995). For dock 
workers, truck drivers, and railroad workers, the estimated range of 
median exposures is respectively 46 to 110 g/m3, 4 
to 56 g/m3, and 49 to 191 g/m3. 
The range of medians observed at different underground coal mines is 55 
to 2100 g/m3, with filters employed at mines 
showing the lower concentrations. For underground M/NM mines, the 
corresponding range is 68 to 1835 g/m3, and for 
surface mines it is 19 to 160 g/m3.
[GRAPHIC] [TIFF OMITTED] TP09AP98.007

    As shown in Figure III-4, some miners are exposed to far higher 
concentrations of dpm than are any other populations for which data 
have been collected. Indeed, median dpm concentrations observed in some 
underground mines are up to 200 times as high as average environmental 
exposures in the most heavily polluted urban areas, and up to 10 times 
as high as median exposures estimated for the most heavily exposed 
workers in other occupational groups.
III.2. Health Effects Associated with DPM Exposures.

[[Page 17527]]

    This section reviews all the various health effects (of which MSHA 
is aware) that may be associated with exposure to diesel particulate. 
The review is divided into three main sections: acute effects, such as 
diminished pulmonary function and eye irritation; chronic effects, such 
as lung cancer; and mechanisms of toxicity. Prior to that review, 
however, the relevance of certain types of information will be 
considered. This discussion will address the relevance of health 
effects observed in animals, health effects that are reversible, and 
health effects associated with fine particulate matter in the ambient 
air.
III.2.a. Relevancy Considerations.
    III.2.a.i. Relevance of Health Effects Observed in Animals. Since 
the lungs of different species may react differently to particle 
inhalation, it is necessary to treat the results of animal studies with 
some caution. Evidence from animal studies can nevertheless be 
valuable, and those respondents to MSHA's ANPRM who addressed this 
question urged consideration of all animal studies related to the 
health effects of diesel exhaust.
    Unlike humans, laboratory animals are bred to be homogeneous and 
can be randomly selected for either non-exposure or exposure to varying 
levels of a potentially toxic agent. This permits setting up 
experimental and control groups of animals that do not differ 
biologically prior to exposure. The consequences of exposure can then 
be determined by comparing responses in the experimental and control 
groups. After a prescribed duration of deliberate exposure, laboratory 
animals can also be sacrificed, dissected, and examined. This can 
contribute to an understanding of mechanisms by which inhaled particles 
may exert their effects on health. For this reason, discussion of the 
animal evidence is placed in the section entitled ``Mechanisms of 
Toxicity'' below.
    Animal evidence also can help isolate the cause of adverse health 
effects observed among humans exposed to a variety of potentially 
hazardous substances. If, for example, the epidemiological data is 
unable to distinguish between several possible causes of increased risk 
of disease in a certain population, then controlled animal studies may 
provide evidence useful in suggesting the most likely explanation--and 
provide that information years in advance of definitive evidence from 
human observations.
    Furthermore, results from animal studies may also serve as a check 
on the credibility of observations from epidemiological studies of 
human populations. If a particular health effect is observed in animals 
under controlled laboratory conditions, this tends to corroborate 
observations of similar effects in humans.
    Accordingly, MSHA believes that judicious use of evidence from 
animal studies is appropriate. The extent to which MSHA relies upon 
such evidence to draw specific conclusions will be

[[Page 17528]]

discussed below in connection with those conclusions.
    III.2.a.ii. Relevance of Health Effects That Are Reversible. Some 
reported health effects associated with dpm are apparently reversible--
i.e., if the worker is moved away from the source for a few days, the 
health problem goes away. A good example is eye irritation.
    In response to the ANPRM, questions were raised as to whether so-
called ``reversible'' effects can constitute a ``material'' impairment. 
For example, one commenter argued that ``it is totally inappropriate 
for the agency to set permissible exposure limits based on temporary, 
reversible sensory irritation'' because such effects cannot be a 
``material'' impairment of health or functional capacity within the 
definition of the Mine Act (American Mining Congress, 87-0-21, 
Executive Summary, p. 1, and Appendix A).
    MSHA does not agree with this categorical view. Although the 
legislative history of the Mine Act is silent concerning the meaning of 
the term ``material impairment of health or functional capacity,'' and 
the issue has not been litigated within the context of the Mine Act, 
the statutory language about risk in the Mine Act is similar to that 
under the OSH Act. A similar argument was dispositively resolved in 
favor of the Occupational Safety and Health Administration (OSHA) by 
the 11th Circuit Court of Appeals in AFLCIO v. OSHA, 965 F.2d 962, 974 
(1992) (popularly known as the ``PEL's'' decision).
    In that case, OSHA proposed new limits on 428 diverse substances. 
It grouped these into 18 categories based upon the primary health 
effects of those substances: e.g., neuropathic effects, sensory 
irritation, and cancer. (54 FR 2402). Challenges to this rule included 
the assertion that a ``sensory irritation'' was not a ``material 
impairment of health or functional capacity'' which could be regulated 
under the OSH Act. Industry petitioners argued that since irritant 
effects are transient in nature, they did not constitute a ``material 
impairment.'' The Court of Appeals decisively rejected this argument.
    The court noted OSHA's position that effects such as stinging, 
itching and burning of the eyes, tearing, wheezing, and other types of 
sensory irritation can cause severe discomfort and be seriously 
disabling in some cases. Moreover, there was evidence that workers 
exposed to these sensory irritants could be distracted as a result of 
their symptoms, thereby endangering other workers and increasing the 
risk of accidents. (Id. at 974). This evidence included information 
from NIOSH about the general consequences of sensory irritants on job 
performance, as well as testimony by commenters on the proposed rule 
supporting the view that such health effects should be regarded as 
material health impairments. While acknowledging that ``irritation'' 
covers a spectrum of effects, some of which can be trivial, OSHA had 
concluded that the health effects associated with exposure to these 
substances warranted action--to ensure timely medical treatment, reduce 
the risks from increased absorption, and avoid a decreased resistance 
to infection (Id. at 975). Finding OSHA's evaluation adequate, the 
Court of Appeals rejected petitioners' argument and stated the 
following:

    We interpret this explanation as indicating that OSHA finds that 
although minor irritation may not be a material impairment, there is 
a level at which such irritation becomes so severe that employee 
health and job performance are seriously threatened, even though 
those effects may be transitory. We find this explanation adequate. 
OSHA is not required to state with scientific certainty or precision 
the exact point at which each type of sensory or physical irritation 
becomes a material impairment. Moreover, section 6(b)(5) of the Act 
charges OSHA with addressing all forms of ``material impairment of 
health or functional capacity,'' and not exclusively ``death or 
serious physical harm'' or ``grave danger'' from exposure to toxic 
substances. See 29 U.S.C. 654(a)(1), 655(c). [Id. at 974.]

    III.2.a.iii. Relevance of Health Effects Associated with Fine 
Particulate Matter in Ambient Air. There have been many studies in 
recent years designed to determine whether the mix of particulate 
matter in ambient air is harmful to health. The evidence linking 
particulates in air pollution to health problems has long been 
compelling enough to warrant direction from the Congress to limit the 
concentration of such particulates (see part II, section 5 of this 
preamble). In recent years, the evidence of harmful effects due to 
airborne particulates has increased, and, moreover, has suggested that 
``fine'' particulates (i.e., particles less than 2.5 m in 
diameter) are more strongly associated than ``coarse'' particulates 
(i.e., respirable particles greater than 2.5 m in diameter) 
with the adverse health effects observed (EPA, 1996).
    MSHA recognizes that there are two difficulties involved in 
utilizing the evidence from such studies in assessing risks to miners 
from occupational dpm exposures. First, although dpm is a fine 
particulate, ambient air also contains fine particulates other than 
dpm. Therefore, health effects associated with exposures to fine 
particulate matter in air pollution studies are not associated 
specifically with exposures to dpm or any other one kind of fine 
particulate matter. Second, observations of adverse health effects in 
segments of the general population do not necessarily apply to the 
population of miners. Since, due to age and selection factors, the 
health of miners differs from that of the public as a whole, it is 
possible that fine particles might not affect miners, as a group, to 
the same extent as the general population.
    Nevertheless, there are compelling reasons to consider this body of 
evidence. Since dpm is a type of respirable particle, information about 
health effects associated with exposures to respirable particles in 
general, and especially to fine particulate matter, is certainly 
relevant, even if difficult to apply directly to dpm exposures. Adverse 
health effects in the general population have been observed at ambient 
atmospheric particulate concentrations well below those studied in 
occupational settings. Furthermore, there is extensive literature 
showing that occupational dust exposures contribute to Chronic 
Obstructive Pulmonary Diseases (COPD), thereby compromising the 
pulmonary reserve of some miners, and that miners experience COPD at a 
significantly higher rate than the general population (Becklake 1989, 
1992; Oxman 1993; NIOSH 1995). This would appear to place affected 
miners in a subpopulation specifically identified as susceptible to the 
adverse health effects of respirable particle pollution (EPA, 1996). 
The Mine Act requires standards that ``* * * most adequately assure on 
the basis of the best available evidence that no miner suffer material 
impairment of health or functional capacity * * *'' (Section 101(a)(6), 
emphasis added).
    In sum, MSHA believes it would be a serious omission to ignore the 
body of evidence from air pollution studies and the Agency is, 
therefore, taking that evidence into account. The Agency would, 
however, welcome additional scientific information and analysis on ways 
of applying this body of evidence to miners experiencing acute and/or 
chronic dpm exposures. MSHA is especially interested in receiving 
information on whether the elevated prevalence of COPD among miners 
makes them, as a group, highly susceptible to the harmful effects of 
fine particulate air pollution, including dpm.
III.2.b. Acute Health Effects
    Information relating to the acute health effects of dpm includes 
anecdotal reports of symptoms experienced by exposed miners, studies 
based on

[[Page 17529]]

exposures to diesel emissions, and studies based on exposures to 
particulate matter in the ambient air. These will be discussed in turn.
    III.2.b.i. Symptoms Reported by Exposed Miners. Miners working in 
mines with diesel equipment have long reported adverse effects after 
exposure to diesel exhaust. For example, at the workshops on dpm 
conducted in 1995, a miner reported headaches and nausea among several 
operators after short periods of exposure (dpm Workshop; Mt. Vernon, 
IL, 1995). Another miner reported that the smoke from equipment using 
improper fuel or not well maintained is an irritant to nose and throat 
and impairs vision. ``We've had people sick time and time again * * * 
at times we've had to use oxygen for people to get them to come back 
around to where they can feel normal again.'' (dpm Workshop; Beckley, 
WV, 1995). Other miners (dpm Workshops; Beckley, WV, 1995; Salt Lake 
City, UT, 1995), reported similar symptoms in the various mines where 
they worked.
    Kahn et al. (1988) conducted a study of the prevalence and 
seriousness of such complaints, based on United Mine Workers of America 
records and subsequent interviews with the miners involved. The review 
involved reports at five underground coal mines in Utah and Colorado 
between 1974 and 1985. Of the 13 miners reporting symptoms: 12 reported 
mucous membrane irritation, headache and light-headiness; eight 
reported nausea; four reported heartburn; three reported vomiting and 
weakness, numbness, and tingling in extremities; two reported chest 
tightness; and two reported wheezing (although one of these complained 
of recurrent wheezing without exposure). All of these incidents were 
severe enough to result in lost work time due to the symptoms (which 
subsided within 24 to 48 hours).
    MSHA welcomes additional information about such effects including 
information from medical personnel who have treated miners and 
information on work time lost, together with information about the 
exposures of miners for whom such effects have been observed. The 
Agency would be especially interested in comparisons of effects 
observed in workers subjected to filtered exhaust as compared to those 
subjected to unfiltered exhaust.
    III.2.b.ii. Studies Based on Exposures to Diesel Emissions. Several 
scientific studies have been conducted to investigate acute effects of 
exposure to diesel emissions.
    In a clinical study (Battigelli, 1965), volunteers were exposed to 
different levels of diesel exhaust and then the degree of eye 
irritation was measured. Exposure for ten minutes to diesel exhaust 
produced ``intolerable'' irritation in some subjects while the average 
irritation score was midway between ``some'' irritation and a 
``conspicuous but tolerable'' irritation level. Cutting the exposure by 
50% significantly reduced the irritation.
    In a study of underground iron ore miners exposed to diesel 
emissions, Jrgensen and Svensson (1970), found no difference in 
spirometry measurements taken before and after a work shift. Similarly, 
Ames et al. (1982), in a study of coal miners exposed to diesel 
emissions, detected no statistically significant relationship between 
exposure and pulmonary function. However, the authors noted that the 
lack of a positive result might be due to the low concentrations of 
diesel emissions involved.
    Gamble et al. (1978) did observe decreases in pulmonary function 
over a single shift in salt miners exposed to diesel emissions. 
Pulmonary function appeared to deteriorate in relation to the 
concentration of diesel exhaust, as indicated by NO2; but 
this effect was confounded by the presence of NO2 due to the 
use of explosives.
    Gamble et al. (1987a) assessed response to diesel exposure among 
232 bus garage workers by means of a questionnaire and before- and 
after-shift spirometry. No significant relationship was detected 
between diesel exposure and change in pulmonary function. However, 
after adjusting for age and smoking status, a significantly elevated 
prevalence of reported symptoms was found in the high-exposure group. 
The strongest associations with exposure were found for eye irritation, 
labored breathing, chest tightness, and wheeze. The questionnaire was 
also used to compare various acute symptoms reported by the garage 
workers and a similar population of workers at a lead acid battery 
plant who were not exposed to diesel fumes. The prevalence of work-
related eye irritations, headaches, difficult or labored breathing, 
nausea, and wheeze was significantly higher in the diesel bus garage 
workers, but the prevalence of work-related sneezing was significantly 
lower.
    Ulfvarson et al. (1987) studied effects over a single shift on 47 
stevedores exposed to dpm at particle concentrations ranging from 130 
g/m\3\3 to 1000 g/m\3\. A statistically significant 
loss of pulmonary function was observed, with recovery after 3 days of 
no occupational exposure.
    To investigate whether removal of the particles from diesel exhaust 
might reduce the ``acute irritative effect on the lungs'' observed in 
their earlier study, Ulfvarson and Alexandersson (1990) compared 
pulmonary effects in a group of 24 stevedores exposed to unfiltered 
diesel exhaust to a group of 18 stevedores exposed to filtered exhaust, 
and to a control group of 17 occupationally unexposed workers. Workers 
in all three groups were nonsmokers and had normal spirometry values, 
adjusted for sex, age, and height, prior to the experimental workshift.
    In addition to confirming the earlier observation of significantly 
reduced pulmonary function after a single shift of occupational 
exposure, the study found that the stevedores in the group exposed only 
to filtered exhaust had 50-60% less of a decline in forced vital 
capacity (FVC) than did those stevedores who worked with unfiltered 
equipment. Similar results were observed for a subgroup of six 
stevedores who were exposed to filtered exhaust on one shift and 
unfiltered exhaust on another. No loss of pulmonary function was 
observed for the unexposed control group. The authors suggested that 
these results ``support the idea that the irritative effects of diesel 
exhausts to the lungs [sic] is the result of an interaction between 
particles and gaseous components and not of the gaseous components 
alone.'' They concluded that ``* * * it should be a useful practice to 
filter off particles from diesel exhausts in work places even if 
potentially irritant gases remain in the emissions.''
    Rudell et al., (1996) carried out a series of double-blind 
experiments on 12 healthy, non-smoking subjects to investigate whether 
a particle trap on the tailpipe of an idling diesel engine would reduce 
acute effects of diesel exhaust, compared with exposure to unfiltered 
exhaust. Symptoms associated with exposure included headache, 
dizziness, nausea, tiredness, tightness of chest, coughing, and 
difficulty in breathing, but the most prominent were found to be 
irritation of the eyes and nose, and a sensation of unpleasant smell. 
Among the various pulmonary function tests performed, exposure was 
found to result in significant changes only as measured by increased 
airway resistance and specific airway resistance. The ceramic wall flow 
particle trap reduced the number of particles by 46 percent, but 
resulted in no significant attenuation of symptoms or lung function 
effects. The authors concluded that diluted diesel exhaust caused 
increased symptoms of the eyes and nose, unpleasant smell, and 
bronchoconstriction, but that the 46 percent reduction in median 
particle

[[Page 17530]]

number concentration observed was not sufficient to protect against 
these effects in the populations studied.
    Wade and Newman (1993) documented three cases in which railroad 
workers developed persistent asthma following exposure to diesel 
emissions while riding immediately behind the lead engines of trains 
having no caboose. None of these workers were smokers or had any prior 
history of asthma or other respiratory disease. Although this is the 
only published report MSHA knows of directly relating exposure to 
diesel emissions with the development of asthma, there have been a 
number of recent studies indicating that dpm exposure can induce 
bronchial inflammation and respiratory immunological allergic responses 
in humans. These are reviewed in Peterson and Saxon (1996) and Diaz-
Sanchez (1997).
    III.2.b.iii. Studies Based on Exposures to Particulate Matter in 
Ambient Air. As early as the 1930's, as a result of an incident in 
Belgium's industrial Meuse Valley, it was known that large increases in 
particulate air pollution, created by winter weather inversions, could 
be associated with large simultaneous increases in mortality and 
morbidity. More than 60 persons died from this incident, and several 
hundred suffered respiratory problems. The mortality rate during the 
episode was more than ten times higher than normal, and it was 
estimated that 3,179 sudden deaths would occur if a similar incident 
occurred in London. Although no measurements of pollutants in the 
ambient air during the episode are available, high PM levels were 
obviously present (EPA, 1996).
    A significant elevation in particulate matter (along with 
SO2 and its oxidation products) was measured during a 1948 
incident in Donora, PA. Of the Donora population, 42.7 percent 
experienced some adverse health effect, mainly due to irritation of the 
respiratory tract. Twelve percent of the population reported difficulty 
in breathing, with a steep rise in frequency as age progressed to 55 
years (Schrenk, 1949).
    Approximately as projected by Firket (1931), an estimated 4,000 
deaths occurred in response to a 1952 episode of extreme air pollution 
in London. The nature of these deaths is unknown, but there is clear 
evidence that bronchial irritation, dyspnea, bronchospasm, and, in some 
cases, cyanosis occurred with unusual prevalence (Martin, 1964).
    These three episodes ``left little doubt about causality regarding 
the induction of serious health effects by very high concentrations of 
particle-laden air pollutant mixtures'' and stimulated additional 
research to characterize exposure-response relationships (EPA, 1996). 
Based on several analyses of the 1952 London data, along with several 
additional acute exposure mortality analyses of London data covering 
later time periods, the U.S. Environmental Protection Agency (EPA) 
concluded that increased risk of mortality is associated with exposure 
to particulate and SO2 levels in the range of 500-1000 
g/m3. The EPA also concluded that relatively small, 
but statistically significant increases in mortality risk exist at 
particulate levels below 500 g/m3, with no 
indications of any specific threshold level yet indicated at lower 
concentrations (EPA, 1986).
    Subsequently, between 1986 and 1996, increasingly sophisticated 
particulate measurements and statistical techniques have enabled 
investigators to address these questions more quantitatively. The 
studies on acute effects carried out since 1986 are reviewed in the 
1996 EPA Air Quality Criteria for Particulate Matter, which forms the 
basis for the discussion below (EPA, 1996).
    At least 21 studies have been conducted that evaluate associations 
between acute mortality and morbidity effects and various measures of 
fine particulate levels in the ambient air. These studies are 
identified in Tables III-2 and III-3. Table III-2 lists 11 studies that 
measured primarily fine particulate matter using filter-based optical 
techniques and, therefore, provide mainly qualitative support for 
associating observed effects with fine particles. Table III-3 lists 
quantitative results from 10 studies that reported gravimetric 
measurements of either the fine particulate fraction or of components, 
such as sulfates, that serve as indicators.
    A total of 38 studies examining relationships between short-term 
particulate levels and increased mortality, including nine with fine 
particulate measurements, were published between 1988 and 1996 (EPA, 
1996). Most of these found statistically significant positive 
associations. Daily or several-day elevations of particulate 
concentrations, at average levels as low as 18-58 g/
m3, were associated with increased mortality, with stronger 
relationships observed in those with preexisting respiratory and 
cardiovascular disease. Overall, these studies suggest that an increase 
of 50 g/m3 in the 24-hour average of 
PM10 is associated with a 2.5 to 5-percent increase in the 
risk of mortality in the general population. Based on Schwartz et al. 
(1996), the relative risk of mortality in the general population 
increased by 2.6 to 5.5 percent per 25 g/m3 of fine 
particulate (PM2.5) (EPA, 1996).
    A total of 22 studies were published on associations between short-
term particulate levels and hospital admissions, outpatient visits, and 
emergency room visits for respiratory disease, Chronic Obstructive 
Pulmonary Disease (COPD), pneumonia, and heart disease (EPA, 1996). 
Fifteen of these studies were focussed on the elderly. Of the seven 
that dealt with all ages (or in one case, persons less than 65 years 
old), all showed positive results. All of the five studies relating 
fine particulate measurements to increased hospitalization, listed in 
Tables III-2 and III-3, dealt with general age populations and showed 
statistically significant associations. The estimated increase in risk 
ranges from 3 to 16 percent per 25 g/m3 of fine 
particulate. Overall, these studies are indicative of acute morbidity 
effects being related to fine particulate matter and support the 
mortality findings.
    Most of the 14 published quantitative studies on ambient 
particulate exposures and acute respiratory symptoms were restricted to 
children (EPA, 1996). Although they generally showed positive 
associations, and may be of considerable biological relevance, evidence 
of toxicity in children is not necessarily applicable to adults. The 
few studies on adults have not produced statistically significant 
evidence of a relationship.
    Fourteen studies since 1982 have investigated associations between 
ambient particulate levels and loss of pulmonary function (EPA, 1996). 
In general, these studies suggest a short term effect, especially in 
symptomatic groups such as asthmatics, but most were carried out on 
children only. In a study of adults with mild COPD, Pope and Kanner 
(1993) found a 2910 ml decrease in 1-second Forced 
Expiratory Volume (FEV1) per 50 g/m3 
increase in PM10, which is similar in magnitude to the 
change generally observed in the studies on children. In another study 
of adults, with PM10 ranging from 4 to 137 g/
m3, Dusseldorp et al. (1995) found 45 and 77 ml/sec 
decreases, respectively, for evening and morning Peak Expiratory Flow 
Rate (PEFR) per 50 g/m3 increase in PM10 
(EPA, 1996). In the only study carried out on adults that specifically 
measured fine particulate (PM2.5), Perry et al. (1983) did 
not detect any association of exposure with loss of pulmonary function. 
This study, however, was conducted on only 24 adults (all asthmatics) 
exposed at relatively low concentrations of PM2.5

