Determination of Concentration of Respirable Coal Mine Dust

Federal RegisterJul 7, 2000

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DEPARTMENT OF LABOR

Mine Safety and Health Administration

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

30 CFR Part 72

RIN 1219-AB18

Determination of Concentration of Respirable Coal Mine Dust

AGENCIES:

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

ACTION:

Proposed rule; notice of hearings.

SUMMARY:

This proposal announces that the Secretary of Labor and the Secretary of Health and Human Services (the Secretaries) would find in accordance with sections 101 (30 U.S.C. 811) and 202(f)(2) (30 U.S.C. 842(f)(2)) of the Federal Mine Safety and Health Act of 1977 (Mine Act) that the average concentration of respirable dust to which each miner in the active workings of a coal mine is exposed can be accurately measured over a single shift. The Secretaries are proposing to rescind a previous 1972 finding, by the Secretary of the Interior and the Secretary of Health, Education, and Welfare, on the validity of such single-shift sampling. Today's proposal addresses the final decision and order in

NMA

Secretary of Labor,

issued by the United States Court of Appeals for the 11th Circuit on September 4, 1998 (153 F. 3d 1264). That case vacated a 1997 Joint Finding and MSHA's proposed policy concerning the use of single, full-shift respirable dust measurements to determine noncompliance when the applicable respirable dust standard was exceeded.

The Agencies are also announcing that they will hold public hearings on the joint proposed rule within 45 to 60 days of its publication. The hearings will be held in the following locations: Prestonsburg, Kentucky (Jenny Wiley State Park); Morgantown, West Virginia; and Salt Lake City, Utah.

DATES:

Comments concerning this proposed rule should be submitted on or before August 7, 2000.

The hearing dates, times and specific locations will be announced by a separate document in the

Federal Register

. The rulemaking record will remain open 7 days after the last public hearing.

ADDRESSES:

You may use mail, facsimile (fax), or electronic mail to send your comments to MSHA. Clearly identify comments as such and send them—(1) By mail to Carol J. Jones, Director, Office of Standards, Regulations, and Variances, MSHA, 4015 Wilson Boulevard, Room 631, Arlington, VA 22203;

(2) By fax to MSHA, Office of Standards, Regulations, and Variances, 703-235-5551; or

(3) By electronic mail to comments@msha.gov.

FOR FURTHER INFORMATION CONTACT:

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

SUPPLEMENTARY INFORMATION:

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

I. Table of Contents

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

The preamble discussion follows this outline:

I. Table of Contents

II. Introduction

III. General Discussion

A. The 1971/1972 Joint Notice of Finding

IV. NIOSH Mission Statement and Assessment of the Joint Finding

V. MSHA Mission Statement and Overview of the Respirable Dust Program

A. The Coal Mine Respirable Dust Program

B. The Spot Inspection Program (SIP)

C. The Keystone Decision

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

VI. Procedural and Litigation History of This Proposal

VII. Health Effects

A. Introduction

B. Hazard Identification

1. Agent: Coal

2. Physical State: Coal Mine Dust

3. Biological Action: Respirable Coal Mine Dust

C. Health Effects of Respirable Coal Mine Dust

1. Description of Major Health Effects

a. Simple Coal Workers' Pneumoconiosis (CWP) and Progressive Massive Fibrosis (PMF)

b. Other Health Effects

2. Toxicological Literature

3. Epidemiological Literature

a. Simple Coal Workers' Pneumoconiosis (CWP) and Progressive Massive Fibrosis (PMF)

b. Other Health Effects

VIII. Quantitative Risk Assessment

IX. Significance of Risk

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

A. Measurement Objective

1. The Airborne Dust to be Measured

2. Time Period to Which the Measurement Applies

3. Area Represented by the Measurement

4. Justification for the Proposed Measurement Objective

B. Accuracy Criterion

C. Validity of the Sampling Process

1. Sampler Unit Performance

2. Sample Collection Procedures

3. Sample Processing

a. Weighing and Recording

b. Sample Validity Checks

D. Measurement Uncertainty and Dust Concentration Variability

1. Sources of Measurement Uncertainty

(a) Coefficient of Variation, Weighing—CV

weight

(b) Coefficient of Variation, Pump—CV

pump

sampler

2. Sources of Dust Concentration Variability

(a) Spatial Variability

(b) Shift-to-shift Variability

3. Other Factors Considered

(a) Proportion of Oversized Particles

(b) Anomalous Events

(d) Reduced Dust Standards

(e) Dusty Clothing

E. Accuracy of Single, Full-Shift Measurement

1. Quantification of Measurement Uncertainty

a. Experience Gained from Use of Control Filters

2. Verification of Method Accuracy

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

XII. Feasibility Issues

A. Technological Feasibility

B. Economic Feasibility

XIII. Regulatory Impact Analysis

A. Costs and Benefits: Executive Order 12866

1. Compliance Costs

2. Benefits

B. Regulatory Flexibility Certification and Initial Regulatory Flexibility Analysis

XIV. Other Statutory Requirements

A. Unfunded Mandates Reform Act of 1995

B. Paperwork Reduction Act of 1995

C. National Environmental Protection Act

D. Executive Order 12630 (Governmental Actions and Interference with Constitutionally Protected Property Rights)

E. Executive Order 12988 (Civil Justice)

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

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

H. Executive Order 13132 (Federalism)

XV. Public Hearings

Appendix A. The Effects of Averaging Dust Concentration Measurements

Appendix B. Why Are Individual Measurements Unbiased?

I. The Value of the MRE Conversion Factor

II. Conforming to the ACGIH and ISO Standard

III. Effects of Other Variables

Appendix C. Components of Coefficient of Variation Total (CV

total

)

I. Weighing Uncertainty

(a) Derivation of Coefficient of Variation of Weight (CV

weight

)

(b) Values Expressing Weight-Gain Uncertainty

(i) New Analysis of New Data Set of Negative Weight Gain for Data of Unexposed Filters

(d) Comparing Weight Gains Obtained From Paired Samples

II. Pump Variability

III. Intersampler Variability

Appendix D. Data Submitted by Previous Commenters

I. Paired Sample Data Submitted by the NMA

II. Paired Sample Data Submitted by Mountain Coal Company

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

IV. Exposure Data Submitted by the NMA

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

Appendix E. References

XVI. Regulatory Text

II. Introduction

For as long as miners have taken coal from the ground, many have suffered respiratory problems due to their occupational exposures to respirable coal mine dust. These respiratory problems, range from mild impairment of respiratory function to more severe diseases, such as silicosis and progressive massive fibrosis (PMF). For some miners, the impairment of their respiratory systems is so severe, they die prematurely. There is a clear dose-response relationship between miners' cumulative exposures (

i.e.,

dose multiplied by the time exposed to the coal mine dust) to respirable coal mine dust and the severity of resulting respiratory conditions. On each and every workshift, it is essential to prevent miners from being exposed to respirable coal mine dust concentrations that exceed the mandated exposure limits.

The Federal Coal Mine Health and Safety Act of 1969 (Coal Act) established the first comprehensive dust standard for underground U.S. coal mines by setting a limit of 2.0 milligrams of respirable coal mine dust per cubic meter of air (mg/m

). The 2.0 mg/m

standard limits the concentration of respirable coal mine dust permitted in the mine atmosphere during each shift to which each miner in the active workings of a mine is exposed. Congress was convinced that the only way each miner could be protected from black lung disease or other occupational dust diseases was by limiting the amount of respirable coal mine dust allowed in the air that miners breathe.

The Coal Act was subsequently amended by the Federal Mine Safety and Health Act of 1977 (Mine Act), 30 U.S.C. 801

et seq.

The standard limiting respirable dust in the mine atmosphere to 2.0 mg/m

was retained in the Mine Act, which also required that “each operator shall continuously maintain the average concentration of respirable dust in the mine atmosphere during each shift to which each miner in the active workings of such mine is exposed at or below 2.0 milligrams of respirable dust per cubic meter of air,” Section 202(b)(2) (30 U.S.C.842(b)). (Other provisions in the Mine Act, Sections 205 and 203(b)(2) (30 U.S.C. 845 and 843(b)(2)), provide for lowering the applicable standard when quartz is present and when miners with evidence of the development of pneumoconiosis have elected to work in a low-dust work environment).

Today, dust levels in underground U.S. coal mines are significantly lower than they were when the Coal Act was passed. Federal mine inspector sampling results during 1968-1969 showed that the average dust concentration in the environment of a continuous miner operator was 7.7 mg/m

. Current sampling (FY 1998) indicates that the average dust level for a continuous miner operator has been reduced by 86 percent to 1.1 mg/m

. Despite this progress, the Secretaries believe that respirable coal mine dust continues to present a serious health risk to coal miners. In November 1995, the National Institute for Occupational Safety and Health (NIOSH) issued a comprehensive review of the literature concerning occupational exposure to respirable coal mine dust in its Criteria Document (NIOSH Criteria Document, 1995). NIOSH concluded, among other things, that coal miners in our country continue to be at increased risk for developing respiratory disease as a result of their exposure to respirable coal mine dust. Although it is beyond the scope of this rulemaking, in its 1995 Criteria Document, NIOSH recommended a time weighted average exposure limit to respirable coal mine dust of 1.0 mg/m

, up to ten hours per day for a 40-hour work week.

The Secretary of Labor and the Secretary of Health and Human Services believe that miners' health can be further protected from the debilitating effects of occupational respiratory disease by limiting their exposures to respirable coal mine dust exceeding the applicable standards. MSHA's improved program to eliminate overexposures on each and every shift includes multiple rulemakings. Through this proposal, MSHA would be able to use single, full-shift respirable coal mine dust samples to more effectively identify overexposures and address them. Other overexposures to respirable coal mine dust would be prevented through finalizing a proposed rule that would require each underground coal mine operator to have a verified mine ventilation plan. MSHA would verify the effectiveness of the mine ventilation plan for each mechanized mining unit (MMU) to controlling respirable dust under typical mining conditions. Furthermore, that proposal would revoke underground operator compliance and abatement sampling. Consequently in underground coal mines, MSHA intends to increase the number of compliance inspections per year, and MSHA would conduct abatement sampling for non-compliance determinations. The notice of proposed rulemaking to promulgate new regulations to require operators to have a verified ventilation plan in underground coal mines is published elsewhere in today's

Federal Register

III. General Discussion

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

the sampling process is addressed, including the performance of the approved sampler unit, sample collection procedures, and sample processing. The concept of measurement uncertainty is then addressed, and why sources of dust concentration variability and various other factors are not relevant to the proposal. In addition, the proposal summarizes the health effects of occupational exposure to respirable coal mine dust and presents MSHA's quantitative risk assessment (QRA). Finally, the proposal explains how the total measurement uncertainty is quantified, and how the accuracy of a single, full-shift measurement meets the NIOSH Accuracy Criterion. Several Appendices, which contain relevant technical information, are attached and incorporated in this notice. Appendix E contains the references used throughout this notice of proposed rulemaking.

The proposed rule is consistent with Executive Order 12866, the Regulatory Flexibility Act, the Small Business Regulatory Enforcement Fairness Act (SBREFA), the National Environmental Policy Act (NEPA), the Paperwork Reduction Act, the Unfunded Mandates Reform Act, and the Mine Act.

A. The 1971/1972 Joint Notice of Finding

In 1971, the Secretary of the Interior and the Secretary of Health, Education, and Welfare proposed, and in 1972 issued, a joint finding under the Coal Act. The finding concluded that a single, full-shift measurement of respirable dust would not, after applying valid statistical techniques, accurately represent the atmospheric conditions to which the miner is continuously exposed. For the reasons that follow, the Secretaries believe that the 1972 joint finding was incorrect.

Section 202(b)(2) of the Coal Act provided that “each operator shall continuously maintain the average concentration of respirable dust in the mine atmosphere during each shift to which each miner in the active workings of such mine is exposed at or below the applicable respirable dust standard.” In addition, the term “average concentration” was defined in section 202(f) of the Coal Act as follows:

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

Therefore, 18 months after the statute was enacted, the “average concentration” of respirable dust in coal mines was to be measured over a single shift only, unless the Secretaries found that doing so would not accurately represent mine atmospheric conditions during such shift. If the Secretaries found that a single shift measurement would not, after applying valid statistical techniques, accurately represent mine atmospheric conditions during such shift, then the interim practice of averaging measurements “over a number of continuous production shifts” was to continue.

On December 16, 1969, the U.S. Congress published a Conference Report in support of the new Coal Act. The Report refers to section 202(f) by noting that:

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

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

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

]

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

In February, 1972, the final finding was issued (37 FR 3833). It concluded that:

After careful consideration of all comments, suggestions, and objections, it is the conclusion of the Secretary of the Interior and the Secretary of Health, Education, and Welfare that a valid statistical technique was employed in the computer analysis of the data referred to in the proposed notice [footnote omitted] and that the data utilized was accurate and supported the proposed finding. Both Departments also intend periodically to review this finding as new technology develops and as new dust sampling data becomes available.

The Departments intend to revise part 70 of title 30, Code of Federal Regulations, to improve dust measuring techniques in order to ascertain more precisely the dust exposure of miners. To complement the present system of averaging dust measurements, it is anticipated that the proposed revision would use a measurement over a single shift to determine compliance with respirable dust standards taking into account (1) The variation of dust and instrument conditions inherent in coal mining operations, (2) the quality control tolerance allowed in the manufacture of personal sampler capsules, and (3) the variation in weighing precision allowed in the Bureau of Mines laboratory in Pittsburgh.

The proposed finding, as set forth at 36 FR 13286, that a measurement of respirable dust over a single shift only, will not, after applying valid statistical techniques to such measurement, accurately represent the

atmospheric conditions

to which the miner under consideration is continuously exposed,

is hereby adopted without change (emphasis added).

