[Federal Register Volume 65, Number 131 (Friday, July 7, 2000)]
[Proposed Rules]
[Pages 42068-42122]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-14075]



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Part II





Department of Labor





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Mine Safety and Health Administration



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Department of Health and Human Services





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Centers for Disease Control and Prevention



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30 CFR Part 72



Determination of Concentration of Respirable Coal Mine Dust; Proposed 
Rule

30 CFR Parts 70, 75 and 90



Verification of Underground Coal Mine Operators' Dust Control Plans and 
Compliance Sampling for Respirable Dust; Proposed Rule

  Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed 
Rules  

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DEPARTMENT OF LABOR

Mine Safety and Health Administration

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

30 CFR Part 72

RIN 1219-AB18


Determination of Concentration of Respirable Coal Mine Dust

AGENCIES: Mine Safety and Health Administration (MSHA), Labor, National 
Institute for Occupational Safety and Health, Centers for Disease 
Control and Prevention, Department of Health and Human Services (DHHS).

ACTION: Proposed rule; notice of hearings.

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SUMMARY: This proposal announces that the Secretary of Labor and the 
Secretary of Health and Human Services (the Secretaries) would find in 
accordance with sections 101 (30 U.S.C. 811) and 202(f)(2) (30 U.S.C. 
842(f)(2)) of the Federal Mine Safety and Health Act of 1977 (Mine Act) 
that the average concentration of respirable dust to which each miner 
in the active workings of a coal mine is exposed can be accurately 
measured over a single shift. The Secretaries are proposing to rescind 
a previous 1972 finding, by the Secretary of the Interior and the 
Secretary of Health, Education, and Welfare, on the validity of such 
single-shift sampling. Today's proposal addresses the final decision 
and order in NMA v. Secretary of Labor, issued by the United States 
Court of Appeals for the 11th Circuit on September 4, 1998 (153 F. 3d 
1264). That case vacated a 1997 Joint Finding and MSHA's proposed 
policy concerning the use of single, full-shift respirable dust 
measurements to determine noncompliance when the applicable respirable 
dust standard was exceeded.
    The Agencies are also announcing that they will hold public 
hearings on the joint proposed rule within 45 to 60 days of its 
publication. The hearings will be held in the following locations: 
Prestonsburg, Kentucky (Jenny Wiley State Park); Morgantown, West 
Virginia; and Salt Lake City, Utah.

DATES: Comments concerning this proposed rule should be submitted on or 
before August 7, 2000.
    The hearing dates, times and specific locations will be announced 
by a separate document in the Federal Register. The rulemaking record 
will remain open 7 days after the last public hearing.

ADDRESSES: You may use mail, facsimile (fax), or electronic mail to 
send your comments to MSHA. Clearly identify comments as such and send 
them--(1) By mail to Carol J. Jones, Director, Office of Standards, 
Regulations, and Variances, MSHA, 4015 Wilson Boulevard, Room 631, 
Arlington, VA 22203;
    (2) By fax to MSHA, Office of Standards, Regulations, and 
Variances, 703-235-5551; or
    (3) By electronic mail to [email protected].

FOR FURTHER INFORMATION CONTACT: Carol J. Jones, Director, Office of 
Standards, Regulations and Variances; MSHA; 703-235-1910. Copies of 
this proposed rule in alternative formats may be obtained by calling 
(703) 235-1910. The alternative formats available are large print, 
electronic file on computer disk, and audiotape. The proposed rule is 
also available on the Internet at http://www.msha.gov.

SUPPLEMENTARY INFORMATION: In accordance with sections 101 and 202(f) 
of the Mine Act (30 U.S.C. 811 and 842(f)), this proposed mandatory 
standard is published jointly by the Secretaries of the Departments of 
Labor, and Health and Human Services.

I. Table of Contents

    The preamble to this proposed rule on the accuracy of single shift 
exposure measurements discusses events leading to the proposed rule, 
health effects of exposure to respirable coal mine dust, degree and 
significance of the reduction in the number of shifts during which 
there are overexposures, an analysis of the technological and 
economical feasibility of this proposed rule, and regulatory impact and 
regulatory flexibility analyses.
    The preamble discussion follows this outline:

I. Table of Contents
II. Introduction
III. General Discussion
    A. The 1971/1972 Joint Notice of Finding
IV. NIOSH Mission Statement and Assessment of the Joint Finding
V. MSHA Mission Statement and Overview of the Respirable Dust 
Program
    A. The Coal Mine Respirable Dust Program
    B. The Spot Inspection Program (SIP)
    C. The Keystone Decision
    D. The Interim Single-Sample Enforcement Policy (ISSEP)
VI. Procedural and Litigation History of This Proposal
VII. Health Effects
    A. Introduction
    B. Hazard Identification
    1. Agent: Coal
    2. Physical State: Coal Mine Dust
    3. Biological Action: Respirable Coal Mine Dust
    C. Health Effects of Respirable Coal Mine Dust
    1. Description of Major Health Effects
    a. Simple Coal Workers' Pneumoconiosis (CWP) and Progressive 
Massive Fibrosis (PMF)
    b. Other Health Effects
    2. Toxicological Literature
    3. Epidemiological Literature
    a. Simple Coal Workers' Pneumoconiosis (CWP) and Progressive 
Massive Fibrosis (PMF)
    b. Other Health Effects
VIII. Quantitative Risk Assessment
IX. Significance of Risk
X. Issues Regarding Accuracy of a Single, Full-Shift Measurement
    A. Measurement Objective
    1. The Airborne Dust to be Measured
    2. Time Period to Which the Measurement Applies
    3. Area Represented by the Measurement
    4. Justification for the Proposed Measurement Objective
    B. Accuracy Criterion
    C. Validity of the Sampling Process
    1. Sampler Unit Performance
    2. Sample Collection Procedures
    3. Sample Processing
    a. Weighing and Recording
    b. Sample Validity Checks
    D. Measurement Uncertainty and Dust Concentration Variability
    1. Sources of Measurement Uncertainty
    (a) Coefficient of Variation, Weighing--CVweight
    (b) Coefficient of Variation, Pump--CVpump
    (c) Coefficient of Variation, Sampler--CVsampler
    2. Sources of Dust Concentration Variability
    (a) Spatial Variability
    (b) Shift-to-shift Variability
    3. Other Factors Considered
    (a) Proportion of Oversized Particles
    (b) Anomalous Events
    (c) Conversion Factor Used in the Dust Concentration Calculation
    (d) Reduced Dust Standards
    (e) Dusty Clothing
    E. Accuracy of Single, Full-Shift Measurement
    1. Quantification of Measurement Uncertainty
    a. Experience Gained from Use of Control Filters
    2. Verification of Method Accuracy
XI. Proposed New Finding and Proposed Rescission of the 1972 Joint 
Finding
XII. Feasibility Issues
    A. Technological Feasibility
    B. Economic Feasibility
XIII. Regulatory Impact Analysis
    A. Costs and Benefits: Executive Order 12866
    1. Compliance Costs
    2. Benefits
    B. Regulatory Flexibility Certification and Initial Regulatory 
Flexibility Analysis
XIV. Other Statutory Requirements
    A. Unfunded Mandates Reform Act of 1995
    B. Paperwork Reduction Act of 1995
    C. National Environmental Protection Act

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    D. Executive Order 12630 (Governmental Actions and Interference 
with Constitutionally Protected Property Rights)
    E. Executive Order 12988 (Civil Justice)
    F. Executive Order 13045 (Protection of Children from 
Environmental Health Risks and Safety Risks)
    G. Executive Order 13084 Consultation and Coordination with 
Indian Tribal Governments
    H. Executive Order 13132 (Federalism)
XV. Public Hearings
Appendix A. The Effects of Averaging Dust Concentration Measurements
Appendix B. Why Are Individual Measurements Unbiased?
    I. The Value of the MRE Conversion Factor
    II. Conforming to the ACGIH and ISO Standard
    III. Effects of Other Variables
Appendix C. Components of Coefficient of Variation Total 
(CVtotal)
    I. Weighing Uncertainty
    (a) Derivation of Coefficient of Variation of Weight 
(CVweight)
    (b) Values Expressing Weight-Gain Uncertainty
    (c) Negative Weight-Gain Measurements
    (i) New Analysis of New Data Set of Negative Weight Gain for 
Data of Unexposed Filters
    (d) Comparing Weight Gains Obtained From Paired Samples
    II. Pump Variability
    III. Intersampler Variability
Appendix D. Data Submitted by Previous Commenters
    I. Paired Sample Data Submitted by the NMA
    II. Paired Sample Data Submitted by Mountain Coal Company
    III. Exposure Data Submitted by Jim Walter Resources, Inc.
    IV. Exposure Data Submitted by the NMA
    V. Sequential Exposure Data Submitted by Jim Walter Resources, 
Inc.
Appendix E. References
XVI. Regulatory Text

II. Introduction

    For as long as miners have taken coal from the ground, many have 
suffered respiratory problems due to their occupational exposures to 
respirable coal mine dust. These respiratory problems, range from mild 
impairment of respiratory function to more severe diseases, such as 
silicosis and progressive massive fibrosis (PMF). For some miners, the 
impairment of their respiratory systems is so severe, they die 
prematurely. There is a clear dose-response relationship between 
miners' cumulative exposures (i.e., dose multiplied by the time exposed 
to the coal mine dust) to respirable coal mine dust and the severity of 
resulting respiratory conditions. On each and every workshift, it is 
essential to prevent miners from being exposed to respirable coal mine 
dust concentrations that exceed the mandated exposure limits.
    The Federal Coal Mine Health and Safety Act of 1969 (Coal Act) 
established the first comprehensive dust standard for underground U.S. 
coal mines by setting a limit of 2.0 milligrams of respirable coal mine 
dust per cubic meter of air (mg/m\3\). The 2.0 mg/m\3\ standard limits 
the concentration of respirable coal mine dust permitted in the mine 
atmosphere during each shift to which each miner in the active workings 
of a mine is exposed. Congress was convinced that the only way each 
miner could be protected from black lung disease or other occupational 
dust diseases was by limiting the amount of respirable coal mine dust 
allowed in the air that miners breathe.
    The Coal Act was subsequently amended by the Federal Mine Safety 
and Health Act of 1977 (Mine Act), 30 U.S.C. 801 et seq. The standard 
limiting respirable dust in the mine atmosphere to 2.0 mg/m\3\ was 
retained in the Mine Act, which also required that ``each operator 
shall continuously maintain the average concentration of respirable 
dust in the mine atmosphere during each shift to which each miner in 
the active workings of such mine is exposed at or below 2.0 milligrams 
of respirable dust per cubic meter of air,'' Section 202(b)(2) (30 
U.S.C.842(b)). (Other provisions in the Mine Act, Sections 205 and 
203(b)(2) (30 U.S.C. 845 and 843(b)(2)), provide for lowering the 
applicable standard when quartz is present and when miners with 
evidence of the development of pneumoconiosis have elected to work in a 
low-dust work environment).
    Today, dust levels in underground U.S. coal mines are significantly 
lower than they were when the Coal Act was passed. Federal mine 
inspector sampling results during 1968-1969 showed that the average 
dust concentration in the environment of a continuous miner operator 
was 7.7 mg/m\3\. Current sampling (FY 1998) indicates that the average 
dust level for a continuous miner operator has been reduced by 86 
percent to 1.1 mg/m\3\. Despite this progress, the Secretaries believe 
that respirable coal mine dust continues to present a serious health 
risk to coal miners. In November 1995, the National Institute for 
Occupational Safety and Health (NIOSH) issued a comprehensive review of 
the literature concerning occupational exposure to respirable coal mine 
dust in its Criteria Document (NIOSH Criteria Document, 1995). NIOSH 
concluded, among other things, that coal miners in our country continue 
to be at increased risk for developing respiratory disease as a result 
of their exposure to respirable coal mine dust. Although it is beyond 
the scope of this rulemaking, in its 1995 Criteria Document, NIOSH 
recommended a time weighted average exposure limit to respirable coal 
mine dust of 1.0 mg/m\3\, up to ten hours per day for a 40-hour work 
week.
    The Secretary of Labor and the Secretary of Health and Human 
Services believe that miners' health can be further protected from the 
debilitating effects of occupational respiratory disease by limiting 
their exposures to respirable coal mine dust exceeding the applicable 
standards. MSHA's improved program to eliminate overexposures on each 
and every shift includes multiple rulemakings. Through this proposal, 
MSHA would be able to use single, full-shift respirable coal mine dust 
samples to more effectively identify overexposures and address them. 
Other overexposures to respirable coal mine dust would be prevented 
through finalizing a proposed rule that would require each underground 
coal mine operator to have a verified mine ventilation plan. MSHA would 
verify the effectiveness of the mine ventilation plan for each 
mechanized mining unit (MMU) to controlling respirable dust under 
typical mining conditions. Furthermore, that proposal would revoke 
underground operator compliance and abatement sampling. Consequently in 
underground coal mines, MSHA intends to increase the number of 
compliance inspections per year, and MSHA would conduct abatement 
sampling for non-compliance determinations. The notice of proposed 
rulemaking to promulgate new regulations to require operators to have a 
verified ventilation plan in underground coal mines is published 
elsewhere in today's Federal Register.

III. General Discussion

    The issues related to this notice of proposed rulemaking are 
complex and highly technical. The Agencies have organized this proposal 
to allow interested persons to first consider pertinent introductory 
material on the Agencies' 1972 notice and its 1999 recission, and a 
short overview of the NIOSH mission and assessment of this proposal, as 
well as those aspects of MSHA's coal mine respirable dust program 
relevant to this proposal. Following this introductory material is a 
discussion of the ``measurement objective,'' or what the Secretaries 
intend to measure with a single, full-shift measurement, and the use of 
the NIOSH Accuracy Criterion for determining whether a single, full-
shift measurement will ``accurately represent'' the full-shift 
atmospheric dust concentration. Next, the validity of

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the sampling process is addressed, including the performance of the 
approved sampler unit, sample collection procedures, and sample 
processing. The concept of measurement uncertainty is then addressed, 
and why sources of dust concentration variability and various other 
factors are not relevant to the proposal. In addition, the proposal 
summarizes the health effects of occupational exposure to respirable 
coal mine dust and presents MSHA's quantitative risk assessment (QRA). 
Finally, the proposal explains how the total measurement uncertainty is 
quantified, and how the accuracy of a single, full-shift measurement 
meets the NIOSH Accuracy Criterion. Several Appendices, which contain 
relevant technical information, are attached and incorporated in this 
notice. Appendix E contains the references used throughout this notice 
of proposed rulemaking.
    The proposed rule is consistent with Executive Order 12866, the 
Regulatory Flexibility Act, the Small Business Regulatory Enforcement 
Fairness Act (SBREFA), the National Environmental Policy Act (NEPA), 
the Paperwork Reduction Act, the Unfunded Mandates Reform Act, and the 
Mine Act.

A. The 1971/1972 Joint Notice of Finding

    In 1971, the Secretary of the Interior and the Secretary of Health, 
Education, and Welfare proposed, and in 1972 issued, a joint finding 
under the Coal Act. The finding concluded that a single, full-shift 
measurement of respirable dust would not, after applying valid 
statistical techniques, accurately represent the atmospheric conditions 
to which the miner is continuously exposed. For the reasons that 
follow, the Secretaries believe that the 1972 joint finding was 
incorrect.
    Section 202(b)(2) of the Coal Act provided that ``each operator 
shall continuously maintain the average concentration of respirable 
dust in the mine atmosphere during each shift to which each miner in 
the active workings of such mine is exposed at or below the applicable 
respirable dust standard.'' In addition, the term ``average 
concentration'' was defined in section 202(f) of the Coal Act as 
follows:

    * * * the term ``average concentration'' means a determination 
which accurately represents the atmospheric conditions with regard 
to respirable dust to which each miner in the active workings of a 
mine is exposed (1) as measured during an 18 month period following 
the date of enactment of this Act, over a number of continuous 
production shifts to be determined by the Secretary of the Interior 
and the Secretary of Health, Education and Welfare, and (2) as 
measured thereafter, over a single shift only, unless the Secretary 
of the Interior and the Secretary of Health, Education and Welfare 
find, in accordance with the provisions of section 101 of this Act, 
that such single shift measurements will not, after applying valid 
statistical techniques to such measurement, accurately represent 
such atmospheric conditions during such shift.

    Therefore, 18 months after the statute was enacted, the ``average 
concentration'' of respirable dust in coal mines was to be measured 
over a single shift only, unless the Secretaries found that doing so 
would not accurately represent mine atmospheric conditions during such 
shift. If the Secretaries found that a single shift measurement would 
not, after applying valid statistical techniques, accurately represent 
mine atmospheric conditions during such shift, then the interim 
practice of averaging measurements ``over a number of continuous 
production shifts'' was to continue.
    On December 16, 1969, the U.S. Congress published a Conference 
Report in support of the new Coal Act. The Report refers to section 
202(f) by noting that:

    At the end of this 18 month period, it requires that the 
measurements be over one production shift only, unless the 
Secretar[ies] * * * find, in accordance with the standard setting 
procedures of section 101, that single shift measurements will not 
accurately represent the atmospheric conditions during the measured 
shift to which the miner is continuously exposed (Conference Report, 
page 75).

    This Report is inconsistent with the wording of the section 202(f), 
which seeks to apply a single, full-shift measurement to ``accurately 
represent such atmospheric conditions during such shift.'' Section 
202(f) does not mention continuous exposure. The Secretaries believe 
that the use of this phrase, ``continuously exposed'', is confusing, 
and to the extent that any weight of interpretation can be given to the 
legislative history, that the Senate's Report of its bill provides a 
clearer interpretation of section 202(f) when read together with the 
statutory language. The Senate Committee noted in part that:

    The committee * * * intends that the dust level not exceed the 
specified standard during any shift. It is the committee's intention 
that the average dust level at any job, for any miner in any active 
working place during each and every shift, shall be no greater than 
the standard. [Standard = 2 mg/m\3\]

    Following passage of the Coal Act, the Bureau of Mines (MSHA's 
predecessor Agency within the Department of the Interior) expressed a 
preference for multi-shift sampling. Correspondence exchanged during 
that time period of 1969 to 1971 reflected concern over the 
technological feasibility of controlling dust levels to the limits 
established, and the potentially disruptive effects of mine closure 
orders because of noncompliance with the respirable dust limits. Both 
industry and government officials feared that basing noncompliance 
determinations on single, full-shift measurements would increase those 
problems. In June 1971, the then-Associate Solicitor for Mine Safety 
and Health at the Department of the Interior issued a legal 
interpretation of section 202(f), concluding that the average dust 
concentration was to be determined by measurements that accurately 
represent respirable dust in the mine atmosphere over time rather than 
during a shift. On July 17, 1971, the Secretaries of the Interior and 
of Health, Education, and Welfare issued a proposed notice of finding 
under section 202(f) of the Coal Act. The finding concluded that, ``a 
single shift measurement of respirable dust will not, after applying 
valid statistical techniques to such measurement, accurately represent 
the atmospheric conditions to which the miner is continuously exposed'' 
(36 FR 13286).
    In February, 1972, the final finding was issued (37 FR 3833). It 
concluded that:

    After careful consideration of all comments, suggestions, and 
objections, it is the conclusion of the Secretary of the Interior 
and the Secretary of Health, Education, and Welfare that a valid 
statistical technique was employed in the computer analysis of the 
data referred to in the proposed notice [footnote omitted] and that 
the data utilized was accurate and supported the proposed finding. 
Both Departments also intend periodically to review this finding as 
new technology develops and as new dust sampling data becomes 
available.
    The Departments intend to revise part 70 of title 30, Code of 
Federal Regulations, to improve dust measuring techniques in order 
to ascertain more precisely the dust exposure of miners. To 
complement the present system of averaging dust measurements, it is 
anticipated that the proposed revision would use a measurement over 
a single shift to determine compliance with respirable dust 
standards taking into account (1) The variation of dust and 
instrument conditions inherent in coal mining operations, (2) the 
quality control tolerance allowed in the manufacture of personal 
sampler capsules, and (3) the variation in weighing precision 
allowed in the Bureau of Mines laboratory in Pittsburgh.
    The proposed finding, as set forth at 36 FR 13286, that a 
measurement of respirable dust over a single shift only, will not, 
after applying valid statistical techniques to such measurement, 
accurately represent the

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atmospheric conditions to which the miner under consideration is 
continuously exposed, is hereby adopted without change (emphasis 
added).

    As explained in the 1971 proposed finding, the average 
concentration of all ten full-shift samples (from one occupation) 
submitted from each working section under the regulations in effect at 
the time (these were the ``basic samples'' referred to in the proposed 
notice of finding) was compared with the average concentration of the 
two most recently submitted samples, then to the three most recently 
submitted samples, then to the four most recently submitted samples, 
etc. In discussing the results of these comparisons, the Secretaries 
stated that ``* * * the average of the two most recently submitted 
samples of respirable dust was statistically equivalent to the average 
concentration of the current basic samples for each working section in 
only 9.6 percent of the comparisons.''
    The title of the 1971/1972 notice and the conclusion it reaches are 
clearly inconsistent. The title states that it is a ``Notice of Finding 
That Single Shift Measurements of Respirable Dust Will Not Accurately 
Represent Atmospheric Conditions During Such Shift.'' However, the 
conclusion states that, ``* * * a single shift measurement * * * will 
not, after applying valid statistical techniques * * * accurately 
represent the atmospheric conditions to which the miner is continuously 
exposed'' (emphasis added).
    The Secretaries have determined that section 202(f) would require a 
determination of accuracy with respect to ``atmospheric conditions 
during such shift,'' not ``atmospheric conditions to which the miner is 
continuously exposed'' (37 FR 3833) (emphasis added). The Secretaries 
believe that the 1972 Finding does not apply the Mine Act's requirement 
at Section 202(f), 30 U.S.C. 842. The statistical analysis referenced 
in the 1971/1972 proposed and final findings simply did not address the 
accuracy of a single, full-shift measurement in representing 
atmospheric conditions during the shift on which it was taken. For this 
and other reasons, such as advancements in sampling technology, set 
forth in the notice, the Secretaries hereby propose to rescind the 1972 
joint final finding.

IV. NIOSH Mission Statement and Assessment of the Joint Finding

    The National Institute for Occupational Safety and Health (NIOSH) 
was created by Congress in the Occupational Safety and Health Act in 
1970. The Act established NIOSH as part of the Department of Health, 
Education, and Welfare (currently NIOSH is a part of the Department of 
Health and Human Services) to identify the causes of work-related 
diseases and injuries, evaluate the hazards of new technologies, create 
new ways to control hazards to protect workers, and make 
recommendations for new occupational safety and health standards. Under 
section 501 of the Mine Act (30 U.S.C. 951), Congress gave specific 
research responsibilities to NIOSH in the field of coal and other mine 
health. These responsibilities include the authority to conduct 
studies, research, experiments and demonstrations, in order ``to 
develop new or improved means and methods of reducing concentrations of 
respirable dust in the mine atmosphere of active workings of the coal 
or other mine,'' and also ``to develop techniques for the prevention 
and control of occupational diseases of miners * * *''
    When the initial finding, issued under section 202(f) of the Coal 
Act, was published in 1972, both the Secretary of the Interior and the 
Secretary of Health, Education, and Welfare (the predecessor to the 
Department of Health and Human Services) indicated that the finding 
would be reassessed as new technology was developed, or new data became 
available. The Secretary of Health and Human Services, through 
delegated authority to NIOSH, has reconsidered the provisions of 
section 202(f) of the Mine Act (30 U.S.C. 842(f)), reviewed the current 
state of technology and other scientific advances since 1972, and has 
determined that the following innovations and technological 
advancements are important factors in the reassessment of the 1971/1972 
joint finding.
    In 1977, NIOSH published its ``Sampling Strategies Manual,'' which 
provided a framework for the statistical treatment of occupational 
exposure data (DHEW (NIOSH) Publication No. 77-173; Sec. 4.2.1). 
Additionally, that year, NIOSH first published the NIOSH Accuracy 
Criterion, which was developed as a goal for methods to be used by OSHA 
for compliance determinations (DHEW (NIOSH) Publication No. 77-185; pp. 
1-5). In 1980, new mine health standards issued by the Secretary of 
Labor (30 CFR parts 70, 71, and 90) improved the quality of the 
sampling process by revising sampling, maintenance, and calibration 
procedures. Through the mid-nineteen-eighties, MSHA continued to refine 
and improve its sampling process. In 1984, a fully-automated, robotic 
weighing system was introduced along with state-of-the-art electronic 
microbalances. Prior to 1984, filter capsules used in sampling were 
manually weighed by MSHA personnel using semi-micro balances, making 
precision weights to the nearest 0.1 mg (100 micrograms). In 1994, the 
balances were further upgraded, and in 1995 the weighing system was 
again improved, increasing weighing sensitivity to the microgram level. 
Also, in 1987, electronic flow-control sampling pump technology was 
introduced in the coal mine dust sampling program with the use of Mine 
Safety Appliances FlowLiteTM pumps.\1\ These new pumps 
compensate for the changing filter flow-resistance that occurs due to 
dust deposited during the sampling period. The second generation of 
constant-flow sampling pumps was introduced in 1994, with the 
introduction of the Mine Safety Appliances Escort ELF pump. 
The automatic correction provided by these new pumps improves the 
stability of the sampler air flow rates and reduces the inaccuracies 
that were inherent in the 1970-1980s vintage sampling pumps. One 
further improvement was made in 1992 with the introduction of the new 
tamper-resistant filter cassettes. Because of these evolving 
improvements to the sampling process, a better understanding of 
statistical methods applied to method accuracy, and a reconsideration 
of the requirements of section 202(f) of the Mine Act (30 U.S.C. 
842(f)), the Secretary of Health and Human Services has determined that 
the previous joint finding should be reevaluated.
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    \1\ Reference to specific equipment, trade names or 
manufacturers does not imply endorsement by NIOSH or MSHA.
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V. MSHA Mission Statement and Overview of the Respirable Dust 
Program

    With the enactment of the Mine Act, Congress recognized that ``the 
first priority and concern of all in the coal or other mining industry 
must be the health and safety of its most precious resource--the 
miner.'' Congress further realized that there ``is an urgent need to 
provide more effective means and measures for improving the working 
conditions and practices in the Nation's coal or other mines in order 
to prevent death and serious physical harm, and in order to prevent 
occupational diseases originating in such mines.'' With these goals in 
mind, MSHA is given the responsibility to protect the health and safety 
of the Nation's coal and other miners by enforcing the provisions of 
the Mine Act.

[[Page 42072]]

A. The Coal Mine Respirable Dust Program

    In 1970, federal regulations were issued by MSHA's predecessor 
agency that established a comprehensive coal mine operator dust 
sampling program for underground mines. The program required the 
environment of the occupation on a working section exposed to the 
highest respirable dust concentration to be sampled--the ``high risk 
occupation'' concept. All other occupations on the section were assumed 
to be protected if the high risk occupation was in compliance. Under 
this program, each operator was required to initially collect and 
submit ten valid respirable dust samples to determine the average dust 
concentration across ten production shifts. If the analysis showed the 
average dust concentration to be within the applicable dust standard, 
the operator was required to submit only five valid samples a month. If 
compliance continued to be demonstrated, the operator was required to 
take only five valid samples every other month. The initial, monthly, 
and bimonthly sampling cycles were referred to as the ``original,'' 
``standard,'' and ``alternative sampling'' cycles, respectively. When 
the average dust concentration exceeded the applicable standard, the 
operator reverted back to the standard monthly sampling cycle.
    In addition to sampling the high risk occupation at specified 
frequencies, each miner was sampled individually at different 
intervals. However, these early individual sample results were not used 
for enforcement but were provided to NIOSH for medical research 
purposes. Also required to be sampled every 90 days in underground 
mines, beginning in 1971, and in surface mines, beginning in 1974, were 
individuals who had evidence of the development of pneumoconiosis and 
exercised their option to transfer to a low dust area.
    Federal regulations establishing a comprehensive operator dust 
sampling program for surface coal mines were issued in 1972. Under this 
program, each miner was sampled initially prior to July 1, 1972, and 
then either semiannually, if the initial sample exceeded 1.0 mg/m\3\ 
but was less than 2.0 mg/m\3\, or annually if the initial sample was 
1.0 mg/m\3\ or less.
    MSHA revised these regulations in April 1980 (45 FR 23990) to 
reduce the operator sampling burden, to simplify the sampling process, 
and to enhance the overall quality of the sampling program. The result 
was to replace the various sampling cycles in effect in underground and 
surface coal mines with a bimonthly sampling cycle and to eliminate the 
requirement that each miner be sampled. Unlike the underground sampling 
requirements, operators of surface coal mines were required to sample 
bimonthly only after a ``designated work position'' (DWP) was 
established by MSHA. Once established, only one sample is required to 
be collected each bimonthly period. Under the revised regulations, MSHA 
could also withdraw the designation of work positions for sampling if 
samples taken by the operator and by MSHA demonstrated continuing 
compliance with the applicable dust standard. These are the regulations 
that currently govern the mine operator dust sampling program at both 
underground and surface coal mines, and which, in the case of 
underground mines, continue to be based on the high risk occupation 
concept, now referred to as the ``designated occupation'' or ``D.O.'' 
sampling concept.
    It should be noted that the April 1980 preamble to the final rule, 
amending the regulations for underground coal mines, explicitly refers 
to the use of single versus multiple samples as it applies to the 
operator respirable dust sampling program (45 FR 23997):

    Compliance determinations will generally be based on the average 
concentration of respirable dust measured by five valid respirable 
dust samples taken by the operator during five consecutive shifts, 
or five shifts worked on consecutive days. Therefore, the sampling 
results upon which compliance determinations are made will more 
accurately represent the dust in the mine atmosphere than would the 
results of only a single sample taken on a single shift. In 
addition, MSHA believes the revised sampling and maintenance and 
calibration procedures prescribed by the final rule will 
significantly improve the accuracy of sampling results.

    At the time of these amendments, MSHA examined section 202(b)(2) of 
the Coal Act, which was retained unchanged in the 1977 Mine Act. The 
Agency stated in the preamble to the final rule that:

    Although single-[full] shift respirable dust sampling would be 
most compatible with this single-shift standard, Congress recognized 
that variability in sampling results could render single-shift 
samples insufficient for compliance determinations. Consequently, 
Congress defined ``average concentration'' in section 202(f) of the 
1969 Coal Act which is also retained in the 1977 Act.

    MSHA believes that this interpretation merely recognized the two 
ways of measurement authorized in section 202(f), and expressed the 
preference on the part of MSHA in 1980 to retain multi-shift sampling 
in the operator sampling program. The phrase used in the preamble to 
the final rule reflects that MSHA understood that the 2.0 mg/m\3\ limit 
was a single-shift standard, meaning that it was not to be exceeded on 
a shift. The preamble referenced the continuous multi-shift sampling 
and single-shift sampling conducted by the Secretary of the Interior 
and the Secretary of Health, Education, and Welfare, and noted that in 
the 1971/1972 proposed and final findings:

    ``It had been determined after applying valid statistical 
techniques, * * * that a single shift sample should not be relied 
upon for compliance determinations when the respirable dust 
concentration being measured was near 2.0 mg/m\3\. Accordingly, the 
[Secretaries] prescribed consecutive multi-shift samples to enforce 
the respirable dust standard.''

    The preamble provides no further explanation for the statement that 
single-shift samples should not be relied on when the respirable dust 
concentration being measured was near 2.0 mg/m\3\. Thus, the 1980 final 
rule, which reduced the number of samples that operators were required 
to take for compliance determinations, merely reiterated the rationale 
behind the 1971/1972 proposed and final findings concerning single-
shift samples, and did not address the accuracy of a single, full-shift 
measurement.
    MSHA continues to take an active role in sampling for respirable 
dust and has recently expanded its sampling to more than once annually 
at each surface and underground coal mine. During these inspections, 
MSHA inspectors collect samples on multiple occupations to determine 
whether miners are being overexposed to respirable coal mine dust; to 
assess the effectiveness of the operator's dust control program; to 
quantify the level of respirable crystalline silica (quartz) in the 
work environment and whether there is a need to adjust the applicable 
dust standard; and to identify occupations in underground mines, other 
than the ``D.O.'', and occupations in surface mines, that are at risk 
of being overexposed and should be routinely monitored by the mine 
operator.
    Depending on the concentration of respirable coal mine dust 
measured, an MSHA inspector may terminate sampling after the first day 
if levels are very low, or continue for up to five shifts or days 
before making a compliance or noncompliance determination. For example, 
MSHA inspection procedures require inspectors to sample at least five 
occupations, if available, on each mechanized mining unit (MMU) on the

[[Page 42073]]

first day of sampling. Based on the first shift of sampling, the 
operator is cited if the average of those measurements exceeds the 
applicable standard. However, if the average falls below the standard, 
but one or more of the measurements exceed the applicable standard, 
additional samples are collected on the subsequent production shift or 
day. The results of the first and second shift of sampling on all 
occupations are then averaged to determine if the applicable standard 
is exceeded. Additionally, when an inspector continues sampling after 
the first shift because a previous measurement exceeds the standard, 
MSHA's procedures call for all measurements taken on a given occupation 
to be averaged within that occupation, across all sampling shifts. If 
the average of measurements taken over more than one shift on all 
occupations is equal to or less than the applicable standard, but the 
average of measurements taken on any one occupation exceeds the value 
in a decision table developed by MSHA, the operator is cited for 
violation of the applicable standard.

B. The Spot Inspection Program (SIP)

    In response to concerns about possible tampering with dust samples 
in 1991, MSHA convened the Coal Mine Respirable Dust Task Group (Task 
Group) to review the Agency's respirable dust program. The Task Group 
was directed to consider all aspects of the current program in its 
review, including the role of the individual miner in the sampling 
program; the feasibility of MSHA conducting all sampling; and the 
development of new and improved monitoring technology, including 
technology to continuously monitor the mine environment. Among the 
issues addressed by the Task Group was the actual dust concentration to 
which miners are exposed. As part of the Task Group review, MSHA 
developed a special respirable dust ``spot inspection program'' (SIP).
    This program was designed to provide the Agency with information on 
the dust levels to which underground miners are typically exposed. 
Because of the large number of mines and MMUs (mechanized mining units) 
involved and the need to obtain data within a short time frame, 
respirable dust sampling during the SIP was limited to a single shift 
or day, a departure from MSHA's normal sampling procedures. The term 
``MMU'' is defined in 30 CFR 70.2(h) to mean a unit of mining 
equipment, including hand loading equipment, used for the production of 
material. As a result, MSHA decided that if the average of multiple 
occupation measurements taken on an MMU during any one-day inspection 
did not exceed the applicable standard, the inspector would review the 
result of each individual full-shift sample. If any individual full-
shift measurement exceeded the applicable standard by an amount 
specified by MSHA, a citation would be issued for noncompliance, 
requiring the mine operator to take immediate corrective action to 
lower the average dust concentration in the mine atmosphere in order to 
protect miners.
    During the SIP inspections, MSHA inspectors cited violations of the 
2.0 mg/m\3\ standard if either the average of the five measurements 
taken on a single shift was equal to or greater than 2.1 mg/m\3\, or 
any single, full-shift measurement was equal to or exceeded 2.5 mg/
m\3\. Similar adjustments were made when the 2.0 mg/m\3\ standard was 
reduced due to the presence of quartz dust in the mine atmosphere.\2\
---------------------------------------------------------------------------

    \2\ Quartz may be present in the coal seam and therefore may 
become airborne during coal production. MSHA regulates coal miners' 
work-shift exposure to quartz since it may be deposited in the lungs 
of miners and cause silicosis. MSHA's current standard for 
respirable coal mine dust, 2.0 mg/m\3\, also requires quartz levels 
to be 5% or lower. Otherwise, if the percent of quartz is higher 
than 5%, the respirable coal mine dust exposure limit must be 
adjusted downward based on this formula: Respirable dust standard 
(mg/m\3\)= {(10 mg/m\3\)/(%Quartz)} For example, if the respirable 
dust contains 15 percentage of quartz the respirable coal mine dust 
standard would be 0.67 mg/m\3\ since 10 mg/m\3\ divided by 15 equals 
0.67 mg/m\3\.
---------------------------------------------------------------------------

    The procedures issued by MSHA's Coal Mine Safety and Health 
Division during the SIP were similar to those used by the MSHA Metal/
Nonmetal Mine Safety and Health Division and the Occupational Safety 
and Health Administration (OSHA) when determining whether to cite based 
on a single, full-shift measurement. That practice provides for a 
margin of error reflecting an adjustment for uncertainty in the 
measurement process (i.e., sampling and analytical error, ``SAE''). The 
margin of error thus allows citations to be issued only where there is 
a high level of confidence that the applicable standard has been 
exceeded.
    Based on the data from the SIP inspections, the Task Group 
concluded that MSHA's practice of making noncompliance determinations 
solely on the average of multiple-sample results did not always result 
in citations in situations where miners were known to be overexposed to 
respirable coal mine dust. For example, if measurements obtained for 
five different occupations within the same MMU were 4.1, 1.0, 1.0, 2.5, 
and 1.4 mg/m\3\, the average concentration would be 2.0 mg/m\3\. 
Although the dust concentrations for two occupations exceed the 
applicable standard, under MSHA procedures, no citation would have been 
issued nor any corrective action required to reduce dust levels to 
protect miners' health. Instead, MSHA policy required the inspector to 
return to the mine the next day that coal was being produced and resume 
sampling in order to decide if the mine was in compliance or not in 
compliance.
    Thus, the SIP inspections revealed instances of overexposure that 
were masked by the averaging of results across different occupations. 
This showed that miners would not be adequately protected if 
noncompliance determinations were based solely on the average of 
multiple measurements. The process of averaging dilutes a high 
measurement made at one location with lower measurements made 
elsewhere.
    The Task Group also recognized that the results of the first full-
shift samples taken by an inspector during a respirable dust inspection 
are likely to reflect higher dust concentrations than samples collected 
on subsequent shifts or days during the same inspection. MSHA's 
comparison of the average dust concentration of inspector samples taken 
on the same occupation on both the first and second day of a multiple-
day sampling inspection showed that the average concentration of all 
samples taken on the first day of an inspection was almost twice as 
high as the average concentration of samples taken on the second day. 
MSHA recognized that sampling on successive days does not always result 
in measurements that are representative of everyday respirable dust 
exposures in the mine because mine operators can anticipate the 
continuation of inspector sampling and make adjustments in dust control 
parameters or production rates to lower dust levels during the 
subsequent sampling.
    In response to these findings, in November 1991, MSHA decided to 
permanently adopt the single, full-shift inspection policy initiated 
during the SIP for all mining types.

C. The Keystone Decision

    In 1991, three citations based on single, full-shift measurements 
were issued under the SIP to the Keystone Coal Mining Corporation. The 
violations were contested, and an administrative law judge from the 
Federal Mine Safety and Health Review Commission (Commission) vacated 
the citations. The decision was appealed by the Secretary of Labor to 
the Commission because the Secretary believed that the administrative 
law judge was in error in

[[Page 42074]]

finding that rulemaking was required under section 202(f) of the Mine 
Act (30 U.S.C. 842(f)) for the Secretary to use single, full-shift 
measurements for noncompliance determinations. In addition, the 
Secretary contended that the 1971/1972 finding pertained to operator 
sampling and that the SIP at issue involved only MSHA sampling. The 
Commission, which affirmed the decision of the administrative law 
judge, found that:

    Title II [of the Mine Act] applies to both operator sampling and 
to MSHA actions to ensure compliance, including sampling by MSHA. 
Section 202(g) specifically provides for MSHA spot inspections. 
Nothing in Sec. 202(f) or Sec. 202(g) suggests that Sec. 202(f) 
applies differently to MSHA sampling. Thus, the 1971 finding, issued 
for purposes of title II, applies broadly to both MSHA and operator 
sampling of the mine atmosphere.

    The Commission also held that the revised MSHA policy was in 
contravention of the 1971/1972 finding and could only be altered if the 
requirements of the Mine Act and the Administrative Procedure Act, 5 
U.S.C. 550, were met. Through this proposed notice of rulemaking, MSHA 
is now attempting to meet those requirements.