[[Page 17531]]

and, therefore, had very little power to detect any such association.
III.2.c. Chronic Health Effects
    During the 1995 dpm workshops, miners reported observable adverse 
health effects among those who have worked a long time in dieselized 
mines. For example, a miner (dpm Workshop; Salt Lake City, UT, 1995), 
stated that miners who work with diesel ``have spit up black stuff 
every night, big black--what they call black (expletive) ***[they] have 
the congestion every night*** the 60-year-old man working there 40 
years.'' Scientific investigation of the chronic health effects of dpm 
exposure includes studies based specifically on exposures to diesel 
emissions and studies based more generally on exposures to fine 
particulate matter in the ambient air. Only the evidence from human 
studies will be addressed in this section. Data from genotoxicology 
studies and studies on laboratory animals will be discussed later, in 
the section on potential mechanisms of toxicity.
    III.2.c.i. Studies Based on Exposures to Diesel Emissions. The 
discussion will summarize the epidemiological literature on chronic 
effects other than cancer, and then concentrate on the epidemiology of 
cancer in workers exposed to dpm.
    III.2.c.i.A. Chronic Effects Other than Cancer. There have been a 
number of epidemiological studies that investigated relationships 
between diesel exposure and the risk of developing persistent 
respiratory symptoms, (i.e., chronic cough, chronic phlegm, and 
breathlessness), or measurable loss in lung function. Three studies 
involved coal miners (Reger et al., 1982; Ames et al., 1984; Jacobson 
et al., 1988); four studies involved metal and nonmetal miners 
(Jorgenson & Svensson, 1970; Attfield, 1979; Attfield et al., 1982; 
Gamble et al., 1983). Three studies involved other groups of workers--
railroad workers (Battigelli et al., 1964), bus garage workers (Gamble 
et al., 1987), and stevedores (Purdham et al., 1987).
    Reger et al. (1982) examined the prevalence of respiratory symptoms 
and the level of pulmonary function among more than 1,600 underground 
and surface coal miners, comparing results for workers (matched for 
smoking status, age, height, and years worked underground) at diesel 
and non-diesel mines. Those working at underground dieselized mines 
showed some increased respiratory symptoms and reduced lung function, 
but a similar pattern was found in surface miners who presumably would 
have experienced less diesel exposure. Miners in the dieselized mines, 
however, had worked underground for less than 5 years on average.
    In a study of 1,118 coal miners, Ames et al. (1984) did not detect 
any pattern of chronic respiratory effects associated with exposure to 
diesel emissions. The analysis, however, took no account of baseline 
differences in lung function or symptom prevalence, and the authors 
noted a low level of exposure to diesel-exhaust contaminants in the 
exposed population.
    In a cohort of 19,901 coal miners investigated over a 5-year 
period, Jacobsen et al. (1988) found increased work absence due to 
self-reported chest illness in underground workers exposed to diesel 
exhaust, as compared to surface workers, but found no correlation with 
their estimated level of exposure.
    Jorgenson & Svensson (1970) found higher rates of chronic 
productive bronchitis, for both smokers and nonsmokers, among 
underground iron ore miners exposed to diesel exhaust as compared to 
surface workers at the same mine. No significant difference was found 
in spirometry results.
    Using questionnaires collected from 4,924 miners at 21 metal and 
nonmetal mines, Attfield (1979) evaluated the effects of exposure to 
silica dust and diesel exhaust and obtained inconclusive results with 
respect to diesel exposure. For both smokers and non-smokers, miners 
occupationally exposed to diesel for five or more years showed an 
elevated prevalence of persistent cough, persistent phlegm, and 
shortness of breath, as compared to miners exposed for less than five 
years, but the differences were not statistically significant. Four 
quantitative indicators of diesel use failed to show consistent trends 
with symptoms and lung function.
    Attfield et al. (1982) reported on a medical surveillance study of 
630 white male miners at 6 potash mines. No relationships were found 
between measures of diesel use or exposure and various health indices, 
based on self-reported respiratory symptoms, chest radiographs, and 
spirometry.
    In a study of salt miners, Gamble et al. (1983) observed some 
elevation in cough, phlegm, and dyspnea associated with mines ranked 
according to level of diesel exhaust exposure. No association between 
respiratory symptoms and estimated cumulative diesel exposure was found 
after adjusting for differences among mines. However, since the mines 
varied widely with respect to diesel exposure levels, this adjustment 
may have masked a relationship.
    Battigelli et al. (1964) compared pulmonary function and complaints 
of respiratory symptoms in 210 railroad repair shop employees, exposed 
to diesel for an average of 10 years, to a control group of 154 
unexposed railroad workers. Respiratory symptoms were less prevalent in 
the exposed group, and there was no difference in pulmonary function; 
but no adjustment was made for differences in smoking habits.
    In a study of workers at four diesel bus garages in two cities, 
Gamble et al. (1987b) investigated relationships between tenure (as a 
surrogate for cumulative exposure) and respiratory symptoms, chest 
radiographs, and pulmonary function. The study population was also 
compared to an unexposed control group of workers with similar 
socioeconomic background.
    After indirect adjustment for age, race, and smoking, the exposed 
workers showed an increased prevalence of cough, phlegm, and wheezing, 
but no association was found with tenure. Age-and height-adjusted 
pulmonary function was found to decline with duration of exposure, but 
was elevated on average, as compared to the control group.
    The number of positive radiographs was too small to support any 
conclusions. The authors concluded that the exposed workers may have 
experienced some chronic respiratory effects.
    Purdham et al. (1987) compared baseline pulmonary function and 
respiratory symptoms in 17 exposed stevedores to a control group of 11 
port office workers. After adjustment for smoking, there was no 
statistically significant difference in self-reported respiratory 
symptoms between the two groups. However, after adjustment for smoking, 
age, and height, exposed workers showed lower baseline pulmonary 
function, consistent with an obstructive ventilatory defect, as 
compared to both the control group and the general metropolitan 
population.
    In a recent review of these studies, Cohen and Higgins (1995) 
concluded that they did not provide strong or consistent evidence for 
chronic, nonmalignant respiratory effects associated with occupational 
exposure to diesel exhaust. These reviewers stated, however, that 
``several studies are suggestive of such effects * * * particularly 
when viewed in the context of possible biases in study design and 
analysis.'' MSHA agrees that the studies are inconclusive but 
suggestive of possible effects.
    III.2.c.i.B. Cancer. Because diesel exhaust has long been known to 
contain traces of carcinogenic compounds (e.g., benzene in the gaseous 
fraction and

[[Page 17532]]

benzopyrene and nitropyrene in the dpm fraction), a great deal of 
research has been conducted to determine if occupational exposure to 
diesel exhaust actually results in an increased risk of cancer. 
Evidence that exposure to dpm increases the risk of developing cancer 
comes from three kinds of studies: human studies, genotoxicological 
studies, and animal studies. MSHA places the most weight on evidence 
from the human epidemiological studies and views the genotoxicological 
and animal studies as lending support to the epidemiological evidence.
    In the epidemiological studies, it is generally impossible to 
disassociate exposure to dpm from exposure to the gasses and vapors 
that form the remainder of whole diesel exhaust. However, the animal 
evidence shows no significant increase in the risk of lung cancer from 
exposure to the gaseous fraction alone (Heinrich et al., 1986; Iwai et 
al., 1986; Brightwell et al., 1986). Therefore, dpm, rather than the 
gaseous fraction of diesel exhaust, is assumed to be the agent 
associated with an excess risk of lung cancer.
    III.2.c.i.B.i. Lung Cancer. Beginning in 1957, at least 43 
epidemiological studies have been published examining relationships 
between diesel exhaust exposure and the prevalence of lung cancer. The 
most recent published reviews of these studies are by Mauderly (1992), 
Cohen and Higgins (1995), Stober and Abel (1996), Morgan et al. (1997), 
and Dawson et al. (1998). In addition, in response to the ANPRM, 
several commenters provided MSHA with their own reviews. Two 
comprehensive statistical ``meta-analyses'' of the epidemiological 
literature are also available: Lipsett and Alexeeff (1998) and Bhatia 
et al. (1998). These meta-analyses, which analyze and combine results 
from the various epidemiological studies, both suggest a statistically 
significant increase of 30 to 40 percent in the risk of lung cancer, 
attributable to occupational dpm exposure. The studies themselves, 
along with MSHA's comments on each study, are summarized in Tables III-
4 (24 cohort studies) and III-5 (19 case-control studies).\8\ Presence 
or absence of an adjustment for smoking habits is highlighted, and 
adjustments for other potentially confounding factors are indicated 
when applicable.
---------------------------------------------------------------------------

    \8\ For simplicity, the epidemiological studies considered here 
are placed into two broad categories. A cohort study compares the 
health of persons having different exposures, diets, etc. A case-
control study starts with two defined groups that differ in terms of 
their health and compares their exposure characteristics.
---------------------------------------------------------------------------

    Some degree of association between occupational dpm exposure and an 
excess risk of lung cancer was observed in 38 of the 43 studies 
reviewed by MSHA: 18 of the 19 case-control studies and 20 of the 24 
cohort studies. However, the 38 studies reporting a positive 
association vary considerably in the strength of evidence they present. 
As shown in Tables III-4 and III-5, statistically significant results 
were reported in 24 of the 43 studies: 10 of the 18 positive case-
control studies and 14 of the 20 positive cohort studies.\9\ In six of 
the 20 cohort studies and nine of the 18 case-control studies showing a 
positive association, the association observed was not statistically 
significant.
---------------------------------------------------------------------------

    \9\ A statistically significant result is a result unlikely to 
have arisen by chance in the group, or statistical sample, of 
persons being studie. An association arising by chance would have no 
predictive value for workers outside the sample. Failure to achieve 
statistical significance in an individual study can arise because of 
inherent limitations in the study, such as a small number of 
subjects in the sample or a short period of observation. Therefore, 
the lack of statistical significance in an individual study does not 
demonstrate that the results of that study were due merely to 
chance--only that the study (viewed in isolation) is inconclusive.
---------------------------------------------------------------------------

    Because workers tend to be healthier than non-workers, the 
incidence of disease found among workers exposed to a toxic substance 
may be lower than the rate prevailing in the general population, but 
higher than the rate occurring in an unexposed population of workers. 
This phenomenon, called the ``healthy worker effect,'' also applies 
when the rate observed among exposed workers is greater than that found 
in the general population. In this case, assuming a study is unbiased 
with respect to other factors such as smoking, comparison with the 
general population will tend to underestimate the excess risk of 
disease attributable to the substance being investigated. Several 
studies drew comparisons against the general population, including both 
workers and nonworkers, with no compensating adjustment for the healthy 
worker effect. Therefore, in these studies, the excess risk of lung 
cancer attributable to dpm exposure is likely to have been 
underestimated, thereby making it more difficult to obtain a 
statistically significant result.
    Five of the 43 studies listed in Tables III-4 and III-5 are 
negative--i.e., a lower rate of lung cancer was found among exposed 
workers than in the control population used for comparison. None of 
these five results, however, were statistically significant. Four of 
the five were cohort studies that drew comparisons against the general 
population and did not take the healthy worker effect into account. The 
remaining negative study was a case-control study in which vehicle 
drivers and locomotive engineers were compared to clerical workers.
    Two cohort studies (Waxweiler et al., 1973; Ahlman et al., 1991) 
were performed specifically on groups of miners, and one (Boffetta et 
al., 1988) addressed miners as a subgroup of a larger population. 
Although an elevated prevalence of lung cancer was found among miners 
in both the 1973 and 1991 studies, the results were not statistically 
significant. The 1988 study found, after adjusting for smoking patterns 
and other occupational exposures, an 18-percent increase in the lung 
cancer rate among all workers occupationally exposed to diesel exhaust 
and a 167-percent increase among miners (relative risk = 2.67). The 
latter result is statistically significant.
    In addition, four case-control studies, all of which adjusted for 
smoking, found elevated rates of lung cancer associated with mining. 
The results for miners in three of these studies (Benhamou et al., 
1988; Morabia et al., 1992; Siemiatycki et al., 1988) are given little 
weight because of potential confounding by occupational exposures to 
other carcinogens. The other study (Lerchen et al., 1987) showed a 
marginally significant result for underground non-uranium miners, but 
this was based on very few cases and the extent of diesel exposure 
among these miners was not reported. Although they do not pertain 
specifically to mining environments, other studies showing 
statistically significant results (most notably those by Garshick et 
al., 1987 and 1988) are based on far more data, contain better diesel 
exposure information, and are less susceptible to confounding by 
extraneous risk factors.
    Since none of the existing human studies is perfect and many 
contain major deficiencies, it is not surprising that reported results 
differ in magnitude and statistical significance. Shortcomings 
identified in both positive and negative studies include: possible 
misclassification with respect to exposure; incomplete or questionable 
characterization of the exposed population; unknown or uncertain 
quantification of diesel exhaust exposure; incomplete, uncertain, or 
unavailable history of exposure to tobacco smoke and other carcinogens; 
and insufficient sample size, dpm exposure, or latency period (i.e., 
time since exposure) to detect a carcinogenic effect if one exists. 
Indeed, in their review of these studies, Stober and Abel (1996) 
conclude that ``In this field * * *

[[Page 17533]]

epidemiology faces its limits (Taubes, 1995) * * * Many of these 
studies were doomed to failure from the very beginning.''
    Such problems, however, are not unique to epidemiological studies 
involving diesel exhaust but are common sources of uncertainty in 
virtually all epidemiological research involving cancer. Indeed, 
deficiencies such as exposure misclassification, small sample size, and 
short latency make it difficult to detect a relationship even when one 
exists. Therefore, the fact that 38 out of 43 studies showed any excess 
risk of lung cancer associated with dpm exposure may itself be a 
significant result, even if the evidence in most of those 38 studies is 
relatively weak.\10\ The sheer number of studies showing such an 
association readily distinguishes this body of evidence from those 
criticized by Taubes (1995), where weak evidence is available from only 
a single study.
---------------------------------------------------------------------------

    \10\ The high proportion of positive studies is statistically 
significant according to the 2-tailed sign test, which rejects, at a 
high confidence level, the null hypothesis that each study is 
equally likely to be positive or negative. Assuming that the studies 
are independent, and that there is no systematic bias in one 
direction or the other, the probability of 38 or more out of 43 
studies being either positive or negative is less than one per 
million under the null hypothesis.
---------------------------------------------------------------------------

    At the same time, MSHA recognizes that simply tabulating outcomes 
can sometimes be misleading, since there are generally a variety of 
outcomes that could render a study positive or negative and some 
studies use related data sets. Therefore, rather than limiting its 
assessment to such a tabulation, MSHA is basing its evaluation with 
respect to lung cancer largely on the two comprehensive meta-analyses 
(Lipsett and Alexeeff, 1998; Bhatia et al., 1998) described later, in 
the ``material impairments'' section of this risk assessment. In 
addition to restricting themselves to independent studies meeting 
certain minimal requirements, both meta-analyses investigated and 
rejected publication bias as an explanation for the generally positive 
results reported.
    All of the studies showing negative or statistically insignificant 
positive associations were either based on relatively short observation 
or follow-up periods, lacked good information about dpm exposure, 
involved low duration or intensity of dpm exposure, or, because of 
inadequate sample size, lacked the statistical power to detect effects 
of the magnitude found in the ``positive'' studies. As stated by 
Boffetta et al. (1988, p. 404), studies failing to show a statistically 
significant association--

    * * * often had low power to detect any association, had 
insufficient latency periods, or compared incidence or mortality 
rates among workers to national rates only, resulting in possible 
biases caused by the `healthy worker effect.'

    Some respondents to the ANPRM argued that such methodological 
weaknesses may explain why not all of the studies showed a 
statistically significant association between dpm exposure and an 
increased prevalence of lung cancer. According to these commenters, if 
an epidemiological study shows a statistically significant result, this 
often occurs in spite of methodological weaknesses rather than because 
of them. Limitations such as potential exposure misclassification, 
inadequate latency, inadequate sample size, and insufficient duration 
of exposure all make it more difficult to obtain a statistically 
significant result when a real relationship exists.
    On the other hand, Stober and Abel (1996) argue, long with Morgan 
et al. (1997) and some commenters, that even in those epidemiological 
studies showing a statistically significant association, the magnitude 
of relative or excess risk observed is too small to demonstrate any 
causal link between dpm exposure and cancer. Their reasoning is that in 
these studies, errors in the collection or interpretation of smoking 
data can create a bias in the results larger than any potential 
contribution attributable to diesel particulate. They propose that 
studies failing to account for smoking habits should be disqualified 
from consideration, and that evidence of an association from the 
remaining studies should be discounted because of potential confounding 
due to erroneous, incomplete, or otherwise inadequate characterization 
of smoking histories.
    MSHA concurs with Cohen and Higgins (1995), Lipsett and Alexeeff 
(1998), and Bhatia et al. (1998) in not accepting this view. MSHA does 
recognize that unknown exposures to tobacco smoke or other human 
carcinogens, such as asbestos, can distort the results of some lung 
cancer studies. MSHA also agrees that significant differences in the 
distribution of confounding factors, such as smoking history, between 
study and control groups can lead to misleading results. MSHA also 
recognizes, however, that it is not possible to design a human 
epidemiological study that perfectly controls for all potentially 
confounding factors. Some degree of informed subjective judgement is 
always required in evaluating the potential significance of unknown or 
uncontrolled factors.
    Sixteen of the published epidemiological studies involving lung 
cancer did, in fact, control or adjust for exposure to tobacco smoke, 
and some of these also controlled or adjusted for exposure to asbestos 
and other carcinogenic substances (e.g., Garshick et al., 1987; 
Steenland et al., 1990; Boffetta et al., 1988). All but one of these 16 
epidemiological studies reported some degree of excess risk associated 
with exposure to diesel particulate, with statistically significant 
results reported in seven. These results are less likely to be 
confounded than results from studies with no adjustment. In addition, 
several of the other studies drew comparisons against internal control 
groups or control groups likely to have similar smoking habits as the 
exposed groups (e.g., Garshick et al., 1988; Gustavsson et al., 1990; 
and Hansen, 1993). MSHA places more weight on these studies than on 
studies drawing comparisons against dissimilar groups with no controls 
or adjustments.
    According to Stober and Abel, the potential confounding effects of 
smoking are so strong that they could explain even statistically 
significant results observed in studies where smoking was explicitly 
taken into account. MSHA agrees that variable exposures to non-diesel 
lung carcinogens, including relatively small errors in smoking 
classification, could bias individual studies. However, the potential 
confounding effect of tobacco smoke and other carcinogens can cut in 
either direction. Spurious positive associations of dpm exposure with 
lung cancer would arise only if the group exposed to dpm had a greater 
exposure to these confounders than the unexposed control group used for 
comparison. If, on the contrary, the control group happened to be more 
exposed to confounders, then this would tend to make the association 
between dpm exposure and lung cancer appear negative. Therefore, 
although smoking effects could potentially distort the results of any 
single study, this effect could reasonably be expected to make only 
about half the studies that were explicitly adjusted for smoking come 
out positive. Smoking is unlikely to have been responsible for finding 
an excess prevalence of lung cancer in 15 out of 16 studies in which a 
smoking adjustment was applied. Based on a 2-tailed sign test, this 
possibility can be rejected at a confidence level greater than 99.9 
percent.
    Even in the 27 studies involving lung cancer for which no smoking 
adjustment was made, tobacco smoke and other carcinogens are important 
confounders only to the extent that the

[[Page 17534]]

populations exposed and unexposed to diesel exhaust differed 
systematically with respect to these other exposures. Twenty-three of 
these studies, however, reported some degree of excess lung cancer risk 
associated with diesel exposure. This result could be attributed to 
non-diesel exposures only in the unlikely event that, in nearly all of 
these studies, diesel-exposed workers happened to be more highly 
exposed to these other carcinogens than the control groups of workers 
unexposed to diesel. All five studies not showing any association 
(Kaplan, 1959; DeCoufle, 1977; Waller, 1981; Edling, 1987; and Bender, 
1989) may have failed to detect such a relationship because of too 
small a study group, lack of accurate exposure information, low 
duration or intensity of exposure, and/or insufficient latency or 
follow-up time.
    It is also significant that the two most comprehensive, complete, 
and well-controlled studies available (Garshick et al., 1987 and 1988) 
both point in the direction of an association between dpm exposure and 
an excess risk of lung cancer. These studies took care to address 
potential confounding by tobacco smoke and asbestos exposures. In 
response to the ANPRM, a consultant to the National Coal Association 
who was critical of all other available studies acknowledged that these 
two:

    * * * have successfully controlled for severally [sic] 
potentially important confounding factors * * * Smoking represents 
so strong a potential confounding variable that its control must be 
nearly perfect if an observed association between cancer and diesel 
exhaust is * * * [inferred to be causal]. In this regard, two 
observations are relevant. First, both case-control [Garshick et 
al., 1987] and cohort [Garshick et al., 1988] study designs revealed 
consistent results. Second, an examination of smoking related causes 
of death other than lung cancer seemed to account for only a 
fraction of the association observed between diesel exposure and 
lung cancer. A high degree of success was apparently achieved in 
controlling for smoking as a potentially confounding variable. 
[Submission 87-0-10, Robert A. Michaels, RAM TRAC Corporation, 
prepared for National Coal Association].

    Potential biases due to extraneous risk factors are unlikely to 
account for a significant part of the excess risk in all studies 
showing an association. Excess rates of lung cancer were associated 
with dpm exposure in all epidemiologic studies of sufficient size and 
scope to detect such an excess. Although it is possible, in any 
individual study, that the potentially confounding effects of 
differential exposure to tobacco smoke or other carcinogens could 
account for the observed elevation in risk otherwise attributable to 
diesel exposure, it is unlikely that such effects would give rise to 
positive associations in 38 out of 43 studies. As stated by Cohen and 
Higgins (1995):

    * * * elevations [of lung cancer] do not appear to be fully 
explicable by confounding due to cigarette smoking or other sources 
of bias. Therefore, at present, exposure to diesel exhaust provides 
the most reasonable explanation for these elevations. The 
association is most apparent in studies of occupational cohorts, in 
which assessment of exposure is better and more detailed analyses 
have been performed. The largest relative risks are often seen in 
the categories of most probable, most intense, or longest duration 
of exposure. In general population studies, in which exposure 
prevalence is low and misclassification of exposure poses a 
particularly serious potential bias in the direction of observing no 
effect of exposure, most studies indicate increased risk, albeit 
with considerable imprecision. [Cohen and Higgins (1995), p. 269].

    III.2.c.i.B.ii. Bladder Cancer. With respect to cancers other than 
lung cancer, MSHA's review of the literature identified only bladder 
cancer as a possible candidate for a causal link to dpm. Cohen and 
Higgins (1995) identified and reviewed 14 epidemiological case-control 
studies containing information related to dpm exposure and bladder 
cancer. All but one of these studies found elevated risks of bladder 
cancer among workers in jobs frequently associated with dpm exposure. 
Findings were statistically significant in at least four of the studies 
(statistical significance was not evaluated in three).
    These studies point quite consistently toward an excess risk of 
bladder cancer among truck or bus drivers, railroad workers, and 
vehicle mechanics. However, the four available cohort studies do not 
support a conclusion that exposure to dpm is responsible for the excess 
risk of bladder cancer associated with these occupations. Furthermore, 
most of the case-control studies did not distinguish between exposure 
to diesel-powered equipment and exposure to gasoline-powered equipment 
for workers having the same occupation. When such a distinction was 
drawn, there was no evidence that the prevalence of bladder cancer was 
higher for workers exposed to the diesel-powered equipment.
    This, along with the lack of corroboration from existing cohort 
studies, suggests that the excessive rates of bladder cancer observed 
may be a consequence of factors other than dpm exposure that are also 
associated with these occupations. For example, truck and bus drivers 
are subjected to vibrations while driving and may tend to have 
different dietary and sleeping habits than the general population. For 
these reasons, MSHA does not find that any convincing evidence 
currently exists for a causal relationship between dpm exposure and 
bladder cancer.
    III.2.c.ii. Studies Based on Exposures to Fine Particulate in 
Ambient Air.
    Longitudinal studies examine responses at given locations to 
changes in conditions over time, whereas cross-sectional studies 
compare results from locations with different conditions at a given 
point in time. Prior to 1990, cross sectional studies were generally 
used to evaluate the relationship between mortality and long-term 
exposure to particulate matter, but unaddressed spatial confounders and 
other methodological problems inherent in such studies limited their 
usefulness (EPA, 1996).
    Two recent prospective cohort studies provide better evidence of a 
link between excess mortality rates and exposure to fine particulate, 
although the uncertainties here are greater than with the short-term 
exposure studies conducted in single communities. The two studies are 
known as the Six Cities study (Dockery et al., 1993), and the American 
Cancer Society (ACS) study (Pope et al., 1995).\11\ The first study 
followed about 8,000 adults in six U.S. cities over 14 years; the 
second looked at survival data for half a million adults in 151 U.S. 
cities for 7 years. After adjusting for potential confounders, 
including smoking habits, the studies considered differences in 
mortality rates between the most polluted and least polluted cities.
---------------------------------------------------------------------------

    \11\ A third such study only looked at TSP, rather than fine 
particulate. It did not find a significant association between total 
mortality and TSP. It is known as the California Seventh Day 
Adventist study (Abbey et al., 1991).
---------------------------------------------------------------------------

    Both the Six Cities study and the ACS study found a significant 
association between increased concentration of PM2.5 and 
total mortality.\12\ The authors of the Six Cities Study concluded that 
the results suggest that exposures to fine particulate air pollution 
``contributes to excess mortality in certain U.S. cities.'' The ACS 
study, which not only controlled for smoking habits and various 
occupational exposures, but also, to some extent, for passive exposure 
to tobacco smoke, found results qualitatively consistent with those of 
the Six Cities Study.\13\ In the

[[Page 17535]]

ACS study, however, the estimated increase in mortality associated with 
a given increase in fine particulate exposure was lower, though still 
statistically significant. In both studies, the largest increase 
observed was for cardiopulmonary mortality. Both studies also showed an 
increased risk of lung cancer associated with increased exposure to 
fine particulate, but these results were not statistically significant.
---------------------------------------------------------------------------

    \12\ The Six Cities study also found such relationships at 
elevated levels of PM15/10 and sulfates. The ACS study 
was designed to follow up on the fine particle result of the Six 
Cities study, but also looked at sulfates.
    \13\ The Six Cities study did not find a statistically 
significant increase in risk among non-smokers, suggesting that this 
group might not be as sensitive to adverse health effects from 
exposure to fine particulate; however, the ACS study, with more 
statistical power, did find an association even for non-smokers.
---------------------------------------------------------------------------