As explained in the 1971 proposed finding, the average concentration of all ten full-shift samples (from one occupation) submitted from each working section under the regulations in effect at the time (these were the “basic samples” referred to in the proposed notice of finding) was compared with the average concentration of the two most recently submitted samples, then to the three most recently submitted samples, then to the four most recently submitted samples, etc. In discussing the results of these comparisons, the Secretaries stated that “* * * the average of the two most recently submitted samples of respirable dust was statistically equivalent to the average concentration of the current basic samples for each working section in only 9.6 percent of the comparisons.”

The title of the 1971/1972 notice and the conclusion it reaches are clearly inconsistent. The title states that it is a “Notice of Finding That Single Shift Measurements of Respirable Dust Will Not Accurately Represent Atmospheric Conditions During Such Shift.” However, the conclusion states that, “* * * a single shift measurement * * * will not, after applying valid statistical techniques * * * accurately represent the atmospheric conditions to which the miner is

continuously

exposed” (emphasis added).

The Secretaries have determined that section 202(f) would require a determination of accuracy with respect to “atmospheric conditions during such shift,” not “atmospheric conditions

to which the miner is continuously exposed”

(37 FR 3833) (emphasis added). The Secretaries believe that the 1972 Finding does not apply the Mine Act's requirement at Section 202(f), 30 U.S.C. 842. The statistical analysis referenced in the 1971/1972 proposed and final findings simply did not address the accuracy of a single, full-shift measurement in representing atmospheric conditions during the shift on which it was taken. For this and other reasons, such as advancements in sampling technology, set forth in the notice, the Secretaries hereby propose to rescind the 1972 joint final finding.

IV. NIOSH Mission Statement and Assessment of the Joint Finding

The National Institute for Occupational Safety and Health (NIOSH) was created by Congress in the Occupational Safety and Health Act in 1970. The Act established NIOSH as part of the Department of Health, Education, and Welfare (currently NIOSH is a part of the Department of Health and Human Services) to identify the causes of work-related diseases and injuries, evaluate the hazards of new technologies, create new ways to control hazards to protect workers, and make recommendations for new occupational safety and health standards. Under section 501 of the Mine Act (30 U.S.C. 951), Congress gave specific research responsibilities to NIOSH in the field of coal and other mine health. These responsibilities include the authority to conduct studies, research, experiments and demonstrations, in order “to develop new or improved means and methods of reducing concentrations of respirable dust in the mine atmosphere of active workings of the coal or other mine,” and also “to develop techniques for the prevention and control of occupational diseases of miners * * *”

When the initial finding, issued under section 202(f) of the Coal Act, was published in 1972, both the Secretary of the Interior and the Secretary of Health, Education, and Welfare (the predecessor to the Department of Health and Human Services) indicated that the finding would be reassessed as new technology was developed, or new data became available. The Secretary of Health and Human Services, through delegated authority to NIOSH, has reconsidered the provisions of section 202(f) of the Mine Act (30 U.S.C. 842(f)), reviewed the current state of technology and other scientific advances since 1972, and has determined that the following innovations and technological advancements are important factors in the reassessment of the 1971/1972 joint finding.

In 1977, NIOSH published its “Sampling Strategies Manual,” which provided a framework for the statistical treatment of occupational exposure data (DHEW (NIOSH) Publication No. 77-173; Sec. 4.2.1). Additionally, that year, NIOSH first published the NIOSH Accuracy Criterion, which was developed as a goal for methods to be used by OSHA for compliance determinations (DHEW (NIOSH) Publication No. 77-185; pp. 1-5). In 1980, new mine health standards issued by the Secretary of Labor (30 CFR parts 70, 71, and 90) improved the quality of the sampling process by revising sampling, maintenance, and calibration procedures. Through the mid-nineteen-eighties, MSHA continued to refine and improve its sampling process. In 1984, a fully-automated, robotic weighing system was introduced along with state-of-the-art electronic microbalances. Prior to 1984, filter capsules used in sampling were manually weighed by MSHA personnel using semi-micro balances, making precision weights to the nearest 0.1 mg (100 micrograms). In 1994, the balances were further upgraded, and in 1995 the weighing system was again improved, increasing weighing sensitivity to the microgram level. Also, in 1987, electronic flow-control sampling pump technology was introduced in the coal mine dust sampling program with the use of Mine Safety Appliances FlowLite

pumps.

These new pumps compensate for the changing filter flow-resistance that occurs due to dust deposited during the sampling period. The second generation of constant-flow sampling pumps was introduced in 1994, with the introduction of the Mine Safety Appliances Escort ELF® pump. The automatic correction provided by these new pumps improves the stability of the sampler air flow rates and reduces the inaccuracies that were inherent in the 1970-1980s vintage sampling pumps. One further improvement was made in 1992 with the introduction of the new tamper-resistant filter cassettes. Because of these evolving improvements to the sampling process, a better understanding of statistical methods applied to method accuracy, and a reconsideration of the requirements of section 202(f) of the Mine Act (30 U.S.C. 842(f)), the Secretary of Health and Human Services has determined that the previous joint finding should be reevaluated.

Reference to specific equipment, trade names or manufacturers does not imply endorsement by NIOSH or MSHA.

V. MSHA Mission Statement and Overview of the Respirable Dust Program

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

A. The Coal Mine Respirable Dust Program

In 1970, federal regulations were issued by MSHA's predecessor agency that established a comprehensive coal mine operator dust sampling program for underground mines. The program required the environment of the occupation on a working section exposed to the highest respirable dust concentration to be sampled—the “high risk occupation” concept. All other occupations on the section were assumed to be protected if the high risk occupation was in compliance. Under this program, each operator was required to initially collect and submit ten valid respirable dust samples to determine the average dust concentration across ten production shifts. If the analysis showed the average dust concentration to be within the applicable dust standard, the operator was required to submit only five valid samples a month. If compliance continued to be demonstrated, the operator was required to take only five valid samples every other month. The initial, monthly, and bimonthly sampling cycles were referred to as the “original,” “standard,” and “alternative sampling” cycles, respectively. When the average dust concentration exceeded the applicable standard, the operator reverted back to the standard monthly sampling cycle.

In addition to sampling the high risk occupation at specified frequencies, each miner was sampled individually at different intervals. However, these early individual sample results were not used for enforcement but were provided to NIOSH for medical research purposes. Also required to be sampled every 90 days in underground mines, beginning in 1971, and in surface mines, beginning in 1974, were individuals who had evidence of the development of pneumoconiosis and exercised their option to transfer to a low dust area.

Federal regulations establishing a comprehensive operator dust sampling program for surface coal mines were issued in 1972. Under this program, each miner was sampled initially prior to July 1, 1972, and then either semiannually, if the initial sample exceeded 1.0 mg/m

but was less than 2.0 mg/m

, or annually if the initial sample was 1.0 mg/m

or less.

MSHA revised these regulations in April 1980 (45 FR 23990) to reduce the operator sampling burden, to simplify the sampling process, and to enhance the overall quality of the sampling program. The result was to replace the various sampling cycles in effect in underground and surface coal mines with a bimonthly sampling cycle and to eliminate the requirement that each miner be sampled. Unlike the underground sampling requirements, operators of surface coal mines were required to sample bimonthly only after a “designated work position” (DWP) was established by MSHA. Once established, only one sample is required to be collected each bimonthly period. Under the revised regulations, MSHA could also withdraw the designation of work positions for sampling if samples taken by the operator and by MSHA demonstrated continuing compliance with the applicable dust standard. These are the regulations that currently govern the mine operator dust sampling program at both underground and surface coal mines, and which, in the case of underground mines, continue to be based on the high risk occupation concept, now referred to as the “designated occupation” or “D.O.” sampling concept.

It should be noted that the April 1980 preamble to the final rule, amending the regulations for underground coal mines, explicitly refers to the use of single versus multiple samples as it applies to the operator respirable dust sampling program (45 FR 23997):

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

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

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

MSHA believes that this interpretation merely recognized the two ways of measurement authorized in section 202(f), and expressed the preference on the part of MSHA in 1980 to retain multi-shift sampling in the operator sampling program. The phrase used in the preamble to the final rule reflects that MSHA understood that the 2.0 mg/m

limit was a single-shift standard, meaning that it was not to be exceeded on a shift. The preamble referenced the continuous multi-shift sampling and single-shift sampling conducted by the Secretary of the Interior and the Secretary of Health, Education, and Welfare, and noted that in the 1971/1972 proposed and final findings:

“It had been determined after applying valid statistical techniques, * * * that a single shift sample should not be relied upon for compliance determinations when the respirable dust concentration being measured was near 2.0 mg/m

. Accordingly, the [Secretaries] prescribed consecutive multi-shift samples to enforce the respirable dust standard.”

The preamble provides no further explanation for the statement that single-shift samples should not be relied on when the respirable dust concentration being measured was near 2.0 mg/m

. Thus, the 1980 final rule, which reduced the number of samples that operators were required to take for compliance determinations, merely reiterated the rationale behind the 1971/1972 proposed and final findings concerning single-shift samples, and did not address the accuracy of a single, full-shift measurement.

MSHA continues to take an active role in sampling for respirable dust and has recently expanded its sampling to more than once annually at each surface and underground coal mine. During these inspections, MSHA inspectors collect samples on multiple occupations to determine whether miners are being overexposed to respirable coal mine dust; to assess the effectiveness of the operator's dust control program; to quantify the level of respirable crystalline silica (quartz) in the work environment and whether there is a need to adjust the applicable dust standard; and to identify occupations in underground mines, other than the “D.O.”, and occupations in surface mines, that are at risk of being overexposed and should be routinely monitored by the mine operator.

Depending on the concentration of respirable coal mine dust measured, an MSHA inspector may terminate sampling after the first day if levels are very low, or continue for up to five shifts or days before making a compliance or noncompliance determination. For example, MSHA inspection procedures require inspectors to sample at least five occupations, if available, on each mechanized mining unit (MMU) on the

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

The Spot Inspection Program (SIP)

In response to concerns about possible tampering with dust samples in 1991, MSHA convened the Coal Mine Respirable Dust Task Group (Task Group) to review the Agency's respirable dust program. The Task Group was directed to consider all aspects of the current program in its review, including the role of the individual miner in the sampling program; the feasibility of MSHA conducting all sampling; and the development of new and improved monitoring technology, including technology to continuously monitor the mine environment. Among the issues addressed by the Task Group was the actual dust concentration to which miners are exposed. As part of the Task Group review, MSHA developed a special respirable dust “spot inspection program” (SIP).

This program was designed to provide the Agency with information on the dust levels to which underground miners are typically exposed. Because of the large number of mines and MMUs (mechanized mining units) involved and the need to obtain data within a short time frame, respirable dust sampling during the SIP was limited to a single shift or day, a departure from MSHA's normal sampling procedures. The term “MMU” is defined in 30 CFR 70.2(h) to mean a unit of mining equipment, including hand loading equipment, used for the production of material. As a result, MSHA decided that if the average of multiple occupation measurements taken on an MMU during any one-day inspection did not exceed the applicable standard, the inspector would review the result of each individual full-shift sample. If any individual full-shift measurement exceeded the applicable standard by an amount specified by MSHA, a citation would be issued for noncompliance, requiring the mine operator to take immediate corrective action to lower the average dust concentration in the mine atmosphere in order to protect miners.

During the SIP inspections, MSHA inspectors cited violations of the 2.0 mg/m

standard if either the average of the five measurements taken on a single shift was equal to or greater than 2.1 mg/m

, or any single, full-shift measurement was equal to or exceeded 2.5 mg/m

. Similar adjustments were made when the 2.0 mg/m

standard was reduced due to the presence of quartz dust in the mine atmosphere.

Quartz may be present in the coal seam and therefore may become airborne during coal production. MSHA regulates coal miners' work-shift exposure to quartz since it may be deposited in the lungs of miners and cause silicosis. MSHA's current standard for respirable coal mine dust, 2.0 mg/m

, also requires quartz levels to be 5% or lower. Otherwise, if the percent of quartz is higher than 5%, the respirable coal mine dust exposure limit must be adjusted downward based on this formula: Respirable dust standard (mg/m

)= {(10 mg/m

)/(%Quartz)} For example, if the respirable dust contains 15 percentage of quartz the respirable coal mine dust standard would be 0.67 mg/m

since 10 mg/m

divided by 15 equals 0.67 mg/m

The procedures issued by MSHA's Coal Mine Safety and Health Division during the SIP were similar to those used by the MSHA Metal/Nonmetal Mine Safety and Health Division and the Occupational Safety and Health Administration (OSHA) when determining whether to cite based on a single, full-shift measurement. That practice provides for a margin of error reflecting an adjustment for uncertainty in the measurement process (

i.e.

, sampling and analytical error, “SAE”). The margin of error thus allows citations to be issued only where there is a high level of confidence that the applicable standard has been exceeded.

Based on the data from the SIP inspections, the Task Group concluded that MSHA's practice of making noncompliance determinations solely on the average of multiple-sample results did not always result in citations in situations where miners were known to be overexposed to respirable coal mine dust. For example, if measurements obtained for five different occupations within the same MMU were 4.1, 1.0, 1.0, 2.5, and 1.4 mg/m

, the average concentration would be 2.0 mg/m

. Although the dust concentrations for two occupations exceed the applicable standard, under MSHA procedures, no citation would have been issued nor any corrective action required to reduce dust levels to protect miners' health. Instead, MSHA policy required the inspector to return to the mine the next day that coal was being produced and resume sampling in order to decide if the mine was in compliance or not in compliance.

Thus, the SIP inspections revealed instances of overexposure that were masked by the averaging of results across different occupations. This showed that miners would not be adequately protected if noncompliance determinations were based solely on the average of multiple measurements. The process of averaging dilutes a high measurement made at one location with lower measurements made elsewhere.

