[Federal Register Volume 62, Number 250 (Wednesday, December 31, 1997)]
[Notices]
[Pages 68372-68395]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-33934]



[[Page 68371]]

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Part III

Department of Labor
_______________________________________________________________________
Mine Safety and Health Administration
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Department of Health and Human Services
_______________________________________________________________________
Centers for Disease Control and Prevention
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Mine Shift Atmospheric Conditions; Respirable Dust Sample; Notice



Coal Mine Respirable Dust Standard Noncompliance Determinations; Notice



Proposed Information Collection Request Submitted for Public Comment 
and Recommendations; Single, Full-Shift Respirable Dust Measurements; 
Notice

  Federal Register / Vol. 62, No. 250 / Wednesday, December 31, 1997 / 
Notices  

[[Page 68372]]



DEPARTMENT OF LABOR

Mine Safety and Health Administration

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention
RIN 1219-AA82


Mine Shift Atmospheric Conditions; Respirable Dust Sample

AGENCIES: Mine Safety and Health Administration, Labor, National 
Institute for Occupational Safety and Health, Centers for Disease 
Control and Prevention, HHS.

ACTION: Final notice of joint finding.

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SUMMARY: This notice announces that the Secretary of Labor and the 
Secretary of Health and Human Services (the Secretaries) find, in 
accordance with sections 101 and 202(f)(2) of the Federal Mine Safety 
and Health Act of 1977 (Mine Act), 30 U.S.C. 811 and 842(f) 
respectively, 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. This notice should be read 
in conjunction with the notice published separately by the Mine Safety 
and Health Administration (MSHA) elsewhere in today's Federal Register. 
The Secretaries are rescinding the previous finding, which was proposed 
on July 17, 1971 and issued on February 23, 1972, by the Secretary of 
the Interior and the Secretary of Health, Education and Welfare.

EFFECTIVE DATE: This notice will be effective on March 2, 1998.

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

SUPPLEMENTARY INFORMATION: In accordance with section 202(f)(2) and 
section 101 of the Mine Act, this notice is published jointly by the 
Secretaries of the Departments of Labor, and Health and Human Services.

I. Introduction

    For as long as miners have taken coal from the ground, the presence 
of respirable dust in coal mines has been a source of health problems 
for miners. Coal workers' pneumoconiosis, one of the most insidious of 
occupational diseases, is caused by deposits of coal mine dust in the 
lung and is known as ``black lung disease.'' The disability that may 
result from these deposits can range from slightly impaired lung 
function to significant decreases in lung function resulting in 
breathlessness, recurrent chest illness, and even heart failure. In 
addition, the disease may progress even after the miner is no longer 
exposed to coal mine dust.
    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/m3). The 2.0 mg/
m3 standard sets a limit on 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 disease was by limiting 
the amount of respirable 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/m3 
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). (Other 
provisions in the Mine Act, sections 205 and 203(b)(2), provide for 
lowering the applicable standard when quartz is present and when miners 
with evidence 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 show that the average dust 
concentration in the environment of a continuous miner operator was 7.7 
mg/m3. Current sampling indicates that the average dust 
level for that occupation has been reduced by 83 percent to 1.3 mg/
m3. Despite this progress, the Secretaries believe that 
occupational lung disease continues to present a serious health risk to 
coal miners. In November 1995, the National Institute for Occupational 
Safety and Health (NIOSH) issued a criteria document which concluded 
that coal miners in our country continue to be at risk for developing 
black lung disease.
    The Secretary of Labor believes that miners' health can be further 
protected from the debilitating effects of black lung disease by 
improving their workplace conditions through more effective assessment 
of respirable dust concentrations during individual, full shifts. On 
February 18, 1994, the Secretary of Labor and the Secretary of Health 
and Human Services published a notice in the Federal Register proposing 
to find 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 in accordance with section 
202(f)(2) of the Mine Act (56 FR 8357). Additionally, the Secretaries 
proposed to rescind the previous finding, which was proposed on July 
17, 1971 (36 FR 13286) and issued on February 23, 1972 (37 FR 3833), by 
the Secretary of the Interior and the Secretary of Health, Education 
and Welfare.

II. General Discussion

    The issues related to this finding are complex and highly 
technical. The Agencies have organized this final notice to allow 
interested persons to first consider pertinent introductory material on 
the Agencies' 1972 notice and its recision, and a short overview of the 
NIOSH mission and assessment of this finding, as well as those aspects 
of MSHA's coal mine respirable dust program relevant to this finding. 
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 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 finding. Finally, the notice explains how the total measurement 
uncertainty was quantified, and how the accuracy of a single, full-
shift measurement was shown to meet the NIOSH Accuracy Criterion. 
Several Appendices, which contain relevant technical information, are 
attached and incorporated with this notice. The Agencies have 
additionally included references to the Appendices throughout this 
notice.

[[Page 68373]]

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 shift 
measurement 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 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.

    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 F.R. 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 atmospheric conditions to which the miner 
under consideration is continuously exposed, is hereby adopted 
without change.

    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

[[Page 68374]]

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) requires 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). 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 set forth in the notice, the 
Secretaries hereby rescind the 1972 joint final finding.

III. 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 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, Congress gave specific research responsibilities to NIOSH in the 
field of coal or 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 the National Institute for Occupational Safety 
and Health, has reconsidered the provisions of section 202(f) of the 
Mine Act, 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. 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 1984, a 
fully-automated, robotic weighing system was introduced along with 
state-of-the-art electronic microbalances. 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 MSA 
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 MSA 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, 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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IV. 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.

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, which 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 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 standard, the operator reverted back to the standard 
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.
    MSHA revised these regulations in April 1980 (45 FR 23990) to 
reduce the operator sampling burden, to simplify the sampling process, 
and to enhance

[[Page 68375]]

the overall quality of the sampling program. The result was to replace 
the various sampling cycles with a bimonthly sampling cycle and to 
eliminate the requirement that each miner be sampled. These are the 
regulations that currently govern the mine operator dust sampling 
program, and which 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 preamble to the final rule amending the 
regulations in April 1980 (45 FR 23997), explicitly refers to the use 
of single versus multiple samples as it applies to the operator 
respirable dust sampling program.