    The few studies on associations between chronic PM2.5 
exposure and morbidity in adults show effects that are difficult to 
separate from PM10 measures and measures of acid aerosols. 
The available studies, however, do show positive associations between 
particulate air pollution and adverse health effects for those with 
pre-existing respiratory or cardiovascular disease; and as mentioned 
earlier, there is a large body of evidence showing that respiratory 
diseases classified as COPD are significantly more prevalent among 
miners than in the general population. It also appears that PM exposure 
may exacerbate existing respiratory infections and asthma, increasing 
the risk of severe outcomes in individuals who have such conditions 
(EPA, 1996).
III.2.d. Mechanisms of Toxicity
    As described in Part II, the particulate fraction of diesel exhaust 
is made up of aggregated soot particles. Each soot particle consists of 
an insoluble, elemental carbon core and an adsorbed, surface coating of 
relatively soluble organic compounds, such as polycyclic aromatic 
hydrocarbons (PAH's). When released into an atmosphere, the soot 
particles formed during combustion tend to aggregate into larger 
particles.
    The literature on deposition of fine particles in the respiratory 
tract is reviewed in Green and Watson (1995) and U.S. EPA (1996). The 
mechanisms responsible for the broad range of potential particle-
related health effects will vary depending on the site of deposition. 
Once deposited, the particles may be cleared from the lung, 
translocated into the interstitium, sequestered in the lymph nodes, 
metabolized, or be otherwise transformed by various mechanisms.
    As suggested by Figure II-1 of this preamble, most of the 
aggregated particles making up dpm never get any larger than one 
micrometer in diameter. Particles this small are able to penetrate into 
the deepest regions of the lungs, called alveoli. In the alveoli, the 
particles can mix with and be dispersed by a substance called 
surfactant, which is secreted by cells lining the alveolar surfaces.
    MSHA would welcome any additional information, not already covered 
in the surveys cited above, on fine particle deposition in the 
respiratory tract, especially as it might pertain to lung loading in 
miners exposed to a combination of diesel particulate and other dusts. 
Any such additional information will be placed into the public record 
and considered by MSHA before a final rule is adopted.
    III.2.d.i. Effects Other than Cancer. A number of controlled animal 
studies have been undertaken to ascertain the toxic effects of exposure 
to diesel exhaust and its components. Watson and Green (1995) reviewed 
approximately 50 reports describing noncancerous effects in animals 
resulting from the inhalation of diesel exhaust. While most of the 
studies were conducted with rats or hamsters, some information was also 
available from studies conducted using cats, guinea pigs, and monkeys. 
The authors also correlated reported effects with different descriptors 
of dose. From their review of these studies, Watson and Green concluded 
that:
    (a) Animals exposed to diesel exhaust exhibit a number of 
noncancerous pulmonary effects, including chronic inflammation, 
epithelial cell hyperplasia, metaplasia, alterations in connective 
tissue, pulmonary fibrosis, and compromised pulmonary function.
    (b) Cumulative weekly exposure to diesel exhaust of 70 to 80 
mghr/m3 or greater are associated with the presence 
of chronic inflammation, epithelial cell proliferation, and depressed 
alveolar clearance in chronically exposed rats.
    (c) The extrapolation of responses in animals to noncancer 
endpoints in humans is uncertain. Rats were the most sensitive animal 
species studied.
    Subsequent to the review by Watson and Green, there have been a 
number of animal studies on allergic immune responses to dpm. Takano et 
al. (1997) investigated the effects of dpm injected into mice through 
an intratracheal tube and found manifestations of allergic asthma, 
including enhanced antigen-induced airway inflammation, increased local 
expression of cytokine proteins, and increased production of antigen-
specific immunoglobulins. The authors concluded that the study 
demonstrated dpm's enhancing effects on allergic asthma and that the 
results suggest that dpm is ``implicated in the increasing prevalence 
of allergic asthma in recent years.'' Similarly, Ichinose et al. (1997) 
found that five different strains of mice injected intratracheally with 
dpm exhibited manifestations of allergic asthma, as expressed by 
enhanced airway inflammation, which were correlated with an increased 
production of antigen-specific immunoglobulin due to the dpm. The 
authors concluded that dpm enhances manifestations of allergic airway 
inflammation and that ``* * * the cause of individual differences in 
humans at the onset of allergic asthma may be related to differences in 
antigen-induced immune responses * * *.''
    Several laboratory animal studies have been performed to ascertain 
whether the effects of diesel exhaust are attributable specifically to 
the particulate fraction. (Heinrich et al., 1986; Iwai et al., 1986; 
Brightwell et al., 1986). These studies compare the effects of chronic 
exposure to whole diesel exhaust with the effects of filtered exhaust 
containing no particles. The studies demonstrate that when the exhaust 
is sufficiently diluted to nullify the effects of gaseous irritants 
(NO2 and SO2), irritant vapors (aldehydes), CO, 
and other systemic toxicants, diesel particles are the prime etiologic 
agents of noncancer health effects. Exposure to dpm produced changes in 
the lung that were much more prominent than those evoked by the gaseous 
fraction alone. Marked differences in the effects of whole and filtered 
diesel exhaust were also evident from general toxicological indices, 
such as body weight, lung weight, and pulmonary histopathology. This 
provides strong evidence that the toxic component in diesel emissions 
producing the effects noted in other animal studies is due to the 
particulate fraction.
    The mechanisms that may lead to adverse health effects in humans 
from inhaling fine particulates are not fully understood, but potential 
mechanisms that have been hypothesized for non-cancerous outcomes are 
summarized in Table III-6. A comprehensive review of the toxicity 
literature is provided in U.S. EPA (1996).
    Deposition of particulates in the human respiratory tract could 
initiate events leading to increased airflow obstruction, impaired 
clearance, impaired host defenses, or increased epithelial 
permeability. Airflow obstruction could result from laryngeal 
constriction or bronchoconstriction secondary to stimulation of 
receptors in extrathoracic or intrathoracic airways. In addition to 
reflex airway narrowing, reflex or local stimulation of mucus secretion 
could lead to mucus hypersecretion and could eventually lead to mucus 
plugging in small airways.
    Pulmonary changes that contribute to cardiovascular responses 
include a

[[Page 17536]]

variety of mechanisms that can lead to hypoxemia, including 
bronchoconstriction, apnea, impaired diffusion, and production of 
inflammatory mediators. Hypoxia can lead to cardiac arrhythmias and 
other cardiac electrophysiologic responses that, in turn, may lead to 
ventricular fibrillation and ultimately cardiac arrest. Furthermore, 
many respiratory receptors have direct cardiovascular effects. For 
example, stimulation of C-fibers leads to bradycardia and hypertension, 
and stimulation of laryngeal receptors can result in hypertension, 
cardiac arrhythmia, bradycardia, apnea, and even cardiac arrest. Nasal 
receptor or pulmonary J-receptor stimulation can lead to vagally 
mediated bradycardia and hypertension (Widdicombe, 1988).
    In addition to possible acute toxicity of particles in the 
respiratory tract, chronic exposure to particles that deposit in the 
lung may induce inflammation. Inflammatory responses can lead to 
increased permeability and possibly diffusion abnormality. Furthermore, 
mediators released during an inflammatory response could cause release 
of factors in the clotting cascade that may lead to an increased risk 
of thrombus formation in the vascular system (Seaton, 1995). Persistent 
inflammation, or repeated cycles of acute lung injury and healing, can 
induce chronic lung injury. Retention of the particles may be 
associated with the initiation and/or progression of COPD.
    III.2.d.ii. Lung Cancer.
    III.2.d.ii.A. Genotoxicological Evidence. Many studies have shown 
that diesel soot, or its organic component, can increase the likelihood 
of genetic mutations during the biological process of cell division and 
replication. A survey of the applicable scientific literature is 
provided in Shirname-More (1995). What makes this body of research 
relevant to the risk of cancer is that mutations in critical genes can 
sometimes initiate, promote, or advance a process of carcinogenesis.
    The determination of genotoxicity has frequently been made by 
treating diesel soot with organic solvents such as dichloromethane and 
dimethyl sulfoxide. The solvent removes the organic compounds from the 
carbon core. After the solvent evaporates, the mutagenic potential of 
the extracted organic material is tested by applying it to bacterial, 
mammalian, or human cells propagated in a laboratory culture. In 
general, the results of these studies have shown that various 
components of the organic material can induce mutations and chromosomal 
aberrations.
    A critical issue is whether whole diesel particulate is mutagenic 
when dispersed by substances present in the lung. Since the laboratory 
procedure for extracting organic material with solvents bears little 
resemblance to the physiological environment of the lung, it is 
important to establish whether dpm as a whole is genotoxic, without 
solvent extraction. Early research indicated that this was not the case 
and, therefore, that the active genotoxic materials adhering to the 
carbon core of diesel particles might not be biologically damaging or 
even available to cells in the lung (Brooks et al., 1980; King et al., 
1981; Siak et al., 1981). A number of more recent research papers, 
however, have shown that dpm, without solvent extraction, can cause DNA 
damage when the soot is dispersed in the pulmonary surfactant that 
coats the surface of the alveoli (Wallace et al., 1987; Keane et al., 
1991; Gu et al., 1991; Gu et al., 1992). From these studies, NIOSH has 
concluded:

    * * * the solvent extract of diesel soot and the surfactant 
dispersion of diesel soot particles were found to be active in 
procaryotic cell and eukaryotic cell in vitro genotoxicity assays. 
The cited data indicate that respired diesel soot particles on the 
surface of the lung alveoli and respiratory bronchioles can be 
dispersed in the surfactant-rich aqueous phase lining the surfaces, 
and that genotoxic material associated with such dispersed soot 
particles is biologically available and genotoxically active. 
Therefore, this research demonstrates the biological availability of 
active genotoxic materials without organic solvent interaction. 
[Cover letter to NIOSH response to ANPRM.]

From this conclusion, it follows that dpm itself, and not only its 
organic extract, can cause genetic mutations when dispersed by a 
substance present in the lung.
    The biological availability of the genotoxic components is also 
supported directly by studies showing genotoxic effects of exposure to 
whole dpm. The formation of DNA adducts is an important indicator of 
genotoxicity and potential carcinogenicity. If DNA adducts are not 
repaired, then a mutation or chromosomal aberration can occur during 
normal mitosis (i.e., cell replication). Hemminki et al. (1994) found 
that DNA adducts were significantly elevated in nonsmoking bus 
maintenance and truck terminal workers, as compared to a control group 
of hospital mechanics, with the highest adduct levels found among 
garage and forklift workers. Similarly, Nielsen et al. (1996) found 
that DNA adducts were significantly increased in bus garage workers and 
mechanics exposed to dpm as compared to a control group.
    III.2.d.ii.B. Evidence from Animal Studies. Bond et al. (1990) 
investigated differences in peripheral lung DNA adduct formation among 
rats, hamsters, mice, and monkeys exposed to dpm at a concentration of 
8100 g/m3 for 12 weeks. Mice and hamsters showed no 
increase of DNA adducts in their peripheral lung tissue, whereas rats 
and monkeys showed a 60 to 80% increase. The increased prevalence of 
lung DNA adducts in monkeys suggests that, with respect to DNA adduct 
formation, the human lungs' response to dpm inhalation may more closely 
resemble that of the rat than that of the hamster or mouse.
    Mauderly (1992) and Busby and Newberne (1995) provide reviews of 
the scientific literature relating to excess lung cancers observed 
among laboratory animals chronically exposed to filtered and unfiltered 
diesel exhaust. The experimental data demonstrate that chronic exposure 
to whole diesel exhaust increases the risk of lung cancer in rats and 
that dpm is the causative agent. This carcinogenic effect has been 
confirmed in two strains of rats and in at least five laboratories. 
Experimental results for animal species other than the rat, however, 
are either inconclusive or, in the case of Syrian hamsters, suggestive 
of no carcinogenic effect. This is consistent with the observation, 
mentioned above, that lung DNA adduct formation is increased among 
exposed rats but not among exposed hamsters or mice.
    The conflicting results for rats and hamsters indicate that the 
carcinogenic effects of dpm exposure may be species-dependent. Indeed, 
monkey lungs have been reported to respond quite differently than rat 
lungs to both diesel exhaust and coal dust (Nikula, 1997). Therefore, 
the results from rat experiments do not, by themselves, infer any 
excess risk due to dpm exposure for humans. The human epidemiological 
data, however, indicate that humans comprise a species that, like rats 
and unlike hamsters, suffer a carcinogenic response to dpm exposure. 
Therefore, MSHA considers the rat studies at least relevant to an 
evaluation of the risk for humans.
    When dpm is inhaled, a number of adverse effects that may 
contribute to carcinogenesis are discernable by microscopic and 
biochemical analysis. For a comprehensive review of these effects, see 
Watson and Green (1995). In brief, these effects begin with 
phagocytosis, which is essentially an attack on the diesel particles by 
cells called alveolar macrophages. The macrophages engulf and ingest 
the diesel particles, subjecting them to detoxifying enzymes. Although 
this is a normal physiological response to the

[[Page 17537]]

inhalation of foreign substances, the process can produce various 
chemical byproducts injurious to normal cells. In attacking the diesel 
particles, the activated macrophages release chemical agents that 
attract neutrophils (a type of white blood cell that destroys 
microorganisms) and additional alveolar macrophages. As the lung burden 
of diesel particles increases, aggregations of particle-laden 
macrophages form in alveoli adjacent to terminal bronchioles, the 
number of Type II cells lining particle-laden alveoli increases, and 
particles lodge within alveolar and peribronchial tissues and 
associated lymph nodes. The neutrophils and macrophages release 
mediators of inflammation and oxygen radicals, which have been 
implicated in causing various forms of chromosomal damage, genetic 
mutations, and malignant transformation of cells (Weitzman and Gordon, 
1990). Eventually, the particle-laden macrophages are functionally 
altered, resulting in decreased viability and impaired phagocytosis and 
clearance of particles. This series of events may result in pulmonary 
inflammatory, fibrotic, or emphysematous lesions that can ultimately 
develop into cancerous tumors.
    Such reactions have also been observed in rats exposed to high 
concentrations of fine particles with no organic component (Mauderly et 
al., 1994; Heinrich et al., 1994 and 1995; Nikula et al., 1995). Rats 
exposed to titanium dioxide or pure carbon (``carbon-black'') 
particles, which are not considered to be genotoxic, developed lung 
cancers at about the same rate as rats exposed to whole diesel exhaust. 
Therefore, it appears that the toxicity of dpm, at least in some 
species, may result largely from a biochemical response to the particle 
itself rather than from specific effects of the adsorbed organic 
compounds.
    Some researchers have interpreted the carbon-black and titanium 
dioxide studies as also suggesting that (1) the carcinogenic mechanism 
in rats depends on massive overloading of the lung and (2) that this 
may provide a mechanism of carcinogenesis specific to rats which does 
not occur in other rodents or in humans (Oberdorster, 1994; Watson and 
Valberg, 1996). Some commenters on the ANPRM cited the lack of any link 
between lung cancer and coal dust or carbon black exposure as evidence 
that carbon particles, by themselves, are not carcinogenic in humans. 
Coal mine dust, however, consists almost entirely of particles larger 
than those forming the carbon core of dpm or used in the carbon-black 
and titanium dioxide rat studies. Furthermore, although there have been 
eight studies \14\ reporting no excess risk of lung cancer among coal 
miners (Liddell, 1973; Costello et al., 1974; Armstrong et al., 1979; 
Rooke et al., 1979; Ames et al., 1983; Atuhaire et al., 1985; Miller 
and Jacobsen, 1985; Kuempel et al., 1995), five studies have reported 
an elevated risk of lung cancer for those exposed to coal dust 
(Enterline, 1972; Rockette, 1977; Correa et al., 1984; Levin et al., 
1988; Morfeld et al., 1997). The positive results in two of these 
studies (Enterline, 1972; Rockette, 1977) were statistically 
significant. Furthermore, excess lung cancers have been reported among 
carbon black production workers (Hodgson and Jones, 1985; Siemiatycki, 
1991; Parent et al., 1996). MSHA is not aware of any evidence that a 
mechanism of carcinogenesis due to fine particle overload is 
inapplicable to humans. Studies carried out on rodents certainly do not 
provide such evidence.
---------------------------------------------------------------------------

    \14\ The Agency has recently learned of another report, from the 
University of Newcastle, Australia, that found no elevated risk of 
lung cancer among coal miners. Although the Agency has not been able 
to acquire this report in time to include it in the present risk 
assessment, it will be reviewed and considered in the risk 
assessment prior to any final action. The Agency would also welcome 
information on any additional studies or reports on this issue of 
which it is not currently aware.
---------------------------------------------------------------------------

    The carbon-black and titanium dioxide studies indicate that lung 
cancers in rats exposed to dpm may be induced by a mechanism that does 
not require the bioavailability of genotoxic organic compounds adsorbed 
on the elemental carbon particles. These studies do not, however, prove 
that the only significant agent of carcinogenesis in rats exposed to 
diesel particulate is the non-soluble carbon core. Nor do the carbon-
black studies prove that the only significant mechanism of 
carcinogenesis due to diesel particulate is lung overload. Due to the 
relatively high doses administered in the rat studies, it is 
conceivable that an overload phenomenon masks or parallels other 
potential routes to cancer. It may be that effects of the genotoxic 
organic compounds are merely masked or displaced by overloading in the 
rat studies. Gallagher et al. (1994) exposed different groups of rats 
to diesel exhaust, carbon black, or titanium dioxide and detected 
species of lung DNA adducts in the rats exposed to dpm that were not 
found in the controls or rats exposed to carbon black or titanium 
dioxide.
    Particle overload may provide the dominant route to lung cancer at 
very high concentrations of fine particulate, while genotoxic 
mechanisms may provide the primary route under lower-level exposure 
conditions. In humans exposed over a working lifetime to doses 
insufficient to cause overload, carcinogenic mechanisms unrelated to 
overload may dominate, as indicated by the human epidemiological 
studies and the data on human DNA adducts cited above. Therefore, the 
carbon black results observed in the rat studies do not preclude the 
possibility that the organic component of dpm has important genotoxic 
effects in humans (Nauss et al., 1995).
    Even if the genotoxic organic compounds in dpm were biologically 
unavailable and played no role in human carcinogenesis, this would not 
rule out the possibility of a genotoxic route to lung cancer (even for 
rats) due to the presence of dpm particles themselves. For example, as 
a byproduct of the biochemical response to the presence of dpm in the 
alveoli, free oxidant radicals may be released as macrophages attempt 
to digest the particles. There is evidence that dpm can both induce 
production of active oxygen agents and also depress the activity of 
naturally occurring antioxidant enzymes (Mori, 1996; Sagai, 1993). 
Oxidants can induce carcinogenesis either by reacting directly with 
DNA, or by stimulating cell replication, or both (Weitzman and Gordon, 
1990). This would provide a mutagenic route to lung cancer with no 
threshold. Therefore, the carbon black and titanium dioxide studies 
cited above do not prove that dpm exposure has no incremental, 
genotoxic effects or that there is a threshold below which dpm exposure 
poses no risk of causing lung cancer.
    It is noteworthy, however, that dpm exposure levels recorded in 
some mines have been almost as high as laboratory exposures 
administered to rats showing a clearly positive response. Intermittent, 
occupational exposure levels greater than about 500 g/m\3\ dpm 
may overwhelm the human lung clearance mechanism (Nauss et al., 1995). 
Therefore, concentrations at levels currently observed in some mines 
could be expected to cause overload in some humans, possibly inducing 
lung cancer by a mechanism similar to what occurs in rats. MSHA would 
like to receive additional scientific information on this issue, 
especially as it relates to lung loading in miners exposed to a 
combination of diesel particulate and other dusts.
    As suggested above, such a mechanism would not necessarily be the 
only route to carcinogenesis in humans and, therefore, would not imply 
that dpm concentrations too low to

[[Page 17538]]

cause overload are safe for humans. Furthermore, a proportion of 
exposed individuals can always be expected to be more susceptible than 
normal. Therefore, at lower dpm concentrations, particle overload may 
still provide a route to lung cancer in susceptible humans. At even 
lower concentrations, other routes to carcinogenesis in humans may 
predominate, possibly involving genotoxic effects.
III.3. Characterization of Risk
    Having reviewed the evidence of health effects associated with 
exposure to dpm, MSHA has evaluated that evidence to ascertain whether 
exposure levels currently existing in mines warrant regulatory action 
pursuant to the Mine Act. The criteria for this evaluation are 
established by the Mine Act and related court decisions. Section 
101(a)(6)(A) provides that:

    The Secretary, in promulgating mandatory standards dealing with 
toxic materials or harmful physical agents under this subsection, 
shall set standards which most adequately assure on the basis of the 
best available evidence that no miner will suffer material 
impairment of health or functional capacity even if such miner has 
regular exposure to the hazards dealt with by such standard for the 
period of his working life.

    Based on court interpretations of similar language under the 
Occupational Safety and Health Act, there are three questions that need 
to be addressed: (1) whether health effects associated with dpm 
exposure constitute a ``material impairment'' to miner health or 
functional capacity; (2) whether exposed miners are at significant 
excess risk of incurring any of these material impairments; and (3) 
whether the proposed rule will substantially reduce such risks.
    The criteria for evaluating the health effects evidence do not 
require scientific certainty. As noted by Justice Stevens in an 
important case on risk involving the Occupational Safety and Health 
Administration, the need to evaluate risk does not mean an agency is 
placed into a ``mathematical straightjacket.'' [Industrial Union 
Department, AFL-CIO v. American Petroleum Institute, 448 U.S. 607, 100 
S.Ct. 2844 (1980), hereinafter designated the ``Benzene'' case]. When 
regulating on the edge of scientific knowledge, certainty may not be 
possible; and--

so long as they are supported by a body of reputable scientific 
thought, the Agency is free to use conservative assumptions in 
interpreting the data * * * risking error on the side of 
overprotection rather than underprotection. [Id. at 656].

The statutory criteria for evaluating the health evidence do not 
require MSHA to wait for absolute precision. In fact, MSHA is required 
to use the ``best available evidence.'' (Emphasis added).
III.3.a. Material Impairments to Miner Health or Functional Capacity
    From its review of the literature cited in Part III.2, MSHA has 
tentatively concluded that underground miners exposed to current levels 
of dpm are at excess risk of incurring the following three kinds of 
material impairment: (i) sensory irritations and respiratory symptoms; 
(ii) death from cardiovascular, cardiopulmonary, or respiratory causes; 
and (iii) lung cancer. The basis for linking these with dpm exposure is 
summarized in the following three subsections.
    III.3.a.i. Sensory Irritations and Respiratory Symptoms. Kahn et 
al. (1988), Battigelli (1965), Gamble et al. (1987a) and Rudell et al. 
(1996) identified a number of debilitating acute responses to diesel 
exhaust exposure: irritation of the eyes, nose and throat; headaches, 
nausea, and vomiting; chest tightness and wheeze. These symptoms were 
also reported by miners at the 1995 workshops. In addition, Ulfvarson 
et al. (1987, 1990) found evidence of reduced lung function in workers 
exposed to dpm for a single shift.
    Although there is evidence that such symptoms subside within one to 
three days of no occupational exposure, a miner who must be exposed to 
dpm day after day in order to earn a living may not have time to 
recover from such effects. Hence, the opportunity for a so-called 
``reversible'' health effect to reverse itself may not be present for 
many miners. Furthermore, effects such as stinging, itching and burning 
of the eyes, tearing, wheezing, and other types of sensory irritation 
can cause severe discomfort and can, in some cases, be seriously 
disabling. Also, workers experiencing sufficiently severe sensory 
irritations can be distracted as a result of their symptoms, thereby 
endangering other workers and increasing the risk of accidents. For 
these reasons, MSHA considers such irritations to constitute ``material 
impairments'' of health or functional capacity within the meaning of 
the Act, regardless of whether or not they are reversible. Further 
discussion of why MSHA believes reversible effects can constitute 
material impairments can be found earlier in this risk assessment, in 
the section entitled ``Relevance of Health Effects that are 
Reversible.''
    The best available evidence also points to more severe respiratory 
consequences of exposure to dpm. Significant associations have been 
detected between acute environmental exposures to fine particulates and 
debilitating respiratory impairments in adults, as measured by lost 
work days, hospital admissions, and emergency room visits. Short-term 
exposures to fine particulates, or particulate air pollution in 
general, have been associated with significant increases in the risk of 
hospitalization for both pneumonia and COPD (EPA, 1996).
    The risk of severe respiratory effects is exemplified by specific 
cases of persistent asthma linked to diesel exposure (Wade and Newman, 
1993). There is considerable evidence for a causal connection between 
dpm exposure and increased manifestations of allergic asthma and other 
allergic respiratory diseases, coming from recent experiments on 
animals and human cells (Peterson and Saxon, 1996; Diaz-Sanchez, 1997; 
Takano et al., 1997; Ichinose et al., 1997). Such health outcomes are 
clearly ``material impairments'' of health or functional capacity 
within the meaning of the Act.
    III.3.a.ii. Excess Risk of Death from Cardiovascular, 
Cardiopulmonary, or Respiratory Causes. The evidence from air pollution 
studies identifies death, largely from cardiovascular or respiratory 
causes, as an endpoint significantly associated with acute exposures to 
fine particulates. The weight of epidemiological evidence indicates 
that short-term ambient exposure to particulate air pollution 
contributes to an increased risk of daily mortality. Time-series 
analyses strongly suggest a positive effect on daily mortality across 
the entire range of ambient particulate pollution levels. Relative risk 
estimates for daily mortality in relation to daily ambient particulate 
concentration are consistently positive and statistically significant 
across a variety of statistical modeling approaches and methods of 
adjustment for effects of relevant covariates such as season, weather, 
and co-pollutants. After thoroughly reviewing this body of evidence, 
the U.S. Environmental Protection Agency (EPA) concluded:

    It is extremely unlikely that study designs not yet employed, 
covariates not yet identified, or statistical techniques not yet 
developed could wholly negate the large and consistent body of 
epidemiological evidence * * *.