The Task Group also recognized that the results of the first full-shift samples taken by an inspector during a respirable dust inspection are likely to reflect higher dust concentrations than samples collected on subsequent shifts or days during the same inspection. MSHA's comparison of the average dust concentration of inspector samples taken on the same occupation on both the first and second day of a multiple-day sampling inspection showed that the average concentration of all samples taken on the first day of an inspection was almost twice as high as the average concentration of samples taken on the second day. MSHA recognized that sampling on successive days does not always result in measurements that are representative of everyday respirable dust exposures in the mine because mine operators can anticipate the continuation of inspector sampling and make adjustments in dust control parameters or production rates to lower dust levels during the subsequent sampling.

In response to these findings, in November 1991, MSHA decided to permanently adopt the single, full-shift inspection policy initiated during the SIP for all mining types.

C. The Keystone Decision

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

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

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

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

The Interim Single-Sample Enforcement Policy (ISSEP)

On February 3, 1998, MSHA published a corrected notice in the

Federal Register

(63 FR 5687) announcing its final policy on the use of single, full-shift measurements to determine noncompliance and issue citations, based on samples collected by MSHA inspectors, when the applicable respirable dust standard is exceeded. The enforcement policy, thereafter referred to as ISSEP, which took effect on May 7, 1998, provides better protection to miners' health because it enabled MSHA to more effectively identify overexposures that were previously masked by the averaging of results across different occupations. Again, through the proposed single, full-shift sample approach, citations for noncompliance with the respirable coal mine dust standard would be able to be made for overexposures which would not be identified through the current procedure of averaging multiple-sample results. For example, if measurements obtained for five different occupations within the same MMU were 4.1, 1.0, 1.0, 2.6, and 0.8 mg/m

, the average concentration would be 1.9 mg/m

. Although the dust concentrations for two occupations statistically exceeded the applicable standard, under the current practice, of averaging results, no citation would be issued nor any corrective action required to reduce dust levels to protect miners' health. The ISSEP was in place until September 9, 1998, when MSHA reinstituted its previous procedure of averaging sample results for noncompliance determinations after the 11th Circuit Court of Appeals vacated the Agencies' 1998 Finding and MSHA's final policy.

Under the ISSEP, MSHA followed its existing dust sampling procedures in regard to where and how many samples an inspector collects during a sampling shift at underground and surface coal mines. While the Agency continued its practice of collecting multiple occupational samples at each MMU, the minimum number of occupations monitored was reduced from five to three, focusing only on those occupations at high risk of being overexposed. As part of the ISSEP, inspectors carried with them a control filter when conducting respirable dust sampling. This control filter, which was unexposed, was used to adjust the weight gain obtained on each of the exposed filters. Any change in weight of the unexposed control filter was subtracted from the change in weight of each exposed filter. For the exposed filter to be valid, the control and exposed filter must have been both pre-and post-weighed on the same days. If the control filter was either missing or invalid, the measurement(s) were not used for enforcement purposes and the entity type (

i.e.

, mining section) was to be resampled. An operator was found to be in violation of the applicable dust standard when a single, full-shift measurement met or exceeded the Citation Threshold Value (CTV) corresponding to the dust standard in effect. Each CTV listed in

Chapter 1 of the Coal Mine Health Inspection Procedures Handbook

(PH89-V-1(10)) was calculated to ensure that citations would be issued only when a measurement demonstrated, with at least 95-percent confidence, that the applicable standard had been exceeded.

No more than one citation was to be issued based on single, full-shift measurements from the same MMU, if the sampled occupations were exposed to the same dust generating sources. Issuance of separate citations were to be considered only after determining that the affected occupations were exposed to different dust generating sources.

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

When a single, full-shift measurement exceeded the applicable standard but was less than the CTV, a citation was not to be issued since noncompliance was not demonstrated at a sufficiently high confidence level. Instead, the MMU or other entity type sampled was to be targeted for additional sampling to verify the adequacy of the operator's dust control measures to maintain compliance, with special emphasis directed toward working environments with applicable standards below 2.0 mg/m

. If subsequent sampling exceeded the applicable standard but not the CTV, the MSHA district responsible for inspecting the mine would thoroughly review the dust control parameters stipulated in the operator's approved ventilation or respirable dust control plan (applicable to surface mines and Part 90 miners) to determine if the parameters should be upgraded.

The process by which a violation of the applicable standard was to be abated by a mine operator remained unchanged. That is, an operator must first take corrective action to reduce the average dust concentration to within the permissible level, and then sample each production or normal work shift until five valid respirable dust samples are taken. MSHA considers a violation to be abated when the average dust concentration measured by these five valid samples was at or below the applicable standard. Under the ISSEP, MSHA inspectors sampled 1,662 MMUs and other entity types, such as roof bolter DAs and Part 90 miners, in underground mines; and some 860 DWPs and over 3,700 nondesignated work positions at surface mining operations. The Agency issued a total of 309 excessive dust citations based on the results of single, full-shift samples, involving 182 MMUs and 113 other underground entity types, and 14 surface work positions. Of the 1,662 MMUs sampled, 182 or 11 percent were cited, compared to the 27 percent MSHA had projected based on inspector sampling results for 1995. Also, it is important to point out that only 14 of the over 4,500 surface entities sampled were found to be out of compliance. These sampling inspections, which showed a significant decline in the number of cited instances of noncompliance compared to previous experience under the SIP and the earlier projections documented in the 1998 notices, reveal that mine operators are capable of maintaining dust concentrations at or below the applicable standard on every shift.

VI. Procedural and Litigation History of This Proposal

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

Joint Notice of Finding in the

Federal Register

(59 FR 8357). The Joint Notice proposed to rescind the 1972 finding by the Secretaries of the Interior and Health, Education and Welfare, and instead, find that a single, full-shift measurement will accurately represent the atmospheric conditions with regard to the respirable dust concentration during the shift on which it was taken. Concurrently, MSHA published a separate notice in the

Federal Register

announcing its intention to use both single, full-shift measurements and the average of multiple, full-shift measurements for noncompliance determinations under the MSHA respirable coal mine dust program (59 FR 8356). That notice was published to inform the mining public of how the Agency intended to implement its new enforcement procedure utilizing single, full-shift samples, and to solicit public comment on the procedure.

After a notice and comment procedure extending over some three and one-half years, which also included three public hearings, the Agencies published a final corrected notice of finding in the

Federal Register

(63 FR 5664) on February 3, 1998.

The National Mining Association (NMA) along with the Alabama Coal Association petitioned the United States Court of Appeals for the 11th Circuit to review the 1998 Notice of Finding (Joint Finding) issued by the Mine Safety and Health Administration (MSHA) and the National Institute for Occupational Safety and Health (NIOSH), and additionally asked for an emergency motion for stay of the Joint Finding pending review. The motion for an emergency stay was denied by the Court.

On appeal NMA argued, among other things, that the agency had not met the requirements of section 101(a)(6)(A) of the Federal Mine Safety and Health Act of 1977 (Mine Act) (30 U.S.C. 811(a)(6)(A)) because it failed to address material impairment of health and economic and technological feasibility. MSHA and the Department of Labor responded that the agencies addressed the positive effect of the notice on miner health, and also concluded in the course of performing the analysis required under the Regulatory Flexibility Act that the economic impact of the Joint Finding was not significant. On September 4, 1998, the United States Court of Appeals for the 11th Circuit issued a decision in the case of

National Mining Association

Secretary of Labor

, (153 F.3d 1264). The Court of Appeals vacated the Joint Finding and concluded that the agency was required to “satisfy the requirements of Section 811(a)(6)” by “demonstrat[ing] that the new standard (a) adequately assures that no miner will suffer a material impairment of health, on the basis of the best available evidence; (b) uses the latest available scientific data in the field; (c) is feasible [in both an economic and technological sense]; and (d) is based on experience gained under the Mine Act and other health and safety laws,” supra, at 1268-1269. The Court then concluded that “the record contains no finding of economic feasibility,” and that MSHA therefore “failed to comply with Section 811(a)(6) of the Mine Act.” MSHA asked the Court for a clarification of its decision by filing a Motion for Clarification. The Court, without opinion, denied the Secretary's motion on November 11, 1998.

MSHA and NIOSH understand the Court's ruling as requiring the Agencies to comply with all requirements under section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)). Therefore, in response to the Court's ruling, the Secretaries are proposing today to add a new mandatory health standard to 30 CFR part 72. Pursuant to section 202(f) of the Mine Act (30 U.S.C. 842(f)), the 1972 joint notice of finding would be rescinded and a new finding would be made that a single, full-shift measurement will accurately represent atmospheric conditions to which a miner is exposed during such shift. This finding is the basis for the new proposed mandatory health standard.

The Secretaries believe that single, full-shift measurements must be implemented into the MSHA coal mine respirable dust program as quickly as possible in order to better protect miners' health. Therefore, in order to speed the process of reproposing this critical measurement technique, the Secretaries are incorporating the record of the previous 1998 Joint Finding into the record for this proposal and adding appropriate new data and information to support this rulemaking under section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)). The Secretaries have used as much of the original wording as possible from the vacated final finding in this notice of proposed rulemaking. References to previous comments and commenters in the body of this proposal are meant to apply to previous comments received in response to the earlier proposed Joint Finding that was ultimately vacated by the U.S. Court of Appeals for the 11th Circuit.

VII. Health Effects

A. Introduction

Since the 1800s, occupational respiratory disease associated with working in a coal mine has been commonly referred to as “Black Lung.” As coal is mined, respirable-sized dust is generated. Depending upon the mine location and its geologic features, silica may also be present in the mine atmosphere. Dust in air that is breathed by miners has the potential to be deposited in their lungs. Some of this dust may be retained. Coal mine dust remaining in the lungs of miners for prolonged periods of time has the potential to result in respiratory diseases, sometimes even after occupational exposure to respirable coal mine dust has stopped. There is a clear and direct relationship between miners' cumulative exposures (

i.e.,

dose multiplied by the time exposed to the coal mine dust) to respirable coal mine dust and the severity of resulting respiratory conditions (as discussed more extensively, later in this section).

Diseases resulting from long-term retention of coal mine dust in the lung include chronic coal workers' pneumoconiosis (simple CWP), progressive massive fibrosis (PMF), silicosis, and chronic obstructive pulmonary disease (COPD) (

e.g.,

asthma, chronic bronchitis, emphysema). Historically, the medical term, “pneumoconiosis”, has included simple CWP and PMF and their sub-categories. Chronic, or simple, CWP is partitioned into three levels of severity, proceeding from lowest to highest: Category 1, category 2, and category 3. Progressive Massive Fibrosis is similarly divided into three categories of increasing levels of severity: A, B and C.

Miners with simple CWP have a substantially increased risk of developing PMF. In the advanced stages of pneumoconiosis (

i.e.,

PMF), a significant loss of lung function may occur and respiratory symptoms (

e.g.,

breathlessness, wheezing) may persist. Miners are at risk of increased morbidity and premature mortality due to simple CWP, PMF and various other respiratory diseases.

Factors that are important in the development of simple CWP, PMF and COPD include the type of dust (

e.g.,

coal and/or silica), dust concentration (to which the miner was exposed), number of years of exposure, age of the miner (often measured as age at time of medical examination), and rank of the coal (the higher the rank the greater the risk).

In 1998, MSHA estimated that approximately 45,000 miners and

39,000 miners were employed at underground and surface coal mines, respectively (Mattos, 1999). A small percentage of the mining involved anthracite coal, the highest rank coal, while most involved bituminous coal which is a medium rank coal.

There are complementary data sources, described below, which provide estimates of the prevalence of occupational respiratory disease among coal miners. Together these data demonstrate the progress over the last thirty years in the reduction of occupational respiratory disease among coal miners, as well as the need for further action to reduce occupational lung disease among today's coal miners.

Estimates of the prevalence of simple CWP and PMF among the underground coal miners are gathered from the x-ray program, through which operators are required to provide miners the opportunity to be evaluated periodically for the presence of occupational lung disease, mandated pursuant to Section 203(a) of the Mine Act (30 U.S.C. 843(a)). However, miners are not required to participate. From 1970 to 1995,the prevalence of simple CWP and PMF among miners participating in the mandated x-ray program has dropped from 11 percent to 3 percent (MSHA, Internal Chart, 1998).

In accordance with 30 CFR part 50, those cases of occupational illnesses which both surface and underground coal mine operators learn of must be reported to MSHA. Under this requirement, mine operators reported 224 cases of pneumoconiosis (simple CWP and PMF, combined) in 1998 (Mattos, 1999). Of these, 138 cases occurred among coal miners who worked underground, while the remaining 86 cases occurred among surface coal miners (Mattos, 1999). There were also 14 cases of silicosis, eight in underground mines, reported to MSHA in 1998 in accordance with 30 CFR part 50 (Mattos, 1999). Since miners participate in both these programs at their own discretion, these data do not include the occupational health experience of all coal miners. The prevalence of occupational lung disease among participating miners may significantly differ from the prevalence among non-participants. Thus, the data from these programs may not be representative of the true magnitude of the prevalence of simple CWP and PMF among today's coal miners.

In the 1990s, MSHA conducted a series of one-time medical surveillance programs, in various regions of the country, to develop a more accurate estimate of the prevalence of simple CWP and PMF. Through these special programs, MSHA tried to minimize obstacles which may prevent some miners from either participating in or reporting to operators the results of respiratory diagnostic procedures. Nine geographical cohorts of miners, from around the country, were encouraged to participate in an independent x-ray program (MSHA, Internal Chart, 1999). These cohorts included eight active surface coal mining communities in the states of Pennsylvania, Kentucky and West Virginia, as well as the towns of Poteau, Oklahoma and Gillette, Wyoming. A ninth cohort included underground miners in Kentucky. The process was designed to encourage miner participation by providing for a greater degree of anonymity than may be available under the program provided by Section 203(a) of the Mine Act (30 U.S.C. 843(a)). Across the eight surface cohorts surveyed, the prevalence rate of simple CWP and PMF combined, among participants was 4.8%. The prevalence rate among the participating underground Kentucky miners was 9.2%.

