42068 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

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 singleshift sampling. Today’s proposal

addresses the final decision and order in

NMA v. Secretary of Labor, issued by

the United States Court of Appeals for

the 11th Circuit on September 4, 1998

(153 F. 3d 1264). That case vacated a

1997 Joint Finding and MSHA’s

proposed policy concerning the use of

single, full-shift respirable dust

measurements to determine

noncompliance when the applicable

respirable dust standard was exceeded.

The Agencies are also announcing

that they will hold public hearings on

the joint proposed rule within 45 to 60

days of its publication. The hearings

will be held in the following locations:

Prestonsburg, Kentucky (Jenny Wiley

State Park); Morgantown, West Virginia;

and Salt Lake City, Utah.

DATES: Comments concerning this

proposed rule should be submitted on

or before August 7, 2000.

The hearing dates, times and specific

locations will be announced by a

separate document in the Federal

Register. The rulemaking record will

remain open 7 days after the last public

hearing.

ADDRESSES: You may use mail, facsimile

(fax), or electronic mail to send your

comments to MSHA. Clearly identify

comments as such and send them—(1)

By mail to Carol J. Jones, Director, Office

of Standards, Regulations, and

Variances, MSHA, 4015 Wilson

Boulevard, Room 631, Arlington, VA

22203;

(2) By fax to MSHA, Office of

Standards, Regulations, and Variances,

703–235–5551; or

(3) By electronic mail to

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—

CVweight

(b) Coefficient of Variation, Pump—CVpump

(c) Coefficient of Variation, Sampler—

CVsampler

2. Sources of Dust Concentration

Variability

(a) Spatial Variability

(b) Shift-to-shift Variability

3. Other Factors Considered

(a) Proportion of Oversized Particles

(b) Anomalous Events

(c) Conversion Factor Used in the Dust

Concentration Calculation

(d) Reduced Dust Standards

(e) Dusty Clothing

E. Accuracy of Single, Full-Shift

Measurement

1. Quantification of Measurement

Uncertainty

a. Experience Gained from Use of Control

Filters

2. Verification of Method Accuracy

XI. Proposed New Finding and Proposed

Rescission of the 1972 Joint Finding

XII. Feasibility Issues

A. Technological Feasibility

B. Economic Feasibility

XIII. Regulatory Impact Analysis

A. Costs and Benefits: Executive Order

12866

1. Compliance Costs

2. Benefits

B. Regulatory Flexibility Certification and

Initial Regulatory Flexibility Analysis

XIV. Other Statutory Requirements

A. Unfunded Mandates Reform Act of 1995

B. Paperwork Reduction Act of 1995

C. National Environmental Protection Act

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42069

D. Executive Order 12630 (Governmental

Actions and Interference with

Constitutionally Protected Property

Rights)

E. Executive Order 12988 (Civil Justice)

F. Executive Order 13045 (Protection of

Children from Environmental Health

Risks and Safety Risks)

G. Executive Order 13084 Consultation and

Coordination with Indian Tribal

Governments

H. Executive Order 13132 (Federalism)

XV. Public Hearings

Appendix A. The Effects of Averaging Dust

Concentration Measurements

Appendix B. Why Are Individual

Measurements Unbiased?

I. The Value of the MRE Conversion Factor

II. Conforming to the ACGIH and ISO

Standard

III. Effects of Other Variables

Appendix C. Components of Coefficient of

Variation Total (CVtotal)

I. Weighing Uncertainty

(a) Derivation of Coefficient of Variation of

Weight (CVweight)

(b) Values Expressing Weight-Gain

Uncertainty

(c) Negative Weight-Gain Measurements

(i) New Analysis of New Data Set of

Negative Weight Gain for Data of

Unexposed Filters

(d) Comparing Weight Gains Obtained

From Paired Samples

II. Pump Variability

III. Intersampler Variability

Appendix D. Data Submitted by Previous

Commenters

I. Paired Sample Data Submitted by the

NMA

II. Paired Sample Data Submitted by

Mountain Coal Company

III. Exposure Data Submitted by Jim Walter

Resources, Inc.

IV. Exposure Data Submitted by the NMA

V. Sequential Exposure Data Submitted by

Jim Walter Resources, Inc.

Appendix E. References

XVI. Regulatory Text

II. Introduction

For as long as miners have taken coal

from the ground, many have suffered

respiratory problems due to their

occupational exposures to respirable

coal mine dust. These respiratory

problems, range from mild impairment

of respiratory function to more severe

diseases, such as silicosis and

progressive massive fibrosis (PMF). For

some miners, the impairment of their

respiratory systems is so severe, they die

prematurely. There is a clear doseresponse 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/m3). The 2.0

mg/m3 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/m3 was retained in the Mine

Act, which also required that ‘‘each

operator shall continuously maintain

the average concentration of respirable

dust in the mine atmosphere during

each shift to which each miner in the

active workings of such mine is exposed

at or below 2.0 milligrams of respirable

dust per cubic meter of air,’’ Section

202(b)(2) (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/

m3. 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/m3.

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/m3, 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, fullshift 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, fullshift 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

42070 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

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/

m3]

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

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42071

1Reference to specific equipment, trade names or

manufacturers does not imply endorsement by

NIOSH or MSHA.

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, fullshift 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-nineteeneighties, MSHA continued to refine and

improve its sampling process. In 1984,

a fully-automated, robotic weighing

system was introduced along with stateof-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 flowcontrol sampling pump technology was

introduced in the coal mine dust

sampling program with the use of Mine

Safety Appliances FlowLiteTM pumps.1

These new pumps compensate for the

changing filter flow-resistance that

occurs due to dust deposited during the

sampling period. The second generation

of constant-flow sampling pumps was

introduced in 1994, with the

introduction of the Mine Safety

Appliances Escort ELF pump. The

automatic correction provided by these

new pumps improves the stability of the

sampler air flow rates and reduces the

inaccuracies that were inherent in the

1970–1980s vintage sampling pumps.

One further improvement was made in

1992 with the introduction of the new

tamper-resistant filter cassettes. Because

of these evolving improvements to the

sampling process, a better

understanding of statistical methods

applied to method accuracy, and a

reconsideration of the requirements of

section 202(f) of the Mine Act (30 U.S.C.

842(f)), the Secretary of Health and

Human Services has determined that the

previous joint finding should be

reevaluated.

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.

42072 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

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/m3 but was less than

2.0 mg/m3, or annually if the initial

sample was 1.0 mg/m3 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/m3 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/m3. Accordingly, the

[Secretaries] prescribed consecutive multishift samples to enforce the respirable dust

standard.’’

The preamble provides no further

explanation for the statement that

single-shift samples should not be relied

on when the respirable dust

concentration being measured was near

2.0 mg/m3. Thus, the 1980 final rule,

which reduced the number of samples

that operators were required to take for

compliance determinations, merely

reiterated the rationale behind the 1971/

1972 proposed and final findings

concerning single-shift samples, and did

not address the accuracy of a single,

full-shift measurement.

MSHA continues to take an active role

in sampling for respirable dust 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

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42073

2Quartz may be present in the coal seam and

therefore may become airborne during coal

production. MSHA regulates coal miners’ workshift 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/m3, 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/m3)= {(10

mg/m3)/(%Quartz)} For example, if the respirable

dust contains 15 percentage of quartz the respirable

coal mine dust standard would be 0.67 mg/m3 since

10 mg/m3 divided by 15 equals 0.67 mg/m3.

first day of sampling. Based on the first

shift of sampling, the operator is cited

if the average of those measurements

exceeds the applicable standard.

However, if the average falls below the

standard, but one or more of the

measurements exceed the applicable

standard, additional samples are

collected on the subsequent production

shift or day. The results of the first and

second shift of sampling on all

occupations are then averaged to

determine if the applicable standard is

exceeded. Additionally, when an

inspector continues sampling after the

first shift because a previous

measurement exceeds the standard,

MSHA’s procedures call for all

measurements taken on a given

occupation to be averaged within that

occupation, across all sampling shifts. If

the average of measurements taken over

more than one shift on all occupations

is equal to or less than the applicable

standard, but the average of

measurements taken on any one

occupation exceeds the value in a

decision table developed by MSHA, the

operator is cited for violation of the

applicable standard.

B. The Spot Inspection Program (SIP)

In response to concerns about

possible tampering with dust samples in

1991, MSHA convened the Coal Mine

Respirable Dust Task Group (Task

Group) to review the Agency’s

respirable dust program. The Task

Group was directed to consider all

aspects of the current program in its

review, including the role of the

individual miner in the sampling

program; the feasibility of MSHA

conducting all sampling; and the

development of new and improved

monitoring technology, including

technology to continuously monitor the

mine environment. Among the issues

addressed by the Task Group was the

actual dust concentration to which

miners are exposed. As part of the Task

Group review, MSHA developed a

special respirable dust ‘‘spot inspection

program’’ (SIP).

This program was designed to provide

the Agency with information on the

dust levels to which underground

miners are typically exposed. Because of

the large number of mines and MMUs

(mechanized mining units) involved

and the need to obtain data within a

short time frame, respirable dust

sampling during the SIP was limited to

a single shift or day, a departure from

MSHA’s normal sampling procedures.

The term ‘‘MMU’’ is defined in 30 CFR

70.2(h) to mean a unit of mining

equipment, including hand loading

equipment, used for the production of

material. As a result, MSHA decided

that if the average of multiple

occupation measurements taken on an

MMU during any one-day inspection

did not exceed the applicable standard,

the inspector would review the result of

each individual full-shift sample. If any

individual full-shift measurement

exceeded the applicable standard by an

amount specified by MSHA, a citation

would be issued for noncompliance,

requiring the mine operator to take

immediate corrective action to lower the

average dust concentration in the mine

atmosphere in order to protect miners.

During the SIP inspections, MSHA

inspectors cited violations of the 2.0

mg/m3 standard if either the average of

the five measurements taken on a single

shift was equal to or greater than 2.1

mg/m3, or any single, full-shift

measurement was equal to or exceeded

2.5 mg/m3. Similar adjustments were

made when the 2.0 mg/m3 standard was

reduced due to the presence of quartz

dust in the mine atmosphere.2

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/m3, the

average concentration would be 2.0 mg/

m3. 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 multipleday 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

42074 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

3MSHA 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.

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.

D. The Interim Single-Sample

Enforcement Policy (ISSEP)

On February 3, 1998, MSHA

published a corrected notice in the

Federal Register (63 FR 5687)

announcing its final policy on the use

of single, full-shift measurements to

determine noncompliance and issue

citations, based on samples collected by

MSHA inspectors, when the applicable

respirable dust standard is exceeded.

The enforcement policy, thereafter

referred to as ISSEP, which took effect

on May 7, 1998, provides better

protection to miners’ health because it

enabled MSHA to more effectively

identify overexposures that were

previously masked by the averaging of

results across different occupations.

Again, through the proposed single, fullshift 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/m3, the average

concentration would be 1.9 mg/m3.

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 preand post-weighed on the same days. If

the control filter was either missing or

invalid, the measurement(s) were not

used for enforcement purposes and the

entity type (i.e., mining section) was to

be resampled. An operator was found to

be in violation of the applicable dust

standard when a single, full-shift

measurement met or exceeded the

Citation Threshold Value (CTV)

corresponding to the dust standard in

effect. Each CTV listed in Chapter 1 of

the Coal Mine Health Inspection

Procedures Handbook (PH89–V–1(10))

was calculated to ensure that citations

would be issued only when a

measurement demonstrated, with at

least 95-percent confidence, that the

applicable standard had been

exceeded.3 No more than one citation

was to be issued based on single, fullshift 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.

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/

m3. 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

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42075

Joint Notice of Finding in the Federal

Register (59 FR 8357). The Joint Notice

proposed to rescind the 1972 finding by

the Secretaries of the Interior and

Health, Education and Welfare, and

instead, find that a single, full-shift

measurement will accurately represent

the atmospheric conditions with regard

to the respirable dust concentration

during the shift on which it was taken.

Concurrently, MSHA published a

separate notice in the Federal Register

announcing its intention to use both

single, full-shift measurements and the

average of multiple, full-shift

measurements for noncompliance

determinations under the MSHA

respirable coal mine dust program (59

FR 8356). That notice was published to

inform the mining public of how the

Agency intended to implement its new

enforcement procedure utilizing single,

full-shift samples, and to solicit public

comment on the procedure.

After a notice and comment

procedure extending over some three

and one-half years, which also included

three public hearings, the Agencies

published a final corrected notice of

finding in the Federal Register (63 FR

5664) on February 3, 1998.

The National Mining Association

(NMA) along with the Alabama Coal

Association petitioned the United States

Court of Appeals for the 11th Circuit to

review the 1998 Notice of Finding (Joint

Finding) issued by the Mine Safety and

Health Administration (MSHA) and the

National Institute for Occupational

Safety and Health (NIOSH), and

additionally asked for an emergency

motion for stay of the Joint Finding

pending review. The motion for an

emergency stay was denied by the

Court.

On appeal NMA argued, among other

things, that the agency had not met the

requirements of section 101(a)(6)(A) of

the Federal Mine Safety and Health Act

of 1977 (Mine Act) (30 U.S.C.

811(a)(6)(A)) because it failed to address

material impairment of health and

economic and technological feasibility.

MSHA and the Department of Labor

responded that the agencies addressed

the positive effect of the notice on miner

health, and also concluded in the course

of performing the analysis required

under the Regulatory Flexibility Act that

the economic impact of the Joint

Finding was not significant. On

September 4, 1998, the United States

Court of Appeals for the 11th Circuit

issued a decision in the case of National

Mining Association v. Secretary of

Labor, (153 F.3d 1264). The Court of

Appeals vacated the Joint Finding and

concluded that the agency was required

to ‘‘satisfy the requirements of Section

811(a)(6)’’ by ‘‘demonstrat[ing] that the

new standard (a) adequately assures that

no miner will suffer a material

impairment of health, on the basis of the

best available evidence; (b) uses the

latest available scientific data in the

field; (c) is feasible [in both an economic

and technological sense]; and (d) is

based on experience gained under the

Mine Act and other health and safety

laws,’’ supra, at 1268–1269. The Court

then concluded that ‘‘the record

contains no finding of economic

feasibility,’’ and that MSHA therefore

‘‘failed to comply with Section 811(a)(6)

of the Mine Act.’’ MSHA asked the

Court for a clarification of its decision

by filing a Motion for Clarification. The

Court, without opinion, denied the

Secretary’s motion on November 11,

1998.

MSHA and NIOSH understand the

Court’s ruling as requiring the Agencies

to comply with all requirements under

section 101(a)(6)(A) of the Mine Act (30

U.S.C. 811(a)(6)(A)). Therefore, in

response to the Court’s ruling, the

Secretaries are proposing today to add a

new mandatory health standard to 30

CFR part 72. Pursuant to section 202(f)

of the Mine Act (30 U.S.C. 842(f)), the

1972 joint notice of finding would be

rescinded and a new finding would be

made that a single, full-shift

measurement will accurately represent

atmospheric conditions to which a

miner is exposed during such shift. This

finding is the basis for the new

proposed mandatory health standard.

The Secretaries believe that single,

full-shift measurements must be

implemented into the MSHA coal mine

respirable dust program as quickly as

possible in order to better protect

miners’ health. Therefore, in order to

speed the process of reproposing this

critical measurement technique, the

Secretaries are incorporating the record

of the previous 1998 Joint Finding into

the record for this proposal and adding

appropriate new data and information to

support this rulemaking under section

101(a)(6)(A) of the Mine Act (30 U.S.C.

811(a)(6)(A)). The Secretaries have used

as much of the original wording as

possible from the vacated final finding

in this notice of proposed rulemaking.

References to previous comments and

commenters in the body of this proposal

are meant to apply to previous

comments received in response to the

earlier proposed Joint Finding that was

ultimately vacated by the U.S. Court of

Appeals for the 11th Circuit.

VII. Health Effects

A. Introduction

Since the 1800s, occupational

respiratory disease associated with

working in a coal mine has been

commonly referred to as ‘‘Black Lung.’’

As coal is mined, respirable-sized dust

is generated. Depending upon the mine

location and its geologic features, silica

may also be present in the mine

atmosphere. Dust in air that is breathed

by miners has the potential to be

deposited in their lungs. Some of this

dust may be retained. Coal mine dust

remaining in the lungs of miners for

prolonged periods of time has the

potential to result in respiratory

diseases, sometimes even after

occupational exposure to respirable coal

mine dust has stopped. There is a clear

and direct relationship between miners’

cumulative exposures (i.e., dose

multiplied by the time exposed to the

coal mine dust) to respirable coal mine

dust and the severity of resulting

respiratory conditions (as discussed

more extensively, later in this section).