    There is also substantial evidence of a relationship between 
chronic exposure to fine particulates and an excess (age-adjusted) risk 
of mortality, especially from cardiopulmonary diseases. The Six Cities 
and ACS studies of ambient air particulates both found a significant 
association between chronic exposure to fine particles and excess 
mortality. In

[[Page 17539]]

both studies, after adjusting for smoking habits, a statistically 
significant excess risk of cardiopulmonary mortality was found in the 
city with the highest average concentration of fine particulate (i.e., 
PM2.5) as compared to the city with the lowest. Both studies 
also found excess deaths due to lung cancer in the cities with the 
higher average level of PM2.5, but these results were not 
statistically significant (EPA, 1996). The EPA concluded that--

    * * * the chronic exposure studies, taken together, suggest 
there may be increases in mortality in disease categories that are 
consistent with long-term exposure to airborne particles and that at 
least some fraction of these deaths reflect cumulative PM impacts 
above and beyond those exerted by acute exposure events* * * There 
tends to be an increasing correlation of long-term mortality with PM 
indicators as they become more reflective of fine particle levels 
(EPA, 1996).

    Whether associated with acute or chronic exposures, the excess risk 
of death that has been linked to pollution of the air with fine 
particles like dpm is clearly a ``material impairment'' of health or 
functional capacity within the meaning of the Act.
    III.3.a.iii. Lung Cancer. It is clear that lung cancer constitutes 
a ``material impairment'' of health or functional capacity within the 
meaning of the Act. Questions have been raised however, as to whether 
the evidence linking dpm exposure with an excess risk of lung cancer 
demonstrates a causal connection (Stober and Abel, 1996; Watson and 
Valberg, 1996; Cox, 1997; Morgan et al., 1997; Silverman, 1998).
    MSHA recognizes that no single one of the existing epidemiological 
studies, viewed in isolation, provides conclusive evidence of a causal 
connection between dpm exposure and an elevated risk of lung cancer in 
humans. Consistency and coherency of results, however, do provide such 
evidence. Although no epidemiological study is flawless, studies of 
both cohort and case-control design have quite consistently shown that 
chronic exposure to diesel exhaust, in a variety of occupational 
circumstances, is associated with an increased risk of lung cancer. 
With only rare exceptions, involving too few workers and/or observation 
periods too short to have a good chance of detecting excess cancer 
risk, the human studies have shown a greater risk of lung cancer among 
exposed workers than among comparable unexposed workers.
    Lipsett and Alexeeff (1998) performed a comprehensive statistical 
meta-analysis of the epidemiological literature on lung cancer and dpm 
exposure. This analysis systematically combined the results of the 
studies summarized in Tables III-4 and III-5. Some studies were 
eliminated because they did not allow for a period of at least 10 years 
for the development of clinically detectable lung cancer. Others were 
eliminated because of bias resulting from incomplete ascertainment of 
lung cancer cases in cohort studies or because they examined the same 
cohort population as another study. One study was excluded because 
standard errors could not be calculated from the data presented. The 
remaining 30 studies were analyzed using both a fixed-effects and a 
random-effect analysis of variance (ANOVA) model. Sources of 
heterogeneity in results were investigated by subset analysis; using 
categorical variables to characterize each study's design; target 
population (general or industry-specific); occupational group; source 
of control or reference population; latency; duration of exposure; 
method of ascertaining occupation; location (North America or Europe); 
covariate adjustments (age, smoking, and/or asbestos exposure); and 
absence or presence of a clear healthy worker effect (as manifested by 
lower than expected all-cause mortality in the occupational population 
under study).
    Sensitivity analyses were conducted to evaluate the sensitivity of 
results to inclusion criteria and to various assumptions used in the 
analysis. This included substitution of excluded ``redundant'' studies 
of same cohort population for the included studies and exclusion of 
studies involving questionable exposure to dpm. An influence analysis 
was also conducted to examine the effect of dropping one study at a 
time, to determine if any individual study had a disproportionate 
effect on the ANOVA. Potential effects of publication bias were also 
investigated. The authors concluded:

    The results of this meta-analysis indicate a consistent positive 
association between occupations involving diesel exhaust exposure 
and the development of lung cancer. Although substantial 
heterogeneity existed in the initial pooled analysis, stratification 
on several factors identified a relationship that persisted 
throughout various influence and sensitivity analyses * * *.
    This meta-analysis provides evidence consistent with the 
hypothesis that exposure to diesel exhaust is associated with an 
increased risk of lung cancer. The pooled estimates clearly reflect 
the existence of a positive relationship between diesel exhaust and 
lung cancer in a variety of diesel-exposed occupations, which is 
supported when the most important confounder, cigarette smoking, is 
measured and controlled. There is suggestive evidence of an 
exposure-response relationship in the smoking adjusted studies as 
well. Many of the subset analyses indicated the presence of 
substantial heterogeneity among the pooled estimates. Much of the 
heterogeneity observed, however, is due to the presence or absence 
of adjustment for smoking in the individual study risk estimates, to 
occupation-specific influences on exposure, to potential selection 
biases, and other aspects of study design.

    A second, independent meta-analysis of epidemiological studies 
published in peer-reviewed journals was conducted by Bhatia et al. 
(1998).\15\ In this analysis, studies were excluded if actual work with 
diesel equipment ``could not be confirmed or reliably inferred'' or if 
an inadequate latency period was allowed for cancer to develop, as 
indicated by less than 10 years from time of first exposure to end of 
follow-up. Studies of miners were also excluded, because of potential 
exposure to radon and silica. Likewise, studies were excluded if they 
exhibited selection bias or examined the same cohort population as a 
study published later. A total of 29 independent studies from 23 
published sources were identified as meeting the inclusion criteria. 
After assigning each of these 29 studies a weight proportional to its 
estimated precision, pooled relative risks were calculated based on the 
following groups of studies: all 29 studies; all case-control studies; 
all cohort studies; cohort studies using internal reference 
populations; cohort studies making external comparisons; studies 
adjusted for smoking; studies not adjusted for smoking; and studies 
grouped by occupation (railroad workers, equipment operators, truck 
drivers, and bus workers). Elevated risks were shown for exposed 
workers overall and within every individual group of studies analyzed. 
A positive duration-response relationship was observed in those studies 
presenting results according to employment duration. The weighted, 
pooled estimates of relative risk were identical for case-control and 
cohort studies and nearly identical for studies with or without smoking 
adjustments. Based on their stratified analysis, the authors argued 
that--
---------------------------------------------------------------------------

    \15\ To address potential publication bias, the authors 
identified several unpublished studies on truck drivers and noted 
that elevated risks for exposed workers observed in these studies 
were similar to those in the published studies utilized. Based on 
this and a `'funnel plot'' for the included studies, the authors 
concluded that there was no indication of publication bias.

the heterogeneity in observed relative risk estimates may be 
explained by differences between studies in methods, in populations 
studied and comparison groups used, in latency intervals, in 
intensity and duration of

[[Page 17540]]

exposure, and in the chemical and physical characteristics of diesel 
exhaust.

They concluded that the elevated risk of lung cancer observed among 
exposed workers was unlikely to be due to chance, that confounding from 
smoking is unlikely to explain all of the excess risk, and that ``this 
meta-analysis supports a causal association between increased risks for 
lung cancer and exposure to diesel exhaust.''
    As discussed earlier in the section entitled ``Mechanisms of 
Toxicity,'' animal studies have confirmed that diesel exhaust can 
increase the risk of lung cancer in some species and shown that dpm 
(rather than the gaseous fraction of diesel exhaust) is the causal 
agent. MSHA, however, views results from animal studies as subordinate 
to the results obtained from human studies. Since the human studies 
show increased risk of lung cancer at dpm levels lower than what might 
be expected to cause overload, they provide evidence that overload may 
not be the only mechanism at work among humans. The fact that dpm has 
been proven to cause lung cancer in laboratory rats is of interest 
primarily in supporting the plausibility of a causal interpretation for 
relationships observed in the human studies.
    Similarly, the genotoxicological evidence provides additional 
support for a causal interpretation of associations observed in the 
epidemiological studies. This evidence shows that dpm dispersed by 
alveolar surfactant can have mutagenic effects, thereby providing a 
genotoxic route to carcinogenesis independent of overloading the lung 
with particles. Chemical byproducts of phagocytosis may provide another 
genotoxic route. Inhalation of diesel emissions has been shown to cause 
DNA adduct formation in peripheral lung cells of rats and monkeys, and 
increased levels of human DNA adducts have been found in association 
with occupational exposures. Therefore, there is little basis for 
postulating that a threshold exists, demarcating overload, below which 
dpm would not be expected to induce lung cancers in humans.
    Results from the epidemiological studies, the animal studies, and 
the genotoxicological studies are coherent and mutually reinforcing. 
After considering all these results, MSHA has concluded that the 
epidemiological studies, supported by the experimental data 
establishing the plausibility of a causal connection, provide strong 
evidence that chronic occupational dpm exposure increases the risk of 
lung cancer in humans.
III.3.b. Significance of the Risk of Material Impairment to Miners
    The fact that there is substantial evidence that dpm exposure can 
materially impair miner health in several ways does not imply that 
miners will necessarily suffer such impairments. This section will 
consider the significance of the risk faced by miners exposed to dpm.
    III.3.b.i. Definition of a Significant Risk. The benzene case, 
referred to earlier in this section, provides the starting point for 
MSHA's analysis of this issue. Soon after its enactment in 1970, OSHA 
adopted a ``consensus'' standard on exposure to benzene, as required 
and authorized by the OSH Act. The basic part of the standard was an 
average exposure limit of 10 parts per million over an 8-hour workday. 
The consensus standard had been established over time to deal with 
concerns about poisoning from this substance (448 U.S. 607, 617). 
Several years later, NIOSH recommended that OSHA alter the standard to 
take into account evidence suggesting that benzene was also a 
carcinogen. (Id., at 619 et seq.). Although the ``evidence in the 
administrative record of adverse effects of benzene exposure at 10 ppm 
is sketchy at best,'' OSHA was operating under a policy that there was 
no safe exposure level to a carcinogen. (Id., at 631). Once the 
evidence was adequate to reach a conclusion that a substance was a 
carcinogen, the policy required the agency to set the limit at the 
lowest level feasible for the industry. (Id., at 613). Accordingly, the 
Agency proposed lowering the permissible exposure limit to 1 ppm.
    The Supreme Court rejected this approach. Noting that the OSH Act 
requires ``safe or healthful employment,'' the court stated that--

    * * * `safe' is not the equivalent of `risk-free' * * * a 
workplace can hardly be considered `unsafe' unless it threatens the 
workers with a significant risk of harm. Therefore, before he can 
promulgate any permanent health or safety standard, the Secretary is 
required to make a threshold finding that a place of employment is 
unsafe--in the sense that significant risks are present and can be 
eliminated or lessened by a change in practices. [Id., at 642, 
italics in original.]

The court went on to explain that it is the Agency that determines how 
to make such a threshold finding:

    First, the requirement that a `significant' risk be identified 
is not a mathematical straitjacket. It is the Agency's 
responsibility to determine, in the first instance, what it 
considered to be a `significant' risk. Some risks are plainly 
acceptable and others are plainly unacceptable. If, for example, the 
odds are one in a billion that a person will die from cancer by 
taking a drink of chlorinated water, the risk clearly could not be 
considered significant. On the other hand, if the odds are one in a 
thousand that regular inhalation of gasoline vapors that are 2% 
benzene will be fatal, a reasonable person might well consider the 
risk significant and take appropriate steps to decrease or eliminate 
it. Although the Agency has no duty to calculate the exact 
probability of harm, it does have an obligation to find that a 
significant risk is present before it can characterize a place of 
employment as `unsafe.' [Id., at 655.]

The court noted that the Agency's ``* * * determination that a 
particular level of risk is `significant' will be based largely on 
policy considerations.'' (Id., note 62.)
    III.3.b.ii. Evidence of Significant Risk at Current Exposure 
Levels. In evaluating the significance of the risks to miners, a key 
factor is the very high concentrations of diesel particulate to which a 
number of those miners are currently exposed--compared to ambient 
atmospheric levels in even the most polluted urban environments, and to 
workers in diesel-related occupations for which positive 
epidemiological results have been observed. Figure III-4 compared the 
range of median dpm exposures measured for mine workers at various 
mines to the range of geometric means (i.e., estimated medians) 
reported for other occupations, as well as to ambient environmental 
levels. Figure III-5 presents a similar comparison, based on the 
highest mean dpm level observed at any individual mine, the highest 
mean level reported for any occupational group other than mining, and 
the highest monthly mean concentration of dpm estimated for ambient air 
at any site in the Los Angeles basin.\16\ As shown in Figure III-5, 
underground miners are currently exposed at mean levels up to 10 times 
higher than the highest mean exposure reported for other occupations, 
and up to 100 times higher than comparable environmental levels of 
diesel particulate.

    \16\ For comparability with occupational lifetime exposure 
levels, the environmental ambient air concentration has been 
multiplied by a factor of approximately 4.7. This factor reflects a 
45-year occupational lifetime with 240 working days per year, as 
opposed to a 70-year environmental lifetime with 365-days per year, 
and assumes that air inhaled during a work shift comprises half the 
total air inhaled during a 24-hour day.

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    Given the significantly increased mortality and other acute, 
adverse health effects associated with increments of 25 g/m\3\ 
in fine particulate concentration (Table III-3), the relative risk for 
some miners, especially those already suffering respiratory problems, 
appears to be extremely high. Acute responses to dpm exposures have 
been detected in studies of stevedores, whose exposure was likely to 
have been less than one-tenth the exposure of some miners on the job.
    Both existing meta-analyses of human studies relating dpm exposure 
and lung cancer suggest that, on average, occupational exposure is 
responsible for a 30- to 40-percent increase in lung cancer risk across 
all industries studied (Lipsett and Alexeeff, 1998; Bhatia et al., 
1998). Moreover, the epidemiological studies providing the evidence of 
this increased risk involved average exposure levels estimated to be 
far below levels to which some underground miners are currently 
exposed. Specifically, the elevated risk of lung cancer observed in the 
two most extensively studied industries--trucking (including dock 
workers) and railroads--was associated with average exposure levels 
estimated to be far below levels observed in underground mines. The 
highest average concentration of dpm reported for dock workers--the 
most highly exposed occupational group within the trucking industry--is 
about 55 g/m\3\ total elemental carbon at an individual dock 
(NIOSH, 1990). This translates, on average, to no more than about 110 
g/m\3\ of dpm. Published measurements of dpm for railworkers 
have generally been less than 140 g/m\3\ (measured as 
respirable particulate matter other than cigarette smoke). The reported 
mean of 224 g/m\3\ for hostlers displayed in Figure III-5 
represents only the worst case occupational subgroup (Woskie et al., 
1988). Indeed, although MSHA views extrapolations from animal studies 
as subordinate to results obtained from human studies, it is noteworthy 
that dpm exposure levels recorded in some underground mines (Figures 
III-1 and III-2) have been well within the exposure range that produced 
tumors in rats (Nauss et al., 1995).
    The significance of the lung cancer risk to exposed underground 
miners is also supported by a recent NIOSH report (Stayner et al., 
1998), which summarizes a number of published quantitative risk 
assessments. These assessments are broadly divided into those based on 
human studies and those based on animal studies. Depending on the 
particular studies, assumptions, and methods of assessment used, 
estimates of the exact degree of risk vary widely even within each 
broad category. MSHA

[[Page 17542]]

recognizes that a conclusive assessment of the quantitative 
relationship between lung cancer risk and specific exposure levels is 
not possible at this time, given the limitations in currently available 
epidemiological data and questions about the applicability to humans of 
responses observed in rats. However, all of the very different 
approaches and methods published so far, as described in Stayner et al. 
1998, have produced results indicating that levels of dpm exposure 
measured at some underground mines present an unacceptably high risk of 
lung cancer for miners--a risk significantly greater than the risk they 
would experience without the dpm exposure.
    Quantitative risk estimates based on the human studies were 
generally higher than those based on analyses of the rat inhalation 
studies. As indicated by Tables 3 and 4 of Stayner et al. 1998, a 
working lifetime of exposure to dpm at 500 g/m\3\ yields 
estimates of excess lung cancer risk ranging from about 1 to 200 excess 
cases of lung cancer per thousand workers based on the rat inhalation 
studies and from about 50 to 800 per 1000 based on the epidemiological 
assessments. Even the lowest of these estimates indicates a risk that 
is clearly significant under the quantitative rule of thumb established 
in the benzene case. [Industrial Union vs. American Petroleum; 448 U.S. 
607, 100 S.Ct. 2844 (1980)].
    Stayner et al. 1998 concluded their report by stating:

    The risk estimates derived from these different models vary by 
approximately three orders of magnitude, and there are substantial 
uncertainties surrounding each of these approaches. Nonetheless, the 
results from applying these methods are consistent in predicting 
relatively large risks of lung cancer for miners who have long-term 
exposures to high concentrations of DEP [i.e., dpm]. This is not 
surprising given the fact that miners may be exposed to DEP [dpm] 
concentrations that are similar to those that induced lung cancer in 
rats and mice, and substantially higher than the exposure 
concentrations in the positive epidemiologic studies of other worker 
populations.

    The Agency is also aware that a number of other governmental and 
nongovernmental bodies have concluded that the risks of dpm are of 
sufficient significance that exposure should be limited:

    (1) In 1988, after a thorough review of the literature, the 
National Institute for Occupational Safety and Health (NIOSH) 
recommended that whole diesel exhaust be regarded as a potential 
occupational carcinogen and controlled to the lowest feasible 
exposure level. The document did not contain a recommended exposure 
limit.
    (2) In 1995, the American Conference of Governmental Industrial 
Hygienists placed on the Notice of Intended Changes in their 
Threshold Limit Values (TLV's) for Chemical Substances and Physical 
Agents and Biological Exposure Indices Handbook a recommended TLV of 
150 g/m\3\ for exposure to whole diesel particulate.
    (3) The Federal Republic of Germany has determined that diesel 
exhaust has proven to be carcinogenic in animals and classified it 
as an A2 in their carcinogenic classification scheme. An A2 
classification is assigned to those substances shown to be clearly 
carcinogenic only in animals but under conditions indicative of 
carcinogenic potential at the workplace. Based on that 
classification, technical exposure limits for dpm have been 
established, as described in part II of this preamble. These are the 
minimum limits thought to be feasible in Germany with current 
technology and serve as a guide for providing protective measures at 
the workplace.
    (4) The Canada Centre for Mineral and Energy Technology (CANMET) 
currently has an interim recommendation of 1000 g/m\3\ 
respirable combustible dust. The recommendation was made by an Ad 
hoc committee made up of mine operators, equipment manufacturers, 
mining inspectorates and research agencies. As discussed in part II 
of this preamble, the committee has presently established a goal of 
500 g/m\3\ as the recommended limit.
    (5) Already noted in this preamble is the U.S. Environmental 
Protection Agency's recently enacted regulation of fine particulate 
matter, in light of the significantly increased health risks 
associated with environmental exposure to such particulates. In some 
of the areas studied, fine particulate is composed primarily of dpm; 
and significant mortality and morbidity effects were also noted in 
those areas.
    (6) The California Environmental Protection Agency (CALEPA) has 
tentatively concluded that diesel exhaust appears to meet the 
definition of a toxic air contaminant (as stated in their Health and 
Safety Code, Section 39655). According to that section, a toxic air 
contaminant is an air pollutant which may cause or contribute to an 
increase in mortality or in serious illness, or which may pose a 
present or potential hazard to human health. At the present time, 
this tentative conclusion is still subject to revision.
    (7) The International Programme on Chemical Safety (IPCS), which 
is a joint venture of the World Health Organization, the 
International Labour Organisation, and the United Nations 
Environment Programme, has issued a health criteria document on 
diesel fuel and exhaust emissions (IPCS, 1996). This document states 
that the data support a conclusion that inhalation of diesel exhaust 
is of concern with respect to both neoplastic and non-neoplastic 
diseases. It also states that the particulate phase appears to have 
the greatest effect on health, and both the particle core and the 
associated organic materials have biological activity, although the 
gas-phase components cannot be disregarded.
    Based on both the epidemiological and toxicological evidence, 
the IPCS criteria document concluded that diesel exhaust is 
``probably carcinogenic to humans'' and recommended that ``in the 
occupational environment, good work practices should be encouraged, 
and adequate ventilation must be provided to prevent excessive 
exposure.'' Quantitative relationships between human lung cancer 
risk and dpm exposure were derived using a dosimetric model that 
accounted for differences between experimental animals and humans, 
lung deposition efficiency, lung particle clearance rates, lung 
surface area, ventilation, and elution rates of organic chemicals 
from the particle surface.

    As the Supreme Court pointed out in the benzene case, the 
appropriate definition of significance also depends on policy 
considerations of the Agency involved. In the case of MSHA, those 
policy considerations include special attention to the history of the 
Mine Act. That history is intertwined with the toll to the mining 
community due to silicosis and coal miners' pneumoconiosis (``black 
lung''), along with billions of dollars in Federal expenditures.
    At one of the 1995 workshops on diesel particulate cosponsored by 
MSHA, a miner noted:

    People, they get complacent with things like this. They begin to 
believe, well, the government has got so many regulations on so many 
things. If this stuff was really hurting us, they wouldn't allow it 
in our coal mines * * * (dpm Workshop; Beckley, WV, 1995).

Referring to some commenters' position that further scientific study 
was necessary before a limit on dpm exposure could be justified, 
another miner said:

    * * * if I understand the Mine Act, it requires MSHA to set the 
rules based on the best set of available evidence, not possible 
evidence * * * Is it going to take us 10 more years before we kill 
out, or are we going to do something now * * *? (dpm Workshop; 
Beckley, WV, 1995).

Concern with the risk of waiting for additional scientific evidence to 
support regulation of dpm was also expressed by another miner who 
testified:

    What are the consequences that the threshold limit values are 
too high and it's loss of human lives, sickness, whatever, compared 
to what are the consequences that the values are too low? I mean, 
you don't lose nothing if they're too low, maybe a little money. But 
* * * I got the indication that the diesel studies in rats could no 
way be compared to humans because their lungs are not the same * * * 
But * * * if we don't set the limits, if you remember probably last 
year when these reports come out how the government used human 
guinea pigs for radiation, shots, and all this, and aren't we doing 
the same thing by using coal miners as guinea pigs to set the value? 
(dpm Workshop; Beckley, WV, 1995).

[[Page 17543]]

III.3.c. Substantial Reduction of Risk by Proposed Rule
    A review of the best available evidence indicates that reducing the 
very high exposures currently existing in underground mines can 
substantially reduce health risks to miners--and that greater 
reductions in exposure would result in even lower levels of risk. 
Although there are substantial uncertainties involved in converting 24-
hour environmental exposures to 8-hour occupational exposures, Table 
III-3 suggests that reducing occupational dpm concentrations by as 
little as 75 g/m3 (corresponding to a reduction of 
25 g/m3 in 24-hour ambient atmospheric 
concentration) could lead to significant reductions in the risk of 
various adverse acute responses, ranging from respiratory irritations 
to mortality. The Agency recognizes that a conclusive, quantitative 
dose-response relationship has not been established between dpm and 
lung cancer in humans. However, the epidemiological studies relating 
dpm exposure to excess lung cancer were conducted on populations whose 
average exposure is estimated to be less than 200 g/
m3 and less than one tenth of average exposures observed in 
some underground mines. Therefore, the best available evidence 
indicates that lifetime occupational exposure at levels currently 
existing in some underground mines presents a significant excess risk 
of lung cancer.
    In the case of underground coal mines, calculations by the Agency 
indicate that the filtration required by the proposed rule would reduce 
dpm concentrations to below 200 g/m3 in most 
underground coal mines.\17\ The Agency recognizes that although health 
risks would be substantially reduced, the best available evidence 
indicates a significant risk of adverse health effects could remain. 
However, as explained in Part V of this preamble, MSHA has tentatively 
concluded that, because of both technology and cost considerations, the 
underground coal mining sector as a whole cannot feasibly reduce dpm 
concentrations further at this time.
---------------------------------------------------------------------------

    \17\ These calculations are discussed in detail in Part V, which 
reviews the extent to which the proposed rule meets the Agency's 
statutory obligation to attain the highest degree of health and 
safety protection feasible for a miner.
---------------------------------------------------------------------------

Conclusions

    MSHA has reviewed a considerable body of evidence to ascertain 
whether and to what level dpm should be controlled. It has evaluated 
the information in light of the legal requirements governing regulatory 
action under the Mine Act. Particular attention was paid to issues and 
questions raised by the mining community in response to the Agency's 
Advance Notice of Proposed Rulemaking and at workshops on dpm held in 
1995. Based on its review of the record as a whole to date, the agency 
has tentatively determined that the best available evidence warrants 
the following conclusions:

    1. The health effects associated with exposure to dpm can 
materially impair miner health or functional capacity. These 
material impairments include sensory irritations and respiratory 
symptoms; death from cardiovascular, cardiopulmonary, or respiratory 
causes; and lung cancer.
    2. At exposure levels currently observed in underground mines, 
many miners are presently at significant risk of incurring these 
material impairments over a working lifetime.
    3. The proposed rule for underground coal mines is justified 
because the reduction in dpm exposure levels that would result from 
implementation of the proposed rule would substantially reduce the 
significant health risks currently faced by underground miners 
exposed to dpm.