D. The Interim Single-Sample Enforcement Policy (ISSEP)

    On February 3, 1998, MSHA published a corrected notice in the 
Federal Register (63 FR 5687) announcing its final policy on the use of 
single, full-shift measurements to determine noncompliance and issue 
citations, based on samples collected by MSHA inspectors, when the 
applicable respirable dust standard is exceeded. The enforcement 
policy, thereafter referred to as ISSEP, which took effect on May 7, 
1998, provides better protection to miners' health because it enabled 
MSHA to more effectively identify overexposures that were previously 
masked by the averaging of results across different occupations. Again, 
through the proposed single, full-shift sample approach, citations for 
noncompliance with the respirable coal mine dust standard would be able 
to be made for overexposures which would not be identified through the 
current procedure of averaging multiple-sample results. For example, if 
measurements obtained for five different occupations within the same 
MMU were 4.1, 1.0, 1.0, 2.6, and 0.8 mg/m\3\, the average concentration 
would be 1.9 mg/m\3\. Although the dust concentrations for two 
occupations statistically exceeded the applicable standard, under the 
current practice, of averaging results, no citation would be issued nor 
any corrective action required to reduce dust levels to protect miners' 
health. The ISSEP was in place until September 9, 1998, when MSHA 
reinstituted its previous procedure of averaging sample results for 
noncompliance determinations after the 11th Circuit Court of Appeals 
vacated the Agencies' 1998 Finding and MSHA's final policy.
    Under the ISSEP, MSHA followed its existing dust sampling 
procedures in regard to where and how many samples an inspector 
collects during a sampling shift at underground and surface coal mines. 
While the Agency continued its practice of collecting multiple 
occupational samples at each MMU, the minimum number of occupations 
monitored was reduced from five to three, focusing only on those 
occupations at high risk of being overexposed. As part of the ISSEP, 
inspectors carried with them a control filter when conducting 
respirable dust sampling. This control filter, which was unexposed, was 
used to adjust the weight gain obtained on each of the exposed filters. 
Any change in weight of the unexposed control filter was subtracted 
from the change in weight of each exposed filter. For the exposed 
filter to be valid, the control and exposed filter must have been both 
pre-and post-weighed on the same days. If the control filter was either 
missing or invalid, the measurement(s) were not used for enforcement 
purposes and the entity type (i.e., mining section) was to be 
resampled. An operator was found to be in violation of the applicable 
dust standard when a single, full-shift measurement met or exceeded the 
Citation Threshold Value (CTV) corresponding to the dust standard in 
effect. Each CTV listed in Chapter 1 of the Coal Mine Health Inspection 
Procedures Handbook (PH89-V-1(10)) was calculated to ensure that 
citations would be issued only when a measurement demonstrated, with at 
least 95-percent confidence, that the applicable standard had been 
exceeded.\3\ No more than one citation was to be issued based on 
single, full-shift measurements from the same MMU, if the sampled 
occupations were exposed to the same dust generating sources. Issuance 
of separate citations were to be considered only after determining that 
the affected occupations were exposed to different dust generating 
sources.
---------------------------------------------------------------------------

    \3\ MSHA plans to issue a revised Coal Mine Health Inspection 
Procedures Handbook after publication of this proposed standard as a 
final rule. The Handbook would list the CTVs.
---------------------------------------------------------------------------

    When a single, full-shift measurement exceeded the applicable 
standard but was less than the CTV, a citation was not to be issued 
since noncompliance was not demonstrated at a sufficiently high 
confidence level. Instead, the MMU or other entity type sampled was to 
be targeted for additional sampling to verify the adequacy of the 
operator's dust control measures to maintain compliance, with special 
emphasis directed toward working environments with applicable standards 
below 2.0 mg/m\3\. If subsequent sampling exceeded the applicable 
standard but not the CTV, the MSHA district responsible for inspecting 
the mine would thoroughly review the dust control parameters stipulated 
in the operator's approved ventilation or respirable dust control plan 
(applicable to surface mines and Part 90 miners) to determine if the 
parameters should be upgraded.
    The process by which a violation of the applicable standard was to 
be abated by a mine operator remained unchanged. That is, an operator 
must first take corrective action to reduce the average dust 
concentration to within the permissible level, and then sample each 
production or normal work shift until five valid respirable dust 
samples are taken. MSHA considers a violation to be abated when the 
average dust concentration measured by these five valid samples was at 
or below the applicable standard. Under the ISSEP, MSHA inspectors 
sampled 1,662 MMUs and other entity types, such as roof bolter DAs and 
Part 90 miners, in underground mines; and some 860 DWPs and over 3,700 
nondesignated work positions at surface mining operations. The Agency 
issued a total of 309 excessive dust citations based on the results of 
single, full-shift samples, involving 182 MMUs and 113 other 
underground entity types, and 14 surface work positions. Of the 1,662 
MMUs sampled, 182 or 11 percent were cited, compared to the 27 percent 
MSHA had projected based on inspector sampling results for 1995. Also, 
it is important to point out that only 14 of the over 4,500 surface 
entities sampled were found to be out of compliance. These sampling 
inspections, which showed a significant decline in the number of cited 
instances of noncompliance compared to previous experience under the 
SIP and the earlier projections documented in the 1998 notices, reveal 
that mine operators are capable of maintaining dust concentrations at 
or below the applicable standard on every shift.

VI. Procedural and Litigation History of This Proposal

    On February 18, 1994, the Secretary of Labor and the Secretary of 
Health and Human Services published a proposed

[[Page 42075]]

Joint Notice of Finding in the Federal Register (59 FR 8357). The Joint 
Notice proposed to rescind the 1972 finding by the Secretaries of the 
Interior and Health, Education and Welfare, and instead, find that a 
single, full-shift measurement will accurately represent the 
atmospheric conditions with regard to the respirable dust concentration 
during the shift on which it was taken. Concurrently, MSHA published a 
separate notice in the Federal Register announcing its intention to use 
both single, full-shift measurements and the average of multiple, full-
shift measurements for noncompliance determinations under the MSHA 
respirable coal mine dust program (59 FR 8356). That notice was 
published to inform the mining public of how the Agency intended to 
implement its new enforcement procedure utilizing single, full-shift 
samples, and to solicit public comment on the procedure.
    After a notice and comment procedure extending over some three and 
one-half years, which also included three public hearings, the Agencies 
published a final corrected notice of finding in the Federal Register 
(63 FR 5664) on February 3, 1998.
    The National Mining Association (NMA) along with the Alabama Coal 
Association petitioned the United States Court of Appeals for the 11th 
Circuit to review the 1998 Notice of Finding (Joint Finding) issued by 
the Mine Safety and Health Administration (MSHA) and the National 
Institute for Occupational Safety and Health (NIOSH), and additionally 
asked for an emergency motion for stay of the Joint Finding pending 
review. The motion for an emergency stay was denied by the Court.
    On appeal NMA argued, among other things, that the agency had not 
met the requirements of section 101(a)(6)(A) of the Federal Mine Safety 
and Health Act of 1977 (Mine Act) (30 U.S.C. 811(a)(6)(A)) because it 
failed to address material impairment of health and economic and 
technological feasibility. MSHA and the Department of Labor responded 
that the agencies addressed the positive effect of the notice on miner 
health, and also concluded in the course of performing the analysis 
required under the Regulatory Flexibility Act that the economic impact 
of the Joint Finding was not significant. On September 4, 1998, the 
United States Court of Appeals for the 11th Circuit issued a decision 
in the case of National Mining Association v. Secretary of Labor, (153 
F.3d 1264). The Court of Appeals vacated the Joint Finding and 
concluded that the agency was required to ``satisfy the requirements of 
Section 811(a)(6)'' by ``demonstrat[ing] that the new standard (a) 
adequately assures that no miner will suffer a material impairment of 
health, on the basis of the best available evidence; (b) uses the 
latest available scientific data in the field; (c) is feasible [in both 
an economic and technological sense]; and (d) is based on experience 
gained under the Mine Act and other health and safety laws,'' supra, at 
1268-1269. The Court then concluded that ``the record contains no 
finding of economic feasibility,'' and that MSHA therefore ``failed to 
comply with Section 811(a)(6) of the Mine Act.'' MSHA asked the Court 
for a clarification of its decision by filing a Motion for 
Clarification. The Court, without opinion, denied the Secretary's 
motion on November 11, 1998.
    MSHA and NIOSH understand the Court's ruling as requiring the 
Agencies to comply with all requirements under section 101(a)(6)(A) of 
the Mine Act (30 U.S.C. 811(a)(6)(A)). Therefore, in response to the 
Court's ruling, the Secretaries are proposing today to add a new 
mandatory health standard to 30 CFR part 72. Pursuant to section 202(f) 
of the Mine Act (30 U.S.C. 842(f)), the 1972 joint notice of finding 
would be rescinded and a new finding would be made that a single, full-
shift measurement will accurately represent atmospheric conditions to 
which a miner is exposed during such shift. This finding is the basis 
for the new proposed mandatory health standard.
    The Secretaries believe that single, full-shift measurements must 
be implemented into the MSHA coal mine respirable dust program as 
quickly as possible in order to better protect miners' health. 
Therefore, in order to speed the process of reproposing this critical 
measurement technique, the Secretaries are incorporating the record of 
the previous 1998 Joint Finding into the record for this proposal and 
adding appropriate new data and information to support this rulemaking 
under section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)). 
The Secretaries have used as much of the original wording as possible 
from the vacated final finding in this notice of proposed rulemaking. 
References to previous comments and commenters in the body of this 
proposal are meant to apply to previous comments received in response 
to the earlier proposed Joint Finding that was ultimately vacated by 
the U.S. Court of Appeals for the 11th Circuit.

VII. Health Effects

A. Introduction

    Since the 1800s, occupational respiratory disease associated with 
working in a coal mine has been commonly referred to as ``Black Lung.'' 
As coal is mined, respirable-sized dust is generated. Depending upon 
the mine location and its geologic features, silica may also be present 
in the mine atmosphere. Dust in air that is breathed by miners has the 
potential to be deposited in their lungs. Some of this dust may be 
retained. Coal mine dust remaining in the lungs of miners for prolonged 
periods of time has the potential to result in respiratory diseases, 
sometimes even after occupational exposure to respirable coal mine dust 
has stopped. There is a clear and direct relationship between miners' 
cumulative exposures (i.e., dose multiplied by the time exposed to the 
coal mine dust) to respirable coal mine dust and the severity of 
resulting respiratory conditions (as discussed more extensively, later 
in this section).
    Diseases resulting from long-term retention of coal mine dust in 
the lung include chronic coal workers' pneumoconiosis (simple CWP), 
progressive massive fibrosis (PMF), silicosis, and chronic obstructive 
pulmonary disease (COPD) (e.g., asthma, chronic bronchitis, emphysema). 
Historically, the medical term, ``pneumoconiosis'', has included simple 
CWP and PMF and their sub-categories. Chronic, or simple, CWP is 
partitioned into three levels of severity, proceeding from lowest to 
highest: Category 1, category 2, and category 3. Progressive Massive 
Fibrosis is similarly divided into three categories of increasing 
levels of severity: A, B and C.
    Miners with simple CWP have a substantially increased risk of 
developing PMF. In the advanced stages of pneumoconiosis (i.e., PMF), a 
significant loss of lung function may occur and respiratory symptoms 
(e.g., breathlessness, wheezing) may persist. Miners are at risk of 
increased morbidity and premature mortality due to simple CWP, PMF and 
various other respiratory diseases.
    Factors that are important in the development of simple CWP, PMF 
and COPD include the type of dust (e.g., coal and/or silica), dust 
concentration (to which the miner was exposed), number of years of 
exposure, age of the miner (often measured as age at time of medical 
examination), and rank of the coal (the higher the rank the greater the 
risk).
    In 1998, MSHA estimated that approximately 45,000 miners and

[[Page 42076]]

39,000 miners were employed at underground and surface coal mines, 
respectively (Mattos, 1999). A small percentage of the mining involved 
anthracite coal, the highest rank coal, while most involved bituminous 
coal which is a medium rank coal.
    There are complementary data sources, described below, which 
provide estimates of the prevalence of occupational respiratory disease 
among coal miners. Together these data demonstrate the progress over 
the last thirty years in the reduction of occupational respiratory 
disease among coal miners, as well as the need for further action to 
reduce occupational lung disease among today's coal miners.
    Estimates of the prevalence of simple CWP and PMF among the 
underground coal miners are gathered from the x-ray program, through 
which operators are required to provide miners the opportunity to be 
evaluated periodically for the presence of occupational lung disease, 
mandated pursuant to Section 203(a) of the Mine Act (30 U.S.C. 843(a)). 
However, miners are not required to participate. From 1970 to 1995,the 
prevalence of simple CWP and PMF among miners participating in the 
mandated x-ray program has dropped from 11 percent to 3 percent (MSHA, 
Internal Chart, 1998).
    In accordance with 30 CFR part 50, those cases of occupational 
illnesses which both surface and underground coal mine operators learn 
of must be reported to MSHA. Under this requirement, mine operators 
reported 224 cases of pneumoconiosis (simple CWP and PMF, combined) in 
1998 (Mattos, 1999). Of these, 138 cases occurred among coal miners who 
worked underground, while the remaining 86 cases occurred among surface 
coal miners (Mattos, 1999). There were also 14 cases of silicosis, 
eight in underground mines, reported to MSHA in 1998 in accordance with 
30 CFR part 50 (Mattos, 1999). Since miners participate in both these 
programs at their own discretion, these data do not include the 
occupational health experience of all coal miners. The prevalence of 
occupational lung disease among participating miners may significantly 
differ from the prevalence among non-participants. Thus, the data from 
these programs may not be representative of the true magnitude of the 
prevalence of simple CWP and PMF among today's coal miners.
    In the 1990s, MSHA conducted a series of one-time medical 
surveillance programs, in various regions of the country, to develop a 
more accurate estimate of the prevalence of simple CWP and PMF. Through 
these special programs, MSHA tried to minimize obstacles which may 
prevent some miners from either participating in or reporting to 
operators the results of respiratory diagnostic procedures. Nine 
geographical cohorts of miners, from around the country, were 
encouraged to participate in an independent x-ray program (MSHA, 
Internal Chart, 1999). These cohorts included eight active surface coal 
mining communities in the states of Pennsylvania, Kentucky and West 
Virginia, as well as the towns of Poteau, Oklahoma and Gillette, 
Wyoming. A ninth cohort included underground miners in Kentucky. The 
process was designed to encourage miner participation by providing for 
a greater degree of anonymity than may be available under the program 
provided by Section 203(a) of the Mine Act (30 U.S.C. 843(a)). Across 
the eight surface cohorts surveyed, the prevalence rate of simple CWP 
and PMF combined, among participants was 4.8%. The prevalence rate 
among the participating underground Kentucky miners was 9.2%.
    Also, as part of its ongoing effort to ``end black lung now and 
forever,'' beginning in October 1999, MSHA implemented a pilot program 
to provide miners at both surface and underground mines with 
confidential health screening. Referred to as the ``Miners' Choice 
Health Screening'', the program addresses the key recommendations of 
the Secretary's Advisory Committee by (1) increasing participation 
toward the 85-percent level and (2) expanding the scope of the 
eligibility to include surface coal miners and surface coal mine 
independent contractors. The pilot program will operate separately from 
the existing Coal Workers' X-ray Surveillance Program administered by 
NIOSH. Since the Miners' Choice Health Screenings' inception, over 
7,000 miners have been screened, with the participation rate in most 
areas exceeding 50 percent. With half of the x-rays taken during the 
first six months having been processed by NIOSH, preliminary results 
indicate a prevalence rate of approximately 2.25 percent.
    The National Institute for Occupational Safety and Health (NIOSH) 
and the Mine Safety and Health Administration (MSHA) are concerned 
about the prevalence of occupational lung disease among today's miners. 
Epidemiological studies from the U.S. and abroad have consistently 
shown that underground and surface coal miners are at risk of 
developing simple CWP, PMF, silicosis, and chronic obstructive 
pulmonary disease (NIOSH Criteria Document, 1995).

B. Hazard Identification

1. Agent: Coal
    Coal is a fossil fuel derived from partial degradation of 
vegetation. Through its combustion, energy is produced which makes coal 
a valuable global commodity. It has been estimated that over one-third 
of the world uses energy provided by coal (Manahan, 1994). 
Approximately 1,800 underground and surface coal mines are in operation 
in the United States annually producing slightly over a billion short 
tons of coal (Mattos, 1999).
    Coal may be classified on the basis of its type, grade, and rank. 
The type of coal is based upon the plant material (e.g., lignin, 
cellulose) from which it originated. The grade of coal refers to its 
chemical purity. Although coal is largely carbon, it may also contain 
other elements such as hydrogen, oxygen, nitrogen, and sulfur. ``Hard'' 
coal refers to coal with a higher carbon content (i.e., 90-95%) than 
``soft'' coal (i.e., 65-75%). Coal rank relates to geologic age, 
indexed by its fixed carbon content, down to 65%, and then by its 
heating value. Volatile matter varies inversely with the fixed carbon 
value. The most commonly described coal ranks include lignite (low 
rank), bituminous coal (medium rank), and anthracite (high rank) 
(Manahan, 1994).
2. Physical State: Coal Mine Dust
    Aerosols are a suspension of solid or liquid particles in air 
(Mercer, 1973); they may be dusts which are solid particles suspended 
in the air. Coal dust may be freshly generated or may be re-suspended 
from surfaces on which it is deposited in mines. As discussed below, 
coal mine dust may be inhaled by miners, depending upon the particle 
size.
    Coal mine dust is a heterogenous mixture, signifying that all coal 
particles do not have the same chemical composition. The particles are 
influenced by the type, grade, and rank of coal from which they were 
generated (Manahan, 1994). Irrespective of differences in coal 
characteristics, these dusts are water-insoluble, which is important 
biologically and physiologically. Unlike soluble dusts which may 
readily pass into the respiratory system and be cleared via the 
circulatory system, insoluble dusts may remain in the lungs for 
prolonged periods of time. Thus, a variety of cellular responses may 
result that could eventually lead to lung disease.

[[Page 42077]]

3. Biological Action: Respirable Coal Mine Dust
    The principal route of occupational exposure to respirable coal 
mine dust occurs via inhalation. As a miner breathes, coal mine dust 
enters the nose and/or mouth and may pass into the mid airways (e.g., 
bronchi, terminal bronchioles) and lower airways (e.g., respiratory 
bronchioles, alveolar ducts).
    Coal mine dust has a size distribution that is estimated to range 
between 1 and 100 micrometer (m) (1 m = 
10-6 m) (Silverman, et al., 1971). The size of coal 
particles is critical in determining the level of the respiratory tract 
at which deposition and retention occur (American Conference of 
Governmental Industrial Hygienists, 1999; American Industrial Hygiene 
Association, 1997).
    Particles that are above 10 m are largely filtered in the 
nasal passages, although some of these particles may reach the thoracic 
(or tracheal-bronchial) region of the lung (e.g., 6% of 20 m) 
(American Conference of Governmental Industrial Hygienists, 1999). 
Thus, there is evidence that ``oversized'' particles (i.e., >10 
m) can move beyond the nose, deeper into the respiratory 
tract. Particles below 10 m may easily move throughout the 
respiratory tract. As particle size decreases from 10 to 5 m, 
however, there is greater penetration into the mid and lower regions of 
the lung. Particles that are approximately 1-2 m are the most 
likely to be deposited in the lung (American Conference of Governmental 
Industrial Hygienists, 1999; Mercer, 1973). During mouth breathing, 
there may be a slight upward shift in the particle deposition curve 
such that 2-3 m-sized particles are the most likely to be 
deposited in the respiratory tract (Heyder, et al., 1986). Irrespective 
of nasal or mouth breathing, the potential respiratory tract 
penetration of particles whose size is approximately 10 m or 
less is important because particles in the respirable size range 
deposit in the deep lung where clearance is much slower.
    For the purposes of this rule, ``respirable dust'' is defined as 
dust collected with a sampling device approved by the Secretary of 
Labor and the Secretary of the Department of Health and Human Services 
(DHHS) in accordance with 30 CFR Part 74 (Coal Mine Dust Personal 
Sampler Units). In practice, the coal mine dust personal sampler unit 
has been used in the U.S. The particles collected with an approved 
sampler approximate that portion of the dust which may be deposited in 
the lung (West, 1990; 1992). It does not, however, indicate pulmonary 
retention (i.e., those particles remaining in the lung). For those 
particles that are deposited in the lung, clearance mechanisms normally 
operate to assist in their removal. For example, within the thoracic 
(tracheal-bronchial) region of the lung, cilia (i.e., hairlike 
projections) line the airways and are covered by a thin layer of mucus. 
They assist in particle clearance by beating rhythmically to project 
particles toward the throat where they may be swallowed, coughed, 
sneezed, or expectorated. This rhythmic beating action is effective in 
removing particles fairly quickly (i.e., hours or days). Within the 
alveolar region of the lung, particles may be engulfed by pulmonary 
macrophages. These large ``wandering cells'' may remove particles via 
the blood or lymphatics. This process, unlike the movement of the cilia 
is much slower (i.e., months or years). Thus, some particles, 
particularly those that are insoluble, may remain in the alveolar 
region for long periods of time, despite the fact that pulmonary 
clearance is not impaired. It is the pulmonary retention of coal mine 
dust which may be the impetus for respiratory disease.
    It is also important to note that silica may be present in the coal 
seam, within dirt bands in the coal seam, and in rock above and below 
coal seams. Of the silica found in coal mines, quartz is the form which 
is found. Thus, quartz may become airborne during coal removal 
operations (Manahan, 1994). Miners may inhale dust that is a mixture of 
quartz and coal. MSHA is concerned with the inhalation of quartz since 
it may be deposited in the lungs of miners and produce silicosis. This 
is a restrictive lung disease which is characterized by a stiffening of 
the lungs (West, 1990; 1992). Silicosis has been seen in coal miners 
(e.g., surface miners, drillers, roofbolters) (Balaan, et al., 1993). 
Silicosis may develop acutely (i.e., 6 months to 2 years) following 
intense exposure to high levels of respirable crystalline quartz. 
Silicosis has also been observed in coal miners following chronic 
exposure (i.e., 15 years or more), but may be accelerated (i.e., 7-10 
years) in some cases (Balaan, et al., 1993). Silicosis is irreversible 
and may lead to other illnesses and premature mortality. People with 
silicosis have increased risk of pulmonary tuberculosis infection and 
an increased risk of lung cancer (Althouse, et al., 1995; International 
Agency for Research on Cancer, 1997). MSHA's current standard of 2.0 
mg/m3 for respirable coal dust requires that quartz levels 
be 5% or lower. Otherwise, the 2.0 mg/m3 respirable coal 
dust exposure limit does not apply and must be adjusted downward for 
percentage of quartz. If coal dust contains more than 5% quartz, then 
the following formula is applied (30 CFR 70.101; 30 CFR 71.101).
    Respirable dust standard (mg/m3)= {(10 mg/
m3)/(%Quartz)}
    The intent of this formula is to maintain miner exposures to quartz 
below 0.1 mg/m3 (100 g/m3).

C. Health-Related Effects of Respirable Coal Mine Dust

1. Description of Major Health Effects
    Consistently, epidemiological studies have demonstrated miners to 
be at risk of developing respiratory symptoms, a loss of lung function, 
and lung disease as a consequence of occupational exposure to 
respirable coal mine dust. As noted previously, risk factors include 
type(s) of dust, dust concentration, duration of exposure, age of the 
miner (often measured as age at time of medical examination), and coal 
rank.
a. Simple Coal Workers' Pneumoconiosis (Simple CWP) and Progressive 
Massive Fibrosis (PMF)
    In earlier stages of pneumoconiosis the term, ``simple coal 
workers' pneumoconiosis'' (simple CWP), has been used, while in more 
advanced stages, the terms ``complicated CWP'' and PMF have been used 
interchangeably. Simple CWP and PMF involve the lung parenchyma and are 
produced by deposition and retention of respirable coal dust in the 
lung.
    To determine if a miner has simple CWP or PMF, chest x-rays are 
taken and classified by a certified radiologist or reader. Opacities 
are identified on chest films and then classified using a scale of 0-3 
(e.g., simple CWP category 1), where higher category values indicate 
increasing concentration of opacities. In some instances, two category 
values may be given. For example, simple CWP category 2/3 signifies 
that the reader decided the film was category 2, but suspected that it 
might have been category 3. The International Labour Office (ILO) has 
provided a full description of the criteria for these classifications 
(ILO, 1980).
    Simple CWP can be associated with a loss of lung function and with 
premature mortality (Morgan, et al., 1974; Jacobsen, 1976; Cochrane, et 
al., 1979; Parkes, 1982). MSHA recognizes that simple CWP increases the 
risk of developing PMF substantially (Cochrane, 1962; Jacobsen, et al., 
1971; McLintock, et al., 1971; Balaan, et al., 1993).
    Progressive massive fibrosis (PMF) is associated with decreased 
lung function

[[Page 42078]]

and increased premature mortality (Rasmussen, et al., 1968; Atuhaire, 
et al., 1985; Miller and Jacobsen, 1985; Attfield and Wagner, 1992). 
Progressive massive fibrosis is also associated with increases in 
respiratory symptoms such as chest tightness, cough, and shortness of 
breath. Miners with PMF also have an increased risk of acquiring 
infections and pulmonary tuberculosis (Petsonk and Attfield, 1994; Yi 
and Zhang, 1996). Finally, miners with PMF have an increased risk of 
right-side heart failure (i.e., cor pulmonale) (Cotes and Steel, 1987).
b. Other Health Effects
    During a medical examination, a miner may be questioned by his 
physician about symptoms such as cough, phlegm production, chest 
tightness, shortness of breath, and wheezing. Occupational physicians 
may also conduct pulmonary function tests using spirometry or 
plethysmography. Pulmonary performance may be assessed via repeated 
measurements of lung volumes and capacities, such as the forced 
expiratory volume in one second (FEV1), vital capacity (VC), 
forced vital capacity (FVC), residual volume (RV), and total lung 
capacity (TLC) (West, 1990; 1992). Changes in lung volumes and 
capacities may indicate a loss of the integrity of the lung (i.e., 
respiratory system). More importantly, they can provide information for 
diagnosis of diseases affecting the airways and/or elasticity of the 
lung (i.e., obstructive vs. restrictive lung disease) (West, 1990; 
1992).
    The term, chronic obstructive pulmonary disease (COPD), refers to 
three disease processes that are often difficult to properly diagnose 
and differentiate: chronic bronchitis, emphysema, and asthma (Coggon 
and Taylor, 1998; Garshick, et al., 1996; West, 1990; 1992). As 
indicated by several studies, the exposure of miners to respirable coal 
mine dust place them at increased risk of developing COPD. Furthermore, 
COPD may occur in miners with or without the presence of simple CWP or 
PMF.
    Chronic Obstructive Pulmonary Disease (COPD) is characterized by 
airflow limitations, and thus there is a loss of pulmonary function. As 
in simple CWP or PMF, a miner with COPD may have a variety of 
respiratory symptoms (e.g., shortness of breath, cough, sputum 
production, and wheezing) and may be at increased risk of acquiring 
infections. Chronic Obstructive Pulmonary Disease is associated with 
increased premature mortality (Hansen, et al., 1999; Meijers, et al., 
1997).
    Briefly, in chronic bronchitis and in asthma, there is excess 
mucous secretion in the mid-lower airways (West, 1990; 1992). In 
contrast, emphysema is characterized by dilatation (enlargement) of 
alveoli that are distal to the terminal bronchioles, which leads to 
poor gas exchange (i.e., poor transfer of oxygen and carbon dioxide). 
Additionally, there is a breakdown of the interstitium between the 
alveoli. These pathological changes may be confirmed upon autopsy. With 
asthma, the airflow limitations may be partially or completely 
reversible, while they are only partially reversible with chronic 
bronchitis and emphysema.
    The Mine Safety and Health Administration (MSHA) and the NIOSH 
recognize that respiratory symptoms, loss of lung function, and COPD 
may impair the ability of a miner to perform his job and may diminish 
his quality of life. Additionally, miners having such health effects 
are at increased risk of morbidity (e.g., from cardio-pulmonary 
disease, infections) and premature mortality.
2. Toxicological Literature
    To better understand the human health effects of exposure to 
respirable coal mine dust and to more fully characterize the associated 
risks, it is important to consider data that have been obtained in 
animal based toxicological studies. To date, sub-acute studies (a study 
with a duration of 30 days, or less, in which multiple exposures of the 
same agent are given) and chronic studies (a study with a duration of 
more than 3-months, in which multiple exposures of the same agent are 
given) attempted to mimic miners' exposures. Inhalation was generally 
the route of exposure, although several studies have also employed 
instillation techniques (i.e., a method which places a known quantity 
of dust into the trachea or bronchi).
    Most recent toxicological studies have been short-term studies, 
largely focusing on ``lung overload'' (Snipes, 1996; Oberdorster, 1995; 
Morrow, 1988, 1992; Witschi, 1990), species-dependent lung responses 
(Nikula, et al., 1997a,b; Mauderly, 1996; Lewis, et al., 1989; Moorman, 
et al., 1975), and particle size-dependent lung inflammation (Soutar, 
et al., 1997). The data have shown that pulmonary clearance of 
particles may become impaired, potentially leading to inflammatory and 
other cellular responses in the lung. Although overloading has not been 
demonstrated in humans, the finding of reduced lung clearance among 
retired U.S. coal miners (Freedman and Robinson, 1988) is consistent 
with this possibility.
    The data from Moorman, et al. (1975), Lewis, et al. (1989), and 
Nikula, et al. (1997a,b) are noteworthy for several reasons. First, 
these groups of investigators conducted chronic inhalation toxicity 
studies (i.e., chronic bioassays). This is important since miners' 
exposures also occur via inhalation, and over a working lifetime. 
Secondly, the investigators used an exposure concentration of 2.0 mg/
m\3\ in their bioassays. As noted above, this is the current MSHA 
standard for respirable coal mine dust. Thirdly, the exposures involved 
nonhuman primates, whose responses are thought to closely mimic those 
of man. Some of the key findings of these studies included: deposition 
of coal dust in the animals' lungs, retention of coal dust in alveolar 
tissue, altered lung defense mechanisms, reduced pulmonary airflows, 
and hyperinflation of the lungs. One of the shortcomings of these 
studies is that complete dose-response relationships were not 
developed. However, at higher exposure concentrations, greater effects 
may be expected which is a basic tenet of toxicology. Thus, at exposure 
concentrations above 2.0 mg/m\3\, MSHA and NIOSH believe that more 
severe obstructive lung disease may occur.
3. Epidemiological Literature
    Epidemiology studies have consistently demonstrated the serious 
health effects of exposure to high levels of respirable coal mine dust 
(i.e., above 2.0 mg/m\3\) over a working lifetime. Table VII-1 lists 
epidemiology studies since 1986 whose results will be discussed on the 
basis of the type of observed health effect. Studies completed even 
earlier including the early work of Cochrane (1962), McLintock, et al. 
(1971), and Jacobsen, et al. (1971) demonstrated the adverse health 
effects (e.g., simple CWP, PMF) of respirable coal mine dust in British 
coal miners.
    Both early and recent studies have shown that the lung is the major 
target organ (i.e., organ in which toxic effects occur) when exposure 
to respirable coal mine dust occurs. As seen in Table VII-1, numerous 
studies of miners have been conducted. Recent U.S. studies were 
conducted using data from one or more of the first four rounds of the 
National Study of Coal Workers' Pneumoconiosis (NSCWP), and have 
provided extensive data on miners' health. Many of these studies 
demonstrated that miners are at increased risk of multiple, concurrent 
respiratory ailments (Attfield and

[[Page 42079]]

Seixas, 1995; Kuempel, et al., 1997; Meijers, et al., 1997; Seixas, et 
al., 1992).

   Table VII-1.--Respirable Coal Mine Dust Epidemiological Studies, by
                 Reported Outcomes From 1986 to Present
------------------------------------------------------------------------
                Studies                         Reported outcomes
------------------------------------------------------------------------
Meijers, et al., 1997..................  PMF, CWP, COPD, LLF.
Maclaren, et al., 1989.................  PMF, CWP, LLF, RS.
Kuempel*, et al., 1995.................  PMF, CWP, COPD.
Bourgkard et al., 1998.................  PMF, CWP, LLF.
  Kuempel*, et al., 1997
  Love, et al., 1997
  Love, et al., 1992
Attfield and Morring*,1992b............  PMF, CWP.
  Attfield and Seixas*, 1995
  Hodous and Attfield*, 1990
  Hurley and Jacobsen, 1986
  Hurley and Maclaren, 1987
  Hurley, et al., 1987
  Starzynski, et al., 1996
  Yi and Zhang, 1996
Wang, et al., 1997.....................  CWP, LLF.
Goodwin and Attfield*, 1998............  CWP.
  Morfeld, et al., 1997                  ...............................
Marine, et al., 1988...................  COPD, LLF, RS.
  Seixas*, et al., 1993
  Soutar and Hurley, 1986
Carta, et al., 1996....................  LLF, RS.
  Henneberger and Attfield*,1997
  Henneberger and Attfield*,1996
  Seixas*, et al., 1992
Attfield and Hodous*, 1992.............  LLF.
  Lewis, et al., 1996
------------------------------------------------------------------------
COPD: Chronic obstructive pulmonary disease.
CWP: Simple coal workers' pneumoconiosis.
LLF: Loss of lung function.
PMF: Progressive massive fibrosis.
RS: Respiratory symptoms.
* Studies of U.S. Miners Who Participated in the National Study of Coal
  Workers' Pneumoconiosis (NSCWP).

a. Simple Coal Workers' Pneumoconiosis (Simple CWP) and Progressive 
Massive Fibrosis (PMF)
    Studies following Cochrane (1962) and McLintock et al., (1971) have 
confirmed that the risk of PMF increases with increasing category of 
simple CWP (Hurley and Jacobsen, 1986; Hurley, et al., 1987; Hurley and 
Maclaren, 1988; Hodous and Attfield, 1990). However, the risk of PMF 
was greater than previously predicted among miners with simple CWP 
category 1 or without simple CWP (i.e., category 0) (Hurley, et al., 
1987). The risk of PMF increased with increasing cumulative exposure, 
regardless of the initial category of simple CWP (Hurley, et al., 
1987), indicating that reducing dust exposures is a more effective 
means of reducing the risk of PMF than reliance on detection of simple 
CWP.
    Attfield and Seixas (1995) have demonstrated a relationship between 
cumulative exposure to respirable coal mine dust and predicted 
prevalence of pneumoconiosis (i.e., simple CWP, PMF). They studied a 
group of approximately 3,200 men who worked in underground bituminous 
coal mines. The U.S. miners and ex-miners had participated in Round 1 
(1970-1972) or Round 2 (1972-1975) of the NSCWP and were examined again 
between 1985 and 1988. Chest x-rays were read to determine the number 
of cases of simple CWP and PMF. Dust exposure estimates were generated 
from measurements of dust concentrations as well as from work history. 
A logistic (or logit) regression model was used to estimate prevalence 
of simple CWP and PMF. In this statistical analysis, proportions are 
transformed to natural logarithmic values, i.e., y = 1n [p/(1-p)], 
before a linear model is fit to the data (Armitage, 1977). The logistic 
model assumes that the data have a binomial distribution (e.g., 
presence or absence of PMF) for a given set of covariate values (e.g., 
age, coal rank, dust exposure, pack-years of smoking). Using logistic 
modeling, relationships were developed between cumulative dust exposure 
and prevalence of simple CWP (category 1+, category 2+) and PMF. These 
relationships were the key strengths of the Attfield and Seixas study 
and serve as the basis for the Quantitative Risk Assessment of this 
rule.
    The recent paper of Kuempel, et al., (1997) has provided a detailed 
discussion and quantitative presentation of excess risks associated 
with respirable coal dust exposures. Their study was based upon results 
from previous studies of some 9,000 underground coal miners who 
participated in the NSCWP (Attfield and Morring, 1992b; Attfield and 
Seixas, 1995). Kuempel, et al., estimated excess (exposure-
attributable) prevalence of simple CWP and PMF (i.e., number of cases 
of disease present in a population at a specified time, divided by the 
number of persons in the population at that specified time). Point 
estimates of excess risk of PMF ranged from 1/1000 to 167/1000 among 
miners exposed at the current MSHA standard for respirable coal mine 
dust. These estimates were based upon dust exposure that occurred over 
a miner's working lifetime (e.g., 8 hours per day, 5 days a week, 50 
weeks per year, over a period of 45 years). Actual occupational 
lifetime exposure may be more, due to extended work shifts and work 
weeks. The point estimates of PMF presented by Kuempel, et al., (1997) 
were related to coal rank, where higher estimates (e.g., 167/1000) were 
obtained for high-rank coal (anthracite coal) and somewhat lower 
estimates were obtained for medium/low rank bituminous coal (e.g., 21/
1000). Within each coal rank, the estimates of simple CWP cases were at 
least twice as high as those for PMF (e.g., 167/1000 PMF vs. 380/1000 
simple CWP1).
    The data of Attfield and Seixas (1995) and Kuempel, et al., (1995; 
1997) were consistent with previous data of Attfield and Morring 
(1992b) who reported relationships between estimated dust exposure and 
predicted prevalence of simple CWP or PMF. They also noted that 
exposure-response relationships were steeper for higher ranks of coal 
such as anthracite, and concluded that the risks for anthracite miners 
appeared to be greater than for miners exposed to lower rank coal dust. 
Attfield and Morring (1992b) used similar methods as described above 
(i.e., logistic modeling), but included miners from Round 1 of the 
NSCWP (1969-1971); thus representing an earlier time point in the NSCWP 
when the respirable coal mine dust concentrations were much higher than 
they are today.
    Recently, Goodwin and Attfield (1998) reported that there were 
concerns regarding methodological inconsistencies across surveys given 
during the four rounds of the NSCWP. In particular, they noted the 
discordance in classification of simple CWP and PMF among readers of 
chest films. Despite potential discordance, Goodwin and Attfield (1998) 
have confirmed previous findings of a decline in simple CWP prevalence 
from 1969 to 1988. Yet, these analyses also demonstrated that simple 
CWP has not been eliminated. The Round 4 prevalence rates were 3.9 
percent for simple CWP category 1 and higher, and 0.9 percent for 
category 2 and higher. This illustrates the need for continued efforts 
to reduce dust exposures.
    Given the current system for monitoring exposures and identifying 
overexposures in the U.S., miners are at increased risk of developing 
simple CWP and PMF from a working lifetime exposure to respirable coal 
mine dust (Kuempel, et al., 1997, 1995; Attfield and Seixas, 1995; 
Goodwin and Attfield, 1998; Attfield and Morring, 1992b). Whenever 
overexposures (i.e., excursions above the applicable

[[Page 42080]]

standard) occur, the long-term mean exposure of miners may be 
increased, thereby causing an upward shift on the exposure-response 
curve. Such a shift then places these overexposed coal miners at 
increased risk of developing and dying prematurely from simple CWP and 
PMF.
    The Attfield and Seixas epidemiological study (1995) is the most 
appropriate to use in estimating the benefit of reduction of 
overexposures. The authors applied scientific rigor to the collection, 
categorization, and analyses of the radiographic evidence for the group 
of 3,194 underground bituminous coal miners who participated in Round 
4, 1985-1988, of the National Study of Coal Workers' Pneumoconiosis 
(NSCWP); this study population excludes 86 miners for whom there was 
missing exposure data or unreadable x-rays. Radiologic evidence was 
carefully collected and analyzed by multiple independent, NIOSH 
certified B readers to identify stages of simple CWP and PMF. In the 
targeted population of 5,557 miners, the participating miners (3,280) 
were similar to the non-participants (2,277) with regard to age at the 
first medical examination and prevalence of simple CWP category 1 or 
greater. The non-participants had worked slightly longer, yet had lower 
prevalence of simple CWP category 2 or greater, than the participants. 
This study describes the differences among current miners and ex-miners 
(health-related or job-related) in the relationships between the 
estimated cumulative exposure to respirable coal mine dust and 
prevalence of simple CWP category 1 or greater. Such data and 
relationships were not available in other U.S. studies and non-U.S. 
studies.
    A potential limitation in the U.S. studies is the possible bias in 
the exposure data, which has been the subject of several studies (Boden 
and Gold, 1984; Seixas et al., 1991; Attfield and Hearl, 1996). An 
advantage of the Attfield and Seixas 1995 study (and the earlier 
studies based on the same data set) is that the larger mines included 
in these epidemiological studies were shown to have exposure data with 
relatively small bias (Attfield and Hearl, 1996). Another limitation in 
exposure data used in the U.S. studies is that the airborne dust 
concentrations used to estimate individual miners' cumulative exposures 
to respirable coal mine dust were based on average concentrations 
within job category (these average values were combined with data of 
each individual miner's duration employed in a given job). The earlier 
U.S. exposure-response studies of miners participating in the first 
medical survey of the NSCWP (Attfield and Morring, 1992b; Attfield and 
Hodous, 1992; Kuempel, et al., 1995) relied primarily on exposure 
measurements from a dust sampling survey during 1968-1969 to estimate 
miners' exposures before 1970 (Attfield and Morring, 1992a). An 
advantage of the Attfield and Seixas 1995 study is that, in addition to 
the pre-1970 exposure estimates, more detailed exposure data were 
available to estimate miners' exposures from 1970 to 1987, during which 
the mean airborne concentrations were stratified by mine, job, and year 
(Seixas, et al., 1991).
    The most complete exposure data available are those for coal miners 
in the United Kingdom (Hurley, et al., 1987; Hurley and Maclaren, 1987; 
Soutar and Hurley, 1986; Marine, et al., 1988; Maclaren, et al., 1989). 
These studies include medical examinations and individual estimates of 
exposure for more than 50,000 miners for up to 30 years. The U.S. 
studies are consistent with these U.K. studies in demonstrating the 
risks of developing occupational respiratory diseases from exposure to 
respirable coal mine dust. These risks increase with increasing 
exposure concentration and duration, and with exposure to dust of 
higher ranked coal. The quantitative assessment of risk and associated 
benefits were based on the Attfield and Seixas (1995) study because, in 
addition to the advantages described above, it best represents the 
recent conditions experienced by miners in the U.S. This quantitative 
assessment follows in Section VIII. The international studies provide 
an important basis for comparison with the U.S. findings, and several 
of the recent international studies are described in detail here.
    Bourgkard, et al., (1998) conducted a 4-year study of a group of 
French coal miners who were employed in underground and surface mines. 
The investigators examined the prognostic role of cumulative dust 
exposure, smoking patterns, respiratory symptoms, lung CT scans, and 
lung function indices for chest x-ray worsening and evolution to simple 
CWP and PMF. Bourgkard, et al., (1998), through selection of a younger 
worker population (i.e., 35-48 years old at start of study), attempted 
to focus on the early stages of simple CWP. In essence, they hoped to 
identify those miners who needed to be relocated to less dusty 
workplaces or who needed to be clinically monitored. Bourgkard, et al., 
(1998) concluded that there was an association between cumulative dust 
exposure and what was termed chest x-ray ``worsening'' (i.e., increase 
in reader-designated category signifying progression of simple CWP). 
Their conclusion, however, was based on pooling of the data (i.e., 
three combined groups of miners) who had different cumulative exposures 
(i.e., 20, 66 and 85 mg-yr/m3).
    Love, et al., (1997, 1992) reported on occupational exposures and 
the health of British opencast (i.e., surface or strip) coal miners. 
They studied a group of approximately 1,200 miners who were employed at 
sites in England, Scotland, and Wales. The mean age of the men was 41; 
many had worked in the mining industry since the 1970s. To determine 
dust exposure levels, full-shift personal samples were collected. Most 
were respirable dust samples which were collected using Casella 
cyclones according to the procedures described by the British Health 
and Safety Executive (HSE). Thus exposure determinations would be 
comparable to exposure determinations obtained in U.S. surface coal 
mines since both measure respirable dust according to the BMRC 
criteria.
    These investigators found a doubling in the relative risk of 
developing profusion of simple CWP category 0/1 for every 10 years of 
work in the dustiest jobs in surface mines. These respirable coal dust 
exposures were under 1 mg/m3. Love, et al., (1992, 1997), 
like other investigators, emphasized the need for monitoring and 
controlling exposures to respirable coal mine dust, particularly in 
high risk operations (e.g., drillers, drivers of bulldozers).
    Meijers, et al., (1997) studied Dutch coal miners who were examined 
between 1952 and 1963, and who were followed until the end of 1991. 
They reported an increased risk of mortality from simple CWP and PMF 
among miners who had generally worked underground for 20 or more years. 
Their conclusions were based upon dramatic increases in standardized 
mortality ratios (SMRs). There were several limitations in this study, 
however.
    Morfeld, et al., (1997) published a recent paper that investigated 
the risk of developing simple CWP in German miners and addressed the 
occupational exposure limit for respirable coal dust in Germany. Their 
study included approximately 5,800 miners who worked underground from 
the late 1970s to mid-1980s. Morfeld, et al., observed increases in 
relative risks (RRs) of developing early x-ray changes, category 0/1, 
that were exposure-dependent. Relative risks (RRs) increased with 
higher dust concentrations.