Diseases resulting from long-term

retention of coal mine dust in the lung

include chronic coal workers’

pneumoconiosis (simple CWP),

progressive massive fibrosis (PMF),

silicosis, and chronic obstructive

pulmonary disease (COPD) (e.g., asthma,

chronic bronchitis, emphysema).

Historically, the medical term,

‘‘pneumoconiosis’’, has included simple

CWP and PMF and their sub-categories.

Chronic, or simple, CWP is partitioned

into three levels of severity, proceeding

from lowest to highest: Category 1,

category 2, and category 3. Progressive

Massive Fibrosis is similarly divided

into three categories of increasing levels

of severity: A, B and C.

Miners with simple CWP have a

substantially increased risk of

developing PMF. In the advanced stages

of pneumoconiosis (i.e., PMF), a

significant loss of lung function may

occur and respiratory symptoms (e.g.,

breathlessness, wheezing) may persist.

Miners are at risk of increased morbidity

and premature mortality due to simple

CWP, PMF and various other respiratory

diseases.

Factors that are important in the

development of simple CWP, PMF and

COPD include the type of dust (e.g., coal

and/or silica), dust concentration (to

which the miner was exposed), number

of years of exposure, age of the miner

(often measured as age at time of

medical examination), and rank of the

coal (the higher the rank the greater the

risk).

In 1998, MSHA estimated that

approximately 45,000 miners and

42076 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

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 resuspended 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.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42077

3. Biological Action: Respirable Coal

Mine Dust

The principal route of occupational

exposure to respirable coal mine dust

occurs via inhalation. As a miner

breathes, coal mine dust enters the nose

and/or mouth and may pass into the

mid airways (e.g., bronchi, terminal

bronchioles) and lower airways (e.g.,

respiratory bronchioles, alveolar ducts).

Coal mine dust has a size distribution

that is estimated to range between 1 and

100 micrometer (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 trachealbronchial) 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 (trachealbronchial) region of the lung, cilia (i.e.,

hairlike projections) line the airways

and are covered by a thin layer of

mucus. They assist in particle clearance

by beating rhythmically to project

particles toward the throat where they

may be swallowed, coughed, sneezed, or

expectorated. This rhythmic beating

action is effective in removing particles

fairly quickly (i.e., hours or days).

Within the alveolar region of the lung,

particles may be engulfed by pulmonary

macrophages. These large ‘‘wandering

cells’’ may remove particles via the

blood or lymphatics. This process,

unlike the movement of the cilia is

much slower (i.e., months or years).

Thus, some particles, particularly those

that are insoluble, may remain in the

alveolar region for long periods of time,

despite the fact that pulmonary

clearance is not impaired. It is the

pulmonary retention of coal mine dust

which may be the impetus for

respiratory disease.

It is also important to note that silica

may be present in the coal seam, within

dirt bands in the coal seam, and in rock

above and below coal seams. Of the

silica found in coal mines, quartz is the

form which is found. Thus, quartz may

become airborne during coal removal

operations (Manahan, 1994). Miners

may inhale dust that is a mixture of

quartz and coal. MSHA is concerned

with the inhalation of quartz since it

may be deposited in the lungs of miners

and produce silicosis. This is a

restrictive lung disease which is

characterized by a stiffening of the lungs

(West, 1990; 1992). Silicosis has been

seen in coal miners (e.g., surface miners,

drillers, roofbolters) (Balaan, et al.,

1993). Silicosis may develop acutely

(i.e., 6 months to 2 years) following

intense exposure to high levels of

respirable crystalline quartz. Silicosis

has also been observed in coal miners

following chronic exposure (i.e., 15

years or more), but may be accelerated

(i.e., 7–10 years) in some cases (Balaan,

et al., 1993). Silicosis is irreversible and

may lead to other illnesses and

premature mortality. People with

silicosis have increased risk of

pulmonary tuberculosis infection and

an increased risk of lung cancer

(Althouse, et al., 1995; International

Agency for Research on Cancer, 1997).

MSHA’s current standard of 2.0 mg/m3

for respirable coal dust requires that

quartz levels be 5% or lower. Otherwise,

the 2.0 mg/m3 respirable coal dust

exposure limit does not apply and must

be adjusted downward for percentage of

quartz. If coal dust contains more than

5% quartz, then the following formula

is applied (30 CFR 70.101; 30 CFR

71.101).

Respirable dust standard (mg/m3)=

{(10 mg/m3)/(%Quartz)}

The intent of this formula is to

maintain miner exposures to quartz

below 0.1 mg/m3 (100 μg/m3).

C. Health-Related Effects of Respirable

Coal Mine Dust

1. Description of Major Health Effects

Consistently, epidemiological studies

have demonstrated miners to be at risk

of developing respiratory symptoms, a

loss of lung function, and lung disease

as a consequence of occupational

exposure to respirable coal mine dust.

As noted previously, risk factors include

type(s) of dust, dust concentration,

duration of exposure, age of the miner

(often measured as age at time of

medical examination), and coal rank.

a. Simple Coal Workers’

Pneumoconiosis (Simple CWP) and

Progressive Massive Fibrosis (PMF)

In earlier stages of pneumoconiosis

the term, ‘‘simple coal workers’

pneumoconiosis’’ (simple CWP), has

been used, while in more advanced

stages, the terms ‘‘complicated CWP’’

and PMF have been used

interchangeably. Simple CWP and PMF

involve the lung parenchyma and are

produced by deposition and retention of

respirable coal dust in the lung.

To determine if a miner has simple

CWP or PMF, chest x-rays are taken and

classified by a certified radiologist or

reader. Opacities are identified on chest

films and then classified using a scale

of 0–3 (e.g., simple CWP category 1),

where higher category values indicate

increasing concentration of opacities. In

some instances, two category values

may be given. For example, simple CWP

category 2/3 signifies that the reader

decided the film was category 2, but

suspected that it might have been

category 3. The International Labour

Office (ILO) has provided a full

description of the criteria for these

classifications (ILO, 1980).

Simple CWP can be associated with a

loss of lung function and with

premature mortality (Morgan, et al.,

1974; Jacobsen, 1976; Cochrane, et al.,

1979; Parkes, 1982). MSHA recognizes

that simple CWP increases the risk of

developing PMF substantially

(Cochrane, 1962; Jacobsen, et al., 1971;

McLintock, et al., 1971; Balaan, et al.,

1993).

Progressive massive fibrosis (PMF) is

associated with decreased lung function

42078 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

and increased premature mortality

(Rasmussen, et al., 1968; Atuhaire, et

al., 1985; Miller and Jacobsen, 1985;

Attfield and Wagner, 1992). Progressive

massive fibrosis is also associated with

increases in respiratory symptoms such

as chest tightness, cough, and shortness

of breath. Miners with PMF also have an

increased risk of acquiring infections

and pulmonary tuberculosis (Petsonk

and Attfield, 1994; Yi and Zhang, 1996).

Finally, miners with PMF have an

increased risk of right-side heart failure

(i.e., cor pulmonale) (Cotes and Steel,

1987).

b. Other Health Effects

During a medical examination, a

miner may be questioned by his

physician about symptoms such as

cough, phlegm production, chest

tightness, shortness of breath, and

wheezing. Occupational physicians may

also conduct pulmonary function tests

using spirometry or plethysmography.

Pulmonary performance may be

assessed via repeated measurements of

lung volumes and capacities, such as

the forced expiratory volume in one

second (FEV1), vital capacity (VC),

forced vital capacity (FVC), residual

volume (RV), and total lung capacity

(TLC) (West, 1990; 1992). Changes in

lung volumes and capacities may

indicate a loss of the integrity of the

lung (i.e., respiratory system). More

importantly, they can provide

information for diagnosis of diseases

affecting the airways and/or elasticity of

the lung (i.e., obstructive vs. restrictive

lung disease) (West, 1990; 1992).

The term, chronic obstructive

pulmonary disease (COPD), refers to

three disease processes that are often

difficult to properly diagnose and

differentiate: chronic bronchitis,

emphysema, and asthma (Coggon and

Taylor, 1998; Garshick, et al., 1996;

West, 1990; 1992). As indicated by

several studies, the exposure of miners

to respirable coal mine dust place them

at increased risk of developing COPD.

Furthermore, COPD may occur in

miners with or without the presence of

simple CWP or PMF.

Chronic Obstructive Pulmonary

Disease (COPD) is characterized by

airflow limitations, and thus there is a

loss of pulmonary function. As in

simple CWP or PMF, a miner with

COPD may have a variety of respiratory

symptoms (e.g., shortness of breath,

cough, sputum production, and

wheezing) and may be at increased risk

of acquiring infections. Chronic

Obstructive Pulmonary Disease is

associated with increased premature

mortality (Hansen, et al., 1999; Meijers,

et al., 1997).

Briefly, in chronic bronchitis and in

asthma, there is excess mucous

secretion in the mid-lower airways

(West, 1990; 1992). In contrast,

emphysema is characterized by

dilatation (enlargement) of alveoli that

are distal to the terminal bronchioles,

which leads to poor gas exchange (i.e.,

poor transfer of oxygen and carbon

dioxide). Additionally, there is a

breakdown of the interstitium between

the alveoli. These pathological changes

may be confirmed upon autopsy. With

asthma, the airflow limitations may be

partially or completely reversible, while

they are only partially reversible with

chronic bronchitis and emphysema.

The Mine Safety and Health

Administration (MSHA) and the NIOSH

recognize that respiratory symptoms,

loss of lung function, and COPD may

impair the ability of a miner to perform

his job and may diminish his quality of

life. Additionally, miners having such

health effects are at increased risk of

morbidity (e.g., from cardio-pulmonary

disease, infections) and premature

mortality.

2. Toxicological Literature

To better understand the human

health effects of exposure to respirable

coal mine dust and to more fully

characterize the associated risks, it is

important to consider data that have

been obtained in animal based

toxicological studies. To date, sub-acute

studies (a study with a duration of 30

days, or less, in which multiple

exposures of the same agent are given)

and chronic studies (a study with a

duration of more than 3-months, in

which multiple exposures of the same

agent are given) attempted to mimic

miners’ exposures. Inhalation was

generally the route of exposure,

although several studies have also

employed instillation techniques (i.e., a

method which places a known quantity

of dust into the trachea or bronchi).

Most recent toxicological studies have

been short-term studies, largely focusing

on ‘‘lung overload’’ (Snipes, 1996;

Oberdorster, 1995; Morrow, 1988, 1992;

Witschi, 1990), species-dependent lung

responses (Nikula, et al., 1997a,b;

Mauderly, 1996; Lewis, et al., 1989;

Moorman, et al., 1975), and particle

size-dependent lung inflammation

(Soutar, et al., 1997). The data have

shown that pulmonary clearance of

particles may become impaired,

potentially leading to inflammatory and

other cellular responses in the lung.

Although overloading has not been

demonstrated in humans, the finding of

reduced lung clearance among retired

U.S. coal miners (Freedman and

Robinson, 1988) is consistent with this

possibility.

The data from Moorman, et al. (1975),

Lewis, et al. (1989), and Nikula, et al.

(1997a,b) are noteworthy for several

reasons. First, these groups of

investigators conducted chronic

inhalation toxicity studies (i.e., chronic

bioassays). This is important since

miners’ exposures also occur via

inhalation, and over a working lifetime.

Secondly, the investigators used an

exposure concentration of 2.0 mg/m3 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/m3, 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/m3) 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

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42079

Seixas, 1995; Kuempel, et al., 1997;

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

TABLE VII–1.—RESPIRABLE COAL

MINE DUST EPIDEMIOLOGICAL STUDIES, BY REPORTED OUTCOMES

FROM 1986 TO PRESENT

Studies Reported outcomes

Meijers, et al., 1997 ........... PMF, CWP,

COPD, LLF.

Maclaren, et al., 1989 ........ PMF, CWP,

LLF, RS.

Kuempel*, et al., 1995 ....... PMF, CWP,

COPD.

Bourgkard et al., 1998 ....... PMF, CWP,

LLF.

Kuempel*, et al., 1997

Love, et al., 1997

Love, et al., 1992

Attfield and Morring*,1992b PMF, CWP.

Attfield and Seixas*,

1995

Hodous and Attfield*,

1990

Hurley and Jacobsen,

1986

Hurley and Maclaren,

1987

Hurley, et al., 1987

Starzynski, et al., 1996

Yi and Zhang, 1996

Wang, et al., 1997 ............. CWP, LLF.

Goodwin and Attfield*,

1998.

CWP.

Morfeld, et al., 1997

Marine, et al., 1988 ........... COPD, LLF, RS.

Seixas*, et al., 1993

Soutar and Hurley, 1986

Carta, et al., 1996 .............. LLF, RS.

Henneberger and

Attfield*,1997

Henneberger and

Attfield*,1996

Seixas*, et al., 1992

Attfield and Hodous*, 1992 LLF.

Lewis, et al., 1996

COPD: Chronic obstructive pulmonary disease. CWP: Simple coal workers’ pneumoconiosis.

LLF: Loss of lung function.

PMF: Progressive massive fibrosis.

RS: Respiratory symptoms.

* Studies of U.S. Miners Who Participated in

the National Study of Coal Workers’ Pneumoconiosis (NSCWP).

a. Simple Coal Workers’

Pneumoconiosis (Simple CWP) and

Progressive Massive Fibrosis (PMF)

Studies following Cochrane (1962)

and McLintock et al., (1971) have

confirmed that the risk of PMF increases

with increasing category of simple CWP

(Hurley and Jacobsen, 1986; Hurley, et

al., 1987; Hurley and Maclaren, 1988;

Hodous and Attfield, 1990). However,

the risk of PMF was greater than

previously predicted among miners

with simple CWP category 1 or without

simple CWP (i.e., category 0) (Hurley, et

al., 1987). The risk of PMF increased

with increasing cumulative exposure,

regardless of the initial category of

simple CWP (Hurley, et al., 1987),

indicating that reducing dust exposures

is a more effective means of reducing

the risk of PMF than reliance on

detection of simple CWP.

Attfield and Seixas (1995) have

demonstrated a relationship between

cumulative exposure to respirable coal

mine dust and predicted prevalence of

pneumoconiosis (i.e., simple CWP,

PMF). They studied a group of

approximately 3,200 men who worked

in underground bituminous coal mines.

The U.S. miners and ex-miners had

participated in Round 1 (1970–1972) or

Round 2 (1972–1975) of the NSCWP and

were examined again between 1985 and

1988. Chest x-rays were read to

determine the number of cases of simple

CWP and PMF. Dust exposure estimates

were generated from measurements of

dust concentrations as well as from

work history. A logistic (or logit)

regression model was used to estimate

prevalence of simple CWP and PMF. In

this statistical analysis, proportions are

transformed to natural logarithmic

values, i.e., y = 1n [p/(1¥p)], before a

linear model is fit to the data (Armitage,

1977). The logistic model assumes that

the data have a binomial distribution

(e.g., presence or absence of PMF) for a

given set of covariate values (e.g., age,

coal rank, dust exposure, pack-years of

smoking). Using logistic modeling,

relationships were developed between

cumulative dust exposure and

prevalence of simple CWP (category 1+,

category 2+) and PMF. These

relationships were the key strengths of

the Attfield and Seixas study and serve

as the basis for the Quantitative Risk

Assessment of this rule.

The recent paper of Kuempel, et al.,

(1997) has provided a detailed

discussion and quantitative presentation

of excess risks associated with

respirable coal dust exposures. Their

study was based upon results from

previous studies of some 9,000

underground coal miners who

participated in the NSCWP (Attfield and

Morring, 1992b; Attfield and Seixas,

1995). Kuempel, et al., estimated excess

(exposure-attributable) prevalence of

simple CWP and PMF (i.e., number of

cases of disease present in a population

at a specified time, divided by the

number of persons in the population at

that specified time). Point estimates of

excess risk of PMF ranged from 1/1000

to 167/1000 among miners exposed at

the current MSHA standard for

respirable coal mine dust. These

estimates were based upon dust

exposure that occurred over a miner’s

working lifetime (e.g., 8 hours per day,

5 days a week, 50 weeks per year, over

a period of 45 years). Actual

occupational lifetime exposure may be

more, due to extended work shifts and

work weeks. The point estimates of PMF

presented by Kuempel, et al., (1997)

were related to coal rank, where higher

estimates (e.g., 167/1000) were obtained

for high-rank coal (anthracite coal) and

somewhat lower estimates were

obtained for medium/low rank

bituminous coal (e.g., 21/1000). Within

each coal rank, the estimates of simple

CWP cases were at least twice as high

as those for PMF (e.g., 167/1000 PMF vs.

380/1000 simple 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

42080 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

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 nonparticipants 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 xray ‘‘worsening’’ (i.e., increase in readerdesignated category signifying

progression of simple CWP). Their

conclusion, however, was based on

pooling of the data (i.e., three combined

groups of miners) who had different

cumulative exposures (i.e., 20, 66 and

85 mg-yr/m3).