    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-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/
m3 limit was a single-shift standard, which 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/m3. 
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/m3. 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 by conducting inspections annually at each surface and underground 
coal mine. During these inspections, MSHA inspectors collect samples on 
multiple occupations to determine compliance with the applicable 
standard, assess the effectiveness of the operator's dust control 
program, quantify the level of crystalline silica (quartz) in the work 
environment, and identify occupations other than the ``D.O.'' which may 
be at risk and should be monitored by the mine operator.
    Depending on the concentration of 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. MSHA inspection procedures require 
inspectors to sample at least five occupations, if available, on each 
mechanized mining unit (MMU) on the first day 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 it, additional samples are collected on 
the subsequent production shift or day. The results of the first and 
second day 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 day because a previous 
measurement exceeds the standard, MSHA's procedures call for all 
measurements taken on a given occupation to be averaged individually 
for that occupation. If the average of measurements taken over more 
than one day 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 (based on the 
cumulative concentration for two or more samples exceeding 10.4 mg/m 
\3\, which is equivalent to a 5-measurement average exceeding 2.0 mg/m 
\3\), the operator is cited for exceeding 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. As part of that 
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 greater than or equal to 2.1 mg/m \3\, or 
any single, full-shift measurement exceeded or equaled 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.
    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

[[Page 68376]]

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). 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 concentration for two occupations exceeds 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.
    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 shift inspection policy initiated during 
the SIP.

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 finding that rulemaking was required under 
section 202(f) of the Mine Act 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.

V. Executive Order 12866 and Regulatory Impact Analysis

    MSHA has designated this joint finding as a significant action; it 
has been reviewed by OMB under E.O. 12866. MSHA estimates that the 
total annual costs associated with the implementation of this finding 
will be $707,950, of which $446,125 will be incurred by underground 
coal mines and $261,825, incurred by surface coal operations. MSHA 
projects that this finding will result in reductions of future cases of 
occupational lung disease and attendant cost savings. MSHA has prepared 
a separate regulatory impact analysis which is available to the public 
upon request.

VI. Procedural History of the Current Notices

    As a result of the innovations and technological advancements 
described earlier, and the decision in Keystone Coal v. Secretary of 
Labor, 16 FMSHRC 6 (January 4, 1994), the Secretary of Labor and the 
Secretary of Health and Human Services published a proposed joint 
notice in the Federal Register on February 18, 1994 (59 FR 8357), 
pursuant to sections 101 and 202(f)(2) of the Mine Act. The notice 
proposed to rescind the 1971/1972 proposed and final findings by the 
Secretaries of the Interior and Health, Education and Welfare, and 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 
respirable dust measurements and the average of multiple, full-shift 
respirable dust measurements for noncompliance determinations (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 new 
procedure.
    The comment period on the proposed joint finding was scheduled to 
close on April 19, 1994, but was extended to May 20, 1994, in response 
to requests from the mining community (59 FR 16958). Subsequently, 
public comments were received, including comments from both labor and 
industry.
    On July 6, 1994, in response to requests from the mining community, 
a public hearing was held on both notices in Morgantown, West Virginia 
(59 FR 29348). Also, in response to additional requests from the mining 
community, a second hearing was held on July 19, 1994, in Salt Lake 
City, Utah. To allow for the submission of post-hearing comments, the 
record was held open until August 5, 1994.
    The hearings on the proposed joint notice were conducted by a joint 
MSHA/NIOSH panel. Presenters at the Morgantown hearing included 
international and local representatives of the United Mine Workers of 
America (UMWA), several mine operators, and a panel presentation from 
the American Mining Congress (AMC) and the National Coal Association 
(NCA). Presenters at the Salt Lake City hearing included the Utah 
Mining Association, several mine operators, and another joint AMC/NCA 
panel. The joint MSHA/NIOSH panel received prepared remarks from the 
presenters and asked questions as well. The joint agency panel also 
responded to questions from the presenters.
    To ensure that all issues raised were fully considered, MSHA and 
NIOSH conducted a thorough review of existing data, engaged in an 
extensive literature

[[Page 68377]]