[[Page 42081]]

    Starzynski, et al., (1996) conducted a mortality study on a group 
of 11,224 Polish males diagnosed with silicosis, simple CWP, or PMF 
between 1970 and 1985. This cohort was subdivided by occupation into 
four subcohorts: Coal miners (63%); employees of underground work 
enterprises (8%) (i.e., drift cutting and shaft construction jobs); 
metallurgical industry and iron, and nonferrous foundry workers (16%); 
and refractory materials, china, ceramics and quarry workers. The 
investigators found that coal miners had a slight, statistically 
significant excess overall mortality (i.e., all causes) as indicated by 
a Standardized Mortality Ratio (SMR) of 105 (with a 95% Confidence 
Interval (C.I.) of 100-110). Also, excess of deaths from diseases of 
the respiratory system among coal miners was nearly four times that of 
the referent population (SMR of 383 with a 95% C.I. of 345-424). The 
study of Starzynski, et al., (1996) agrees with others that there is 
premature mortality among coal miners from simple CWP and PMF. 
Unfortunately, there is little or no information presented on miner 
work history, exposure assessment (e.g., respirable coal mine dust, 
silica), and mine environment (e.g., coal rank(s), underground vs. 
surface mining).
    Yi and Zhang (1996) conducted a study to measure the progression 
from simple CWP to PMF or death among a cohort of 2,738 miners with 
simple CWP who were employed at the Huai-Bei coal mine in China. 
Relative risks (i.e., RRs) were calculated for progression from simple 
CWP category 1 to simple CWP category 3 and for progression from simple 
CWP category 3 to death. Their results demonstrated that miners with 
simple CWP category 1 are at risk of developing simple CWP category 2 
and simple CWP category 3 (e.g., RRs of 1.101 and 2.360, respectively). 
They also found that miners with PMF had a decreased life expectancy. 
Other risk factors for development of PMF included long-term work 
underground, and drilling. This study was limited by a lack of exposure 
assessment, estimation of miner smoking histories, and use of a 
radiological classification system that differs from that of the ILO.
    Hurley and Maclaren (1987) studied British coal miners who were 
examined between 1953 and 1978, over 5-year intervals. They have shown 
that exposure to respirable coal dust increases the risks of developing 
simple CWP and of progressing to PMF. As seen in their data analysis, 
these responses were dependent upon dust concentration and coal rank. 
That is, greater responses were seen at higher dust concentrations and 
with higher rank coal (i.e., increasing per cent carbon). The 
investigators also noted that estimated risks were unaffected by 
changes in the proportion of miners with simple CWP who transferred 
jobs. The authors concluded that ``limiting exposure to respirable coal 
dust is the only reliable way of limiting the risks of radiological 
changes to miners.''
b. Other Health Effects
    As noted in Table VII-1, there were 16 studies in which the loss of 
lung function (LLF) was examined in coal miners. Six of these studies 
also included an evaluation of respiratory symptoms (RS) in the miners. 
There were five studies describing chronic obstructive pulmonary 
disease (COPD) in miners.
    Henneberger and Attfield (1997; 1996), Kuempel, et al. (1997), 
Seixas, et al., (1993), Attfield and Hodous (1992), and Seixas, et al., 
(1992) evaluated data from pulmonary function tests and standardized 
questionnaires to miners in the NSCWP. A common finding in their 
studies was an increase in respiratory symptoms such as cough, 
shortness of breath, and wheezing. The symptoms were dependent upon the 
dust concentration to which the miners had been exposed, with more 
pronounced symptoms occurring after long-term exposures to higher 
exposure levels. These studies also demonstrated that a loss of lung 
function occurred among miners.
    Attfield and Hodous (1992) studied U.S. miners who had spent 18 
years underground (on average) and who participated in Round 1 (1969-
1971) of the NSCWP. They observed that greater reductions in pulmonary 
function were associated with exposure to higher ranks of coal (i.e., 
anthracite vs. bituminous vs. lignite). Using linear regression models, 
Kuempel et al., (1997) predicted the excess (exposure attributable) 
prevalence of lung function decrements among miners with cumulative 
exposures to respirable coal mine dust of 2 mg/m3 for 45 
years (i.e., 90 mg-yr/m3). The excess prevalence estimates 
were 315 and 139 cases per thousand for forced expiratory volume in one 
second (FEV1) of 80% and 65% of predicted normal values, 
respectively, among never-smoking miners (a sub-group of 977 NSCWP 
participants studied in Seixas et al., 1993). Such reductions in 
FEV1 are clinically significant; FEV1 80% (of 
predicted normal values) is a measure that is used to determine 
ventilatory defects (American Thoracic Society, 1991). Three recent 
studies found impaired FEV1 to be a predictor of increased 
pre-mature mortality (Weiss, et al., 1995; Meijers, et al., 1997; 
Hansen et al., 1999).
    Seixas, et al. (1993) conducted an analyses of 977 underground coal 
miners who began working in or after 1970 and were participants of both 
NSCWP Round 2 (1972-1975) and Round 4 (1985-1988). They found a rapid 
loss of lung function in miners and further declines in lung function 
with continuing exposure to coal mine dust. Collectively these studies 
have shown that the prevalence of decreased lung function was 
proportional to cumulative exposure. That is, with exposure to higher 
coal dust levels over a working lifetime, there were more miners who 
experienced a loss of lung function. Also, the types of respiratory 
symptoms and patterns of pulmonary function decrements observed by both 
Attfield and Hodous (1992) Seixas, et al. (1992;1993) are 
characteristic of COPD.
    The U.S. findings on respiratory symptoms and loss of lung function 
in miners have agreed with those of previous British studies by Marine, 
et al., (1988) and Soutar and Hurley (1986). Marine, et al., (1988) 
analyzed data from British coal miners and focused their attention on 
respiratory conditions other than simple CWP and PMF. In particular, 
they examined the Forced Expiratory Volume in one second 
(FEV1) among smoking and nonsmoking miners and, on the basis 
of reported respiratory symptoms, identified those miners with 
bronchitis. Using these data, logistic regression models were used to 
estimate the prevalence of chronic bronchitis and loss of lung 
function. Marine, et al., concluded that both exposure to respirable 
coal mine dust and smoking independently cause decrements in lung 
function; their contributions to COPD appeared to be additive in coal 
miners.
    Soutar and Hurley (1986) examined the relationship between dust 
exposure and lung function in British coal miners and ex-miners. The 
men who were studied were employed in coal mines in the 1950s and were 
followed up and examined 22 years later. These miners and ex-miners 
were categorized as smokers, ex-smokers, or nonsmokers. The Forced 
Expiratory Volume in one second (FEV1), the Forced Vital 
Capacity (FVC), and the FEV1/FVC ratios decreased in all 
study groups and these reductions in lung function were inversely 
proportional to dust exposure. Thus, Soutar and Hurley concluded that 
exposure to respirable coal mine dust can cause severe respiratory 
impairment, even without the presence of simple CWP or PMF. They 
speculated that the pathology of coal dust-induced

[[Page 42082]]

lung disease differs from that induced by smoking.
    Recent studies from China (Wang, et al., 1997) and the European 
community (Bourgkard, et al., 1998; Carta, et al., 1996; Lewis, S., et 
al., 1996) have also supported the British and U.S. findings which 
demonstrated the correlation between occupational exposure to coal dust 
and respiratory symptoms and loss of lung function in miners.
    Wang, et al., (1997) examined lung function in underground coal 
miners and other workers from several other factories in Chongqing, 
China. For their study, information was obtained on exposure duration, 
results of radiographic tests, and smoking history. Pulmonary function 
tests were performed, providing the Forced Expiratory Volume in one 
second (FEV1), the Forced Vital Capacity (FVC), and 
FEV1/FVC data. Additionally, the diffusing capacity for 
carbon monoxide (DLCO) was measured. This is an indicator of 
diffusion impairment at the ``blood-gas barrier'' which may occur, for 
example, when this barrier becomes thickened (West, 1990; 1992). Wang, 
et al., (1997) found that there was impairment of pulmonary function 
among the coal miners and they had evidence of obstructive disease. 
Like other studies, such effects were observed among coal miners even 
in the absence of simple CWP. Pulmonary function was further decreased 
when simple CWP was present. This study did not provide exposure 
measurements and there was no consideration of exposure-response 
relationships. Also, silica exposures and their potential effects were 
not examined in the underground coal miners.
    As noted above, Bourgkard, et al., (1998) was interested in the 
earlier stages of simple CWP (i.e., Categories 0/1 and 1/0) and the 
prognostic role of cumulative dust exposure, smoking patterns, 
respiratory symptoms, lung CT scans, and lung function indices for 
chest x-ray worsening and evolution to simple CWP category 1/1 or 
higher. Over a 4-year period, they studied French coal miners who were 
employed in underground and surface mines. Bourgkard, et al., (1998) 
found that, at the first medical examination, the ratio of the Forced 
Expiratory Volume in one second (FEV1) to the Forced Vital 
Capacity (FVC) (i.e., FEV1/FVC) and other airflows 
determined from a forced expiration (West, 1990; 1992) were lower among 
miners who later developed simple CWP category 1/1 or higher. These 
miners also experienced more wheezing at the first medical examination. 
Thus, the results of their study suggested that lung function changes 
may serve as an early indicator of miners who are at increased risk of 
developing simple CWP and PMF and who should be monitored more closely.
    Carta, et al., (1996) have examined the role of dust exposure on 
the prevalence of respiratory symptoms and loss of lung function in a 
group of young Italian coal miners (i.e., mean age at hire 28.9 years, 
mean age at first survey 31.2 years). These miners worked underground 
and were exposed to lignite (i.e., low rank coal) which had a 5-7% 
sulfur content. They were followed for a period of 11 years, from 1983 
and 1993. Carta, et al., (1996) found few abnormalities on miner chest 
x-rays taken throughout the 11-year study. However, there was an 
increased prevalence of respiratory symptoms and loss of lung function. 
This was particularly noteworthy since dust exposures were often below 
1.0 mg/m\3\; the cumulative dust exposure for the whole cohort was 6.7 
mg-yr/m\3\ after the first survey. Thus, Carta, et al., (1996) 
demonstrated that miners experience respiratory effects of exposure to 
dust generated from a lower rank coal and at lower concentrations. They 
have recommended yearly measurements of lung function for miners.
    Lewis, et al., (1996) studied a group of British miners, many of 
whom entered the coal industry in the 1970s. Based upon chest x-rays, 
the miners had no evidence of simple CWP or PMF. The objective of this 
study was to determine whether coal mining (i.e., exposure to 
respirable coal mine dust) is an independent risk factor for impairment 
of lung function. Lewis, et al. (1996) found that there was a loss of 
lung function in miners (smokers and nonsmokers), particularly among 
miners who were under approximately 55 years of age. For miners who 
smoked, there was a greater loss of lung function than in nonsmoking 
miners with the same level of exposure to respirable coal mine dust. 
Above age 55, the loss of lung function was similar for miners and 
their controls, although all smokers continued to exhibit a greater 
loss of lung function than nonsmokers. Lewis, et al., (1996) concluded 
that the deficits in lung function may occur in the absence of simple 
CWP and PMF, and independent from the effects of smoking.
    There have been two recent mortality studies that have demonstrated 
a relationship between exposure to respirable coal mine dust and 
development of COPD. This association was reported by Kuempel, et al., 
(1995) in the U.S., and by Meijers, et al. (1997) in the Netherlands. 
These two groups of investigators have reported that occupationally-
induced COPD (e.g., chronic bronchitis, emphysema) can occur in miners, 
with or without the presence of simple CWP or PMF. They also found that 
the risk of premature mortality from COPD was elevated among miners and 
could be separated from the effects of smoking and age.
    Kuempel, et al. (1995) found an increase in relative risk (RR) of 
premature mortality from COPD among U.S. coal miners who participated 
in the NSCWP from 1969 through 1971. In their data analysis, the 
exposure-response relationship was evaluated using the Cox proportional 
hazards model. This model assumes that the hazard ratio between 
nonexposed and exposed groups does not significantly change with time. 
When fitting a curve to the data (e.g., log-linear), cumulative 
exposure was expressed as a categorical or continuous variable. Due to 
model limitations (e.g., less statistical power, influence of category 
scheme, use of lowest exposure group for comparisons vs. use of non-
exposed group), Kuempel, et al. (1995) believed that the exposure data 
should be expressed as a continuous variable. If, for example, the 
cumulative exposure was 90 mg-yr/m\3\ (i.e., 2 mg/m\3\ for 45 years), 
then the relative risk of mortality from chronic bronchitis or 
emphysema was 7.67. Kuempel, et al. (1995) also showed that relative 
risk decreased with lower cumulative exposures (i.e., below 90 mg-yr/
m\3\) and increased with higher cumulative exposures (i.e., above 90 
mg-yr/m\3\. Thus, these investigators demonstrated a statistically 
significant exposure-response relationship for COPD.
    Meijers, et al. (1997) have shown, among Dutch miners, reductions 
in lung volumes and capacities are good predictors of the increased 
risk of premature mortality from COPD. For example, a diminished forced 
expiratory volume in one second (FEV1) or a diminished ratio 
of the FEV1 to the forced vital capacity \4\ (FVC) (i.e., 
FEV1/FVC) upon medical examination was associated with a 
significantly increased standardized mortality ratio (SMR) for COPD 
(322 and 212, respectively). In other words, miners with diminished 
lung capacity based on FEV1 were two to three times more 
likely to die prematurely due to COPD than miners who had normal lung 
function. In contrast, SMRs for COPD were not significantly increased 
in miners with normal lung volumes and capacities.

[[Page 42083]]

These data support prior conclusions of Seixas, et al. (1992, 1993) and 
Attfield and Hodous (1992) based on morbidity studies.
---------------------------------------------------------------------------

    \4\ Forced vital capacity (FVC) is the total volume of gas that 
can be exhaled with a forced expiration after a full inspiration; 
The vital capacity measured with a FVC may be less than that 
measured with a slower exhalation (West, 1992).
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VIII. Quantitative Risk Assessment

    As mentioned previously, in addition to this proposed notice of 
rulemaking, today's Federal Register contains another NPRM, 
Verification of Dust Control Plan (RIN 1219-AB18), ``plan 
verification.'' In combination, these rules present MSHA's strengthened 
plan to meet the Mine Act's requirement that a miner's exposure to 
respirable coal mine dust be at or below the applicable standard on 
each and every shift. MSHA's improved program to eliminate 
overexposures on each and every shift includes the simultaneous 
implementation of an improved tool to identify overexposures (i.e., 
inspectors use of single, full-shift samples for noncompliance 
determinations) and a new regulation requiring operators implement 
verified ventilation plans in underground coal mines.
    Having reviewed the reported health effects associated with 
exposure to coal mine dust, MSHA and NIOSH have evaluated the evidence 
to determine whether the current regulatory strategy can be improved. 
The criteria for this evaluation is established by the Mine Act under 
section 101(a)(6)(A) [30 U.S.C. 811(a)(6)(A)] which 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 must 
be addressed: (1) Whether health effects associated with the current 
pattern of overexposures on individual shifts constitute a material 
impairment to miner health or functional capacity; (2) whether the 
current pattern of overexposures on individual shifts places miners at 
a significant risk of incurring any of these material impairments; and 
(3) whether the proposed rules would substantially reduce those risks.
    The criteria for evaluating the health effects evidence do not 
require scientific certainty. The need to evaluate risk does not mean 
that an agency is placed into a ``mathematical straightjacket.'' See 
Industrial Union Department, AFL-CIO v. American Petroleum Institute, 
448 U.S. 607, 100 S.Ct 2844 (1980), otherwise known as the ``Benzene'' 
decision. 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 and NIOSH to wait for absolute certainty and precision. 
MSHA and NIOSH are required to use the ``best available evidence'' 
(section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)).
    As explained earlier, MSHA's objective in strengthening the 
requirements for verifying the effectiveness of dust control plans, and 
in enforcing effective plans through the new enforcement policy 
proposed in this notice, is to ensure that no miner is exposed to an 
excessive concentration (i.e., a concentration in excess of the 
applicable standard) of respirable dust on any individual shift. Annual 
inspector samples have demonstrated overexposures on individual shifts 
in many mines. Data compiled from the far more frequent, bimonthly, 
operator sampling program show that in many mines, the applicable dust 
standard is exceeded on a substantial percentage of the production 
shifts. This pattern has persisted for many years, and, since 
individual shift excursions above the applicable standard are permitted 
under the existing program, the same pattern can be expected to 
continue over the working lifetime of affected miners--unless an effort 
is made to eliminate excess exposures on individual shifts. In this 
quantitative risk assessment (QRA), MSHA will demonstrate that reducing 
coal mine dust concentrations, over a 45-year occupational lifetime, to 
no more than the applicable standard on just that percentage of shifts 
currently showing an excess, thereby lowering the cumulative exposure 
to respirable coal mine dust than would otherwise occur, would 
significantly reduce the risk of both simple CWP and PMF among miners. 
We have estimated the health benefits of the two rules arising from the 
elimination of overexposures on all shifts at only those MMUs 
exhibiting a pattern of recurrent overexposures on individual 
shifts.\5\
---------------------------------------------------------------------------

    \5\ By ``exhibiting a pattern of recurrent overexposures,'' MSHA 
means that, at a 95-percent confidence level, the applicable 
standard is exceeded on at least six shifts per year.
---------------------------------------------------------------------------

    Based on 1999 operator data, there were 704 MMUs (out of 1,251 
total) at which dust concentrations for the designated occupation 
(D.O.) samples exceeded the applicable standard on at least two of the 
sampling shifts (MSHA, Data file:Operator.ZIP).\6\ MSHA considers these 
704 MMUs, representing more than half of all underground coal miners 
working in production areas, to have exhibited a pattern of recurrent 
overexposures.\7\ Valid operator D.O. samples were collected on a total 
of 18,569 shifts at these 704 MMUs, and the applicable standard was 
exceeded on 3,977 of these shifts, or about 21.4 percent. For this 21.4 
percent, the mean excess above the standard, as measured for the D.O. 
only, was 1.04 mg/m\3\.
---------------------------------------------------------------------------

    \6\ If a different definition of ``exhibiting a recurrent 
pattern of overexposures'' were used in these analyses the estimate 
of the reduction in risk and associated benefits would be different. 
For example, if the criterion were that four or more D.O. bimonthly 
exposure measurements exceeded the applicable standard then, with 
95% confidence, at least 20 shifts would be overexposures in a year 
of 384 shifts. Using the four as the criterion, this would reduce 
the population for whom we are estimating benefits, and the 
estimated number of prevented cases would decrease by 19%.
    \7\ MSHA estimates an MMU average of 384 production shifts per 
year. Since mine operators are required to submit five valid 
designated operator (D.O.) samples to MSHA every two months, there 
would typically be 30 valid D.O. samples--representing 30 of the 384 
production shifts--for each MMU that was in operation for the full 
year. If dust concentrations on two or more of the sampled shifts 
exceeded the standard, then it follows, at a 95-percent confidence 
level, that the standard was exceeded on at least six shifts over 
the full year.
---------------------------------------------------------------------------

    These results are based on a large number of shifts (an average of 
more than 26 at each of the 704 MMUs). Therefore, assuming 
representative operating conditions on these shifts, the results can be 
extrapolated to all production shifts, including those that were not 
sampled, at these same 704 MMUs. With 95-percent confidence, the 
overall percentage of production shifts on which the D.O. sample 
exceeded the standard was between 20.6 percent and 22.2 percent for 
1999. At the same confidence level, again assuming representative 
operating conditions, the overall mean excess on noncompliant shifts at 
these MMUs was between 0.96 mg/m\3\ and 1.12 mg/m\3\. If operators tend 
to reduce production and/or increase dust controls on sampled shifts, 
as some commenters to the previous single, full-shift sample rulemaking 
and the Dust Committee have alleged, then the true values could be 
higher than even the upper endpoints of these 99-percent confidence 
intervals.
    In 1998, MSHA attempted to enforce compliance on individual shifts. 
Therefore, to compare the 1999 pattern

[[Page 42084]]

of excess exposures on individual shifts to that of previous years 
under the current enforcement policy, MSHA examined the regular 
bimonthly D.O. sample data submitted to MSHA by mine operators in the 
eight years from 1990 through 1997. The same three parameters were 
considered as discussed above for 1999: (1) The percentage of MMUs 
exhibiting a pattern of recurrent overexposures, as indicated by at 
least two of the valid measurements above the applicable standard in a 
given year; (2) for those and only those MMUs exhibiting recurrent 
overexposures, the overall percentage of production shifts on which the 
D.O. was overexposed, as estimated by the percentage of valid 
measurements above the applicable standard; and (3) for the MMUs 
identified as exhibiting recurrent overexposures, the mean excess above 
the applicable standard, as calculated for just those valid 
measurements that exceeded the applicable standard in a given year.
    Although MSHA found minor differences between individual years, 
there was no statistically significant upward or downward trend in any 
of these three parameters over the 1990-1997 time period (see Table 
VIII-1). In 1999, the percentage of MMUs exhibiting a pattern of 
recurrent overexposures (Parameter #1) was approximately 56 percent. 
Also in 1999, for those MMUs exhibiting a pattern of recurrent 
overexposures, the overall percentage of production shifts on which the 
D.O. was overexposed (Parameter #2) was approximately 21 percent. In 
1999, the average excess above the applicable standard (Parameter #3) 
for MMUs exhibiting recurrent overexposures was 1.0 mg/m\3\, a 
significant decrease from prior years. MSHA attributes this decrease to 
two important changes in the Agency's inspection program, beginning 
near the end of 1998. These changes, which both resulted in increased 
inspector presence, were: (1) An increase in the frequency of MSHA dust 
sampling at underground coal mines; and (2) initiation of monthly spot 
inspections at mines experiencing difficulty in maintaining consistent 
compliance with the applicable dust standard.

     Table VIII-1.--1990-1997, Distribution of Parameters of Annual Overexposure to Respirable Coal Mine Dust
----------------------------------------------------------------------------------------------------------------
                                                                   Parameter #1    Parameter #2    Parameter #3
                            1990-1997                                (Percent)       (Percent)       (mg/m\3\)
----------------------------------------------------------------------------------------------------------------
Number of Years.................................................               8               8               8
Median..........................................................            52.6            20.5            1.23
Mean (Standard Error)...........................................     50.9 (1.62)     20.6 (0.32)   1.25 (0.020)
----------------------------------------------------------------------------------------------------------------
Parameter #1: percentage of MMUs exhibiting a pattern of recurrent overexposures.
Parameter #2: for those MMUs exhibiting a pattern of recurrent overexposures, the percentage of production
  shifts on which the D.O. was overexposed.
Parameter #3: for those MMUs exhibiting a pattern of recurrent overexposures, the mean excess above the
  applicable standard among valid D.O. measurements that exceeded the applicable standard.

    The available data suggest that unless changes are made to enforce 
the dust standard on every shift, the same average pattern of 
overexposures observed in 1999 will persist into the future. Therefore, 
we conclude that without the proposed changes:
     More than one-half of all MMUs would continue to have a 
pattern of recurrent overexposures on individual shifts;
     At those MMUs with recurrent overexposures, full-shift 
average respirable dust concentrations for the D.O. would continue to 
exceed the applicable standards on about 21 percent of all production 
shifts;
     Among those shifts on which D.O. exposure exceeds the 
applicable standards, the mean excess for the D.O. would continue to be 
approximately 1.0 mg/m\3\.
    We invite public comment on whether these three parameters, based 
on operators' regular 1999 bimonthly samples, under-represent or over-
represent the frequency and/or magnitude of excessive dust 
concentrations on all individual shifts--including those that are not 
sampled.
    If all overexposures on individual shifts are eliminated, the 
reduction in total respirable coal mine dust inhaled by a miner over a 
working lifetime will depend on the following factors: The average 
volume of air inhaled on each shift that would otherwise have exceeded 
the applicable standard, the degree of reduction in respirable dust 
concentration in the air inhaled on such shifts, and the number of such 
shifts per working lifetime. If a miner inhales ten cubic meters of air 
on a shift (U.S. EPA, 1980), reducing the respirable dust concentration 
in that air by 1.0 mg/m\3\ would result in 10 mg less dust inhaled on 
that shift alone. Assuming the miner works 240 shifts per year, then 
reducing inhaled respirable dust by an average of 10 mg on 21 percent 
of the shifts would reduce the total dust inhaled by 504 mg per year, 
or nearly 22,700 mg over a 45-year working lifetime:

1.0 mg per m\3\ of inhaled air
 x  10 m\3\ inhaled air per shift
 x  50.4 affected shifts (i.e., 21% of 240) per work year
 x  45 work years per working lifetime
= 22,680 mg less dust inhaled per working lifetime.

    The Secretaries invite comments on the health benefits expected 
from reducing the total coal mine dust inhaled over a working lifetime 
by this amount.
    In Section VII, the strengths and weaknesses of various 
epidemiological studies were presented, supporting the selection of 
Attfield and Seixas (1995) as the study that provides the best 
available estimate of material health impairment with respect to CWP 
and PMF. Two of the distinguishing qualities of this study are the 
dose-response relationship over a miners' lifetime and the fact that 
these data best represent the recent conditions experienced by miners 
in the U.S. Using this relationship, it is possible to evaluate the 
impact on risk of both simple CWP and PMF expected from bringing dust 
concentrations down to or below the applicable standard on every shift. 
This is the only contemporary epidemiological study of simple CWP and 
PMF providing such a relationship.
    Attfield and Seixas used two or three B readers to identify the 
profusion of opacities using the ILO classification scheme. If three 
readings were available, the median value was used. If two readings 
were available, the higher of the two ILO categories was recorded. 
Eighty radiographs were eliminated because only one reading was 
available. The most inclusive category of CWP 1+ includes simple CWP, 
categories 1, 2, 3, as well as PMF. Category CWP 2+ does

[[Page 42085]]

not include simple CWP, category 1, but does include the more severe 
simple CWP categories, 2 and 3, as well as PMF. The third category used 
in their report was PMF, denoting any category of large opacities.
    Attfield and Seixas (1995) provided logistic regression models for 
the prevalence for CWP 1+, CWP 2+ and PMF as a function of cumulative 
dust exposure, expressed as the product of dust concentration measured 
in the mine atmosphere and duration of exposure at that concentration. 
These models can be used to estimate the impact on miners' risk of both 
simple CWP and PMF of reducing lifetime accumulated exposure by 
eliminating excessive exposures on a given percentage of individual 
shifts.
    At the MMUs being considered (those exhibiting a pattern of 
recurrent overexposures), bringing dust concentrations down to no more 
than the applicable standard on each and every production shift would 
reduce D.O. exposures on the affected shifts by an average of 1.04 mg/
m\3\. Assuming this average reduction applies to only 21 percent of the 
shifts, the effect would be to reduce cumulative exposure, for each 
miner exposed at or above the D.O. level, by 0.22 mg-yr/m\3\ over the 
course of a working year (i.e., 21 percent of shifts in one year, times 
1.04 mg/m\3\ per shift). Therefore, over a 45-year working lifetime, 
the benefit to each affected miner would, on average, amount to a 
reduction in accumulated exposure of approximately 10 mg-yr/m\3\ (i.e., 
45 years times 0.22 mg-yr/m\3\ per year). If, as some miners have 
testified, operator dust samples currently submitted to MSHA tend to 
under-represent either the frequency or magnitude (or both) of 
individual full-shift excursions above the applicable standard, then 
eliminating such excursions would provide a lifetime reduction of even 
more than 10 mg-yr/m\3\ for each exposed miner.
    The Attfield and Seixas models predict the prevalence of CWP 1+, 
CWP 2+, and PMF for miners who have accumulated a given amount of 
exposure, expressed in units of mg-yr/m\3\, by the time they attain a 
specified age. Benefits of reducing cumulative exposure can be 
estimated by calculating the difference between predictions with and 
without the reduction. For example, suppose a miner begins work at age 
20 and retires at age 65. By the year of retirement, that miner is 
expected to accumulate nearly 10 mg-yr/m\3\ less exposure if individual 
shift excursions are eliminated. For 65-year-old miners, reducing 
accumulated dust exposure by a total of 10 mg-yr/m\3\ reduces the 
predicted prevalence of CWP 1+ by at least 11 per thousand (See Table 
VIII-2).
    This 11 per thousand, however, applies only to miners of age 65. 
The Attfield and Seixas models provide different predictions for each 
year of age that a miner attains. The predicted benefit turns out to be 
smaller for younger miners and larger for older miners. This is partly 
because younger miners will have accumulated less exposure reduction 
from the proposed changes, and partly because the Attfield and Seixas 
models depend directly on age as well as on cumulative exposure. The 
health effects of recurrent overexposures can occur long after the 
overexposures occurred. Even after a miner retires and is no longer 
exposed to respirable coal mine dust, the extra risk attributable to an 
extra 10 mg-year/m\3\, accumulated earlier, continues to increase with 
age. Consequently, the benefit to be gained from eliminating individual 
shift excursions also continues to increase after a miner is no longer 
exposed. For example, assuming no additional exposure after age 65, the 
predicted reduction in average prevalence of CWP1+ increases from 12 
per thousand at age 65 to 17 per thousand at age 70. Presumably, the 
increasingly greater predicted reduction in risk of disease after age 
65 is due to the latent effects of the reduction in earlier exposure.
    To project the benefits of the two rules expected from eliminating 
overexposures on individual shifts, MSHA applied the Attfield and 
Seixas models to a hypothetical population of miners who, on average, 
begin working at age 20 and retire at age 65, assuming different 
lifetimes. The risks for three different ages have been presented to 
show a range of risk depending on the lifetime: 65, 73, and 80 years. 
During the 45 ``working years'' between 20 and 65, the lifetime benefit 
accumulates at a rate of 0.22 mg-yr/m\3\ of reduced exposure per year, 
reaching a maximum of about 10 mg-yr/m\3\ at age 65. Between ages 65 
and 80, the accumulated reduction in dust exposure remains at an 
estimated average of 10 mg-yr/m\3\, but the benefit in terms of both 
simple CWP and PMF risk continues to increase, as explained previously.
    The expected lifetime for all American males conditional on their 
having reached 20 years of age, is 73 years (calculated from: U.S. 
Census March 1997, Table 18; U.S. Census March 1997, Table 119).\8\ On 
average, the best estimate of the lifetime benefit to exposed miners is 
expressed by the reduction in prevalence of disease at age 73. Carrying 
out the calculation at a 73-year average lifetime, MSHA expects that, 
at the MMUs under consideration, bringing dust concentrations down to 
no more than the applicable standard on each shift will:
---------------------------------------------------------------------------

    \8\ Since females have a greater life expectancy than males, 
expected benefits would increase if the proportion of female miners 
increases substantially in the future.
---------------------------------------------------------------------------

     Reduce the combined risk of simple CWP and PMF by at least 
18.0 cases per 1000 affected D.O. miners; \9\
---------------------------------------------------------------------------

    \9\ ``affected D.O. miners'' include all miners who work at the 
56-percent of MMUs under consideration and who are exposed to dust 
concentrations similar to the D.O. over a 45-year working lifetime.
---------------------------------------------------------------------------

     Reduce the combined risk of simple CWP (category 2 and 3) 
and PMF by at least 9.8 cases per 1000 affected D.O. miners;
     Reduce the risk of PMF by at least 5.1 cases per 1000 
affected D.O. miners.
    Presented in the first row of Table VIII-2 are the average 
reductions in risk for simple CWP and PMF combined, and PMF alone, over 
an occupational lifetime, among affected D.O. miners who live to ages 
65, 73, and 80, who have worked at an MMU exhibiting a pattern of 
recurrent overexposures. Across health outcomes, the benefit due to the 
predicted reduction in cumulative exposure to respirable coal mine 
dust, through limiting miners' exposure to no more than the applicable 
standard on each and every shift, increases with age.
    When the dust concentration measured for the D.O. exceeds the 
applicable standard, measurements for at least some of the other miners 
may also exceed the standard on the same shift, though usually by a 
lesser amount. Furthermore, although the D.O. represents the occupation 
most likely to receive the highest exposure, other miners working in 
the same MMU may be exposed to even higher concentrations than the D.O. 
on some shifts. Therefore, in addition to the affected D.O. miners, 
there is a population of other affected miners who are also expected to 
experience a significant reduction in risk as a result of eliminating 
overexposures on their individual shifts.
    To estimate how many miners other than the D.O. would be 
substantially affected, MSHA examined the results from all valid dust 
samples collected by MSHA inspectors in underground MMUs during 1999 
(MSHA, Data file:Inspctor.zip). Within each MMU, the inspector 
typically takes one full-shift sample on the D.O. and, on the same 
shift, four or more additional samples representing other occupations.

[[Page 42086]]

On 896 shifts, at a total of 450 distinct MMUs, the D.O. measurement 
exceeded the applicable standard and there were at least three valid 
measurements for other occupations available for comparison. There was 
an average of 1.2 non-D.O. measurements in excess of the standard on 
shifts for which the D.O. measurement exceeded the standard.\10\ For 
non-D.O. measurements that exceeded the standard on the same shift as a 
D.O. measurement, the mean excess above the standard was approximately 
(0.8 mg/m3).\11\
---------------------------------------------------------------------------

    \10\ With 95-percent confidence, on shifts for which the D.O. 
measurement exceeds the standard, the mean number of other 
occupational measurements also exceeding the standard is at least 
1.11.
    \11\ With 95-percent confidence, the mean excess is at least 
0.72 mg/m3.
---------------------------------------------------------------------------

    Combining these results with the 21-percent rate of excessive 
exposures observed for the D.O. on individual shifts, it is reasonable 
to infer that, at the MMUs under consideration, an average of 1.2 other 
miners, in addition to the one classified as D.O., is currently 
overexposed on at least 21 percent of all production shifts. Over the 
course of a working year, the reduction in exposure expected for these 
other miners is 0.17 mg-yr/m3 (i.e., 21 percent of one year, 
times 0.8 mg/m3).
    To assess the reduction in risk expected from eliminating all 
single-shift exposures for faceworkers experiencing lower exposures 
than the D.O., MSHA again applied the Attfield and Seixas models to 
miners who begin working at age 20, retire at age 65, assuming various 
lifetimes: 65, 73, and 80 years. This time, however, the resulting 
decrease in predicted prevalence was multiplied by 1.2/7 = 0.171, to 
reflect the fact that the assumed rate of overexposure applies, on 
average, to about 17 percent of the faceworkers not classified as the 
D.O.\12\
---------------------------------------------------------------------------

    \12\ There are an estimated 7 non-D.O. miners for each D.O. 
miner, and an average of 1.2 of these 7 miners are overexposed.
---------------------------------------------------------------------------

    In the second row of Table VIII-2, we see that over an occupational 
lifetime, the beneficial average reduction in risk for simple CWP and 
PMF combined, and for PMF alone, increases with age. However, the 
magnitude of the risk reduction is smaller for the affected non-D.O.s 
than the affected D.O.s. This is expected because the estimated 
probability that a non-D.O. will be overexposed on a given shift is 
only 17 percent of the corresponding probability for the D.O. Based on 
this calculation for the MMUs under consideration, the predicted 
reduction in risk for faceworkers other than the D.O. who live an 
expected lifetime of 73 years is at least: 2.3 fewer cases of PMF or 
simple CWP, per thousand affected miners; 1.3 fewer cases of PMF or 
simple CWP, categories 2 or 3, per thousand affected miners; and 0.7 
fewer cases of PMF per thousand affected miners.
    Various data, assumptions and caveats were used to conduct the 
quantitative risk assessment. Therefore, we request any information 
which would enable us to conduct more accurate analyses of the 
estimated health benefits of the single, full-shift sample rule and 
plan verification rule, both individually, and in combination.

   Table VIII-2.--By Age, Average Reduction in Risk for Occupational Respiratory Disease per 1,000 Affected Underground Coal Miners Expected to Result
                                     From Implementation of Single, Full-Shift Sampling and Plan Verification Rules
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           Reduction in risk for occupational respiratory disease per 1,000 affected miners
                                             -----------------------------------------------------------------------------------------------------------
                                               Simple CWPa  (categories 1, 2 or   Simple CWP  (categories 2 or 3) or                  PMF
                                                          3) or PMFb                              PMF                -----------------------------------
                Type of miner                ------------------------------------------------------------------------                 Age
                                                              Age                                 Age                -----------------------------------
                                             ------------------------------------------------------------------------
                                                  65          73          80          65          73          80          65          73          80
--------------------------------------------------------------------------------------------------------------------------------------------------------
Affected Designated Occupation Minersc......        11.0        18.0        25.0         3.7         9.8        21.0         1.8         5.1        12.0
Affected Non-Designated Occupation Minersd..         1.4         2.3         3.3         0.5         1.3         2.7         0.2         0.7        1.5
--------------------------------------------------------------------------------------------------------------------------------------------------------
a Simple CWP: simple coal workers' pneumoconiosis.
b PMF: progressive massive fibrosis.
c Affected Designated Occupation (D.O.) Miners: includes all miners who work at the 56-percent of the Mechanized Mining Units under consideration and
  who are exposed to dust concentrations similar to the D.O., over a 45-year occupational lifetime.
d Affected Non-Designated Occupation (Non-D.O.) Miners: includes all underground faceworkers under consideration who are not classified as the D.O.