Love, et al., (1997, 1992) reported on

occupational exposures and the health

of British opencast (i.e., surface or strip)

coal miners. They studied a group of

approximately 1,200 miners who were

employed at sites in England, Scotland,

and Wales. The mean age of the men

was 41; many had worked in the mining

industry since the 1970s. To determine

dust exposure levels, full-shift personal

samples were collected. Most were

respirable dust samples which were

collected using Casella cyclones

according to the procedures described

by the British Health and Safety

Executive (HSE). Thus exposure

determinations would be comparable to

exposure determinations obtained in

U.S. surface coal mines since both

measure respirable dust according to the

BMRC criteria.

These investigators found a doubling

in the relative risk of developing

profusion of simple CWP category 0/1

for every 10 years of work in the

dustiest jobs in surface mines. These

respirable coal dust exposures were

under 1 mg/m3. Love, et al., (1992,

1997), like other investigators,

emphasized the need for monitoring and

controlling exposures to respirable coal

mine dust, particularly in high risk

operations (e.g., drillers, drivers of

bulldozers).

Meijers, et al., (1997) studied Dutch

coal miners who were examined

between 1952 and 1963, and who were

followed until the end of 1991. They

reported an increased risk of mortality

from simple CWP and PMF among

miners who had generally worked

underground for 20 or more years. Their

conclusions were based upon dramatic

increases in standardized mortality

ratios (SMRs). There were several

limitations in this study, however.

Morfeld, et al., (1997) published a

recent paper that investigated the risk of

developing simple CWP in German

miners and addressed the occupational

exposure limit for respirable coal dust

in Germany. Their study included

approximately 5,800 miners who

worked underground from the late

1970s to mid-1980s. Morfeld, et al.,

observed increases in relative risks

(RRs) of developing early x-ray changes,

category 0/1, that were exposuredependent. Relative risks (RRs)

increased with higher dust

concentrations.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42081

Starzynski, et al., (1996) conducted a

mortality study on a group of 11,224

Polish males diagnosed with silicosis,

simple CWP, or PMF between 1970 and

1985. This cohort was subdivided by

occupation into four subcohorts: Coal

miners (63%); employees of

underground work enterprises (8%)

(i.e., drift cutting and shaft construction

jobs); metallurgical industry and iron,

and nonferrous foundry workers (16%);

and refractory materials, china, ceramics

and quarry workers. The investigators

found that coal miners had a slight,

statistically significant excess overall

mortality (i.e., all causes) as indicated

by a Standardized Mortality Ratio (SMR)

of 105 (with a 95% Confidence Interval

(C.I.) of 100–110). Also, excess of deaths

from diseases of the respiratory system

among coal miners was nearly four

times that of the referent population

(SMR of 383 with a 95% C.I. of 345–

424). The study of Starzynski, et al.,

(1996) agrees with others that there is

premature mortality among coal miners

from simple CWP and PMF.

Unfortunately, there is little or no

information presented on miner work

history, exposure assessment (e.g.,

respirable coal mine dust, silica), and

mine environment (e.g., coal rank(s),

underground vs. surface mining).

Yi and Zhang (1996) conducted a

study to measure the progression from

simple CWP to PMF or death among a

cohort of 2,738 miners with simple CWP

who were employed at the Huai-Bei coal

mine in China. Relative risks (i.e., RRs)

were calculated for progression from

simple CWP category 1 to simple CWP

category 3 and for progression from

simple CWP category 3 to death. Their

results demonstrated that miners with

simple CWP category 1 are at risk of

developing simple CWP category 2 and

simple CWP category 3 (e.g., RRs of

1.101 and 2.360, respectively). They

also found that miners with PMF had a

decreased life expectancy. Other risk

factors for development of PMF

included long-term work underground,

and drilling. This study was limited by

a lack of exposure assessment,

estimation of miner smoking histories,

and use of a radiological classification

system that differs from that of the ILO.

Hurley and Maclaren (1987) studied

British coal miners who were examined

between 1953 and 1978, over 5-year

intervals. They have shown that

exposure to respirable coal dust

increases the risks of developing simple

CWP and of progressing to PMF. As

seen in their data analysis, these

responses were dependent upon dust

concentration and coal rank. That is,

greater responses were seen at higher

dust concentrations and with higher

rank coal (i.e., increasing per cent

carbon). The investigators also noted

that estimated risks were unaffected by

changes in the proportion of miners

with simple CWP who transferred jobs.

The authors concluded that ‘‘limiting

exposure to respirable coal dust is the

only reliable way of limiting the risks of

radiological changes to miners.’’

b. Other Health Effects

As noted in Table VII–1, there were

16 studies in which the loss of lung

function (LLF) was examined in coal

miners. Six of these studies also

included an evaluation of respiratory

symptoms (RS) in the miners. There

were five studies describing chronic

obstructive pulmonary disease (COPD)

in miners.

Henneberger and Attfield (1997;

1996), Kuempel, et al. (1997), Seixas, et

al., (1993), Attfield and Hodous (1992),

and Seixas, et al., (1992) evaluated data

from pulmonary function tests and

standardized questionnaires to miners

in the NSCWP. A common finding in

their studies was an increase in

respiratory symptoms such as cough,

shortness of breath, and wheezing. The

symptoms were dependent upon the

dust concentration to which the miners

had been exposed, with more

pronounced symptoms occurring after

long-term exposures to higher exposure

levels. These studies also demonstrated

that a loss of lung function occurred

among miners.

Attfield and Hodous (1992) studied

U.S. miners who had spent 18 years

underground (on average) and who

participated in Round 1 (1969–1971) of

the NSCWP. They observed that greater

reductions in pulmonary function were

associated with exposure to higher

ranks of coal (i.e., anthracite vs.

bituminous vs. lignite). Using linear

regression models, Kuempel et al.,

(1997) predicted the excess (exposure

attributable) prevalence of lung function

decrements among miners with

cumulative exposures to respirable coal

mine dust of 2 mg/m3 for 45 years (i.e.,

90 mg-yr/m3). The excess prevalence

estimates were 315 and 139 cases per

thousand for forced expiratory volume

in one second (FEV1) of <80% and

<65% of predicted normal values,

respectively, among never-smoking

miners (a sub-group of 977 NSCWP

participants studied in Seixas et al.,

1993). Such reductions in FEV1 are

clinically significant; FEV1 <80% (of

predicted normal values) is a measure

that is used to determine ventilatory

defects (American Thoracic Society,

1991). Three recent studies found

impaired FEV1 to be a predictor of

increased pre-mature mortality (Weiss,

et al., 1995; Meijers, et al., 1997; Hansen

et al., 1999).

Seixas, et al. (1993) conducted an

analyses of 977 underground coal

miners who began working in or after

1970 and were participants of both

NSCWP Round 2 (1972–1975) and

Round 4 (1985–1988). They found a

rapid loss of lung function in miners

and further declines in lung function

with continuing exposure to coal mine

dust. Collectively these studies have

shown that the prevalence of decreased

lung function was proportional to

cumulative exposure. That is, with

exposure to higher coal dust levels over

a working lifetime, there were more

miners who experienced a loss of lung

function. Also, the types of respiratory

symptoms and patterns of pulmonary

function decrements observed by both

Attfield and Hodous (1992) Seixas, et al.

(1992;1993) are characteristic of COPD.

The U.S. findings on respiratory

symptoms and loss of lung function in

miners have agreed with those of

previous British studies by Marine, et

al., (1988) and Soutar and Hurley

(1986). Marine, et al., (1988) analyzed

data from British coal miners and

focused their attention on respiratory

conditions other than simple CWP and

PMF. In particular, they examined the

Forced Expiratory Volume in one

second (FEV1) among smoking and

nonsmoking miners and, on the basis of

reported respiratory symptoms,

identified those miners with bronchitis.

Using these data, logistic regression

models were used to estimate the

prevalence of chronic bronchitis and

loss of lung function. Marine, et al.,

concluded that both exposure to

respirable coal mine dust and smoking

independently cause decrements in lung

function; their contributions to COPD

appeared to be additive in coal miners.

Soutar and Hurley (1986) examined

the relationship between dust exposure

and lung function in British coal miners

and ex-miners. The men who were

studied were employed in coal mines in

the 1950s and were followed up and

examined 22 years later. These miners

and ex-miners were categorized as

smokers, ex-smokers, or nonsmokers.

The Forced Expiratory Volume in one

second (FEV1), the Forced Vital

Capacity (FVC), and the FEV1/FVC

ratios decreased in all study groups and

these reductions in lung function were

inversely proportional to dust exposure.

Thus, Soutar and Hurley concluded that

exposure to respirable coal mine dust

can cause severe respiratory

impairment, even without the presence

of simple CWP or PMF. They speculated

that the pathology of coal dust-induced

42082 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

4Forced 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).

lung disease differs from that induced

by smoking.

Recent studies from China (Wang, et

al., 1997) and the European community

(Bourgkard, et al., 1998; Carta, et al.,

1996; Lewis, S., et al., 1996) have also

supported the British and U.S. findings

which demonstrated the correlation

between occupational exposure to coal

dust and respiratory symptoms and loss

of lung function in miners.

Wang, et al., (1997) examined lung

function in underground coal miners

and other workers from several other

factories in Chongqing, China. For their

study, information was obtained on

exposure duration, results of

radiographic tests, and smoking history.

Pulmonary function tests were

performed, providing the Forced

Expiratory Volume in one second

(FEV1), the Forced Vital Capacity (FVC),

and FEV1/FVC data. Additionally, the

diffusing capacity for carbon monoxide

(DLCO) was measured. This is an

indicator of diffusion impairment at the

‘‘blood-gas barrier’’ which may occur,

for example, when this barrier becomes

thickened (West, 1990; 1992). Wang, et

al., (1997) found that there was

impairment of pulmonary function

among the coal miners and they had

evidence of obstructive disease. Like

other studies, such effects were

observed among coal miners even in the

absence of simple CWP. Pulmonary

function was further decreased when

simple CWP was present. This study did

not provide exposure measurements and

there was no consideration of exposureresponse relationships. Also, silica

exposures and their potential effects

were not examined in the underground

coal miners.

As noted above, Bourgkard, et al.,

(1998) was interested in the earlier

stages of simple CWP (i.e., Categories 0/

1 and 1/0) and the prognostic role of

cumulative dust exposure, smoking

patterns, respiratory symptoms, lung CT

scans, and lung function indices for

chest x-ray worsening and evolution to

simple CWP category 1/1 or higher.

Over a 4-year period, they studied

French coal miners who were employed

in underground and surface mines.

Bourgkard, et al., (1998) found that, at

the first medical examination, the ratio

of the Forced Expiratory Volume in one

second (FEV1) to the Forced Vital

Capacity (FVC) (i.e., FEV1/FVC) and

other airflows determined from a forced

expiration (West, 1990; 1992) were

lower among miners who later

developed simple CWP category 1/1 or

higher. These miners also experienced

more wheezing at the first medical

examination. Thus, the results of their

study suggested that lung function

changes may serve as an early indicator

of miners who are at increased risk of

developing simple CWP and PMF and

who should be monitored more closely.

Carta, et al., (1996) have examined the

role of dust exposure on the prevalence

of respiratory symptoms and loss of

lung function in a group of young Italian

coal miners (i.e., mean age at hire 28.9

years, mean age at first survey 31.2

years). These miners worked

underground and were exposed to

lignite (i.e., low rank coal) which had a

5–7% sulfur content. They were

followed for a period of 11 years, from

1983 and 1993. Carta, et al., (1996)

found few abnormalities on miner chest

x-rays taken throughout the 11-year

study. However, there was an increased

prevalence of respiratory symptoms and

loss of lung function. This was

particularly noteworthy since dust

exposures were often below 1.0 mg/m3;

the cumulative dust exposure for the

whole cohort was 6.7 mg-yr/m3 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 exposureresponse 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/m3

(i.e., 2 mg/m3 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/m3) and increased with higher

cumulative exposures (i.e., above 90 mgyr/m3. Thus, these investigators

demonstrated a statistically significant

exposure-response relationship for

COPD.

Meijers, et al. (1997) have shown,

among Dutch miners, reductions in lung

volumes and capacities are good

predictors of the increased risk of

premature mortality from COPD. For

example, a diminished forced expiratory

volume in one second (FEV1) or a

diminished ratio of the FEV1 to the

forced vital capacity 4 (FVC) (i.e., FEV1/

FVC) upon medical examination was

associated with a significantly increased

standardized mortality ratio (SMR) for

COPD (322 and 212, respectively). In

other words, miners with diminished

lung capacity based on FEV1 were two

to three times more likely to die

prematurely due to COPD than miners

who had normal lung function. In

contrast, SMRs for COPD were not

significantly increased in miners with

normal lung volumes and capacities.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42083

5By ‘‘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.

6 If a different definition of ‘‘exhibiting a

recurrent pattern of overexposures’’ were used in

these analyses the estimate of the reduction in risk

and associated benefits would be different. For

example, if the criterion were that four or more D.O.

bimonthly exposure measurements exceeded the

applicable standard then, with 95% confidence, at

least 20 shifts would be overexposures in a year of

384 shifts. Using the four as the criterion, this

would reduce the population for whom we are

estimating benefits, and the estimated number of

prevented cases would decrease by 19%.

7MSHA 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 data support prior conclusions of

Seixas, et al. (1992, 1993) and Attfield

and Hodous (1992) based on morbidity

studies.

VIII. Quantitative Risk Assessment

As mentioned previously, in addition

to this proposed notice of rulemaking,

today’s Federal Register contains

another NPRM, Verification of Dust

Control Plan (RIN 1219–AB18), ‘‘plan

verification.’’ In combination, these

rules present MSHA’s strengthened plan

to meet the Mine Act’s requirement that

a miner’s exposure to respirable coal

mine dust be at or below the applicable

standard on each and every shift.

MSHA’s improved program to eliminate

overexposures on each and every shift

includes the simultaneous

implementation of an improved tool to

identify overexposures (i.e., inspectors

use of single, full-shift samples for

noncompliance determinations) and a

new regulation requiring operators

implement verified ventilation plans in

underground coal mines.

Having reviewed the reported health

effects associated with exposure to coal

mine dust, MSHA and NIOSH have

evaluated the evidence to determine

whether the current regulatory strategy

can be improved. The criteria for this

evaluation is established by the Mine

Act under section 101(a)(6)(A) [30

U.S.C. 811(a)(6)(A)] which provides

that:

The Secretary, in promulgating mandatory

standards dealing with toxic materials or

harmful physical agents under this

subsection, shall set standards which most

adequately assure on the basis of the best

available evidence that no miner will suffer

material impairment of health or functional

capacity even if such miner has regular

exposure to the hazards dealt with by such

standard for the period of his working life.

Based on Court interpretations of

similar language under the

Occupational Safety and Health Act,

there are three questions that must be

addressed: (1) Whether health effects

associated with the current pattern of

overexposures on individual shifts

constitute a material impairment to

miner health or functional capacity; (2)

whether the current pattern of

overexposures on individual shifts

places miners at a significant risk of

incurring any of these material

impairments; and (3) whether the

proposed rules would substantially

reduce those risks.

The criteria for evaluating the health

effects evidence do not require scientific

certainty. The need to evaluate risk does

not mean that an agency is placed into

a ‘‘mathematical straightjacket.’’ See

Industrial Union Department, AFL–CIO

v. American Petroleum Institute, 448

U.S. 607, 100 S.Ct 2844 (1980),

otherwise known as the ‘‘Benzene’’

decision. When regulating on the edge

of scientific knowledge, certainty may

not be possible and,

so long as they are supported by a body of

reputable scientific thought, the Agency is

free to use conservative assumptions in

interpreting the data * * * risking error on

the side of overprotection rather than

underprotection (Id at 656).

The statutory criteria for evaluating the

health evidence do not require MSHA

and NIOSH to wait for absolute

certainty and precision. MSHA and

NIOSH are required to use the ‘‘best

available evidence’’ (section

101(a)(6)(A) of the Mine Act (30 U.S.C.

811(a)(6)(A)).