search, sought an independent analysis of the scientific validity of 
single, full-shift measurements, and conducted additional testing. 
These efforts resulted in the collection of a significant amount of 
information, which was made a part of the public record on September 9, 
1994 (59 FR 50007). To allow interested parties the opportunity to 
review and comment on the supplemental material, the Agencies extended 
the comment period from September 30 to November 30, 1994.
    After the close of the comment period, the Agencies reviewed all of 
the comments, data and other information submitted into the record. 
Some of the commenters raised questions regarding the accuracy of 
single, full-shift measurements and challenged the Agencies' estimate 
of measurement imprecision inherent in sample collection and analysis. 
While reviewing these issues, the Agencies concluded that the term 
``accurately represent'' as used in section 202(f) needed to be defined 
because of the issues which commenters raised. In response, the 
Agencies reopened the record on March 12, 1996, to provide a criterion 
for ``accuracy'', to supply new data and statistical analytical 
analyses on the precision of coal mine respirable dust measurements 
obtained using approved sampling equipment, and to allow the public to 
review and submit comments on the supplemental information (61 FR 
10012). In addition, the March 12 notice identified certain refinements 
in MSHA's measurement process as applied to inspector samples. These 
modifications, currently in place, involve the measurement of both pre-
and post-exposure filter weights to the nearest microgram on a scale 
calibrated using the established procedure in MSHA's laboratory, and 
discontinuing the practice of truncating the recorded weights used in 
calculating the dust concentration (that is, MSHA no longer ignores 
digits representing hundredths and thousandths of a milligram).
    The new comment period was scheduled to close on April 11, 1996, 
but was extended until June 10, 1996, in response to requests from the 
mining community. Additionally, on April 11, 1996, the Agencies 
announced their intention to conduct a second public hearing on the 
content of the March 12 notice (61 FR 16123). On May 10, 1996, a public 
hearing conducted by a joint MSHA/NIOSH panel was held in Washington, 
DC. One scheduled presenter, representing the UMWA, appeared at this 
hearing.
    Some commenters expressed concern for the procedures used by the 
Agencies in making a new finding, asserting that MSHA and NIOSH were 
not complying with the rulemaking provisions of the Mine Act. These 
commenters contended that the recision of the final finding and 
implementation by MSHA of single, full-shift sampling can only be 
effectuated through notice and comment rulemaking. These commenters 
argue that because MSHA failed to appeal the Keystone case, MSHA was 
bound by the Commission decision in that case which mandated notice and 
comment rulemaking to rescind the prior finding and authorize use of 
single samples by the Agency.
    MSHA and NIOSH have considered these comments, but believe that the 
process they have chosen to follow is consistent with the requirement 
of section 202(f) of the Mine Act, which provides that a finding shall 
be made ``in accordance with the provisions of section 101'' of the 
Mine Act. Section 101 contains the procedural requirements for 
promulgation of mandatory health and safety standards, including 
provision for notice and comment. All interested parties were given 
ample opportunity for notice and comment at every stage of 
consideration of the proposed joint finding. The Agencies are not 
developing, promulgating, or revising a mandatory health standard in 
this notice, nor is the 2.0 mg/m \3\ respirable dust standard being 
revised. Moreover, the Agencies have made a finding that the average 
concentration of respirable dust in the mine atmosphere to which each 
miner in the active workings of a coal mine is exposed during a shift 
can be accurately measured with a single, full-shift sample. This is a 
scientific finding contemplated by section 202(f) of the Mine Act. 
While one commenter asserted that the Secretaries were not following 
proper notice and comment procedures in section 101 [e.g., sections 
101(a)(1) through (9)], the only example given by the commenter is the 
fact that the notice was published in the ``Notice'' section, rather 
than the ``Proposed Rules'' or ``Rules and Regulations'' section of the 
Federal Register. Because this is not a mandatory safety and health 
standard, there is no need for the Secretaries to publish the finding 
as a proposed rule, or to address feasibility, for example, which would 
be required under section 101(a)(6)(A) when a mandatory safety or 
health standard is promulgated. The Secretaries have properly complied 
with all the procedural elements of section 101 which apply to this 
notice.
    Some commenters referenced section 101(a)(9) of the Mine Act, 30 
U.S.C. 811(a)(9), which provides that no mandatory standard shall 
reduce the protection afforded miners by an existing standard under the 
Mine Act. As stated previously, this scientific finding does not 
constitute rulemaking and is not a promulgation of a mandatory health 
standard. Rather, it is a ``finding'' under the Mine Act, established 
in the same manner as the initial finding, in 1972, the effect of which 
is to increase health protection for miners by allowing single, full-
shift measurements to be used to determine average concentrations 
during a single work shift instead of continuing to rely solely on 
averaging the results of several days of sampling or sampling across 
various occupations on the same shift.
    In MSHA's notice published on February 18, 1994 (59 FR 8356), the 
Agency specifically noted that any change to the substantive procedure 
for mine operator respirable dust sampling governed by MSHA regulations 
would require rulemaking by MSHA.

VII. Issues Regarding Accuracy of a Single, Full-Shift Measurement

    Some 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, 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); 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 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 commenters asserted 
that the dust concentration that should be measured is dust 
concentration averaged over a period greater than a single shift. Some 
commenters noted that dust concentrations can vary during a shift and 
that dust concentration is 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

[[Page 68378]]

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 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.'' Later in section 202(f), 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 respirable dust as the dust measured by an approved 
sampler unit.
2. Time Period to Which the Measurement Applies
    Section 202(b)(2) provides that each mine operator ``* * * shall 
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. 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.'' 
For the purpose of this notice, the Secretaries have determined that 
``atmospheric conditions'' mean the fluctuating concentration of 
respirable coal mine dust during a single shift. These are the 
atmospheric conditions to which a sampler unit is exposed. Therefore, 
the present 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. As articulated by the United States 
Court of Appeals for the 10th Circuit in American Mining Congress (AMC) 
versus 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.'' Because the 
Secretary of Labor intends to prevent excessive exposure by limiting 
dust concentration at every location in the active workings, the area 
represented by any respirable dust measurement must be the sampling 
location.
    Some 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 false 
premise that the measurement objective in section 202(f) is something 
other than the average atmospheric conditions during a single shift at 
the sampling location. It is true that these mean quantities described 
by some commenters cannot be accurately estimated using a single, full-
shift measurement, but the Secretaries make no claim of doing so, nor 
are they required to make such considerations.
    Some commenters argued that Congress intended that the measurement 
objective be a long-term average. Specifically, some 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, 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 versus 
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.
    Some 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 commenters maintained that the measurement 
objective is 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 prevent excessive exposure to respirable dust.
    Several 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. Section 202(a) of the Mine Act, however, 
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.
    Accordingly, the Secretaries define the measurement objective to be 
the accurate determination of the average atmospheric conditions, or 
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 
commenters, the Agencies found that the term ``accurately represent,'' 
as used

[[Page 68379]]

in section 202(f) in connection with a single shift measurement, was 
not defined in the Mine Act. Therefore, in their March 12, 1996 notice, 
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. This criterion requires that measurements come within 25 
percent of the corresponding true dust concentration at least 95 
percent of the time [1].
    One 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 is not 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 criteria 
for the method is 35 percent at 95 percent confidence at 
the permissible exposure limit.
    Some commenters contended that the NIOSH Accuracy Criterion does 
not conform with international standards recently adopted by the 
European Committee for Standardization (CEN) [2]. Contrary to these 
assertions, the NIOSH Accuracy Criterion not only conforms to the CEN 
criterion but is, in fact, more stringent. 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.
    The NIOSH Accuracy Criterion is relevant and widely recognized and 
accepted in the occupational health professions. Further, commenters 
proposed no alternative criteria for accuracy. Accordingly, for 
purposes of section 202(f) of the Mine Act, the Secretaries 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'' [1]. Similarly, the CEN criterion for method accuracy 
specifies that ``testing of a procedure shall be carried out under 
laboratory conditions.'' 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 VII.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 [1,3]. 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 determined in the same laboratory, any bias in 
the weighing process attributable to the laboratory is mathematically 
canceled out by subtraction. Furthermore, as will be discussed later, a 
control (i.e., unexposed) filter capsule will be pre-and post-weighed 
along with the exposed filter capsules. The weight gain of the exposed 
capsule will be adjusted by the weight gain or loss of the control 
filter capsule. Therefore, any bias that may be associated with day-to-
day changes in laboratory conditions or introduced during storage and 
handling of the filter capsules is also mathematically canceled out. 
Moreover, the concentration of respirable dust is effectively defined 
by section 202(e) of the Mine Act 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 
have concluded 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 cannot be 
reduced by making multiple measurements. Other comments regarding 
measurement bias are addressed in Appendix A.
    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