IX. Significance of Risk

    The criteria for evaluating the evidence to determine whether these 
proposed standards improve the regulatory strategy for controlling 
exposures to respirable coal mine dust are established by the Mine Act 
pursuant to section 101(a)(6)(A) (30 U.S.C. 811(a)(6)(A))which 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 must 
be addressed: (1) Whether health effects associated with the current 
pattern of overexposures on individual shifts constitute a material 
impairment to miner health or functional capacity; (2) whether the 
current pattern of overexposures on individual shifts places miners at 
a significant risk of incurring any of these material impairments; and 
(3) whether the proposed rules would substantially reduce those risks.
    The statutory criteria for evaluating the health evidence do not 
require MSHA and NIOSH to wait for absolute certainty and precision. 
MSHA and NIOSH are required to use the ``best available evidence'' 
(section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)). The 
need to evaluate risk does not mean that an agency is placed

[[Page 42087]]

into a ``mathematical straightjacket.'' See Industrial Union 
Department, AFL-CIO v. American Petroleum Institute, 448 U.S. 607, 100 
S.Ct 2844 (1980), otherwise known as the ``Benzene'' decision. 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).

    We have taken steps in our quantitative risk assessment to conduct 
a balanced analysis using available data. Some of our assumptions were 
conservative, while others were not.\13\
---------------------------------------------------------------------------

    \13\ In the context of the field of risk assessment, a 
``conservative'' assumption is one that results in an estimate of 
more protection for workers than a less conservative assumption 
would. Therefore, estimated benefits are greater under assumptions 
that are ``conservative'' in this sense.
---------------------------------------------------------------------------

    In identifying the number and percentage of MMUs exhibiting a 
pattern of recurrent overexposures on individual shifts we choose to 
include only those MMUs with two or more 1999-operator bimonthly 
samples in excess of the applicable standard, rather than the 
population of MMUs with any overexposures.\14\ Also, the quantitative 
risk assessment estimates of reduction in risk are averages across MMUs 
exhibiting a pattern of recurrent overexposures. For those miners who 
work at mines exhibiting a pattern of recurrent overexposures which 
differs from the one applied in the Quantitative Risk Assessment, their 
reduction in risk would be more than or less than the expected average, 
depending on whether or not their overexposures are at a higher or 
lower than average rate and intensity.
---------------------------------------------------------------------------

    \14\ By ``exhibiting a pattern of recurrent overexposures,'' 
means that, at a 95-percent confidence level, the applicable 
standard is exceeded on at least six shifts per year.
---------------------------------------------------------------------------

    Another important decision impacting choice in this risk assessment 
involves the use of the traditional coal miner work schedule of 8-hours 
per day, 5-days per week, 48-weeks per year. Many of today's miners 
work longer hours per day, month, and year than the traditional work 
schedule. These longer work hours increase miners' cumulative exposure 
to respirable coal mine dust beyond the parameters of exposure used in 
our estimates of risk. Even so, to the extent that a proportion of 
miners may have a more limited work schedule (and occupational 
exposure), either in number of years, weeks per year, or hours per 
week, their expected health benefit would have to be adjusted downward, 
all other variables being constant.
    Also, because of heavy, physical work, some miners may work at 
ventilatory rates in excess of the above-cited 10 cubic meters per 8-
hour shift; an estimate of this ventilatory rate is 13.5 cubic meters 
per 8-hour shift (ICRP, 1994). The sub-population of miners with higher 
breathing rates would inhale more respirable coal mine dust than would 
otherwise occur given the same environmental exposures, thereby 
increasing their risks for the development of simple CWP and PMF.
    In the Quantitative Risk Assessment, to estimate average reduction 
in exposure, we chose the best available data sets: 1999 operator 
bimonthly samples for D.O.s and N.D.O.s., respectively. Currently, both 
operator bimonthly and inspector samples \15\ may be taken on 
production shifts that may not reflect typical production levels.\16\ 
Although other factors may mediate the amount of airborne respirable 
dust such as, ventilation and water sprays, on average, higher 
production is correlated with increased quantities of airborne 
respirable coal mine dust (Webster, et al., 1990; Haney, et al., 1993; 
Green, et al., 1994). Some previous commenters and the Dust Advisory 
Committee have alleged that operators tend to reduce production and/or 
increase dust controls on sampled shifts. Based on MSHA's and NIOSH's 
experience and expertise, and previous comments, we believe the 
production levels observed on sampling shifts are indeed lower than 
typical (See discussion in Benefits section). We also believe at some 
MMUs, more engineering controls at higher levels of efficacy are used 
during sampling shifts than on the majority of shifts (See discussion 
in Benefits section). Thus, it is reasonable to conclude that the 
number of MMUs exhibiting a pattern of recurrent overexposures is 
greater than the 704 captured in this Quantitative Risk Assessment. 
Furthermore, the severity and rate of overexposures to respirable coal 
mine dust among the 704 MMUs exhibiting a pattern of recurrent 
overexposures are probably also greater than we have estimated. We have 
derived our best estimate of the risk reduction using the best 
available data. Yet due to limitations in these data, we believe that 
we have underestimated the magnitude and frequency of typical 
respirable coal mine exposures. To the extent that our values 
underestimate the true reduction in respirable coal mine dust 
exposures, we have underestimated the benefits of these rules.
---------------------------------------------------------------------------

    \15\ Valid MSHA inspector samples require production to be at 
least 60-percent of the average production for the last 30-days. 
Valid operator bimonthly samples must be taken on a normal 
production shift (i.e., a production shift during which the amount 
of material produced in a MMU is at least 50 percent of the average 
production reported for the last set of five valid samples) (30 CFR 
70.101).
    \16\ Therefore assuming representative operating conditions on 
these shifts, in our QRA the results were extrapolated to all 
production shifts, including those that were not sampled, at those 
same 704 MMUs.
---------------------------------------------------------------------------

    Other aspects of our risk assessment methodology reflect more 
conservative choices including the selection of an occupational 
lifetime of 45-years. Various factors may affect the consistency of the 
type and duration of jobs miners hold and hence their associated 
cumulative exposure levels. For example, some miners who lose their 
jobs upon mine closure are employed by other mines, sometimes in less-
exposed jobs. Some miners may chose to move from job to job over their 
careers at underground coal mines, sometimes preferring positions away 
from the mining face. Moreover, if the trend of increasing 
mechanization continues, there will be fewer miners, and for some of 
them, their occupational lifetimes will be shorter.
    For reasons already explained, we believe these choices are 
appropriate for this risk assessment. We also recognize that use of the 
most conservative approach at every step of the risk assessment 
analysis could produce mathematical risk estimates which, because of 
the additive effect of multiple conservative assumptions, may overstate 
the likely risk. We believe this QRA for simple CWP and PMF strikes a 
reasonable balance based on available data. To the extent that we may 
have underestimated the magnitude of overexposures which would be 
prevented, we believe the actual benefits to be greater than we have 
estimated.
    It should be noted that reductions in the prevalence of simple CWP 
and PMF attributable to eliminating individual shift overexposures are 
not expected to materialize immediately after the overexposures have 
been substantially reduced or eliminated. Because these diseases 
typically arise after many years of cumulative exposure, allowing for a 
period of latency, the beneficial effects of reducing exposures are 
expected to become evident only after a sufficient time has passed that 
the reduction in cumulative exposure could have its effect. The total 
realized benefits would not be fully evident until after the youngest 
of today's underground coal miners retire.
    Finally, even standing alone without simultaneously requiring that 
mine

[[Page 42088]]

operators verify the effectiveness of their mine ventilation plans, the 
proposed standard allowing MSHA to use single, full-shift samples to 
identify overexposures requiring corrective action would provide miners 
with health benefits (See detailed discussion in Quantitative Risk 
Assessment). Both the prospect of being cited for overexposures and 
actual issuance of additional citations due to this rule would serve to 
compel mine operators to be more attentive to the level of respirable 
dust in their mines. Therefore, it is reasonable to expect, over time, 
a further decline in the number of shifts during which the 
concentration of respirable coal mine dust is at or above the 
applicable standard. Thus, the use of full-shift single samples will in 
and of itself, on average, lower miners' cumulative exposure to 
respirable coal mine dust. Since cumulative exposure to respirable coal 
mine dust is the main determinant in the development of both simple CWP 
and PMF, the Agencies are confident that the use of single, full-shift 
samples, by itself, and even without the impact of a verified dust 
control plan, would result in better health protection to miners 
(Jacobsen, et al., 1977; Hurley, et al., 1987; Kuempel, et al., 1995; 
Attfield and Morring, 1992; Attfield and Seixas, 1995).
    While there may be some concern from mine operators that the use of 
single, full-shift samples could dramatically increase the number of 
MSHA citations for overexposure to respirable coal mine dust, MSHA's 
1998 Interim Single-Sample Enforcement Policy (ISSEP) has demonstrated 
that mine operators can maintain coal mine dust concentrations at or 
below the applicable standard.
    As discussed in greater detail later in this notice, under ISSEP 
(May 7, 1998-September 9, 1998), of the 1,662 MMUs sampled, 182 or 11 
percent were cited and only 14 of the 4,600 surface entities sampled 
were found to be out of compliance.
    The anticipated increase in MSHA citations due to the use of single 
full-shift sampling would be the result of identifying overexposures 
which the current method of sampling masks due to the averaging of 
samples. Such overexposures and their prospective medical impact on the 
health of miners has been the subject of a Federal Mine Safety and 
Health Review Commission case which was affirmed by the Court of 
Appeals. Consolidation Coal Co. v. Secretary of Labor, 5 FMSHRC 378 
(March 1983), aff'd, 8 FMSHRC 890 (June 1986), 824 F.2d 1071 (D.C. Cir. 
1987).
    In affirming an MSHA citation designated as ``significant and 
substantial'' under Section 104(a) of the Mine Act based on a mine 
operator's bimonthly dust samples which had an average concentration of 
respirable dust of 4.1 milligrams per cubic meter of air, the 
Commissioner quoted the administrative law judge who explained in 
detail the potentially damaging health effects of respirable coal mine 
dust:

    It is clear that the exposure covered by the dust samples which 
resulted in the citation herein in itself would neither cause nor 
significantly contribute to chronic bronchitis or coal workers 
pneumoconiosis. It is also clear that longer exposure to the same 
dust levels can in a significant number of instances cause or 
significantly contribute to chronic bronchitis or to coal workers 
pneumoconiosis. There is no question that chronic bronchitis and 
coal workers' pneumoconiosis are illnesses ``of a reasonably serious 
nature.'' There is no question that each unit of exposure time is 
important in contributing to the disease. I think it would be 
illogical and unrealistic to hold that a serious disease results 
from a long series of insignificant and unsubstantial exposures. Dr. 
Hodous testified that the disease results from ``an aggressive 
accumulation of dust and every drop in the bucket hurts.'' How much 
the drop will hurt may depend in part on the status of the bucket 
when the drop falls. If the bucket is full or nearly full, the drop 
may cause it to overflow. If a miner has worked 20 or 30 years in an 
underground coal mine, a 2 month exposure to excessive dust may be 
enough to cause the first signs of coal workers' pneumoconiosis, or 
to transform simple pneumoconiosis to a complicated form of the 
disease and possibly lead to progressive massive fibrosis. If the 
bucket is empty when the drop falls, in itself it won't mean much. 
If the miner exposed to excessive dust for a 2-month period is a new 
miner with healthy lungs, he probably will not be adversely 
affected, if his exposure stops. But if the exposure continues for 
20 years (six 2-month periods each year), that miner too will be at 
risk to contract black lung.
    I conclude that every drop in the bucket, every two month 
sampling period where excessive dust is present, significantly and 
substantially contributes to a health hazard--the hazard of 
contracting chronic bronchitis or coal workers' pneumoconiosis. 
(emphasis added)

Consolidation Coal, 5 FMSHRC at 389-90 (citations omitted) (footnotes 
omitted). See also Consolidation Coal, 8 FMSHRC at 897 (``There is no 
dispute, however, that overexposure to respirable dust can result in 
chronic bronchitis and pneumoconiosis.'') and Consolidation Coal, 824 
F.2d at 1086 (using the legislative history of the Mine Act and the 
administrative law judge's ``drop in the bucket'' analogy to strike 
down the mine operator's argument that ``no single violation of the 
respirable dust standard could ever be designated as significant and 
substantial.'').
    While Consolidation Coal, supra, dealt with overexposures 
identified under the operator sampling program, it is obvious that 
overexposures identified from the MSHA inspector sampling program 
similarly affect a miner's cumulative exposure to respirable coal mine 
dust.
    Thus, the same analogy would apply to overexposures identified 
through single, full-shift exposures. MSHA and NIOSH firmly believe 
that noncompliance determinations based on single, full-shift 
measurement will improve working conditions for miners because mine 
operators will be compelled either to implement and maintain more 
effective dust controls to minimize the chances of being found in 
noncompliance by an MSHA inspector, or to take corrective actions to 
lower those dust concentrations that are shown to be in excess of the 
applicable standard.
    To the extent that the use of single, full-shift samples reduce a 
miner's cumulative exposure to respirable coal mine dust, as compared 
to the current method of dust sampling, it reduces a miner's risk of 
developing occupational respiratory disease. The proposed mandatory 
standard would provide for fewer drops in each miner's exposure bucket. 
The health benefit that each miner receives from this rule will vary 
depending on ``how full their bucket is'' when the rule is implemented 
as well as other mediating factors, such as the percentage of quartz 
and rank of the coal.
    Yet, all miners, irrespective of their cumulative exposure to 
respirable coal mine dust, would benefit by having fewer drops (i.e., 
shifts with overexposures to respirable coal mine dust) placed in their 
buckets over the course of each miner's working life because this 
reduction would reduce their occupational hazard--the risk of 
developing simple CWP or PMF. Therefore, the Agencies reiterate that 
health benefits would accrue to miners due to single, full-shift sample 
rule alone even in the absence of a regulatory requirement for a 
verified dust control plan at each underground coal mine.

X. Issues Regarding Accuracy of a Single, Full-shift Measurement

    Some previous commenters questioned the accuracy of single, full-
shift measurements, and challenged the Secretaries' assessment of 
measurement accuracy. Some commenters questioned the Secretaries' 
interpretation of section 202(b) of the Mine Act (30 U.S.C.

[[Page 42089]]

842(b)), while others agreed with the interpretation. The following 
issues were generally raised: The measurement objective as defined by 
the Mine Act; the definition of the term ``accurately represent'', as 
used in section 202(f) (30 U.S.C. 842(f)); the validity of the sampling 
process; measurement uncertainty and dust concentration variability; 
and the accuracy of a single, full-shift measurement.

A. Measurement Objective

    Some previous comments reflected a general misunderstanding of what 
the Secretaries intend to measure with a single, full-shift 
measurement, i.e., the measurement objective. For example, some 
previous commenters asserted that the dust concentration that should be 
measured is dust concentration averaged over a period greater than a 
single shift. Some previous commenters noted that dust concentrations 
can vary during a shift and that dust concentrations are not uniform 
throughout a miner's work area. In order to clarify the intent of the 
Secretaries, the explanation that follows describes the elements of the 
measurement objective and how the measurement objective relates to the 
requirements of section 202(f).
    To evaluate the accuracy of a dust sampling method, it is necessary 
to specify the airborne dust to be measured, the time period to which 
the measurement applies, and the area represented by the measurement. 
Once specified, these items can be combined into a measurement 
objective. The measurement objective represents the goal of the 
sampling and analytical method to be utilized.
1. The Airborne Dust to be Measured
    Section 202(f) of the Mine Act (30 U.S.C. 842(f)) states that 
``average concentration'' means

    * * * a determination [i.e., measurement] which accurately 
represents the atmospheric conditions with regard to respirable dust 
to which each miner in the active workings of a mine is exposed * * 
*

The phrase ``atmospheric conditions'' is used to refer to the 
concentration of respirable dust. Therefore, the airborne dust to be 
measured is respirable dust. Section 202(e) defines the concentration 
of respirable dust as the dust measured by an approved device.
2. Time Period to Which the Measurement Applies
    Section 202(b)(2) provides that each mine operator ``* * * shall 
continuously maintain the average concentra tion of respirable dust in 
the mine atmosphere during each shift to which each miner *; * * is 
exposed'' at or below the applicable standard. In section 202(f) 
``average concentration'' is defined as an atmospheric condition 
measured ``over a single shift only, unless * * * such single shift 
measurement will not, after applying valid statistical techniques, 
accurately represent such atmospheric conditions during such shift.''
    Some previous commenters argued that Congress intended that the 
measurement objective be a long-term average. Specifically, some of 
these commenters stated that because coal dust exposure is related to 
chronic health effects, the exposure limit should be applied to dust 
concentrations averaged over a miner's lifetime. These commenters 
identified the measurement objective as being the dust concentration 
averaged over a long, but unspecified, term and argued that a single, 
full-shift measurement cannot accurately estimate this long-term 
average.
    If the objective of section 202(b) were to estimate dust 
concentration averaged over a lifetime of exposure, then the 
Secretaries would agree that a single, full-shift sample, or even 
multiple samples collected during a single inspection, would not 
provide the basis for an accurate measurement. Section 202(b) of the 
Mine Act (30 U.S.C. 842(b)), however, does not mention long-term 
averaging, rather it explicitly requires that the average dust 
concentration be continuously maintained at or below the applicable 
standard during each shift (emphasis added). Furthermore, in 
Consolidation Coal Company v. Secretary of Labor 8 FMSHRC 890, (1986), 
aff'd 824 F.2d 1071, (D.C. Cir. 1987), the Commission found that each 
episode of a miner's overexposure to respirable dust significantly and 
substantially contributes to the health hazard of contracting chronic 
bronchitis or coal workers' pneumoconiosis, diseases of a fairly 
serious nature.
    If exposure is limited on each shift, then this will ensure that a 
miner's total lifetime exposure will not be excessive. In the context 
of the proposed finding, the Secretaries have determined that 
``atmospheric conditions'' means the fluctuating concentration of 
respirable coal mine dust during a single shift. These are the 
atmospheric conditions to which a miner at the sampling location would 
be exposed. Therefore, the proposed finding pertains only to the 
accuracy in representing the average of the fluctuating dust 
concentration over a single shift.
3. Area Represented by the Measurement
    The Mine Act gives the Secretary of Labor the discretion to 
determine the area to be represented by respirable dust measurements 
collected over a single shift. Section 202(a) of the Mine Act (30 
U.S.C. 842(a)) refers to ``the amount of respirable dust in the mine 
atmosphere to which each miner in the active workings of such mine is 
exposed'' measured ``* * * at such locations * * *'' as prescribed by 
the Secretary of Labor. It is sufficient for the purposes of the Mine 
Act that the sampler unit accurately represent the amount of respirable 
dust at such locations only. As articulated by the United States Court 
of Appeals for the 10th Circuit in American Mining Congress (AMC) v. 
Marshall, 671 F.2d 1251 (1982), the Secretary of Labor may place the 
sampler unit in any area or location ``* * * reasonably calculated to 
prevent excessive exposure to respirable dust.''
    Some previous commenters submitted evidence that dust 
concentrations can vary significantly near the mining face, and that 
these variations may extend into areas where miners are located. That 
is, the average dust concentration over a full shift is not identical 
at every point within a miner's work area. These commenters submitted 
several bodies of data purporting to show significant discrepancies 
between simultaneous dust concentration measurements collected within a 
relatively small distance of one another. Several previous commenters 
maintained that the measurement objective is, or should be, to 
accurately measure the average concentration within some arbitrary 
sphere about the head of the miner, and that multiple measurements 
within this sphere are necessary to obtain an accurate measurement.
    The Secretaries recognize that dust concentrations in the mine 
environment can vary from location to location, even within a small 
area near a miner. As mentioned earlier, the Mine Act does not specify 
the area that the measurement is supposed to represent, and the sampler 
unit may therefore be placed in any location, reasonably calculated to 
determine excessive exposure to respirable dust.
    Because the Secretary of Labor intends to prevent excessive 
exposures by limiting dust concentrations at every location in the 
active workings, it is sufficient that each measurement accurately 
represent the respirable dust concentration at the corresponding 
sampling location only. Limiting the dust concentration at every such 
location ensures that no miner in the

[[Page 42090]]

active workings will be exposed to excessive respirable dust.
    Several previous commenters suggested that the measurement 
objective should be a miner's ``true exposure'' or what the miner 
actually inhales. The Secretaries do not intend to use a single, full-
shift measurement to estimate any miner's ``true exposure,'' because no 
sampling device can exactly duplicate the particle inhalation and 
deposition characteristics of a miner at any work rate (these 
characteristics change with work rate), let alone at the various work 
rates occurring over the course of a shift. Limiting the respirable 
dust concentration at every location in the active workings to which 
miners are exposed ensures that the respirable dust concentration 
actually inhaled by any miner is limited.
4. Justification for the Proposed Measurement Objective
    A number of previous commenters identified the dust concentration 
to be estimated as either the mean dust concentration over some period 
greater than an individual shift, the mean dust concentration over some 
spatially distributed region of the mine, or a ``grand mean'' 
consisting of some combination of the above. These comments were based 
on the premise that the measurement objective should be something other 
than the average atmospheric conditions during a single shift at the 
sampling location. It is true that the mean quantities described by 
some commenters cannot accurately be estimated using a single, full-
shift measurement, but the Secretaries make no claim of doing so, nor 
do they believe that a broader measurement objective would be desirable 
for enforcement purposes.
    The Secretaries believe that MSHA's proposed use of single, full-
shift samples for enforcement purposes would eliminate an important 
source of sampling bias due to averaging, as explained in Appendix A. 
Under MSHA's existing enforcement procedures, measurements made at the 
dustiest occupational locations or during the dustiest shifts sampled 
are diluted by averaging them with measurements made under less dusty 
conditions. This practice has frequently caused failures to cite clear 
cases of excessive dust concentration. Therefore, the Secretaries 
believe that enforcement based on averaging does not provide miners 
with the greatest level of protection possible under the current 
exposure limit for respirable coal mine dust.
    Some previous commenters proposed that MSHA continue to average at 
least five separate measurements prior to making a noncompliance 
determination. They stated that abandoning this practice would reduce 
the accuracy of noncompliance determinations. Several of these 
commenters maintained that the average of dust measurements obtained at 
the same occupational location on different shifts more accurately 
represents dust exposure to a miner than a single, full-shift 
measurement. These commenters argued that not averaging measurements 
would reduce accuracy to unacceptable levels.
    Other previous commenters agreed with MSHA and NIOSH that the 
averaging of multiple samples can dilute and mask specific instances of 
overexposure. Some of these commenters stated that averaging not only 
distorts the estimate of dust concentration applicable to individual 
shifts, but also biases the estimate of exposure levels over a longer 
term. According to these commenters, this is because dust control 
measures and work practices affecting dust concentrations are 
frequently modified in response to the presence of an MSHA inspector 
over more than a single shift. These commenters argued that the 
presence of the MSHA inspector causes the mine operator to be more 
attentive to dust control than normal.
    Section 202(b) of the Mine Act currently requires each mine 
operator to ``continuously maintain the average concentration of 
respirable dust in the mine atmosphere during each shift to which each 
miner is exposed'' at or below the applicable standard. The greater the 
variation in mining conditions from shift to shift, the less likely it 
is that a multi-shift average will reflect the average dust 
concentration to which a miner is exposed on any individual shift. 
Appendix A contains further discussion of this issue.
    Accordingly, the Secretaries would define the measurement objective 
to be the accurate determination of the average concentration of 
respirable dust at a sampling location over a single shift.

B. Accuracy Criterion

    A ``single shift measurement'' means the calculated dust 
concentration resulting from a valid single, full-shift sample of 
respirable coal mine dust. In reviewing the various issues raised by 
previous commenters, the Agencies found that the term ``accurately 
represent,'' as used in section 202(f) (30 U.S.C. 842(f)) in connection 
with a single shift measurement, was not defined in the Mine Act. 
Therefore, on March 12, 1996, (61 FR 10012), the Secretaries proposed 
to apply an accuracy criterion developed and adopted by NIOSH in 
judging whether a single, full-shift measurement will ``accurately 
represent'' the full-shift atmospheric dust concentration. The NIOSH 
Accuracy Criterion requires that measurements come within 25 percent of 
the corresponding true dust concentration at least 95 percent of the 
time (Kennedy, et al., 1995). MSHA and NIOSH again are proposing to use 
the NIOSH Accuracy Criterion.
    One previous commenter opposed the application of the NIOSH 
Accuracy Criterion since it ignores environmental variability. For 
reasons explained above, the Secretaries have restricted the 
measurement objective to an individual shift and sampling location. 
Therefore, environmental variability beyond what occurs at the sampling 
location on a single shift would not be relevant to assessing 
measurement accuracy.
    For over 20 years, the NIOSH Accuracy Criterion has been used by 
NIOSH and others in the occupational health professions to validate 
sampling and analytical methods. This accuracy criterion was devised as 
a goal for the development and acceptance of sampling and analytical 
methods capable of generating reliable exposure data for contaminants 
at or near the Occupational Safety and Health Administration's (OSHA) 
permissible exposure limits.
    OSHA has frequently employed a version of the NIOSH Accuracy 
Criterion when issuing new or revised single substance standards. For 
example, OSHA's benzene standard provides: ``[m]onitoring shall be 
accurate, to a confidence level of 95 percent, to within plus or minus 
25 percent for airborne concentrations of benzene'' (29 CFR 
1910.1028(e)(6)). Similar wording can be found in the OSHA standards 
for vinyl chloride (29 CFR 1917), arsenic (29 CFR 1918), lead (29 CFR 
1925), 1,2-dibromo-3-chloropropane (29 CFR 1044), acrylonitrile (29 CFR 
1045), ethylene oxide (29 CFR 1047), and formaldehyde (29 CFR 1048). 
Note that for vinyl chloride and acrylonitrile, the accuracy criterion 
for the method is 35 percent at 95 percent confidence at 
the permissible exposure limit.
    Some previous commenters contended that the NIOSH Accuracy 
Criterion does not conform with international standards recently 
adopted by the European Committee for Standardization (CEN) (European 
Standard No. EN 482, 1994). Contrary to these assertions, the NIOSH 
Accuracy Criterion not only conforms to the CEN criterion but is, in 
fact, more stringent.

[[Page 42091]]

The CEN criterion requires that 95 percent of the measurements fall 
within 30 percent of the true concentration, compared to 
25 percent under the NIOSH criterion. Consequently, any 
sampling and analytical method that meets the NIOSH Accuracy Criterion 
will also meet the CEN criterion. Furthermore, EN 482 imposes no 
control over inaccuracy in the measurement of sampling and analytical 
accuracy itself.
    The NIOSH Accuracy Criterion is relevant and widely recognized and 
accepted in the occupational health professions. Further, previous 
commenters proposed no alternative criteria for accuracy. Accordingly, 
for purposes of section 202(f) of the Mine Act (30 U.S.C.842(f)), the 
Secretaries would consider a single, full-shift measurement to 
``accurately represent'' atmospheric conditions at the sampling 
location, if the sampling and analytical method used meets the NIOSH 
Accuracy Criterion.
    Several commenters suggested that method accuracy should be 
determined under actual mining conditions rather than in a laboratory 
or in a controlled environment. Although the NIOSH Accuracy Criterion 
does not require field testing, it recognizes that field testing ``does 
provide further test of the method.'' However, in order to avoid 
confusing real differences in dust concentration with measurement 
errors when testing is done in the field, ``precautions may have to be 
taken to ensure that all samplers are exposed to the same 
concentrations'' (Kennedy, et al., 1995). Similarly, the CEN criterion 
for method accuracy specifies that ``testing of a procedure shall be 
carried out under laboratory conditions.'' (European Standard No. EN 
482, 1994)
    To determine, so far as possible, the accuracy of its sampling and 
analytical method under actual mining conditions, MSHA conducted 22 
field tests in an underground coal mine. To provide a valid basis for 
assessing accuracy, 16 sampler units were exposed to the same dust 
concentration during each field test using a specially designed 
portable chamber. The data from these field experiments were used by 
NIOSH in its ``direct approach'' to determining whether or not MSHA's 
method meets the long-established NIOSH Accuracy Criterion. (See 
section X.E.2. of this notice).
    In response to the March 12, 1996 notice, a commenter claimed that 
the supplementary information and analyses introduced into the public 
record by that notice addressed the precision of a single, full-shift 
measurement rather than its accuracy. According to this commenter, by 
focusing on precision, important sources of systematic error had been 
overlooked. The Secretaries agree with the comment that precision is 
not the same thing as accuracy. The accuracy of a measurement depends 
on both precision and bias (Kennedy, et al., 1995). Precision refers to 
consistency or repeatability of results, while bias refers to a 
systematic error that is present in every measurement. Since the NIOSH 
Accuracy Criterion requires that measurements consistently fall within 
a specified percentage of the true concentration, the criterion covers 
both precision and uncorrectable bias.
    Since the amount of dust present on a filter capsule used by an 
MSHA inspector is measured by subtracting the pre-exposure weight from 
the post-exposure weight, any bias present in both weight measurements 
is mathematically canceled out by subtraction. Furthermore, as will be 
discussed later, a control (i.e., unexposed) filter capsule has been 
and would continue to be pre- and post-weighed along with the exposed 
filter capsules. The weight gain of the exposed capsule would be 
adjusted by the weight gain or loss of the control filter capsule. 
Therefore, any bias that may be associated with differences in pre-and 
post-exposure laboratory conditions, or with changes introduced during 
storage and handling of the filter capsules would also be 
mathematically canceled out. Moreover, the concentration of respirable 
dust is effectively defined by section 202(e) of the Mine Act (30 
U.S.C. 842(e)) and the implementing regulations in 30 CFR parts 70, 71, 
and 90 to be whatever is measured with an approved sampler unit after 
multiplication by the MRE-equivalent conversion factor prescribed by 
the Secretary of Labor. Therefore, the Secretaries would conclude that 
the improved sampling and analytical method is statistically unbiased. 
This means that such measurements contain no systematic error. It 
should also be noted that since any systematic error would be present 
in all measurements, measurement bias would not be reduced by making 
multiple measurements. Other comments regarding measurement bias are 
addressed in Appendix B.
    For unbiased sampling and analytical methods, a standard 
statistic--called the coefficient of variation (CV)--is used to 
determine if the method meets the NIOSH Accuracy Criterion. The CV, 
which is expressed as either a fraction (e.g., 0.05) or a percentage 
(e.g., 5 percent), quantifies measurement accuracy for an unbiased 
method. An unbiased method meets the NIOSH Accuracy Criterion if the 
``true'' CV is no more than 0.128 (12.8 percent). However, since it is 
not possible to determine the true CV with 100-percent confidence, the 
NIOSH Accuracy Criterion contains the additional requirement that there 
be 95-percent confidence that measurements by the method will come 
within 25 percent of the true concentration 95 percent of the time. 
Stated in mathematically equivalent terms, an unbiased method meets the 
NIOSH Accuracy Criterion if there is 95-percent confidence that the 
true CV is less than or equal to 0.128 (12.8 percent).

C. Validity of Sampling Process

    A single, full-shift measurement of respirable coal mine dust is 
obtained with an approved sampler unit, which is either worn or carried 
by the miner directly to and from the sampling location and remains 
operational during the entire shift or for eight hours, whichever time 
is less. A portable, battery-powered pump draws dust-laden mine air at 
a flow rate of 2 liters per minute (L/min) through a 10-mm nylon 
cyclone, a particle-size selector that removes non-respirable particles 
from the airstream. Non-respirable particles tend to be removed from 
the airstream by the nose and upper respiratory airways. Such particles 
fall to the bottom of the cyclone body called the ``grit pot,'' while 
smaller, respirable particles (of the size that would normally enter 
into the lungs) pass through the cyclone, directly into the inlet of 
the filter cassette. This airstream is directed through the pre-weighed 
filter leaving the particles deposited on the filter surface. This 
collection filter is enclosed in an aluminum capsule to prevent leakage 
of sample air around the filter and the loss of any dust dislodged due 
to impact. The filter capsule is sealed in a protective plastic 
enclosure, called a cassette, to prevent contamination. After 
completion of sampling, the filter cassette is sent to MSHA's 
Respirable Dust Processing Laboratory in Pittsburgh, Pennsylvania, 
where it is weighed to determine the weight gain in milligrams or the 
amount of dust collected on the filter surface. The concentration of 
respirable dust, expressed as milligrams per cubic meter (mg/m3) of 
air, is determined by dividing the observed weight gain by the volume 
of mine air passing through the filter and then multiplying this 
quantity by a conversion factor (discussed in Appendix B) prescribed by 
the Secretaries.
    Some previous comments generally addressed the quality and 
reliability of the equipment used for sampling.

[[Page 42092]]

Specific concerns were expressed about the quality of filter cassettes 
and the reliability of sampling pumps used by MSHA inspectors, due to 
their age and condition. Other commenters questioned the effect of 
sampling and work practices on the validity of a sample.
    The validity of the sampling process is an important aspect of 
maintaining accurate measurements. Since passage of the Coal Act, there 
has been an ongoing effort by MSHA and NIOSH to improve the accuracy 
and reliability of the entire sampling process. In 1980, MSHA issued 
new regulations revising sampling, maintenance and calibration 
procedures in 30 CFR parts 70, 71, and 90. These regulatory provisions 
were designed to minimize human and mechanical errors and ensure that 
samples collected with approved sampler units in the prescribed manner 
would accurately represent the full-shift, average atmospheric dust 
concen tration at the location of the sampler unit. These provisions 
require: (1) Certification of competence of all individuals involved in 
the sampling process and in maintaining the sampling equipment; (2) 
calibration of each sampler unit at least every 200 hours; (3) 
examination, testing, and maintenance of units before each sampling 
shift to ensure that the units are in proper working order; and (4) 
checking of sampler units during sampling to ensure that they are 
operating properly and at the proper flow rate. In addition, 
significant changes, such as robotic weighing and the use of electronic 
balances were made in 1984, 1994, and 1995 that improved the 
reliability of sample weighings at MSHA's Respirable Dust Processing 
Laboratory. These changes are discussed below in section X.C.3.
    All of these efforts improved the accuracy and reliability of the 
sampling process since the time of the 1971/1972 proposed and final 
findings. A discussion follows concerning the three elements which 
constitute the sampling process: sampler unit performance, collection 
procedures, and sample processing.
1. Sampler Unit Performance
    In accordance with the provisions of section 202(e) of the Mine Act 
(30 U.S.C. 842(e)), NIOSH administers a comprehensive certification 
process under 30 CFR part 74 to approve dust sampler units for use in 
coal mines. To be approved for use, a sampler unit must meet stringent 
technical and performance requirements governing the quantity of 
respirable dust collected and flow rate consistency over an 8-hour 
period when operated at the prescribed flow rate. As necessary, NIOSH 
also conducts performance audits of approved sampler units purchased on 
the open market to determine if the units are being manufactured in 
accordance with the specifications upon which the approval was issued.
    The system of technical and quality assurance checks currently in 
place is designed to prevent a defective sampler unit from being 
manufactured and made commercially available to the mining industry or 
to MSHA. In the event that these checks identify a potential problem 
with the manufacturing process, established procedures require 
immediate action to correct the problem.
    In 1992, NIOSH approved the use of new tamper-resistant filter 
cassettes with features that enhanced the integrity of the sample 
collected. A backflush valve was incorporated into the outlet of the 
cassette, preventing reverse airflow through the filter cassette, and 
an internal flow diverter was added to the filter capsule, reducing the 
possibility of dust dislodged from the filter surface from falling out 
of the capsule inlet.
    Also, in 1999, based on recent MSHA studies, Kogut, et al. (1999), 
involving the weighing stability of the current filter design and in an 
effort to standardize the manufacturing process, the filter cassette 
manufacturer submitted for NIOSH approval a modification to the current 
design. The change involves replacing the Tyvek'' support pad with a 
stainless steel wheel, similar to the one located on the inlet side of 
the collection filter. A similar modification was incorporated in 
sampling filters employed by OSHA over the past several years. Upon 
NIOSH approval, the new cassette would be used in MSHA inspector 
sampling, thereby improving the stability of sample weights.
    Several previous commenters questioned the quality of the filter 
cassettes used in the sampling program, expressing concern as to 
whether the cassettes always meet MSHA specifications. These concerns 
primarily involve filter-to-foil distance and floppiness of the 
filters, which are manufacturing characteristics specific to filters 
and filter capsules, not related to part 74 performance requirements. 
The Secretaries believe that such characteristics would have no effect 
on the accuracy of a single, full-shift measurement because, unlike the 
part 74 requirements, they would not affect the amount of dust 
deposition.
    Previous commenters also questioned the condition of sampling pumps 
used by MSHA inspectors, stating that many of the pumps are 10 to 20 
years old and are not maintained as well as they could be. They claimed 
that the age and condition of these pumps call into question not only 
whether the sampling equipment could meet part 74 requirements if 
tested, but also the accuracy of the measurement.
    MSHA believes that this concern is unwarranted, since in 1995, MSHA 
replaced all pumps in use by inspectors with new constant-flow pumps 
that incorporate the latest technology in pump design. These pumps 
provide more consistent flow throughout the sampling period. In 
addition to using new pumps, inspection procedures require MSHA 
inspectors to make a minimum of two flow rate checks to ensure that the 
sampler unit is operating properly. A sample is voided if the proper 
flow rate was not maintained during the final check at the conclusion 
of the sampling shift. In fiscal year 1998, only 151 samples or 0.4 
percent of the 37,042 inspector samples processed were voided because 
the sampling pump either failed to operate throughout the entire 
sampling period or failed to maintain the proper flow rate during the 
final check. Units found not meeting the requirements of part 74 are 
immediately repaired, adjusted, or removed from service. Nevertheless, 
MSHA recognizes that as these pumps age, deterioration of the 
performance of older pumps could become a concern. However, there is no 
evidence that the age of the equipment affects its operational 
performance if the equipment is maintained as prescribed by 30 CFR 
parts 70, 71, and 90.
    Some previous commenters suggested that the accuracy of a dust 
sample may be compromised when a miner is operating equipment, due to 
vibration from the machinery. The potential effect of vibration on the 
accuracy of a respirable dust measurement was recognized by NIOSH in 
1981. An investigation, supported by NIOSH, was conducted by the Los 
Alamos National Laboratory which found that vibration has an 
insignificant effect on sampler performance (Gray and Tillery, 1981).
2. Sample Collection Procedures
    MSHA regulations at 30 CFR parts 70, 71, and 90 prescribe the 
manner in which mine operators are to take respirable dust samples. The 
collection procedures are designed to ensure that the samples 
accurately represent the amount of respirable dust in the mine 
atmosphere to which miners are exposed on the shift sampled. Samples 
taken in accordance with these procedures are considered to be valid.