                Table III-2.--Studies of Acute Health Effects Using Filter Based Optical Indicators of Fine Particles in the Ambient Air                
--------------------------------------------------------------------------------------------------------------------------------------------------------
                City                                 Study years                       Indicator*                           Reference                   
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                    Acute Mortality                                                                     
--------------------------------------------------------------------------------------------------------------------------------------------------------
London..............................  1963-1972, winters.......................  BS                     Thurston et al., 1989.                          
                                      1965-1972, winters.......................  .....................  Ito et al., 1993.                               
                                      1975-1987................................  .....................  Katsouyanni et al., 1990.                       
Athens..............................  July, 1987...............................  BS                     Katsouyanni et al., 1993.                       
                                      1984-1988................................  .....................  Touloumi et al., 1994.                          
                                      1970-1979................................  .....................  Shumway et al., 1988.                           
Los Angeles.........................  1970-1979................................  KM                     Kinney and Ozkaynak, 1991.                      
Santa Clara.........................  1980-1986, winters.......................  COH                    Fairley, 1990.                                  
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                Increased Hospitalization                                                               
--------------------------------------------------------------------------------------------------------------------------------------------------------
Barcelona...........................  1985-1989................................  BS                     Sunyer et al., 1993.                            
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           Acute Change in Pulmonary Function                                                           
--------------------------------------------------------------------------------------------------------------------------------------------------------
Wageningen, Netherlands.............  .........................................  BS                     Hoek and Brunkreef, 1993.                       
Netherlands.........................  .........................................  BS                     Roemer et al., 1993.                            
--------------------------------------------------------------------------------------------------------------------------------------------------------
*BS (black smoke), KM (carbonaceous material), and COH (coefficient of haze) are optical measurements that are most directly related to elemental carbon
  concentrations, but only indirectly to mass. Site specific calibrations and/or comparisons of such optical measurements with gravimetric mass         
  measurements in the same time and city are needed to make inferences about particle mass. However, all three of these indicators preferentially       
  measure carbon particles found in the fine fraction of total airborne particulate matter. (EPA, 1996).                                                


 Table III-3.--Studies of Acute Health Effects Using Gravimetric Indicators of Fine Particles in the Ambient Air
----------------------------------------------------------------------------------------------------------------
                                                           RR( CI)/25                               
                                        Indicator             g/m3 PM          Mean PM levels (min/    
                                                                  increase                  max)        
----------------------------------------------------------------------------------------------------------------
                                                Acute Mortality                                                 
----------------------------------------------------------------------------------------------------------------
Six CitiesA                                                                                                     

[[Page 17544]]

                                                                                                                
    Portage, WI................  PM2.5..................  1.030 (0.993,1.071)....  11.2 (7.8)       
    Topeka, KS.................  PM2.5..................  1.020 (0.951,1.092)....  12.2 (7.4)       
    Boston, MA.................  PM2.5..................  1.056 (1.038,1.0711)...  15.7 (9.2)       
    St. Louis, MO..............  PM2.5..................  1.028 (1.010,1.043)....  18.7 (10.5)      
    Kingston/Knoxville, TN.....  PM2.5..................  1.035 (1.005,1.066)....  20.8 (9.6)       
    Steubenville, OH...........  PM2.5..................  1.025 (0.998,1.053)....  29.6 (21.9)      
----------------------------------------------------------------------------------------------------------------
                                            Increased Hospitalization                                           
----------------------------------------------------------------------------------------------------------------
Ontario, CANB..................  SO4=...................  1.03 (1.02,1.04).......  Min/Max = 3.1-8.2            
Ontario, CANC..................  SO4=...................  1.03 (1.02,1.04).......  Min/Max = 2.0-7.7            
                                 O3.....................  1.03 (1.02,1.05)         .............................
NYC/Buffalo, NYD...............  SO4=...................  1.05 (1.01,1.10).......  NR                           
Toronto, CAND..................  H+ (Nmol/m3)...........  1.16 (1.03,1.30)\1\....  28.8 (NR/391)                
                                 SO4=...................  1.12 (1.00,1.24).......  7.6 (NR, 48.7)               
                                 PM2.5..................  1.15 (1.02,1.78).......  18.6 (NR, 66.0)              
----------------------------------------------------------------------------------------------------------------
                                         Increased Respiratory Symptoms                                         
----------------------------------------------------------------------------------------------------------------
Southern CaliforniaF...........  SO4=...................  1.48 (1.14,1.91).......  R = 2-37                     
Six CitiesG....................  PM2.5..................  1.19 (1.01,1.42)\2\....  18.0 (7.2,37)\3\             
    (Cough)....................  PM2.5 Sulfur...........  1.23 (0.95,1.59)\2\....  2.5 (3.1,61)\3\              
                                 H+.....................  1.06 (0.87,1.29)\2\....  18.1 (0.8,5.9)\3\            
Six CitiesG....................  PM2.5..................  1.44 (1.15-1.82)\2\....  18.0 (7.2,37)\3\             
    (Lower Resp. Symp.)........  PM2.5 Sulfur...........  1.82 (1.28-2.59)\2\....  2.5 (0.8,5.9)\3\             
                                 H+.....................  1.05 (0.25-1.30)\3\....  18.1 (3.1,61)\3\             
Denver, COP....................  PM2.5..................  0.0012 (0.0043)\3\.....  0.41-73                      
    (Cough, adult asthmatics)..  SO4=...................  0.0042 (0.00035)\3\....  0.12-12                      
                                 H+.....................  0.0076 (0.0038)\3\.....  2.0-41                       
----------------------------------------------------------------------------------------------------------------
                                             Decreased Lung Function                                            
----------------------------------------------------------------------------------------------------------------
Uniontown, PAE.................  PM2.5..................  PEFR 23.1 (-0.3,36.9)    25/88 (NR/88)                
                                                           (per 25 g/m3).                              
Seattle, WAQ...................  bext...................  FEV1 42 ml (12,73).....  5/45                         
    Asthmatics.................  calibrated by PM2.5....  FVC 45 ml (20,70)                                     
----------------------------------------------------------------------------------------------------------------
(EPA, 1996)                                                                                                     
                                                                                                                
A Schwartz et al. (1996a).                                                                                      
B Burnett et al. (1994).                                                                                        
C Burnett et al. (1995).                                                                                        
D Thurston et al. (1992, 1994).                                                                                 
E Neas et al. (1995).                                                                                           
F Ostro et al. (1993).                                                                                          
G Schwartz et al. (1994).                                                                                       
Q Koenig et al. (1993).                                                                                         
P Ostro et al. (1991).                                                                                          
 Min/Max 24-h PM indicator level shown in parentheses unless otherwise noted as (S.D.), 10  
  and 90 percentile (10,90).                                                                                    
* Change per 100 nmoles/m3.                                                                                     
** Change per 20 g/m3 for PM2.5; per 5 g/m3 for PM2.5 sulfur; per 25 nmoles/m3 for H+.        
*** 50th percentile value (10,90 percentile).                                                                   
**** Coefficient and SE in parenthesis.                                                                         


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                         Table III-6.--Hypothesized Mechanisms of Particulate Toxicity a                        
----------------------------------------------------------------------------------------------------------------
                Response                                               Description                              
----------------------------------------------------------------------------------------------------------------
Increased Airflow Obstruction..........  PM exposure may aggravate existing respiratory symptoms which feature  
                                          airway obstruction. PM-induced airway narrowing or airway obstruction 
                                          from increased mucous secretion may increase abnormal ventilation/    
                                          perfusion ratios in the lung and create hypoxia. Hypoxia may lead to  
                                          cardiac arrhythmias and other cardiac electrophysiologic responses    
                                          that in turn may lead to ventricular fibrillation and ultimately      
                                          cardiac arrest. For those experiencing airflow obstruction, increased 
                                          airflow into non-obstructed areas of the lung may lead to increased   
                                          particle deposition and subsequent deleterious effects on remaining   
                                          lung tissue, further exacerbating existing disease processes. More    
                                          frequent and severe symptoms may be present or more rapid loss of     
                                          function.                                                             
Impaired Clearance.....................  PM exposure may impair clearance by promoting hypersecretion of mucus  
                                          which in turn results in plugging of airways. Alterations in clearance
                                          may also extend the time that particles or potentially harmful        
                                          biogenic aerosols reside in the tracheobronchial region of the lung.  
                                          Consequently alterations in clearance from either disturbance of the  
                                          mucociliary escalator or of macrophage function may increase          
                                          susceptibility to infection, produce an inflammatory response, or     
                                          amplify the response to increased burdens of PM. Acid aerosols impair 
                                          mucociliary clearance.                                                
Altered Host Defense...................  Responses to an immunological challenge (e.g., infection), may enhance 
                                          the subsequent response to inhalation of nonspecific material (e.g.,  
                                          PM). PM exposure may also act directly on macrophage function which   
                                          may not only affect clearance of particles but also increase          
                                          susceptibility and severity of infection by altering their            
                                          immunological function. Therefore, depression or over-activation of   
                                          the immune system, caused by exposure to PM, may be involved in the   
                                          pathogenesis of lung disease. Decreased respiratory defense may result
                                          in increased risk of mortality from pneumonia and increased morbidity 
                                          (e.g., infection).                                                    
Cardiovascular Perturbation............  Pulmonary responses to PM exposure may include hypoxia,                
                                          bronchoconstriction, apnea, impaired diffusion, and production of     
                                          inflammatory mediators that can contribute to cardiovascular          
                                          perturbation. Inhaled particles could act at the level of the         
                                          pulmonary vasculature by increasing pulmonary vascular resistance and 
                                          further increase ventilation/perfusion abnormalities and hypoxia.     
                                          Generalized hypoxia could result in pulmonary hypertension and        
                                          interstitial edema that would impose further workload on the heart. In
                                          addition, mediators released during an inflammatory response could    
                                          cause release of factors in the clotting cascade that may lead to     
                                          increased risk of thrombus formation in the vascular system. Finally, 
                                          direct stimulation by PM of respiratory receptors found throughout the
                                          respiratory tract may have direct cardiovascular effects (e.g.,       
                                          bradycardia, hypertension, arrhythmia, apnea and cardiac arrest).     
Epithelial Lining Changes..............  PM or its pathophysiological reaction products may act at the alveolar 
                                          capillary membrane by increasing the diffusion distances across the   
                                          respiratory membrane (by increasing its thickness) and causing        
                                          abnormal ventilation/perfusion ratios. Inflammation caused by PM may  
                                          increase ``leakiness'' in pulmonary capillaries leading eventually to 
                                          increased fluid transudation and possibly to interstitial edema in    
                                          susceptible individuals. PM induced changes in the surfactant layer   
                                          leading to increased surface tension would have the same effect.      
Inflammatory Response..................  Diseases which increase susceptibility to PM toxicity involve          
                                          inflammatory response (e.g., asthma, COPD, and infection). PM may     
                                          induce or enhance inflammatory responses in the lung which may lead to
                                          increased permeability, diffusion abnormality, or increased risk of   
                                          thrombus formation in vascular system. Inflammation from PM exposure  
                                          may also decrease phagocytosis by alveolar macrophages and therefore  
                                          reduce particle clearance. (See discussions above for other           
                                          inflammatory effects from PM exposure.)                               
----------------------------------------------------------------------------------------------------------------
a This table reproduces Table V-2 of the EPA staff paper. The citation in the staff paper indicates the table is
  derived from information in the EPA criteria document on particulate matter (p. 13-67 to 72; p. 11-179 to 185)
  and information in Appendix D of EPA staff paper.                                                             

IV. Discussion of Proposed Rule

    This part of the preamble explains, section-by-section, the 
provisions of the proposed rule. As appropriate, this part references 
discussions in other parts of this preamble: in particular, the 
background discussions on measurement methods and controls in part II, 
and the feasibility discussions in part V.
    The proposed rule would add a new subpart to 30 CFR part 72, 
Subpart D--Diesel Particulate Matter--Underground, and would also add 
two new sections (Secs. 72.500 and 72.510). The proposal would also 
amend existing Sec. 75.371 in 30 CFR part 75.

Sec. 72.500  Diesel Particulate Filtration Systems

Summary
    The proposed rule would require the installation and maintenance of 
high-efficiency particulate filters on the most polluting types of 
diesel equipment in underground coal mines.
    Proposed Sec. 72.500(a) would require that beginning 18 months 
after the date the rule is promulgated, any piece of permissible 
diesel-powered equipment operated in an underground coal mine must be 
equipped with a system capable of removing, on average, at least 95% of 
the mass of the dpm emitted from the engine.
    Paragraph (b) would require that beginning 30 months after the rule 
is promulgated, any nonpermissible piece of ``heavy duty'' diesel-
powered equipment operated in an underground coal mine be equipped with 
a system capable of removing, on average, at least 95% of the mass of 
the dpm emitted from the engine. ``Heavy duty'' for this purpose is 
defined by existing Sec. 75.1908(a).
    Paragraph (c) would require that any exhaust aftertreatment device 
installed to reduce the emission of dpm be maintained in accordance 
with manufacturer specifications.
    Paragraph (d) would set forth the Agency's requirements for 
determining whether a system is capable of removing, on average, at 
least 95% of diesel particulate matter by mass. It states that a 
filtration system would be tested by comparing the results of emission 
tests of an engine with and without the filtration system in place, 
using the test cycle specified in Table E-3 of 30 CFR 7.89, ``Tests to 
Determine

[[Page 17556]]

Particulate Index.'' The proposed rule would also require that the 
filtration system submitted for testing be representative of those 
actually intended for mining use.
Discussion of Alternatives
    Alternative approaches for this sector considered by the Agency are 
discussed in detail in part V of this preamble concerning feasibility. 
MSHA's decision to propose an approach requiring a technology capable 
of reducing engine emissions by a specified amount was driven by 
several considerations.
    First, the Agency is not confident that there is a measurement 
method for dpm that will provide accurate, consistent and verifiable 
results at lower concentration levels in underground coal mines. The 
available measurement methods for determining dpm concentrations in 
underground coal mines were carefully evaluated by the Agency, 
including field testing, before the Agency reached this conclusion. The 
problems are discussed in detail in part II of this preamble. The 
Agency is continuing to collect data and is consulting with NIOSH to 
resolve questions about the measurement of dpm in underground coal 
mines. If at some future time it can be established that a particular 
measurable component of dpm (e.g., the elemental carbon component of 
dpm) can be used to accurately quantify the level of dpm, the Agency 
would reevaluate the question of measurement at underground coal mines 
in that light.
    Second, filtration systems for the diesel equipment used in this 
sector are available at a reasonable cost, and if properly maintained 
can provide generally consistent, highly effective elimination of dpm 
from underground mine atmospheres.
    Finally, the Agency believes that alternative approaches that would 
require each combination of engine plus filtration system to meet a 
defined dpm emissions requirement might well provide inadequate 
protection. The statute requires the Agency to adopt the feasible 
approach that provides maximum protection.
Types of Equipment To Be Filtered
    MSHA's field data on dpm emissions in underground coal mines is 
reviewed in part III of this preamble. The data indicates that it is 
currently the permissible equipment used for face haulage that 
contributes most to high dpm levels, but heavy-duty outby equipment can 
also generate significant dpm emissions.
    Because of its statutory obligation to attain the highest degree of 
safety and health protection for miners, with feasibility a 
consideration, the Agency explored the implications of requiring all 
diesel-powered equipment to be filtered; but as discussed in part V of 
the preamble, the Agency has tentatively concluded that the high costs 
of filtering all light-duty outby equipment may not be feasible for 
this sector at this time.
    However, MSHA welcomes information about light-duty equipment which 
may be making a significant contribution to dpm emissions in particular 
mines or particular situations, and MSHA may consider including in the 
final rule filtration requirements to address any such problems. The 
Agency would also welcome comment on whether it would be feasible for 
this sector to implement a requirement that any new light-duty 
equipment added to a mine's fleet be filtered. By way of a rough cost 
estimate, if turnover is only 10% a year, for example, the cost of such 
an approach would be only about a tenth of that for filtering all 
light-duty outby. To the extent there may be technological restraints 
on filtering light-duty equipment with 95% filters, the Agency would 
welcome comment on the feasibility of requiring that 60-90% filtration 
be used on some or all of the light-duty fleet. And the agency is 
interested in comments as to whether it is likely that, in response to 
the market for high-efficiency filters on other types of equipment, 
there will soon be developed high-efficiency ceramic filters suitable 
for light-duty equipment. MSHA welcomes comment on these and other 
approaches dealing with light-duty equipment in underground coal mines, 
and will continue to study this issue in light of the record.
Timeframe for Implementation
    On permissible equipment, the filters can simply be installed 
directly on the tailpipes; accordingly, the rule would require these 
filters to be installed within 18 months. In the case of outby 
equipment, scrubbers and cooling system upgrades will need to be added 
to cool the exhaust before the filters are installed, or a dry 
technology system utilized. Accordingly, an additional year is provided 
for such equipment.
95% Effective
    The proposed rule would define effectiveness of a filtration system 
in removing dpm mass by reference to a laboratory test, using an engine 
for the test representative of those to be actually used in mining. The 
test involves: (a) measuring the average dpm mass of the emissions from 
the engine (under steady state load conditions specified in Table E-3 
of section 7.89 of title 30 of the Code of Federal Regulations) before 
the filtration system is added; (b) measuring again after the 
filtration system is added; and (c) determining the efficiency of the 
filtration system by comparing the results.
    As discussed in the background materials in part II of this 
preamble (including MSHA's toolbox, reprinted as an Appendix at the end 
of this document), there are several systems presently on the market 
capable of achieving such reductions. Current permissible engines used 
in underground coal mines are equipped with power packages that protect 
the engine against fire and explosion hazards. Power packages are 
installed with either water scrubbers (wet systems) or with heat 
exchanger technology (dry systems). For both cases, paper filters have 
been installed on these systems. The paper filter can be used on 
permissible equipment due to the limitation of the exhaust gas 
temperature to below 302 deg.F; above that temperature, the paper could 
catch fire and burn.
    Information concerning the particulate removal capability of these 
filters has been well documented in field studies and laboratory tests. 
Overall, the paper filters, when attached to a dry system and when 
tested in the laboratory on an engine dynamometer using the test cycle 
specified in the proposed rule, achieve greater than 95% diesel 
particulate removal (Gautam, dpm Workshop; Beckley, WV, 1995). Field 
studies have indicated diesel particulate removal using the paper 
filters on wet systems up to 90% using a wet permissible system (BOM RI 
9508).
    Nonpermissible equipment can utilize such paper filters if the 
exhaust is cooled through the addition of heat exchangers or other 
devices. Dry technology can also be utilized.
    As noted in part II, ceramic filters may in the future be capable 
of achieving reductions of at least 95% in dpm mass. MSHA would welcome 
information on the development of ceramic filters which can or will 
soon meet such capabilities. Ceramic filters can be used directly on 
hot emissions, and hence might be a particularly attractive alternative 
for nonpermissible equipment. But whether paper, ceramic or some other 
media, the same test would be utilized to determine particulate removal 
capabilities.
Maintenance
    The proposed rule would require that any filtration system 
installed to reduce the emission of dpm be maintained in

[[Page 17557]]

accordance with manufacturer specifications (e.g., changing disposable 
filters at the proper interval), ensuring cooling devices added to 
nonpermissible equipment are maintained.
Enforcement
    Since a concentration limit is not being established, the proposed 
rule does not require environmental monitoring of dpm concentrations by 
either operators or by MSHA specialists. Enforcement of the proposed 
underground coal requirements would be through observation by MSHA 
inspectors. Inspectors would observe whether an aftertreatment device 
that passed the effectiveness test is actually installed on each piece 
of equipment on which one is required, and whether diesel equipment was 
emitting black smoke during changes in acceleration or otherwise 
suggesting lack of required maintenance.
    It should be noted that the training and qualifications of those 
who perform maintenance of diesel-powered equipment is governed by 30 
CFR 75.1915, pursuant to MSHA's diesel equipment rule.

Sec. 72.510  Miner Health Training

    Paragraph (a) of this section requires hazard awareness training of 
underground coal miners who can reasonably be expected to be exposed to 
dpm. Paragraph (b) includes provisions on records retention, access and 
transfer.
    To ensure miners can better contribute to dpm reduction efforts, 
underground coal miners who can reasonably be expected to be exposed to 
diesel emissions must be annually trained about the hazards associated 
with that exposure and in the controls being used by the operator to 
limit dpm concentrations.
    Proposed Sec. 72.510(a) would require any underground coal miner 
``who can reasonably be expected to be exposed to diesel emissions'' to 
be trained annually in: (a) the health risks associated with dpm 
exposure; (b) the methods used in the mine to control dpm 
concentrations; (c) identification of the personnel responsible for 
maintaining those controls; and (d) actions miners must take to ensure 
the controls operate as intended.
    The purpose of the proposed requirement is to promote miner 
awareness. Exposure to diesel particulate is associated with a number 
of harmful effects as discussed in part III of this preamble, and the 
safe level is unknown. Miners who work in mines where they are exposed 
to this risk ought to be reminded of the hazard often enough to make 
them active and committed partners in implementing actions that will 
reduce that risk.
    The training need only be provided to underground coal miners who 
can reasonably be expected to be exposed at the mine. The training is 
to be provided by operators; hence, it is to be without fee to the 
miner.
    The rule places no constraints on the operator as to how to 
accomplish this training. MSHA believes that the required training can 
be provided at minimal cost and with minimal disruption. The proposal 
would not require any special qualifications for instructors, nor would 
it specify the hours of instruction.
    Instruction could take place at safety meetings before the shift 
begins, devoting one of those meetings to the topic of dpm would be a 
very easy way to convey the necessary information. Simply providing 
miners with a copy of MSHA's ``toolbox,'' and reviewing how to use it 
in an individual mine, can cover several of the training requirements. 
One-on-one discussions that cover the required topics is another 
approach that can be used.
    Operators could also choose to include a discussion on diesel 
emissions in their part 48 training, provided the plan is approved by 
MSHA. There is no existing requirement that part 48 training include a 
discussion of the hazards and control of diesel emissions. While mine 
operators are free to cover additional topics during the part 48 
training sessions, the topics that must be covered during the required 
time frame may make it impracticable to cover other matters within the 
prescribed time limits. Where the time is available in mines using 
diesel-powered equipment, operators would be free to include the dpm 
instruction in their part 48 training plans. The Agency does not 
believe special language in the proposed rule is required to permit 
this action under part 48, but welcomes comment in this regard.
    To assist mine operators with the proposed training requirement, it 
is MSHA's intent to develop an instruction outline that mine operators 
can use as a guide for training personnel. Instruction materials will 
be provided with the outline.
    The proposal does not require the mine operator to separately 
certify the completion of the dpm training, but some evidence that the 
training took place would have to be produced upon request. A serial 
log with the employee's signature is an acceptable practice.
    Proposed Sec. 72.510(b)(1) would require that any log or record 
produced signifying that the training had taken place would be retained 
at the mine site for one year.
    The records need to be where an inspector can view them during the 
course of an inspection, as the information in the records may 
determine how the inspection proceeds. But if the mine site has a fax 
machine or computer terminal, MSHA would permit the records to be 
maintained elsewhere so long as they are readily accessible. MSHA's 
approach in this regard is consistent with Office of Management and 
Budget Circular A-130.
    Under proposed paragraph (b)(2) mine operators must promptly 
provide access to the training records upon request from an authorized 
representative of the Secretary of Labor, the Secretary of Health and 
Human Services, or from an authorized representative of miners. If an 
operator ceases to do business, all training records of employees are 
expected to be transferred to any successor operator. The successor 
operator will be expected to maintain those training records for the 
required one year period unless the successor operator has undertaken 
to retrain the employees.