Also, as part of its ongoing effort to “end black lung now and forever,” beginning in October 1999, MSHA implemented a pilot program to provide miners at both surface and underground mines with confidential health screening. Referred to as the “Miners’ Choice Health Screening”, the program addresses the key recommendations of the Secretary's Advisory Committee by (1) increasing participation toward the 85-percent level and (2) expanding the scope of the eligibility to include surface coal miners and surface coal mine independent contractors. The pilot program will operate separately from the existing Coal Workers' X-ray Surveillance Program administered by NIOSH. Since the Miners' Choice Health Screenings' inception, over 7,000 miners have been screened, with the participation rate in most areas exceeding 50 percent. With half of the x-rays taken during the first six months having been processed by NIOSH, preliminary results indicate a prevalence rate of approximately 2.25 percent.

The National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA) are concerned about the prevalence of occupational lung disease among today's miners. Epidemiological studies from the U.S. and abroad have consistently shown that underground and surface coal miners are at risk of developing simple CWP, PMF, silicosis, and chronic obstructive pulmonary disease (NIOSH Criteria Document, 1995).

B. Hazard Identification

1. Agent: Coal

Coal is a fossil fuel derived from partial degradation of vegetation. Through its combustion, energy is produced which makes coal a valuable global commodity. It has been estimated that over one-third of the world uses energy provided by coal (Manahan, 1994). Approximately 1,800 underground and surface coal mines are in operation in the United States annually producing slightly over a billion short tons of coal (Mattos, 1999).

Coal may be classified on the basis of its type, grade, and rank. The type of coal is based upon the plant material (

e.g.

, lignin, cellulose) from which it originated. The grade of coal refers to its chemical purity. Although coal is largely carbon, it may also contain other elements such as hydrogen, oxygen, nitrogen, and sulfur. “Hard” coal refers to coal with a higher carbon content (

i.e.

, 90-95%) than “soft” coal (

i.e.

, 65-75%). Coal rank relates to geologic age, indexed by its fixed carbon content, down to 65%, and then by its heating value. Volatile matter varies inversely with the fixed carbon value. The most commonly described coal ranks include lignite (low rank), bituminous coal (medium rank), and anthracite (high rank) (Manahan, 1994).

2. Physical State: Coal Mine Dust

Aerosols are a suspension of solid or liquid particles in air (Mercer, 1973); they may be dusts which are solid particles suspended in the air. Coal dust may be freshly generated or may be re-suspended from surfaces on which it is deposited in mines. As discussed below, coal mine dust may be inhaled by miners, depending upon the particle size.

Coal mine dust is a heterogenous mixture, signifying that all coal particles do not have the same chemical composition. The particles are influenced by the type, grade, and rank of coal from which they were generated (Manahan, 1994). Irrespective of differences in coal characteristics, these dusts are water-insoluble, which is important biologically and physiologically. Unlike soluble dusts which may readily pass into the respiratory system and be cleared via the circulatory system, insoluble dusts may remain in the lungs for prolonged periods of time. Thus, a variety of cellular responses may result that could eventually lead to lung disease.

3. Biological Action: Respirable Coal Mine Dust

The principal route of occupational exposure to respirable coal mine dust occurs via inhalation. As a miner breathes, coal mine dust enters the nose and/or mouth and may pass into the mid airways (

e.g.

, bronchi, terminal bronchioles) and lower airways (

e.g.

, respiratory bronchioles, alveolar ducts).

Coal mine dust has a size distribution that is estimated to range between 1 and 100 micrometer (μm) (1 μm = 10

−6

m) (Silverman,

et al.

, 1971). The size of coal particles is critical in determining the level of the respiratory tract at which deposition and retention occur (American Conference of Governmental Industrial Hygienists, 1999; American Industrial Hygiene Association, 1997).

Particles that are above 10 μm are largely filtered in the nasal passages, although some of these particles may reach the thoracic (or tracheal-bronchial) region of the lung (

e.g.

, 6% of 20 μm) (American Conference of Governmental Industrial Hygienists, 1999). Thus, there is evidence that “oversized” particles (

i.e.

, >10 μm) can move beyond the nose, deeper into the respiratory tract. Particles below 10 μm may easily move throughout the respiratory tract. As particle size decreases from 10 to 5 μm, however, there is greater penetration into the mid and lower regions of the lung. Particles that are approximately 1-2 μm are the most likely to be deposited in the lung (American Conference of Governmental Industrial Hygienists, 1999; Mercer, 1973). During mouth breathing, there may be a slight upward shift in the particle deposition curve such that 2-3 μm-sized particles are the most likely to be deposited in the respiratory tract (Heyder,

et al.

, 1986). Irrespective of nasal or mouth breathing, the potential respiratory tract penetration of particles whose size is approximately 10 μm or less is important because particles in the respirable size range deposit in the deep lung where clearance is much slower.

For the purposes of this rule, “respirable dust” is defined as dust collected with a sampling device approved by the Secretary of Labor and the Secretary of the Department of Health and Human Services (DHHS) in accordance with 30 CFR Part 74 (Coal Mine Dust Personal Sampler Units). In practice, the coal mine dust personal sampler unit has been used in the U.S. The particles collected with an approved sampler approximate that portion of the dust which may be deposited in the lung (West, 1990; 1992). It does not, however, indicate pulmonary retention (

i.e.

, those particles remaining in the lung). For those particles that are deposited in the lung, clearance mechanisms normally operate to assist in their removal. For example, within the thoracic (tracheal-bronchial) region of the lung, cilia (

i.e.

, hairlike projections) line the airways and are covered by a thin layer of mucus. They assist in particle clearance by beating rhythmically to project particles toward the throat where they may be swallowed, coughed, sneezed, or expectorated. This rhythmic beating action is effective in removing particles fairly quickly (

i.e.

, hours or days). Within the alveolar region of the lung, particles may be engulfed by pulmonary macrophages. These large “wandering cells” may remove particles via the blood or lymphatics. This process, unlike the movement of the cilia is much slower (

i.e.

, months or years). Thus, some particles, particularly those that are insoluble, may remain in the alveolar region for long periods of time, despite the fact that pulmonary clearance is not impaired. It is the pulmonary retention of coal mine dust which may be the impetus for respiratory disease.

It is also important to note that silica may be present in the coal seam, within dirt bands in the coal seam, and in rock above and below coal seams. Of the silica found in coal mines, quartz is the form which is found. Thus, quartz may become airborne during coal removal operations (Manahan, 1994). Miners may inhale dust that is a mixture of quartz and coal. MSHA is concerned with the inhalation of quartz since it may be deposited in the lungs of miners and produce silicosis. This is a restrictive lung disease which is characterized by a stiffening of the lungs (West, 1990; 1992). Silicosis has been seen in coal miners (

e.g.

, surface miners, drillers, roofbolters) (Balaan,

et al.

, 1993). Silicosis may develop acutely (

i.e.

, 6 months to 2 years) following intense exposure to high levels of respirable crystalline quartz. Silicosis has also been observed in coal miners following chronic exposure (

i.e.

, 15 years or more), but may be accelerated (

i.e.

, 7-10 years) in some cases (Balaan,

et al.

, 1993). Silicosis is irreversible and may lead to other illnesses and premature mortality. People with silicosis have increased risk of pulmonary tuberculosis infection and an increased risk of lung cancer (Althouse,

et al.

, 1995; International Agency for Research on Cancer, 1997). MSHA's current standard of 2.0 mg/m

for respirable coal dust requires that quartz levels be 5% or lower. Otherwise, the 2.0 mg/m

respirable coal dust exposure limit does not apply and must be adjusted downward for percentage of quartz. If coal dust contains more than 5% quartz, then the following formula is applied (30 CFR 70.101; 30 CFR 71.101).

Respirable dust standard (mg/m

)= {(10 mg/m

)/(%Quartz)}

The intent of this formula is to maintain miner exposures to quartz below 0.1 mg/m

(100 μg/m

C. Health-Related Effects of Respirable Coal Mine Dust

1. Description of Major Health Effects

Consistently, epidemiological studies have demonstrated miners to be at risk of developing respiratory symptoms, a loss of lung function, and lung disease as a consequence of occupational exposure to respirable coal mine dust. As noted previously, risk factors include type(s) of dust, dust concentration, duration of exposure, age of the miner (often measured as age at time of medical examination), and coal rank.

a. Simple Coal Workers' Pneumoconiosis (Simple CWP) and Progressive Massive Fibrosis (PMF)

In earlier stages of pneumoconiosis the term, “simple coal workers’ pneumoconiosis” (simple CWP), has been used, while in more advanced stages, the terms “complicated CWP” and PMF have been used interchangeably. Simple CWP and PMF involve the lung parenchyma and are produced by deposition and retention of respirable coal dust in the lung.

To determine if a miner has simple CWP or PMF, chest x-rays are taken and classified by a certified radiologist or reader. Opacities are identified on chest films and then classified using a scale of 0-3 (

e.g.

, simple CWP category 1), where higher category values indicate increasing concentration of opacities. In some instances, two category values may be given. For example, simple CWP category 2/3 signifies that the reader decided the film was category 2, but suspected that it might have been category 3. The International Labour Office (ILO) has provided a full description of the criteria for these classifications (ILO, 1980).

Simple CWP can be associated with a loss of lung function and with premature mortality (Morgan,

et al.

, 1974; Jacobsen, 1976; Cochrane,

et al.

, 1979; Parkes, 1982). MSHA recognizes that simple CWP increases the risk of developing PMF substantially (Cochrane, 1962; Jacobsen,

et al.

, 1971; McLintock,

et al.

, 1971; Balaan,

et al.

, 1993).

Progressive massive fibrosis (PMF) is associated with decreased lung function

and increased premature mortality (Rasmussen,

et al.

, 1968; Atuhaire,

et al.

, 1985; Miller and Jacobsen, 1985; Attfield and Wagner, 1992). Progressive massive fibrosis is also associated with increases in respiratory symptoms such as chest tightness, cough, and shortness of breath. Miners with PMF also have an increased risk of acquiring infections and pulmonary tuberculosis (Petsonk and Attfield, 1994; Yi and Zhang, 1996). Finally, miners with PMF have an increased risk of right-side heart failure (

i.e.

, cor pulmonale) (Cotes and Steel, 1987).

b. Other Health Effects

During a medical examination, a miner may be questioned by his physician about symptoms such as cough, phlegm production, chest tightness, shortness of breath, and wheezing. Occupational physicians may also conduct pulmonary function tests using spirometry or plethysmography. Pulmonary performance may be assessed via repeated measurements of lung volumes and capacities, such as the forced expiratory volume in one second (FEV

), vital capacity (VC), forced vital capacity (FVC), residual volume (RV), and total lung capacity (TLC) (West, 1990; 1992). Changes in lung volumes and capacities may indicate a loss of the integrity of the lung (

i.e.

, respiratory system). More importantly, they can provide information for diagnosis of diseases affecting the airways and/or elasticity of the lung (

i.e.

, obstructive vs. restrictive lung disease) (West, 1990; 1992).

The term, chronic obstructive pulmonary disease (COPD), refers to three disease processes that are often difficult to properly diagnose and differentiate: chronic bronchitis, emphysema, and asthma (Coggon and Taylor, 1998; Garshick,

et al.

, 1996; West, 1990; 1992). As indicated by several studies, the exposure of miners to respirable coal mine dust place them at increased risk of developing COPD. Furthermore, COPD may occur in miners with or without the presence of simple CWP or PMF.

Chronic Obstructive Pulmonary Disease (COPD) is characterized by airflow limitations, and thus there is a loss of pulmonary function. As in simple CWP or PMF, a miner with COPD may have a variety of respiratory symptoms (

e.g.

, shortness of breath, cough, sputum production, and wheezing) and may be at increased risk of acquiring infections. Chronic Obstructive Pulmonary Disease is associated with increased premature mortality (Hansen,

et al.

, 1999; Meijers,

et al.

, 1997).

Briefly, in chronic bronchitis and in asthma, there is excess mucous secretion in the mid-lower airways (West, 1990; 1992). In contrast, emphysema is characterized by dilatation (enlargement) of alveoli that are distal to the terminal bronchioles, which leads to poor gas exchange (

i.e.,

poor transfer of oxygen and carbon dioxide). Additionally, there is a breakdown of the interstitium between the alveoli. These pathological changes may be confirmed upon autopsy. With asthma, the airflow limitations may be partially or completely reversible, while they are only partially reversible with chronic bronchitis and emphysema.

The Mine Safety and Health Administration (MSHA) and the NIOSH recognize that respiratory symptoms, loss of lung function, and COPD may impair the ability of a miner to perform his job and may diminish his quality of life. Additionally, miners having such health effects are at increased risk of morbidity (

e.g.,

from cardio-pulmonary disease, infections) and premature mortality.

2. Toxicological Literature

To better understand the human health effects of exposure to respirable coal mine dust and to more fully characterize the associated risks, it is important to consider data that have been obtained in animal based toxicological studies. To date, sub-acute studies (a study with a duration of 30 days, or less, in which multiple exposures of the same agent are given) and chronic studies (a study with a duration of more than 3-months, in which multiple exposures of the same agent are given) attempted to mimic miners' exposures. Inhalation was generally the route of exposure, although several studies have also employed instillation techniques (

i.e.,

a method which places a known quantity of dust into the trachea or bronchi).