[[Page 42093]]

    Several previous commenters questioned the effects of sampling and 
work practices on the validity of a sample. Instances were cited where 
the sampling unit was accidentally dropped, with the potential for the 
sample to become contaminated. Previous commenters also pointed out 
that work activities requiring crawling, duck walking, bending, or 
kneeling could cause the sampling hose to snag. Such activities could 
also cause the sampling head assembly to be impacted or torn off a 
person's garment, possibly contaminating the sample. These commenters 
stated that sampler units are sometimes treated harshly while being 
worn by miners, mishandled when being transferred from one miner to 
another, or handled casually at the end of a work shift.
    These commenters also maintained that it is impossible for MSHA 
inspectors or mine operators to continuously observe collection of a 
sample in order to ensure its validity, and that, for this reason, the 
reliability and accuracy of the sampling equipment, when used under 
actual mining conditions, is not the same as when tested and certified 
in a laboratory. Averaging multiple samples would, according to these 
commenters, provide some ``leeway'' in the system, by reducing the 
impact of an aberrant sample.
    While MSHA and NIOSH would agree that it is not possible to 
continuously observe the collection of each sample, MSHA inspectors are 
normally in the general vicinity of the sampling location, and 
therefore would have knowledge of the specific conditions under which 
samples are taken. In addition, MSHA inspectors are instructed to ask 
miners wearing the sampler units whether anything that could have 
affected the validity of the sample occurred during the shift. If so, 
the inspector would note this on the data card and request that the 
sample be examined to determine its validity.
    Other previous commenters expressed concern that, if special dust 
control measures are in effect during sampling, a single, full-shift 
measurement may fail to represent atmospheric conditions during shifts 
when samples are not collected. The Secretaries believe that this 
concern is beyond the scope of this new proposal, which, as described 
in the discussion of measurement objective, deals solely with the 
accuracy of a measurement in representing atmospheric conditions on the 
shift being sampled. One previous commenter recommended that MSHA, 
NIOSH, or the Bureau of Mines (now a part of NIOSH) should evaluate the 
need for standardizing the MSHA respirable dust sampling procedures. In 
fact, the procedures for respirable dust sampling have already been 
standardized under the revised 1980 MSHA regulations codified at 30 CFR 
parts 70, 71 and 90.
    As previously mentioned, as part of the ISSEP discussion, MSHA 
inspectors are also using unexposed control filters to eliminate any 
bias that may be associated with day-to-day changes in laboratory 
conditions or introduced during storage and handling of the filter 
capsules. A control filter is an unexposed filter that was pre-weighed 
on the same day as the filter used for sampling. This control filter is 
used to adjust the weight gain obtained on each exposed filter. Any 
change in weight of the control filter is subtracted from the change in 
weight of each exposed filter. MSHA began using control filters on May 
7, 1998, with the implementation of the ISSEP, and has continued this 
practice, even after reverting back to basing noncompliance 
determinations on an average of multiple samples following the ruling 
of the 11th Circuit Court of Appeals discussed earlier. The control 
filter, which is carried by the inspector in a shirt or coverall pocket 
during the sampling inspection, is plugged to prevent exposure to the 
mine environment. The experience gained from the use of control filters 
under ISSEP is discussed in section V.D.
    Also, once NIOSH approves the modified design mentioned earlier, 
MSHA inspectors would use only filters incorporating a stainless steel 
support wheel. These filters, according to MSHA studies, demonstrated 
better weighing stability as compared to filters employing 
Tyvek material for the support pad.
3. Sample Processing
    Sample processing consists of weighing the exposed and control 
(unexposed) filters, recording the weight changes, and examining 
certain samples in order to verify their validity. Sample processing 
also includes electronic transmission of the results to MSHA's MIS 
center where dust concentrations are computed. The results are then 
transmitted to MSHA enforcement personnel and to mine operators.
(a) Weighing and Recording Procedures
    The procedures and analytical equipment, as well as the facility 
used by MSHA to process respirable coal mine dust samples have been 
continuously improved since 1970 to maintain a state-of-the-art 
laboratory. From 1970 to 1984, samples were manually weighed using 
semimicro balances. This process was automated in 1994 with the 
installation of a state-of-the-art robotic system and electronic 
balances, which increased the precision of sample-weight 
determinations. Weighing precision was further improved in 1994, when 
both the robotic system and balances were upgraded. Also, beginning in 
early 1998, all respirable coal mine dust samples were being processed 
in a new, specially designed clean room facility that maintains the 
temperature and humidity of the environment at 72 2 deg.F 
and 50 5%, respectively. Using a modified HEPA filtration 
system, the environment is maintained at a clean room classification of 
1000 (near optimum for clean room cleanliness).
    The full benefit of the 1994 improvements of the weighing system 
for inspector samples was, however, not attained until mid-1995, when 
MSHA implemented two modifications to its procedures for processing 
inspector samples. One modification involved pre- and post-weighing 
filter capsules to the nearest microgram (0.001 mg) within MSHA's 
laboratory. Prior to mid-1995, filters had been weighed in the 
manufacturer's (Mine Safety and Appliances Co.) laboratory before 
sampling, and then in MSHA's laboratory after sampling. MSHA is 
currently pre-weighing all such filters in its own laboratory. To 
maintain the integrity of the weighing process, eight percent of all 
filters are systematically weighed a second time. If a significant 
deviation is found, the balance is recalibrated and all filters with 
questionable weights are reweighed.
    The other modification was to discontinue the practice of 
truncating (to 0.1 mg) the recorded weights used in calculating dust 
concentrations. This means that MSHA is now using all significant 
digits associated with the weighing capability of the balance (0.001mg) 
when processing inspector samples. These modifications improved the 
overall accuracy of the measurement process.
    To eliminate the potential for any bias that may be associated with 
day-to-day changes in laboratory conditions or introduced during 
storage and handling of the filters, MSHA is also using control filters 
in its enforcement program. Any change in the weight of the control 
filter is subtracted from the measured change in weight of the exposed 
filter.\17\
---------------------------------------------------------------------------

    \17\ If a control filter either shows a weight gain greater than 
100 micrograms (g) or a weight loss greater than 30 
g, the control filter is voided and the concentration 
measurement(s) are not used for enforcement purposes.
---------------------------------------------------------------------------

    Since MSHA began pre- and post-weighing filters to the nearest 
g, coal

[[Page 42094]]

mine operators have asked to use filters pre-weighed to a g to 
collect optional samples that they submit to MSHA for quartz analysis. 
The use of these pre-weighed filters would eliminate the need to sample 
multiple shifts in order to obtain sufficient dust mass on the 
collection filter for quartz analysis. Currently, filters used by coal 
mine operators to sample in accordance with 30 CFR parts 70, 71, and 90 
are pre-weighed by the filter manufacturer, Mine Safety Appliances Co., 
to the nearest 10 g. Therefore, only samples taken with 
filters preweighed to the nearest 10 g, with a net weight gain 
of at least 450 g, contain sufficient dust mass to permit the 
percentage of quartz to be determined.
    In 1996, Mine Safety Appliances Company upgraded their equipment 
used to pre-weigh filter capsules and now uses the same balance as 
MSHA's Coal Dust Processing Laboratory, thereby permitting weight 
determinations to be made to the nearest g.
    The requirement that inspector samples be pre- and post-weighed in 
the same laboratory was developed prior to adopting control filters and 
was based on the assumption that no control filters were being used. 
Since use of the control filters adjusts for differences that may exist 
in laboratory conditions on the days of pre- and post-weighing, it is 
no longer necessary to pre- and post-weigh the filters in the same 
laboratory.
    To determine the viability of using exposed filters pre-weighed by 
Mine Safety Appliances Co. and post-weighed by MSHA in establishing the 
percentage of quartz, the Agency conducted a study to quantify weighing 
variability between the Mine Safety Appliances Co. and MSHA 
laboratories (Parobeck, et al., 1997). Based on this study, the overall 
imprecision of an interlaboratory weight-gain measurement was estimated 
to be 11.5 for capsules with a stainless steel filter support pad. This 
estimate closely matches the 11.6 result reported for capsules with 
stainless steel support pads in a more recent study (Kogut, et al., 
1999). In this more recent study, unexposed capsules were pre-weighed 
by MSHA, assembled into cassettes by Mine Safety Appliances Co., sent 
out to the field and carried during an inspection, and then post-
weighed by MSHA.''
    Using the higher of these two estimates, NIOSH has reassessed the 
accuracy of MSHA's improved sampling and analytical method, which 
incorporates a control filter adjustment and employs filter capsules 
with a stainless steel support pad. NIOSH has concluded that the 
control filter adjustment will correct for any potential biases due to 
differences in laboratory conditions, so that it is no longer necessary 
to pre- and post-weigh filter capsules in the same laboratory (Grayson, 
1999b). Therefore, in accordance with NIOSH, MSHA is proposing to 
change the existing processing procedures for inspector samples from 
pre- and post-weighing in the same laboratory (with adjustment by a 
control filter) to pre- and post-weighing of samples to the nearest 
 in different laboratories (with continued adjustment by a 
control filter). The Agencies would welcome comments on this proposed 
change.
    To insure the precision and accuracy of the pre-weight of filters 
used by inspectors, MSHA plans to institute a program to monitor the 
daily production of filters weighed to the nearest g by the 
manufacturer. The program will conform to MIL-STD-105D, which defines 
the criteria currently used to monitor the quality of pre-weighed 
filters used in MSHA's operator sampling program.
(b) Sample Validity Checks
    All respirable dust samples collected and submitted as required by 
30 CFR parts 70, 71, and 90 are considered valid unless the dust 
deposition pattern on the collection filter appears to be abnormal or 
other special circumstances are noted that would cause MSHA to examine 
the sample further. Several previous commenters expressed concern about 
the potential contamination of samples with ``oversized particles.'' 
Such contamination, according to one commenter, can result in 
aberrational weight gains. These commenters noted that current 
procedures do not systematically ensure that samples collected by MSHA 
contain no oversized particles. It was recommended that MSHA analyze, 
for the presence of oversized particles, any dust sample that exceeds 
the applicable dust standard. Also suggested for such an analysis was 
any sample with a weight gain significantly different from other 
samples taken in the same area.
    Standard laboratory procedures, involving visual, and microscopic 
examination as necessary, are used to verify the validity of samples. 
Samples with a weight gain of 1.4 milligrams (g) or more are 
examined visually for abnormalities such as the presence of large dust 
particles (which can occur from agglomeration of smaller particles), 
abnormal discoloration, abnormal dust deposition pattern on the filter, 
or any apparent contamination by materials other than respirable coal 
mine dust. Also examined are samples weighing 0.1 mg or less for 
insufficient dust particle count. Similar checks are also performed in 
direct response to specific inspector or operator concerns noted on the 
dust data card to which each sample is attached.
    The previous commenters' concerns about the contamination of 
samples with oversized particles are based on the assumption that all 
oversized particles, defined as dust particles greater than 10 
micrometers (m) in size, are not respirable and therefore 
should be totally excluded from any sample taken with an approved 
sampler unit. However, it has long been known that some particles 
greater than 10  can be inhaled, and that some of these 
particles can reach the alveoli of the lungs (Lippman and Albert, 
1969). According to the British National Coal Board, ``particles as 
large as 20 microns (i.e. micrometers) mean diameter may be deposited, 
although most ``lung dust'' lies in the range below 10 microns 
diameter'' (Goddard, et al., 1973). Furthermore, it is known that, due 
to the irregular shapes of dust particles, the respirable dust 
collected by the MRE instrument (the dust sampler used by the British 
Medical Research Establishment in the epidemiological studies on which 
the U.S. coal dust standard was based) may include some dust particles 
as large as 20 micrometers (Goddard, et al., 1973). Moreover, MSHA 
studies have shown that nearly all samples taken with approved sampler 
units, even when operated in the prescribed manner, contain some 
oversized particles (Tomb, August 31, 1981). Since section 202(e) of 
the Mine Act (30 U.S.C. 842(e)) defines concentration of respirable 
dust to be that measured by an approved sampler unit, and because the 
approved sampler unit will collect some oversized particles, the 
Secretaries do not consider a sample to be ``contaminated'' because it 
contains some oversized particles.
    The Secretaries recognize that there are occasions when oversized 
particles can properly be considered a contaminant. For example, an 
excessive number of such particles could enter the filter capsule if 
the sampling head assembly is accidentally or deliberately turned 
upside down or ``dumped'' (possibly causing some of the contents of the 
cyclone grit pot to be deposited on the collection filter), if the pump 
malfunctions, or if the entire sampler unit is dropped. When MSHA has 
reason to believe that such contamination has occurred, the suspect 
sample is examined to verify its validity.
    Contrary to the assertions of some previous commenters, checking 
for

[[Page 42095]]

oversized particles is not standard industrial hygiene practice. 
Nevertheless, MSHA checks any dust sample suspected of containing an 
excessive number of oversized particles. MSHA's laboratory procedures 
require any sample exhibiting an excessive weight gain (over 6 mg) or 
showing evidence of being ``dumped'' to be examined for the presence of 
an excessive number of oversized particles (MSHA Method P-4, August 
1989). Samples identified by an inspector or mine operator as possibly 
contaminated are also examined. If this examination indicates that the 
sample contains an excessive number of oversized particles according to 
MSHA's established criteria, then that sample is considered to be 
invalid, is voided and not used. In fiscal year 1998, only one sample 
of the 37,042 inspector samples processed was found to contain an 
excessive number of oversize particles and thus was not used.
    While rough handling of the sampler unit or an accidental mishap 
could conceivably cause a sample with a weight gain less than 6 mg to 
become contaminated, as claimed by some previous commenters, studies 
show that short-term accidental inclinations of the cyclone will not 
affect respirable mass measurements made with currently approved 
sampler units (Treaftis and Tomb, 1974). Sampler units currently used 
are built to withstand the rigors of the mine environment, and are 
therefore less susceptible to contamination than suggested by some 
previous commenters. In any event, the Secretaries believe that the 
validity checks currently in place, as discussed above, would detect 
such samples.

D. Measurement Uncertainty and Dust Concentration Variability

    Overall variability in measurements collected on different shifts 
and sampling locations comes from two sources: (1) Environmental 
variability in the true dust concentration and (2) errors in measuring 
the dust concentration in a specific environment. The major portion of 
overall measurement variability reflects real variability in dust 
concentration on different shifts or at different sampling locations 
(Nicas, et al., 1991).\18\
---------------------------------------------------------------------------

    \18\ Although MSHA and NIOSH accept the finding presented by 
Nicas, et al. (1991) that environmental variability generally 
exceeds analytical variability, the Agencies do not accept the 
authors' conclusions with regard to how this finding should affect 
enforcement policy.
---------------------------------------------------------------------------

    Variability in the dust concentration is under the control of the 
mine operator and does not depend on the degree to which the dust 
concentration can be accurately measured. Measurement uncertainty, on 
the other hand, stems from the differing measurement results that could 
arise, at a given sampling location on a given shift, because of 
potential sampling and analytical errors. Therefore, unlike variability 
in dust concentration, measurement uncertainty depends directly on the 
accuracy of the measurement system. Measurement errors generally 
contribute only a small portion of the overall variability observed in 
datasets consisting of dust concentration measurements.
    Numerous previous commenters identified sources of measurement 
uncertainty and dust concentration variability that they believed 
should be considered when determining whether or not a measurement 
accurately represents such atmospheric conditions. Because the 
measurement objective is to accurately represent the average dust 
concentration at the sampling location over a single shift, it does not 
take into consideration dust concentration variability between shifts 
or locations. Sources of dust concentration variability would not be 
considered by the Secretaries in determining whether a measurement is 
accurate. Consequently, the Secretaries have concluded that the only 
sources of variability relevant to establishing accuracy of a single, 
full-shift measurement for purposes of section 202(f) of the Mine Act 
(30 U.S.C. 842(f)) would be those related to sampling and analytical 
error.
1. Sources of measurement uncertainty
    Filter capsules are weighed prior to sampling. After a single, 
full-shift sample is collected, the filter capsule is weighed a second 
time, and the weight gain (g) is obtained by subtracting the pre-
exposure weight from the post-exposure weight, which will then be 
adjusted for the weight gain or loss observed in the control filter 
capsule. A measurement (x) of the atmospheric condition sampled is then 
calculated by Equation 1:
[GRAPHIC] [TIFF OMITTED] TP07JY00.002

where:

x is the single, full-shift dust concentration measurement (mg/m\3\);
1.38 is a constant MRE-equivalent conversion factor; g is the observed 
weight gain (mg) after adjustment for the control filter capsule; and
v is the estimated total volume of air pumped through the filter during 
a typical full shift.

    The Secretaries recognize that random variability, inherent in any 
measurement process, may cause x to deviate either above or below the 
true dust concentration. The difference between x and the true dust 
concentration is the measurement error, which may be either positive or 
negative. Measurement uncertainty arises from a combination of 
potential errors in the process of collecting a sample and potential 
errors in the process of analyzing the sample. These potential errors 
introduce a degree of uncertainty when x is used to represent the true 
dust concentration.
    The statistical measure used by the Secretaries to quantify 
uncertainty in a single, full-shift measurement is the total sampling 
and analytical coefficient of variation, or CVtotal. The 
CVtotal quantifies the magnitude of probable sampling and 
analytical errors and is expressed as either a fraction (e.g., 0.05) or 
as a percent (e.g., 5 percent) of the true concentration. For example, 
if a single, full-shift measurement (x) is collected in a mine 
atmosphere with true dust concentration equal to 1.5 mg/m\3\, and the 
standard deviation of potential sampling and analytical errors 
associated with x is equal to 0.075 mg/m\3\, the uncertainty associated 
with x would be expressed by the ratio of the standard deviation to the 
true dust concentration: CVtotal = 0.075/1.5 = 0.05, or 5 
percent.
    Based on a review of the scientific literature, the Secretaries in 
their March 12, 1996 notice concerning the NIOSH Accuracy Criterion 
identified three sources of uncertainty in a single, full-shift 
measurement, which together make up CVtotal:
    (a) CVweight--variability attributable to weighing 
errors or handling associated with exposed and control filter capsules. 
This covers any variability in the process of weighing the exposed or 
control filter capsules prior to sampling (pre-weighing), assembling 
the exposed and control filter cassettes, transporting

[[Page 42096]]

the filter cassettes to and from the mine, and weighing the exposed and 
control filter capsules after sampling (post-weighing).
    (b) CVpump--variability in the total volume of air 
pumped through the filter capsule. This covers variability associated 
with calibration of the pump rotameter, \19\ variability in adjustment 
of the flow rate at the beginning of the shift, and variation in the 
flow rate during sampling. It should be noted that variation in flow 
rate during sampling was identified as a separate component of 
variability in MSHA's February 18, 1994, notice. Here, it is included 
within CVpump.
---------------------------------------------------------------------------

    \19\ The rotameter consists of a weight or ``float'' which is 
free to move up and down within a vertical tapered tube which is 
larger at the top than the bottom. Air being drawn through the 
filter cassette passes through the rotameter, suspending the 
``float'' within the tube. The pump is ``calibrated'' by drawing air 
through a calibration device (usually what is known as a bubble 
meter) at the desired flow rate and marking the position of the 
float on the tube. The processes of marking the position on the tube 
(laboratory calibration) and adjusting the pump speed in the field 
so that the float is positioned at the mark are both subject to 
error.
---------------------------------------------------------------------------

    (c) CVsampler--variability in the fraction of dust 
trapped on the filter. This is attributable to physical differences 
among cyclones. This component was introduced in the material submitted 
into the record in September 1994.
    These three components of measurement uncertainty can be combined 
to form an indirect estimate of CVtotal by means of the 
standard propagation of errors formula:
[GRAPHIC] [TIFF OMITTED] TP07JY00.003

    These three components are discussed in greater detail, along with 
responses to specific previous comments, in Appendix B.
2. Sources of Dust Concentration Variability
    Previous commenters also raised issues related to sources of dust 
concentration variability. Some of these commenters maintain that the 
Secretaries should include in CVtotal additional components 
representing the effects of shift-to-shift variability and variability 
related to location (spatial variability). These comments reflect a 
misunderstanding of the measurement objective as intended by the Mine 
Act (see Section X.A. of this notice).
    Exposure variability due to job, location, shift, production level, 
effectiveness of engineering controls, and work practices will be 
different from mine to mine. This type of variability has nothing to do 
with measurement accuracy and depends on factors under the control of 
the mine operator. The sampler unit is not intended to account for 
these factors.
(a) Spatial Variability
    Previous commenters stated that CVtotal should account 
for spatial variability, or the differences in concentration related to 
location. The Secretaries agree that dust concentrations vary between 
locations in a coal mine, even within a relatively small area. However, 
real variations in concentration between locations, while sometimes 
substantial, do not contribute to measurement error. As stated earlier, 
the measurement objective would be to accurately measure average 
atmospheric conditions, or concentration of respirable dust, at a 
sampling location over a single shift.
(b) Shift-to-shift Variability
    Previous commenters stated that CVtotal should take into 
account the differences or variations in dust concentration that occur 
shift to shift. Although the Secretaries would agree that dust 
concentrations vary from shift to shift, the measurement objective is 
to measure average atmospheric conditions on the specific shift 
sampled. This result would be consistent with the Mine Act, which 
requires that concentrations of respirable mine dust be maintained at 
or below the applicable standard during each shift.
3. Other Factors Considered
(a) Proportion of Oversized Particles
    Previous commenters expressed concern that respirable dust cyclones 
are handled in a rough manner in normal use and occasionally turned 
upside down. According to one commenter, this type of handling would 
cause more large particles to be deposited on the filter in the mine 
environment than when used in the laboratory. This commenter knew of no 
data that could be used to evaluate the error associated with such 
occurrences and recommended that a study be commissioned to measure the 
proportion of non-respirable particles on the filters after they are 
weighed to MSHA standards.
    After considering this recommendation, the Secretaries would 
conclude that the available evidence shows that short-term inclinations 
of the cyclone, as might frequently occur during sampling, will not 
affect respirable dust measurements made with approved sampler units 
(Treaftis and Tomb, 1974). The weight of the sampler head assembly 
makes it extremely unlikely that a sampler unit could be turned upside 
down in normal use. Furthermore, with a field study of the type 
recommended, variability in the field measurements due to normal 
handling would be confounded with variability due to real differences 
in atmospheric conditions. Therefore, the Secretaries believe that such 
a study would not be useful in establishing variability in measurements 
due to differences in handling of the sampler unit.
(b) Anomalous Events
    Previous commenters asserted that unpredictable, infrequent events, 
such as a ``face blowout'' on a longwall (a violent expulsion of coal 
together with large quantities of coal dust and/or methane gas) or high 
winds at a surface mine, can cause rapid loading of a filter capsule 
and thereby distort a measurement to show an excessive dust 
concentration based on a single, full-shift sample when, they argue, 
the dust standard had not been exceeded. In fact, if such an occurrence 
were to cause a measurement above the applicable standard, the dust 
standard would be violated. No evidence was previously presented to 
demonstrate that short-term high exposures can overload a dust sampling 
filter or cause the sampling device to malfunction. Nor was evidence 
presented to demonstrate that miners are not also exposed to the same 
high dust concentrations as the sampler unit when such events occur. 
The Secretaries would conclude that such events are results of the 
dynamic and ever-changing mine environment--an environment to which the 
miner is exposed. The sampler unit is designed to measure the 
atmospheric condition at a specific sampling location over a full 
shift. If such events occur, the sampler unit will accurately record 
the atmospheric condition to which it is exposed.

[[Page 42097]]

(c) MRE Conversion Factor Used in the Dust Concentration Calculation
    Several previous commenters questioned the 1.38 MRE-conversion 
factor used in Equation 1. This factor is used to convert a measurement 
obtained with the type of dust sampler unit currently approved for use 
in coal mines to an equivalent concentration as measured with an MRE 
gravimetric dust sampler. The term ``MRE instrument'' is defined in 30 
CFR Sec. 70.2 (i). The conversion factor is necessary because the coal 
mine dust standard was derived from British data collected with an MRE 
instrument, which collects a larger fraction of coal mine dust than 
does the approved dust sampling unit (Tomb, et al., 1973). The 1.38 
constant has been established by the Secretaries as applying to the 
currently approved dust sampler unit described in 30 CFR part 74.
    Some previous commenters contended that variability involved in the 
data analysis used in establishing the conversion factor should be 
taken into account in determining CVtotal. This suggestion 
demonstrates a misunderstanding of the difference between measurement 
imprecision and measurement bias. The 1.38 factor applies to every 
sampler unit currently approved under part 74. Since the same 
conversion factor is applied to every measurement, any error in the 
value used would cause a measurement bias but would have no effect on 
measurement imprecision. Since Congress defined respirable dust in 
section 202(e) of the Mine Act (30 U.S.C. 842(e)) as whatever is 
collected by a currently approved sampler unit, a measurement 
incorporating the 1.38 factor is unbiased by definition. Further 
discussion is provided in Appendix B on why use of the 1.38 factor does 
not introduce a bias. Appendix B also addresses comments relating to 
other aspects of the 1.38 conversion factor; comments regarding the 
fact that MSHA's sampler unit does not conform to other definitions of 
respirable dust; and questions concerning the effect of static charge 
on sampler unit performance.
(d) Reduced Dust Standards
    One commenter pointed out that in estimating CVtotal, MSHA and 
NIOSH did not take into account any potential errors associated with 
silica analysis. The commenter argued that since silica analysis is 
used to establish reduced dust standards, MSHA and NIOSH had failed to 
demonstrate ``* * * accuracy for all samples `across the range of 
possible reduced dust standards.'' '
    This commenter confuses the accuracy of a respirable dust 
concentration measurement with the accuracy of the procedure used to 
establish a reduced dust standard. MSHA has a separate program in which 
silica analysis is used to set the applicable respirable coal mine dust 
standard, in accordance with section 205 of the Mine Act (30 U.S.C. 
845), when the respirable dust in the mine atmosphere of the active 
workings contains more than 5 percent quartz. As shown by Equation 1, 
no silica analysis is used in a single, full-shift measurement of the 
respirable dust concentration. Therefore, the Secretaries would not 
agree with the comment that CVtotal should include a 
component representing potential errors in silica analysis.
(e) Dusty Clothing
    Several previous commenters pointed out that local factors such as 
dusty clothing could cause concentrations in the immediate vicinity of 
the sampler unit to be unrepresentative of a larger area. Dust from a 
miner's clothing nevertheless represents a potential hazard to the 
miner. No evidence was previously presented to demonstrate that miners 
are not also exposed to dust originating from dusty clothing.

E. Accuracy of a Single, Full-shift Measurement

1. Quantification of Measurement Uncertainty
    Several previous commenters argued that MSHA underestimated 
CVtotal in its February 18, 1994 proposed notice of Joint 
Finding and suggested alternative estimates ranging from 16 to 50 
percent. These commenters cited several published studies and submitted 
five sets of data in support of these higher estimates. Statistical 
analyses of the data were also submitted.
    MSHA and NIOSH reviewed all of the studies referenced by the 
previous commenters. The review showed that all of the estimates of 
measurement variability were from studies carried out prior to 
improvements mandated by the 1980 MSHA revisions to dust sampling 
regulations, discussed earlier in ``Validity of the Sampling Process'' 
(see Section X.C.). For example, the General Accounting Office (GAO) 
\20\ and the National Bureau of Standards (NBS, now the National 
Institute of Standards and Technology) studies were conducted in 1975. 
The National Academy of Sciences report, which analyzed the same data 
as the NBS and GAO reports, was issued in 1980. The review further 
showed that the measurement variability quantified in these studies 
included effects of spatial variability--a component of variability the 
Secretaries deliberately exclude when determining the accuracy of a 
sampling and analytical method as discussed in section X.D.2.(a). 
Additionally, since past studies frequently relied on combining 
estimates of variability components obtained from different bodies of 
data, some of them also suffered from methodological problems related 
to combining individual sources of uncertainty. For example, in 1984, a 
NIOSH study identified several conceptual errors in earlier studies 
that had led to double-or even triple-counting of some variability 
components (Bowman, et al., 1984). Although all the data and analyses 
submitted by previous commenters included effects of spatial 
variability, one of these data sets, consisting of paired sample 
results, contained sufficient information to indicate that weighing 
imprecision was less than what MSHA had assumed in its February 18, 
1994 notice. However, without an independent estimate of spatial 
variability applicable to these samples, it is not mathematically 
possible to utilize this data set to estimate variability attributable 
to the sampler unit or the volume of air sampled. A second data set 
consisted only of differences in dust concentration between paired 
samples, making it impossible to use it even for evaluating weighing 
imprecision. The remaining three data sets included effects of shift-
to-shift variability, which, like spatial variability, would not be 
relevant to the measurement objective. Therefore, none of these data 
could be used to estimate overall measurement imprecision. Further 
details are provided in Appendix C.
---------------------------------------------------------------------------

    \20\ Many of the recommendations in the GAO report were later 
adopted and implemented by MSHA.
---------------------------------------------------------------------------

    One of the previous commenters particularly questioned the value 
MSHA used in its February 18, 1994 proposed notice of Joint Finding to 
represent variability in initially setting the pump flow rate. In 
response to this commenter's suggestion, MSHA conducted a study to 
verify the magnitude of this variability component. This study 
simulated flow rate adjustment under realistic operating conditions by 
including a number of persons checking and adjusting initial flow rate 
under various working situations (Tomb, September 1, 1994). Results 
showed the coefficient of variation associated with the initial flow

[[Page 42098]]

rate adjustment to be 3  0.5 percent, which is less than 
the 5-percent value used by MSHA in the February 1994 notice. In 
addition, based on a review of published results, the Secretaries would 
conclude that the component of uncertainty associated with the combined 
effects of variability in flow rate during sampling and potential 
errors in calibration is actually less than 3 percent. As explained in 
Appendix B, these two sources of uncertainty can be combined to 
estimate CVpump. After reviewing the available data and the 
comments submitted, the Secretaries would conclude that the best 
estimate of CVpump is 4.2 percent. Additional details 
regarding CVpump, along with the Secretaries' responses to 
comments, are presented in Appendix B.
    Intersampler variability, represented by CVsampler, 
accounts for uncertainty due to physical differences from sampler to 
sampler. Most of the previous commenters ignored this source of 
uncertainty. As explained in Appendix B, the Secretaries would adopt a 
5-percent estimate of CVsampler.
    To address previous commenters' concerns that the Agencies had 
underestimated CVtotal, MSHA conducted a field study to 
directly estimate the overall measurement precision attainable when 
dust samples are collected with currently approved sampler units and 
analyzed using state-of-the-art analytical techniques. The study 
involved simultaneous field measurements of the same coal mine dust 
cloud using sampling pumps incorporating constant flow technology. 
Using a specially designed portable dust chamber, 22 tests were 
conducted at various locations in an underground coal mine. Each test 
consisted of collecting 16 dust samples simultaneously and at the same 
location. No adjustments in the flow rate were made beyond what would 
routinely have been done by an MSHA inspector.
    Prior to the field study, two modifications to MSHA's sampling and 
analytical method had been considered by MSHA and NIOSH: (1) Measuring 
both the pre-and post-exposure weights to the nearest microgram 
(g) on a balance calibrated using the established procedure 
within MSHA's Respirable Dust Processing Laboratory; and (2) 
discontinuing the practice of truncating the recorded weights used in 
calculating the dust concentration. These modifications were 
incorporated into the design of the field study.
    One previous commenter characterized the field study as being 
``woefully incomplete'' because it was conducted ``in a tightly 
controlled environment * * * not subject to normal environmental 
variation.'' While it is true that the samples within each test were 
not subject to normal environmental variability, this was because the 
experiment was deliberately designed to avoid confusing spatial 
variability in dust concentration with measurement error. However, 
pumps were handled and flow rates were checked in the same manner as 
during routine sampling. Furthermore, the sampler units were 
disassembled and reassembled in the normal manner to remove and replace 
dust cassettes.
    Previous commenters also questioned the value that MSHA used in the 
February 1994 proposed notice of Joint Finding to represent uncertainty 
due to potential weighing errors. In September 1994, MSHA submitted 
into the record an analysis based on replicated weighings for 300 
unexposed filter capsules, each of which was weighed once by the 
cassette manufacturer and twice in MSHA's laboratory (Kogut, May 12, 
1994). An estimate of weighing imprecision derived from this analysis 
was used by NIOSH in its September 20, 1995 assessment of MSHA's 
sampling and analytical procedure (discussed in more detail later in 
section X.E.)
    In the March 12, 1996 notice concerning the NIOSH Accuracy 
Criterion, MSHA described the results of an investigation into repeated 
weighings of the same capsules made over a 218-day period using MSHA's 
automatic weighing system. It was noted that after approximately 30 
days, filter capsules left exposed and unprotected gained a small 
amount of weight--an average of 0.8 g (micrograms) per day. 
Neither NIOSH nor MSHA considered this a problem, since all dust 
samples are analyzed within 24 hours of receipt and are not left 
exposed and unprotected. However, more recent data collected to 
quantify weighing variability between the Mine Safety Appliances Co. 
and MSHA laboratories showed that filter capsules tend to gain a small 
amount of weight even when stored in plastic cassettes (Parobeck, et 
al., 1997). To check this result, 75 unexposed filter cassettes that 
had been distributed to MSHA's district offices were recalled and the 
filter capsules were reweighed. On average, the weight gain was about 
40 g over a time period of roughly 150 days. Statistical 
analyses of these data performed by MSHA and NIOSH confirmed the 
previous result (Parobeck, et al., 1997; Wagner, May 28, 1997). While 
the cause has not been established, it is hypothesized that at least 
some of the observed weight gain may be the result of outgassing from 
the plastic cassette onto the filter capsule. If uncorrected, any 
systematic change in weight not due to coal mine dust would introduce a 
bias in dust concentration measurements.
    One commenter had previously stated that the Secretaries were 
addressing only precision, thereby implying that potential biases were 
being ignored. To eliminate the potential for any bias due to a 
spurious gain or loss of filter capsule weight, MSHA has used control 
filter capsules in its enforcement program since April 30, 1998. Any 
change in weight observed for the control filter capsule will be 
subtracted from the measured change in weight of the exposed filter 
capsule. Each control filter capsule will be pre-weighed with the other 
filter capsules, will be stored and transported with the other 
capsules, and will be on the inspector's person during the day of 
sampling. This 1998 modification to MSHA's inspector sampling and 
analytical procedure will ensure an unbiased estimate of the true 
weight gain (Wagner, May 28, 1997).
(a) Experience Gained From Use of Control Filters
    As explained above under the headings of ``Sample Processing'' and 
``Quantification of Measurement Uncertainty'', evidence of relatively 
small weight gains in unexposed filter capsules led MSHA, in 1998, to 
begin using unexposed control filters to adjust the weight gains 
measured for exposed filters. Under the new system, respirable coal 
mine dust samples taken by MSHA inspectors are matched with unexposed 
control filter capsules. For an inspector sample to be valid, the 
matching, unexposed control filter capsule must have been weighed on 
the same two days as the exposed capsule--initially before exposure and 
then, for a second time, afterwards.
    From April 30, 1998 through December 31, 1998, a total of 5,578 
such control filter capsules were weighed for the second time in MSHA's 
laboratory after having been sent out to the field. Although MSHA's new 
processing system was not fully implemented before April 30, 1998, many 
of these control filter capsules which were constructed with 
Tyvek, along with the corresponding exposed capsules, were 
initially weighed prior to 1998. The time intervals between first and 
second weighings ranged from 32 to 608 days. Excluding six filter 
capsules that were broken, misidentified, improperly labeled, or 
contaminated, weight gains measured for the remaining 5,572 unexposed 
filter capsules ranged from a maximum of 420 g down to a 
negative 317 g (i.e., a weight loss of 317 g). 
Approximately 50% of the unexposed

[[Page 42099]]

filter capsules showed a weight gain of 15 g or more. The mean 
weight gain measurement (counting losses as negative gains) was 14.0 
g, and the standard deviation was 24.6 g. The initial 
and second weight measurements for each of these control filter 
capsules which were constructed with Tyvek support pads, 
along with the measurement dates, are being placed into the public 
record for analysis and comment by interested parties.
    As explained earlier, if an unexposed control filter either shows a 
weight gain greater than 100 g or a weight loss greater than 
30 g, then, instead of using it to make any adjustment, MSHA 
simply voids the corresponding coal mine respirable dust sample. This 
occurred in 126 cases, leaving 5,446 cases in which the control filter 
was actually used to adjust a dust sample. For these 5,446 control 
filters, the mean weight gain measurement was 14.8 g, and the 
standard deviation was 19.2 g. Consequently, weight gains 
observed in exposed filters were reduced by about 15 g, on 
average, through the end of 1998. This corresponds to an average 
reduction in measured dust concentration of about 0.02 mg/m3 
for a 480-minute dust sample. Individual dust concentration 
measurements, however, were reduced by up to 0.14 mg/m3 
(corresponding to a 100-g weight gain measured for the control 
filter) or increased by up to 0.04 mg/m3 (corresponding to a 
30-g weight loss for the control filter).
    Variability in unexposed filter weight gain measurements, as 
expressed by the standard deviation of 24.6 g, consists of 
three components: (1) random weighing errors; (2) spurious but real 
changes in weight, such as might be due to contamination or outgassing 
from the plastic filter cassette onto the filter capsule; and (3) 
effects of any changes in laboratory conditions between the first and 
second weighings. Each of these three effects also contributes to 
uncertainty in the amount of coal mine dust accumulated on an exposed 
filter.
    MSHA's purpose in using unexposed control filters to adjust weight 
gains measured for exposed filters is to eliminate the second and third 
of these components as sources of measurement uncertainty for the 
exposed filters. Unfortunately, the control filter adjustment cannot 
eliminate the first component, comprised of random weighing errors. To 
the contrary, making the adjustment based on a single control filter 
doubles the number of weighings required to establish weight gain for 
an exposed filter. This increases (by a factor of 2) 
uncertainty due to the random error potentially associated with each 
weighing. Therefore, there is a tradeoff in applying the control filter 
adjustment: the adjustment improves accuracy only if it succeeds in 
reducing uncertainty due to changes in laboratory conditions and 
spurious changes in filter weight by an amount greater than the 
increase in uncertainty resulting from the additional weighings 
required.
    Estimates representing the first component (i.e., the standard 
deviation of random errors in measuring the change in weight of a 
filter capsule) are presented in Appendix C and range from 8.2 
g to 11.3 g for Tyvek-supported filters 
under MSHA's current procedures. Even if the true value were so high as 
11.3 g, then applying the control filter adjustment increased 
this source of uncertainty to no more than 11.32 = 
16.0 g. This is still substantially less than the 24.6 
g standard deviation observed in CNTRL_98, which includes, in 
addition to random weighing errors, the effects of variability in 
laboratory conditions and spurious but real changes in filter weight 
(MSHA, Data file: CNTRL_98, 1999). Therefore, so long as the control 
filter adjustment successfully eliminated these latter sources of 
variability, its net effect was to reduce uncertainty in the amount of 
respirable coal mine dust deposited on an exposed filter.
    Control filters, however, fully eliminate the effects of day-to-day 
variation in laboratory conditions and spurious changes in filter 
weight only if these effects are consistent for all filters weighed on 
the same days and sent out to the same field location for the same 
length of time between weighings. In the absence of evidence to the 
contrary, MSHA and NIOSH consider this to be a reasonable assumption in 
the case of laboratory effects: any systematic differences in 
laboratory conditions between the dates of initial and final weighing 
should have essentially the same effect on weights recorded for 
unexposed filter capsules as for exposed filter capsules.
    The remaining component of uncertainty, resulting from spurious but 
real weight changes such as might be caused by outgassing or 
contamination, is eliminated by the control filter adjustment only to 
the extent that such effects are consistent for all filters pre-weighed 
on the same day, sent out to the same field location, and then post-
weighed on the same day. MSHA checked this assumption for currently 
approved filter capsules--i.e., those employing Tyvek support 
pads--using a body of control filter data being placed into the public 
record (MSHA, Data file: NHSCP_99, 1999).
    The NHSCP_99 dataset consists of 108 ``batches'' in which several 
control filter capsules were first weighed on the same day, taken to 
the same mine site (but left unexposed), and then all weighed again on 
the same day in 1999. For example, a batch of six capsules may have 
been initially weighed on December 19, 1997, left unexposed during a 
mine visit on February 23, 1999, and then weighed for the second time 
on March 2, 1999. The NHSCP_99 data set contains information on a total 
of 564 filter capsules, divided into 108 such batches so that, on 
average, there were about five unexposed filter capsules per batch. The 
time interval between initial and final weighings averaged 335 days and 
ranged from 136 to 694 days. Closely matching results from CNTRL_98, 
the overall mean weight gain recorded for these unexposed filter 
capsules was about 14 g, and the overall standard deviation 
was about 25 g.
    If changes in weight are indeed consistent for control filters 
subjected to similar handling and aging effects, then variability in 
weight gains within batches should not significantly exceed variability 
attributable to random weighing errors alone. MSHA's statistical 
analysis of NHSCP_99, however, indicated that variability in weight 
gains within batches was significantly greater than what can be 
attributed to random weighing errors under current processing 
procedures (Kogut, et al., 1999). MSHA's estimate of the standard 
deviation of weight gains measured for unexposed filters within batches 
was 19.8 g. This suggests that, for filter capsules employing 
Tyvek support pads, the effects on weight gain of handling, 
aging, and/or environment may not be uniform--even when the filter 
capsules are treated similarly.
    MSHA then performed a field experiment to determine if modifying 
the filter capsule would reduce variability due to spurious changes in 
weight (Kogut, et al., 1999). In this experiment, 300 unexposed filter 
capsules employing the standard Tyvek support pad were 
compared with a matched set of 300 unexposed modified capsules 
employing a stainless steel support pad (MSHA, Data file: MFSC.xls, 
1999). Ninety-nine different MSHA inspectors used three of each type of 
filter capsule as controls during coal mine dust inspections at 100 
different MMUs in 100 different mines. All six unexposed capsules used 
in an inspection were carried and handled by the inspector in the same 
way as during routine dust inspections. Also in accordance with MSHA's 
normal practice, all filter capsules in the batch used for an 
inspection were pre- and

[[Page 42100]]

post-weighed on the same pair of days at MSHA's Respirable Dust 
Weighing Laboratory.
    MSHA's statistical analysis of the MFCS data indicated that 
substituting a stainless steel support pad for the Tyvek 
support pad currently in use, in both exposed and unexposed filter 
capsules, could significantly improve measurement accuracy. This 
modification reduced the standard deviation of weight gains measured 
for unexposed filters within batches to 11.6 g.
    MSHA and NIOSH would welcome further statistical analysis of the 
datasets being placed into the public record with this notice. The 
Agencies would also welcome suggestions on how MSHA might further 
modify its analytical procedures to reduce uncertainty in the amount of 
dust deposited on an individual filter.
2. Verification of Method Accuracy
    NIOSH's first independent analysis of MSHA's sampling and 
analytical method involved MSHA's 1995 field study data.\21\ These data 
incorporated certain improvements that NIOSH had proposed for MSHA's 
sampling and analytical method. As described elsewhere in this notice, 
these improvements were later adopted for all MSHA inspector samples. 
From these data, NIOSH determined, with 95-percent confidence, that the 
true CVtotal for MSHA's proposed sampling and analytical 
method was less than the target maximum value of 12.8 percent for dust 
concentrations of 0.2 mg/m\3\ or greater (Wagner, 1995). This 
demonstrated that MSHA's sampling and analytical method for collecting 
and processing single full-shift samples would meet the NIOSH Accuracy 
Criterion whenever the true dust concentration was at least 0.2 mg/
m\3\.
---------------------------------------------------------------------------

    \21\ With its field study, MSHA exceeded the usual requirements 
for determining the accuracy of a sampling and analytical method, as 
described by NIOSH (Kennedy, et al., 1995) and the European 
Community (European Standard No. EN 482, 1994). Both of these 
require only a laboratory determination of method accuracy.
---------------------------------------------------------------------------

    In the same report NIOSH also applied an indirect approach for 
assessing the accuracy of MSHA's sampling and analytical method. The 
indirect approach involved combining separate estimates of weighing 
imprecision, pump-related variability, and variability associated with 
physical differences between individual sampler units. This indirect 
approach also indicated that MSHA's sampling and analytical method 
would meet the NIOSH Accuracy Criterion at concentrations greater than 
or equal to 0.2 mg/m\3\, thereby corroborating the analysis of MSHA's 
field data.
    As discussed above, MSHA later obtained data suggesting that filter 
capsules containing Tyvek backup pads sometimes exhibit 
spurious changes in weight. Although the changes observed were 
relatively small, compared to weight gains required for MSHA's 
noncompliance determinations, this led MSHA to begin using unexposed 
control filters in its enforcement program. As explained in Appendices 
A and B, the use of a control filter adjustment eliminates systematic 
errors due to such effects, but also affects the precision of a single, 
full-shift measurement. Consequently, NIOSH reassessed the accuracy of 
MSHA's sampling and analytical method, taking into account the effects 
of using a control filter capsule (Wagner, May 28, 1997). After 
accounting for the effects of control filter capsules on both bias and 
precision, NIOSH concluded, based on both its direct and indirect 
approaches, that a single, full-shift measurement will meet the NIOSH 
Accuracy Criterion at true dust concentrations greater than or equal to 
0.3 mg/m\3\.
    As part of its ongoing commitment to improving the sampling and 
analytical method, MSHA recently compiled data showing that weight 
stability of the filter capsule would be improved by substituting 
stainless steel support grids for the Tyvek support pads 
currently in use (Kogut et al., 1999). Therefore, NIOSH again 
reassessed the accuracy of MSHA's method, this time taking into account 
the proposal to switch to stainless steel support grids (Grayson, 
1999a; 1999b). After accounting for the effects of switching to 
stainless steel support grids, and of using unexposed control filters 
to adjust for any potential systematic errors that might remain, NIOSH 
once again concluded that a single, full-shift measurement will meet 
the NIOSH Accuracy Criterion at true dust concentrations greater than 
or equal to 0.3 mg/m\3\.
    One previous commenter stated that the Secretaries ``have not 
addressed the `accuracy' of a single sample collected from an 
environment where the concentration is unknown.'' The purpose of any 
measurement process is to produce an estimate of an unknown quantity. 
The Secretaries have concluded that MSHA's sampling and analytical 
method for inspectors meets the NIOSH Accuracy Criterion for true 
concentrations at or above 0.3 mg/m\3\, but it is also possible to 
calculate the range of measurements for which the Accuracy Criterion is 
fulfilled. Since CVtotal increases at the lower 
concentrations, all that is necessary is to determine the lowest 
measurement at which the NIOSH Accuracy Criterion is met. This is done 
as follows. If the true concentration exactly equaled the lowest 
concentration at which MSHA's sampling and analytical method meets the 
Accuracy Criterion (i.e., 0.3 mg/m\3\), then no more than 5% of single, 
full-shift measurements would be expected to exceed 0.36 mg/m\3\ 
(Wagner, May 28, 1997). Conversely, if a measurement equals or exceeds 
0.36 mg/m\3\, it can be inferred, with at least 95% confidence, that 
the true dust concentration equals or exceeds 0.3 mg/m\3\ (Wagner, May 
28, 1997). Consequently, the Secretaries conclude that MSHA's improved 
sampling and analytical method satisfies the NIOSH Accuracy Criterion 
whenever a single, full-shift measurement is at or above 0.36 mg/m\3\.
    The Secretaries recognize that future technological improvements in 
MSHA's sampling and analytical method may reduce CVtotal 
below its current value. Also, as additional data are accumulated, 
updated estimates of CVtotal may become available. However, 
so long as the method remains unbiased and CVtotal remains 
below 12.8 percent, at a 95-percent confidence level, the sampling and 
analytical method will continue to meet the NIOSH Accuracy Criterion, 
and the present finding will continue to be valid.