Amendment to Sec. 75.371 Ventilation Plan Modification

    The proposed rule would amend existing Sec. 75.371 to add one new 
requirement to an underground coal mine's ventilation control plan. The 
information is limited, but is critical to the control of dpm. The 
proposed added paragraph (qq) would require the ventilation plan to 
contain a list of the diesel-powered units used by the mine operator 
together with information about any unit's emission control or 
filtration system. Included in that information should be details 
relative to the efficiency of the system and the method(s) used to 
establish the efficiency of the system for removing dpm. Any amendments 
to a mine's ventilation plan must, of course, be accomplished pursuant 
to the requirements of 30 CFR 75.370.

General Effective Date

    The proposed rule provides that unless otherwise specified, its 
provisions take effect 60 days after the date of promulgation of the 
final rule.
    Some provisions of the proposed rule contain delayed effective 
dates that provide more time for technical assistance to mine 
operators. For example, the first filtration requirements

[[Page 17558]]

for underground coal mining equipment would be delayed for 18 months.

V. Adequacy of protection and feasibility of proposed rule

    The Mine Act requires that in promulgating a standard, the 
Secretary, based on the best available evidence, shall attain the 
highest degree of health and safety protection for the miner with 
feasibility a consideration.

Overview

    This part begins with a summary of the pertinent legal 
requirements, followed by a general profile of the economic health and 
prospects of the coal mining industry.
    The discussion then turns to the rule being proposed by the Agency 
for underground coal mines. MSHA is proposing to require that mine 
operators utilize a particular technological approach to reduce the 
levels of dpm which result from the emissions generated by diesel 
equipment engines. No specific concentration limit for dpm would be 
established for the underground coal sector. Miner hazard awareness 
training would also be required by the proposal.
    This part evaluates the proposed rule for underground coal mines to 
ascertain if, as required by the statute, it achieves the highest 
degree of protection for underground coal miners that it is feasible, 
both technologically and economically, for underground coal mine 
operators to provide.
    Regulatory alternatives to the proposed rule are also reviewed in 
this regard, for example, establishing a dpm concentration limit for 
underground coal mines, with operator flexibility on choice of control 
technologies. After review and considerable study of these 
alternatives, the Agency has tentatively concluded that compliance with 
these alternatives discussed below are not technologically or 
economically feasible for underground coal mine operators at this time. 
MSHA has also tentatively concluded that the approach being proposed is 
both economically and technologically feasible for this sector.

Pertinent Legal Requirements

    Section 101(a)(6)(A) of the
    Federal Mine Safety and Health Act of 1977 (Mine Act) states that 
MSHA's promulgation of health standards must:

    * *  * [A]dequately assure, on the basis of the best available 
evidence, that no miner will suffer material impairment of health or 
functional capacity even if such miner has regular exposure to the 
hazards dealt with by such standard for the period of his working 
life.

    The Mine Act also specifies that the Secretary of Labor 
(Secretary), in promulgating mandatory standards pertaining to toxic 
materials or harmful physical agents, base such standards upon:

    * * * [R]esearch, demonstrations, experiments, and such other 
information as may be appropriate. In addition to the attainment of 
the highest degree of health and safety protection for the miner, 
other considerations shall be the latest available scientific data 
in the field, the feasibility of the standards, and experience 
gained under this and other health and safety laws. Whenever 
practicable, the mandatory health or safety standard promulgated 
shall be expressed in terms of objective criteria and of the 
performance desired. [Section 101(a)(6)(A)].

    Thus, the Mine Act requires that the Secretary, in promulgating a 
standard, based on the best available evidence, attain the highest 
degree of health and safety protection for the miner with feasibility a 
consideration.
    In relation to feasibility, the legislative history of the Mine Act 
states that:

    * * * This section further provides that ``other 
considerations'' in the setting of health standards are ``the latest 
available scientific data in the field, the feasibility of the 
standards, and experience gained under this and other health and 
safety laws.'' While feasibility of the standard may be taken into 
consideration with respect to engineering controls, this factor 
should have a substantially less significant role. Thus, the 
Secretary may appropriately consider the state of the engineering 
art in industry at the time the standard is promulgated. However, as 
the circuit courts of appeal have recognized, occupational safety 
and health statutes should be viewed as ``technology-forcing'' 
legislation, and a proposed health standard should not be rejected 
as infeasible when the necessary technology looms in today's 
horizon. AFL-CIO v. Brennan, 530 F.2d 109 (1975); Society of the 
Plastics Industry v. OSHA, 509 F.2d 1301, cert. denied, 427 U.S. 992 
(1975).
    Similarly, information on the economic impact of a health 
standard which is provided to the Secretary of Labor at a hearing or 
during the public comment period, may be given weight by the 
Secretary. In adopting the language of [this section], the Committee 
wishes to emphasize that it rejects the view that cost benefit 
ratios alone may be the basis for depriving miners of the health 
protection which the law was intended to insure. S. Rep. No. 95-181, 
95th Cong., 1st Sess. 21 (1977).

    Court decisions have clarified the meaning of feasibility. The 
Supreme Court, in American Textile Manufacturers' Institute v. Donovan 
(OSHA Cotton Dust), 452 U.S. 490, 101 S.Ct. 2478 (1981), defined the 
word ``feasible'' as ``capable of being done, executed, or effected.'' 
The Court stated that a standard would not be considered economically 
feasible if an entire industry's competitive structure was threatened. 
According to the Court, the appropriate inquiry into a standard's 
economic feasibility is whether the standard is capable of being 
achieved.
    Courts do not expect hard and precise predictions from agencies 
regarding feasibility. Congress intended for the ``arbitrary and 
capricious standard'' to be applied in judicial review of MSHA 
rulemaking (S.Rep. No. 95-181, at 21.) Under this standard, MSHA need 
only base its predictions on reasonable inferences drawn from the 
existing facts. MSHA is required to produce reasonable assessment of 
the likely range of costs that a new standard will have on an industry. 
The agency must also show that a reasonable probability exists that the 
typical firm in an industry will be able to develop and install 
controls that will meet the standard. See, Citizens to Preserve Overton 
Park v. Volpe, 401 U.S. 402, 91 S.Ct. 814 (1971); Baltimore Gas & 
Electric Co. v. NRDC, 462 U.S. 87 103 S.Ct. 2246, (1983); Motor Vehicle 
Manufacturers Assn. v. State Farm Mutual Automobile Insurance Co., 463 
U.S. 29, 103 S.Ct. 2856 (1983); International Ladies' Garment Workers' 
Union v. Donovan, 722 F.2d 795, 232 U.S. App. D.C. 309 (1983), cert. 
denied, 469 U.S. 820 (1984); Bowen v. American Hospital Assn., 476 U.S. 
610, 106 S.Ct. 2101 (1986).
    In developing a health standard, MSHA must also show that modern 
technology has at least conceived some industrial strategies or devices 
that are likely to be capable of meeting the standard, and which 
industry is generally capable of adopting. United Steelworkers of 
America v. Marshall, 647 F.2d 1189, 1272 (1980). If only the most 
technologically advanced companies in an industry are capable of 
meeting the standard, then that would be sufficient demonstration of 
feasibility (this would be true even if only some of the operations met 
the standard for some of the time). American Iron and Steel Institute 
v. OSHA, 577 F.2d 825 (3d Cir. 1978); see also, Industrial Union 
Department, AFL-CIO v. Hodgson, 499 F.2d 467 (1974).

Industry Profile

    The industry profile provides background information describing the 
structure and economic characteristics of the coal mining industry. 
This information was considered by MSHA as appropriate in reaching 
tentative conclusions about the economic feasibility of various 
regulatory alternatives. MSHA welcomes the

[[Page 17559]]

submission of additional economic information about the coal mining 
industry, and about underground coal mining in particular, that will 
help it make final determinations about the economic feasibility of the 
proposed rule.
    This profile provides data on the number of mines, their size, the 
number of employees in each segment, as well as selected market 
characteristics. This profile does not provide information about the 
use of diesel engines in the industry; information in that regard was 
provided in the first section of part II of this preamble.
    Although this particular rulemaking does not apply to the surface 
coal sector, information about surface coal mines is provided here in 
order to give context for the discussions on underground mining.

Overall Mining Industry

    MSHA divides the mining industry into two major segments based on 
commodity, the coal mining industry and the metal and nonmetal (M&NM) 
mining industry. These major industry segments are further divided 
based on type of operation (underground mines, surface mines, and 
independent mills, plants, shops, and yards). MSHA maintains its own 
data on mine type, size, and employment. MSHA also collects data on the 
number of contractors and contractor employees by major industry 
segment.
    With respect to mine size, the mining community has traditionally 
regarded a ``small'' mine as being one with less than 20 miners. This 
has been a useful dividing line for a number of purposes, including 
rulemaking, because the nature of the safety and health issues facing 
such entities tends to be different than for larger mines. MSHA 
recognizes, however, that the definition of ``small entity'' used by 
the Small Business Administration in the mining sector is different--
500 employees or less. In order to accommodate both perspectives when 
analyzing the impact of this proposed rule on the mining industry, MSHA 
has prepared its Preliminary Regulatory Economic Analysis (PREA) in 
such a way as to focus on the special impacts of both size categories--
those with less than 20 employees, and those with less than 500 
employees (basically all mines). In this profile, however, the term 
``small mine'' refers to one with less than 20 miners.
    Table V-1 presents the number of small and large coal mines and the 
corresponding number of miners, excluding contractors, by major 
industry segment and mine type. Table V-2 presents MSHA data on the 
numbers of independent contractors and the corresponding numbers of 
employees by major industry segment and the size of the operation based 
on employment.

 Table V-1.--Distribution of Operations and Employment (Excluding Contractors) by Mine Type, Commodity, and Size
----------------------------------------------------------------------------------------------------------------
                                         Small (<20 EES)        Large (20              Total         
                                   --------------------------           EES)           -------------------------
             Mine type                                       --------------------------                         
                                     Number of    Number of    Number of    Number of    Number of    Number of 
                                       mines        miners       mines        miners       mines        miners  
----------------------------------------------------------------------------------------------------------------
Coal:                                                                                                           
    Underground...................          426        4,371          545       46,206          971       50,577
    Surface.......................          776        4,705          370       28,314        1,146       33,019
    Shp/Yrd/Mll/Plnt..............          399        2,538          128        5,010          527        7,548
    Office workers................  ...........          657  ...........        4,500  ...........        5,157
                                   -----------------------------------------------------------------------------
        Total coal mines..........        1,601       12,271        1,043       84,030        2,644      96,301 
----------------------------------------------------------------------------------------------------------------
Source: U.S. Department of Labor, Mine Safety and Health Administration, Office of Standards, Regulations, and  
  Variances, based on preliminary 1996 MIS data (quarter 1-quarter 4, 1996). MSHA estimates assume that office  
  workers are distributed between large and small operations the same as non-office workers.                    


 Table V-2.--Distribution of Contractors (Contr) and Contractor Employees (Miners) by Major Industry Segment and
                                                Size of Operation                                               
----------------------------------------------------------------------------------------------------------------
                                           Small (<20)          Large (20)             Total         
            Contractors            -----------------------------------------------------------------------------
                                     No. contr    No. miners   No. contr    No. miners   No. contr    No. miners
----------------------------------------------------------------------------------------------------------------
Coal:                                                                                                           
    Other than office.............        3,606       13,954          297       13,792        3,903       27,746
    Office workers................  ...........        1,034  ...........        1,022  ...........        2,056
                                   -----------------------------------------------------------------------------
        Total coal................        3,606       14,988          297       14,814        3,903      29,802 
----------------------------------------------------------------------------------------------------------------
Source: U.S. Department of Labor, Mine Safety and Health Administration, Office of Standards, Regulations, and  
  Variances, based on preliminary 1996 MIS data (quarter 1--quarter 4, 1996). MSHA estimates assume that office 
  workers are distributed between large and small contractors the same as non-office workers.                   

    MSHA separates the U.S. coal mining industry into two major 
commodity groups, bituminous and anthracite. The bituminous group 
includes the mining of subbituminous coal and lignite. Bituminous 
operations represent over 93% of the coal mining operations, employ 
over 98% of the coal miners, and account for over 99% of the coal 
production. About 60% of the bituminous operations are small; whereas, 
about 90% of the anthracite operations are small.
    Underground bituminous mines are more mechanized than anthracite 
mines in that most, if not all, underground anthracite mines still 
hand-load. Over 70% of the underground bituminous mines use continuous 
mining and longwall mining methods. The remaining use drills, cutters, 
and scoops. As noted in the first section of part II of this preamble, 
although underground coal mines generally use electrical powered 
equipment, a growing number of underground coal

[[Page 17560]]

mines use diesel-powered equipment. (See Table II-1).
    Surface mining methods include drilling, blasting, and hauling and 
are similar for all commodity types. Most surface mines use front-end 
loaders, bulldozers, shovels, or trucks for coal haulage. A few still 
use rail haulage. Although some coal may be crushed to facilitate 
cleaning or mixing, coal processing usually involves cleaning, sizing, 
and grading. As noted in section 1 of part II of this preamble, diesel 
power is used extensively in surface mines for all these operations.
    Preliminary data for 1996 (MSHA/DMIS, Coal, CM-441, 1996) indicate 
that there are about 2,650 active coal mines of which 1,600 are small 
mines (about 60% of the total) and 1,050 are large mines (about 40% of 
the total). These data indicate employment at coal mines to be about 
96,300 of which 12,275 (13% of the total) worked at small mines and 
84,025 (87% of the total) worked at large mines. (Ibid.). MSHA 
estimates that the average employment is 8 miners at small coal mines 
and 81 miners at large coal mines.
    The U.S. Department of Energy, Energy Information Administration, 
reported that the U.S. coal industry produced a record 1.06 billion 
tons of coal in 1996 with a value of approximately $20 billion. Of the 
several different types of coal commodities, bituminous and 
subbituminous coal account for 91% of all coal production (about 940 
million tons). The remainder of U.S. coal production is lignite (86 
million tons) and anthracite (4 million tons). Although anthracite 
offers superior burning qualities, it contributes only a small and 
diminishing share of total coal production. Less than 0.4% of U.S. coal 
production in 1996 was anthracite (DOE/EIA, 1997, p. 209).
    Mines east of the Mississippi account for about 53% of the current 
U.S. coal production. For the period 1949 through 1996, coal production 
east of the Mississippi River fluctuated from a low of 395 million tons 
in 1954 to 630 million tons in 1990. During this same period, however, 
coal production west of the Mississippi increased each year from a low 
of 20 million tons in 1959 to a record 505 million tons in 1996. 
(Ibid.). The growth in western coal is due in part to environmental 
concerns that led to increased demand for low-sulfur coal, which is 
concentrated in the West. In addition, surface mining which is more 
prevalent in the West has increased in productivity due to the 
technological developments of oversized power shovels and draglines.
    The 1996 estimate of the average value of coal at the point of 
production is about $19 per ton for bituminous coal and lignite. 
(Ibid., at 221). MSHA chose to use $19 per ton as the value for all 
coal production because anthracite contributes such a small amount to 
total production that the higher value per ton of anthracite does not 
greatly impact the total value. The total value of coal production in 
1996 was approximately $20 billion of which about $0.9 billion was 
produced by small mines and $19.1 billion was produced by large mines.
    Coal is used for several purposes including the production of 
electricity. The predominant consumer of U.S. coal is the electric 
utility industry which used 898 million tons of coal in 1996 or 84% of 
the coal produced. Other coal consumers include coke plants (31 million 
tons), residential and commercial consumption (6 million tons), and 
miscellaneous other industrial uses (71 million tons). This last 
category includes the use of coal products in the manufacturing of 
other products, such as plastics, dyes, drugs, explosives, solvents, 
refrigerants, and fertilizers. (Ibid., at 205).
    The U.S. coal industry enjoys a fairly constant domestic demand due 
to electric utility usage of coal. MSHA does not expect a substantial 
change in coal demand by utilities in the near future because of the 
high conversion costs of changing a fuel source in the electric utility 
industry. Energy experts predict that coal will continue to be the 
dominant fuel source of choice for power plants built in the future.

Adequacy of Miner Protection Provided by the Proposed Rule for 
Underground Coal Mines

    In evaluating the protection provided by the proposed rule, it 
should be remembered that MSHA has measured dpm concentrations in 
production areas and haulageways of underground coal mines as high as 
3,650DPM g/m3 with a mean concentration 
of 644DPM g/m3. See Table III-1 and 
Figure III-1 in part III of this preamble. As discussed in detail in 
part III of the preamble, these concentrations place underground coal 
miners at significant risk of material impairment of their health, and 
the evidence supports the proposition that reducing the exposure 
reduces the risk. Therefore, to address this risk, the Agency is 
proposing to develop requirements which reduce these concentrations as 
much as is both technologically and economically feasible for this 
sector as a whole.
    The proposed rule would require the installation of high-efficiency 
filters on all permissible and heavy-duty outby diesel-powered 
equipment in underground coal mines. Operators would have 18 months to 
install these filters on permissible diesel equipment, and an 
additional 12 months to do the same for heavy-duty nonpermissible 
diesel equipment (as defined by 30 CFR 75.1908(a)).
    As an example of what filtration can achieve, take the case of a 
single-section mine with three Ramcars (94hp, indirect injection) and a 
section airflow of 45,000 cfm. MSHA measured concentrations of dpm in 
this mine at 610DPM g/m3. Of this 
amount, 25DPM g/m3 was coming from the 
intake to the section, and the remaining 585DPM g/
m3 was emitted by the engines. Reducing the engine emissions 
by 95% through the use of aftertreatment filters would reduce the dpm 
emitted to 29DPM g/m3. With an intake 
amount of 25DPM g/m3, the ambient 
concentration would be about 54DPM g/m3. 
Similarly, dramatic results can be achieved in almost any situation if 
the filters achieve in practice the predicted reduction in particulate 
matter; and as the coal fleet turns over, in accordance with the 
existing diesel equipment rule, to the exclusive use of approved 
engines, the combination of that change and the use of 95% filters 
should keep ambient dpm concentrations at much lower levels than at 
present.
    There are some reasons for caution. MSHA's experience with the 
high-efficiency filters is limited. While they are capable in 
laboratory tests of achieving a 95% reduction in dpm mass, and this has 
been confirmed in some field tests, the Agency has not tested them 
under a variety of actual mining conditions. As discussed in part IV, 
determination of the efficiency of any filter media is greatly 
dependent upon the test used to determine efficiency or collection 
capacity. Therefore, actual performance may be different in the field 
due to individual mining conditions (e.g., ventilation changes), 
changes of the equipment due to maintenance, and the type of engine 
used.
    Two factors that come into play are the ventilation rate and the 
ambient dpm intake into the section. If ventilation levels drop below 
the nameplate requirements for gaseous emissions, or if many pieces of 
equipment throughout the mine create a high ambient level of dpm, 
implementation of the proposed rule may not bring concentrations down 
as effectively as suggested in the prior example. On the other hand, if 
the ventilation rate is maintained at a higher level, the engine 
emissions would be better diluted and the ambient

[[Page 17561]]

concentration could offset any decrease in filter efficiency under 
actual mining conditions.
    Table V-3 summarizes information from a series of simulations 
designed to illustrate these variables. The simulations were performed 
using the tool discussed in the Appendix to this part (MSHA's 
``Estimator'') for a mine section with a 94 horsepower engine, with a 
0.3 gm/hp-hr dpm emission rate and a nameplate airflow, 5500 cfm. The 
engine was operated during an eight hour shift. The estimator was used 
to calculate the values. The same results would be obtained for 
multiple pieces of equipment provided that the nameplate airflow is 
additive for each piece of equipment.

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    In Table V-3, the intake dpm (second column) increases after every 
fourth row. Within each group of four rows, the ventilation (first 
column) increases from one row to the next. The last 3 columns display 
the ambient dpm concentration with a particular filter efficiency. The 
first four rows represent a situation where there is no intake dpm. If 
the mine is ventilated with four times the nameplate airflow (row 4), 
the ambient dpm concentration using a filter operating at 95% (last 
column) is reduced to 38DPM g/m\3\. If the filter 
in this situation only works in practice at 85% efficiency in removing 
dpm, the ambient dpm concentration is only reduced to 113DPM 
g/m\3\. And if the ventilation is reduced to the nameplate 
airflow (first column) and the filter is only 85% efficient, the 
ambient dpm climbs to 452DPM g/m\3\. The last four 
rows display the parallel situation but with an ambient intake 
concentration to the section of 75DPM g/m\3\. In 
this situation, depending on ventilation and filter effectiveness, the 
ambient dpm concentration ranges from 113DPM to 
527DPM g/m\3\.
    In the example discussed above--a single section mine with three 94 
hp Ramcars--the airflow of 45,000 cfm represents three times the 
current nameplate requirements. If this airflow were reduced to the 
current nameplate requirements, the ambient dpm would have been 
1620DPM g/m\3\, and would have been reduced by 95% 
effective filters to 105DPM g/m\3\.
    It should be remembered that the proposed rule does not require the 
filtration of light-duty equipment; hence, mines with significant light 
duty equipment will have this exhaust as an ``intake'' in such 
calculations. Also, many underground coal mines may use more than the 
nameplate ventilation to lower methane concentrations at the face.
    Based on its experience as to the general effects of mining 
conditions on the expected efficiency of equipment, and on ventilation 
rates, MSHA believes that the proposed rule for this sector will 
substantially reduce the concentrations of dpm to which underground 
coal miners are exposed. But in order to ensure that the maximum 
protection feasible is being provided, the Agency has considered some 
alternatives.
(1) Establish a Concentration Limit in Coal
    Under such an approach, a diesel particulate concentration limit 
would be phased in and operators could select any combination of 
controls that keep ambient dpm concentrations below the limit.
    After careful analysis, the agency has determined that it is not 
yet ready to conclude that it is technologically feasible to establish 
a dpm concentration limit for underground coal mines. The problem, as 
discussed in part IV, is that significant questions remain as to 
whether there is a sampling and analytical system that can provide 
consistent and accurate measurements of dpm in areas of underground 
coal mines where there is a heavy concentration of coal dust. The 
Agency is continuing to work on the technical issues involved, and 
should it determine that these technological problems have been 
resolved, it will notify the mining community and proceed accordingly.
(2) Alternatives to 95% Filters on Permissible and Heavy-duty Equipment
    In part IV of this preamble, the agency outlines some approaches 
that might be considered as alternatives to the requirement in the 
proposal that all permissible and heavy-duty equipment must have a 95% 
aftertreatment filter installed and properly maintained.
    The first alternative would in essence provide some credit in 
filter selection to those operators who use engines that significantly 
reduce ambient mine dpm concentration. Under this approach, the engine 
and aftertreatment filter would be bench tested as a unit; and if the 
emissions from the unit are below a certain level (e.g., 
120DPM g/m\3\, using 50% of the name plate 
ventilation, the emissions limit applicable under Pennsylvania law), 
the package would be acceptable without regard to the efficiency of 
just the filter component. The second option would also provide credit 
in filter selection for extra ventilation used in an underground coal 
mine. If the bench test of the combined engine and filter package was 
conducted at the name plate ventilation, a mine's use of more than that 
level of ventilation would be factored into the calculation of what 
package would be acceptable.
    One practical effect of these approaches would be to permit some 
operators to save the costs of installing heat exchangers or other 
exhaust-cooling devices on nonpermissible heavy-duty equipment. Such 
devices are necessary in order for this equipment to be fitted with 
paper filters--and at the moment, these are the only filters on the 
market capable of providing 95% and more filtration capability. (It is 
not out of the realm of possibility that once a market develops for 95% 
filters, makers of ceramic filters will develop models that reach this 
level of efficiency--hence obviating the need for the heat exchangers 
or other exhaust cooling technology on the outby equipment; information 
or comment on this point would be welcome).
    It is not clear to the Agency, however, that it would be 
appropriate, under the statute, to take such an approach. With the 
proper equipment to cool the exhaust, a 95% paper filter can be 
installed on any piece of heavy-duty equipment in coal mines--and of 
course directly on any permissible piece of equipment. And, as 
indicated herein, the Agency is tentatively concluding that such an 
approach is economically feasible as well. Installing a 95% efficient 
filter on an engine lowers the dpm concentration in the mine more than 
would installing a less efficient filter. Hence for engines which, with 
a 95% filter, can reduce emissions below 120DPM g/
m\3\ (or whatever emissions limit is set), the alternative approach 
would seem to provide miners with less protection.
    In some cases, however, use of such an alternative approach could 
actually result in a reduction of mine dpm--by forcing out certain 
older, high-polluting engines. It is not clear to MSHA that 95% 
filtration of the engines used on the majority of permissible machines 
in underground coal mines can meet an emissions limit of 
120DPM g/m\3\ using MSHA's name plate ventilation. 
The engines involved just produce too much diesel particulate. 
Accordingly, adopting a rule with an emissions limit of 
120DPM g/m\3\ would in effect require these 
existing permissible engines to be replaced with cleaner engines. Of 
course, it follows that such a rule would be more costly than the one 
proposed, because it would require the 95% filters plus the replacement 
of these engines.
    The second alternative (emissions limit plus credit for 
ventilation) appears to be less protective in all cases. To provide 
mines who need extra ventilation for other reasons (e.g., to keep 
methane in check) with a credit for this fact in determining the 
required filter efficiency would not reduce dpm concentrations as much 
as simply requiring a 95% filter.
    The Agency welcomes comments on these approaches and information 
that will help it assess them in light of the requirements of the Mine 
Act.
    MSHA recognizes that a specification standard does not allow for 
the use of future alternative technologies that might provide the same 
or enhanced protection at the same or lower cost. MSHA welcomes comment 
as to whether and how the proposed rule can be modified to enhance its 
flexibility in this regard.