Most recent toxicological studies have been short-term studies, largely focusing on “lung overload” (Snipes, 1996; Oberdorster, 1995; Morrow, 1988, 1992; Witschi, 1990), species-dependent lung responses (Nikula,

et al.,

1997a,b; Mauderly, 1996; Lewis,

et al.,

1989; Moorman,

et al.,

1975), and particle size-dependent lung inflammation (Soutar,

et al.,

1997). The data have shown that pulmonary clearance of particles may become impaired, potentially leading to inflammatory and other cellular responses in the lung. Although overloading has not been demonstrated in humans, the finding of reduced lung clearance among retired U.S. coal miners (Freedman and Robinson, 1988) is consistent with this possibility.

The data from Moorman,

et al.

(1975), Lewis,

et al.

(1989), and Nikula,

et al.

(1997a,b) are noteworthy for several reasons. First, these groups of investigators conducted chronic inhalation toxicity studies (

i.e.,

chronic bioassays). This is important since miners' exposures also occur via inhalation, and over a working lifetime. Secondly, the investigators used an exposure concentration of 2.0 mg/m

in their bioassays. As noted above, this is the current MSHA standard for respirable coal mine dust. Thirdly, the exposures involved nonhuman primates, whose responses are thought to closely mimic those of man. Some of the key findings of these studies included: deposition of coal dust in the animals' lungs, retention of coal dust in alveolar tissue, altered lung defense mechanisms, reduced pulmonary airflows, and hyperinflation of the lungs. One of the shortcomings of these studies is that complete dose-response relationships were not developed. However, at higher exposure concentrations, greater effects may be expected which is a basic tenet of toxicology. Thus, at exposure concentrations above 2.0 mg/m

, MSHA and NIOSH believe that more severe obstructive lung disease may occur.

3. Epidemiological Literature

Epidemiology studies have consistently demonstrated the serious health effects of exposure to high levels of respirable coal mine dust (

i.e.,

above 2.0 mg/m

) over a working lifetime. Table VII-1 lists epidemiology studies since 1986 whose results will be discussed on the basis of the type of observed health effect. Studies completed even earlier including the early work of Cochrane (1962), McLintock,

et al.

(1971), and Jacobsen,

et al.

(1971) demonstrated the adverse health effects (

e.g.,

simple CWP, PMF) of respirable coal mine dust in British coal miners.

Both early and recent studies have shown that the lung is the major target organ (

i.e.,

organ in which toxic effects occur) when exposure to respirable coal mine dust occurs. As seen in Table VII-1, numerous studies of miners have been conducted. Recent U.S. studies were conducted using data from one or more of the first four rounds of the National Study of Coal Workers' Pneumoconiosis (NSCWP), and have provided extensive data on miners' health. Many of these studies demonstrated that miners are at increased risk of multiple, concurrent respiratory ailments (Attfield and

Seixas, 1995; Kuempel,

et al.,

1997; Meijers,

et al.,

1997; Seixas,

et al.,

1992).

Table VII-1.—Respirable Coal Mine Dust Epidemiological Studies, by Reported Outcomes From 1986 to Present

Studies

Reported outcomes

Meijers,

et al.,

1997

PMF, CWP, COPD, LLF.

Maclaren,

et al.,

1989

PMF, CWP, LLF, RS.

Kuempel*,

et al.,

1995

PMF, CWP, COPD.

Bourgkard

et al.,

1998

PMF, CWP, LLF.

Kuempel*,

et al.,

1997

Love,

et al.,

1997

Love,

et al.,

1992

Attfield and Morring*,1992b

PMF, CWP.

Attfield and Seixas*, 1995

Hodous and Attfield*, 1990

Hurley and Jacobsen, 1986

Hurley and Maclaren, 1987

Hurley,

et al.,

1987

Starzynski,

et al.,

1996

Yi and Zhang, 1996

Wang,

et al.,

1997

CWP, LLF.

Goodwin and Attfield*, 1998

CWP.

Morfeld,

et al.,

1997

Marine,

et al.,

1988

COPD, LLF, RS.

Seixas*,

et al.,

1993

Soutar and Hurley, 1986

Carta,

et al.,

1996

LLF, RS.

Henneberger and Attfield*,1997

Henneberger and Attfield*,1996

Seixas*,

et al.,

1992

Attfield and Hodous*, 1992

LLF.

Lewis,

et al.,

1996

COPD: Chronic obstructive pulmonary disease.

CWP: Simple coal workers' pneumoconiosis.

LLF: Loss of lung function.

PMF: Progressive massive fibrosis.

RS: Respiratory symptoms.

* Studies of U.S. Miners Who Participated in the National Study of Coal Workers' Pneumoconiosis (NSCWP).

a. Simple Coal Workers' Pneumoconiosis (Simple CWP) and Progressive Massive Fibrosis (PMF)

Studies following Cochrane (1962) and McLintock

et al.,

(1971) have confirmed that the risk of PMF increases with increasing category of simple CWP (Hurley and Jacobsen, 1986; Hurley,

et al.,

1987; Hurley and Maclaren, 1988; Hodous and Attfield, 1990). However, the risk of PMF was greater than previously predicted among miners with simple CWP category 1 or without simple CWP (

i.e.,

category 0) (Hurley,

et al.,

1987). The risk of PMF increased with increasing cumulative exposure, regardless of the initial category of simple CWP (Hurley,

et al.,

1987), indicating that reducing dust exposures is a more effective means of reducing the risk of PMF than reliance on detection of simple CWP.

Attfield and Seixas (1995) have demonstrated a relationship between cumulative exposure to respirable coal mine dust and predicted prevalence of pneumoconiosis (

i.e.,

simple CWP, PMF). They studied a group of approximately 3,200 men who worked in underground bituminous coal mines. The U.S. miners and ex-miners had participated in Round 1 (1970-1972) or Round 2 (1972-1975) of the NSCWP and were examined again between 1985 and 1988. Chest x-rays were read to determine the number of cases of simple CWP and PMF. Dust exposure estimates were generated from measurements of dust concentrations as well as from work history. A logistic (or logit) regression model was used to estimate prevalence of simple CWP and PMF. In this statistical analysis, proportions are transformed to natural logarithmic values,

i.e.,

y = 1n [p/(1−p)], before a linear model is fit to the data (Armitage, 1977). The logistic model assumes that the data have a binomial distribution (

e.g.,

presence or absence of PMF) for a given set of covariate values (

e.g.,

age, coal rank, dust exposure, pack-years of smoking). Using logistic modeling, relationships were developed between cumulative dust exposure and prevalence of simple CWP (category 1+, category 2+) and PMF. These relationships were the key strengths of the Attfield and Seixas study and serve as the basis for the Quantitative Risk Assessment of this rule.

The recent paper of Kuempel,

et al.,

(1997) has provided a detailed discussion and quantitative presentation of excess risks associated with respirable coal dust exposures. Their study was based upon results from previous studies of some 9,000 underground coal miners who participated in the NSCWP (Attfield and Morring, 1992b; Attfield and Seixas, 1995). Kuempel,

et al.,

estimated excess (exposure-attributable) prevalence of simple CWP and PMF (

i.e.,

number of cases of disease present in a population at a specified time, divided by the number of persons in the population at that specified time). Point estimates of excess risk of PMF ranged from 1/1000 to 167/1000 among miners exposed at the current MSHA standard for respirable coal mine dust. These estimates were based upon dust exposure that occurred over a miner's working lifetime (

e.g.,

8 hours per day, 5 days a week, 50 weeks per year, over a period of 45 years). Actual occupational lifetime exposure may be more, due to extended work shifts and work weeks. The point estimates of PMF presented by Kuempel,

et al.,

(1997) were related to coal rank, where higher estimates (

e.g.,

167/1000) were obtained for high-rank coal (anthracite coal) and somewhat lower estimates were obtained for medium/low rank bituminous coal (

e.g.,

21/1000). Within each coal rank, the estimates of simple CWP cases were at least twice as high as those for PMF (

e.g.,

167/1000 PMF vs. 380/1000 simple CWP≥1).

The data of Attfield and Seixas (1995) and Kuempel,

et al.,

(1995; 1997) were consistent with previous data of Attfield and Morring (1992b) who reported relationships between estimated dust exposure and predicted prevalence of simple CWP or PMF. They also noted that exposure-response relationships were steeper for higher ranks of coal such as anthracite, and concluded that the risks for anthracite miners appeared to be greater than for miners exposed to lower rank coal dust. Attfield and Morring (1992b) used similar methods as described above (

i.e.,

logistic modeling), but included miners from Round 1 of the NSCWP (1969-1971); thus representing an earlier time point in the NSCWP when the respirable coal mine dust concentrations were much higher than they are today.

Recently, Goodwin and Attfield (1998) reported that there were concerns regarding methodological inconsistencies across surveys given during the four rounds of the NSCWP. In particular, they noted the discordance in classification of simple CWP and PMF among readers of chest films. Despite potential discordance, Goodwin and Attfield (1998) have confirmed previous findings of a decline in simple CWP prevalence from 1969 to 1988. Yet, these analyses also demonstrated that simple CWP has not been eliminated. The Round 4 prevalence rates were 3.9 percent for simple CWP category 1 and higher, and 0.9 percent for category 2 and higher. This illustrates the need for continued efforts to reduce dust exposures.

Given the current system for monitoring exposures and identifying overexposures in the U.S., miners are at increased risk of developing simple CWP and PMF from a working lifetime exposure to respirable coal mine dust (Kuempel,

et al.,

1997, 1995; Attfield and Seixas, 1995; Goodwin and Attfield, 1998; Attfield and Morring, 1992b). Whenever overexposures (

i.e.,

excursions above the applicable

standard) occur, the long-term mean exposure of miners may be increased, thereby causing an upward shift on the exposure-response curve. Such a shift then places these overexposed coal miners at increased risk of developing and dying prematurely from simple CWP and PMF.

The Attfield and Seixas epidemiological study (1995) is the most appropriate to use in estimating the benefit of reduction of overexposures. The authors applied scientific rigor to the collection, categorization, and analyses of the radiographic evidence for the group of 3,194 underground bituminous coal miners who participated in Round 4, 1985-1988, of the National Study of Coal Workers' Pneumoconiosis (NSCWP); this study population excludes 86 miners for whom there was missing exposure data or unreadable x-rays. Radiologic evidence was carefully collected and analyzed by multiple independent, NIOSH certified B readers to identify stages of simple CWP and PMF. In the targeted population of 5,557 miners, the participating miners (3,280) were similar to the non-participants (2,277) with regard to age at the first medical examination and prevalence of simple CWP category 1 or greater. The non-participants had worked slightly longer, yet had lower prevalence of simple CWP category 2 or greater, than the participants. This study describes the differences among current miners and ex-miners (health-related or job-related) in the relationships between the estimated cumulative exposure to respirable coal mine dust and prevalence of simple CWP category 1 or greater. Such data and relationships were not available in other U.S. studies and non-U.S. studies.

A potential limitation in the U.S. studies is the possible bias in the exposure data, which has been the subject of several studies (Boden and Gold, 1984; Seixas

et al.,

1991; Attfield and Hearl, 1996). An advantage of the Attfield and Seixas 1995 study (and the earlier studies based on the same data set) is that the larger mines included in these epidemiological studies were shown to have exposure data with relatively small bias (Attfield and Hearl, 1996). Another limitation in exposure data used in the U.S. studies is that the airborne dust concentrations used to estimate individual miners' cumulative exposures to respirable coal mine dust were based on average concentrations within job category (these average values were combined with data of each individual miner's duration employed in a given job). The earlier U.S. exposure-response studies of miners participating in the first medical survey of the NSCWP (Attfield and Morring, 1992b; Attfield and Hodous, 1992; Kuempel,

et al.,

1995) relied primarily on exposure measurements from a dust sampling survey during 1968-1969 to estimate miners' exposures before 1970 (Attfield and Morring, 1992a). An advantage of the Attfield and Seixas 1995 study is that, in addition to the pre-1970 exposure estimates, more detailed exposure data were available to estimate miners' exposures from 1970 to 1987, during which the mean airborne concentrations were stratified by mine, job, and year (Seixas,

et al.,

1991).

The most complete exposure data available are those for coal miners in the United Kingdom (Hurley,

et al.,

1987; Hurley and Maclaren, 1987; Soutar and Hurley, 1986; Marine,

et al.,

1988; Maclaren,

et al.,

1989). These studies include medical examinations and individual estimates of exposure for more than 50,000 miners for up to 30 years. The U.S. studies are consistent with these U.K. studies in demonstrating the risks of developing occupational respiratory diseases from exposure to respirable coal mine dust. These risks increase with increasing exposure concentration and duration, and with exposure to dust of higher ranked coal. The quantitative assessment of risk and associated benefits were based on the Attfield and Seixas (1995) study because, in addition to the advantages described above, it best represents the recent conditions experienced by miners in the U.S. This quantitative assessment follows in Section VIII. The international studies provide an important basis for comparison with the U.S. findings, and several of the recent international studies are described in detail here.

Bourgkard,

et al.,

(1998) conducted a 4-year study of a group of French coal miners who were employed in underground and surface mines. The investigators examined the prognostic role of cumulative dust exposure, smoking patterns, respiratory symptoms, lung CT scans, and lung function indices for chest x-ray worsening and evolution to simple CWP and PMF. Bourgkard,

et al.,

(1998), through selection of a younger worker population (

i.e.,

35-48 years old at start of study), attempted to focus on the early stages of simple CWP. In essence, they hoped to identify those miners who needed to be relocated to less dusty workplaces or who needed to be clinically monitored. Bourgkard,

et al.,

(1998) concluded that there was an association between cumulative dust exposure and what was termed chest x-ray “worsening” (

i.e.,

increase in reader-designated category signifying progression of simple CWP). Their conclusion, however, was based on pooling of the data (

i.e.,

three combined groups of miners) who had different cumulative exposures (

i.e.,

20, 66 and 85 mg-yr/m

Love,

et al.,

(1997, 1992) reported on occupational exposures and the health of British opencast (

i.e.,

surface or strip) coal miners. They studied a group of approximately 1,200 miners who were employed at sites in England, Scotland, and Wales. The mean age of the men was 41; many had worked in the mining industry since the 1970s. To determine dust exposure levels, full-shift personal samples were collected. Most were respirable dust samples which were collected using Casella cyclones according to the procedures described by the British Health and Safety Executive (HSE). Thus exposure determinations would be comparable to exposure determinations obtained in U.S. surface coal mines since both measure respirable dust according to the BMRC criteria.