As explained earlier, MSHA’s

objective in strengthening the

requirements for verifying the

effectiveness of dust control plans, and

in enforcing effective plans through the

new enforcement policy proposed in

this notice, is to ensure that no miner is

exposed to an excessive concentration

(i.e., a concentration in excess of the

applicable standard) of respirable dust

on any individual shift. Annual

inspector samples have demonstrated

overexposures on individual shifts in

many mines. Data compiled from the far

more frequent, bimonthly, operator

sampling program show that in many

mines, the applicable dust standard is

exceeded on a substantial percentage of

the production shifts. This pattern has

persisted for many years, and, since

individual shift excursions above the

applicable standard are permitted under

the existing program, the same pattern

can be expected to continue over the

working lifetime of affected miners—

unless an effort is made to eliminate

excess exposures on individual shifts. In

this quantitative risk assessment (QRA),

MSHA will demonstrate that reducing

coal mine dust concentrations, over a

45-year occupational lifetime, to no

more than the applicable standard on

just that percentage of shifts currently

showing an excess, thereby lowering the

cumulative exposure to respirable coal

mine dust than would otherwise occur,

would significantly reduce the risk of

both simple CWP and PMF among

miners. We have estimated the health

benefits of the two rules arising from the

elimination of overexposures on all

shifts at only those MMUs exhibiting a

pattern of recurrent overexposures on

individual shifts.5

Based on 1999 operator data, there

were 704 MMUs (out of 1,251 total) at

which dust concentrations for the

designated occupation (D.O.) samples

exceeded the applicable standard on at

least two of the sampling shifts (MSHA,

Data file:Operator.ZIP).6 MSHA

considers these 704 MMUs, representing

more than half of all underground coal

miners working in production areas, to

have exhibited a pattern of recurrent

overexposures.7 Valid operator D.O.

samples were collected on a total of

18,569 shifts at these 704 MMUs, and

the applicable standard was exceeded

on 3,977 of these shifts, or about 21.4

percent. For this 21.4 percent, the mean

excess above the standard, as measured

for the D.O. only, was 1.04 mg/m3.

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/m3 and 1.12 mg/m3. 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

42084 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

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/m3,

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/m3)

Number of Years ......................................................................................................................... 8 8 8

Median ......................................................................................................................................... 52.6 20.5 1.23

Mean (Standard Error) ................................................................................................................. 50.9 (1.62) 20.6 (0.32) 1.25 (0.020)

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

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

overexposed.

Parameter #3: for those MMUs exhibiting a pattern of recurrent overexposures, the mean excess above the applicable standard among valid

D.O. measurements that exceeded the applicable standard.

The available data suggest that unless

changes are made to enforce the dust

standard on every shift, the same

average pattern of overexposures

observed in 1999 will persist into the

future. Therefore, we conclude that

without the proposed changes:

• More than one-half of all MMUs

would continue to have a pattern of

recurrent overexposures on individual

shifts;

• At those MMUs with recurrent

overexposures, full-shift average

respirable dust concentrations for the

D.O. would continue to exceed the

applicable standards on about 21

percent of all production shifts;

• Among those shifts on which D.O.

exposure exceeds the applicable

standards, the mean excess for the D.O.

would continue to be approximately 1.0

mg/m3.

We invite public comment on

whether these three parameters, based

on operators’ regular 1999 bimonthly

samples, under-represent or overrepresent 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/m3

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 m3 of inhaled air

× 10 m3 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 doseresponse 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

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42085

8Since females have a greater life expectancy

than males, expected benefits would increase if the

proportion of female miners increases substantially

in the future.

9 ‘‘affected D.O. miners’’ include all miners who

work at the 56-percent of MMUs under

consideration and who are exposed to dust

concentrations similar to the D.O. over a 45-year

working lifetime.

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/m3. 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/m3 over the course

of a working year (i.e., 21 percent of

shifts in one year, times 1.04 mg/m3 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/m3 (i.e., 45

years times 0.22 mg-yr/m3 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/m3 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/

m3, 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/m3 less exposure if individual

shift excursions are eliminated. For 65-

year-old miners, reducing accumulated

dust exposure by a total of 10 mg-yr/m3

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/

m3, 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/m3 of reduced exposure

per year, reaching a maximum of about

10 mg-yr/m3 at age 65. Between ages 65

and 80, the accumulated reduction in

dust exposure remains at an estimated

average of 10 mg-yr/m3, but the benefit

in terms of both simple CWP and PMF

risk continues to increase, as explained

previously.

The expected lifetime for all

American males conditional on their

having reached 20 years of age, is 73

years (calculated from: U.S. Census

March 1997, Table 18; U.S. Census

March 1997, Table 119).8 On average,

the best estimate of the lifetime benefit

to exposed miners is expressed by the

reduction in prevalence of disease at age

73. Carrying out the calculation at a 73-

year average lifetime, MSHA expects

that, at the MMUs under consideration,

bringing dust concentrations down to no

more than the applicable standard on

each shift will:

• Reduce the combined risk of simple

CWP and PMF by at least 18.0 cases per

1000 affected D.O. miners; 9

• 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 fullshift sample on the D.O. and, on the

same shift, four or more additional

samples representing other occupations.

42086 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

10With 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.

11With 95-percent confidence, the mean excess is

at least 0.72 mg/m3.

12There 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.

On 896 shifts, at a total of 450 distinct

MMUs, the D.O. measurement exceeded

the applicable standard and there were

at least three valid measurements for

other occupations available for

comparison. There was an average of 1.2

non-D.O. measurements in excess of the

standard on shifts for which the D.O.

measurement exceeded the standard.10

For non-D.O. measurements that

exceeded the standard on the same shift

as a D.O. measurement, the mean excess

above the standard was approximately

(0.8 mg/m3).11

Combining these results with the 21-

percent rate of excessive exposures

observed for the D.O. on individual

shifts, it is reasonable to infer that, at

the MMUs under consideration, an

average of 1.2 other miners, in addition

to the one classified as D.O., is currently

overexposed on at least 21 percent of all

production shifts. Over the course of a

working year, the reduction in exposure

expected for these other miners is 0.17

mg-yr/m3 (i.e., 21 percent of one year,

times 0.8 mg/m3).

To assess the reduction in risk

expected from eliminating all singleshift exposures for faceworkers

experiencing lower exposures than the

D.O., MSHA again applied the Attfield

and Seixas models to miners who begin

working at age 20, retire at age 65,

assuming various lifetimes: 65, 73, and

80 years. This time, however, the

resulting decrease in predicted

prevalence was multiplied by 1.2/7 =

0.171, to reflect the fact that the

assumed rate of overexposure applies,

on average, to about 17 percent of the

faceworkers not classified as the D.O.12

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 CWPa

(categories 1, 2 or 3) or PMFb

Simple CWP

(categories 2 or 3) or PMF PMF

Age Age Age

65 73 80 65 73 80 65 73 80

Affected Designated

Occupation Minersc 11.0 18.0 25.0 3.7 9.8 21.0 1.8 5.1 12.0

Affected Non-Designated Occupation

Minersd .................... 1.4 2.3 3.3 0.5 1.3 2.7 0.2 0.7 1.5

aSimple CWP: simple coal workers’ pneumoconiosis.

bPMF: progressive massive fibrosis.

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

the D.O.

IX. Significance of Risk

The criteria for evaluating the

evidence to determine whether these

proposed standards improve the

regulatory strategy for controlling

exposures to respirable coal mine dust

are established by the Mine Act

pursuant to section 101(a)(6)(A) (30

U.S.C. 811(a)(6)(A))which provides that:

The Secretary, in promulgating mandatory

standards dealing with toxic materials or

harmful physical agents under this

subsection, shall set standards which most

adequately assure on the basis of the best

available evidence that no miner will suffer

material impairment of health or functional

capacity even if such miner has regular

exposure to the hazards dealt with by such

standard for the period of his working life.

Based on Court interpretations of

similar language under the

Occupational Safety and Health Act,

there are three questions that must be

addressed: (1) Whether health effects

associated with the current pattern of

overexposures on individual shifts

constitute a material impairment to

miner health or functional capacity; (2)

whether the current pattern of

overexposures on individual shifts

places miners at a significant risk of

incurring any of these material

impairments; and (3) whether the

proposed rules would substantially

reduce those risks.

The statutory criteria for evaluating

the health evidence do not require

MSHA and NIOSH to wait for absolute

certainty and precision. MSHA and

NIOSH are required to use the ‘‘best

available evidence’’ (section

101(a)(6)(A) of the Mine Act (30 U.S.C.

811(a)(6)(A)). The need to evaluate risk

does not mean that an agency is placed

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42087

13 In the context of the field of risk assessment,

a ‘‘conservative’’ assumption is one that results in

an estimate of more protection for workers than a

less conservative assumption would. Therefore,

estimated benefits are greater under assumptions

that are ‘‘conservative’’ in this sense.

14By ‘‘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.

15 Valid MSHA inspector samples require

production to be at least 60-percent of the average

production for the last 30-days. Valid operator

bimonthly samples must be taken on a normal

production shift (i.e., a production shift during

which the amount of material produced in a MMU

is at least 50 percent of the average production

reported for the last set of five valid samples) (30

CFR 70.101).

16Therefore 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.

into a ‘‘mathematical straightjacket.’’

See Industrial Union Department, AFL–

CIO v. American Petroleum Institute,

448 U.S. 607, 100 S.Ct 2844 (1980),

otherwise known as the ‘‘Benzene’’

decision. When regulating on the edge

of scientific knowledge, certainty may

not be possible and,

so long as they are supported by a body of

reputable scientific thought, the Agency is

free to use conservative assumptions in

interpreting the data . . . risking error on the

side of overprotection rather than

underprotection (Id at 656).

We have taken steps in our

quantitative risk assessment to conduct

a balanced analysis using available data.

Some of our assumptions were

conservative, while others were not.13

In identifying the number and

percentage of MMUs exhibiting a

pattern of recurrent overexposures on

individual shifts we choose to include

only those MMUs with two or more

1999-operator bimonthly samples in

excess of the applicable standard, rather

than the population of MMUs with any

overexposures.14 Also, the quantitative

risk assessment estimates of reduction

in risk are averages across MMUs

exhibiting a pattern of recurrent

overexposures. For those miners who

work at mines exhibiting a pattern of

recurrent overexposures which differs

from the one applied in the Quantitative

Risk Assessment, their reduction in risk

would be more than or less than the

expected average, depending on

whether or not their overexposures are

at a higher or lower than average rate

and intensity.

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 abovecited 10 cubic meters per 8-hour shift;

an estimate of this ventilatory rate is

13.5 cubic meters per 8-hour shift (ICRP,

1994). The sub-population of miners

with higher breathing rates would

inhale more respirable coal mine dust

than would otherwise occur given the

same environmental exposures, thereby

increasing their risks for the

development of simple CWP and PMF.

In the Quantitative Risk Assessment,

to estimate average reduction in

exposure, we chose the best available

data sets: 1999 operator bimonthly

samples for D.O.s and N.D.O.s.,

respectively. Currently, both operator

bimonthly and inspector samples 15 may

be taken on production shifts that may

not reflect typical production levels.16

Although other factors may mediate the

amount of airborne respirable dust such

as, ventilation and water sprays, on

average, higher production is correlated

with increased quantities of airborne

respirable coal mine dust (Webster, et

al., 1990; Haney, et al., 1993; Green, et

al., 1994). Some previous commenters

and the Dust Advisory Committee have

alleged that operators tend to reduce

production and/or increase dust

controls on sampled shifts. Based on

MSHA’s and NIOSH’s experience and

expertise, and previous comments, we

believe the production levels observed

on sampling shifts are indeed lower

than typical (See discussion in Benefits

section). We also believe at some

MMUs, more engineering controls at

higher levels of efficacy are used during

sampling shifts than on the majority of

shifts (See discussion in Benefits

section). Thus, it is reasonable to

conclude that the number of MMUs

exhibiting a pattern of recurrent

overexposures is greater than the 704

captured in this Quantitative Risk

Assessment. Furthermore, the severity

and rate of overexposures to respirable

coal mine dust among the 704 MMUs

exhibiting a pattern of recurrent

overexposures are probably also greater

than we have estimated. We have

derived our best estimate of the risk

reduction using the best available data.

Yet due to limitations in these data, we

believe that we have underestimated the

magnitude and frequency of typical

respirable coal mine exposures. To the

extent that our values underestimate the

true reduction in respirable coal mine

dust exposures, we have underestimated

the benefits of these rules.

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

42088 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

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 fullshift sampling would be the result of

identifying overexposures which the

current method of sampling masks due

to the averaging of samples. Such

overexposures and their prospective

medical impact on the health of miners

has been the subject of a Federal Mine

Safety and Health Review Commission

case which was affirmed by the Court of

Appeals. Consolidation Coal Co. v.

Secretary of Labor, 5 FMSHRC 378

(March 1983), aff’d, 8 FMSHRC 890

(June 1986), 824 F.2d 1071 (D.C. Cir.

1987).

In affirming an MSHA citation

designated as ‘‘significant and

substantial’’ under Section 104(a) of the

Mine Act based on a mine operator’s

bimonthly dust samples which had an

average concentration of respirable dust

of 4.1 milligrams per cubic meter of air,

the Commissioner quoted the

administrative law judge who explained

in detail the potentially damaging

health effects of respirable coal mine

dust:

It is clear that the exposure covered by the

dust samples which resulted in the citation

herein in itself would neither cause nor

significantly contribute to chronic bronchitis

or coal workers pneumoconiosis. It is also

clear that longer exposure to the same dust

levels can in a significant number of

instances cause or significantly contribute to

chronic bronchitis or to coal workers

pneumoconiosis. There is no question that

chronic bronchitis and coal workers’

pneumoconiosis are illnesses ‘‘of a

reasonably serious nature.’’ There is no

question that each unit of exposure time is

important in contributing to the disease. I

think it would be illogical and unrealistic to

hold that a serious disease results from a long

series of insignificant and unsubstantial

exposures. Dr. Hodous testified that the

disease results from ‘‘an aggressive

accumulation of dust and every drop in the

bucket hurts.’’ How much the drop will hurt

may depend in part on the status of the

bucket when the drop falls. If the bucket is

full or nearly full, the drop may cause it to

overflow. If a miner has worked 20 or 30

years in an underground coal mine, a 2

month exposure to excessive dust may be

enough to cause the first signs of coal

workers’ pneumoconiosis, or to transform

simple pneumoconiosis to a complicated

form of the disease and possibly lead to

progressive massive fibrosis. If the bucket is

empty when the drop falls, in itself it won’t

mean much. If the miner exposed to

excessive dust for a 2-month period is a new

miner with healthy lungs, he probably will

not be adversely affected, if his exposure

stops. But if the exposure continues for 20

years (six 2-month periods each year), that

miner too will be at risk to contract black

lung.

I conclude that every drop in the bucket,

every two month sampling period where

excessive dust is present, significantly and

substantially contributes to a health hazard—

the hazard of contracting chronic bronchitis

or coal workers’ pneumoconiosis. (emphasis

added)

Consolidation Coal, 5 FMSHRC at 389–

90 (citations omitted) (footnotes

omitted). See also Consolidation Coal, 8

FMSHRC at 897 (‘‘There is no dispute,

however, that overexposure to

respirable dust can result in chronic

bronchitis and pneumoconiosis.’’) and

Consolidation Coal, 824 F.2d at 1086

(using the legislative history of the Mine

Act and the administrative law judge’s

‘‘drop in the bucket’’ analogy to strike

down the mine operator’s argument that

‘‘no single violation of the respirable

dust standard could ever be designated

as significant and substantial.’’).

While Consolidation Coal, supra,

dealt with overexposures identified

under the operator sampling program, it

is obvious that overexposures identified

from the MSHA inspector sampling

program similarly affect a miner’s

cumulative exposure to respirable coal

mine dust.

Thus, the same analogy would apply

to overexposures identified through

single, full-shift exposures. MSHA and

NIOSH firmly believe that

noncompliance determinations based on

single, full-shift measurement will

improve working conditions for miners

because mine operators will be

compelled either to implement and

maintain more effective dust controls to

minimize the chances of being found in

noncompliance by an MSHA inspector,

or to take corrective actions to lower

those dust concentrations that are

shown to be in excess of the applicable

standard.

To the extent that the use of single,

full-shift samples reduce a miner’s

cumulative exposure to respirable coal

mine dust, as compared to the current

method of dust sampling, it reduces a

miner’s risk of developing occupational

respiratory disease. The proposed

mandatory standard would provide for

fewer drops in each miner’s exposure

bucket. The health benefit that each

miner receives from this rule will vary

depending on ‘‘how full their bucket is’’

when the rule is implemented as well as

other mediating factors, such as the

percentage of quartz and rank of the

coal.

Yet, all miners, irrespective of their

cumulative exposure to respirable coal

mine dust, would benefit by having

fewer drops (i.e., shifts with

overexposures to respirable coal mine

dust) placed in their buckets over the

course of each miner’s working life

because this reduction would reduce

their occupational hazard—the risk of

developing simple CWP or PMF.

Therefore, the Agencies reiterate that

health benefits would accrue to miners

due to single, full-shift sample rule

alone even in the absence of a regulatory

requirement for a verified dust control

plan at each underground coal mine.

X. Issues Regarding Accuracy of a

Single, Full-shift Measurement

Some previous commenters

questioned the accuracy of single, fullshift measurements, and challenged the

Secretaries’ assessment of measurement

accuracy. Some commenters questioned

the Secretaries’ interpretation of section

202(b) of the Mine Act (30 U.S.C.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42089

842(b)), while others agreed with the

interpretation. The following issues

were generally raised: The measurement

objective as defined by the Mine Act;

the definition of the term ‘‘accurately

represent’’, as used in section 202(f) (30

U.S.C. 842(f)); the validity of the

sampling process; measurement

uncertainty and dust concentration

variability; and the accuracy of a single,

full-shift measurement.