[[Page 68380]]

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 the 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 is operated 
portal to portal. The unit 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 are particles that tend to be removed from the airstream by 
the nose and upper respiratory airways. These 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. The 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 again to determine the 
weight gain in milligrams, which is the amount of dust collected on the 
filter. The concentration of respirable dust, expressed as milligrams 
per cubic meter (mg/m\3\ ) of air, is determined by dividing the weight 
gain by the volume of mine air passing through the filter and then 
multiplying this quantity by a conversion factor (discussed below in 
Appendix A) prescribed by the Secretary.
    Some comments generally addressed the quality and reliability of 
the equipment used for sampling. Specific concerns were expressed about 
the quality of filter cassettes and the reliability, due to their age 
and condition, of sampling pumps used by MSHA inspectors. 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 error and ensure that 
samples collected with approved sampler units in the prescribed manner 
would accurately represent the full-shift, average atmospheric dust 
concentration 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 using 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 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, 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. NIOSH also conducts annual 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 these checks identify a potential problem with 
the manufacturing process, the system requires immediate action to 
identify and 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 falling out of 
the capsule inlet.
    Several commenters questioned the quality of the filter cassettes 
used in the sampling program, expressing concern about whether the 
cassettes always meet MSHA specifications. These concerns primarily 
involve filter-to-foil distance and floppiness of the filters, which 
are manufacturing characteristics not related to part 74 performance 
requirements. The Secretaries believe that such characteristics 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.
    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.
    This concern is unwarranted. 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, 
MSHA inspectors are required to make a minimum of two flow rate checks 
to ensure that the sampler unit is operating properly. The sample is 
voided if the proper flow rate was not being maintained during the 
final check at the conclusion of the sampling shift. 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

[[Page 68381]]

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 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 [4].
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.
    Several 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. 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 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 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 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 affect the validity of the 
sample had occurred during the shift.
    Other 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 notice, 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 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 are already standardized under the revised 
1980 MSHA regulations codified at 30 CFR parts 70, 71 and 90.
    MSHA inspectors will also begin using control filter capsules 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 capsule is an unexposed filter 
capsule that was pre-weighed on the same day as the filter capsules 
used during a sampling inspection. These control filter capsules will 
be carried by the inspector, but will remain plugged and not be exposed 
to the mine environment.
3. Sample Processing
    Sample processing consists of weighing the filter capsules, 
recording the weight gains, and examining certain samples in order to 
verify their validity. Sample processing also includes electronic 
transmission of the results to MSHA's computer center where dust 
concentrations are computed. The results are then distributed to MSHA 
enforcement personnel and to mine operators.
    (a) Weighing and recording procedures. One commenter cited a 
personal experience in which anomalies were noted in the pre-exposed 
weights recorded by the dust cassette manufacturer. The commenter was 
concerned that such anomalies indicated poor quality control in the 
manufacturer's weighing process, implying that this would cause a 
significant number of single, full-shift measurements to be inaccurate.
    The procedures and analytical equipment used by MSHA to process 
respirable coal mine dust samples have improved since 1970. From 1970 
to 1984, samples were manually weighed using semimicro balances. In 
1984, the process was automated with 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 balance were upgraded.
    The full benefit of the 1994 improvements of the weighing system 
for inspector samples was, however, not fully attained until mid-1995, 
when MSHA implemented two modifications to its procedures for 
processing inspector samples. One modification involved measuring both 
the pre- and post-exposed weights to the nearest microgram (0.001 mg) 
on a balance calibrated using the established procedure within MSHA's 
laboratory. Prior to mid-1995, filter capsules had been weighed in the 
manufacturer's laboratory before sampling, and then in MSHA's 
laboratory after sampling. MSHA is now pre-weighing all such filter 
capsules in its own laboratory, which will significantly reduce the 
potential for anomalous pre-exposed weights of filter capsules used by 
inspectors. To maintain the integrity of these pre-exposed weights, 
eight percent of all capsules are systematically weighed a second time. 
If a significant deviation is found, the balance is recalibrated and 
all filter capsules with questionable weights are reweighed.
    The other modification was to discontinue the practice of 
truncating the recorded weights used in calculating dust concentration. 
This means that MSHA no longer ignores digits representing hundredths 
and thousandths of a milligram 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 filter capsules, MSHA will use control 
filter capsules in its enforcement program. Any change in weight of the 
control filter capsule will be subtracted from the change in weight of 
the exposed filter capsule.
    (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 a questionable appearance of the filter capsule or other 
special circumstances are noted that would

[[Page 68382]]