XI. Proposed New Finding and Proposed Rescission of the 1972 Joint 
Finding

    The Secretaries have concluded that sufficient data exist for 
determining the uncertainty associated with a single, full-shift 
measurement; rigorous requirements are in place, as specified by 30 CFR 
parts 70, 71, and 90, to ensure the validity of a respirable coal mine 
dust sample; and valid statistical techniques were used to determine 
that MSHA's improved dust sampling and analytical method meets the 
NIOSH Accuracy Criterion. For these reasons the Secretaries would find 
that a single, full-shift measurement at or above 0.36 mg/m\3\ will 
accurately represent atmospheric conditions to which a miner is exposed 
during such shift. Therefore, pursuant to section 202(f) (30 U.S.C. 
842(f)) and in accordance with section 101 (30 U.S.C. 811) of the Mine 
Act, the 1972 joint notice of finding would be rescinded.

XII. Feasibility Issues

    Section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)) 
requires the Secretary of Labor to set standards which most adequately 
assure, on the basis of the best available evidence, that

[[Page 42101]]

no miner will suffer material impairment of health or functional 
capacity even if such miner has regular exposure to such hazards dealt 
with by such standard over his or her working lifetime. Standards 
promulgated under this section must be based upon research, 
demonstrations, experiments, and such other information as may be 
appropriate. MSHA, in setting health standards, is required to achieve 
the highest degree of health and safety protection for the miner, and 
must consider the latest available scientific data in the field, the 
feasibility of the standards, and experience gained under this and 
other health and safety laws.
    In relation to promulgating health standards, 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 this 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.
* * * * *

    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 section 102(a)(5)(A), 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, at 21-22 (1977), reprinted in 1977 U.S.C.C.A.N. 
3421-22.
    In American Textile Manufacturers' Institute v. Donovan, 452 U.S. 
490, 508-509 (1981), the Supreme Court defined the word ``feasible'' as 
``capable of being done, executed, or effected.'' The Court further 
stated, however, that a standard would not be considered economically 
feasible if an entire industry's competitive structure were threatened. 
In promulgating standards, hard and precise predictions from agencies 
regarding feasibility are not required.

A. Technological Feasibility

    MSHA, in consultation with NIOSH, believes that compliance 
determination based on an inspector, single, full-shift exposure 
measurement would be technologically feasible for the mining industry. 
An agency must 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. American Iron and Steel Institute v. OSHA, (AISI-II) 939 F.2d 
975, 980 (D.C. Cir. 1991); American Iron and Steel Institute v. OSHA, 
(AISI-I) 577 F.2d 825 (3d Cir. 1978) at 832-835; and Industrial Union 
Dep't., AFL-CIO v. Hodgson, 499 F.2d 467, 478 (D.C. Cir. 1974).
    This NPRM would not be a technology-forcing standard. The single, 
full-shift sample rule when promulgated predominantly affects MSHA's 
procedures since MSHA alone conducts inspector sampling. After the 
promulgation of single, full-shift sample rule, coal mine operators 
would continue to comply with the existing respirable dust 
concentration limit of 2.0 mg/m\3\. Such compliance with the applicable 
standard has proven feasible over the years. Furthermore, single, full-
shift samples were found to be technologically feasible during the 
prior effective Interim Single-Sample Enforcement Policy (ISSEP), March 
2, 1998 through September 4, 1998 (see section V.D. of the preamble 
detailing the ISSEP).

B. Economic Feasibility

    MSHA, in consultation with NIOSH, believes that the single full 
shift sample (SFSS) rule would be economically feasible for the coal 
mining industry. The coal mining industry would incur costs of 
approximately $1.8 million yearly to comply with the proposed SFSS 
rule. Coal mine operators would also incur approximately an additional 
$0.2 million yearly in penalty costs associated with the additional 
citations arising from the proposed SFSS rule. That the total $2.0 
million borne yearly by the coal mining industry as a result of the 
proposed SFSS rule is well less than 1 percent (about 0.01 percent) of 
the industry's yearly revenues of $19.8 billion provides convincing 
evidence that the proposed rule is economically feasible.
    Economic feasibility does not guarantee the continued existence of 
individual employers--``A standard is not infeasible simply because it 
is financially burdensome, * * * or even because it threatens the 
survival of some companies within an industry:'' United Steelworkers of 
America v. Marshall, 647 F.22d 1189, 1265 (D.C. Cir. 1981).
    This rule would not threaten the industry's competitive structure. 
After the promulgation of single, full-shift sample rule the Agencies 
expect that coal mine operators would continue to comply with the 
existing respirable dust concentration limit of 2.0 mg/m\3\. Single, 
full-shift samples were found to be economically feasible during two 
prior effective periods--July 15, 1991 through December 31, 1993, and 
March 2, 1998 through September 4, 1998--when noncompliance 
determinations were based on the results of MSHA inspector single 
samples. No disruption in mining activity was attributed to MSHA's 
single-sample enforcement policy during either of these periods.

XIII. Regulatory Impact Analysis

    MSHA's improved program to eliminate overexposures on each and 
every shift includes (1) the simultaneous implementation of the use of 
inspector single, full-shift respirable coal mine dust samples to 
identify overexposures more effectively in both underground and surface 
coal mines (single, full-shift sample), and (2) in underground coal 
mines, verified ventilation plans to maintain miners' respirable dust 
exposure at or below the applicable standard on each and every shift 
(plan verification). The plan verification NPRM is published elsewhere 
in today's Federal Register. This part of the preamble reviews several 
impact analyses which the Agencies are required to provide in 
connection with the single, full-shift sample proposed rulemaking. 
Since single, full-shift sample and plan verification are complementary 
NPRMs intended to be promulgated at the same time, the detailed 
presentation of assumptions and estimates for each are available in the 
same Preliminary Regulatory Economic Analysis (PREA)(MSHA, December 
1999).
    Assumptions for single, full-shift sample requirements are based 
upon information provided by MSHA technical personnel. We encourage the 
mining community to provide detailed comments in this regard to ensure 
that single, full-shift sample cost assumptions and estimates are as 
accurate as possible.

A. Costs and Benefits: Executive Order 12866

    In accordance with Executive Order 12866, the Agencies have 
prepared a detailed PREA of the estimated costs and benefits associated 
with the proposed rule for the underground and surface coal mining 
sectors. We have fulfilled this requirement for the proposed rule and 
determined that this rulemaking is not a significant regulatory action. 
The key findings of the PREA are summarized below.
1. Compliance Costs
    The Agencies estimate that the cost of this NPRM would be 
approximately $1.8 million annually, of which all but

[[Page 42102]]

about $5,200 would be borne by underground coal mine operators (the 
residual $5,200 to be borne by surface coal mine operators). Table 
XIII-1 summarizes the estimated compliance costs by provision, for 
underground and surface coal mines, for the following three mine size 
categories: (1) those employing fewer than 20 workers; (2) those 
employing between 20 and 500 workers; and (3) those employing more than 
500 workers.
    The compliance costs arising from the single, full-shift sample 
NPRM would occur as a result of a slight increase in the number of MSHA 
inspector citations issued to underground and surface coal mine 
operators due to the determination of noncompliance with the respirable 
coal mine dust standard being based on inspector single, full-shift 
samples rather than the average of multiple inspector exposure 
measurements. The additional citations due to single, full-shift sample 
would require mine operators to undertake the following actions and to 
incur associated compliance costs: take corrective action(s) in order 
to get back into compliance with the applicable respirable coal mine 
dust standard; perform abatement sampling; complete dust data cards; 
send abatement samples to MSHA; post abatement sample results; write 
respirable dust plans; and post or give a copy of dust plans.
    In addition to these estimated compliance costs, mine operators 
would incur yearly penalty cost increases of about $0.2 million. 
Penalty costs conventionally are not considered to be a cost of a rule 
(and, in fact, are clearly not a compliance cost) but merely a transfer 
payment from a party violating a rule to the government. Therefore, the 
penalty costs are not included as part of the compliance costs of the 
proposed SFSS rule noted above. These penalty costs are relevant, 
however, in determining the economic feasibility of the proposed SFSS 
rule.
    The derivation of the above cost figures are presented in Chapter 
IV of the PREA that accompanies this rule.

             Table XIII-1.--Summary of Compliance Costs for Single, Full-Shift Sample Proposed Rule
----------------------------------------------------------------------------------------------------------------
                                                                     > 20 emp.
           Estimated costs by category               < 20 emp.          500         > 500 emp.         Total
----------------------------------------------------------------------------------------------------------------
                                             UNDERGROUND COAL MINES
----------------------------------------------------------------------------------------------------------------
Corrective Actions..............................        $328,488      $1,266,767         $19,527      $1,614,782
Abatement Sampling..............................          38,658         128,264           1,129         168,051
Dust Data Cards.................................             717           2,588              37           3,343
Send Sample to MSHA.............................           1,200           4,331              62           5,593
Post Sample Results.............................             241             865              12           1,117
Write Dust Plan.................................             151             302               0             453
Post or Give Dust Plan..........................               3               5               0               8
                                                 ---------------------------------------------------------------
    Total Underground...........................         369,457       1,403,122          20,769       1,793,348
----------------------------------------------------------------------------------------------------------------
                                               SURFACE COAL MINES
----------------------------------------------------------------------------------------------------------------
Corrective Actions..............................             366           2,194               0           2,560
Abatement Sampling..............................             594           1,394               0           1,989
Dust Data Cards.................................               3              13               0              17
Send Sample to MSHA.............................               6              22               0              28
Post Sample Results.............................               4               8               0              12
Write Dust Plan.................................             151             453               0             604
Post or Give Dust Plan..........................               3               8               0              10
                                                 ---------------------------------------------------------------
    Total Underground...........................           1,127           4,094               0           5,220
----------------------------------------------------------------------------------------------------------------
                                       UNDERGROUND AND SURFACE COAL MINES
----------------------------------------------------------------------------------------------------------------
Corrective Actions..............................         328,854       1,268,961          19,527       1,617,342
Abatement Sampling..............................          39,252         129,658           1,129         170,040
Dust Data Cards.................................             720           2,602              37           1,282
Send Sample to MSHA.............................           1,205           4,353              62           5,621
Post Sample Results.............................             245             873              12           1,129
Write Dust Plan.................................             302             756               0           1,058
Post or Give Dust Plan..........................               5              13               0              18
                                                 ---------------------------------------------------------------
    Grand Total.................................         370,584       1,407,215          20,769      1,798,568
----------------------------------------------------------------------------------------------------------------
\*\ Totals may vary due to rounding.

2. Benefits
    Occupational exposure to excessive levels of respirable coal mine 
dust imposes significant health risks. These include the following 
adverse health outcomes: simple coal workers' pneumoconiosis (simple 
CWP), progressive massive fibrosis (PMF), silicosis, and chronic 
obstructive pulmonary disease (COPD) (e.g., asthma, chronic bronchitis, 
emphysema) (see the Health Effects section for details). Cumulative 
exposure to respirable coal mine dust is the main determinant in the 
development of both simple CWP and PMF although other factors such as 
the percentage of quartz in the respirable dust and the type of coal 
also affect the risk of miners developing simple CWP and PMF (Jacobsen, 
et al., 1977; Hurley, et al., 1987; Kuempel, et al., 1995; Attfield and 
Morring, 1992; Attfield and Seixas, 1995). The true magnitude of 
occupationally induced simple CWP and PMF among today's coal miners is 
unknown, although prevalence estimates are available from various 
surveillance systems. For example, from 1970 to 1995, the prevalence of 
simple CWP and PMF

[[Page 42103]]

among miners, based on the operator sponsored x-ray program, dropped 
from 11 percent to 3 percent (MSHA, Internal Chart, 1998). Also, later 
rounds of the National Study for Coal Worker's Pneumoconiosis 
consistently demonstrated, through prevalence rates in the range of 
2.9-3.9 percent, that simple CWP and PMF have not been eliminated.
    Through the joint promulgation of single, full-shift sample and 
plan verification rules, miners would be further protected from the 
debilitating effects of occupational respiratory disease by limiting 
their exposures to respirable coal mine dust to no more than the 
applicable standard on each and every shift.\22\ Reducing respirable 
coal mine dust concentrations over a 45-year occupational lifetime to 
no more than the applicable standard on just that percentage of shifts 
currently showing an excess would lower the cumulative exposure, 
thereby significantly reducing the risk of both simple CWP and PMF 
among miners. We have estimated the health benefits of the two rules 
arising from the elimination of overexposures on all shifts at only 
those MMUs exhibiting a pattern of recurrent overexposures on 
individual shifts.
---------------------------------------------------------------------------

    \22\ For details, see the Quantitative Risk Assessment and 
Significance of Risk sections.
---------------------------------------------------------------------------

    Based on 1999 operator data, there were 704 MMUs (out of 1,251) at 
which regular (not abatement) designated occupational (D.O.) samples 
exceeded the applicable standard on at least two of the sampling shifts 
reported in 1999 (MSHA, Data file: Operator.ZIP).\23\ MSHA considers 
these 704 MMUs, representing more than one-half of all underground coal 
miners working in production areas, to have exhibited a pattern of 
recurrent overexposures. Based on valid D.O. operator samples collected 
on a total of 18,569 shifts at these 704 MMUs, the applicable standard 
was exceeded on about on 3,977 of these shifts or 21.4 percent.
---------------------------------------------------------------------------

    \23\ If a different definition of ``exhibiting a recurrent 
pattern of overexposures'' were used in these analyses the estimate 
of the reduction in risk and associated benefits would be different. 
For example, if the criterion were that four or more D.O. bimonthly 
exposure measurements exceeded the applicable standard then, with 
95% confidence, at least 20 shifts would be overexposures in a year 
of 384 shifts. Using the four as the criterion, this would reduce 
the population for whom we are estimating benefits, and the 
estimated number of prevented cases would decrease by 19%.
---------------------------------------------------------------------------

    At the MMUs being considered (those exhibiting a pattern of 
recurrent overexposures),\24\ bringing dust concentrations down to no 
more than the applicable standard on each and every production shift 
would reduce D.O. exposures on the affected shifts by an average of 
1.04 mg/m\3\. Assuming this average reduction applies to only 21 
percent of the shifts, the effect would be to reduce cumulative 
exposure, for each miner exposed at or above the D.O. level, by 0.22 
mg-yr/m\3\ over the course of a working year (i.e., 21 percent of 
shifts in one year times 1.04 mg/m\3\ per shift). Therefore, over a 45-
year working lifetime, the benefit to each affected D.O. miner would, 
on average, amount to a reduction in accumulated exposure of 
approximately 10 mg-yr/m\3\ (i.e., 45 years times 0.22 mg-yr/m\3\ per 
year). If, as some miners have testified, operator dust samples 
currently submitted to MSHA tend to under-represent either the 
frequency or magnitude (or both) of individual full-shift excursions 
above the applicable standard, then eliminating such excursions would 
provide a lifetime reduction of even more than 10 mg-yr/m\3\ for each 
exposed miner.
---------------------------------------------------------------------------

    \24\ MSHA estimates an MMU average of 384 production shifts per 
year. Since miner operators are required to submit five valid 
designated operator (D.O.) samples to MSHA every two months, there 
would typically be 30 valid D.O. samples-for each MMU that was in 
operation for the full year. If dust concentrations on two or more 
of the sampled shifts exceed the standard, then it follows, at a 95-
percent confidence level, that the standard was exceeded on at least 
six shifts over the full year.
---------------------------------------------------------------------------

    When the dust concentration measured for the D.O. exceeds the 
applicable standard, measurements for at least some of the other miners 
working in the same MMU may also exceed the standard on the same shift, 
though usually by a smaller amount. Furthermore, although the D.O. 
represents the occupation most likely to receive the highest exposure, 
other miners working in the same MMU may be exposed to even higher 
concentrations than the D.O. on some shifts. Therefore, in addition to 
the affected D.O. miners, there is a population of other affected 
miners who are also expected to experience a significant reduction in 
risk as a result of eliminating overexposures on their individual 
shifts.
    To estimate how many miners other than the D.O. would be 
substantially affected, MSHA examined the results from all valid dust 
samples collected by MSHA inspectors in underground MMUs during 1999 
(MSHA, Data file: Inspctor.zip). Within each MMU, the inspector 
typically takes one full-shift sample on the D.O. and, on the same 
shift, four or more additional samples representing other occupations. 
On 896 shifts, at a total of 450 distinct MMUs, the D.O. measurement 
exceeded the applicable standard, and there were at least three valid 
measurements for other occupations available for comparison. There was 
an average of 1.2 non-D.O. measurements in excess of the standard on 
shifts for which the D.O. measurement exceeded the standard.\25\ For 
non-D.O. measurements that exceeded the standard on the same shift as a 
D.O. measurement, the mean excess above the standard was approximately 
(0.8 mg/m\3\).\26\
---------------------------------------------------------------------------

    \25\ With 95-percent confidence, on shifts for which the D.O. 
measurement exceeds the standard, the mean number of other 
occupational measurements also exceeding the standard is at least 
1.11.
    \26\ With 95-percent confidence, the mean excess is at least 
0.72 mg/m\3\
---------------------------------------------------------------------------

    Combining these results with the 21-percent rate of excessive 
exposures observed for the D.O. on individual shifts, it is reasonable 
to infer that, at the MMUs under consideration, an average of 1.2 other 
miners, in addition to the one classified as D.O., is currently 
overexposed on at least 21 percent of all production shifts. Over the 
course of a working year, the reduction in exposure expected for these 
affected non-designated occupational (N.D.O.) miners, is 0.17 mg-yr/
m\3\ (i.e., 21 percent of one year, times 0.8 mg/m\3\).
    The expected lifetime for all American males, conditional on their 
having reached 20 years of age, is 73 years (U.S. Census March 1997, 
Table 18; U.S. Census March 1997, Table 119).\27\ On average, the best 
estimate of the lifetime benefit to exposed miners is expressed by the 
reduction in prevalence of disease at age 73. To project the reduction 
in risk of simple CWP and PMF among affected D.O.s and N.D.O.s, MSHA 
applied its best estimate of dose response to a hypothetical cohort of 
underground coal miners who work on an MMU exhibiting a pattern of 
recurrent overexposure, and who, on average, begin working at age 20, 
retire at age 65, and live to age 73. Strengths and weaknesses of 
various epidemiological studies were presented in the Health Effects 
section supporting the selection of Attfield and Seixas (1995) as the 
study that provides the best available estimate of material impairment 
with respect to simple CWP and PMF. Two of the distinguishing qualities 
of Attfield and Seixas (1995) are the dose-response relationship over a 
miner's lifetime and the fact that these data best represent the recent 
conditions experienced by miners in the U.S. Using this relationship, 
it is possible to evaluate the impact on risk of both simple CWP and 
PMF expected from

[[Page 42104]]

bringing respirable coal mine dust concentrations down to or below the 
applicable standard on every shift. This is the only contemporary 
epidemiological study of simple CWP and PMF providing such a 
relationship.
---------------------------------------------------------------------------

    \27\ Since females have a greater life expectancy than males, 
the expected benefits would increase if the proportion of female 
miners increases substantially in the future.
---------------------------------------------------------------------------

    To estimate the benefits (i.e., number of cases of simple CWP and 
PMF prevented) of single, full-shift sample and plan verification rules 
combined, we applied these estimates of risk reduction to the estimated 
sub-populations of affected miners. As of February 12, 1999, there were 
984 producing MMUs; \28\ applying the pattern of recurrent 
overexposures among MMUs as identified in the Quantitative Risk 
Assessment, 56 percent, by mine size, we estimate there to be 552 
affected MMUs (MSHA Table, November 18, 1999; MSHA Table, February 12, 
1999). Based on MSHA's experience, we would expect one D.O. and seven 
N.D.O.s for each shift of production at each MMU. Therefore, among 
underground coal miners working on an MMU, we estimate 12.5% to be 
designated occupational miners and 87.5% to be non-designated 
occupational miners.
---------------------------------------------------------------------------

    \28\ Nine hundred and eighty-four refers to the number of MMUs 
operating on February 12, 1999. The 1,443 number mentioned 
previously refers to all MMUs in operation at any time in 1999.
---------------------------------------------------------------------------

    The benefits that would accrue to coal miners exposed to respirable 
coal mine dust and to mine operators, and ultimately to society at 
large, are substantial and take a number of forms. These proposed rules 
would reduce a significant health risk to underground coal miners, 
reducing the potential for illnesses and premature death and their 
attendant costs to miners, their employers, their families, and 
society.
    The joint promulgation of these rules should realize a positive 
economic impact on the Department of Labor's (DOL's) Black Lung Program 
and relatedly on mine operators. The Black Lung Program compensates 
eligible miners and their survivors under the Black Lung Benefits Act. 
This program provides monthly payments and medical benefits (diagnostic 
and treatment) to miners who are found to be totally disabled by black 
lung disease, including cases of PMF and simple CWP. In 1986, DOL's 
Employment Standards Administration reported that 12% of approved cases 
of Black Lung Program were identified as cases of PMF based on chest 
radiographs, while sixty-four percent had simple CWP based on chest 
radiographs (ESA, 1986). For miners who stopped working in coal mines 
after 1969 and for whom the DOL can establish that the miner worked for 
the same operator for at least one calendar year, and that miner had at 
least 125 working days in that year, that operator is financially 
responsible for the miner's Black Lung benefit payment. If a 
responsible operator cannot be identified for an eligible miner, 
benefit payments are made by the Black Lung Disability Trust Fund. To 
the extent that these rules reduce overexposures to respirable coal 
mine dust, there should be fewer Black Lung Program cases. Therefore, 
over time, the associated financial outlay by responsible operators 
through either insurance premiums or direct payments of Black Lung 
benefits should be lower than would otherwise occur. The financial 
impact could be substantial (see discussion in Chapter IV, of the 
PREA). In 1980, the Black Lung Program estimated average lifetime 
payouts for responsible operators for married miners of about $248,700 
dollars, assuming a 7-percent annual increase (ESA, 1980). In fiscal 
year 1999, 443 claims for Black Lung Benefits were accepted as new 
cases; sixty-six percent (293) are the financial responsibility of coal 
mine operators (Peed, 2000).
    The most tangible benefit of these rules is the number of cases of 
simple CWP and PMF which would be prevented. Table XIII-2 presents the 
estimated number of cases of simple CWP and PMF that would be prevented 
among the 56 percent of MMUs currently exhibiting a pattern of 
recurrent overexposures. For all categories of simple CWP and PMF 
combined, we estimate 37 fewer of these cases among affected miners, 
than would otherwise occur without the promulgation of single, full-
shift sample and plan verification rules. Eleven of these cases would 
be the most severe form of coal miners pneumoconiosis, PMF, and as such 
these cases could be interpreted as prevented premature deaths due to 
occupational exposure to respirable coal mine dust. Since simple CWP 
predisposes the development of PMF, it is important that it also be 
prevented (Balaan, et al., 1993).
    As discussed in the Significance of Risk sections, MSHA believes 
this QRA for simple CWP and PMF strikes a reasonable balance based on 
available data. Yet, our estimates likely understate the true impact of 
these rules since our analyses are restricted to a sub-population of 
affected miners, those working at MMUs exhibiting a pattern of 
recurrent overexposures, not the broader population of coal miners who 
would benefit from these rules. Furthermore, to estimate the average 
overexposure which would be prevented, MSHA had to use data collected 
for compliance purposes, which may not represent typical environmental 
conditions and the associated respirable coal mine dust exposure in 
underground coal mines.
    The degree to which the exposure level of respirable coal mine dust 
on sampling shifts may not be representative of typical exposure levels 
is affected by the following factors:
    (1) There exists a positive relationship between coal production 
and generation of respirable coal mine dust;
    (2) Current sampling procedures permit sampling measurements to be 
taken at the mid-range of the distribution of the level of production--
sampling measurements must be taken on shifts with production at least 
60% of the average production during the last 30 days and at least 50% 
of average production for the last valid set of bimonthly samples for 
inspector and operator samples, respectively;
    (3) Miners have reported and MSHA data have demonstrated lower 
levels of production on sampling shifts versus non-sampling shifts 
(MSHA, September 1993);
    (4) On some sampling shifts, miners have reported that more 
engineering controls may be used than on other shifts, thus reducing 
the measured amount of respirable coal mine dust;
    (5) MSHA analyses have demonstrated, even when controlling for 
production, in mines with fewer than 125 employees, on continuous 
mining MMUs, respirable coal mine dust exposures were much higher 
during the unannounced Spot Inspection Program (SIP) sampling shifts 
than on shifts operators sampled--this is consistent with the effect of 
increasing engineering controls on shifts during which bimonthly 
samples are conducted compared to the level of use of engineering 
controls used on shifts for which the operator does not expect sampling 
to be conducted given the same production level (Denk, 1993);
    (6) Across mine size, designated area samples have been found to be 
larger for shifts on which unannounced compliance sampling occurred 
compared to operator sampling shifts--in one study they differed by at 
least a factor of 40 percent in large mines and 100 percent in the 
smallest mines (Ibid., pp. 211-212); and
    (7) Existing MSHA technical information indicates that some 
reduction in production levels occurs during some sampling periods on 
longwalls (Denk, 1990).
    Therefore, at a bare minimum, over an occupational lifetime (45-
years) for miners who live to age 73 who worked

[[Page 42105]]

at MMUs exhibiting a pattern of recurrent overexposures, we estimate at 
least 37 fewer cases of pneumoconiosis (simple CWP and PMF) than would 
otherwise occur without the promulgation of these rules.
    Our current quantitative estimate of benefits demonstrates and 
qualitative discussions punctuate that these rules would have a 
significant positive impact on the health of our nation's coal miners 
when promulgated. Yet, due to the limitations in these data, we believe 
our benefit estimate may understate the number of cases of simple CWP 
and PMF which would be prevented over an occupational lifetime.
    MSHA believes that cases of simple CWP and PMF would also be 
prevented among other types of underground miners, such as roofbolters 
working in designated areas (D.A.). Based on MSHA experience it is 
reasonable to expect roofbolter D.A.'s pattern of overexposures for 
respirable coal mine dust to be similar to that for miners with the 
highest exposure on a MMU. If so, we would expect 13 additional cases 
of simple CWP and PMF to be prevented. Affected D.A.s include D.A.s who 
work at the 56 percent of the MMUs under consideration who are exposed 
to dust concentrations similar to the D.O., over a 45-year occupational 
lifetime (MSHA Table, November 1999; MSHA Table, February 1999).
    Also, it is reasonable to expect surface miners' health to be 
further protected by the promulgation of the SFSS rule alone since it 
would identify and require resolution of overexposures not previously 
identified and may thereby lower some miners' cumulative exposure to 
respirable coal mine dust. Furthermore, to the extent that cumulative 
exposure to respirable coal mine dust affects other adverse health 
outcomes, such as silicosis and chronic obstructive pulmonary disease, 
it is reasonable to expect a reduction in the number of cases and/or in 
the severity of cases for these diseases among surface and underground 
coal miners.
    Although the effect cannot readily be quantified, to the extent 
that these rules would also reduce the cumulative exposure to 
respirable coal mine dust among some miners working in those MMUs 
currently not exhibiting overexposures, it is reasonable to expect that 
we would observe an incremental benefit among that sub-population of 
coal miners. Moreover, to the extent that the cumulative dust exposure 
is reduced for miners working in the ``outby'' areas, away from the 
mining face (i.e., MMU) where coal is extracted from the coal seam, 
they too may realize occupational health benefits due to the 
simultaneous promulgation of these proposals. Therefore, our best 
estimate of 37 prevented cases of simple CWP and PMF, combined, among 
all affected miners likely underestimates the true benefit realized by 
the coal mining workforce through the reduction of overexposures to no 
more than the applicable standard on each shift.
    Clearly, PMF is associated with premature death. Since simple CWP 
may evolve to PMF, even after occupational exposure has ceased, it has 
the propensity to become a life-threatening illness. By reducing the 
total number of simple CWP and PMF cases among affected miners from 259 
to 222, over 45 years,\29\ these standards are projected to prevent an 
average of four cases of simple CWP and PMF for each 5-year interval.
---------------------------------------------------------------------------

    \29\ Applying the estimated prevalence rate of 3.0 percent to 
the estimated population of affected miners (8,640) results in an 
estimate of 259 cases of simple CWP and PMF.
---------------------------------------------------------------------------

    For all those reasons previously identified, MSHA believes that its 
estimate of 37 prevented cases of simple CWP and PMF over a 45 year 
working life understates the true number of cases of simple CWP and PMF 
which would be prevented. This belief is further supported by the fact 
that during the past few years, the Black Lung Benefits Program has 
been approving roughly 400 claims each year. These claims come from 
individuals whose exposure for the most part came after the current 
standard of 2.0 was established in 1972. Thus, we believe the 
consistent identification, from year to year, of hundreds of new cases 
of simple CWP and PMF per year into the Black Lung Benefits Program 
supports our belief that the true lifetime occupational health benefits 
of the proposed rules are higher than we have estimated. Even assuming 
that the number of new claims would decline in future years simply due 
to the continuing decline in the number of coal miners, MSHA expects 
that assuring that future exposures are maintained below the 2.0 
exposure limit will reduce the number of new cases of simple CWP and 
PMF by considerably more than 1 per year.
    In addition to the prevention of simple CWP and PMF, each of the 
8,640 affected miners at MMUs exhibiting a pattern of recurrent 
overexposures will realize some health benefit by limiting his or her 
cumulative exposure to respirable coal mine dust to no more than the 
applicable standard on each and every shift.
    The expected number of prevented cases of simple CWP and PMF would 
not be realized for some time even after the pattern of overexposures 
has been minimized or eliminated. This is due, in part, to the latency 
(that is, the disease does not develop immediately after exposure) of 
the development of simple CWP and PMF and the pre-existing occupational 
exposure histories of members of the current coal mining workforce. Our 
estimated benefit is based on the estimated number of underground coal 
miners working at the mine face, 17,280. If the size of this workforce 
significantly changed in the future and the projected pattern of 
prevented overexposures remained the same, the number of cases of 
prevented simple CWP and PMF would need to be adjusted to account for 
the change.
    Finally, even standing alone, without simultaneously requiring that 
the effectiveness of underground mine ventilation plans be verified 
(i.e., the Plan Verification NPRM), the proposed standard allowing MSHA 
to use single, full-shift samples to identify overexposures requiring 
corrective action would provide miners with health benefits.\30\ Both 
the prospect of being cited for overexposure and the actual issuance of 
additional citations due to this rule would compel mine operators to be 
more attentive to the level of respirable dust in their mines. 
Therefore, it is reasonable to expect, over time, a further decline in 
the number of shifts during which the concentration of respirable coal 
mine dust is at or above the applicable standard. Thus, implementation 
of the single, full-shift sample strategy will, in and of itself, on 
average, lower miners' cumulative exposure to respirable coal mine 
dust. Since cumulative exposure to respirable coal mine dust is the 
main determinant in the development of both simple CWP and PMF, the 
Agencies are confident that the use of single, full-shift samples, by 
themselves, even without the help of a verified dust control plan, 
would result in better health protection to miners.
---------------------------------------------------------------------------

    \30\ See detailed discussion in the Significance of Risk 
section.
---------------------------------------------------------------------------

    Various data, assumptions and caveats were used to conduct the 
quantitative risk assessment, significance of risk discussion, and 
benefits analyses. Therefore, we request any information which would 
enable us to conduct more accurate analyses of the estimated health 
benefits of the single, full-shift sample rule and plan verification 
rule, both individually, and in combination.

[[Page 42106]]



  Table XIII-2.--Over a Working Lifetime Among Affected Miners, Estimated Number of Cases of CWP \a\ and PMF \b\ Prevented Due to the Implementation of
                                                           Single-Sample and Plan Verification
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                               Simple CWP categories  1, 2, 3 or   Simple CWP categories  2 or 3 or                   PMF
                                                              PMF                                 PMF                -----------------------------------
         Type of miner             Affected  ------------------------------------------------------------------------
                                  miners, n=    Reduction in    Prevented cases,    Reduction in    Prevented cases,    Reduction in    Prevented cases,
                                                  risk \c\             n=             risk \c\             n=             risk \c\             n=
--------------------------------------------------------------------------------------------------------------------------------------------------------
Affected Designated                    1,080        18.0/1,000              19.4         9.8/1,000              10.6           5/1,000               5.5
 Occupational Miners \d\.......
Affected Non-Designated                7,560         2.3/1,000              17.4         1.3/1,000               9.8           1/1,000               5.3
 Occupational Miners e.........
                                ------------------------------------------------------------------------------------------------------------------------
    Total......................        8,640                na                37                na                20                na               11
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Simple CWP: simple coal workers' pneumoconiosis.
\b\ PMF: progressive massive fibrosis.
\c\ Reduction in risk per 1,000 affected miners, over a 45-year working lifetime.
\d\ Affected Designated Occupation (D.O.) Miners: includes all miners who work at the 56-percent of the Mechanized Mining Units under consideration and
  who are exposed to dust concentrations similar to the D.O., over a 45-year occupational lifetime.
\e\ Affected Non-Designated Occupation (Non-D.O.) Miners: includes all underground faceworkers under consideration who are not classified as the D.O.

B. Regulatory Flexibility Certification and Initial Regulatory 
Flexibility Analysis

    The Regulatory Flexibility Act requires MSHA and NIOSH to conduct 
an analysis of the effects of the single, full-shift sample rule on 
small entities. That analysis is summarized here; a copy of the full 
analysis is included in Chapter V of the Agencies' PREA in support of 
the proposed rule. The Agencies encourage the mining community to 
provide comments on this analysis.
    The Small Business Administration generally considers a small 
entity in the mining industry to be one with 500 or fewer workers. MSHA 
has traditionally defined a small mine to be one with fewer than 20 
workers, and has focused special attention on the problems experienced 
by such mines in implementing safety and health rules. Accordingly, the 
Agencies have separately analyzed the impact of the joint notice 
proposed rule both on mines with 500 or fewer workers and on those with 
fewer than 20 workers.
    Pursuant to the Regulatory Flexibility Act, MSHA must determine 
whether the costs of the joint notice 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 would 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. Sec. 605). In evaluating whether 
certification is appropriate, MSHA utilized a ``screening test,'' 
comparing the costs of the joint notice proposed rule to the revenues 
of the affected coal sector. If the estimated costs are less than 1 
percent of revenues for the affected entities, then the rule is assumed 
not to have a significant impact on small mine operators.
    Table XIII-3 compares, for small underground and surface coal mines 
(using both MSHA's and SBA's definition), MSHA's estimated total annual 
compliance costs of the joint notice proposed rule to estimated annual 
revenues.

 Table XIII-3.--Estimated Yearly Revenues and Costs for Single, Full-Shift Sample Proposed Rule for Underground
                                             and Surface Coal Mines
                                             [dollars in thousands]
----------------------------------------------------------------------------------------------------------------
                                                                                                     Costs as
                            Mine size                                Estimated       Estimated     percentage of
                                                                  yearly costs a    revenues b       revenues
----------------------------------------------------------------------------------------------------------------
                                             Underground Coal Mines
----------------------------------------------------------------------------------------------------------------
20..............................................................          $369.0        $249,418             0.1
500 c................................................         1,770.5       6,883,339            0.03
----------------------------------------------------------------------------------------------------------------
                                               Surface Coal Mines
----------------------------------------------------------------------------------------------------------------
20..............................................................             1.1         498,935            0.01
500..................................................             5.2      10,864,156           0.01
----------------------------------------------------------------------------------------------------------------
a Estimated yearly costs are composed of only annual costs. There are no first year costs or annualized costs in
  the proposed rule.

[[Page 42107]]

 
b Data for revenues derived from: U.S. Department of Labor, Mine Safety and Health Administration, Office of
  Standards, Regulations and Variances, based on 1997 Final MIS data (Quarter 1--Quarter 4), CM441, Cycle 1997/
  84; and U.S. Department of Energy, Energy Information Administration, Annual Energy Review 1998, DOE/EIA-
  0384(98), July 1999, p. 203.
c Includes mines with fewer than 20 employees.

    Table XIII-3 shows that under either MSHA's or SBA's definition of 
a small mine, for underground and/or surface coal mines, the estimated 
costs would be significantly less than one percent of revenues. As a 
result, MSHA is certifying that the single, full-shift sample rule for 
underground and surface coal mines would not have a ``significant 
impact on a substantial number of small entities,'' and has performed 
no further analyses.