A. Measurement Objective

Some previous comments reflected a

general misunderstanding of what the

Secretaries intend to measure with a

single, full-shift measurement, i.e., the

measurement objective. For example,

some previous commenters asserted that

the dust concentration that should be

measured is dust concentration

averaged over a period greater than a

single shift. Some previous commenters

noted that dust concentrations can vary

during a shift and that dust

concentrations are not uniform

throughout a miner’s work area. In order

to clarify the intent of the Secretaries,

the explanation that follows describes

the elements of the measurement

objective and how the measurement

objective relates to the requirements of

section 202(f).

To evaluate the accuracy of a dust

sampling method, it is necessary to

specify the airborne dust to be

measured, the time period to which the

measurement applies, and the area

represented by the measurement. Once

specified, these items can be combined

into a measurement objective. The

measurement objective represents the

goal of the sampling and analytical

method to be utilized.

1. The Airborne Dust to be Measured

Section 202(f) of the Mine Act (30

U.S.C. 842(f)) states that ‘‘average

concentration’’ means

* * * a determination [i.e., measurement]

which accurately represents the atmospheric

conditions with regard to respirable dust to

which each miner in the active workings of

a mine is exposed * * *

The phrase ‘‘atmospheric conditions’’ is

used to refer to the concentration of

respirable dust. Therefore, the airborne

dust to be measured is respirable dust.

Section 202(e) defines the concentration

of respirable dust as the dust measured

by an approved device.

2. Time Period to Which the

Measurement Applies

Section 202(b)(2) provides that each

mine operator ‘‘* * * shall

continuously maintain the average

concentra tion of respirable dust in the

mine atmosphere during each shift to

which each miner *; * * is exposed’’ at

or below the applicable standard. In

section 202(f) ‘‘average concentration’’

is defined as an atmospheric condition

measured ‘‘over a single shift only,

unless * * * such single shift

measurement will not, after applying

valid statistical techniques, accurately

represent such atmospheric conditions

during such shift.’’

Some previous commenters argued

that Congress intended that the

measurement objective be a long-term

average. Specifically, some of these

commenters stated that because coal

dust exposure is related to chronic

health effects, the exposure limit should

be applied to dust concentrations

averaged over a miner’s lifetime. These

commenters identified the measurement

objective as being the dust

concentration averaged over a long, but

unspecified, term and argued that a

single, full-shift measurement cannot

accurately estimate this long-term

average.

If the objective of section 202(b) were

to estimate dust concentration averaged

over a lifetime of exposure, then the

Secretaries would agree that a single,

full-shift sample, or even multiple

samples collected during a single

inspection, would not provide the basis

for an accurate measurement. Section

202(b) of the Mine Act (30 U.S.C.

842(b)), however, does not mention

long-term averaging, rather it explicitly

requires that the average dust

concentration be continuously

maintained at or below the applicable

standard during each shift (emphasis

added). Furthermore, in Consolidation

Coal Company v. Secretary of Labor 8

FMSHRC 890, (1986), aff’d 824 F.2d

1071, (D.C. Cir. 1987), the Commission

found that each episode of a miner’s

overexposure to respirable dust

significantly and substantially

contributes to the health hazard of

contracting chronic bronchitis or coal

workers’ pneumoconiosis, diseases of a

fairly serious nature.

If exposure is limited on each shift,

then this will ensure that a miner’s total

lifetime exposure will not be excessive.

In the context of the proposed finding,

the Secretaries have determined that

‘‘atmospheric conditions’’ means the

fluctuating concentration of respirable

coal mine dust during a single shift.

These are the atmospheric conditions to

which a miner at the sampling location

would be exposed. Therefore, the

proposed finding pertains only to the

accuracy in representing the average of

the fluctuating dust concentration over

a single shift.

3. Area Represented by the

Measurement

The Mine Act gives the Secretary of

Labor the discretion to determine the

area to be represented by respirable dust

measurements collected over a single

shift. Section 202(a) of the Mine Act (30

U.S.C. 842(a)) refers to ‘‘the amount of

respirable dust in the mine atmosphere

to which each miner in the active

workings of such mine is exposed’’

measured ‘‘* * * at such locations

* * *’’ as prescribed by the Secretary of

Labor. It is sufficient for the purposes of

the Mine Act that the sampler unit

accurately represent the amount of

respirable dust at such locations only.

As articulated by the United States

Court of Appeals for the 10th Circuit in

American Mining Congress (AMC) v.

Marshall, 671 F.2d 1251 (1982), the

Secretary of Labor may place the

sampler unit in any area or location

‘‘* * * reasonably calculated to prevent

excessive exposure to respirable dust.’’

Some previous commenters submitted

evidence that dust concentrations can

vary significantly near the mining face,

and that these variations may extend

into areas where miners are located.

That is, the average dust concentration

over a full shift is not identical at every

point within a miner’s work area. These

commenters submitted several bodies of

data purporting to show significant

discrepancies between simultaneous

dust concentration measurements

collected within a relatively small

distance of one another. Several

previous commenters maintained that

the measurement objective is, or should

be, to accurately measure the average

concentration within some arbitrary

sphere about the head of the miner, and

that multiple measurements within this

sphere are necessary to obtain an

accurate measurement.

The Secretaries recognize that dust

concentrations in the mine environment

can vary from location to location, even

within a small area near a miner. As

mentioned earlier, the Mine Act does

not specify the area that the

measurement is supposed to represent,

and the sampler unit may therefore be

placed in any location, reasonably

calculated to determine excessive

exposure to respirable dust.

Because the Secretary of Labor

intends to prevent excessive exposures

by limiting dust concentrations at every

location in the active workings, it is

sufficient that each measurement

accurately represent the respirable dust

concentration at the corresponding

sampling location only. Limiting the

dust concentration at every such

location ensures that no miner in the

42090 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

active workings will be exposed to

excessive respirable dust.

Several previous commenters

suggested that the measurement

objective should be a miner’s ‘‘true

exposure’’ or what the miner actually

inhales. The Secretaries do not intend to

use a single, full-shift measurement to

estimate any miner’s ‘‘true exposure,’’

because no sampling device can exactly

duplicate the particle inhalation and

deposition characteristics of a miner at

any work rate (these characteristics

change with work rate), let alone at the

various work rates occurring over the

course of a shift. Limiting the respirable

dust concentration at every location in

the active workings to which miners are

exposed ensures that the respirable dust

concentration actually inhaled by any

miner is limited.

4. Justification for the Proposed

Measurement Objective

A number of previous commenters

identified the dust concentration to be

estimated as either the mean dust

concentration over some period greater

than an individual shift, the mean dust

concentration over some spatially

distributed region of the mine, or a

‘‘grand mean’’ consisting of some

combination of the above. These

comments were based on the premise

that the measurement objective should

be something other than the average

atmospheric conditions during a single

shift at the sampling location. It is true

that the mean quantities described by

some commenters cannot accurately be

estimated using a single, full-shift

measurement, but the Secretaries make

no claim of doing so, nor do they

believe that a broader measurement

objective would be desirable for

enforcement purposes.

The Secretaries believe that MSHA’s

proposed use of single, full-shift

samples for enforcement purposes

would eliminate an important source of

sampling bias due to averaging, as

explained in Appendix A. Under

MSHA’s existing enforcement

procedures, measurements made at the

dustiest occupational locations or

during the dustiest shifts sampled are

diluted by averaging them with

measurements made under less dusty

conditions. This practice has frequently

caused failures to cite clear cases of

excessive dust concentration. Therefore,

the Secretaries believe that enforcement

based on averaging does not provide

miners with the greatest level of

protection possible under the current

exposure limit for respirable coal mine

dust.

Some previous commenters proposed

that MSHA continue to average at least

five separate measurements prior to

making a noncompliance determination.

They stated that abandoning this

practice would reduce the accuracy of

noncompliance determinations. Several

of these commenters maintained that

the average of dust measurements

obtained at the same occupational

location on different shifts more

accurately represents dust exposure to a

miner than a single, full-shift

measurement. These commenters

argued that not averaging measurements

would reduce accuracy to unacceptable

levels.

Other previous commenters agreed

with MSHA and NIOSH that the

averaging of multiple samples can dilute

and mask specific instances of

overexposure. Some of these

commenters stated that averaging not

only distorts the estimate of dust

concentration applicable to individual

shifts, but also biases the estimate of

exposure levels over a longer term.

According to these commenters, this is

because dust control measures and work

practices affecting dust concentrations

are frequently modified in response to

the presence of an MSHA inspector over

more than a single shift. These

commenters argued that the presence of

the MSHA inspector causes the mine

operator to be more attentive to dust

control than normal.

Section 202(b) of the Mine Act

currently requires each mine operator to

‘‘continuously maintain the average

concentration of respirable dust in the

mine atmosphere during each shift to

which each miner is exposed’’ at or

below the applicable standard. The

greater the variation in mining

conditions from shift to shift, the less

likely it is that a multi-shift average will

reflect the average dust concentration to

which a miner is exposed on any

individual shift. Appendix A contains

further discussion of this issue.

Accordingly, the Secretaries would

define the measurement objective to be

the accurate determination of the

average concentration of respirable dust

at a sampling location over a single

shift.

B. Accuracy Criterion

A ‘‘single shift measurement’’ means

the calculated dust concentration

resulting from a valid single, full-shift

sample of respirable coal mine dust. In

reviewing the various issues raised by

previous commenters, the Agencies

found that the term ‘‘accurately

represent,’’ as used in section 202(f) (30

U.S.C. 842(f)) in connection with a

single shift measurement, was not

defined in the Mine Act. Therefore, on

March 12, 1996, (61 FR 10012), the

Secretaries proposed to apply an

accuracy criterion developed and

adopted by NIOSH in judging whether

a single, full-shift measurement will

‘‘accurately represent’’ the full-shift

atmospheric dust concentration. The

NIOSH Accuracy Criterion requires that

measurements come within 25 percent

of the corresponding true dust

concentration at least 95 percent of the

time (Kennedy, et al., 1995). MSHA and

NIOSH again are proposing to use the

NIOSH Accuracy Criterion.

One previous commenter opposed the

application of the NIOSH Accuracy

Criterion since it ignores environmental

variability. For reasons explained above,

the Secretaries have restricted the

measurement objective to an individual

shift and sampling location. Therefore,

environmental variability beyond what

occurs at the sampling location on a

single shift would not be relevant to

assessing measurement accuracy.

For over 20 years, the NIOSH

Accuracy Criterion has been used by

NIOSH and others in the occupational

health professions to validate sampling

and analytical methods. This accuracy

criterion was devised as a goal for the

development and acceptance of

sampling and analytical methods

capable of generating reliable exposure

data for contaminants at or near the

Occupational Safety and Health

Administration’s (OSHA) permissible

exposure limits.

OSHA has frequently employed a

version of the NIOSH Accuracy

Criterion when issuing new or revised

single substance standards. For

example, OSHA’s benzene standard

provides: ‘‘[m]onitoring shall be

accurate, to a confidence level of 95

percent, to within plus or minus 25

percent for airborne concentrations of

benzene’’ (29 CFR 1910.1028(e)(6)).

Similar wording can be found in the

OSHA standards for vinyl chloride (29

CFR 1917), arsenic (29 CFR 1918), lead

(29 CFR 1925), 1,2-dibromo-3-

chloropropane (29 CFR 1044),

acrylonitrile (29 CFR 1045), ethylene

oxide (29 CFR 1047), and formaldehyde

(29 CFR 1048). Note that for vinyl

chloride and acrylonitrile, the accuracy

criterion for the method is ±35 percent

at 95 percent confidence at the

permissible exposure limit.

Some previous commenters

contended that the NIOSH Accuracy

Criterion does not conform with

international standards recently adopted

by the European Committee for

Standardization (CEN) (European

Standard No. EN 482, 1994). Contrary to

these assertions, the NIOSH Accuracy

Criterion not only conforms to the CEN

criterion but is, in fact, more stringent.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42091

The CEN criterion requires that 95

percent of the measurements fall within

±30 percent of the true concentration,

compared to ±25 percent under the

NIOSH criterion. Consequently, any

sampling and analytical method that

meets the NIOSH Accuracy Criterion

will also meet the CEN criterion.

Furthermore, EN 482 imposes no

control over inaccuracy in the

measurement of sampling and analytical

accuracy itself.

The NIOSH Accuracy Criterion is

relevant and widely recognized and

accepted in the occupational health

professions. Further, previous

commenters proposed no alternative

criteria for accuracy. Accordingly, for

purposes of section 202(f) of the Mine

Act (30 U.S.C.842(f)), the Secretaries

would consider a single, full-shift

measurement to ‘‘accurately represent’’

atmospheric conditions at the sampling

location, if the sampling and analytical

method used meets the NIOSH

Accuracy Criterion.

Several commenters suggested that

method accuracy should be determined

under actual mining conditions rather

than in a laboratory or in a controlled

environment. Although the NIOSH

Accuracy Criterion does not require

field testing, it recognizes that field

testing ‘‘does provide further test of the

method.’’ However, in order to avoid

confusing real differences in dust

concentration with measurement errors

when testing is done in the field,

‘‘precautions may have to be taken to

ensure that all samplers are exposed to

the same concentrations’’ (Kennedy, et

al., 1995). Similarly, the CEN criterion

for method accuracy specifies that

‘‘testing of a procedure shall be carried

out under laboratory conditions.’’

(European Standard No. EN 482, 1994)

To determine, so far as possible, the

accuracy of its sampling and analytical

method under actual mining conditions,

MSHA conducted 22 field tests in an

underground coal mine. To provide a

valid basis for assessing accuracy, 16

sampler units were exposed to the same

dust concentration during each field test

using a specially designed portable

chamber. The data from these field

experiments were used by NIOSH in its

‘‘direct approach’’ to determining

whether or not MSHA’s method meets

the long-established NIOSH Accuracy

Criterion. (See section X.E.2. of this

notice).

In response to the March 12, 1996

notice, a commenter claimed that the

supplementary information and

analyses introduced into the public

record by that notice addressed the

precision of a single, full-shift

measurement rather than its accuracy.

According to this commenter, by

focusing on precision, important

sources of systematic error had been

overlooked. The Secretaries agree with

the comment that precision is not the

same thing as accuracy. The accuracy of

a measurement depends on both

precision and bias (Kennedy, et al.,

1995). Precision refers to consistency or

repeatability of results, while bias refers

to a systematic error that is present in

every measurement. Since the NIOSH

Accuracy Criterion requires that

measurements consistently fall within a

specified percentage of the true

concentration, the criterion covers both

precision and uncorrectable bias.

Since the amount of dust present on

a filter capsule used by an MSHA

inspector is measured by subtracting the

pre-exposure weight from the postexposure weight, any bias present in

both weight measurements is

mathematically canceled out by

subtraction. Furthermore, as will be

discussed later, a control (i.e.,

unexposed) filter capsule has been and

would continue to be pre- and postweighed along with the exposed filter

capsules. The weight gain of the

exposed capsule would be adjusted by

the weight gain or loss of the control

filter capsule. Therefore, any bias that

may be associated with differences in

pre-and post-exposure laboratory

conditions, or with changes introduced

during storage and handling of the filter

capsules would also be mathematically

canceled out. Moreover, the

concentration of respirable dust is

effectively defined by section 202(e) of

the Mine Act (30 U.S.C. 842(e)) and the

implementing regulations in 30 CFR

parts 70, 71, and 90 to be whatever is

measured with an approved sampler

unit after multiplication by the MREequivalent conversion factor prescribed

by the Secretary of Labor. Therefore, the

Secretaries would conclude that the

improved sampling and analytical

method is statistically unbiased. This

means that such measurements contain

no systematic error. It should also be

noted that since any systematic error

would be present in all measurements,

measurement bias would not be reduced

by making multiple measurements.

Other comments regarding measurement

bias are addressed in Appendix B.

For unbiased sampling and analytical

methods, a standard statistic—called the

coefficient of variation (CV)—is used to

determine if the method meets the

NIOSH Accuracy Criterion. The CV,

which is expressed as either a fraction

(e.g., 0.05) or a percentage (e.g., 5

percent), quantifies measurement

accuracy for an unbiased method. An

unbiased method meets the NIOSH

Accuracy Criterion if the ‘‘true’’ CV is

no more than 0.128 (12.8 percent).