These investigators found a doubling in the relative risk of developing profusion of simple CWP category 0/1 for every 10 years of work in the dustiest jobs in surface mines. These respirable coal dust exposures were under 1 mg/m

. Love,

et al.,

(1992, 1997), like other investigators, emphasized the need for monitoring and controlling exposures to respirable coal mine dust, particularly in high risk operations (

e.g.,

drillers, drivers of bulldozers).

Meijers,

et al.,

(1997) studied Dutch coal miners who were examined between 1952 and 1963, and who were followed until the end of 1991. They reported an increased risk of mortality from simple CWP and PMF among miners who had generally worked underground for 20 or more years. Their conclusions were based upon dramatic increases in standardized mortality ratios (SMRs). There were several limitations in this study, however.

Morfeld,

et al.,

(1997) published a recent paper that investigated the risk of developing simple CWP in German miners and addressed the occupational exposure limit for respirable coal dust in Germany. Their study included approximately 5,800 miners who worked underground from the late 1970s to mid-1980s. Morfeld,

et al.,

observed increases in relative risks (RRs) of developing early x-ray changes, category 0/1, that were exposure-dependent. Relative risks (RRs) increased with higher dust concentrations.

Starzynski,

et al.,

(1996) conducted a mortality study on a group of 11,224 Polish males diagnosed with silicosis, simple CWP, or PMF between 1970 and 1985. This cohort was subdivided by occupation into four subcohorts: Coal miners (63%); employees of underground work enterprises (8%) (

i.e.,

drift cutting and shaft construction jobs); metallurgical industry and iron, and nonferrous foundry workers (16%); and refractory materials, china, ceramics and quarry workers. The investigators found that coal miners had a slight, statistically significant excess overall mortality (

i.e.,

all causes) as indicated by a Standardized Mortality Ratio (SMR) of 105 (with a 95% Confidence Interval (C.I.) of 100-110). Also, excess of deaths from diseases of the respiratory system among coal miners was nearly four times that of the referent population (SMR of 383 with a 95% C.I. of 345-424). The study of Starzynski,

et al.,

(1996) agrees with others that there is premature mortality among coal miners from simple CWP and PMF. Unfortunately, there is little or no information presented on miner work history, exposure assessment (

e.g.,

respirable coal mine dust, silica), and mine environment (

e.g.,

coal rank(s), underground vs. surface mining).

Yi and Zhang (1996) conducted a study to measure the progression from simple CWP to PMF or death among a cohort of 2,738 miners with simple CWP who were employed at the Huai-Bei coal mine in China. Relative risks (

i.e.,

RRs) were calculated for progression from simple CWP category 1 to simple CWP category 3 and for progression from simple CWP category 3 to death. Their results demonstrated that miners with simple CWP category 1 are at risk of developing simple CWP category 2 and simple CWP category 3 (

e.g.,

RRs of 1.101 and 2.360, respectively). They also found that miners with PMF had a decreased life expectancy. Other risk factors for development of PMF included long-term work underground, and drilling. This study was limited by a lack of exposure assessment, estimation of miner smoking histories, and use of a radiological classification system that differs from that of the ILO.

Hurley and Maclaren (1987) studied British coal miners who were examined between 1953 and 1978, over 5-year intervals. They have shown that exposure to respirable coal dust increases the risks of developing simple CWP and of progressing to PMF. As seen in their data analysis, these responses were dependent upon dust concentration and coal rank. That is, greater responses were seen at higher dust concentrations and with higher rank coal (

i.e.,

increasing per cent carbon). The investigators also noted that estimated risks were unaffected by changes in the proportion of miners with simple CWP who transferred jobs. The authors concluded that “limiting exposure to respirable coal dust is the only reliable way of limiting the risks of radiological changes to miners.”

b. Other Health Effects

As noted in Table VII-1, there were 16 studies in which the loss of lung function (LLF) was examined in coal miners. Six of these studies also included an evaluation of respiratory symptoms (RS) in the miners. There were five studies describing chronic obstructive pulmonary disease (COPD) in miners.

Henneberger and Attfield (1997; 1996), Kuempel,

et al.

(1997), Seixas,

et al.,

(1993), Attfield and Hodous (1992), and Seixas,

et al.,

(1992) evaluated data from pulmonary function tests and standardized questionnaires to miners in the NSCWP. A common finding in their studies was an increase in respiratory symptoms such as cough, shortness of breath, and wheezing. The symptoms were dependent upon the dust concentration to which the miners had been exposed, with more pronounced symptoms occurring after long-term exposures to higher exposure levels. These studies also demonstrated that a loss of lung function occurred among miners.

Attfield and Hodous (1992) studied U.S. miners who had spent 18 years underground (on average) and who participated in Round 1 (1969-1971) of the NSCWP. They observed that greater reductions in pulmonary function were associated with exposure to higher ranks of coal (

i.e.,

anthracite vs. bituminous vs. lignite). Using linear regression models, Kuempel

et al.,

(1997) predicted the excess (exposure attributable) prevalence of lung function decrements among miners with cumulative exposures to respirable coal mine dust of 2 mg/m

for 45 years (

i.e.,

90 mg-yr/m

). The excess prevalence estimates were 315 and 139 cases per thousand for forced expiratory volume in one second (FEV

) of <80% and <65% of predicted normal values, respectively, among never-smoking miners (a sub-group of 977 NSCWP participants studied in Seixas

et al.,

1993). Such reductions in FEV

are clinically significant; FEV

<80% (of predicted normal values) is a measure that is used to determine ventilatory defects (American Thoracic Society, 1991). Three recent studies found impaired FEV

to be a predictor of increased pre-mature mortality (Weiss,

et al.,

1995; Meijers,

et al.,

1997; Hansen

et al.,

1999).

Seixas,

et al.

(1993) conducted an analyses of 977 underground coal miners who began working in or after 1970 and were participants of both NSCWP Round 2 (1972-1975) and Round 4 (1985-1988). They found a rapid loss of lung function in miners and further declines in lung function with continuing exposure to coal mine dust. Collectively these studies have shown that the prevalence of decreased lung function was proportional to cumulative exposure. That is, with exposure to higher coal dust levels over a working lifetime, there were more miners who experienced a loss of lung function. Also, the types of respiratory symptoms and patterns of pulmonary function decrements observed by both Attfield and Hodous (1992) Seixas,

et al.

(1992;1993) are characteristic of COPD.

The U.S. findings on respiratory symptoms and loss of lung function in miners have agreed with those of previous British studies by Marine,

et al.,

(1988) and Soutar and Hurley (1986). Marine,

et al.

, (1988) analyzed data from British coal miners and focused their attention on respiratory conditions other than simple CWP and PMF. In particular, they examined the Forced Expiratory Volume in one second (FEV

) among smoking and nonsmoking miners and, on the basis of reported respiratory symptoms, identified those miners with bronchitis. Using these data, logistic regression models were used to estimate the prevalence of chronic bronchitis and loss of lung function. Marine,

et al.,

concluded that both exposure to respirable coal mine dust and smoking independently cause decrements in lung function; their contributions to COPD appeared to be additive in coal miners.

Soutar and Hurley (1986) examined the relationship between dust exposure and lung function in British coal miners and ex-miners. The men who were studied were employed in coal mines in the 1950s and were followed up and examined 22 years later. These miners and ex-miners were categorized as smokers, ex-smokers, or nonsmokers. The Forced Expiratory Volume in one second (FEV

), the Forced Vital Capacity (FVC), and the FEV

/FVC ratios decreased in all study groups and these reductions in lung function were inversely proportional to dust exposure. Thus, Soutar and Hurley concluded that exposure to respirable coal mine dust can cause severe respiratory impairment, even without the presence of simple CWP or PMF. They speculated that the pathology of coal dust-induced

lung disease differs from that induced by smoking.

Recent studies from China (Wang,

et al.,

1997) and the European community (Bourgkard,

et al.,

1998; Carta,

et al.,

1996; Lewis, S.,

et al.,

1996) have also supported the British and U.S. findings which demonstrated the correlation between occupational exposure to coal dust and respiratory symptoms and loss of lung function in miners.

Wang,

et al.,

(1997) examined lung function in underground coal miners and other workers from several other factories in Chongqing, China. For their study, information was obtained on exposure duration, results of radiographic tests, and smoking history. Pulmonary function tests were performed, providing the Forced Expiratory Volume in one second (FEV

), the Forced Vital Capacity (FVC), and FEV

/FVC data. Additionally, the diffusing capacity for carbon monoxide (DL

) was measured. This is an indicator of diffusion impairment at the “blood-gas barrier” which may occur, for example, when this barrier becomes thickened (West, 1990; 1992). Wang,

et al.,

(1997) found that there was impairment of pulmonary function among the coal miners and they had evidence of obstructive disease. Like other studies, such effects were observed among coal miners even in the absence of simple CWP. Pulmonary function was further decreased when simple CWP was present. This study did not provide exposure measurements and there was no consideration of exposure-response relationships. Also, silica exposures and their potential effects were not examined in the underground coal miners.

As noted above, Bourgkard,

et al.,

(1998) was interested in the earlier stages of simple CWP (

i.e.,

Categories 0/1 and 1/0) and the prognostic role of cumulative dust exposure, smoking patterns, respiratory symptoms, lung CT scans, and lung function indices for chest x-ray worsening and evolution to simple CWP category 1/1 or higher. Over a 4-year period, they studied French coal miners who were employed in underground and surface mines. Bourgkard,

et al.,

(1998) found that, at the first medical examination, the ratio of the Forced Expiratory Volume in one second (FEV

) to the Forced Vital Capacity (FVC) (

i.e.,

FEV

/FVC) and other airflows determined from a forced expiration (West, 1990; 1992) were lower among miners who later developed simple CWP category 1/1 or higher. These miners also experienced more wheezing at the first medical examination. Thus, the results of their study suggested that lung function changes may serve as an early indicator of miners who are at increased risk of developing simple CWP and PMF and who should be monitored more closely.

Carta,

et al.,

(1996) have examined the role of dust exposure on the prevalence of respiratory symptoms and loss of lung function in a group of young Italian coal miners (

i.e.,

mean age at hire 28.9 years, mean age at first survey 31.2 years). These miners worked underground and were exposed to lignite (

i.e.,

low rank coal) which had a 5-7% sulfur content. They were followed for a period of 11 years, from 1983 and 1993. Carta,

et al.,

(1996) found few abnormalities on miner chest x-rays taken throughout the 11-year study. However, there was an increased prevalence of respiratory symptoms and loss of lung function. This was particularly noteworthy since dust exposures were often below 1.0 mg/m

; the cumulative dust exposure for the whole cohort was 6.7 mg-yr/m

after the first survey. Thus, Carta,

et al.,

(1996) demonstrated that miners experience respiratory effects of exposure to dust generated from a lower rank coal and at lower concentrations. They have recommended yearly measurements of lung function for miners.

Lewis,

et al.,

(1996) studied a group of British miners, many of whom entered the coal industry in the 1970s. Based upon chest x-rays, the miners had no evidence of simple CWP or PMF. The objective of this study was to determine whether coal mining (

i.e.,

exposure to respirable coal mine dust) is an independent risk factor for impairment of lung function. Lewis,

et al.

(1996) found that there was a loss of lung function in miners (smokers and nonsmokers), particularly among miners who were under approximately 55 years of age. For miners who smoked, there was a greater loss of lung function than in nonsmoking miners with the same level of exposure to respirable coal mine dust. Above age 55, the loss of lung function was similar for miners and their controls, although all smokers continued to exhibit a greater loss of lung function than nonsmokers. Lewis,

et al.,

(1996) concluded that the deficits in lung function may occur in the absence of simple CWP and PMF, and independent from the effects of smoking.

There have been two recent mortality studies that have demonstrated a relationship between exposure to respirable coal mine dust and development of COPD. This association was reported by Kuempel,

et al.,

(1995) in the U.S., and by Meijers,

et al.

(1997) in the Netherlands. These two groups of investigators have reported that occupationally-induced COPD (

e.g.,

chronic bronchitis, emphysema) can occur in miners, with or without the presence of simple CWP or PMF. They also found that the risk of premature mortality from COPD was elevated among miners and could be separated from the effects of smoking and age.

Kuempel,

et al.

(1995) found an increase in relative risk (RR) of premature mortality from COPD among U.S. coal miners who participated in the NSCWP from 1969 through 1971. In their data analysis, the exposure-response relationship was evaluated using the Cox proportional hazards model. This model assumes that the hazard ratio between nonexposed and exposed groups does not significantly change with time. When fitting a curve to the data (

e.g.,

log-linear), cumulative exposure was expressed as a categorical or continuous variable. Due to model limitations (

e.g.,

less statistical power, influence of category scheme, use of lowest exposure group for comparisons vs. use of non-exposed group), Kuempel,

et al.

(1995) believed that the exposure data should be expressed as a continuous variable. If, for example, the cumulative exposure was 90 mg-yr/m

(

i.e.,

2 mg/m

for 45 years), then the relative risk of mortality from chronic bronchitis or emphysema was 7.67. Kuempel,

et al.

(1995) also showed that relative risk decreased with lower cumulative exposures (

i.e.,

below 90 mg-yr/m

) and increased with higher cumulative exposures (

i.e.,

above 90 mg-yr/m

. Thus, these investigators demonstrated a statistically significant exposure-response relationship for COPD.

Meijers,

et al.