cause MSHA to examine the sample further. Several commenters expressed 
concern about the potential contamination of samples with ``oversize 
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 oversize particles. It was recommended that MSHA analyze, 
for the presence of oversize 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 weighing 1.4 milligrams (mg) or more are examined visually and 
microscopically, as necessary, 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 commenters' concerns about the contamination of samples with 
oversize particles are based on the assumption that all oversize 
particles, defined as dust particles greater than 10 micrometers in 
size, are not respirable and therefore should be totally excluded from 
any sample taken with an approved sampler unit. In fact, it has long 
been known that particles greater then 10 micrometers in size can be 
inhaled, and that some of these particles can reach the alveoli of the 
lungs [5]. 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'' [6]. 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 [6]. Moreover, MSHA studies have shown that nearly all 
samples taken with approved sampler units, even when operated in the 
prescribed manner, contain some oversize particles [7]. Since section 
202(e) of the Mine Act defines concentration of respirable dust to be 
that measured by an approved sampler unit, and because the approved 
sampler unit will collect some oversize particles, the Secretaries do 
not consider a sample to be ``contaminated'' because it contains some 
oversize particles.
    The Secretaries recognize that there are occasions when oversize 
particles can properly be considered a contaminant. For example, an 
excessive number of such particles could be introduced into 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 drawn into the filter capsule), 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 commenters, checking for 
oversize particles is not standard industrial hygiene practice. 
Nevertheless, MSHA checks any dust sample suspected of containing an 
excessive number of oversize 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 oversize particles. 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 oversize particles according to MSHA's established criteria, 
then that sample is considered to be invalid, and is voided and not 
used. In fiscal year 1996, only 83 samples or 0.4 percent of the 20,331 
inspector samples processed were found to contain an excessive number 
of oversize particles and thus were not used.
    While rough handling of the sampler unit or an accidental mishap 
could conceivably cause a sample weighing less than 6 mg to become 
contaminated, as claimed by some commenters, studies show that short-
term accidental inclinations of the cyclone will not affect respirable 
mass measurements made with currently approved sampler units [8]. 
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 commenters. In any event, the Secretaries 
believe that the validity checks currently in place, as discussed 
above, will detect such samples.

D. Measurement Uncertainty and Dust Concentration Variability

    Overall variability in measurements collected on different shifts 
and sampling locations results from the combination of errors 
associated with the measurement of a particular dust concentration and 
variability in dust concentration. Variability in dust concentration 
refers to the differing atmospheric conditions experienced on different 
shifts or at different sampling locations. Measurement uncertainty, on 
the other hand, refers to the differing measurement results that could 
arise, at a given sampling location on a given shift, because of 
potential sampling and analytical errors.
    Numerous 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 will 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 
are 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] TN31DE97.000

where: x is the single, full-shift dust concentration measurement (mg/m 
\3\);
    1.38 is a constant MRE-equivalent conversion factor;

[[Page 68383]]

    g is the observed weight gain (mg) after adjustment for the control 
filter capsule;
    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. 
CVtotal quantifies the magnitude of probable sampling and 
analytical errors and is expressed as either a fraction (e.g., 0.05) or 
as a percentage (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 = 5 percent.
    Based on a review of the scientific literature, the Secretaries in 
their March 12, 1996 notice, identified three sources of uncertainty in 
a single, full-shift measurement, which together make up CV:
    (1) CV--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 the filter cassettes to and from 
the mine, and weighing the exposed and control filter capsules after 
sampling (post-weighing).
    (2) CVpump--variability in the total volume of air 
pumped through the filter capsule. This covers variability associated 
with calibration of the pump rotameter,2 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.
---------------------------------------------------------------------------

    \2\ 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.
---------------------------------------------------------------------------

    (3) 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] TN31DE97.001

    These three components are discussed in greater detail, along with 
responses to specific comments, in Appendix B.
2. Sources of Dust Concentration Variability
    Numerous 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 VII.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, and is under the control of the mine 
operator. The sampler unit is not intended to account for these 
factors.
    (a) Spatial variability. Several 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 is to accurately measure average atmospheric conditions, or 
concentration of respirable dust, at a sampling location over a single 
shift.
    (b) Shift-to-shift variability. Several commenters stated that 
CVtotal should take into account the differences or 
variations in dust concentration that occur shift to shift. Although 
the Secretaries 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 is 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 oversize particles. Several 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 have 
concluded 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 [8]. The weight of the sampler head assembly makes it extremely 
unlikely that a

[[Page 68384]]

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. Several 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 in fact be 
violated. No evidence was 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 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.
    (c) Conversion factor used in the dust concentration calculation. 
Several 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 [9]. 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 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 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 A on 
why use of the 1.38 factor does not introduce a bias. Appendix A 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, 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 do not agree with the comment 
that CVtotal should include a component representing 
potential errors in silica analysis.
    (e) Dusty clothing. Several 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 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 commenters argued that MSHA underestimated 
CVtotal in its February 18, 1994 notice 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 
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.'' For example, 
the General Accounting Office (GAO) 3 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 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 [10].
---------------------------------------------------------------------------

    \3\ Many of the recommendations in the GAO report were later 
adopted and implemented by MSHA.
---------------------------------------------------------------------------

    Although all the data and analyses submitted by commenters included 
effects of spatial variability, one of these data sets, consisting of 
paired sample results, contained sufficient information to indicate 
that weighing imprecision

[[Page 68385]]

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, is not 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.
    One of the commenters particularly questioned the value MSHA used 
in its February 18, 1994 notice 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 [11]. 
Results showed the coefficient of variation associated with the initial 
flow rate adjustment to be 30.5 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 have 
concluded 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 have concluded 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 commenters ignored this source of uncertainty. As 
explained in Appendix B, the Secretaries have adopted a 5-percent 
estimate of CVsampler.
    To address 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 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.
    Commenters also questioned the value that MSHA used in the February 
1994 notice 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 [12]. 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 the March 12, 1996 joint notice, 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 MSA and 
MSHA laboratories showed that filter capsules tend to gain a small 
amount of weight even when stored in plastic cassettes [13]. 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 [13,14]. 
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 will use control 
filter capsules in its enforcement program. 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 modification to 
MSHA's inspector sampling and analytical procedure will assure an 
unbiased estimate of the true weight gain [14].
2. Verification of Method Accuracy
    With its field study, MSHA exceeded the usual requirements for 
determining the accuracy of a sampling and analytical method, as 
described by NIOSH [1] and the European Community [2]. Both of these 
require only a laboratory determination of method accuracy. NIOSH's 
independent analysis of the study data determined, with 95-percent 
confidence, that the