[[Page 17564]]

(3) Accelerate the Time-Frame for Installation of Filters on 
Underground Coal Equipment
    This approach would not change the level of protection ultimately 
provided to miners when the proposed rule is fully implemented. But it 
would ensure miners are protected more quickly, and therefore, needs to 
be considered.
    Under the first phase of the proposed rule, 95% effective filters 
are required on all permissible equipment after 18 months. This 
equipment constitutes only about 19% of the 2,950 pieces of diesel-
powered equipment estimated to be present in underground coal mines; 
but because of where and how it is used (production areas), it produces 
extensive amounts of particulate matter.
    Cutting the 18 month time-frame does not appear to be practicable 
for the industry. Eighteen months to obtain and install a relatively 
new technology is a reasonable time. Time is needed for operators to 
familiarize themselves with this technology. Also, mine personnel have 
to be trained in how to maintain control devices in working order.
    The second stage of the proposal requires the installation of 95% 
filters on heavy-duty nonpermissible equipment after 30 months--a year 
after the permissible equipment must be filtered. Again, speeding up 
this timeframe may not be practicable. If paper filters indeed have to 
be used, this equipment would need to be first equipped with water 
scrubbers, heat exchangers or other systems to cool the exhaust before 
the filtration can be installed, or dry technology installed. Providing 
another year also allows additional time for possible perfection of 
ceramic filtration, with the potential cost savings associated with 
that approach, or other improvements in filtration that could better 
protect miners. MSHA believes that providing the industry an extra year 
to phase in controls for the heavy-duty outby equipment is reasonable.
(4) Require High Efficiency Filters on Any Diesel Equipment in 
Underground Coal Mines
    The proposed rule does not apply to approximately 65% of the 
equipment in the fleet--light-duty outby. While this equipment does not 
pollute as heavily as the equipment being covered by MSHA's proposal, 
it does contribute to the total particulate concentration in 
underground coal mines. And, as noted above, the Agency at this time 
lacks confidence in a measurement system that can detect localized 
concentrations even in outby areas. Accordingly, MSHA has considered 
the possibility of requiring filtration for such equipment.
    The Commonwealth of Pennsylvania has recently adopted legislation 
for universal high-efficiency filtration based on an agreement in the 
mining community of that state. The Pennsylvania law requires the use 
of 95% efficiency filters on all diesel-powered equipment introduced in 
the future into underground coal mines in that state (in addition to 
other requirements). Since, however, the State did not allow the use of 
diesel-powered equipment in underground coal mines prior to enactment 
of this legislation, in practice the new law achieves a goal of 
universal filtration.
    The Agency decided to consider what it would take to bring the rest 
of the industry up to the standard established under the Pennsylvania 
agreement of universal high-efficiency filtration. MSHA has calculated 
that such a requirement would cost the underground coal industry an 
additional $17 million a year. This would increase by 70% the costs per 
operator for the underground coal mining industry. This added cost 
raises questions because for those mines with permissible and heavy-
duty equipment, filtering that equipment can achieve significant 
reductions in existing dpm concentrations. Given the economic profile 
of the coal sector, MSHA has tentatively concluded that such a 
requirement may not be feasible for the underground coal sector at this 
time.
    MSHA welcomes information about light-duty equipment which may be 
making a particular significant contribution to dpm emissions in 
particular mines or particular situations, and which is likely to 
continue to do so after full implementation of the approval 
requirements of the diesel equipment rule. MSHA will consider including 
in the final rule filtration requirements that may be necessary to 
address any such identified problem. The Agency would also welcome 
comment on whether it would be feasible for this sector to implement a 
requirement that any new light-duty equipment added to a mine's fleet 
be filtered. By way of a rough cost estimate, if turnover is only 10% a 
year, for example, the cost of such an approach would be only about a 
tenth of that for filtering all light-duty outby. To the extent there 
may be technological restraints on filtering light-duty equipment with 
95% filters, the Agency would welcome comment on the feasibility of 
requiring that 60-90% filtration be used on some or all of the light-
duty fleet. And the agency is interested in comments as to whether it 
is likely that, in response to the market for high-efficiency filters 
on other types of equipment, there will soon develop high-efficiency 
ceramic filters suitable for light-duty equipment. MSHA welcomes 
comment on these and other approaches to dealing with light-duty 
equipment in underground coal mines, and will continue to study this 
issue in light of the record.
(5) Requiring Certain Engines to Meet Defined Particulate Emission 
Standards
    As discussed in part II of this preamble, the Mine Safety and 
Health Advisory Committee on Standards and Regulations for Diesel-
Powered Equipment in Underground Coal Mines recommended the 
establishment of a particulate index (PI), and MSHA did so in its 
diesel equipment rule. Under that rule, the PI establishes the amount 
of air required to dilute the dpm produced by an engine (as determined 
during its approval test under subpart E of part 7) to 1000 g/
m\3\. In the preamble of the diesel equipment rule, MSHA explicitly 
deferred until this rulemaking the question of whether to require 
engines used in mining environments to meet a particular PI. It noted 
that mine operators and machine manufacturers would find it useful to 
consider the engine PI in selecting and purchasing decisions.
    Since the publication of the PI is a relatively new requirement, 
the agency does not believe it has enough information at this time to 
evaluate the feasibility of a requirement that certain engines must 
meet a particular PI to be used in underground coal mines. Presumably, 
coupling such a requirement with a requirement for a 95% filter would 
provide more protection to miners than requiring only the 95% filter; 
but without information about what is technologically available for any 
type of engines, the Agency would have difficulty in selecting the PI 
to require.
    MSHA solicits comments on whether it should limit the PI or the PI 
per horsepower of engines used in underground coal mines.
    Feasibility of proposed rule for underground coal mining sector. 
The Agency has carefully considered both the technological and economic 
feasibility of the proposed rule for the underground coal mining sector 
as a whole.
    The technology exists to implement the proposed rule's requirements 
for 95% filtration of permissible and ``heavy-duty'' equipment. As 
widely recognized now by the mining community (see, e.g., MSHA's 
``Toolbox''), there are disposable paper

[[Page 17565]]

filters available for permissible coal mine equipment equipped with 
water scrubbers that meet the proposed rule's requirements for 
efficiency. In addition, a dry technology (known as the DST) 
of very high efficiency is also available for this type of equipment. 
Based on its long experience with diesel-powered outby equipment, the 
Agency is also confident that the disposable paper filters can be used 
on this equipment too--once the equipment is equipped with water 
scrubbers, heat exchangers, or other systems to first cool the exhaust 
enough so the paper filters will not burn. The dry technology used on 
permissible equipment can also work on the outby equipment. MSHA 
understands that filtration systems that meet the efficiency 
requirements in the proposed rule, and which are specifically designed 
to fit on outby equipment are under development; additional information 
in this regard would be welcome.
    The total costs for the proposed rule for underground coal mines 
are about $10 million per year beyond the $10.3 million per year costs 
this sector is already absorbing to implement the requirements of 
MSHA's recent diesel equipment rule. The costs per dieselized mine are 
expected to be about $58,000 a year (the diesel equipment rule costs 
per dieselized mine are about $59,000 a year). The proposed rule 
provides adequate time for equipment purchase, installation, and 
training. MSHA has calculated that the costs of the proposed rule 
amount to less than one-half of one percent of the revenues of the 
underground coal mining sector at this time. (The methodology for this 
calculation is discussed in part V of the Agency's PREA). After 
reviewing the economic profile of that sector, and taking into account 
the cost of implementing the related diesel equipment rule, MSHA has 
concluded that the proposed rule is economically feasible for this 
sector as a whole.

Conclusion: Underground Coal Mines

    Based on the best evidence available to it at this time, the Agency 
has concluded that the proposed rule for the underground coal sector 
meets the statutory requirement that it attain the highest degree of 
health and safety protection for the miners in that sector, with 
feasibility a consideration.

Appendix to Part V: Diesel Emission Control Estimator

    As noted in the text of this part, MSHA has developed a model that 
can help it estimate the impact on dpm concentrations of various 
control variables. The model also permits the estimation of actual dpm 
concentrations based upon equipment specifications. This model, or 
simulator, is called the ``Diesel Emission Control Estimator'' (or the 
``Estimator'').
    The model is capable only of simulating conditions in production or 
other confined areas of an underground mine. Air flow distribution 
makes modeling of larger areas more complex. The Estimator can be used 
in any type of underground mine.
    While the calculations involved in this model can be done by hand, 
use of a computer spreadsheet system facilitates prompt comparison of 
the results of alternative combinations of controls. Changing a 
particular entry instantly changes all dependent outputs. Accordingly, 
MSHA developed the Estimator as a spreadsheet format. It can be used in 
any standard spreadsheet program.
    A paper discussing this model has been presented and published as 
an SME Preprint (98-146) in March 1998 at the Society for Mining and 
Exploration Annual Meeting. It was demonstrated at a workshop at the 
Sixth International Mine Ventilation Congress, Pittsburgh, Pa., in June 
1997. The Agency is making available to the mining community the 
software and instructions necessary to enable it to perform simulations 
for specific mining situations. Copies may be obtained by contacting: 
Dust Division, MSHA, Pittsburgh Safety and Health Technology Center, 
Cochrans Mill Road, P.O. Box 18233, Pittsburgh, Pa. 15236. The Agency 
welcomes comments on the proposed rule that include information 
obtained by using the Estimator. The Agency also welcomes comments on 
the model itself, and suggestions for improvements.

Determining the Current DPM Concentration

    The Estimator was designed to provide an indication of what dpm 
concentration will remain in a production area once a particular 
combination of controls is applied. Its baseline is the current dpm 
concentration, which of course reflects actual equipment and work 
practices.
    If the actual ambient dpm concentration is known, this information 
provides the best baseline for determining the outcome from applying 
control technologies. Any method that can reliably determine ambient 
dpm concentrations under the conditions involved can be utilized. A 
description of various methods available to the mining community is 
described in part II of the preamble.
    If the exact dpm concentration is not known, estimates can be 
obtained in several ways. One way is to take a percentage of the 
respirable dust concentration in the area. Studies have shown that dpm 
can range from 50-90% of the respirable dust concentration, depending 
on the specific operation, the size distribution of the dust and the 
level of controls in place. Another method is simply to choose a value 
of 644 for an underground coal mine, or 830 for an underground metal or 
nonmetal mine. These values correspond to the average mean 
concentration which MSHA sampling to date has measured in such 
underground mines. Or, depending upon mine conditions, some other value 
from the range of mean mine concentrations displayed in part III of 
this preamble might be an appropriate baseline--for example, an average 
similar to that of mine sections like the one for which controls are 
required.
    Moreover, the Estimator has been designed to automatically compute 
another estimate of current ambient dpm concentration, and to provide 
outputs using this estimate even when the actual ambient dpm 
concentration is available and used in the model. This is done by using 
emissions data for the engines involved--specific manufacturer 
emissions data where available, or an average using the known range of 
emissions for each type of engine being used.
    As with other estimates of current ambient dpm concentration, using 
engine data to derive this baseline measure does not produce the same 
results as actual dpm measurements. The Agency's experience is that the 
use of published engine emissions rates provides a good estimate of dpm 
exposures when the engines involved are used under heavy duty cycle 
conditions; for light duty cycle equipment, the published emission 
rates will generally overestimate the ambient particulate exposures. 
Also, such an approach assumes that the average ambient concentration 
derived is representative of the workplace where miners actually work 
or travel.

Columns

    An example of a full spreadsheet from the Estimator is displayed as 
Figure V-5. The example here involves the application of various 
controls in an underground metal and nonmetal mine. As illustrated in 
the discussion in this part, the Estimator can be used equally well to 
ascertain what happens to dpm concentrations in an underground coal 
mine when the high-efficiency filters required by the proposed rule are 
used

[[Page 17566]]

under various ventilation and section dpm intake conditions. 
Underground coal mine operators who are interested in ascertaining what 
impact it might have on dpm concentrations in their mines if the 
proposed rule permitted the use of alternative controls, or required 
the use of additional controls (e.g. filters on light duty equipment), 
can use the Estimator for this purpose as well.

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    A full spreadsheet from the Estimator has two columns, labeled A 
and B. Column A displays information on computations where the baseline 
is the measured ambient dpm concentration, or whose baselines are 
estimated as a percentage of respirable dust or by using the mean 
concentration for the sector. Column B displays information on 
computations in which the baseline itself was derived from engine 
emission information entered into the Estimator.
    Sections. The Estimator spreadsheet is divided into 6 sections. 
Sections 1 through 4 contain information on the baseline situation in 
the mine section. Section 5 contains information on proposed new 
controls, and Section 6 displays the dpm concentration expected to 
remain after the application of those new controls. Table V-4 
summarizes the information in each section of the Estimator.

              Table V-4.--Information Needed for or Provided by Each Section of the Estimator Model             
----------------------------------------------------------------------------------------------------------------
      Spreadsheet section                   Input/output                           Mine information             
----------------------------------------------------------------------------------------------------------------
SECTION 1.....................  INPUT..............................  MEASURED DP LEVEL, g/m3.          
SECTION 2.....................  INPUT..............................  ENGINE EMISSIONS, gm/hp-hr.                
                                                                     ENGINE HORSEPOWER, hp.                     
                                                                     OPERATION TIMES, hr.                       
                                                                     SHIFT DURATION, hr.                        
SECTION 3.....................  INPUT..............................  SECTION AIRFLOW, cfm.                      
                                                                     INTAKE DP LEVEL, g/m3.            
SECTION 4.....................  OUTPUT.............................  CURRENT DP LEVEL, g/m3.           
SECTION 5.....................  INPUT..............................  DP CONTROLS:                               
                                                                     AIRFLOW, cfm.                              
                                                                     OXID. CAT. CONVERTER, percent.             
                                                                     ENGINE EMISSIONS, gm/hp-hr.                
                                                                     AFTER-FILTERS, percent.                    
                                                                     CABS, percent.                             
SECTION 6.....................  OUTPUT.............................  PROJECTED DP LEVEL, g/m3.         
----------------------------------------------------------------------------------------------------------------

    Section 1. This is the place to enter data on baseline dpm 
concentrations if obtained by actual measurement or estimate based on 
respirable dust concentration or mean concentration in the mining 
sector. Measurements should be entered in terms of whole diesel 
particulate matter for consistency with engine information. Information 
need not be entered in this section, in which case only engine-emission 
derived estimates will be produced by the Estimator (in Column B).
    Sections 2 and 3. Section 2 is the place to enter data about the 
existing engines and engine use, and section 3 is the place to enter 
data about current ventilation practices. This information is used in 
two ways. First, the Estimator uses this information to derive an 
estimated baseline dpm concentration (for column B). Second, by 
comparing this information with that in section 5 on proposed controls 
that would change engines, engine use, or ventilation practices, the 
Estimator calculates the improvement in dpm that would result.
    The first information entered in section 2 is the dpm emission rate 
(in gm/hp-hr) for each vehicle. The Estimator in its current form 
provides room to enter appropriate identification information for up to 
four vehicles. However, when multiple engines of the same type are 
used, the spreadsheet can be simplified and the number of entries 
conserved by combining the horsepower of these engines. For example, 
two 97 hp, 0.5 gm/hp-hr engines can be entered as a single 194 hp, 0.5 
gm/hp-hr engine. However, if the estimate is to involve

[[Page 17569]]

the use of different controls for each engine, the data for each engine 
must be entered separately. In order to account for the duty cycle, the 
engine operating time for each piece of equipment must then be entered 
in section 2, along with the length of the shift.
    The last item in section 2, the ``average total shift particulate 
output'' in grams, is calculated by the Estimator based on the measured 
concentration entered in section 1 (for column A, or the engine 
emission rates for column B), the intake concentration, engine 
horsepower, engine operating time, and airflow. For column A, the 
average total shift diesel particulate output is calculated from the 
formula:

E(a) = (DPM(m) -I) x (Q(I) / 35200) / [Sum ( Hp(I) x To(I))]

Where:

E(a) = Average engine output, gm/hp-hr
DPM(m) = Measured concentration of diesel particulate, g/
m3
Q(I) = Initial section ventilation, cfm
I = Intake concentration, g/m3
Hp(I) = Individual engine Horsepower, hp
To(I) = Individual engine operating times, hours

    For column B, the average total shift diesel particulate output is 
calculated from the formula:

E(a) = [Sum (E(I) x Hp(I) x To(I))] / [Sum (Hp(I))] / Ts

Where:

E(a) = Average engine output, gm/hp-hr
E(I) = Individual engine emission rates, gm/hp-hr
Hp(I) = Individual engine Horsepower, hp
To(I) = Individual engine operating times, hours
Ts = Shift length, hours

The ``average total shift particulate'' provides useful information in 
determining what types of controls would be most useful. If the average 
output is less than 0.3, controls such as cabs and afterfilters would 
have a large impact on dpm. If the average output is greater than 0.3, 
new engines would have a large impact on dpm.
    There are two data elements concerning existing ventilation in the 
section that must be entered into section 3 of the Estimator: the full 
shift intake dpm concentration, the section air quantity. The former 
can be measured, or an estimate can be used. Based upon MSHA 
measurements to date, an estimate of between 25 and 100 micrograms of 
dpm per cubic meter would account for the dpm contribution coming into 
the section from the rest of the mine.
    The last item in section 3, the airflow per horsepower, is 
calculated by the Estimator from the information entered on these two 
items in sections 2 and 3, as an indication of ventilation system 
performance. If the value is less than 125 cfm/hp, consideration should 
be given to increasing the airflow. If the value is greater than 200 
cfm/hp, primary consideration would focus on controls other than 
increased airflow.
    Section 4. Section 4 only displays information in Column B. Using 
the individual engine emissions, horsepower, operating time, section 
airflow, intake DPM and shift length, the Estimator calculates a 
presumed dpm concentration. The presumed dpm concentration is 
calculated by the formula:

DPM(a) = {[[Sum (E(I) x Hp(I) x To(I))] x 35,300 / Q(I)]+I} x [Ts / 8]

Where:

35,300 is a metric conversion factor
DPM(a) = Shift weighted average concentration of diesel particulate, 
g/m3.
E(I) = Individual engine emission rates, gm/hp-hr
Hp(I) = Individual engine Horsepower, hp
To(I) = Operating time hours
Ts = Shift length, hours
Q(I) = Initial section ventilation, cfm
I = Intake concentration, g/m3.

    Section 5. Information about any combination of controls likely to 
be used to reduce dpm emissions in underground mines--changes in 
airflow, the addition of oxygen catalytic converters, the use of an 
engine that has a lower dpm emission rate, and the addition of either a 
cab or aftertreatment filter--is entered into Section 5. Information is 
entered here, however, only if it involves a change to the baseline 
conditions entered into Sections 2 and 3. Entries are cumulative.
    The first possible control would be to increase the system air 
quantity. The minimum airflow should be either the summation of the 
Particulate Index (PI) for all heavy duty engines in the area of the 
mine, or 200 cfm/hp. The spreadsheet displays the ratio between the air 
quantity in section 5 and that in section 3, and the airflow per 
horsepower.
    The second possible control would be to add an oxidation catalytic 
converter to one or more engines if not initially present. When such 
converters are used, a dpm reduction of up to 20 percent can be 
obtained (as noted in MSHA's toolbox, reprinted as an Appendix to the 
end of this document. The third possible control would be to change one 
or more engines to newer models to reduce emissions. As noted in part 
II of this preamble, clean engine technology has emissions as low as 
0.1 and 0.2 gm/hp-hr.
    Finally, each piece of equipment could be equipped with either a 
cab and an aftertreatment filter. But since MSHA considers it unlikely 
an operator would use both controls, the Estimator is designed to 
assume that no more than one of these two possible controls would be 
used on a particular engine. Ceramic aftertreatment filters that can 
reduce emissions by 65-80% are currently on the market; MSHA is 
soliciting information about the potential for future improvements in 
ceramic filtration efficiency. Paper filters can remove up to 95% or 
more of dpm, but these can only be used on equipment whose exhaust is 
appropriately cooled to avoid igniting the paper (i.e., permissible 
coal equipment, or other equipment equipped with a water scrubber or 
other cooling device). Air conditioned cabs can reduce the exposure of 
the equipment operator by anywhere from 50-80%. (See part II, section 
6, for information on filters and cabs). But while the Estimator will 
produce an estimate of the full shift dpm concentration that includes 
the effects of using such cabs, it should be remembered that such an 
estimate is only directly relevant to equipment operators. Thus, cabs 
are a viable control for sections where the miners are all equipment 
operators, but they will not impact the dpm concentrations to which 
other miners are exposed.
    Section 6. The Estimator displays in this section an estimated full 
shift dpm concentration. If a measured baseline dpm concentration was 
entered in section 1, this information will be displayed in column A. 
Column B displays an estimate based on the engine emissions data.
    Here is how the computations are performed.
    The effect of control application is calculated in Section 6, 
Column A from the following formula:

DPM(c) = {Sum [(To(I) / Ts) x 1000 x [(E(a) / 60) x Hp(I) x (35300 /
Q(I)) x (Q(I) / Q(f)) x (1-R(o)) x (1-R(f)) x (1-R(e))]} + I

Where:

DPM(c) = Diesel particulate concentration after control application/ 
g/m3,
E(a) = Average engine emission rate, gm/hp-hr,
Hp(I) = Individual engine Horsepower, hp.
To(I) = Operating time hours,
I = Intake DPM concentration, g/m3,
Q(I) = Initial section ventilation, cfm,

[[Page 17570]]

Q(f) = Final section ventilation, cfm,
R(o) = Efficiency of oxidation catalytic converter, decimal
R(f) = Efficiency of after filters or cab, decimal,
R(e) = Reduction for new engine technology, decimal, and
R(e) = (Ei--Ef) / Ei

Where:

R(e) = Reduction for new engine technology, decimal,
E(i) = Initial engine emission rates, gm/hp-hr,
E(f) = New engine emission rates, gm/hp-hr,

    The effect of control application is calculated in Section 6, 
Column B from the following formula:

DPM(c) = {Sum[(E(I) x Hp(I) x To(I)) x (35,300 / Q(I)) x (1-R(o)) x (1-
R(f)) x (1-R(e))] x [Q(I) / Q(f)]}+I

Where:

DPM(c) = Diesel particulate concentration after control application/ 
g/m3,
E(I) = Individual engine emission rates, gm/hp-hr,
Hp(I) = Individual engine Horsepower, hp,
To(I) = Operating time hours,
I = Intake DPM concentration, g/m3,
Q(I) = Initial section ventilation, cfm,
Q(f ) = Final section ventilation, cfm,
R(o) = Efficiency of oxidation catalytic converter, decimal,
R(f) = Efficiency of after filters or cab, decimal,
R(e) = Reduction for new engine technology, decimal, and
R(e) = (Ei--Ef) / Ei

Where:

R(e) = Reduction for new engine technology, decimal,
(i) = Initial engine emission rates, gm/hp-hr,
E(f) = New engine emission rates, gm/hp-hr.

VI. Impact Analyses

    This part of the preamble reviews several impact analyses which the 
Agency is required to provide in connection with proposed rulemaking. 
The full text of these analyses can be found in the Agency's PREA.

(A) Costs and Benefits: Executive Order 12866

    In accordance with Executive Order 12866, MSHA has prepared a 
Preliminary Regulatory Economic Analysis (PREA) of the estimated costs 
and benefits associated with the proposed rule for the underground coal 
sector.
    The key conclusions of the PREA are summarized, together with cost 
tables, in part I of this preamble (see Question and Answer 5). The 
complete PREA is part of the record of this rulemaking, and is 
available from MSHA.
    The Agency considers this rulemaking ``significant'' under section 
3(f) of Executive Order 12866, and has so designated the rule in its 
semiannual regulatory agenda (RIN 1219-AA74). However, based upon the 
PREA, MSHA has determined that the proposed rule does not constitute an 
``economically significant'' regulatory action pursuant to section 
3(f)(1) of Executive Order 12866.