(1997) have shown, among Dutch miners, reductions in lung volumes and capacities are good predictors of the increased risk of premature mortality from COPD. For example, a diminished forced expiratory volume in one second (FEV

) or a diminished ratio of the FEV

to the forced vital capacity

(FVC) (

i.e.,

FEV

/FVC) upon medical examination was associated with a significantly increased standardized mortality ratio (SMR) for COPD (322 and 212, respectively). In other words, miners with diminished lung capacity based on FEV

were two to three times more likely to die prematurely due to COPD than miners who had normal lung function. In contrast, SMRs for COPD were not significantly increased in miners with normal lung volumes and capacities.

These data support prior conclusions of Seixas,

et al.

(1992, 1993) and Attfield and Hodous (1992) based on morbidity studies.

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

VIII. Quantitative Risk Assessment

As mentioned previously, in addition to this proposed notice of rulemaking, today's

Federal Register

contains another NPRM, Verification of Dust Control Plan (RIN 1219-AB18), “plan verification.” In combination, these rules present MSHA's strengthened plan to meet the Mine Act's requirement that a miner's exposure to respirable coal mine dust be at or below the applicable standard on each and every shift. MSHA's improved program to eliminate overexposures on each and every shift includes the simultaneous implementation of an improved tool to identify overexposures (

i.e.,

inspectors use of single, full-shift samples for noncompliance determinations) and a new regulation requiring operators implement verified ventilation plans in underground coal mines.

Having reviewed the reported health effects associated with exposure to coal mine dust, MSHA and NIOSH have evaluated the evidence to determine whether the current regulatory strategy can be improved. The criteria for this evaluation is established by the Mine Act under section 101(a)(6)(A) [30 U.S.C. 811(a)(6)(A)] which provides that:

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

Based on Court interpretations of similar language under the Occupational Safety and Health Act, there are three questions that must be addressed: (1) Whether health effects associated with the current pattern of overexposures on individual shifts constitute a material impairment to miner health or functional capacity; (2) whether the current pattern of overexposures on individual shifts places miners at a significant risk of incurring any of these material impairments; and (3) whether the proposed rules would substantially reduce those risks.

The criteria for evaluating the health effects evidence do not require scientific certainty. The need to evaluate risk does not mean that an agency is placed into a “mathematical straightjacket.”

See Industrial Union Department, AFL-CIO

American Petroleum Institute,

448 U.S. 607, 100 S.Ct 2844 (1980), otherwise known as the “Benzene” decision. When regulating on the edge of scientific knowledge, certainty may not be possible and,

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

The statutory criteria for evaluating the health evidence do not require MSHA and NIOSH to wait for absolute certainty and precision. MSHA and NIOSH are required to use the “best available evidence” (section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)).

As explained earlier, MSHA's objective in strengthening the requirements for verifying the effectiveness of dust control plans, and in enforcing effective plans through the new enforcement policy proposed in this notice, is to ensure that no miner is exposed to an excessive concentration (

i.e.

, a concentration in excess of the applicable standard) of respirable dust on any individual shift. Annual inspector samples have demonstrated overexposures on individual shifts in many mines. Data compiled from the far more frequent, bimonthly, operator sampling program show that in many mines, the applicable dust standard is exceeded on a substantial percentage of the production shifts. This pattern has persisted for many years, and, since individual shift excursions above the applicable standard are permitted under the existing program, the same pattern can be expected to continue over the working lifetime of affected miners—unless an effort is made to eliminate excess exposures on individual shifts. In this quantitative risk assessment (QRA), MSHA will demonstrate that reducing coal mine dust concentrations, over a 45-year occupational lifetime, to no more than the applicable standard on just that percentage of shifts currently showing an excess, thereby lowering the cumulative exposure to respirable coal mine dust than would otherwise occur, would significantly reduce the risk of both simple CWP and PMF among miners. We have estimated the health benefits of the two rules arising from the elimination of overexposures on all shifts at only those MMUs exhibiting a pattern of recurrent overexposures on individual shifts.

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

Based on 1999 operator data, there were 704 MMUs (out of 1,251 total) at which dust concentrations for the designated occupation (D.O.) samples exceeded the applicable standard on at least two of the sampling shifts (MSHA, Data file:Operator.ZIP).

MSHA considers these 704 MMUs, representing more than half of all underground coal miners working in production areas, to have exhibited a pattern of recurrent overexposures.

Valid operator D.O. samples were collected on a total of 18,569 shifts at these 704 MMUs, and the applicable standard was exceeded on 3,977 of these shifts, or about 21.4 percent. For this 21.4 percent, the mean excess above the standard, as measured for the D.O. only, was 1.04 mg/m\3\.

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

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

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

In 1998, MSHA attempted to enforce compliance on individual shifts. Therefore, to compare the 1999 pattern

of excess exposures on individual shifts to that of previous years under the current enforcement policy, MSHA examined the regular bimonthly D.O. sample data submitted to MSHA by mine operators in the eight years from 1990 through 1997. The same three parameters were considered as discussed above for 1999: (1) The percentage of MMUs exhibiting a pattern of recurrent overexposures, as indicated by at least two of the valid measurements above the applicable standard in a given year; (2) for those and only those MMUs exhibiting recurrent overexposures, the overall percentage of production shifts on which the D.O. was overexposed, as estimated by the percentage of valid measurements above the applicable standard; and (3) for the MMUs identified as exhibiting recurrent overexposures, the mean excess above the applicable standard, as calculated for just those valid measurements that exceeded the applicable standard in a given year.

Although MSHA found minor differences between individual years, there was no statistically significant upward or downward trend in any of these three parameters over the 1990-1997 time period (see Table VIII-1). In 1999, the percentage of MMUs exhibiting a pattern of recurrent overexposures (Parameter #1) was approximately 56 percent. Also in 1999, for those MMUs exhibiting a pattern of recurrent overexposures, the overall percentage of production shifts on which the D.O. was overexposed (Parameter #2) was approximately 21 percent. In 1999, the average excess above the applicable standard (Parameter #3) for MMUs exhibiting recurrent overexposures was 1.0 mg/m\3\, a significant decrease from prior years. MSHA attributes this decrease to two important changes in the Agency's inspection program, beginning near the end of 1998. These changes, which both resulted in increased inspector presence, were: (1) An increase in the frequency of MSHA dust sampling at underground coal mines; and (2) initiation of monthly spot inspections at mines experiencing difficulty in maintaining consistent compliance with the applicable dust standard.

Table VIII-1.—1990-1997, Distribution of Parameters of Annual Overexposure to Respirable Coal Mine Dust

1990-1997

Parameter #1

(Percent)

Parameter #2

(Percent)

Parameter #3

(mg/m

)

Number of Years

Median

52.6

20.5

1.23

Mean (Standard Error)

50.9 (1.62)

20.6 (0.32)

1.25 (0.020)

Parameter #1: percentage of MMUs exhibiting a pattern of recurrent overexposures.

Parameter #2: for those MMUs exhibiting a pattern of recurrent overexposures, the percentage of production shifts on which the D.O. was overexposed.

Parameter #3: for those MMUs exhibiting a pattern of recurrent overexposures, the mean excess above the applicable standard among valid D.O. measurements that exceeded the applicable standard.

The available data suggest that unless changes are made to enforce the dust standard on every shift, the same average pattern of overexposures observed in 1999 will persist into the future. Therefore, we conclude that without the proposed changes:

• More than one-half of all MMUs would continue to have a pattern of recurrent overexposures on individual shifts;

• At those MMUs with recurrent overexposures, full-shift average respirable dust concentrations for the D.O. would continue to exceed the applicable standards on about 21 percent of all production shifts;

• Among those shifts on which D.O. exposure exceeds the applicable standards, the mean excess for the D.O. would continue to be approximately 1.0 mg/m

We invite public comment on whether these three parameters, based on operators' regular 1999 bimonthly samples, under-represent or over-represent the frequency and/or magnitude of excessive dust concentrations on all individual shifts—including those that are not sampled.

If all overexposures on individual shifts are eliminated, the reduction in total respirable coal mine dust inhaled by a miner over a working lifetime will depend on the following factors: The average volume of air inhaled on each shift that would otherwise have exceeded the applicable standard, the degree of reduction in respirable dust concentration in the air inhaled on such shifts, and the number of such shifts per working lifetime. If a miner inhales ten cubic meters of air on a shift (U.S. EPA, 1980), reducing the respirable dust concentration in that air by 1.0 mg/m

would result in 10 mg less dust inhaled on that shift alone. Assuming the miner works 240 shifts per year, then reducing inhaled respirable dust by an average of 10 mg on 21 percent of the shifts would reduce the total dust inhaled by 504 mg per year, or nearly 22,700 mg over a 45-year working lifetime:

1.0 mg per m

of inhaled air

× 10 m

inhaled air per shift

× 50.4 affected shifts (

i.e.,

21% of 240) per work year

× 45 work years per working lifetime

= 22,680 mg less dust inhaled per working lifetime.

The Secretaries invite comments on the health benefits expected from reducing the total coal mine dust inhaled over a working lifetime by this amount.

In Section VII, the strengths and weaknesses of various epidemiological studies were presented, supporting the selection of Attfield and Seixas (1995) as the study that provides the best available estimate of material health impairment with respect to CWP and PMF. Two of the distinguishing qualities of this study are the dose-response relationship over a miners' lifetime and the fact that these data best represent the recent conditions experienced by miners in the U.S. Using this relationship, it is possible to evaluate the impact on risk of both simple CWP and PMF expected from bringing dust concentrations down to or below the applicable standard on every shift. This is the only contemporary epidemiological study of simple CWP and PMF providing such a relationship.

Attfield and Seixas used two or three B readers to identify the profusion of opacities using the ILO classification scheme. If three readings were available, the median value was used. If two readings were available, the higher of the two ILO categories was recorded. Eighty radiographs were eliminated because only one reading was available. The most inclusive category of CWP 1+ includes simple CWP, categories 1, 2, 3, as well as PMF. Category CWP 2+ does

not include simple CWP, category 1, but does include the more severe simple CWP categories, 2 and 3, as well as PMF. The third category used in their report was PMF, denoting any category of large opacities.

Attfield and Seixas (1995) provided logistic regression models for the prevalence for CWP 1+, CWP 2+ and PMF as a function of cumulative dust exposure, expressed as the product of dust concentration measured in the mine atmosphere and duration of exposure at that concentration. These models can be used to estimate the impact on miners' risk of both simple CWP and PMF of reducing lifetime accumulated exposure by eliminating excessive exposures on a given percentage of individual shifts.

At the MMUs being considered (those exhibiting a pattern of recurrent overexposures), bringing dust concentrations down to no more than the applicable standard on each and every production shift would reduce D.O. exposures on the affected shifts by an average of 1.04 mg/m

. Assuming this average reduction applies to only 21 percent of the shifts, the effect would be to reduce cumulative exposure, for each miner exposed at or above the D.O. level, by 0.22 mg-yr/m

over the course of a working year (

i.e.,

21 percent of shifts in one year, times 1.04 mg/m

per shift). Therefore, over a 45-year working lifetime, the benefit to each affected miner would, on average, amount to a reduction in accumulated exposure of approximately 10 mg-yr/m

(

i.e.,

45 years times 0.22 mg-yr/m

per year). If, as some miners have testified, operator dust samples currently submitted to MSHA tend to under-represent either the frequency or magnitude (or both) of individual full-shift excursions above the applicable standard, then eliminating such excursions would provide a lifetime reduction of even more than 10 mg-yr/m

for each exposed miner.

The Attfield and Seixas models predict the prevalence of CWP 1+, CWP 2+, and PMF for miners who have accumulated a given amount of exposure, expressed in units of mg-yr/m

, by the time they attain a specified age. Benefits of reducing cumulative exposure can be estimated by calculating the difference between predictions with and without the reduction. For example, suppose a miner begins work at age 20 and retires at age 65. By the year of retirement, that miner is expected to accumulate nearly 10 mg-yr/m

less exposure if individual shift excursions are eliminated. For 65-year-old miners, reducing accumulated dust exposure by a total of 10 mg-yr/m

reduces the predicted prevalence of CWP 1+ by at least 11 per thousand (See Table VIII-2).

This 11 per thousand, however, applies only to miners of age 65. The Attfield and Seixas models provide different predictions for each year of age that a miner attains. The predicted benefit turns out to be smaller for younger miners and larger for older miners. This is partly because younger miners will have accumulated less exposure reduction from the proposed changes, and partly because the Attfield and Seixas models depend directly on age as well as on cumulative exposure. The health effects of recurrent overexposures can occur long after the overexposures occurred. Even after a miner retires and is no longer exposed to respirable coal mine dust, the extra risk attributable to an extra 10 mg-year/m

, accumulated earlier, continues to increase with age. Consequently, the benefit to be gained from eliminating individual shift excursions also continues to increase after a miner is no longer exposed. For example, assuming no additional exposure after age 65, the predicted reduction in average prevalence of CWP1+ increases from 12 per thousand at age 65 to 17 per thousand at age 70. Presumably, the increasingly greater predicted reduction in risk of disease after age 65 is due to the latent effects of the reduction in earlier exposure.

To project the benefits of the two rules expected from eliminating overexposures on individual shifts, MSHA applied the Attfield and Seixas models to a hypothetical population of miners who, on average, begin working at age 20 and retire at age 65, assuming different lifetimes. The risks for three different ages have been presented to show a range of risk depending on the lifetime: 65, 73, and 80 years. During the 45 “working years” between 20 and 65, the lifetime benefit accumulates at a rate of 0.22 mg-yr/m

of reduced exposure per year, reaching a maximum of about 10 mg-yr/m

at age 65. Between ages 65 and 80, the accumulated reduction in dust exposure remains at an estimated average of 10 mg-yr/m

, but the benefit in terms of both simple CWP and PMF risk continues to increase, as explained previously.