[[Page 68386]]

true CVtotal for MSHA's sampling and analytical method is 
less than the target maximum value of 12.8 percent for concentrations 
ranging from 0.2 mg/m3 to greater than 2 mg/m3 
[3]. In other words, NIOSH demonstrated that, with two recommended 
modifications, MSHA's sampling and analytical method for collecting and 
processing single, full-shift samples would meet the NIOSH Accuracy 
Criterion at dust concentrations greater than or equal to 0.2 mg/
m3.
    NIOSH also applied an indirect approach for assessing the accuracy 
of MSHA's sampling and analytical method. The indirect approach 
involved combining independently derived estimates, previously placed 
into the public record, of intra-laboratory 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 meets the 
NIOSH Accuracy Criterion at concentrations greater than or equal to 0.2 
mg/m3, thereby corroborating the analysis of MSHA's field 
data.
    These NIOSH analyses predate MSHA's more recent data indicating a 
correctable weight gain bias (discussed above). As explained in 
Appendices A and B, the use of control filter capsules will eliminate 
this bias but also affect the precision of a single, full-shift 
measurement. Consequently, NIOSH reassessed the accuracy of MSHA's 
sampling and analytical method, taking into account the effect of using 
a control filter capsule on the measurement process [14]. 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 dust concentrations greater than or equal to 0.3 
mg/m3.
    One commenter claimed 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. Since the Secretaries 
have concluded that MSHA's sampling and analytical method for 
inspectors meets the NIOSH Accuracy Criterion for true concentrations 
ranging from 0.3 mg/m3 to greater than 2 mg/m3, 
it is possible to calculate the range of measurements for which the 
Accuracy Criterion applies. Since CVtotal increases at the 
lower concentrations, it is important to determine the lowest 
measurement at which the NIOSH Accuracy Criterion is met. 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/m3), no more than 5% of single, full-shift measurements 
would be expected to exceed 0.36 mg/m3 [14]. Conversely, if 
a measurement equals or exceeds 0.36 mg/m3, it can be 
inferred, with at least 95% confidence, that the true dust 
concentration equals or exceeds 0.3 mg/m3 [14]. 
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/m3.
    As a result of the prior analyses, MSHA's existing inspector sample 
processing procedures were changed to reflect the modifications that 
were incorporated into MSHA's field study. MSHA is now pre- and post-
weighing inspector samples in the same laboratory, and reporting the 
pre- and post-exposure weights of inspector samples to the nearest 
microgram (g). As a result of NIOSH's latest analysis, MSHA 
will now require its inspectors to use control filter capsules during 
sampling. In addition, MSHA is now using only constant-flow control 
pumps in the inspector sampling program. MSHA believes that exclusive 
use of constant-flow pumps, as in the field study, further enhances the 
quality of the Agency's sampling program.
    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.

VIII. 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 find that a 
single, full-shift measurement at or above 0.36 mg/m3 will 
accurately represent atmospheric conditions to which a miner is exposed 
during such shift. Therefore, pursuant to section 202(f) and in 
accordance with section 101 of the Mine Act, the 1972 joint notice of 
finding is hereby rescinded.

Appendix A--Why Individual Measurements are Unbiased

    The accuracy of a measurement depends on both precision and bias 
[1,3]. 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, for 
MSHA inspector samples, by subtracting the pre-exposure weight from the 
post-exposure weight observed in the same laboratory, any bias in the 
weighing process attributable to the laboratory is mathematically 
canceled out by subtraction. A control filter capsule will be pre- and 
post-weighted along with the exposed filter capsules. The weight gain 
of each exposed capsule will be adjusted by subtracting the weight gain 
or loss of the control filter capsule. Consequently, any bias 
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 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 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 [6]. 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

[[Page 68387]]

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 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. (MSA) and 
Unico]. These commenters noted that there was some variability in these 
comparisons that MSHA and NIOSH did not consider in estimating 
CVtotal, and noted 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 MSA 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 MSA 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 by these commenters involved collecting side-by-
side samples using MRE and cyclone-based samplers [9]. 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 (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 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 B--Components of CVtotal

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

[[Page 68388]]

a filter capsule are W1=392.275 mg and W2=392.684 
mg, respectively. The true weight gain (G) would then be:

G=W2-W1=0.409 mg.

    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:
g=w2-w1=0.397 mg.

    The error (e) in this particular weight-gain measurement, resulting 
from the combination of a 7 g error in w1 and a -5 
g error in w2, would then be:

e=g-G=(w2-w1)-(W2-W1)=(w2
-W2) -(w1-W1)=-5-7=-12 
g.4

    \4\ 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, 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.
---------------------------------------------------------------------------

    Imprecision in the true weight gain is expressed by 
e, the standard deviation of e. When a weight-gain 
measurement (g) is converted to an MRE-equivalent concentration (in 
units of mg/m3) 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:
[GRAPHIC] [TIFF OMITTED] TN31DE97.002

    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 be used to eliminate potential 
bias, the weight gain measured for the exposed filter (g) will be 
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] TN31DE97.003

    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 in g-g' is represented 
by
[GRAPHIC] [TIFF OMITTED] TN31DE97.004

    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] TN31DE97.005

    Since e is essentially constant with respect to 
dust concentration, CVweight decreases as the dust 
concentration increases.
(b) Values Expressing Weight-Gain Uncertainty
    Table 1 summarizes six different values of 
e that have been mentioned during the proceedings 
related to this notice and two additional values for 
e derived in this appendix from data introduced 
during these proceedings. A ninth value for e is 
derived from newly acquired data being placed into the record along 
with this notice [14]. The nine values listed in Table 1 are not 
inconsistent, but as explained below, represent estimates of weight-
gain imprecision during different historical periods or under different 
sample processing procedures.

                              Table 1.--Standard Deviation of Error in Weight Gain                              
----------------------------------------------------------------------------------------------------------------
                                                                                                     e 
                     Description                                        Reference                   (g)
----------------------------------------------------------------------------------------------------------------
MSHA's historical estimate of upper bound............  59 FR 8356, [15]..........................           97.4
1981 Measurement Assurance Estimate (older             [16,17]...................................           81  
 technology, truncation of weights).                                                                            
Experiment on 300 unexposed, tamper-resistant filter   [12]......................................           29  
 capsules (pre- and post-weighing in different labs;                                                            
 no truncation).                                                                                                
Inspector samples processed between late 1992 and mid  Appendix B................................           51.7
 1995 (truncation of weights; pre- and post-exposure                                                            
 weighing in different labs; adjusted for differences                                                           
 between labs).                                                                                                 
NMA Data (obtained from samples collected by Skyline   Appendix C................................           76  
 Coal, Inc.).                                                                                                   
Value used in NIOSH ``indirect approach'' (pre- and    61 FR 10012, [12].........................            5.8
 post-exposure weighing on same day and in the same                                                             
 lab; derived from Kogut [12]).                                                                                 
MSHA Field Study.....................................  [18,3]....................................            9.1
1996 Measurement Assurance Estimate..................  61 FR 10012, [19].........................            6.5
1997 field data (75 unexposed capsules)..............  [14]......................................            8.2
----------------------------------------------------------------------------------------------------------------