However, since it is not possible to

determine the true CV with 100-percent

confidence, the NIOSH Accuracy

Criterion contains the additional

requirement that there be 95-percent

confidence that measurements by the

method will come within 25 percent of

the true concentration 95 percent of the

time. Stated in mathematically

equivalent terms, an unbiased method

meets the NIOSH Accuracy Criterion if

there is 95-percent confidence that the

true CV is less than or equal to 0.128

(12.8 percent).

C. Validity of Sampling Process

A single, full-shift measurement of

respirable coal mine dust is obtained

with an approved sampler unit, which

is either worn or carried by the miner

directly to and from the sampling

location and remains operational during

the entire shift or for eight hours,

whichever time is less. A portable,

battery-powered pump draws dustladen mine air at a flow rate of 2 liters

per minute (L/min) through a 10-mm

nylon cyclone, a particle-size selector

that removes non-respirable particles

from the airstream. Non-respirable

particles tend to be removed from the

airstream by the nose and upper

respiratory airways. Such particles fall

to the bottom of the cyclone body called

the ‘‘grit pot,’’ while smaller, respirable

particles (of the size that would

normally enter into the lungs) pass

through the cyclone, directly into the

inlet of the filter cassette. This airstream

is directed through the pre-weighed

filter leaving the particles deposited on

the filter surface. This collection filter is

enclosed in an aluminum capsule to

prevent leakage of sample air around the

filter and the loss of any dust dislodged

due to impact. The filter capsule is

sealed in a protective plastic enclosure,

called a cassette, to prevent

contamination. After completion of

sampling, the filter cassette is sent to

MSHA’s Respirable Dust Processing

Laboratory in Pittsburgh, Pennsylvania,

where it is weighed to determine the

weight gain in milligrams or the amount

of dust collected on the filter surface.

The concentration of respirable dust,

expressed as milligrams per cubic meter

(mg/m3) of air, is determined by

dividing the observed weight gain by

the volume of mine air passing through

the filter and then multiplying this

quantity by a conversion factor

(discussed in Appendix B) prescribed

by the Secretaries.

Some previous comments generally

addressed the quality and reliability of

the equipment used for sampling.

42092 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

Specific concerns were expressed about

the quality of filter cassettes and the

reliability of sampling pumps used by

MSHA inspectors, due to their age and

condition. Other commenters

questioned the effect of sampling and

work practices on the validity of a

sample.

The validity of the sampling process

is an important aspect of maintaining

accurate measurements. Since passage

of the Coal Act, there has been an

ongoing effort by MSHA and NIOSH to

improve the accuracy and reliability of

the entire sampling process. In 1980,

MSHA issued new regulations revising

sampling, maintenance and calibration

procedures in 30 CFR parts 70, 71, and

90. These regulatory provisions were

designed to minimize human and

mechanical errors and ensure that

samples collected with approved

sampler units in the prescribed manner

would accurately represent the fullshift, average atmospheric dust concen

tration at the location of the sampler

unit. These provisions require: (1)

Certification of competence of all

individuals involved in the sampling

process and in maintaining the

sampling equipment; (2) calibration of

each sampler unit at least every 200

hours; (3) examination, testing, and

maintenance of units before each

sampling shift to ensure that the units

are in proper working order; and (4)

checking of sampler units during

sampling to ensure that they are

operating properly and at the proper

flow rate. In addition, significant

changes, such as robotic weighing and

the use of electronic balances were

made in 1984, 1994, and 1995 that

improved the reliability of sample

weighings at MSHA’s Respirable Dust

Processing Laboratory. These changes

are discussed below in section X.C.3.

All of these efforts improved the

accuracy and reliability of the sampling

process since the time of the 1971/1972

proposed and final findings. A

discussion follows concerning the three

elements which constitute the sampling

process: sampler unit performance,

collection procedures, and sample

processing.

1. Sampler Unit Performance

In accordance with the provisions of

section 202(e) of the Mine Act (30

U.S.C. 842(e)), NIOSH administers a

comprehensive certification process

under 30 CFR part 74 to approve dust

sampler units for use in coal mines. To

be approved for use, a sampler unit

must meet stringent technical and

performance requirements governing the

quantity of respirable dust collected and

flow rate consistency over an 8-hour

period when operated at the prescribed

flow rate. As necessary, NIOSH also

conducts performance audits of

approved sampler units purchased on

the open market to determine if the

units are being manufactured in

accordance with the specifications upon

which the approval was issued.

The system of technical and quality

assurance checks currently in place is

designed to prevent a defective sampler

unit from being manufactured and made

commercially available to the mining

industry or to MSHA. In the event that

these checks identify a potential

problem with the manufacturing

process, established procedures require

immediate action to correct the

problem.

In 1992, NIOSH approved the use of

new tamper-resistant filter cassettes

with features that enhanced the integrity

of the sample collected. A backflush

valve was incorporated into the outlet of

the cassette, preventing reverse airflow

through the filter cassette, and an

internal flow diverter was added to the

filter capsule, reducing the possibility of

dust dislodged from the filter surface

from falling out of the capsule inlet.

Also, in 1999, based on recent MSHA

studies, Kogut, et al. (1999), involving

the weighing stability of the current

filter design and in an effort to

standardize the manufacturing process,

the filter cassette manufacturer

submitted for NIOSH approval a

modification to the current design. The

change involves replacing the Tyvek’’

support pad with a stainless steel wheel,

similar to the one located on the inlet

side of the collection filter. A similar

modification was incorporated in

sampling filters employed by OSHA

over the past several years. Upon

NIOSH approval, the new cassette

would be used in MSHA inspector

sampling, thereby improving the

stability of sample weights.

Several previous commenters

questioned the quality of the filter

cassettes used in the sampling program,

expressing concern as to whether the

cassettes always meet MSHA

specifications. These concerns primarily

involve filter-to-foil distance and

floppiness of the filters, which are

manufacturing characteristics specific to

filters and filter capsules, not related to

part 74 performance requirements. The

Secretaries believe that such

characteristics would have no effect on

the accuracy of a single, full-shift

measurement because, unlike the part

74 requirements, they would not affect

the amount of dust deposition.

Previous commenters also questioned

the condition of sampling pumps used

by MSHA inspectors, stating that many

of the pumps are 10 to 20 years old and

are not maintained as well as they could

be. They claimed that the age and

condition of these pumps call into

question not only whether the sampling

equipment could meet part 74

requirements if tested, but also the

accuracy of the measurement.

MSHA believes that this concern is

unwarranted, since in 1995, MSHA

replaced all pumps in use by inspectors

with new constant-flow pumps that

incorporate the latest technology in

pump design. These pumps provide

more consistent flow throughout the

sampling period. In addition to using

new pumps, inspection procedures

require MSHA inspectors to make a

minimum of two flow rate checks to

ensure that the sampler unit is operating

properly. A sample is voided if the

proper flow rate was not maintained

during the final check at the conclusion

of the sampling shift. In fiscal year 1998,

only 151 samples or 0.4 percent of the

37,042 inspector samples processed

were voided because the sampling

pump either failed to operate

throughout the entire sampling period

or failed to maintain the proper flow

rate during the final check. Units found

not meeting the requirements of part 74

are immediately repaired, adjusted, or

removed from service. Nevertheless,

MSHA recognizes that as these pumps

age, deterioration of the performance of

older pumps could become a concern.

However, there is no evidence that the

age of the equipment affects its

operational performance if the

equipment is maintained as prescribed

by 30 CFR parts 70, 71, and 90.

Some previous commenters suggested

that the accuracy of a dust sample may

be compromised when a miner is

operating equipment, due to vibration

from the machinery. The potential effect

of vibration on the accuracy of a

respirable dust measurement was

recognized by NIOSH in 1981. An

investigation, supported by NIOSH, was

conducted by the Los Alamos National

Laboratory which found that vibration

has an insignificant effect on sampler

performance (Gray and Tillery, 1981).

2. Sample Collection Procedures

MSHA regulations at 30 CFR parts 70,

71, and 90 prescribe the manner in

which mine operators are to take

respirable dust samples. The collection

procedures are designed to ensure that

the samples accurately represent the

amount of respirable dust in the mine

atmosphere to which miners are

exposed on the shift sampled. Samples

taken in accordance with these

procedures are considered to be valid.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42093

17 If a control filter either shows a weight gain

greater than 100 micrograms (μg) or a weight loss

greater than 30 μg, the control filter is voided and

the concentration measurement(s) are not used for

enforcement purposes.

Several previous commenters

questioned the effects of sampling and

work practices on the validity of a

sample. Instances were cited where the

sampling unit was accidentally

dropped, with the potential for the

sample to become contaminated.

Previous commenters also pointed out

that work activities requiring crawling,

duck walking, bending, or kneeling

could cause the sampling hose to snag.

Such activities could also cause the

sampling head assembly to be impacted

or torn off a person’s garment, possibly

contaminating the sample. These

commenters stated that sampler units

are sometimes treated harshly while

being worn by miners, mishandled

when being transferred from one miner

to another, or handled casually at the

end of a work shift.

These commenters also maintained

that it is impossible for MSHA

inspectors or mine operators to

continuously observe collection of a

sample in order to ensure its validity,

and that, for this reason, the reliability

and accuracy of the sampling

equipment, when used under actual

mining conditions, is not the same as

when tested and certified in a

laboratory. Averaging multiple samples

would, according to these commenters,

provide some ‘‘leeway’’ in the system,

by reducing the impact of an aberrant

sample.

While MSHA and NIOSH would agree

that it is not possible to continuously

observe the collection of each sample,

MSHA inspectors are normally in the

general vicinity of the sampling

location, and therefore would have

knowledge of the specific conditions

under which samples are taken. In

addition, MSHA inspectors are

instructed to ask miners wearing the

sampler units whether anything that

could have affected the validity of the

sample occurred during the shift. If so,

the inspector would note this on the

data card and request that the sample be

examined to determine its validity.

Other previous commenters expressed

concern that, if special dust control

measures are in effect during sampling,

a single, full-shift measurement may fail

to represent atmospheric conditions

during shifts when samples are not

collected. The Secretaries believe that

this concern is beyond the scope of this

new proposal, which, as described in

the discussion of measurement

objective, deals solely with the accuracy

of a measurement in representing

atmospheric conditions on the shift

being sampled. One previous

commenter recommended that MSHA,

NIOSH, or the Bureau of Mines (now a

part of NIOSH) should evaluate the need

for standardizing the MSHA respirable

dust sampling procedures. In fact, the

procedures for respirable dust sampling

have already been standardized under

the revised 1980 MSHA regulations

codified at 30 CFR parts 70, 71 and 90.

As previously mentioned, as part of

the ISSEP discussion, MSHA inspectors

are also using unexposed control filters

to eliminate any bias that may be

associated with day-to-day changes in

laboratory conditions or introduced

during storage and handling of the filter

capsules. A control filter is an

unexposed filter that was pre-weighed

on the same day as the filter used for

sampling. This control filter is used to

adjust the weight gain obtained on each

exposed filter. Any change in weight of

the control filter is subtracted from the

change in weight of each exposed filter.

MSHA began using control filters on

May 7, 1998, with the implementation

of the ISSEP, and has continued this

practice, even after reverting back to

basing noncompliance determinations

on an average of multiple samples

following the ruling of the 11th Circuit

Court of Appeals discussed earlier. The

control filter, which is carried by the

inspector in a shirt or coverall pocket

during the sampling inspection, is

plugged to prevent exposure to the mine

environment. The experience gained

from the use of control filters under

ISSEP is discussed in section V.D.

Also, once NIOSH approves the

modified design mentioned earlier,

MSHA inspectors would use only filters

incorporating a stainless steel support

wheel. These filters, according to MSHA

studies, demonstrated better weighing

stability as compared to filters

employing Tyvek material for the

support pad.

3. Sample Processing

Sample processing consists of

weighing the exposed and control

(unexposed) filters, recording the weight

changes, and examining certain samples

in order to verify their validity. Sample

processing also includes electronic

transmission of the results to MSHA’s

MIS center where dust concentrations

are computed. The results are then

transmitted to MSHA enforcement

personnel and to mine operators.

(a) Weighing and Recording Procedures

The procedures and analytical

equipment, as well as the facility used

by MSHA to process respirable coal

mine dust samples have been

continuously improved since 1970 to

maintain a state-of-the-art laboratory.

From 1970 to 1984, samples were

manually weighed using semimicro

balances. This process was automated in

1994 with the installation of a state-ofthe-art robotic system and electronic

balances, which increased the precision

of sample-weight determinations.

Weighing precision was further

improved in 1994, when both the

robotic system and balances were

upgraded. Also, beginning in early 1998,

all respirable coal mine dust samples

were being processed in a new,

specially designed clean room facility

that maintains the temperature and

humidity of the environment at 72 ±2°F

and 50 ±5%, respectively. Using a

modified HEPA filtration system, the

environment is maintained at a clean

room classification of 1000 (near

optimum for clean room cleanliness).

The full benefit of the 1994

improvements of the weighing system

for inspector samples was, however, not

attained until mid-1995, when MSHA

implemented two modifications to its

procedures for processing inspector

samples. One modification involved

pre- and post-weighing filter capsules to

the nearest microgram (0.001 mg) within

MSHA’s laboratory. Prior to mid-1995,

filters had been weighed in the

manufacturer’s (Mine Safety and

Appliances Co.) laboratory before

sampling, and then in MSHA’s

laboratory after sampling. MSHA is

currently pre-weighing all such filters in

its own laboratory. To maintain the

integrity of the weighing process, eight

percent of all filters are systematically

weighed a second time. If a significant

deviation is found, the balance is

recalibrated and all filters with

questionable weights are reweighed.

The other modification was to

discontinue the practice of truncating

(to 0.1 mg) the recorded weights used in

calculating dust concentrations. This

means that MSHA is now using all

significant digits associated with the

weighing capability of the balance

(0.001mg) when processing inspector

samples. These modifications improved

the overall accuracy of the measurement

process.

To eliminate the potential for any bias

that may be associated with day-to-day

changes in laboratory conditions or

introduced during storage and handling

of the filters, MSHA is also using

control filters in its enforcement

program. Any change in the weight of

the control filter is subtracted from the

measured change in weight of the

exposed filter.17

Since MSHA began pre- and postweighing filters to the nearest μg, coal

42094 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

mine operators have asked to use filters

pre-weighed to a μg to collect optional

samples that they submit to MSHA for

quartz analysis. The use of these preweighed filters would eliminate the

need to sample multiple shifts in order

to obtain sufficient dust mass on the

collection filter for quartz analysis.

Currently, filters used by coal mine

operators to sample in accordance with

30 CFR parts 70, 71, and 90 are preweighed by the filter manufacturer,

Mine Safety Appliances Co., to the

nearest 10 μg. Therefore, only samples

taken with filters preweighed to the

nearest 10 μg, with a net weight gain of

at least 450 μg, contain sufficient dust

mass to permit the percentage of quartz

to be determined.

In 1996, Mine Safety Appliances

Company upgraded their equipment

used to pre-weigh filter capsules and

now uses the same balance as MSHA’s

Coal Dust Processing Laboratory,

thereby permitting weight

determinations to be made to the nearest

μg.

The requirement that inspector

samples be pre- and post-weighed in the

same laboratory was developed prior to

adopting control filters and was based

on the assumption that no control filters

were being used. Since use of the

control filters adjusts for differences that

may exist in laboratory conditions on

the days of pre- and post-weighing, it is

no longer necessary to pre- and postweigh the filters in the same laboratory.

To determine the viability of using

exposed filters pre-weighed by Mine

Safety Appliances Co. and post-weighed

by MSHA in establishing the percentage

of quartz, the Agency conducted a study

to quantify weighing variability between

the Mine Safety Appliances Co. and

MSHA laboratories (Parobeck, et al.,

1997). Based on this study, the overall

imprecision of an interlaboratory

weight-gain measurement was estimated

to be 11.5 for capsules with a stainless

steel filter support pad. This estimate

closely matches the 11.6 result reported

for capsules with stainless steel support

pads in a more recent study (Kogut, et

al., 1999). In this more recent study,

unexposed capsules were pre-weighed

by MSHA, assembled into cassettes by

Mine Safety Appliances Co., sent out to

the field and carried during an

inspection, and then post-weighed by

MSHA.’’

Using the higher of these two

estimates, NIOSH has reassessed the

accuracy of MSHA’s improved sampling

and analytical method, which

incorporates a control filter adjustment

and employs filter capsules with a

stainless steel support pad. NIOSH has

concluded that the control filter

adjustment will correct for any potential

biases due to differences in laboratory

conditions, so that it is no longer

necessary to pre- and post-weigh filter

capsules in the same laboratory

(Grayson, 1999b). Therefore, in

accordance with NIOSH, MSHA is

proposing to change the existing

processing procedures for inspector

samples from pre- and post-weighing in

the same laboratory (with adjustment by

a control filter) to pre- and postweighing of samples to the nearest μ in

different laboratories (with continued

adjustment by a control filter). The

Agencies would welcome comments on

this proposed change.