(B) Regulatory Flexibility Certification

Introduction
    Pursuant to the Regulatory Flexibility Act of 1980, MSHA has 
analyzed the impact of this rule upon small businesses. Further, MSHA 
has made a preliminary determination with respect to whether or not it 
can certify that this proposal will not have a significant economic 
impact on a substantial number of small entities. Under the Small 
Business Regulatory Enforcement Fairness Act (SBREFA) amendments to the 
RFA, MSHA must include in the proposal a factual basis for this 
certification. If the proposed rule does have a significant economic 
impact on a substantial number of small entities, then the Agency must 
develop an initial regulatory flexibility analysis.
    Based upon MSHA's analysis, the Agency has determined that the 
proposed rule will not have a significant economic impact on a 
substantial number of small underground coal mine operators, and has so 
certified to the Small Business Administration (SBA). MSHA specifically 
solicits comments on the cost data and assumptions concerning the 
regulatory flexibility certification statement for underground coal 
mine operators.
    To facilitate public participation in the rulemaking process, MSHA 
will mail a copy of the proposed rule and this preamble to every 
underground coal mine operator. In addition, the regulatory flexibility 
certification, including its factual basis, is reprinted here.
Definition of Small Mine
    Under SBREFA, in analyzing the impact of a proposed rule on small 
entities, MSHA must use the SBA definition for a small entity or, after 
consultation with the SBA Office of Advocacy, establish an alternative 
definition for the mining industry by publishing that definition in the 
Federal Register for notice and comment. MSHA has not taken such an 
action, and hence is required to use the SBA definition.
    The SBA defines a small mining entity as an establishment with 500 
employees or less (13 CFR 121.201). MSHA's use of the 500 or less 
employees includes all employees (miners and office workers). Almost 
all mines (including underground coal mines) fall into this category 
and hence, can be viewed as sharing the special regulatory concerns 
which the RFA was designed to address. That is why MSHA has, for 
example, committed to providing to all underground coal mine operators 
a copy of a compliance guide explaining provisions of this rule.
    The Agency is concerned, however, that looking only at the impacts 
of the proposed rule on all the mines in this sector does not provide 
the Agency with a very complete picture on which to make decisions. 
Traditionally, the Agency has also looked at the impacts of its 
proposed rules on what the mining community refers to as ``small 
mines''--those with fewer than 20 miners. The way these small mines 
perform mining operations is generally recognized as being different 
from the way other mines operate, which has led to special attention by 
the Agency and the mining community.
    This analysis complies with the legal requirements of the RFA for 
an analysis of the impacts on ``small entities'' while continuing 
MSHA's traditional look at ``small mines''. In concluding that it can 
certify that the proposed rule has no significant economic impact on a 
substantial number of small entities in the underground coal sector, 
the Agency determined that this is the case both for underground coal 
mines with 500 or fewer miners and for underground coal mines with 20 
or fewer miners.
The Underground Coal Mines: Factual Basis for Certification
    The Agency's analysis of impacts on ``small entities'' and ``small 
mines'' begins with a ``screening'' analysis. The screening compares 
the estimated compliance costs of the proposed rule for small mine 
operators in each affected sector to the estimated revenues for that 
sector. When estimated compliance costs are less than 1 percent of 
estimated revenues, (at both of the size categories considered), the 
Agency believes it is generally appropriate to conclude that there is 
no significant economic impact on a substantial number of small 
entities. When estimated compliance costs approach or exceed 1 percent 
of revenues, it tends to indicate that further analysis may be 
warranted. The Agency welcomes comment on its approach in this regard.

[[Page 17571]]

Derivation of Costs and Revenues for Screening Analysis
    In the case of this proposed rule, because the compliance costs 
must be absorbed by underground coal mines only, the agency focused its 
attention exclusively on the relationship between costs and revenues 
for underground coal mines, rather than looking at the coal sector as a 
whole.
    The compliance costs for this analysis are presented earlier along 
with an explanation of how they were derived. In deriving compliance 
costs, there were areas where different assumptions had to be made for 
small mines in order to account for the fact that the mining operations 
of small mines are not the same as those of large mines. For example, 
assumptions used to derive compliance costs concerning: the number of 
production shifts per mine, and the number of days the mine operates on 
an annual basis were different depending on whether the mine was 
classified as either a large or small mining operation. In determining 
revenues for underground coal mines, MSHA multiplied underground coal 
production data (in tons) for underground coal mines in specific size 
categories (reported to MSHA quarterly) by $19 per ton (the average 
rounded price per ton). The Agency welcomes comment on alternative data 
sources that can help it more accurately estimate revenues for the 
final rule.
Results of Screening Analysis
    With respect to underground coal mine operators, as can be seen in 
Table VI-1, when the definition of a small mine operator is fewer than 
20 employees, then estimated average per year costs of the proposed 
rule are $8,000 per small mine operator and estimated costs as a 
percentage of revenues are 0.04 percent for small mine operators. When 
the definition of a small mine operator is fewer than 500 employees, 
then estimated average per year costs of the proposed rule are $57,650 
per small mine operator and estimated costs as a percentage of revenues 
are 0.13 percent for small mine operators.
    In both cases, the impact of the proposed costs is less than 1 
percent of revenues, well below the level suggesting that the proposed 
rule might have a significant impact on a substantial number of small 
entities. Accordingly, MSHA has certified that there is no such impact 
for small entities that mine underground coal.

                                       Table VI-1.--Underground Coal Mines                                      
----------------------------------------------------------------------------------------------------------------
                                                               Estimated    Estimated    Estimated              
                                                                 costs       revenue      cost per    Costs as %
                                                                (thous.)    (million)       mine      of revenue
----------------------------------------------------------------------------------------------------------------
Small <20...................................................         $120         $287       $8,000         0.04
Small <500..................................................        9,624        7,359       57,650         0.13
----------------------------------------------------------------------------------------------------------------

    As required under the law, MSHA is complying with its obligation to 
consult with the Chief Counsel for Advocacy on this proposed rule, and 
on the Agency's certification of no significant economic impact in 
underground coal. Consistent with agency practice, notes of any 
meetings with the Chief Counsel's office on this rule, or any written 
communications, will be placed in the rulemaking record. The Agency 
will continue to consult with the Chief Counsel's office as the 
rulemaking process proceeds.

(C) Unfunded Mandates Reform Act of 1995

    MSHA has determined that, for purposes of section 202 of the 
Unfunded Mandates Reform Act of 1995, this proposed rule does not 
include any Federal mandate that may result in increased expenditures 
by State, local, or tribal governments in the aggregate of more than 
$100 million, or increased expenditures by the private sector of more 
than $100 million. Moreover, the Agency has determined that for 
purposes of section 203 of that Act, this proposed rule does not 
significantly or uniquely affect small governments.
    The Unfunded Mandates Reform Act was enacted in 1995. While much of 
the Act is designed to assist the Congress in determining whether its 
actions will impose costly new mandates on State, local, and tribal 
governments, the Act also includes requirements to assist Federal 
agencies to make this same determination with respect to regulatory 
actions.
    Based on the analysis in the Agency's preliminary Regulatory 
Economic Statement, the compliance costs of this proposed rule for the 
underground coal mining industry are about $10 million per year. 
Accordingly, there is no need for further analysis under section 202 of 
the Unfunded Mandates Reform Act.
    MSHA has concluded that small governmental entities are not 
significantly or uniquely impacted by the proposed regulation. The 
proposed rule affects only underground coal mines, and MSHA is not 
aware of any state, local or tribal government ownership interest in 
underground coal mines. MSHA seeks comments of any state, local, and 
tribal government which believes that they may be affected by this 
rulemaking.

(D) Paperwork Reduction Act of 1995 (PRA)

    This proposed rule contains information collections which are 
subject to review by the Office of Management and Budget (OMB) under 
the Paperwork Reduction Act of 1995 (PRA95). Tables VI-1 and VI-2 show 
the estimated annual reporting burden hours associated with each 
proposed information collection requirement. These burden hour 
estimates are an approximation of the average time expected to be 
necessary for a collection of information, and are based on the 
information currently available to MSHA. Included in the estimates are 
the time for reviewing instructions, gathering and maintaining the data 
needed, and completing and reviewing the collection of information.
    MSHA invites comments on: (1) Whether any proposed collection of 
information presented here (and further detailed in the Agency's PREA) 
is necessary for proper performance of MSHA's functions, including 
whether the information will have practical utility; (2) the accuracy 
of MSHA's estimate of the burden of the proposed collection of 
information, including the validity of the methodology and assumptions 
used; (3) ways to enhance the quality, utility, and clarity of 
information to be collected; and (4) ways to minimize the burden of the 
collection of information on respondents, including through the use of 
automated collection techniques, when appropriate, and other forms of 
information technology.
Submission
    The Agency has submitted a copy of this proposed rule to OMB for 
its review and approval of these information

[[Page 17572]]

collections. Interested persons are requested to send comments 
regarding this information collection, including suggestions for 
reducing this burden, to the Office of Information and Regulatory 
Affairs, OMB New Executive Office Bldg., 725 17th St. NW., Rm. 10235, 
Washington, DC 20503, Attn: Desk Officer for MSHA. Submit written 
comments on the information collection not later than April 7, 1998.
    The Agency's complete paperwork submission is contained in the 
PREA, and includes the estimated costs and assumptions for each 
proposed paperwork requirement (these costs are also included in the 
Agency's cost and benefit analyses for the proposed rule). A copy of 
the PREA is available from the Agency. These paperwork requirements 
have been submitted to the Office of Management and Budget for review 
under section 3504(h) of the Paperwork Reduction Act of 1995. 
Respondents are not required to respond to any collection of 
information unless it displays a current valid OMB control number.
Description of Respondents
    Those required to provide the information are mine operators and 
diesel equipment manufacturers.
Description
    The proposed rule would result in additional burden hours 
associated with: the additional training that will be required for 
diesel equipment operators under Sec. 75.1915; the additional changes 
required to be included in the mine ventilation plans under 
Secs. 75.370 and 75.371; the new training requirements in proposed 
Sec. 72.510; and the additional burden hours for equipment 
manufacturers under part 36 in connection with the approval of 
filtration systems that would be required by this rule.
    Tables VI-2 and VI-3 summarize the burden hours for mine operators 
and manufacturers by section.

            Table VI-2.--Underground Coal Mines Burden Hours            
------------------------------------------------------------------------
                    Detail                      Large    Small    Total 
------------------------------------------------------------------------
75.370.......................................       93        9      102
75.371.......................................      158        8      166
75.1915......................................       12        1       13
72.510.......................................      347        5      352
                                              --------------------------
    Total....................................      610       23      633
------------------------------------------------------------------------


        Table VI-3.--Diesel Equipment Manufacturers Burden Hours        
------------------------------------------------------------------------
                             Detail                               Total 
------------------------------------------------------------------------
Part 36........................................................      520
                                                                --------
    Total......................................................      520
------------------------------------------------------------------------

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Ulfvarson, Ulf, and Rolf Alexandersson, ``Reduction in Adverse 
Effect on Pulmonary Function After Exposure to Filtered Diesel 
Exhaust,'' American Journal of Industrial Medicine, 17:341-347, 
1990.
Ulfvarson, Ulf, et al., ``Effects of Exposure to Vehicle Exhaust on 
Health,'' Scandinavian Journal of Work, Environment and Health, 
13:505-512, 1987.
United Kingdom, ``Health Effects of Particles. The Government's 
Preliminary Response to the Reports of the Committee on the Medical 
Effects of Air Pollutants and the Expert Panel on Air Quality 
Standards,'' Department of the Environment, the Department of Health 
and the Department of Transport, November 1995.
United States Code, Title 5, Government Organization and Employees, 
Section 605, Avoidance of Duplicative or Unnecessary Analyses.
United States Code, Title 29, Labor, Section 654(a)(1) and 655(c), 
Duties of Employers and Employees.
United States Department of Energy, Energy Information 
Administration, DOE/EIA-0384(96), Annual Energy Review 1996, pp. 205 
and 209, July 1997.
United States Department of the Interior, Bureau of Mines, 
``Evaluation of a Disposable Diesel Exhaust Filter for Permissible 
Mining Machines,'' Report of Investigations No. 9508, 1994.
United States Department of the Interior, Bureau of Mines, 
``Evaluation of Catalyzed Diesel Particulate Filters Used in an 
Underground Metal Mine, Report of Investigations No. 9478, 1993.
United States Department of the Interior, Bureau of Mines, ``In-
Service Performance of Catalyzed Ceramic Wall-Flow Diesel 
Particulate Filters,'' in Diesels in Underground Coal Mines: 
Measurement and Control of Particulate Emissions, Information 
Circular No. 9324, 1992.
United States Department of the Interior, Bureau of Mines, ``Diesel 
in Underground Mines: Measurement and Control of Particulate 
Emissions,'' Information Circular No. 9324, 1992.
United States Department of the Interior, Bureau of Mines, public 
comment submitted in response to MSHA's January 1992 ANPRM, 87-OFED-
1, July 7, 1992.
United States Department of the Interior, Bureau of Mines, ``Fuel 
Additive and Engine Operation Effects on Diesel Soot Emissions,'' 
Information Circular No. 9238, 1990.
United States Department of the Interior, Bureau of Mines, 
Relationship of Underground Diesel Engine Maintenance to Emissions, 
Vols. I and II, contract H-0292009, 1979.
United States Department of the Interior, United States Geological 
Survey, USDI/USGS, Mineral Commodity Summaries 1997, February 1997.
United Steelworkers of America, AFL-CIO-CLC v. F. Ray Marshall, 647 
F.2d 1189 (1980).
Valberg, Peter A. and Ann Y. Watson, ``Analysis of Diesel-Exhaust 
Unit-Risk Estimates Derived from Animal Bioassays,'' Regulatory 
Toxicology and Pharmacology, 24:30-44, 1996.
Vuk, Carl, Martin Jones, and John Johnson, The Measurement and 
Analysis of the Physical Character of Diesel Particulate Emissions, 
Society of Automotive Engineers, Automotive Engineering Congress and 
Exposition, Detroit, Michigan, February 23-27, 1976.
Wade, J.F., and L.S. Newman, ``Diesel Asthma. Reactive Airways 
Disease Following Overexposure to Locomotive Exhaust,'' Journal of 
Occupational Medicine, 35(2):149-154, February 1993.
Wallace, William, et al., ``Mutagenicity of Diesel Exhaust Particles 
and Oil Shale Particles Dispersed in Lecithin Surfactant,'' Journal 
of Toxicology and Environmental Health, 21:163-171, 1987.
Waller, R.E., ``Trends in Lung Cancer in London in Relation to 
Exposure to Diesel Fumes,'' Environment International, 5:479-483, 
1981.
Watson, Ann Y. and Gareth M. Green, ``Noncancer Effects of Diesel 
Emissions: Animal Studies,'' in Diesel Exhaust: A Critical Analysis 
of Emissions, Exposure, and Health Effects, pp. 141-164, Health 
Effects Institute, Cambridge, MA 1995.
Watts, Winthrop, F., ``Assessment of Occupational Exposure to Diesel 
Emissions,'' in Diesel Exhaust: A Critical Analysis of Emissions, 
Exposure, and Health Effects, pp. 109-123, Health Effects Institute, 
Cambridge, MA., 1995.
Watts, Winthrop, F., et al., ``Diesel Exhaust Aerosol Levels in 
Underground Coal Mines,'' U.S. Bureau of Mines, Information Circular 
No. 9324, pp. 31-39, 1992.
Watts, Winthrop, F., et al., ``Control of Diesel Particulate Matter 
in Underground Coal Mines,'' United States Department of Interior, 
Bureau of Mines, Report of Investigations No. 9276, 1989.
Waxweiler, Richard, et al., ``Mortality of Potash Workers,'' Journal 
of Occupational Medicine, Vol. 15, No. 6, June 1973.
Weitzman, Sigmund A. and Leo Gordon, ``Inflammation and Cancer: Role 
of Phagocyte-Generated Oxidants in Carcinogenesis,'' Blood, 
76(4):655-663, August 15, 1990.
West Virginia House Bill No. 2890, May 5, 1997.
White House Press Release, Office of the Vice President, ``Vice 
President Gore Announces Joint Industry-Government Research Plan to 
Produce the World's Cleanest Diesels,'' July 23, 1997.

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Widdicombe, J. et al., ``Nerve Receptors of the Upper Airway,'' in 
Matthew, O.P. and G. Sant' Ambrogio, eds., Respiratory Function of 
the Upper Airway, pp. 193-231, 1988.
Williams, Roger, et al., ``Associations of Cancer Site and Type with 
Occupation and Industry From the Third National Cancer Survey 
Interview,'' Journal of the National Cancer Institute, Vol. 59, No. 
4, October 1977.
Wong, O., ``Mortality Among Members of a Heavy Construction 
Equipment Operators Union with Potential Exposure to Diesel Exhaust 
Emissions,'' British Journal of Industrial Medicine, 42:435-448, 
1985.
Woskie, Susan R., et al., ``Estimation of the Diesel Exhaust 
Exposures of Railroad Workers: I. Current Exposures,'' American 
Journal of Industrial Medicine, 13:381-394, 1988.
Woskie, Susan R., et al., ``Estimation of the Diesel Exhaust 
Exposures of Railroad Workers: II. National and Historical 
Exposures,'' American Journal of Industrial Medicine, 13:395-404, 
1988.
Zaebst, D.D., et al., ``Quantitative Determination of Trucking 
Industry Workers' Exposures to Diesel Exhaust Particles,'' American 
Industrial Hygiene Association Journal, (52), December 1991.

Supplementary References

    Below is a list of supplemental references that MSHA reviewed 
and considered in the development of the proposed rule. These 
documents are not specifically cited in the preamble discussion, but 
are applicable to MSHA's findings:

Bice, D.E., et al., ``Effects of Inhaled Diesel Exhaust on Immune 
Responses after Lung Immunization,'' Fundamental and Applied 
Toxicology, 5:1075-1086, 1985.
Diaz-Sanchez, D., et al., ``Enhanced Nasal Cytokine Production in 
Human Beings After In Vivo Challenge with Diesel Exhaust 
Particles,'' Journal of Allergy Clinical Immunology, 98:114-123, 
1996.
Diaz-Sanchez, D., et al., ``Diesel Exhaust Particles Induce Local 
IgE Production in Vivo and Alter the Pattern of IgE Messenger RNA 
Isoforms,'' Journal of Clinical Investigation, 94(4):1417-1425, 
1994.
Enya, Takeji, et al., ``3 Nitrobenzanthrone, a Powerful Bacterial 
Mutagen and Suspected Human Carcinogen Found in Diesel Exhaust and 
Airborne Particulates,'' Environmental Science and Technology, 
31:2772-2776, 1997.
Fischer, Torkel, and Bolli Bjarnason, ``Sensitizing and Irritant 
Properties of 3 Environmental Classes of Diesel Oil and Their 
Indicator Dyes,'' Contact Dermatitis, 34:309-315, 1996.
Frew, A.J., and S.S. Salvi, ``Diesel Exhaust Particles and 
Respiratory Allergy,'' Clinical and Experimental Allergy, 27:237-
239, 1997.
Fujimaki, Hidekazu, et al., ``Intranasal Instillation of Diesel 
Exhaust Particles and Antigen in Mice Modulated Cytokine Productions 
in Cervical Lymph Node Cells,'' International Archives of Allergy 
and Immunology, 108:268-273, 1995.
Fujimaki, Hidekazu, et al., ``IL-4 Production in Mediastinal Lymph 
Node Cells in Mice Intratracheally Instilled with Diesel Exhaust 
Particles and Antigen,'' Toxicology, 92:261-268, 1994.
Fujimaki, Hidekazu, et al., ``Inhalation of Diesel Exhaust Enhances 
Antigen-Specific IgE Antibody Production in Mice,'' Toxicology, 
116:227-233, 1997.
Ikeda, Masahiko, et al., ``Impairment of Endothelium-Dependent 
Relaxation by Diesel Exhaust Particles in Rat Thoracic Aorta,'' 
Japanese Journal of Pharmacology, 68:183-189, 1995.
Lovik, Martinus, et al., ``Diesel Exhaust Particles and Carbon Black 
Have Adjuvant Activity on the Local Lymph Node Response and Systemic 
IgE Production to Ovalbumin,'' Toxicology, 121:165-178, 1997.
Muranaka, Masaharu, et al., ``Adjuvant Activity of Diesel-Exhaust 
Particles for the Production of IgE Antibody in Mice,'' J Allergy 
Clin Immunology, 77:616-623, 1986.
Takafuji, Shigeru, et al., ``Diesel-Exhaust Particulates Inoculated 
by the Intranasal Route Have an Adjuvant Activity for IgE Production 
in Mice,'' J Allergy Clin Immunol, 79:639-645, 1987.
Takenaka, Hiroshi, et al., ``Enhanced Human IgE Production Results 
from Exposure to the Aromatic Hydrocarbons from Diesel Exhaust: 
Direct Effects on B-Cell IgE Production,'' J Allergy Clin Immunol, 
95-103-115, 1995.
Terada, Nobushisa, et al., ``Diesel Exhaust Particulates Enhance 
Eosinophil Adhesion to Nasal Epithelial Cells and Cause 
Degranulation,'' International Archives of Allergy and Immunology, 
114:167-174, 1997.
Tsien, Albert, et al., ``The Organic Component of Diesel Exhaust 
Particles and Phenanthrene, a Major Polyaromatic Hydrocarbon 
Constituent, Enhances IgE Production by IgE-Secreting EBV-
Transformed Human B Cells in Vitro,'' Toxicology and Applied 
Pharmacology, 142:256-263, 1997.
Yang, Hui-Min, et al., ``Effects of Diesel Exhaust Particles on the 
Release of Interleukin-1 and Tumor Necrosis Factor-Alpha from Rat 
Alveolar Macrophages,'' Experimental Lung Research, 23:269-284, 
1997.

List of Subjects

30 CFR Part 72

    Coal, Health standards, Mine safety and health, Underground mines, 
Diesel particulate matter.

30 CFR Part 75

    Mine safety and health, Underground coal mines, Ventilation.

    Dated: March 31, 1998.
J. Davitt McAteer,
Assistant Secretary for Mine Safety and Health.

    It is proposed to amend Chapter I of Title 30 of the Code of 
Federal Regulations as follows:

PART 72--[AMENDED]

    1. The authority citation for Part 72 continues to read as follows:

    Authority: 30 U.S.C. 811, 813(h), 957, 961.

    2. Part 72 is amended by adding Subpart D to read as follows:

Subpart D--Diesel Particulate Matter--Underground

72.500  Diesel particulate filtration systems.
72.510  Miner health training.

Subpart D--Diesel Particulate Matter--Underground


Sec. 72.500  Diesel particulate filtration systems.

    (a) As of [insert the date 18 months after the date of publication 
of the final rule], any piece of permissible diesel-powered equipment 
operated in an underground coal mine shall be equipped with a system 
capable of removing, on average, at least 95% of diesel particulate 
matter by mass.
    (b) As of [insert the date 30 months after the date of publication 
of the final rule], any nonpermissible piece of heavy duty diesel-
powered equipment (as defined by Sec. 75.1908(a) of this title) 
operated in an underground coal mine shall be equipped with a system 
capable of removing, on average, at least 95% of diesel particulate 
matter by mass.
    (c) The systems required by this section shall be maintained in 
accordance with manufacturer specifications.
    (d) In determining, for the purposes of this section, whether a 
filtration system is capable of removing, on average, at least 95% of 
diesel particulate matter by mass, emission tests shall be performed to 
compare the mass of diesel particulate matter emitted from an engine 
with and without the filtration system in place. Such tests shall be 
performed using the test cycle specified in Table E-3 of Sec. 7.89 of 
this title. The filtration system tested shall be representative of the 
system intended to be used in mining.


Sec. 72.510  Miner health training.

    (a) All miners at a mine covered by this subpart who can reasonably 
be expected to be exposed to diesel emissions on that property shall be 
trained annually in--

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    (1) The health risks associated with exposure to diesel particulate 
matter;
    (2) The methods used in the mine to control diesel particulate 
matter concentrations;
    (3) Identification of the personnel responsible for maintaining 
those controls; and
    (4) Actions miners must take to ensure the controls operate as 
intended.
    (b)(1) An operator shall retain at the mine site a record that the 
training required by this section has been provided for one year after 
completion of the training. Such record may be retained elsewhere if 
the record is immediately accessible from the mine site by electronic 
transmission.
    (2) Upon request from an authorized representative of the Secretary 
of Labor, the Secretary of Health and Human Services, or from the 
authorized representative of miners, mine operators shall promptly 
provide access to any such training record. Whenever an operator ceases 
to do business, that operator shall transfer such records, or a copy 
thereof, to any successor operator who shall receive these records and 
maintain them for the required period.

PART 75--[AMENDED]

    3. The authority citation for part 75 continues to read as follows:

    Authority: 30 U.S.C. 811.

    4. Section 75.371 is amended by adding paragraph (qq) to read as 
follows:


75.371  Mine ventilation plans; contents.

* * * * *
    (qq) A list of diesel-powered units used by the mine operator 
together with information about any unit's emission control or 
filtration system.

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Appendix to Preamble--Background Discussion MSHA's Toolbox

    Note: This appendix will not appear in the Code of Federal 
Regulations. It is provided here as a guide.
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[FR Doc. 98-8756 Filed 4-8-98; 8:45 am]
BILLING CODE 4510-43-C