The expected lifetime for all American males conditional on their having reached 20 years of age, is 73 years (calculated from: U.S. Census March 1997, Table 18; U.S. Census March 1997, Table 119).

On average, the best estimate of the lifetime benefit to exposed miners is expressed by the reduction in prevalence of disease at age 73. Carrying out the calculation at a 73-year average lifetime, MSHA expects that, at the MMUs under consideration, bringing dust concentrations down to no more than the applicable standard on each shift will:

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

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

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

• Reduce the combined risk of simple CWP (category 2 and 3) and PMF by at least 9.8 cases per 1000 affected D.O. miners;

• Reduce the risk of PMF by at least 5.1 cases per 1000 affected D.O. miners.

Presented in the first row of Table VIII-2 are the average reductions in risk for simple CWP and PMF combined, and PMF alone, over an occupational lifetime, among affected D.O. miners who live to ages 65, 73, and 80, who have worked at an MMU exhibiting a pattern of recurrent overexposures. Across health outcomes, the benefit due to the predicted reduction in cumulative exposure to respirable coal mine dust, through limiting miners' exposure to no more than the applicable standard on each and every shift, increases with age.

When the dust concentration measured for the D.O. exceeds the applicable standard, measurements for at least some of the other miners may also exceed the standard on the same shift, though usually by a lesser amount. Furthermore, although the D.O. represents the occupation most likely to receive the highest exposure, other miners working in the same MMU may be exposed to even higher concentrations than the D.O. on some shifts. Therefore, in addition to the affected D.O. miners, there is a population of other affected miners who are also expected to experience a significant reduction in risk as a result of eliminating overexposures on their individual shifts.

To estimate how many miners other than the D.O. would be substantially affected, MSHA examined the results from all valid dust samples collected by MSHA inspectors in underground MMUs during 1999 (MSHA, Data file:Inspctor.zip). Within each MMU, the inspector typically takes one full-shift sample on the D.O. and, on the same shift, four or more additional samples representing other occupations.

On 896 shifts, at a total of 450 distinct MMUs, the D.O. measurement exceeded the applicable standard and there were at least three valid measurements for other occupations available for comparison. There was an average of 1.2 non-D.O. measurements in excess of the standard on shifts for which the D.O. measurement exceeded the standard.

For non-D.O. measurements that exceeded the standard on the same shift as a D.O. measurement, the mean excess above the standard was approximately (0.8 mg/m

With 95-percent confidence, on shifts for which the D.O. measurement exceeds the standard, the mean number of other occupational measurements also exceeding the standard is at least 1.11.

With 95-percent confidence, the mean excess is at least 0.72 mg/m

Combining these results with the 21-percent rate of excessive exposures observed for the D.O. on individual shifts, it is reasonable to infer that, at the MMUs under consideration, an average of 1.2 other miners, in addition to the one classified as D.O., is currently overexposed on at least 21 percent of all production shifts. Over the course of a working year, the reduction in exposure expected for these other miners is 0.17 mg-yr/m

(

i.e.,

21 percent of one year, times 0.8 mg/m

To assess the reduction in risk expected from eliminating all single-shift exposures for faceworkers experiencing lower exposures than the D.O., MSHA again applied the Attfield and Seixas models to miners who begin working at age 20, retire at age 65, assuming various lifetimes: 65, 73, and 80 years. This time, however, the resulting decrease in predicted prevalence was multiplied by 1.2/7 = 0.171, to reflect the fact that the assumed rate of overexposure applies, on average, to about 17 percent of the faceworkers not classified as the D.O.

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

In the second row of Table VIII-2, we see that over an occupational lifetime, the beneficial average reduction in risk for simple CWP and PMF combined, and for PMF alone, increases with age. However, the magnitude of the risk reduction is smaller for the affected non-D.O.s than the affected D.O.s. This is expected because the estimated probability that a non-D.O. will be overexposed on a given shift is only 17 percent of the corresponding probability for the D.O. Based on this calculation for the MMUs under consideration, the predicted reduction in risk for faceworkers other than the D.O. who live an expected lifetime of 73 years is at least: 2.3 fewer cases of PMF or simple CWP, per thousand affected miners; 1.3 fewer cases of PMF or simple CWP, categories 2 or 3, per thousand affected miners; and 0.7 fewer cases of PMF per thousand affected miners.

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

Table VIII-2.—By Age, Average Reduction in Risk for Occupational Respiratory Disease per 1,000 Affected Underground Coal Miners Expected to Result From Implementation of Single, Full-Shift Sampling and Plan Verification Rules

Type of miner

Reduction in risk for occupational respiratory disease per 1,000 affected miners

Simple CWP

(categories 1, 2 or 3) or PMF

Age

Simple CWP

(categories 2 or 3) or PMF

Age

PMF

Age

Affected Designated Occupation Miners

11.0

18.0

25.0

3.7

9.8

21.0

1.8

5.1

12.0

Affected Non-Designated Occupation Miners

1.4

2.3

3.3

0.5

1.3

2.7

0.2

0.7

1.5

Simple CWP: simple coal workers' pneumoconiosis.

PMF: progressive massive fibrosis.

Affected Designated Occupation (D.O.) Miners: includes all miners who work at the 56-percent of the Mechanized Mining Units under consideration and who are exposed to dust concentrations similar to the D.O., over a 45-year occupational lifetime.

Affected Non-Designated Occupation (Non-D.O.) Miners: includes all underground faceworkers under consideration who are not classified as the D.O.

IX. Significance of Risk

The criteria for evaluating the evidence to determine whether these proposed standards improve the regulatory strategy for controlling exposures to respirable coal mine dust are established by the Mine Act pursuant to section 101(a)(6)(A) (30 U.S.C. 811(a)(6)(A))which provides that:

into a “mathematical straightjacket.”

See Industrial Union Department, AFL-CIO

American Petroleum Institute,

448 U.S. 607, 100 S.Ct 2844 (1980), otherwise known as the “Benzene” decision. When regulating on the edge of scientific knowledge, certainty may not be possible and,

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

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

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

In identifying the number and percentage of MMUs exhibiting a pattern of recurrent overexposures on individual shifts we choose to include only those MMUs with two or more 1999-operator bimonthly samples in excess of the applicable standard, rather than the population of MMUs with any overexposures.

Also, the quantitative risk assessment estimates of reduction in risk are averages across MMUs exhibiting a pattern of recurrent overexposures. For those miners who work at mines exhibiting a pattern of recurrent overexposures which differs from the one applied in the Quantitative Risk Assessment, their reduction in risk would be more than or less than the expected average, depending on whether or not their overexposures are at a higher or lower than average rate and intensity.

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

Another important decision impacting choice in this risk assessment involves the use of the traditional coal miner work schedule of 8-hours per day, 5-days per week, 48-weeks per year. Many of today's miners work longer hours per day, month, and year than the traditional work schedule. These longer work hours increase miners' cumulative exposure to respirable coal mine dust beyond the parameters of exposure used in our estimates of risk. Even so, to the extent that a proportion of miners may have a more limited work schedule (and occupational exposure), either in number of years, weeks per year, or hours per week, their expected health benefit would have to be adjusted downward, all other variables being constant.

Also, because of heavy, physical work, some miners may work at ventilatory rates in excess of the above-cited 10 cubic meters per 8-hour shift; an estimate of this ventilatory rate is 13.5 cubic meters per 8-hour shift (ICRP, 1994). The sub-population of miners with higher breathing rates would inhale more respirable coal mine dust than would otherwise occur given the same environmental exposures, thereby increasing their risks for the development of simple CWP and PMF.

In the Quantitative Risk Assessment, to estimate average reduction in exposure, we chose the best available data sets: 1999 operator bimonthly samples for D.O.s and N.D.O.s., respectively. Currently, both operator bimonthly and inspector samples

may be taken on production shifts that may not reflect typical production levels.

Although other factors may mediate the amount of airborne respirable dust such as, ventilation and water sprays, on average, higher production is correlated with increased quantities of airborne respirable coal mine dust (Webster,

et al.,

1990; Haney,

et al.,

1993; Green,

et al.,

1994). Some previous commenters and the Dust Advisory Committee have alleged that operators tend to reduce production and/or increase dust controls on sampled shifts. Based on MSHA's and NIOSH's experience and expertise, and previous comments, we believe the production levels observed on sampling shifts are indeed lower than typical (See discussion in Benefits section). We also believe at some MMUs, more engineering controls at higher levels of efficacy are used during sampling shifts than on the majority of shifts (See discussion in Benefits section). Thus, it is reasonable to conclude that the number of MMUs exhibiting a pattern of recurrent overexposures is greater than the 704 captured in this Quantitative Risk Assessment. Furthermore, the severity and rate of overexposures to respirable coal mine dust among the 704 MMUs exhibiting a pattern of recurrent overexposures are probably also greater than we have estimated. We have derived our best estimate of the risk reduction using the best available data. Yet due to limitations in these data, we believe that we have underestimated the magnitude and frequency of typical respirable coal mine exposures. To the extent that our values underestimate the true reduction in respirable coal mine dust exposures, we have underestimated the benefits of these rules.

Valid MSHA inspector samples require production to be at least 60-percent of the average production for the last 30-days. Valid operator bimonthly samples must be taken on a normal production shift (

i.e.,

a production shift during which the amount of material produced in a MMU is at least 50 percent of the average production reported for the last set of five valid samples) (30 CFR 70.101).

Therefore assuming representative operating conditions on these shifts, in our QRA the results were extrapolated to all production shifts, including those that were not sampled, at those same 704 MMUs.

Other aspects of our risk assessment methodology reflect more conservative choices including the selection of an occupational lifetime of 45-years. Various factors may affect the consistency of the type and duration of jobs miners hold and hence their associated cumulative exposure levels. For example, some miners who lose their jobs upon mine closure are employed by other mines, sometimes in less-exposed jobs. Some miners may chose to move from job to job over their careers at underground coal mines, sometimes preferring positions away from the mining face. Moreover, if the trend of increasing mechanization continues, there will be fewer miners, and for some of them, their occupational lifetimes will be shorter.

For reasons already explained, we believe these choices are appropriate for this risk assessment. We also recognize that use of the most conservative approach at every step of the risk assessment analysis could produce mathematical risk estimates which, because of the additive effect of multiple conservative assumptions, may overstate the likely risk. We believe this QRA for simple CWP and PMF strikes a reasonable balance based on available data. To the extent that we may have underestimated the magnitude of overexposures which would be prevented, we believe the actual benefits to be greater than we have estimated.

It should be noted that reductions in the prevalence of simple CWP and PMF attributable to eliminating individual shift overexposures are not expected to materialize immediately after the overexposures have been substantially reduced or eliminated. Because these diseases typically arise after many years of cumulative exposure, allowing for a period of latency, the beneficial effects of reducing exposures are expected to become evident only after a sufficient time has passed that the reduction in cumulative exposure could have its effect. The total realized benefits would not be fully evident until after the youngest of today's underground coal miners retire.

Finally, even standing alone without simultaneously requiring that mine

operators verify the effectiveness of their mine ventilation plans, the proposed standard allowing MSHA to use single, full-shift samples to identify overexposures requiring corrective action would provide miners with health benefits (See detailed discussion in Quantitative Risk Assessment). Both the prospect of being cited for overexposures and actual issuance of additional citations due to this rule would serve to compel mine operators to be more attentive to the level of respirable dust in their mines. Therefore, it is reasonable to expect, over time, a further decline in the number of shifts during which the concentration of respirable coal mine dust is at or above the applicable standard. Thus, the use of full-shift single samples will in and of itself, on average, lower miners' cumulative exposure to respirable coal mine dust. Since cumulative exposure to respirable coal mine dust is the main determinant in the development of both simple CWP and PMF, the Agencies are confident that the use of single, full-shift samples, by itself, and even without the impact of a verified dust control plan, would result in better health protection to miners (Jacobsen,

et al.,

1977; Hurley,

et al.,

1987; Kuempel,

et al.,

1995; Attfield and Morring, 1992; Attfield and Seixas, 1995).

While there may be some concern from mine operators that the use of single, full-shift samples could dramatically increase the number of MSHA citations for overexposure to respirable coal mine dust, MSHA's 1998 Interim Single-Sample Enforcement Policy (ISSEP) has demonstrated that mine operators can maintain coal mine dust concentrations at or below the applicable standard.

As discussed in greater detail later in this notice, under ISSEP (May 7, 1998-September 9, 1998), of the 1,662 MMUs sampled, 182 or 11 percent were cited and only 14 of the 4,600 surface entities sampled were found to be out of compliance.

The anticipated increase in MSHA citations due to the use of single full-shift sampling would be the result of identifying overexposures which the current method of sampling masks due to the averaging of samples. Such overexposures and their prospective medical impact on the health of miners has been the subject of a Federal Mine Safety and Health Review Commission case which was affirmed by the Court of Appeals.

Consolidation Coal Co.

Secretary of Labor,

5 FMSHRC 378 (March 1983),

aff'd,

8 FMSHRC 890 (June 1986), 824 F.2d 1071 (D.C. Cir. 1987).

In affirming an MSHA citation designated as “significant and substantial” under Section 104(a) of the Mine Act based on a mine operator's bimonthly dust samples which had an average concentration of respirable dust of 4.1 milligrams per cubic meter of air, the Commissioner quoted the administrative law judge who explained in detail the potentially damaging health effects of respirable coal mine dust:

It is clear that the exposure covered by the dust samples which resulted in the citation herein

in itself

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

I conclude that

every drop in the bucket,

every two month sampling period where excessive dust is present, significantly and substantially contributes to a health hazard—the hazard of contracting chronic bronchitis or coal workers' pneumoconiosis. (emphasis added)

Consolidation Coal,

5 FMSHRC at 389-90 (citations omitted) (footnotes omitted).