To insure the precision and accuracy

of the pre-weight of filters used by

inspectors, MSHA plans to institute a

program to monitor the daily production

of filters weighed to the nearest μg by

the manufacturer. The program will

conform to MIL–STD–105D, which

defines the criteria currently used to

monitor the quality of pre-weighed

filters used in MSHA’s operator

sampling program.

(b) Sample Validity Checks

All respirable dust samples collected

and submitted as required by 30 CFR

parts 70, 71, and 90 are considered valid

unless the dust deposition pattern on

the collection filter appears to be

abnormal or other special circumstances

are noted that would cause MSHA to

examine the sample further. Several

previous commenters expressed concern

about the potential contamination of

samples with ‘‘oversized particles.’’

Such contamination, according to one

commenter, can result in aberrational

weight gains. These commenters noted

that current procedures do not

systematically ensure that samples

collected by MSHA contain no

oversized particles. It was

recommended that MSHA analyze, for

the presence of oversized particles, any

dust sample that exceeds the applicable

dust standard. Also suggested for such

an analysis was any sample with a

weight gain significantly different from

other samples taken in the same area.

Standard laboratory procedures,

involving visual, and microscopic

examination as necessary, are used to

verify the validity of samples. Samples

with a weight gain of 1.4 milligrams (μg)

or more are examined visually for

abnormalities such as the presence of

large dust particles (which can occur

from agglomeration of smaller particles),

abnormal discoloration, abnormal dust

deposition pattern on the filter, or any

apparent contamination by materials

other than respirable coal mine dust.

Also examined are samples weighing

0.1 mg or less for insufficient dust

particle count. Similar checks are also

performed in direct response to specific

inspector or operator concerns noted on

the dust data card to which each sample

is attached.

The previous commenters’ concerns

about the contamination of samples

with oversized particles are based on

the assumption that all oversized

particles, defined as dust particles

greater than 10 micrometers (μm) in

size, are not respirable and therefore

should be totally excluded from any

sample taken with an approved sampler

unit. However, it has long been known

that some particles greater than 10 μ can

be inhaled, and that some of these

particles can reach the alveoli of the

lungs (Lippman and Albert, 1969).

According to the British National Coal

Board, ‘‘particles as large as 20 microns

(i.e. micrometers) mean diameter may

be deposited, although most ‘‘lung dust’’

lies in the range below 10 microns

diameter’’ (Goddard, et al., 1973).

Furthermore, it is known that, due to

the irregular shapes of dust particles,

the respirable dust collected by the MRE

instrument (the dust sampler used by

the British Medical Research

Establishment in the epidemiological

studies on which the U.S. coal dust

standard was based) may include some

dust particles as large as 20 micrometers

(Goddard, et al., 1973). Moreover,

MSHA studies have shown that nearly

all samples taken with approved

sampler units, even when operated in

the prescribed manner, contain some

oversized particles (Tomb, August 31,

1981). Since section 202(e) of the Mine

Act (30 U.S.C. 842(e)) defines

concentration of respirable dust to be

that measured by an approved sampler

unit, and because the approved sampler

unit will collect some oversized

particles, the Secretaries do not consider

a sample to be ‘‘contaminated’’ because

it contains some oversized particles.

The Secretaries recognize that there

are occasions when oversized particles

can properly be considered a

contaminant. For example, an excessive

number of such particles could enter the

filter capsule if the sampling head

assembly is accidentally or deliberately

turned upside down or ‘‘dumped’’

(possibly causing some of the contents

of the cyclone grit pot to be deposited

on the collection filter), if the pump

malfunctions, or if the entire sampler

unit is dropped. When MSHA has

reason to believe that such

contamination has occurred, the suspect

sample is examined to verify its

validity.

Contrary to the assertions of some

previous commenters, checking for

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42095

18Although MSHA and NIOSH accept the finding

presented by Nicas, et al. (1991) that environmental

variability generally exceeds analytical variability,

the Agencies do not accept the authors’ conclusions

with regard to how this finding should affect

enforcement policy.

oversized particles is not standard

industrial hygiene practice.

Nevertheless, MSHA checks any dust

sample suspected of containing an

excessive number of oversized particles.

MSHA’s laboratory procedures require

any sample exhibiting an excessive

weight gain (over 6 mg) or showing

evidence of being ‘‘dumped’’ to be

examined for the presence of an

excessive number of oversized particles

(MSHA Method P–4, August 1989).

Samples identified by an inspector or

mine operator as possibly contaminated

are also examined. If this examination

indicates that the sample contains an

excessive number of oversized particles

according to MSHA’s established

criteria, then that sample is considered

to be invalid, is voided and not used. In

fiscal year 1998, only one sample of the

37,042 inspector samples processed was

found to contain an excessive number of

oversize particles and thus was not

used.

While rough handling of the sampler

unit or an accidental mishap could

conceivably cause a sample with a

weight gain less than 6 mg to become

contaminated, as claimed by some

previous commenters, studies show that

short-term accidental inclinations of the

cyclone will not affect respirable mass

measurements made with currently

approved sampler units (Treaftis and

Tomb, 1974). Sampler units currently

used are built to withstand the rigors of

the mine environment, and are therefore

less susceptible to contamination than

suggested by some previous

commenters. In any event, the

Secretaries believe that the validity

checks currently in place, as discussed

above, would detect such samples.

D. Measurement Uncertainty and Dust

Concentration Variability

Overall variability in measurements

collected on different shifts and

sampling locations comes from two

sources: (1) Environmental variability in

the true dust concentration and (2)

errors in measuring the dust

concentration in a specific environment.

The major portion of overall

measurement variability reflects real

variability in dust concentration on

different shifts or at different sampling

locations (Nicas, et al., 1991).18

Variability in the dust concentration

is under the control of the mine operator

and does not depend on the degree to

which the dust concentration can be

accurately measured. Measurement

uncertainty, on the other hand, stems

from the differing measurement results

that could arise, at a given sampling

location on a given shift, because of

potential sampling and analytical errors.

Therefore, unlike variability in dust

concentration, measurement uncertainty

depends directly on the accuracy of the

measurement system. Measurement

errors generally contribute only a small

portion of the overall variability

observed in datasets consisting of dust

concentration measurements.

Numerous previous commenters

identified sources of measurement

uncertainty and dust concentration

variability that they believed should be

considered when determining whether

or not a measurement accurately

represents such atmospheric conditions.

Because the measurement objective is to

accurately represent the average dust

concentration at the sampling location

over a single shift, it does not take into

consideration dust concentration

variability between shifts or locations.

Sources of dust concentration variability

would not be considered by the

Secretaries in determining whether a

measurement is accurate. Consequently,

the Secretaries have concluded that the

only sources of variability relevant to

establishing accuracy of a single, fullshift measurement for purposes of

section 202(f) of the Mine Act (30 U.S.C.

842(f)) would be those related to

sampling and analytical error.

1. Sources of measurement uncertainty

Filter capsules are weighed prior to

sampling. After a single, full-shift

sample is collected, the filter capsule is

weighed a second time, and the weight

gain (g) is obtained by subtracting the

pre-exposure weight from the postexposure weight, which will then be

adjusted for the weight gain or loss

observed in the control filter capsule. A

measurement (x) of the atmospheric

condition sampled is then calculated by

Equation 1:

x g

v = ⋅ ( ) 138 1 .

where:

x is the single, full-shift dust

concentration measurement (mg/

m3);

1.38 is a constant MRE-equivalent

conversion factor; g is the observed

weight gain (mg) after adjustment

for the control filter capsule; and

v is the estimated total volume of air

pumped through the filter during a

typical full shift.

The Secretaries recognize that random

variability, inherent in any

measurement process, may cause x to

deviate either above or below the true

dust concentration. The difference

between x and the true dust

concentration is the measurement error,

which may be either positive or

negative. Measurement uncertainty

arises from a combination of potential

errors in the process of collecting a

sample and potential errors in the

process of analyzing the sample. These

potential errors introduce a degree of

uncertainty when x is used to represent

the true dust concentration.

The statistical measure used by the

Secretaries to quantify uncertainty in a

single, full-shift measurement is the

total sampling and analytical coefficient

of variation, or CVtotal. The CVtotal

quantifies the magnitude of probable

sampling and analytical errors and is

expressed as either a fraction (e.g., 0.05)

or as a percent (e.g., 5 percent) of the

true concentration. For example, if a

single, full-shift measurement (x) is

collected in a mine atmosphere with

true dust concentration equal to 1.5 mg/

m3, and the standard deviation of

potential sampling and analytical errors

associated with x is equal to 0.075 mg/

m3, the uncertainty associated with x

would be expressed by the ratio of the

standard deviation to the true dust

concentration: CVtotal = 0.075/1.5 = 0.05,

or 5 percent.

Based on a review of the scientific

literature, the Secretaries in their March

12, 1996 notice concerning the NIOSH

Accuracy Criterion identified three

sources of uncertainty in a single, fullshift measurement, which together make

up CVtotal:

(a) CVweight—variability attributable to

weighing errors or handling associated

with exposed and control filter

capsules. This covers any variability in

the process of weighing the exposed or

control filter capsules prior to sampling

(pre-weighing), assembling the exposed

and control filter cassettes, transporting

42096 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

19The rotameter consists of a weight or ‘‘float’’

which is free to move up and down within a

vertical tapered tube which is larger at the top than

the bottom. Air being drawn through the filter

cassette passes through the rotameter, suspending

the ‘‘float’’ within the tube. The pump is

‘‘calibrated’’ by drawing air through a calibration

device (usually what is known as a bubble meter)

at the desired flow rate and marking the position

of the float on the tube. The processes of marking

the position on the tube (laboratory calibration) and

adjusting the pump speed in the field so that the

float is positioned at the mark are both subject to

error.

the filter cassettes to and from the mine,

and weighing the exposed and control

filter capsules after sampling (postweighing).

(b) CVpump—variability in the total

volume of air pumped through the filter

capsule. This covers variability

associated with calibration of the pump

rotameter, 19 variability in adjustment of

the flow rate at the beginning of the

shift, and variation in the flow rate

during sampling. It should be noted that

variation in flow rate during sampling

was identified as a separate component

of variability in MSHA’s February 18,

1994, notice. Here, it is included within

CVpump.

(c) CVsampler—variability in the

fraction of dust trapped on the filter.

This is attributable to physical

differences among cyclones. This

component was introduced in the

material submitted into the record in

September 1994.

These three components of

measurement uncertainty can be

combined to form an indirect estimate

of CVtotal by means of the standard

propagation of errors formula:

CV CV total weight = + 2 + CV CV pump 2 2

sampler

2 ( )

These three components are discussed

in greater detail, along with responses to

specific previous comments, in

Appendix B.

2. Sources of Dust Concentration

Variability

Previous commenters also raised

issues related to sources of dust

concentration variability. Some of these

commenters maintain that the

Secretaries should include in CVtotal

additional components representing the

effects of shift-to-shift variability and

variability related to location (spatial

variability). These comments reflect a

misunderstanding of the measurement

objective as intended by the Mine Act

(see Section X.A. of this notice).

Exposure variability due to job,

location, shift, production level,

effectiveness of engineering controls,

and work practices will be different

from mine to mine. This type of

variability has nothing to do with

measurement accuracy and depends on

factors under the control of the mine

operator. The sampler unit is not

intended to account for these factors.

(a) Spatial Variability

Previous commenters stated that

CVtotal should account for spatial

variability, or the differences in

concentration related to location. The

Secretaries agree that dust

concentrations vary between locations

in a coal mine, even within a relatively

small area. However, real variations in

concentration between locations, while

sometimes substantial, do not contribute

to measurement error. As stated earlier,

the measurement objective would be to

accurately measure average atmospheric

conditions, or concentration of

respirable dust, at a sampling location

over a single shift.

(b) Shift-to-shift Variability

Previous commenters stated that

CVtotal should take into account the

differences or variations in dust

concentration that occur shift to shift.

Although the Secretaries would agree

that dust concentrations vary from shift

to shift, the measurement objective is to

measure average atmospheric conditions

on the specific shift sampled. This

result would be consistent with the

Mine Act, which requires that

concentrations of respirable mine dust

be maintained at or below the

applicable standard during each shift.

3. Other Factors Considered

(a) Proportion of Oversized Particles

Previous commenters expressed

concern that respirable dust cyclones

are handled in a rough manner in

normal use and occasionally turned

upside down. According to one

commenter, this type of handling would

cause more large particles to be

deposited on the filter in the mine

environment than when used in the

laboratory. This commenter knew of no

data that could be used to evaluate the

error associated with such occurrences

and recommended that a study be

commissioned to measure the

proportion of non-respirable particles

on the filters after they are weighed to

MSHA standards.

After considering this

recommendation, the Secretaries would

conclude that the available evidence

shows that short-term inclinations of the

cyclone, as might frequently occur

during sampling, will not affect

respirable dust measurements made

with approved sampler units (Treaftis

and Tomb, 1974). The weight of the

sampler head assembly makes it

extremely unlikely that a sampler unit

could be turned upside down in normal

use. Furthermore, with a field study of

the type recommended, variability in

the field measurements due to normal

handling would be confounded with

variability due to real differences in

atmospheric conditions. Therefore, the

Secretaries believe that such a study

would not be useful in establishing

variability in measurements due to

differences in handling of the sampler

unit.

(b) Anomalous Events

Previous commenters asserted that

unpredictable, infrequent events, such

as a ‘‘face blowout’’ on a longwall (a

violent expulsion of coal together with

large quantities of coal dust and/or

methane gas) or high winds at a surface

mine, can cause rapid loading of a filter

capsule and thereby distort a

measurement to show an excessive dust

concentration based on a single, fullshift sample when, they argue, the dust

standard had not been exceeded. In fact,

if such an occurrence were to cause a

measurement above the applicable

standard, the dust standard would be

violated. No evidence was previously

presented to demonstrate that shortterm high exposures can overload a dust

sampling filter or cause the sampling

device to malfunction. Nor was

evidence presented to demonstrate that

miners are not also exposed to the same

high dust concentrations as the sampler

unit when such events occur. The

Secretaries would conclude that such

events are results of the dynamic and

ever-changing mine environment—an

environment to which the miner is

exposed. The sampler unit is designed

to measure the atmospheric condition at

a specific sampling location over a full

shift. If such events occur, the sampler

unit will accurately record the

atmospheric condition to which it is

exposed.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42097

20Many of the recommendations in the GAO

report were later adopted and implemented by

MSHA.

(c) MRE Conversion Factor Used in the

Dust Concentration Calculation

Several previous commenters

questioned the 1.38 MRE-conversion

factor used in Equation 1. This factor is

used to convert a measurement obtained

with the type of dust sampler unit

currently approved for use in coal mines

to an equivalent concentration as

measured with an MRE gravimetric dust

sampler. The term ‘‘MRE instrument’’ is

defined in 30 CFR § 70.2 (i). The

conversion factor is necessary because

the coal mine dust standard was derived

from British data collected with an MRE

instrument, which collects a larger

fraction of coal mine dust than does the

approved dust sampling unit (Tomb, et

al., 1973). The 1.38 constant has been

established by the Secretaries as

applying to the currently approved dust

sampler unit described in 30 CFR part

74.

Some previous commenters

contended that variability involved in

the data analysis used in establishing

the conversion factor should be taken

into account in determining CVtotal. This

suggestion demonstrates a

misunderstanding of the difference

between measurement imprecision and

measurement bias. The 1.38 factor

applies to every sampler unit currently

approved under part 74. Since the same

conversion factor is applied to every

measurement, any error in the value

used would cause a measurement bias

but would have no effect on

measurement imprecision. Since

Congress defined respirable dust in

section 202(e) of the Mine Act (30

U.S.C. 842(e)) as whatever is collected

by a currently approved sampler unit, a

measurement incorporating the 1.38

factor is unbiased by definition. Further

discussion is provided in Appendix B

on why use of the 1.38 factor does not

introduce a bias. Appendix B also

addresses comments relating to other

aspects of the 1.38 conversion factor;

comments regarding the fact that

MSHA’s sampler unit does not conform

to other definitions of respirable dust;

and questions concerning the effect of

static charge on sampler unit

performance.

(d) Reduced Dust Standards

One commenter pointed out that in

estimating CVtotal, MSHA and NIOSH

did not take into account any potential

errors associated with silica analysis.

The commenter argued that since silica

analysis is used to establish reduced

dust standards, MSHA and NIOSH had

failed to demonstrate ‘‘* * * accuracy

for all samples ‘across the range of

possible reduced dust standards.’’ ’

This commenter confuses the

accuracy of a respirable dust

concentration measurement with the

accuracy of the procedure used to

establish a reduced dust standard.