XIV. Other Statutory Requirements

A. Unfunded Mandates Reform Act of 1995

    For purposes of the Unfunded Mandates Reform Act of 1995, this rule 
does not include any Federal mandate that may result in increased 
expenditures by State, local, and tribal governments, or increased 
expenditures by the private sector of more than $100 million.

B. Paperwork Reduction Act of 1995

    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). The proposed SFSS rule has 
annual burden hours beginning in the first year and recurring every 
year thereafter. Both underground and surface coal mines have paperwork 
provisions under the proposed SFSS rule. Underground coal mine 
operators would incur 2,985 annual burden hours and associated costs of 
$70,822. Surface coal mine operators would incur 29 annual burden hours 
and associated costs of about $1,009. These burden hours relate to 
operators performing abatement sampling, completing dust data cards, 
mailing samples to MSHA for analysis, writing respirable dust plans, 
and posting respirable dust plans. Table XIV-1 shows the burden hours 
and associated costs for each SFSS paperwork provision by mine size for 
underground and surface mines.

       Table XIV-1.--Summary of Mine Operators' Annual Paperwork Burden Hours and Costs Arising From the Single, Full-Shift Sample Proposed Rule *
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                         20 emp.         20 emp.        > 500 emp.               Total
                                                                 ----------------------    500    -------------------------------------------
                             Detail                                                    ----------------------
                                                                     Hrs.      Costs       Hrs.      Costs       Hrs.      Costs       Hrs.      Costs
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                 UNDERGROUND COAL MINES
--------------------------------------------------------------------------------------------------------------------------------------------------------
Abatement Sampling..............................................        575    $13,872      2,080    $50,181         30       $724      2,685    $64,776
Dust Data Cards.................................................         14        716         52      2,589          1         37         67      3,342
Send Samples to MSHA............................................         48        910        173      3,292          2         47        224      4,250
Write Dust Plan.................................................          3        149          6        299          0          0          9        448
Post or Give Dust Plan..........................................        0.1          2        0.2          4          0          0          0          6
                                                                 ---------------------------------------------------------------------------------------
    Total Underground...........................................        640     15,649      2,311     54,364         33        809      2,985     70,822
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                   SURFACE COAL MINES
--------------------------------------------------------------------------------------------------------------------------------------------------------
Abatement Sampling..............................................          5       $121         10       $241          0         $0         15       $362
Dust Data Cards.................................................        0.1          6        0.3         12          0          0        0.4         19
Send Samples to MSHA............................................        0.4          8        0.8         16          0          0        1.2         24
Write Dust Plan.................................................          3        149          9        448          0          0         12        597
Post or Give Dust Plan..........................................        0.1          2        0.3          6          0          0        0.4          7
                                                                 ---------------------------------------------------------------------------------------
    Total Surface...............................................          9        286         20        723          0          0         29      1,009
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           UNDERGROUND AND SURFACE COAL MINES
--------------------------------------------------------------------------------------------------------------------------------------------------------
Abatement Sampling..............................................        580    $13,993      2,090    $50,422         30       $724      2,700    $65,138
Dust Data Cards.................................................         15        722         52      2,602          1         37         68      3,361
Send Samples to MSHA............................................         48        918        174      3,308          2         47        225      4,273
Write Dust Plan.................................................          6        299         15        747          0          0         21      1,046
Post or Give Dust Plan..........................................          0          4          1          9          0          0          1         13
                                                                 ---------------------------------------------------------------------------------------
    Grand Total.................................................        649     15,935      2,332     57,087         33        809      3,014    73,831
--------------------------------------------------------------------------------------------------------------------------------------------------------
* Totals may vary due to rounding.

    MSHA invites public comments and is particularly interested in 
comments which:
    1. Evaluate whether the proposed collection of information 
(presented here and in MSHA's PREA) is necessary for the proper 
performance of the functions of MSHA, including whether the information 
will have practical utility;
    2. Evaluate 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. Enhance the quality, utility, and clarity of the information to 
be collected; and
    4. Minimize the burden of the collection of information on 
respondents, including through the use of appropriate automated, 
electronic, mechanical, or other technological collection techniques or 
other forms of

[[Page 42108]]

information technology, e.g., permitting electronic submissions of 
responses.
Submission
    MSHA and NIOSH have submitted a copy of this proposed rule to OMB 
for its review and approval of these information 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 Building, 725 17th St., NW, Rm. 10235, Washington, DC 20503, 
Attn: Desk Officer for MSHA. Submit written comments on the information 
collection not later than September 5, 2000.
    MSHA's paperwork submission summarized above is explained in detail 
in the PREA. The PREA includes the estimated costs and assumptions for 
each proposed paperwork requirement related to this proposed rule. A 
copy of the PREA is available from MSHA. 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.

C. National Environmental Protection Act

    The National Environmental Policy Act (NEPA) of 1969 requires each 
Federal agency to consider the environmental effects of proposed 
actions and to prepare an Environmental Impact Statement on major 
actions significantly affecting the quality of the human environment. 
MSHA has reviewed the proposed standard in accordance with the 
requirements of the NEPA (42 U.S.C. 4321 et seq.), the regulation of 
the Council on Environmental Quality (40 CFR Part 1500), and the 
Department of Labor's NEPA procedures (29 CFR Part 11). As a result of 
this review, MSHA has preliminarily determined that this proposed 
standard will have no significant environmental impact.
    Commenters are encouraged to submit their comments on this 
determination.

D. Executive Order 12630: Government Actions and Interference with 
Constitutionally Protected Property Rights

    This proposed rule is not subject to Executive Order 12630, 
Governmental Actions and Interference with Constitutionally Protected 
Property Rights, because it does not involve implementation of a policy 
with takings implications.

E. Executive Order 12988: Civil Justice Reform

    The Agency has reviewed Executive Order 12988, Civil Justice 
Reform, and determined that this rulemaking will not unduly burden the 
Federal court system. The regulation has been written so as to provide 
a clear legal standard for affected conduct, and has been reviewed 
carefully to eliminate drafting errors and ambiguities.

F. Executive Order 13045: Protection of Children from Environmental 
Health Risks and Safety Risks

    In accordance with Executive Order 13045, protection of children 
from environmental health risks and safety risks, MSHA has evaluated 
the environmental health or safety effects of the proposed rule on 
children. The Agency has determined that this proposal would not have 
an adverse impact on children.

G. Executive Order 13084 Consultation and Coordination with Indian 
Tribal Governments

    MSHA certifies that this proposed rule does not impose substantial 
direct compliance costs on Indian tribal governments.

H. Executive Order 13132 (Federalism)

    We have reviewed this rule in accordance with Executive Order 13132 
regarding federalism, and have determined that it does not have 
``federalism implications.'' The rule does not ``have substantial 
direct effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government.''

XV. Public Hearings

    The Agencies will hold public hearings on the proposed rule. The 
hearings will be held in Prestonsburg, Kentucky, (Jenny Wiley State 
Resort Park); Morgantown, West Virginia; and Salt Lake City, Utah. The 
hearing dates, times, and specific locations will be announced by a 
separate document in the Federal Register. The hearings will be held 
under Section 101 of the Federal Mine Safety and Health Act of 1977.

Appendix A--The Effects of Averaging Dust Concentration Measurements

    MSHA's measurement objective in collecting a dust sample is to 
determine the average dust concentration at the sampling location on 
the shift sampled. As discussed in the main text, MSHA and NIOSH 
find that a single, full-shift measurement can accurately represent 
the average full-shift dust concentration being measured. 
Nevertheless, because of sampling and analytical errors inherent in 
even the most accurate measurement process, the true value of the 
average dust concentration on the sampled shift can never be known 
with complete certainty. However accurate the representation, a 
measurement can provide only an estimate of the true dust 
concentration.
    Throughout this appendix, some public comments made to February 
18 and June 6, 1994 notices relevant to issues regarding single, 
full-shift sampling will be cited and addressed to emphasize key 
findings on accuracy and the effects of averaging dust concentration 
measurements. Some previous commenters contended that MSHA should 
not rely on single samples for making noncompliance determinations, 
because an average of results from multiple samples would estimate 
the true dust concentration more accurately than any single 
measurement.
    Contrary to the views expressed by these commenters, averaging a 
number of measurements does not necessarily improve the accuracy of 
an estimation procedure. Consider, for example, an archer aiming at 
targets mounted at random and possibly overlapping positions on a 
long partition. Each arrow might be aimed at a different target. 
Suppose that an observer, on the opposite side of the partition from 
the archer, cannot see the targets but must estimate the position of 
each bull's eye by locating protruding arrowheads.
    Each protruding arrowhead provides a measurement of where some 
bull's eye is located. If two arrowheads are found on opposite ends 
of the partition, averaging the positions of these two arrowheads 
would not be a good way of determining where any real target is 
located. To estimate the location of an actual target, it would 
generally be preferable to use the position of a single arrow. The 
average would represent nothing more than a ``phantom'' target 
somewhere near the center, where the archer probably did not aim on 
either shot and where no target may even exist.
    The archery example can be extended to illustrate conditions 
under which averaging dust concentration measurements does or does 
not improve accuracy. If each arrowhead is taken to represent a 
full-shift dust sample, then the true average dust concentration at 
the sampling location on a given shift can be identified with the 
location of the bull's eye at which the corresponding arrow was 
aimed. The accuracy of a measurement refers to how closely the 
measurement can be expected to come to the quantity being measured. 
Statistically, accuracy is the combination of two distinct concepts: 
precision, which pertains to the consistency or variability of 
replicated measurements of exactly the same quantity; and bias, 
which pertains to the average amount by which these replicated 
measurements deviate from the quantity being measured. Bias and 
precision are equally important components of measurement accuracy.
    To illustrate, arrows aimed at the same target might 
consistently hit a sector on the

[[Page 42109]]

lower right side of the bull's eye. The protruding arrowheads would 
provide more or less precise measurements of where the bull's eye 
was located, depending on how tightly they were clustered; but they 
would all be biased to the lower right. On the other hand, the 
arrows might be distributed randomly around the center of the bull's 
eye, and hence unbiased, but spread far out all over the target. The 
protruding arrowheads would then provide unbiased but relatively 
imprecise measurements.
    More complicated situations can easily be envisioned. Arrows 
aimed at a second target would provide biased measurements relative 
to the first target. Alternatively, if the archer always aims at the 
same target, the first shot in a given session might tend to hit 
near the center, with successive shots tending to fall off further 
and further to the lower right as the archer's arm tires; or shots 
might progressively improve, as the archer adjusts aim in response 
to prior results.
    Averaging reduces the effects of random errors in the archer's 
aim, thereby increasing precision in the estimation procedure. If 
the archer always aims at the same target and is equally adept on 
every shot (i.e., if the arrowheads are all randomly and identically 
distributed around a fixed point), then averaging improves the 
estimate's precision without introducing any bias. Averaging in such 
cases provides a more accurate method of estimating the bull's eye 
location than reliance on any single arrowhead. If, however, the 
archer intentionally or unintentionally switches targets, or if the 
archer's aim progressively deteriorates, then averaging can 
introduce or increase bias in the estimate. If the gain in precision 
outweighs this increase in bias, then averaging several independent 
measurements may still improve accuracy. However, averaging can also 
introduce a bias large enough to offset or even surpass the 
improvement in precision. In such cases, the average position of 
several arrowheads can be expected to locate the bull's eye less 
accurately than the position of a single arrowhead.

I. Multi-Locational Averaging

    Some previous commenters opposed MSHA's use of a single, full-
shift measurement for enforcement purposes, claiming that 
determinations based on such measurements would be less accurate 
than those made under MSHA's existing enforcement policy of 
averaging multiple measurements taken on an MMU. There are two 
distinctly different types of multi-locational measurement averages 
that could theoretically be compiled on a given shift: (1) the 
average might combine measurements taken for different occupational 
locations and (2) the average might combine measurements all taken 
for the same occupational location. For MMUs, the averages used in 
MSHA's sampling program usually involve measurements taken for 
different occupational locations on the same shift. These are 
averages of the first type. MSHA's sampling program has never 
utilized averages of the second type. Therefore, those commenters 
who claimed that reliance on a single, full-shift measurement would 
reduce the accuracy of noncompliance determinations, as compared to 
MSHA's existing enforcement policy, are implicitly claiming that 
accuracy is increased by averaging across different occupational 
locations.
    Averaging measurements obtained from different occupational 
locations on an MMU is like averaging together the positions of 
arrows aimed at different targets. The average of such measurements 
is an artificial, mathematical construct that does not correspond to 
the dust concentration for any actual occupational location. 
Therefore, this type of averaging introduces a bias proportional to 
the degree of variability in actual dust concentration at the 
various locations averaged.
    The gain in precision that results from averaging measurements 
taken at different locations outweighs this bias only if variability 
from location to location is smaller than variability in measurement 
error. However, commenters opposed to MSHA's use of single, full-
shift measurements for enforcement purposes argued that this is not 
generally the case and even submitted data and statistical analyses 
in support of this position. Commenters in favor of noncompliance 
determinations based on a single, full-shift measurement agreed that 
variability in dust concentration is extensive for different 
occupational locations and argued that MSHA's existing policy of 
measurement averaging is not sufficiently protective of miners 
working at the dustiest locations.
    Since an average of the first type combines measurement from the 
dustiest location with measurements from less dusty locations, it 
must always fall below the best available estimate of dust 
concentration at the dustiest location. In effect, averaging across 
different occupational locations dilutes the dust concentration 
observed for the most highly exposed occupations or dustiest work 
positions. Therefore, such averaging results in a systematic bias 
against detecting excessive dust concentrations for those miners at 
greatest risk of overexposure.
    A somewhat better case can be made for the second type of multi-
locational averaging, which combines measurements obtained on the 
same shift from a single occupational location. As some previous 
commenters pointed out, however, there is ample evidence that 
spatial variability in dust concentration, even within relatively 
small areas, is frequently much larger than variability due to 
measurement error. Therefore, the same kind of bias introduced by 
averaging across occupational locations would also arise, but on a 
lesser scale, if the average measurement within a relatively small 
radius were used to represent dust concentration at every point in 
the atmosphere to which a miner is exposed. A miner is potentially 
exposed to the atmospheric conditions at any valid sampling 
location. Consistent with the Mine Act and implementing regulations, 
MSHA's enforcement strategy is to limit atmospheric dust 
concentration wherever miners normally work or travel. Therefore, 
the more spatial variability in dust concentration there is within 
the work environment, the less appropriate it is to use measurement 
averaging to enforce the applicable standard by averaging 
measurements obtained at different sampling locations.
    Some of the previous comments implied that instead of measuring 
average dust concentration at a specific sampling location, MSHA's 
objective should be to estimate the average dust concentration 
throughout a miner's ``breathing zone'' or other area near a miner. 
If estimating average dust concentration throughout some zone were 
really the objective of MSHA's enforcement strategy, then averaging 
measurements made at random points within the zone would improve 
precision of the estimate without introducing a bias. This type of 
averaging, however, has never been employed in either the MSHA or 
operator dust sampling programs. MSHA's current policy of averaging 
measurements obtained from different zones does not address spatial 
variability in the area immediately surrounding a sampler unit. 
Therefore, even if averaging measurements from within a zone were 
somehow beneficial, this would not demonstrate that MSHA's existing 
enforcement policy is more reliable than basing noncompliance on a 
single, full-shift measurement.
    Furthermore, if the objective were really to estimate average 
dust concentration throughout some specified zone on a given shift, 
then it would often be necessary to obtain far more than five 
simultaneous measurements within the zone. This is not only because 
of potentially large local differences in dust concentration. In 
order to use such measurements for enforcement purposes, variability 
in dust concentration within the sampled area would have to be 
estimated along with the average dust concentration itself. As some 
previous commenters correctly pointed out, doing this in a 
statistically valid way would generally require at least twenty to 
thirty measurements. One of these commenters also pointed out that 
such an estimate, based on even this many measurements in the same 
zone, could be regarded as accurate only under certain questionable 
assumptions about the distribution of dust concentrations. This 
commenter calculated that hundreds of measurements would be required 
in order to avoid these tenuous assumptions. Clearly, this shows 
that the objective of estimating average dust concentration 
throughout a zone is not consistent with any viable enforcement 
strategy to limit dust concentration on each shift in the highly 
heterogeneous and dynamic mining environment. The large number of 
measurements required to accurately characterize dust concentration 
over even a small area merely demonstrates why it is not feasible to 
base enforcement decisions on estimated atmospheric conditions 
beyond the sampling location.
    MSHA and NIOSH recognize that a single, full-shift measurement 
will not provide an accurate estimate of average dust concentration 
anywhere beyond the sampling location. The Mine Act, however, does 
not require MSHA to estimate average dust concentration at locations 
that are not sampled or to estimate dust concentration averaged over 
any zone or region of the mine.

[[Page 42110]]

Instead, the Mine Act requires that a miner will not be exposed to 
excessive dust wherever he/she normally works or travels. This can 
be accomplished by maintaining the average dust concentration at 
each valid sampling location at or below the applicable standard 
during each shift.

II. Multi-Shift Averaging

    Some previous commenters maintained that in order to reduce the 
risk of erroneous noncompliance determinations, MSHA should average 
measurements obtained from the same occupation on different shifts. 
These commenters contended that the average of measurements from 
several shifts represents the average dust concentration to which a 
miner is exposed more accurately than a single, full-shift 
measurement. Other commenters, who favored noncompliance 
determinations based on single, full-shift measurements, claimed 
that conditions are sometimes manipulated so as to produce unusually 
low dust concentrations on some of the sampled shifts. These 
commenters suggested that, due to these unrepresentative shifts, 
multi-shift averaging can yield unrealistically low estimates of the 
dust concentration to which a miner is typically exposed. Some of 
these commenters also argued that the Mine Act requires the dust 
concentration to be regulated on each shift, and that multi-shift 
averaging is inherently misleading in detecting excessive dust 
concentration on an individual shift.
    Those advocating multi-shift averaging generally assumed that 
the measurement objective is to estimate a miner's average dust 
exposure over a period longer than an individual shift. This 
assumption is flawed, as shown by the fact that section 202(b) of 
the Mine Act specifies that each operator will continuously maintain 
the average concentration of respirable dust in the mine atmosphere 
during each shift at or below the applicable standard. Some of those 
advocating multi-shift averaging, however, suggested that MSHA 
should average measurements obtained on different shifts even if the 
quantity of interest is dust concentration on an individual shift. 
These commenters argued that averaging smooths out the effects of 
measurement errors, and that therefore the average over several 
shifts would represent dust concentration on each shift more 
accurately than the corresponding individual, full-shift 
measurement.
    The Secretaries recognize that there are circumstances, not 
experienced in mining environments, under which averaging across 
shifts could improve the accuracy of an estimate for an individual 
shift. Just as averaging the positions of arrows aimed at nearly 
coinciding targets might better locate the bull's eye than the 
position of any individual arrow, the gain in precision obtained by 
averaging dust concentrations observed on different shifts could, 
under analogous circumstances, outweigh the bias introduced by using 
the average to estimate dust concentration for an individual shift. 
This would be the case, however, only if variability in dust 
concentration among shifts were small compared to variability due to 
measurement imprecision. It would do no good to average the location 
of arrows aimed at different targets unless the targets were at 
nearly identical locations.
    To the contrary, several previous commenters pointed out that 
variability in dust concentration from shift to shift tends to be 
much larger than variability due to measurement error and introduced 
evidence in support of this observation. Measurements on different 
shifts are like arrows aimed at widely divergent targets. The more 
that conditions vary, for any reason, from shift to shift, the more 
bias is introduced by using a multi-shift average to represent dust 
concentration for any individual shift. Under these circumstances, 
any improvement in precision to be gained by simply averaging 
results is small compared to the bias introduced by such averaging. 
Therefore, the Secretaries have concluded that MSHA's existing 
practice of averaging measurements collected on different shifts 
does not improve accuracy in estimating dust concentration to which 
a miner is exposed on any individual shift. To paraphrase one 
previous commenter, averaging Monday's exposure measurement with 
Tuesday's does not improve the estimate of Monday's average dust 
concentration.
    Some previous commenters argued that since the risk of 
pneumoconiosis depends on cumulative exposure, the measurement 
objective should be to estimate the dust concentration to which a 
miner is typically exposed and to identify cases of excessive dust 
concentration over a longer term than a single shift. Other previous 
commenters claimed that a multi-shift average does not provide a 
good estimate of either typical dust concentrations or exposures 
over the longer term. These commenters claimed that different shifts 
are not equally representative of the usual atmospheric conditions 
to which miners are exposed, implying that the average of 
measurements made on different shifts of a multi-day MSHA inspection 
tends to systematically underestimate typical dust concentrations.
    The Secretaries interpret the Mine Act as requiring that dust 
concentrations be kept at or below the applicable standard on each 
and every shift. Nevertheless, the Secretaries recognize that, under 
certain conditions, the average of measurements from multiple shifts 
can be a better estimate of ``typical'' atmospheric conditions than 
a single measurement. This applies, however, only if the sampled 
shifts comprise a random or representative selection of shifts from 
whatever longer term may be under consideration. As shown below, 
evidence to the contrary exists, supporting those commenters who 
maintained that measurements collected over several days of a multi-
day MSHA inspection do not meet this requirement. Therefore, the 
Secretaries have concluded that averaging such measurements is 
likely to be misleading even for the purpose of estimating dust 
concentrations to which miners are typically exposed.
    Whether the objective is to measure average dust concentration 
on an individual shift or to estimate dust concentration typical of 
a longer term, the arguments presented for averaging across shifts 
all depend on the assumption that every shift sampled during an MSHA 
inspection provides an unbiased representation of dust exposure over 
the time period of interest.\31\ To check this assumption, MSHA 
performed a statistical analysis of multi-shift MSHA inspections 
carried out prior to the SIP. This analysis, placed into the record 
in September 1994, examined the pattern of dust concentrations 
measured over the course of these multi-shift inspections and 
compared results from the final shift with results from a subsequent 
single-shift sampling inspection (Kogut, September 6, 1994b).
---------------------------------------------------------------------------

    \31\ Technically, the assumption is that dust concentrations on 
all shifts sampled are independently and identically distributed 
around the quantity being estimated.
---------------------------------------------------------------------------

    The analysis found that dust concentrations measured on 
different shifts of the same MSHA inspection were not randomly 
distributed. The later samples tended to show significantly lower 
results than earlier samples, indicating that dust concentrations on 
later shifts of a single inspection may decline in response to the 
presence of an inspector. Furthermore, the analysis provided 
evidence that the reduction in dust concentration tends to be 
reversed after the inspection is terminated. These two results led 
to the conclusion that averaging dust concentrations measured on 
different shifts of a multi-day MSHA inspection introduces a bias 
toward unrealistically low dust concentrations.
    One previous commenter questioned the validity of this analysis, 
stating that ``there is absolutely no basis in the * * * report for 
the assertion that the trend is reversed after the inspection is 
terminated.'' This commenter apparently overlooked Table 3 of the 
report. That table shows a statistically significant reversal at 
those mine entities included in the analysis that were subsequently 
inspected under MSHA's SIP. Dust concentrations measured at these 
mine entities had declined significantly between the first and last 
days of the multi-shift inspection. It was primarily to address the 
commenter's implication that these reductions reflected permanent 
``adjustments in dust control measures'' that the analysis included 
a comparison with the subsequent SIP inspection. An increase, 
representing a reversal of the previous trend, was observed on the 
single shift of the subsequent inspection, relative to the dust 
concentration measured on the final shift of the previous multi-
shift inspection. This reversal was found to be ``statistically 
significant at a confidence level of more than 99.99 percent.''
    The same commenter also stated that MSHA ``* * * fails to 
address the systematic [selection] bias of the study. MSHA only does 
multiple day sampling when the initial results are higher, but not 
out of compliance.'' It is true that in order to be selected for 
revisitation, a mine entity must have shown relatively high 
concentrations on the first shift--though not, in the case of an 
MMU, so high as to warrant a citation on first shift. Since no 
experimental data were available on mine entities randomly selected 
to receive multi-shift inspections, the only cases in which patterns 
over the course of a multi-shift inspection could be examined

[[Page 42111]]

were cases selected for multi-shift inspection under these criteria.
    Although the impact of the selection criteria was not explicitly 
addressed, it was recognized that entities selected for multi-day 
inspections do not constitute a random selection of mine entities. 
This recognition motivated, in part, the report's comparison of the 
final shift measurement to the dust concentration measured during a 
subsequent single-shift inspection. The magnitude of the average 
reversal indicates that most of the reduction observed over the 
course of the multi-shift inspection cannot be attributed to the 
selection criteria. Furthermore, it was not only mine entities with 
relatively low dust concentration measurements that were left out of 
the study group. Mine entities with the highest dust concentration 
measurements were immediately cited based on the average of 
measurements taken and excluded from the group subjected to multi-
shift dust inspections. Therefore, the effect on the analysis of 
selecting mine entities with relatively high initial dust 
concentration measurements was largely offset by the effect of 
excluding those entities with even higher initial measurements. In 
any event, the magnitude of the average reduction between first and 
last shifts of a multi-shift inspection was significantly greater 
than what can be explained by selection for revisitation due to 
measurement error on the first shift sampled.
    The assumption that multiple shifts sampled during a single MSHA 
inspection are equally representative is clearly violated if, as 
some commenters alleged, operating conditions are deliberately 
altered after the first shift in response to the continued presence 
of an MSHA inspector and then changed back after the inspector 
leaves. However, if samples are collected on successive or otherwise 
systematically determined shifts or days, the assumption can also be 
violated by changes arising as part of the normal mining cycle. As 
one commenter pointed out, multi-shift averaging within a single 
MSHA inspection potentially introduces biases typical of ``campaign 
sampling,'' in which observations of a dynamic process are clustered 
together over a relatively narrow time span. In order to construct 
an unbiased, multi-shift average for each phase of mining activity, 
it would be necessary to collect samples from several shifts 
operating under essentially the same conditions. Alternatively, to 
construct an unbiased, multi-shift estimate of dust concentration 
over a longer term, it would be necessary to collect samples from 
randomly selected shifts over a period great enough to reflect the 
full range of changing conditions. Neither requirement is met by 
multi-shift MSHA inspections because (1) the mine environment is 
dynamic and no two shifts are alike and (2) MSHA inspectors are not 
there long enough to observe every condition in their inspection.
    Based on the analysis presented by Kogut (September 6, 1994b) 
and also on public comments received in response to the February 18 
and June 6, 1994, notices, the Secretaries have concluded that it 
should not be assumed that multiple shifts sampled during a single 
MSHA inspection are equally representative of atmospheric conditions 
to which a miner is typically exposed. This conclusion undercuts the 
rationale for multi-shift averaging within a single MSHA inspection, 
regardless of whether the objective is to estimate dust 
concentration for the individual shifts sampled as it is for MSHA 
inspector sampling or for typical shifts over a longer term as 
implied by some commenters. Measurements collected by MSHA on 
consecutive days or shifts of the same inspection do not comprise a 
random or otherwise representative sample from any larger population 
of shifts that would properly represent a long-term exposure or a 
particular phase of the mining cycle. Therefore, there is no basis 
for assuming that multi-shift averaging improves accuracy or reduces 
the risk of an erroneous enforcement determination.

Appendix B--Why Individual Measurements are Unbiased

    The accuracy of a measurement depends on both precision and bias 
(Kennedy, et al., 1995). Precision refers to consistency or 
repeatability of results, and bias refers to an error that is 
equally present in every measurement. Since the amount of dust 
present on a filter capsule is measured by subtracting the pre-
exposure weight from the post-exposure weight, any bias present in 
both weight measurements is mathematically canceled out by 
subtraction. A control filter capsule is pre- and post-weighed along 
with the exposed filter capsules. The weight gain of each exposed 
capsule is adjusted by subtracting the weight gain or loss of the 
control filter capsule. Consequently, any bias due to differences in 
pre- and post-exposure laboratory conditions, or to changes 
introduced during storage and handling of the filter capsules, is 
also mathematically canceled out. Therefore, since respirable dust 
is defined by section 202(e) of the Mine Act (30 U.S.C. 842(e)) to 
be whatever is measured by an approved sampler unit, the Secretaries 
have concluded that a single, full-shift measurement made with an 
approved sampler unit provides an unbiased representation of average 
dust concentration for the shift and sampling location sampled. Some 
previous commenters, however, suggested that MSHA's sampling and 
analytical method is subject to systematic errors that would have 
the same effect on all measurements. These comments are addressed in 
this appendix.

I. The Value of the MRE Conversion Factor

    The current U.S. coal mine dust standard is based on studies of 
British coal miners. In these studies, full-shift dust measurements 
were made using a sampler employing four horizontal plates which 
removed the large-sized particles by gravitational settlement 
(simulating the action of the nose and throat) and collecting on a 
pre-weighed filter those particles which are normally deposited in 
the lungs (Goddard, et al., 1973). This instrument, known as the 
Mining Research Establishment (MRE) sampler, was designed to collect 
airborne dust according to a collection efficiency curve, developed 
by the British Medical Research Council (BMRC) to approximate the 
deposition of inhaled particles in the lung. Because the MRE 
instrument was large and cumbersome, other samplers using a 10-mm 
nylon cyclone were developed for taking samples of respirable dust 
in U.S. coal mines. However, these cyclone-based samplers collected 
less dust than the MRE instrument. Therefore, a factor was derived 
(1.38) to convert measurements obtained with the cyclone-based 
samplers to measurements obtained with the MRE instrument.
    Two previous commenters noted that the 1.38 conversion factor 
was derived from a comparison of MRE measurements to measurements 
obtained using pumps made by two manufacturers: Mine Safety 
Appliances Co. and Unico. These commenters noted that there was some 
variability in these comparisons that MSHA and NIOSH did not 
consider in estimating CVtotal, and stated that MSHA and 
NIOSH should therefore make allowances for any error or uncertainty 
in the conversion factor. It was also noted that the report deriving 
the conversion factor showed that Mine Safety Appliances Co. pumps 
more closely approximated MRE concentrations than Unico pumps, 
indicating that the 1.38 conversion factor (derived empirically 
using both types of pumps) may systematically overestimate the MRE-
equivalent dust concentration for Mine Safety Appliances Co. 
samplers specifically. This commenter argued that such potential 
bias in the conversion factor should be addressed in order to 
account for the possibility of a systematic error in the conversion.
    The study referred to these previous commenters involved 
collecting side-by-side samples using MRE and cyclone-based samplers 
(Tomb, et al., 1973). The data showed that multiplying the cyclone 
sample concentrations by a constant factor of 1.38 gave values in 
reasonable agreement with MRE measurements. Consequently, a 
conversion factor of 1.38 was adopted for use with approved sampler 
units equipped with the 10-mm nylon cyclone.
    Variability in the operating characteristics of individual 
sampler units is expressed by CVsampler. In response to 
the comment on potential bias, MSHA and NIOSH reviewed the original 
report recommending the 1.38 MRE conversion factor. This report 
contained both an empirical determination, using side-by-side 
comparison data collected in underground coal mines, and a 
theoretical determination of the conversion factor. Two sets of 
field data were collected: one set was collected by mine inspectors 
who visited 200 coal mines across the U.S.; the other set was 
collected by investigators from MSHA's Pittsburgh laboratory at 24 
coal mines. Linear regression was used to analyze both sets of data, 
with the slope of the regression line representing the conversion 
factor. The theoretical determination suggested that the conversion 
factor should be close to a value of 1.35. Analysis of the district 
mine inspector data resulted in a conversion factor of 1.38, while 
analysis of the laboratory investigator data suggested a greater 
conversion factor of 1.45.
    Because the conversion factor derived from the inspector data 
came closer to the theoretical value, the former U.S. Bureau of 
Mines' Pittsburgh Technical Support Center

[[Page 42112]]

(in the Department of Interior) recommended that 1.38 be the value 
adopted for any approved sampler unit operating at 2.0 L/min and 
equipped with a 10-mm nylon cyclone. This recommendation was 
subsequently accepted. The 1.38 conversion factor was not, as 
implied by the commenters, meant to represent the average value to 
be used with two different types of sampler unit, one of which is no 
longer in use. Instead, based largely on the theoretical value, it 
was meant to represent the appropriate value to be used with any 
approved sampler unit operating at 2.0 L/min and equipped with a 10-
mm nylon cyclone. No data or analyses were submitted to suggest that 
this conversion factor, which has been accepted and used for over 
twenty years, should be any other value.

II. Conforming to the ACGIH and ISO Standard

    One commenter implied that the respirable dust cyclone 
specifications used by MSHA result in a different particle 
collection efficiency curve than that specified by the American 
Conference of Governmental Industrial Hygienists (ACGIH) and the 
International Organization for Standardization (ISO) for a 
respirable dust sampler. Other previous commenters questioned 
whether the 2.0 L/min flow rate used by MSHA was appropriate, since 
a NIOSH study recommended using a 1.7 L/min flow rate when 
conforming to the recently adopted ACGIH/ISO specifications for 
collecting respirable particulate mass.
    It is true that MSHA's respirable dust cyclone specifications 
result in a different particle size distribution than that specified 
by ACGIH and ISO. However, this fact has no bearing on the 
conversion to a respirable dust concentration as measured by an MRE 
sampler, which is the basis of the respirable dust standard. The 
1.38 factor used to obtain an MRE-equivalent concentration was 
derived for a cyclone flow rate of 2.0 L/min. If a flow rate of 1.7 
L/min were used, then this would correspond to some other factor for 
converting to an MRE-equivalent dust concentration. Therefore, the 
particle size distribution obtained at 2.0 L/min governs the 
relationship derived between an approved respirable coal mine dust 
sampler and an MRE sampler. The appropriate dust fraction (i.e., the 
fraction corresponding to the 1.38 conversion factor) is sampled so 
long as the specified 2.0 L/min flow rate is maintained.

III. Effects of Other Variables

    The effects of any other variables on the sampled dust fraction 
are covered by the 1.38 conversion factor, so long as these effects 
were present in the data from which the conversion factor was 
obtained. For example, one commenter expressed concern that nylon 
cyclones are subject to performance variations due to static 
charging phenomena. Any systematic effect of static charging on the 
performance characteristics of the nylon cyclone is implicitly 
accounted for in the conversion factor, because the same static 
charging effect would have been present when the comparative 
measurements were obtained for deriving the relationship between an 
approved sampler unit and an MRE instrument. Random effects of 
static charging, i.e., effects that vary from sample to sample, are 
included in CVtotal.

Appendix C--Components of CV total

I. Weighing Uncertainty

(a) Derivation of CVweight

    The weight of a dust sample is determined by weighing each 
filter capsule before and after exposure and then determining the 
weight gain by subtraction. This weight gain is adjusted by 
subtracting any change in weight observed for the unexposed, control 
filter capsule. This practice eliminates potential biases due to any 
possible outgassing of the plastic cassette or other time-related 
factors but introduces two additional weighings. The weighing 
process is designed to control potential effects of temperature, 
humidity, and contamination. However, because the initial and final 
weighings of both the exposed and the control filter capsules are 
each still subject to random error, there is some degree of 
uncertainty in the computed weight of dust collected on the filter.
    For both the control and the exposed filter capsule, the error 
in the weight-gain measurement results from combining two 
independent weighing errors. For example, suppose that the true pre- 
and post-exposure weights of a filter capsule are W1 = 
392.275 mg and W2 = 392.684 mg, respectively. The true 
weight gain (G) would then be:
[GRAPHIC] [TIFF OMITTED] TP07JY00.004

If, due to weighing errors, pre- and post-exposure weights were 
measured at w1 = 392.282 mg and w2 = 392.679 
mg, respectively, then the measured weight gain (g) would be:
[GRAPHIC] [TIFF OMITTED] TP07JY00.005

    The error (e) in this particular weight-gain measurement, 
resulting from the combination of a 7 g error in 
w1 and a5 g error in w2, would then 
be:
[GRAPHIC] [TIFF OMITTED] TP07JY00.006

    Imprecision in the true weight gain is expressed by Qe, the 
standard deviation of e. When a weight-gain measurement (g) is 
converted to an MRE-equivalent concentration (in units of mg/m\3\) 
based on a 480-minute sample at 2.0 L/min, both the actual weight 
gain (G) and the weight-gain error (e) are multiplied by the same 
factor:
---------------------------------------------------------------------------

    \32\ Prior to mid-1995 there were two additional sources of 
uncertainty in the weight gain recorded for MSHA inspector samples. 
First, filter capsules were routinely weighed in different 
laboratories before and after exposure, without use of blank filters 
or control filters, thus subjecting them to interlaboratory 
variability. Second, the pre- and post-exposure weights were both 
truncated down to the nearest exact multiple of 0.1 mg, below the 
weight actually measured, prior to recording weight gain and 
calculating dust concentration.
[GRAPHIC] [TIFF OMITTED] TP07JY00.007


[[Page 42113]]


    Therefore, the standard deviation of the propagated weighing 
error component in a single, full-shift measurement (x = 
g1.438/m\3\) is 1.438e mg/m\3\, 
assuming no adjustment for weight change in the control filter 
capsule.
    Since a control filter capsule will is used to eliminate 
potential bias, the weight gain measured for the exposed filter (g) 
is adjusted by subtracting the change in weight (which may be 
positive or negative) observed for the control filter capsule (g'). 
Therefore, the adjusted measurement of dust concentration is
[GRAPHIC] [TIFF OMITTED] TP07JY00.008

Any change in weight observed for the control filter capsule is 
subject to the same measurement imprecision due to random weighing 
errors, represented by e, as the weight gain 
measurement for an exposed filter. In addition to the weight-gain 
error for the exposed filter whose measured weight gain is g, x' 
will also contain a weight-gain error contributed by the measured 
change in weight of the control filter capsule (g'). Using a 
standard propagation-of-errors formula, the imprecision is 
represented by
[GRAPHIC] [TIFF OMITTED] TP07JY00.009

Therefore, the standard deviation of the propagated weighing error 
component in the adjusted measurement is 
1.438e2 mg/m\3\.
    To form an estimate of CVweight when control filter 
capsules are used, the estimated value of 1.438e 
is multiplied by 2 and expressed as a percentage of the 
true dust concentration being measured (X):
[GRAPHIC] [TIFF OMITTED] TP07JY00.010

Since e is essentially constant with respect to 
dust concentration, CVweight decreases as the dust 
concentration increases.

(b) Values Expressing Uncertainty Due to Random Errors in Weight-
Gain Measurements

    Table C-1 summarizes 13 different estimated values for 
e. Six of these values were mentioned during 
earlier proceedings related to this notice, and two additional 
values for e are derived in this appendix from 
data introduced during these earlier proceedings. Three other values 
for e are derived from data and statistical 
analyses placed into the record along with the Federal Register 
notices published by MSHA and NIOSH on February 3, 1998 (Parobeck, 
et al., 1997; Wagner, May 28, 1997). The remaining two values of 
e are derived in an analysis being placed into 
the record in connection with the present Federal Register notice 
(Kogut, et al., 1999). The 13 values listed in Table C-1 are not 
inconsistent, but as explained below, represent estimates of weight-
gain imprecision during different historical periods or under 
different sample processing procedures. Eleven of these values are 
based on weight gains measured for capsules employing a Tyvek; 
filter support pad. Two are based on capsules with stainless steel 
support pads.

   Table C-1.--Standard Deviation of Error in Weight Gain (e)
------------------------------------------------------------------------
                                                             e
            Description                    Reference        (g)
------------------------------------------------------------------------
MSHA's historical estimate of upper  59 FR 8356; Kogut,            97.4
 bound.                               September 6, 1994a.
1981 measurement assurance           Parobeck, et al.,               81
 estimate; older              1981; Bartley,
 technology, truncation of weights.   September 7, 1994.
300 unexposed tamper-resistant       Kogut, May 12, 1994..           29
 capsules pre- and post-weighed in
 different labs; no
 truncation.
Inspector samples processed between  Appendix C...........         51.7
 late 1992 and mid 1995;
 capsules pre- and post-weighed in
 different labs with truncation;
 estimate adjusted for differences
 between labs.
NMA data obtained from samples       Appendix D...........           76
 collected by Skyline Coal,
 Inc..
Value used in NIOSH ``indirect       61 FR 10012; Kogut,            5.8
 approach'' based on repeated         May 12, 1994.
 measurements on same day and in
 same lab; derived from
 Kogut.
1995 MSHA field study;       Kogut, et al., 1997;           9.1
 capsules pre-weighed, assembled,     Wagner, 1995.
 and post-weighed by MSHA.
1996 measurement assurance estimate  61 FR 10012; Tomb,             6.5
 .                            February 16, 1996.
75 unexposed capsules recalled from  Wagner, May 28, 1997.          8.2
 MSHA field offices .
50 replicate weighings of 16         Parobeck, et al.,             10.3
 unexposed filter capsules .  1997.
50 replicate weighings of 16         Parobeck, et al.,             11.2
 unexposed filter capsules .  1997.
2,640 unexposed ``quality control''  Kogut, et al., 1999..         11.3
 capsules pre-weighed by MSHA,
 assembled by MSA, and subsequently
 post-weighed by MSHA .
300 unexposed capsules pre-weighed   Kogut, et al., 1999..        11.6
 by MSHA, assembled by MSA, carried
 during MSHA inspection, and
 subsequently post-weighed by MSHA.
------------------------------------------------------------------------
 Tyvek support pad.
 stainless steel support pad.
MSA Mine Safety Appliances Co.