    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/m3, or 7 
percent of 2.0 mg/m3, as described in Kogut [15]. It follows 
that the value of e 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/m3 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) [16]. 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

[[Page 68389]]

down to an exact multiple of 0.1 mg. This estimate was used to 
calculate CVweight by Bartley [17], in September 1994.
    Some commenters misread or misunderstood the published NBS 
estimate. One of these 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/
m3 compared to the 0.14 mg/m3 * * * 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. [16]. 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 to 
propagate an MRE-equivalent concentration error of 0.116 mg/
m3. Contrary to the commenters' assertion, this is less--not 
more--than the quantity (0.14 mg/m3) 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 MSA laboratory and 
twice in MSHA's laboratory using current equipment [12]. 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 [3]. 
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, when the most recent 
changes in inspector sample processing were implemented.
    Some 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 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 commenters expressed special concern over the accuracy of pre-
exposure filter capsule weights as measured by MSA. One commenter 
expressed ``grave concern'' with regard to the 12-g systematic 
difference in weights found between MSA and MSHA weighings of the same 
unexposed capsules, as described in MSHA's 1994 analysis [12]. These 
concerns are moot, at least with respect to MSHA's inspector sampling 
program, since all inspector samples are now pre- and post-weighed at 
MSHA's laboratory. Furthermore, any potential bias resulting from 
differences in laboratory conditions on the days of pre- and post-
exposure weighings should 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 C, was an estimate of 
e equal to 76 g  15 
g.5 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.
---------------------------------------------------------------------------

    \5\ To construct a 90-percent confidence interval for 
G, based on the Skyline data, the 15-
g ``standard error of the estimate'' must be 
multiplied by a confidence coefficient of 1.64.
---------------------------------------------------------------------------

    Truncation of weights, and also 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 are weighed both before 
and after sampling in MSHA's laboratory. Furthermore, the results 
recorded and used in calculating dust concentrations are expressed to 
the nearest g. 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 [18]. In this 
study, the filter capsules 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 
[19]. 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 
the

[[Page 68390]]

MSHA's 1995 field study discussed earlier (9.1 g), falls only 
slightly above the 6.5 g laboratory estimate. This suggests 
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 [13]. 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 
provide an estimate of e equal to 8.2 g 
[14]. This estimate, which is based on weighings separated by a span of 
about four to five months, corroborates the 9.1 g estimate 
obtained from MSHA's 1995 field study.
(c) Negative Weight-Gain Measurements
    Some 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 estimated for previous 
processing procedures. Table 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 2.--Probability of Negative Weight-Gain Measurement, Assuming  
                Truncation and e=51.7 g               
------------------------------------------------------------------------
                                      Estimated probability of negative 
   True weight gain G=W2-W1 (mg)                measurement, %          
------------------------------------------------------------------------
0.00...............................                     12.9            
.01................................                      8.4            
.02................................                      5.1            
.03................................                      2.8            
.04................................                      1.5            
.05................................                      0.7            
.06................................                       .4            
.07................................                       .2            
.08................................                      .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 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. Since truncation, and 
especially interlaboratory variability, have now been removed as 
sources of error in weight-gain measurements for inspector samples, 
negative weight-gain measurements are expected to occur less frequently 
than in the past.
(d) Comparing weight gains obtained from paired samples
    Some 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

[[Page 68391]]

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 se, then the 
difference between g1 and g2 has uncertainty due 
to weighing error equal to se2. 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 
1.41se.
    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 [12]) 
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 C 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 
[20]. 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 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 [10], 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 
[11]. 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 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] TN31DE97.006

    This estimate accords well with a more recent finding based on 186 
measurements in an underground mine, using constant flow-control pumps 
[18]. That study estimated CVpump = 4.0 percent and 
concluded that CVpump was unlikely to exceed 4.4 percent.
    Three commenters stated that there are reports of sampling pumps 
being calibrated and used at altitudes differing by as much as 3000 
feet and that, for many pumps, this could result in more than a 3-
percent change in flow rate per 1000 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 [21]. The study showed that both pump performance 
and rotameter calibration were affected by changes in altitude but that 
an approved MSA sampling system, calibrated and adjusted at an altitude 
of

[[Page 68392]]

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 commenters questioned the ability of the older MSA 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 [22]. 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.6 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 condition. 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).
---------------------------------------------------------------------------

    \6\ 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 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 A).
    Intersampler variability was investigated by Bowman et al. [10], 
Bartley et al. [17], and Kogut et al. [18]. 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 MSA 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 et al. 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 [3].

Appendix C--Data Submitted by Commenters

    During the public hearings, several 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 accurately be used to 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/m\3\.
    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

[[Page 68393]]

Appendix B. The value of CVtotal assumed by MSHA and NIOSH 
for the period when the Skyline samples were collected 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 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

SAE* = (CV \2\total + 
CV)\2\spatial)\1/2\.

    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\:

E{(Ln(X1)-Ln(X2)) 2}  
2(SAE*) 2
= 2(CV 2total+CV 2spatial)
= 2[CV 2pump+CV 2sampler+CV 
2 weight+CV 2spatial]
= 2(CVpump+CV 2sampler+CV 
2spatial)+
2(1.438e/*)2
=a0+a1(1/*) 2

    Since no control filter capsules were used in processing the 
Skyline dust samples, CV weight does not, in this analysis, 
contain the 2 factor shown in Equation 3 of Appendix B. The 
intercept of the regression line is 
a0=2(CV\2\pump+CV2+sampler+C
V 2 spatial), 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 CV 2 
spatial.
    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 average 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.

VII. 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.

VIII. 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

[[Page 68394]]

observed for samples within each sequence should progressively 
increase, irrespective of variations in air flow and production levels, 
and that the patterns observed exemplify ``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 then 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 B, 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.

References

    1. Kennedy, E.R., T.J. Fischbach, R. Song, P.M. Eller, and S.A. 
Shulman. Guidelines for Air Sampling and Analytical Method 
Development and Evaluation. U.S. Department of Health and Human 
Services, Public Health Service, National Institute for Occupational 
Safety and Health, DHHS (NIOSH) Publication No. 95-117.
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requirements for the performance of procedures for the measurement 
of chemical agents. European Committee for Standardization (CEN), 
1994.
    3. Wagner, G.R. Letter of October 13, 1995, from Gregory R. 
Wagner, M.D., National Institute for Occupational Safety and Health, 
to Ronald J. Schell, Chief, Division of Health, Coal Mine Safety and 
Health, Mine Safety and Health Administration.
    4. Gray, D.C. and M.I. Tillery. Cyclone vibration effects. Am 
Ind Hyg Assoc J, 42(9):685-688, 1981.
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the Regional Deposition of Inhaled Aerosols in the Human Respiratory 
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Dust in Coal Mines. National Coal Board, 6-12, 1973.
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Tomb, Chief, Dust Division, Pittsburgh Health Technology Center, 
MSHA, to William Sutherland, Chief, Division of Health, Coal Mine 
Safety and Health, MSHA, Subject: Evaluation of Criterion Used to 
Select Respirable Coal Mine Dust Samples for Examination for 
Oversize Particles.
    8. Treaftis, H.N. and T.F. Tomb. Effect of Orientation on 
Cyclone Penetration Characteristics. Am Ind Hyg Assoc J, 35(10):598-
602, 1974.
    9. Tomb, T.F., H.N. Treaftis, R.L. Mundell, and P.S. Parobeck. 
Comparison of Respirable Dust Concentrations Measured With MRE and 
Modified Personal Gravimetric Sampling Equipment. BuMines RI 7772, 
1973.
    10. Bowman, J.D., G.M. Breuer, S.A. Shulman, and D.L. Bartley. 
Precision of Coal Mine Dust Sampling. U.S. Department of Health and 
Human Services, Public Health Service, Centers for Disease Control, 
National Institute for Occupational Safety and Health, NTIS No. PB-
85-220-721, 1984.
    11. Tomb, T.F. Memorandum of September 1, 1994, from Thomas F. 
Tomb, Chief, Dust Division, Pittsburgh Safety and Health Technology 
Center, MSHA, to Ronald J. Schell, Chief, Division of Health, Coal 
Mine Safety and Health, MSHA, Subject: Determination of the 
Precision of Setting the Rotameter Ball to a Calibration Mark on 
Personal Respirable Dust Sampling Pumps.
    12. Kogut, J. Letter of May 12, 1994, from Jon Kogut, MSHA, to 
David Bartley, Division of Physical Sciences and Engineering, NIOSH.
    13. Parobeck, P., J. Kogut, T. Tomb, and L. Raymond. 
Investigation of Weighing Variability Between MSHA and MSA 
Laboratories. Internal MSHA Report 1997.
    14. Wagner, G.R. Letter of May 28, 1997, from Gregory R. Wagner, 
M.D., Acting Associate Director for Mining, National Institute for 
Occupational Safety and Health, to Ronald J. Schell, Chief, Division 
of Health, Coal Mine Safety and Health, MSHA.
    15. Kogut, J. Memorandum of September 6, 1994, from Jon Kogut, 
Mathematical Statistician, Denver Safety and Health Technology 
Center, MSHA, to Ronald J. Schell, Chief, Division of Health, Coal 
Mine Safety and Health, MSHA, Subject: Coal Mine Respirable Dust 
Standard Noncompliance Determinations.
    16. Parobeck, P., T. Tomb, H. Ku, and J. Cameron. Measurement 
Assurance Program for Weighings of Respirable Coal Mine Dust 
Samples. J Qual Tech, 13(3):157-165, 1981.
    17. Barley, D.L. Letter of September 7, 1994, from David L. 
Bartley, Research Physicist, Division of Physical Sciences and 
Engineering, NIOSH, to Ronald J. Schell, Chief, Division of Health, 
Coal Mine Safety and Health, MSHA.
    18. Kogut, J., T.F. Tomb, P.S. Parobeck, A.J. Gero, and K.L. 
Suppers. Measurement Precision With the Coal Mine Dust Personal 
Sampler. Internal MSHA Report, 1995.
    19. Tomb, T.F. Memorandum of February 16, 1996, from Thomas F. 
Tomb, Chief, Dust Division, Pittsburgh Safety and Health Technology 
Center, MSHA, to Ronald J. Schell, Chief, Division of Health, Coal 
Mine Safety and Health, MSHA, Subject: Investigation to Determine 
the Precision of MSHA's Automatic Weighing System for Weighing 
Respirable Coal Mine Dust Samples.
    20. Kissell, F.N. and R.A. Jankowski. Fixed-Point and Personal 
Sampling of Respirable Dust for Coal Mine Face Workers. Paper in

[[Page 68395]]

Proceedings of the 6th US Mine Ventilation Symposium. Society of 
Mining, Metallurgy, and Exploration, Inc (SME), Littleton, CO, 281-
186, 1993.
    21. Treaftis, H.N., T.F. Tomb, and H.F. Carden. Effect of 
altitude on personal respirable dust sampler calibration. Am Ind Hyg 
Assoc J, 37(3):133-138, 1976.
    22. Gero, A.J., P.S. Parobeck, K.L. Suppers, B.P. Apel, and J.D. 
Jolson. The Effect of Altitude, Sample Port Inlet Loading, and 
Temperature on the Volumetric Flow Rate of the MSA Escort 
Elf Constant Flow Rate Pump. Pres. at Second 
International Conference on the Health of Miners, Pittsburgh, PA, 
November 11-13, 1995.

    Dated: December 19, 1997.
J. Davitt McAteer,
Assistant Secretary for Mine Safety and Health.

    Dated: December 19, 1997.
Linda A. Rosentock,
Director, National Institute for Occupational Safety and Health.
[FR Doc. 97-33934 Filed 12-30-97; 8:45 am]
BILLING CODE 4160-18-P 4510-43-P