    In MSHA's February 1994 notice, 1.438e 
(identified as ``variability associated with the pre- and post-
weighing of the filter capsule'') was presented as 0.14 mg/m\3\, or 
7 percent of 2.0 mg/m\3\, as described in Kogut (September 6, 
1994a). It follows that the value of e

[[Page 42114]]

implicitly assumed in MSHA's February 1994 notice (obtained by 
dividing 0.14 by 1.438) was 0.0974 mg (97.4 g). Seven 
percent of 2.0 mg/m\3\ had been used by MSHA from the inception of 
its dust enforcement program to represent an upper bound on weighing 
imprecision in a dust concentration measurement.
    After publication of the February 1994 notice, several other 
candidate values for e were placed into the 
public record. In 1981, based on data collected to implement a 
measurement assurance program in MSHA's weighing laboratory, 
e was estimated using a method developed by the 
NBS to be 0.0807 mg (80.7 g) (Parobeck, et al., 1981). The 
published NBS estimate reflected weighing technology in place at the 
time the article was published (1981), as well as the practice (no 
longer in effect for MSHA inspector samples) of truncating both the 
pre- and post-exposure weights down to an exact multiple of 0.1 mg. 
This estimate was used to calculate CVweight by Bartley 
(September, 1994).
    Some previous commenters misread or misunderstood the published 
NBS estimate. One of these previous commenters claimed that ``the 
only published report of the weighing error in MSHA's laboratory * * 
* was 0.16 mg of variation, which would convert to a concentration 
of 0.20 mg/m\3\ compared to the 0.14 mg/m\3\ * * * MSHA and NIOSH 
used.'' This is incorrect, since the standard deviation of weight-
gain errors (including the effect of truncation) is actually 
identified as 0.0807 mg in the Appendix to Parobeck, et al., (1981). 
The 0.16-mg figure quoted by the commenter is presented in that 
paper as defining a 2-tailed 95-percent confidence limit, for use in 
establishing process control limits. It is derived by multiplying 
e by 2.0. As explained above, the published 
value of e = 0.0807 mg is multiplied by 1.438 
m-\3\ to propagate an MRE-equivalent concentration error 
of 0.116 mg/m\3\. Contrary to the commenters' assertion, this is 
less--not more--than the quantity (0.14 mg/m\3\) assumed in the 
February 1994 notice.
    In September 1994, a more recent analysis was placed into the 
public record, based on repeated weighings of 300 unexposed filter 
capsules, each of which was weighed once in the Mine Safety 
Appliances Co. laboratory and twice in MSHA's laboratory using 
current equipment (Kogut, May 12, 1994). Based on this analysis, 
e was estimated to be 29 g for pre- and 
post-weighings on different days at different laboratories, or 5.8 
g for pre- and post-weighings on the same day within MSHA's 
laboratory. The 5.8-g value was used as part of the NIOSH 
``indirect approach'' in its 1995 accuracy assessment (Wagner, 
1995). Neither of these two estimates, however, reflects the effects 
of truncation or of a mean difference of about 12 g 
discovered between weighings in the two laboratories. Combining 
these two additional effects with the 29-g estimate results 
in an adjusted estimate of e = 51.7 g 
for weighings made in different laboratories and truncated to a 
multiple of 0.1 mg. MSHA and NIOSH regard this 51.7-g value 
to be the best available estimate of e for 
inspector samples processed between late 1992, when the current 
style of (tamper-resistant) cassette was introduced, and mid-1995, 
changes in inspector sample processing were implemented.
    Some previous commenters suggested that the estimates of 
e, placed into the record in September 1994, did 
not adequately account for potential errors in the weighing process 
as it existed at that time. One of these previous commenters 
asserted that truncation error was an additional source of 
uncertainty that had not been accounted for. As explained above, 
however, e accounts for uncertainty deriving 
from both the pre- and post-exposure weighings. Both the 80.7-
g NBS estimate and the 97.4-g value assumed in the 
February 1994 notice included the effects of truncating weight 
measurements to 0.1 mg. Truncation effects are also included in the 
51.7-g estimate.
    Some previous commenters expressed special concern over the 
accuracy of pre-exposure filter capsule weights as measured by Mine 
Safety Appliances Co. One commenter expressed ``grave concern'' with 
regard to the 12-g systematic difference in weights found 
between Mine Safety Appliances Co. and MSHA weighings of the same 
unexposed capsules, as described in MSHA's 1994 analysis (Kogut, May 
12, 1994). These concerns became moot, at least with respect to 
MSHA's inspector sampling program, when MSHA began pre- and post-
weighing all inspector samples at MSHA's laboratory. Furthermore, 
any potential bias resulting from differences in laboratory 
conditions on the days of pre- and post-exposure weighings should 
now be eliminated by the use of control filter capsules. However, 
contrary to this commenter's interpretation, the analysis submitted 
to the record in September 1994 resulted in a substantially lower 
estimate of e than that assumed in the February 
1994 notice--even after adjustment for the 12-g systematic 
difference observed between weighing laboratories. The 51.7-
g estimate discussed above includes this adjustment.
    MSHA and NIOSH also analyzed data submitted by the NMA in 
connection with these proceedings. An important result of that 
analysis, described in Appendix D, was an estimate of 
e equal to 76 g  15 
g.\33\ This estimate is not significantly different, 
statistically, from either the 97.4-g value assumed in the 
February 1994 notice, the 80.7-g NBS estimate, or the 51.7-
g value estimated for samples collected between late 1992 
and mid-1995. Since the NMA data were obtained from samples 
collected by Skyline Coal, Inc. prior to 1995, the Secretaries 
believe these data confirm the 51.7-g value of 
e applicable to the Skyline samples. The 
estimate of e obtained from the Skyline data is, 
however, significantly greater than the value estimated for weight-
gain measurements under MSHA's current inspection program. This is 
explained by the fact that when the Skyline samples were collected, 
all samples were weighed in different laboratories before and after 
sampling, and the weights were truncated to 0.1 mg. before 
calculating the weight gain.
---------------------------------------------------------------------------

    \33\ To construct a 90-percent confidence interval for 
e, based on the Skyline data, the 15-g 
``standard error of the estimate'' must be multiplied by a 
confidence coefficient of 1.64.
---------------------------------------------------------------------------

    Both truncation of weights and the practice of pre- and post-
weighing samples in different laboratories were discontinued for 
inspector samples in mid-1995. Under MSHA's revised procedures for 
processing inspector samples, filter capsules were weighed both 
before and after sampling in MSHA's laboratory. Furthermore, MSHA 
began to use weights recorded to the nearest g in 
calculating dust concentrations. Therefore, the 5.8-g 
estimate of e described above, applying to pre- 
and post-exposure weighings in the same laboratory using current 
equipment and no truncation, was used by NIOSH to calculate 
CVweight as part of the NIOSH ``indirect'' evaluation of 
CVtotal, placed into the public record on March 12, 1996.
    Based on the results of MSHA's 1995 field study, 
e was estimated to be 9.12 g (Kogut, et 
al., 1997). The filter capsules involved in this study were used to 
collect respirable coal mine dust samples in an underground mine 
between pre- and post-exposure weighings in MSHA's laboratory, 
potentially subjecting them to unknown sources of variability in 
weight gain not covered by the laboratory estimates. Substituting 
the estimated value of e = 9.12 g into 
Equation 3 results in a corresponding estimate of 
CVweight that declines as the sampled dust concentration 
increases--ranging from 9.3 percent at dust concentrations of 0.2 
mg/m3 to less than one percent at concentrations greater 
than 2.0 mg/m3. This estimate of CVweight 
applies to the procedure utilizing control filter capsules.
    An updated estimate of e = 6.5 g 
was also calculated using the published NBS procedure for filter 
capsules processed with the current equipment and procedures for 
inspector samples. This estimate, derived from weighing the same 
group of 55 unexposed filter capsules 139 times over a 218-day 
period, was described in material placed into the public record on 
March 12, 1996 (Tomb, February 16, 1996). The 6.5 g 
estimate applies to filter capsules pre- and post-weighed 
robotically on different days within MSHA's laboratory, but it does 
not reflect any potential effects of removing the capsule from the 
laboratory and exposing it in the field between weighings.
    The estimate of imprecision in measured weight gain derived from 
MSHA's 1995 field study discussed earlier (9.1 g), falls 
only slightly above the 6.5-g laboratory estimate. This 
suggested that the process of handling and actually exposing the 
filter capsule in a mine environment does not add appreciably to the 
imprecision in measured weight gain.
    In February 1997, 75 unexposed filter capsules that had been 
pre-weighed in MSHA's laboratory and distributed to MSHA district 
offices were recalled and reweighed. After adjusting for variability 
attributable to the date of initial weighing (i.e., variability that 
would be eliminated by use of a control filter capsule), these data 
provided an estimate of e equal to 8.2 
g (Wagner, May 28, 1997). This estimate, based on weighings 
separated by a span of about four to five months, corroborated the 
9.1-g estimate obtained from MSHA's 1995 field study.

[[Page 42115]]

    An MSHA report placed into the public record with the December 
31, 1997 Federal Register notices described results from an 
experiment in which 32 filter capsules were each weighed on 50 
different days, alternating between the MSHA and Mine Safety 
Appliances Co. laboratories. Sixteen of these capsules employed a 
Tyvek filter support pad of the type approved under 30 CFR 
part 74. The remaining sixteen were of the modified type, in which 
the Tyvek support pad was replaced by a stainless steel 
support pad. The residual variance associated with an individual 
weight measurement was found to be 53.5 g2 for 
filter capsules employing a Tyvek support pad and 62.9 
g2 for capsules employing a stainless steel 
support pad (Parobeck, et al., 1997, Table 3.) These figures 
represent the squared residual variability not ``explained'' by 
repeated handling, elapsed time, changes in laboratory conditions, 
or other terms of the model used in the report. The other sources of 
variability reported (i.e., those ``explained'' by the model) are 
all eliminated by the use of a control filter. Therefore, since 
measurement of a weight gain requires two measurements of weight, 
the corresponding estimates of e are 
(253.5)1/2 = 10.3 g for 
Tyvek-supported filters and 
(262.9)1/2 = 11.2 g for stainless 
steel.
    The final two values for e presented in 
Table C-1 of this appendix are based on filter capsules pre-weighed 
in MSHA's laboratory, sent to Mine Safety Appliances Co. for 
assembly into standard plastic cassettes, and then later weighed a 
second time in MSHA's laboratory. This is currently the normal 
practice for filter capsules used by MSHA inspectors. Both of these 
values, summarized below, are derived in a statistical analysis 
being placed into the public record along with this notice (Kogut, 
et al., 1999, Table A-2). In that analysis, 
``n'' represents the portion of uncertainty in a 
weight gain measurement that a control filter correction cannot be 
expected to eliminate. This includes both weighing imprecision and 
spurious but unsystematic changes in weight, such as might be due to 
random contamination. Therefore, in the present context, 
e can conservatively be identified with 
n.
    In 1998, to maintain quality control for the production of 
filter capsules used in MSHA's enforcement program, 2,640 unexposed 
filter capsules were weighed at MSHA's laboratory before and after 
assembly by Mine Safety Appliances Co. All of these capsules 
employed a Tyvek filter support pad. The estimated value 
for n (here identified with 
e) associated with these capsules was 11.3 
g.
    In 1999, MSHA performed a special Modified Filter Capsule Study 
(MFCS) in which the Tyvek filter support pad was replaced 
by a stainless steel support pad. The purpose of the MFCS was to 
quantify the impact of such a substitution on the accuracy of 
respirable coal mine dust measurements. Based on an analysis of 
weight gains measured for 300 modified filter capsules, 
n (here identified with e) 
was estimated to be 11.6 g. All of these capsules were 
initially weighed in MSHA's laboratory, assembled into cassettes by 
Mine Safety Appliances Co., distributed to MSHA inspectors, carried 
but not exposed during a mine inspection, and then weighed for a 
second time in MSHA's laboratory. The 11.6 g value 
represents the combined effects of weighing imprecision and random 
contamination during assembly, distribution, and field use. It 
therefore provides a conservative estimate of e 
for filter capsules employing stainless steel support pads.

(c) Negative Weight-Gain Measurements

    Some previous commenters pointed out that MSHA routinely voids 
samples when the measured pre-exposure weight of a filter capsule is 
greater than the measured post-exposure weight. According to these 
commenters, such occurrences reflect an unacceptable degree of 
inaccuracy in weight-gain measurements. One commenter asserted that 
such cases are ``of particular significance when only one sample is 
relied upon.'' This commenter attributed such occurrences solely to 
errors in the capsule pre-weight and implied that they should not be 
expected to occur under MSHA's quality assurance program. It was, 
therefore, implied that negative weight-gain measurements are not 
consistent with the degree of uncertainty being attributed to 
weighing error.
    Prior to implementation of the 1995 processing modifications, a 
significant fraction of samples with less than 0.1 mg of true weight 
gain (i.e., G  0.10 mg) could be expected to exhibit negative weight 
gains (i.e., g  -0.1 mg). Contrary to the commenter's 
implication, however, negative weight-gain measurements do not arise 
exclusively from positive pre-exposure weighing errors (i.e., 
w1 > W1). They can also arise, with equal 
likelihood, from negative post-exposure weighing errors (i.e., 
w2  W2).
    What is required for a negative weight gain (w2  
w1) is that e  -G. Since the true weight gain (G) is 
always greater than or equal to zero, this means that a negative 
weight gain is observed when e is sufficiently negative. Under 
standard assumptions of normally distributed errors, 
e fully accounts for the probability of such 
occurrences. Naturally, this probability becomes smaller as G 
increases and also as e decreases.
    The occasional negative weight-gain measurements that have been 
observed are consistent with values of e 
estimated for previous processing procedures. Table C-2 contains the 
probability of a negative weight-gain measurement for true weight 
gains (G) ranging from 0.0 mg to 0.08 mg, assuming 
e = 51.7 g and the previous practice of 
truncation, which has now been discontinued for inspector samples. 
Since the purpose here is to evaluate the probability of negative 
weight gains under MSHA's previous processing procedures, it is also 
assumed that no control filter capsules are used to adjust weight 
gains.

  Table C-2.--Probability of Negative Weight-Gain Measurement, Assuming
               Truncation and e = 51.7 g
------------------------------------------------------------------------
                                                           Estimated
                                                         probability of
           True weight gain G = W2-W1 (mg)                  negative
                                                         measurement, %
------------------------------------------------------------------------
0.00.................................................               12.9
0.01.................................................                8.4
0.02.................................................                5.1
0.03.................................................                2.8
0.04.................................................                1.5
0.05.................................................                0.7
0.06.................................................                0.4
0.07.................................................                0.2
0.08.................................................                0.1
------------------------------------------------------------------------


    Note:  Tabled probabilities (in percent) were obtained from a 
simulation of 35,000 weight-gain measurements at each value of G, 
assuming normally distributed weighing errors and the now 
discontinued practice of measurement truncation.

    One commenter suggested the use of a test based on the frequency 
of negative weight-gain measurements to check the magnitude of the 
MSHA/NIOSH estimate of CVtotal. As proposed by the 
commenter, the test of CVtotal would consist of comparing 
the observed proportion of samples voided due to a negative recorded 
weight gain to the proportion expected, given CVtotal 
equal to the MSHA/NIOSH estimate. If the observed proportion were to 
exceed the expected proportion, then this would constitute evidence 
that CVtotal was being underestimated.
    The commenter miscalculated the expected proportion, because he 
mischaracterized the MSHA/NIOSH estimate of CVtotal as 
constant over the continuum of dust concentrations. The MSHA/NIOSH 
estimate of CVtotal increases as dust concentrations 
decrease. This would cause a higher proportion of negative results 
than what the commenter projected under the MSHA/NIOSH estimate, 
regardless of what statistical distribution of dust concentrations 
is assumed. The commenter's projection also neglected to take into 
account the effects of truncating pre- and post-exposure weights to 
multiples of 0.1 mg. Although this practice has now been 
discontinued for MSHA inspector samples, it is a factor in the 
available historical data.
    In principle, if the statistical distribution of true dust 
concentrations were known, the expected proportion of samples voided 
for negative weight gain could be recalculated to reflect both a 
variable CVtotal and, when applicable, truncation of 
recorded weights. However, under the commenter's proposal, deriving 
the expected proportion of negative measurements would involve not 
only CVtotal, but also an estimate of the distribution of 
true dust concentrations. Such an estimate would rely on the tenuous 
assumption that a mixture of dust concentrations in different 
environments is closely approximated by a lognormal distribution far 
into the lower tail--i.e., even at concentrations extremely near 
zero. Furthermore, valid estimation of the lognormal parameters, 
applicable to dust concentrations near zero, would be

[[Page 42116]]

complicated by measurement errors, especially those resulting in 
negative or zero values. Depending on the data used, truncation 
effects could also confound the analysis.
    Before truncation was discontinued, negative weight-gain 
measurements were caused by various combinations of pre- and post-
exposure weighing and truncation error. Before MSHA began adjusting 
weight gains using an unexposed control filter, differences in 
laboratory conditions on the two weighing days and/or unexplained 
but real systematic weight losses over time may also have 
contributed to the observed frequency of negative weight gains. Now 
that truncation has been removed as a source of error in weight-gain 
measurements for inspector samples, and control filters are used to 
correct for systematic changes, the frequency of negative weight 
gains observed historically is largely irrelevant. Significant 
negative weight-gain measurements--i.e., those that cannot be 
explained by normal weighing imprecision--are expected to occur less 
frequently than in the past.

(d) Comparing Weight Gains Obtained From Paired Samples

    Some previous commenters maintained that ``although there may be 
slight differences between how the samples are dried * * *'' 
differences between the weight gain observed in MSHA samples and 
simultaneous samples collected nearby (and processed at an 
independent laboratory) indicated a greater degree of weighing 
uncertainty than what was being assumed. In response to the 
Secretaries' request for any available data supporting this 
position, results from paired dust samples were provided by two coal 
companies.
    In comparing measurements obtained from paired samples, there 
are several important considerations that some previous commenters 
did not take into account. First, if two different sampler units are 
exposed to identical atmospheres for the same period of time, the 
difference between weight-gain measurements g1 and 
g2 arises, in part, from two independent weight-gain 
measurement errors, e1 and e2. If uncertainty 
due to each of these errors is represented by e, 
then the difference between g1 and g2 has 
uncertainty due to weighing error equal to e;2. 
Consequently, weight gains measured in the same laboratory, on the 
same day, for different filter capsules exposed to identical 
atmospheres can be expected to differ by an amount whose standard 
deviation is 1.41e.
    Furthermore, if the two exposed capsules are processed at 
different laboratories, the difference in weight gains contains an 
additional error term arising from differences between laboratories. 
Evidence was presented that this term (in the notation of Kogut, May 
12, 1994) is far more significant than the intra-lab, intra-day 
weighing error in MSHA's laboratory. Moreover, the additional 
uncertainty introduced by use of a third laboratory also depends on 
unknown weighing imprecision within that laboratory, which may 
differ from that maintained by MSHA's measurement assurance process. 
(See Appendix D for analysis of paired sample data submitted by 
NMA).
    However, the most important consideration in comparing weight 
gains from two different samples is that under real mining 
conditions, the atmospheres sampled may not be identical--even if 
the sampler units are located near one another. Differences in 
atmospheric dust concentrations over relatively small distances have 
been documented (Kissell, et al., 1993). Such differences would be 
expected to produce corresponding differences in weight gain that 
are unrelated to the accuracy of a single, full-shift measurement as 
defined by the measurement objective explained earlier in this 
notice.

II. Pump Variability

    The component of uncertainty due to variability in the pump, 
represented by CVpump, consists of potential errors 
associated with calibration of the pump rotameter, variation in flow 
rate during sampling, and (for those pumps with rotameters) 
variability in the initial adjustment of flow rate when sampling is 
begun. The Secretaries believe that CVpump adequately 
accounts for all uncertainty identified by previous commenters as 
being associated with the volume of air sampled.
    In deriving the Values Table published in MSHA's February 1994 
notice, MSHA used a value of 5 percent to represent uncertainty 
associated with initial adjustment of flow rate at the beginning of 
the shift and another value of 5 percent to represent flow rate 
variability. The 5-percent value for variability in initial flow 
rate adjustment was estimated from a laboratory experiment conducted 
by MSHA in the early 1970s, while the value for flow rate 
variability was based on the allowable flow rate tolerance specified 
in 30 CFR part 74. This part requires that the flow rate of all 
sampling systems not vary by more than 5 percent over a 
full shift with no more than two adjustments. MSHA did not include a 
separate component of variability for pump rotameter calibration 
because it was already included in the 5-percent value used to 
represent flow rate variability.
    Based on a review of published results by Bowman et al. (1984), 
the Secretaries concluded that the component of uncertainty 
associated with the combined effects of variability in flow rate 
during sampling and potential errors in calibration is less than 3 
percent. Therefore, as proposed in the March 12, 1996 notice, the 
Secretaries are now estimating uncertainty due to variability in 
flow rate to be 3 percent.
    Because MSHA could not provide the experimental data supporting 
the 5-percent value used to represent uncertainty associated with 
the initial adjustment of flow rate, one commenter recommended that 
MSHA conduct a new experiment. In response to that request, MSHA 
conducted a study to establish the variability associated with the 
initial flow rate adjustment. The study, placed into the public 
record on September 9, 1994, attempted to emulate realistic 
operating conditions by including a variety of sampling personnel 
making adjustments under various conditions. Results showed the 
coefficient of variation associated with the initial adjustment to 
be 3  0.5 percent (Tomb, September 1, 1994). The 
Secretaries consider this study to provide the best available 
estimate for uncertainty associated with the initial adjustment of a 
sampler unit's flow rate. Therefore, as proposed in the March 12, 
1996 notice, the Secretaries are now estimating uncertainty due to 
variability in the initial adjustment to be 3 percent.
    One previous commenter expressed concern regarding how 
representative MSHA's study on initial flow rate adjustment was of 
actual sampling conditions. The Secretaries consider the conditions 
under which the study was conducted to have adequately mimicked 
conditions under which the flow rate of a coal mine dust sampling 
system is adjusted. This was more rigorous than the original study, 
from which MSHA estimated the 5-percent value assumed in the 
February 12, 1994 notice. The tests were conducted in an underground 
mine, using both experienced and inexperienced persons to make the 
adjustments. Also, the only illumination was supplied by cap lamps 
worn by the person making the adjustments. Tests were conducted for 
adjustments made in three different physical positions: standing, 
kneeling and prone. Inspection personnel participating in the study 
provided guidance as to the methods typically used by inspection 
personnel in adjusting pumps. In fact, environmental conditions 
under which the test was conducted were generally more severe than 
those normally encountered by inspection personnel, since initial 
adjustment of the pumps normally occurs on the surface just before 
the work shift begins.
    The same commenter also questioned why only the variability 
associated with initial adjustment of the flow rate was estimated 
and not the variability associated with subsequent adjustments 
during the shift. This is because the variability associated with 
the subsequent flow rate adjustments of an approved sampler unit is 
already included in the 3-percent value estimated for variability in 
flow rate over the duration of the shift.
    Since variability in the initial flow rate adjustment is 
independent of calibration of the pump rotameter and variability in 
flow rate during sampling, these two sources of uncertainty can be 
combined through the standard propagation of errors formula:
[GRAPHIC] [TIFF OMITTED] TP07JY00.011


[[Page 42117]]


    This estimate accords well with a more recent finding based on 
186 measurements in an underground mine, using constant flow-control 
pumps (Kogut et al., 1997). That study estimated CVpump = 
4.0 percent and concluded that CVpump was unlikely to 
exceed 4.4 percent.
    Three previous commenters stated that there are reports of 
sampling pumps being calibrated and used at altitudes differing by 
as much as 3,000 feet and that, for many pumps, this could result in 
more than a 3-percent change in flow rate per 1,000 feet of 
altitude. MSHA recognized this as a potential problem as early as 
1975. As a result, MSHA conducted a study to ascertain the effect of 
altitude on coal mine dust sampler calibration (Treaftis, et al., 
1976). The study showed that both pump performance and rotameter 
calibration were affected by changes in altitude but that an 
approved Mine Safety Appliances Co. sampling system, calibrated and 
adjusted at an altitude of 800 feet to a flow rate of 2.0 L/min, 
would meet the requirement of 30 CFR 74.3(11) when sampling at an 
altitude of 10,000 feet, even if no adjustment were made to the 
pump. The study also provided equations for adjusting the 
calibration mark on the pump rotameter so that, when sampling at an 
altitude different from the one at which the rotameter was 
calibrated, the appropriate flow rate would be obtained. These 
procedures are used by MSHA inspectors in instances where the 
sampling altitude is significantly different from the altitude where 
the sampling system is calibrated.
    Some previous commenters questioned the ability of the older 
Mine Safety Appliances Co. Model G pumps to meet the same flow rate 
specifications as new pumps. MSHA has discontinued the use of these 
older pumps in its sampling program and will be using only flow-
control pumps. More recent MSHA studies show that these pumps 
continue to meet the flow rate requirement of 30 CFR 74.3(11) at 
altitudes up to 10,000 feet (Gero, et al., 1995). As a result, the 
flow-control pumps currently used by inspectors can be calibrated at 
one altitude and used at another altitude with no additional 
adjustments made to the pumps. Furthermore, all sampler units used 
to measure respirable dust concentrations in coal mine environments 
are required to be approved in accordance with the regulatory 
requirements of 30 CFR part 74, which require flow rate consistency 
to be within  0.1 L/min of the 2.0 L/min flow rate.\34\ 
MSHA's experience over the past 20 years has demonstrated that flow 
rate consistency of older sampling systems will continue to meet the 
requirements specified in part 74, provided the systems are 
regularly calibrated and maintained in approved condi tion. To 
ensure that sampling systems continue to meet the specification of 
part 74, MSHA's policy requires calibration and maintenance by 
specially trained personnel in accordance with MSHA Informational 
Report No. 1121 (revised).
---------------------------------------------------------------------------

    \34\ Section 74.3(13) requires that flow rate in an approved 
sampler unit deviate from 2.0 L/min by no more than 5 percent over 
an 8-hour period, with no more than 2 readjustments after the 
initial setting. However, this is a maximum deviation, and the 
uncertainty associated with pump flow rate, as quantified by its 
coefficient of variation, is 3 percent.
---------------------------------------------------------------------------

III. Intersampler Variability

    Intersampler variability, represented by CVsampler, 
accounts for uncertainty due to physical variations from sampler to 
sampler. Most of the previous commenters ignored this source of 
uncertainty. One commenter, however, stated that 10-mm nylon 
cyclones are subject to performance variations due to static 
charging phenomena (discussed in Appendix B).
    Intersampler variability was investigated by Bowman, et al., 
(1984), Bartley, et al. (1994), and Kogut, et al. (1997). Bowman, et 
al. designed a precision experiment to determine the contribution to 
CVtotal from differences between individual coal mine 
dust sampler units. Based on their experiment, they reported 
CVsampler = 1.6 percent, which included variation in both 
the 10-mm nylon cyclone and the Mine Safety Appliances Co. Model G 
pump. They concluded that this low degree of component variability 
indicates there is excellent uniformity in the mechanical components 
of dust sampler units. Bartley, from his experimental investigation 
of eight 10-mm nylon cyclones, estimated CVsampler to be 
no more than 5 percent for aerosols with a size distribution typical 
of those found in coal mine environments. Based on an analysis 
involving 32 different sampler units, Kogut, J., et al., (1997) 
found that CVsampler was unlikely to exceed 3.1 percent. 
Unlike Bartley's study, however, this analysis relied on new 
cyclones, which might be expected to exhibit less variability than 
older, heavily used cyclones. Therefore, NIOSH used the more 
conservative estimate of 5 percent, with an upper 95-percent 
confidence limit of 9 percent, in its ``indirect approach'' for 
estimating CVtotal and evaluating method accuracy 
(Wagner, 1995).

Appendix D--Data Submitted by Previous Commenters

    During the public hearings, several previous commenters 
indicated they had data showing that MSHA and NIOSH had 
underestimated the overall magnitude of uncertainty associated with 
a single, full-shift measurement. These data and accompanying 
analyses were submitted to the record and evaluated by MSHA and 
NIOSH. Some of the data sets consisted of paired samples, where two 
approved sampler units were placed nearby one another and operated 
for a full shift. One of the resulting samples was analyzed in 
MSHA's laboratory and the other by an independent laboratory. These 
data were represented as showing that single, full-shift 
measurements cannot be used to accurately estimate dust 
concentrations. Other data sets submitted consisted of unpaired 
measurements collected from miners at intervals over varying spans 
of time. These data sets were represented as showing that exposures 
vary widely between shifts and between occupations.

I. Paired Sample Data Submitted by the NMA

    The American Mining Congress and National Coal Association [AMC 
and NCA have since merged into the National Mining Association, 
(NMA)] submitted at the request of MSHA and NIOSH a data set 
consisting of 381 pairs of exposure measurements. These measurements 
had been obtained from the ``designated occupations'' on two 
longwall and six continuous mining sections belonging to Skyline 
Coal, Inc. Two sampling units were placed on each participating 
miner and operated for the full shift. After sampling, one sample 
cassette was sent to MSHA for analysis while the other was analyzed 
at a private laboratory. All samples were reported to be ``portal to 
portal'' samples as required by MSHA regulations. Using these data, 
the NMA estimated an overall CV of 16 percent. Based on this 16-
percent estimate, the NMA suggested that MSHA had underestimated 
measurement uncertainty in its February 1994 notice by 60 percent at 
dust concentrations of 2.0 mg/m3.
    The NMA estimate of 16 percent for overall CV includes not only 
sampling and analytical error, but also variability arising from two 
additional sources: (1) Spatial variability between the locations 
where the two samples were collected; and (2) interlaboratory 
variability introduced by the fact that a third laboratory was 
involved in weighing exposed filter capsules.
    Since the two dust samples within each pair submitted were not 
collected at precisely the same location, differences observed 
between paired samples in the Skyline data are partly due to spatial 
variability. The Secretaries fully recognize and acknowledge that, 
as suggested by the Skyline data, spatial variability in mine dust 
concentrations can exist, even within a relatively small area such 
as the so-called breathing zone of a miner. Consistent with general 
industrial hygiene practice, however, the Secretaries do not 
consider such variability relevant to the accuracy of an individual 
dust concentration measurement.
    The NMA expressed sampling and analytical error as a single 
percentage relative to the average of all dust concentrations that 
happened to be observed in the data analyzed. Contrary to the NMA 
analysis, sampling and analytical error cannot be expressed as a 
constant percentage of the true dust concentration. Because 
e is constant with respect to dust 
concentration, CVweight declines with increasing dust 
concentration, as explained in Appendix C. The value of 
CVtotal assumed by MSHA and NIOSH for the period when the 
Skyline samples were collected (i.e., prior to 1995) is 
approximately 7.5 percent when the true dust concentration 
() is 2.0 mg/m\3\ and approximately 16.2 percent when 
=0.5 mg/m\3\. This is based on applying Equations 2 and 3 
to e=51.7 g, CVpump=4.2 
percent, and CVsampler=5 percent.
    Even if the effects of spatial variability and the third 
laboratory are ignored, and the overall CV is interpreted as an 
average over the range of concentrations encountered, the 16-percent 
value reported by the NMA makes no allowance for the paired 
covariance structure of the data. Therefore, MSHA and NIOSH consider 
the 16-percent value to be erroneous, even under NMA's assumptions.
    MSHA and NIOSH re-analyzed the Skyline data in order to check 
whether these data were consistent with the value of 
e (i.e., 51.7

[[Page 42118]]

g) estimated for the time when the Skyline samples were 
collected. To distinguish the NMA interpretation of sampling and 
analytical error (including spatial variability) from the 
Secretaries' interpretation (excluding spatial variability), SAE 
will denote sampling and analytical error according to the 
Secretaries' interpretation, and SAE* will denote sampling and 
analytical error according to the NMA interpretation. If 
CVspatial denotes the component of SAE* attributable to 
spatial variability for each measurement, it follows that
[GRAPHIC] [TIFF OMITTED] TP07JY00.013

    To estimate SAE* as a function of dust concentration from the 
data provided, a least-squares regression analysis was performed on 
the square of the difference between natural logarithms of dust 
concentrations x1 and x2 observed within each 
pair. Let * denote the true mean dust concentration, not 
only over the full shift sampled, but also over the two locations 
sampled. The expected value (E{}) of each squared 
difference forms the ordinate of the regression line at each value 
of the abscissa (1/*)\2\:
[GRAPHIC] [TIFF OMITTED] TP07JY00.012

Since no control filter capsules were used in processing the Skyline 
dust samples, CVweight does not, in this analysis, 
contain the 2 factor shown in Equation 3 of Appendix C. The 
intercept of the regression line is: 
a0=2(CV2pump+CV2sampler
+CV2spatial), and the slope is 
a1=2(1.438e) \2\. To carry out the 
regression analysis, * was approximated by 
(x1+x2)/2. Regression estimates of the 
parameters a0 and a1 were used to generate 
corresponding estimates of e and 
CV2spatial.
    The least squares estimate of e obtained 
from this analysis is 76.0 g, with standard error of 
15 g. This is not significantly different, 
statistically, from the 51.7-g value estimated for the time 
period when the Skyline samples were collected. Assuming 
CVpump = 4.2 percent and CVsampler = 5 
percent, the value of CVspatial obtained from the least 
squares estimate of a0 is 19.7 percent, with standard 
error of  2.9 percent.

II. Paired Sample Data Submitted by Mountain Coal Company

    Mountain Coal Company submitted a data set consisting of the 
difference (expressed in mg/m\3\) between paired samples collected 
from miners over roughly a one-year period. Two sampler units were 
placed on each participating miner (presumably one on each collar or 
shoulder) and operated for roughly a full shift. One sample cassette 
was sent to MSHA for analysis (post-weighing) while the other was 
analyzed at a private laboratory.
    Mountain Coal Company provided only the differences between 
measurements within each pair and not the concentration measurements 
themselves. Since CVtotal varies with dust concentration, 
and the dust concentrations were not provided, it was impossible to 
form a valid estimate of measurement variability from these data, or 
to determine what part of the observed differences could be 
attributed to weighing error and what part to spatial variability or 
variability attributable to operation of the pump and physical 
differences between sampler units.

III. Exposure Data Submitted by Jim Walter Resources, Inc.

    Jim Walter Resources, Inc. submitted a data set consisting of 
exposure measurements collected from all miners working on two 
longwall sections. Measurements were collected from each miner on 
five consecutive days. This procedure was repeated during five 
sampling cycles over a two-year period. During each sample cycle the 
five measurements for each miner were averaged and compared to the 
respirable dust standard. According to Jim Walter Resources, Inc., 
the sampling plan ``eliminates the effect of the variability of the 
environment and minimizes the error due to the coefficient of 
variation of the pump because all miners [original emphasis] are 
sampled for five shifts,'' and these data ``show the variability of 
the sample pump and of the worker's exposure to respirable dust.''
    In its submission, Jim Walter Resources, Inc. apparently assumed 
that the quantity being measured is average dust concentration 
across a number of shifts, rather than dust concentration averaged 
over a single shift at the sampling location. The Secretaries agree 
that dust concentrations do vary from shift to shift and from job to 
job, as these data illustrate. This variability, however, is largely 
under the control of the mine operator and should not be considered 
when evaluating the accuracy of a single, full-shift measurement.

IV. Exposure Data Submitted by the NMA

    The NMA submitted data consisting of recently collected and 
historical measurements collected from the designated occupations 
(continuous miner operator for continuous mining sections and either 
the headgate or tailgate shearer operator for longwall mining 
sections) for three continuous mining sections and five longwall 
mining sections. According to the NMA analysis, there is a 17-
percent probability that these mines would be cited, even though the 
long-term average is less than the respirable dust standard.
    The NMA failed to recognize that the quantity being measured is 
dust concentration averaged over a single shift at the sampling 
location. The Secretaries agree that exposures do vary from shift to 
shift, as these data illustrate. This variability, however, is 
largely under the control of the mine operator and should not be 
considered when evaluating the accuracy of a single, full-shift 
measurement.

V. Sequential Exposure Data Submitted by Jim Walter Resources, Inc.

    Jim Walter Resources, Inc. submitted data collected from several 
longwall faces. For each longwall, seven dust samples were 
collected, using sampler units placed on the longwall face at least 
48" from the tailgate at the MSHA 061 designated location. Pumps 
were successively turned off in one hour increments, resulting in 
samples covering progressively longer time periods over the course 
of the shift, from one to eight hours. This was repeated on a number 
of days at each longwall.
    Many of the samples showed either the same or less weight gain 
than the previous sample (collected over a shorter time period) 
within a sequence. In the cover letter and written comments 
accompanying these data, it was claimed that the weight gains 
observed for samples within each sequence should progressively 
increase, irrespective of variations in air flow and production 
levels, and that the patterns observed exemplify

[[Page 42119]]

``the variability of sample results with today's equipment and 
weighing techniques.''
    MSHA and NIOSH have concluded that these data cannot be used to 
estimate or otherwise evaluate measurement accuracy for the 
following reasons: First, a highly sensitive and accurate sampling 
device would be expected to produce variable results when exposed to 
even slightly different environments. Since the samples within each 
sequence of seven were not collected at exactly the same point, they 
are subject to spatial variability in dust concentration. It is well 
known that dust concentrations can vary even within small areas 
along a longwall face. Therefore, variability in sample results is 
attributable not only to measurement errors but also to variations 
in dust concentration due to spatial variability.
    Second, even on a production shift, variations in air flow and 
production levels over the course of the shift can result in periods 
within the shift during which the true dust concentration to which a 
sampler is exposed is low or near zero. If a sampler unit is exposed 
to a relatively low dust concentration during the final hour in 
which it is exposed, any difference between that sample and the 
previous sample will tend to be dominated by spatial variability. In 
such cases the increase in weight accumulated during the final hour 
would be statistically insignificant as compared to variability in 
dust concentration at different locations. Without detailed 
knowledge of the airflow and production levels as they varied over 
each shift, it is impossible to determine how many cases of this 
type would be expected. However, approximately one-half of such 
samples would be expected to exhibit less weight gain than the 
previous sample.
    Further, because sample weights were truncated to 0.1 mg at the 
time these data were collected, and because expected weight gains of 
less than 0.1 mg are not uncommon over a one-hour period, there 
would be no apparent increase in recorded weight gain in many cases 
where the two sample results actually differed by a positive amount. 
Therefore, some unknown number of cases showing no difference in 
successive weight gains are attributable to truncation effects. 
Truncation has now been discontinued for samples collected under 
MSHA's inspection program.
    Finally, as has been shown in Appendix C, a certain percentage 
of negative weight-gain measurements at low dust concentrations is 
consistent with the weighing imprecision experienced at the time 
these samples were collected. However, since these data were not 
collected in a controlled environment, it is impossible to determine 
what that percentage should be. Because the weight gain for each 
sample is determined as the difference between two weighings, 
comparison of weight gains between two samples involves a total of 
four independent weighing errors. Therefore, variability 
attributable purely to weighing error in the difference between 
weight gains in two successive samples is greater (by a factor equal 
to ``2) than variability due to weighing error in a single sample. 
Furthermore samples collected over less than a full shift are 
subject to more variability due to random fluctuations in pump air 
flow and cyclone performance than samples collected over a full 
shift. Both of these considerations increase the likelihood that a 
sample will exhibit less weight gain than its predecessor, as 
compared to the likelihood of recording a negative weight gain for a 
single, full-shift sample.

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XVI. Regulatory Text

List of Subjects in 30 CFR Part 72

    Coal, Health standards, Mine safety and health, Underground mines, 
Miscellaneous.

    Dated: May 31, 2000.
Alexis M. Herman,
Secretary, Department of Labor.

    Dated: May 31, 2000.
Donna E. Shalala,
Secretary, Department of Health and Human Services.
    Accordingly, it is proposed by the Department of Labor, Mine Safety 
and Health Administration, 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. Section 72. 500 is added to subpart E of part 72 to read as 
follows:

Sec. 72.500  Single, full-shift measurement of respirable coal mine 
dust.

    The Secretary may use a single, full-shift measurement of 
respirable coal mine dust to determine average concentration on a shift 
if that measurement accurately represents atmospheric conditions to 
which a miner is exposed during such shift.
[FR Doc. 00-14075 Filed 7-6-00; 8:45 am]
BILLING CODE 4510-43-P