MSHA has a separate program in which

silica analysis is used to set the

applicable respirable coal mine dust

standard, in accordance with section

205 of the Mine Act (30 U.S.C. 845),

when the respirable dust in the mine

atmosphere of the active workings

contains more than 5 percent quartz. As

shown by Equation 1, no silica analysis

is used in a single, full-shift

measurement of the respirable dust

concentration. Therefore, the Secretaries

would not agree with the comment that

CVtotal should include a component

representing potential errors in silica

analysis.

(e) Dusty Clothing

Several previous commenters pointed

out that local factors such as dusty

clothing could cause concentrations in

the immediate vicinity of the sampler

unit to be unrepresentative of a larger

area. Dust from a miner’s clothing

nevertheless represents a potential

hazard to the miner. No evidence was

previously presented to demonstrate

that miners are not also exposed to dust

originating from dusty clothing.

E. Accuracy of a Single, Full-shift

Measurement

1. Quantification of Measurement

Uncertainty

Several previous commenters argued

that MSHA underestimated CVtotal in its

February 18, 1994 proposed notice of

Joint Finding and suggested alternative

estimates ranging from 16 to 50 percent.

These commenters cited several

published studies and submitted five

sets of data in support of these higher

estimates. Statistical analyses of the data

were also submitted.

MSHA and NIOSH reviewed all of the

studies referenced by the previous

commenters. The review showed that all

of the estimates of measurement

variability were from studies carried out

prior to improvements mandated by the

1980 MSHA revisions to dust sampling

regulations, discussed earlier in

‘‘Validity of the Sampling Process’’ (see

Section X.C.). For example, the General

Accounting Office (GAO) 20 and the

National Bureau of Standards (NBS,

now the National Institute of Standards

and Technology) studies were

conducted in 1975. The National

Academy of Sciences report, which

analyzed the same data as the NBS and

GAO reports, was issued in 1980. The

review further showed that the

measurement variability quantified in

these studies included effects of spatial

variability—a component of variability

the Secretaries deliberately exclude

when determining the accuracy of a

sampling and analytical method as

discussed in section X.D.2.(a).

Additionally, since past studies

frequently relied on combining

estimates of variability components

obtained from different bodies of data,

some of them also suffered from

methodological problems related to

combining individual sources of

uncertainty. For example, in 1984, a

NIOSH study identified several

conceptual errors in earlier studies that

had led to double-or even triplecounting of some variability

components (Bowman, et al., 1984).

Although all the data and analyses

submitted by previous commenters

included effects of spatial variability,

one of these data sets, consisting of

paired sample results, contained

sufficient information to indicate that

weighing imprecision was less than

what MSHA had assumed in its

February 18, 1994 notice. However,

without an independent estimate of

spatial variability applicable to these

samples, it is not mathematically

possible to utilize this data set to

estimate variability attributable to the

sampler unit or the volume of air

sampled. A second data set consisted

only of differences in dust concentration

between paired samples, making it

impossible to use it even for evaluating

weighing imprecision. The remaining

three data sets included effects of shiftto-shift variability, which, like spatial

variability, would not be relevant to the

measurement objective. Therefore, none

of these data could be used to estimate

overall measurement imprecision.

Further details are provided in

Appendix C.

One of the previous commenters

particularly questioned the value MSHA

used in its February 18, 1994 proposed

notice of Joint Finding to represent

variability in initially setting the pump

flow rate. In response to this

commenter’s suggestion, MSHA

conducted a study to verify the

magnitude of this variability

component. This study simulated flow

rate adjustment under realistic operating

conditions by including a number of

persons checking and adjusting initial

flow rate under various working

situations (Tomb, September 1, 1994).

Results showed the coefficient of

variation associated with the initial flow

42098 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

rate adjustment to be 3 ± 0.5 percent,

which is less than the 5-percent value

used by MSHA in the February 1994

notice. In addition, based on a review of

published results, the Secretaries would

conclude that the component of

uncertainty associated with the

combined effects of variability in flow

rate during sampling and potential

errors in calibration is actually less than

3 percent. As explained in Appendix B,

these two sources of uncertainty can be

combined to estimate CVpump. After

reviewing the available data and the

comments submitted, the Secretaries

would conclude that the best estimate of

CVpump is 4.2 percent. Additional details

regarding CVpump, along with the

Secretaries’ responses to comments, are

presented in Appendix B.

Intersampler variability, represented

by CVsampler, accounts for uncertainty

due to physical differences from

sampler to sampler. Most of the

previous commenters ignored this

source of uncertainty. As explained in

Appendix B, the Secretaries would

adopt a 5-percent estimate of CVsampler.

To address previous commenters’

concerns that the Agencies had

underestimated CVtotal, MSHA

conducted a field study to directly

estimate the overall measurement

precision attainable when dust samples

are collected with currently approved

sampler units and analyzed using stateof-the-art analytical techniques. The

study involved simultaneous field

measurements of the same coal mine

dust cloud using sampling pumps

incorporating constant flow technology.

Using a specially designed portable dust

chamber, 22 tests were conducted at

various locations in an underground

coal mine. Each test consisted of

collecting 16 dust samples

simultaneously and at the same

location. No adjustments in the flow

rate were made beyond what would

routinely have been done by an MSHA

inspector.

Prior to the field study, two

modifications to MSHA’s sampling and

analytical method had been considered

by MSHA and NIOSH: (1) Measuring

both the pre-and post-exposure weights

to the nearest microgram (μg) on a

balance calibrated using the established

procedure within MSHA’s Respirable

Dust Processing Laboratory; and (2)

discontinuing the practice of truncating

the recorded weights used in calculating

the dust concentration. These

modifications were incorporated into

the design of the field study.

One previous commenter

characterized the field study as being

‘‘woefully incomplete’’ because it was

conducted ‘‘in a tightly controlled

environment * * * not subject to

normal environmental variation.’’ While

it is true that the samples within each

test were not subject to normal

environmental variability, this was

because the experiment was deliberately

designed to avoid confusing spatial

variability in dust concentration with

measurement error. However, pumps

were handled and flow rates were

checked in the same manner as during

routine sampling. Furthermore, the

sampler units were disassembled and

reassembled in the normal manner to

remove and replace dust cassettes.

Previous commenters also questioned

the value that MSHA used in the

February 1994 proposed notice of Joint

Finding to represent uncertainty due to

potential weighing errors. In September

1994, MSHA submitted into the record

an analysis based on replicated

weighings for 300 unexposed filter

capsules, each of which was weighed

once by the cassette manufacturer and

twice in MSHA’s laboratory (Kogut, May

12, 1994). An estimate of weighing

imprecision derived from this analysis

was used by NIOSH in its September 20,

1995 assessment of MSHA’s sampling

and analytical procedure (discussed in

more detail later in section X.E.)

In the March 12, 1996 notice

concerning the NIOSH Accuracy

Criterion, MSHA described the results

of an investigation into repeated

weighings of the same capsules made

over a 218-day period using MSHA’s

automatic weighing system. It was noted

that after approximately 30 days, filter

capsules left exposed and unprotected

gained a small amount of weight—an

average of 0.8 μg (micrograms) per day.

Neither NIOSH nor MSHA considered

this a problem, since all dust samples

are analyzed within 24 hours of receipt

and are not left exposed and

unprotected. However, more recent data

collected to quantify weighing

variability between the Mine Safety

Appliances Co. and MSHA laboratories

showed that filter capsules tend to gain

a small amount of weight even when

stored in plastic cassettes (Parobeck, et

al., 1997). To check this result, 75

unexposed filter cassettes that had been

distributed to MSHA’s district offices

were recalled and the filter capsules

were reweighed. On average, the weight

gain was about 40 μg over a time period

of roughly 150 days. Statistical analyses

of these data performed by MSHA and

NIOSH confirmed the previous result

(Parobeck, et al., 1997; Wagner, May 28,

1997). While the cause has not been

established, it is hypothesized that at

least some of the observed weight gain

may be the result of outgassing from the

plastic cassette onto the filter capsule. If

uncorrected, any systematic change in

weight not due to coal mine dust would

introduce a bias in dust concentration

measurements.

One commenter had previously stated

that the Secretaries were addressing

only precision, thereby implying that

potential biases were being ignored. To

eliminate the potential for any bias due

to a spurious gain or loss of filter

capsule weight, MSHA has used control

filter capsules in its enforcement

program since April 30, 1998. Any

change in weight observed for the

control filter capsule will be subtracted

from the measured change in weight of

the exposed filter capsule. Each control

filter capsule will be pre-weighed with

the other filter capsules, will be stored

and transported with the other capsules,

and will be on the inspector’s person

during the day of sampling. This 1998

modification to MSHA’s inspector

sampling and analytical procedure will

ensure an unbiased estimate of the true

weight gain (Wagner, May 28, 1997).

(a) Experience Gained From Use of

Control Filters

As explained above under the

headings of ‘‘Sample Processing’’ and

‘‘Quantification of Measurement

Uncertainty’’, evidence of relatively

small weight gains in unexposed filter

capsules led MSHA, in 1998, to begin

using unexposed control filters to adjust

the weight gains measured for exposed

filters. Under the new system, respirable

coal mine dust samples taken by MSHA

inspectors are matched with unexposed

control filter capsules. For an inspector

sample to be valid, the matching,

unexposed control filter capsule must

have been weighed on the same two

days as the exposed capsule—initially

before exposure and then, for a second

time, afterwards.

From April 30, 1998 through

December 31, 1998, a total of 5,578 such

control filter capsules were weighed for

the second time in MSHA’s laboratory

after having been sent out to the field.

Although MSHA’s new processing

system was not fully implemented

before April 30, 1998, many of these

control filter capsules which were

constructed with Tyvek, along with the

corresponding exposed capsules, were

initially weighed prior to 1998. The

time intervals between first and second

weighings ranged from 32 to 608 days.

Excluding six filter capsules that were

broken, misidentified, improperly

labeled, or contaminated, weight gains

measured for the remaining 5,572

unexposed filter capsules ranged from a

maximum of 420 μg down to a negative

317 μg (i.e., a weight loss of 317 μg).

Approximately 50% of the unexposed

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42099

filter capsules showed a weight gain of

15 μg or more. The mean weight gain

measurement (counting losses as

negative gains) was 14.0 μg, and the

standard deviation was 24.6 μg. The

initial and second weight measurements

for each of these control filter capsules

which were constructed with Tyvek

support pads, along with the

measurement dates, are being placed

into the public record for analysis and

comment by interested parties.

As explained earlier, if an unexposed

control filter either shows a weight gain

greater than 100 μg or a weight loss

greater than 30 μg, then, instead of using

it to make any adjustment, MSHA

simply voids the corresponding coal

mine respirable dust sample. This

occurred in 126 cases, leaving 5,446

cases in which the control filter was

actually used to adjust a dust sample.

For these 5,446 control filters, the mean

weight gain measurement was 14.8 μg,

and the standard deviation was 19.2 μg.

Consequently, weight gains observed in

exposed filters were reduced by about

15 μg, on average, through the end of

1998. This corresponds to an average

reduction in measured dust

concentration of about 0.02 mg/m3 for a

480-minute dust sample. Individual

dust concentration measurements,

however, were reduced by up to 0.14

mg/m3 (corresponding to a 100-μg

weight gain measured for the control

filter) or increased by up to 0.04 mg/m3

(corresponding to a 30-μg weight loss for

the control filter).

Variability in unexposed filter weight

gain measurements, as expressed by the

standard deviation of 24.6 μg, consists

of three components: (1) random

weighing errors; (2) spurious but real

changes in weight, such as might be due

to contamination or outgassing from the

plastic filter cassette onto the filter

capsule; and (3) effects of any changes

in laboratory conditions between the

first and second weighings. Each of

these three effects also contributes to

uncertainty in the amount of coal mine

dust accumulated on an exposed filter.

MSHA’s purpose in using unexposed

control filters to adjust weight gains

measured for exposed filters is to

eliminate the second and third of these

components as sources of measurement

uncertainty for the exposed filters.

Unfortunately, the control filter

adjustment cannot eliminate the first

component, comprised of random

weighing errors. To the contrary,

making the adjustment based on a single

control filter doubles the number of

weighings required to establish weight

gain for an exposed filter. This increases

(by a factor of √2) uncertainty due to the

random error potentially associated

with each weighing. Therefore, there is

a tradeoff in applying the control filter

adjustment: the adjustment improves

accuracy only if it succeeds in reducing

uncertainty due to changes in laboratory

conditions and spurious changes in

filter weight by an amount greater than

the increase in uncertainty resulting

from the additional weighings required.

Estimates representing the first

component (i.e., the standard deviation

of random errors in measuring the

change in weight of a filter capsule) are

presented in Appendix C and range

from 8.2 μg to 11.3 μg for Tyvek-

supported filters under MSHA’s current

procedures. Even if the true value were

so high as 11.3 μg, then applying the

control filter adjustment increased this

source of uncertainty to no more than

11.3·√2 = 16.0 μg. This is still

substantially less than the 24.6 μg

standard deviation observed in

CNTRL_98, which includes, in addition

to random weighing errors, the effects of

variability in laboratory conditions and

spurious but real changes in filter

weight (MSHA, Data file: CNTRL_98,

1999). Therefore, so long as the control

filter adjustment successfully

eliminated these latter sources of

variability, its net effect was to reduce

uncertainty in the amount of respirable

coal mine dust deposited on an exposed

filter.

Control filters, however, fully

eliminate the effects of day-to-day

variation in laboratory conditions and

spurious changes in filter weight only if

these effects are consistent for all filters

weighed on the same days and sent out

to the same field location for the same

length of time between weighings. In the

absence of evidence to the contrary,

MSHA and NIOSH consider this to be

a reasonable assumption in the case of

laboratory effects: any systematic

differences in laboratory conditions

between the dates of initial and final

weighing should have essentially the

same effect on weights recorded for

unexposed filter capsules as for exposed

filter capsules.

The remaining component of

uncertainty, resulting from spurious but

real weight changes such as might be

caused by outgassing or contamination,

is eliminated by the control filter

adjustment only to the extent that such

effects are consistent for all filters preweighed on the same day, sent out to

the same field location, and then postweighed on the same day. MSHA

checked this assumption for currently

approved filter capsules—i.e., those

employing Tyvek support pads—using

a body of control filter data being placed

into the public record (MSHA, Data file:

NHSCP_99, 1999).

The NHSCP_99 dataset consists of 108

‘‘batches’’ in which several control filter

capsules were first weighed on the same

day, taken to the same mine site (but left

unexposed), and then all weighed again

on the same day in 1999. For example,

a batch of six capsules may have been

initially weighed on December 19, 1997,

left unexposed during a mine visit on

February 23, 1999, and then weighed for

the second time on March 2, 1999. The

NHSCP_99 data set contains

information on a total of 564 filter

capsules, divided into 108 such batches

so that, on average, there were about

five unexposed filter capsules per batch.

The time interval between initial and

final weighings averaged 335 days and

ranged from 136 to 694 days. Closely

matching results from CNTRL_98, the

overall mean weight gain recorded for

these unexposed filter capsules was

about 14 μg, and the overall standard

deviation was about 25 μg.

If changes in weight are indeed

consistent for control filters subjected to

similar handling and aging effects, then

variability in weight gains within

batches should not significantly exceed

variability attributable to random

weighing errors alone. MSHA’s

statistical analysis of NHSCP_99,

however, indicated that variability in

weight gains within batches was

significantly greater than what can be

attributed to random weighing errors

under current processing procedures

(Kogut, et al., 1999). MSHA’s estimate of

the standard deviation of weight gains

measured for unexposed filters within

batches was 19.8 μg. This suggests that,

for filter capsules employing Tyvek

support pads, the effects on weight gain

of handling, aging, and/or environment

may not be uniform—even when the

filter capsules are treated similarly.

MSHA then performed a field

experiment to determine if modifying

the filter capsule would reduce

variability due to spurious changes in

weight (Kogut, et al., 1999). In this

experiment, 300 unexposed filter

capsules employing the standard

Tyvek support pad were compared

with a matched set of 300 unexposed

modified capsules employing a stainless

steel support pad (MSHA, Data file:

MFSC.xls, 1999). Ninety-nine different

MSHA inspectors used three of each

type of filter capsule as controls during

coal mine dust inspections at 100

different MMUs in 100 different mines.

All six unexposed capsules used in an

inspection were carried and handled by

the inspector in the same way as during

routine dust inspections. Also in

accordance with MSHA’s normal

practice, all filter capsules in the batch

used for an inspection were pre- and

42100 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

21With its field study, MSHA exceeded the usual

requirements for determining the accuracy of a

sampling and analytical method, as described by

NIOSH (Kennedy, et al., 1995) and the European

Community (European Standard No. EN 482, 1994).

Both of these require only a laboratory

determination of method accuracy.

post-weighed on the same pair of days

at MSHA’s Respirable Dust Weighing

Laboratory.

MSHA’s statistical analysis of the

MFCS data indicated that substituting a

stainless steel support pad for the

Tyvek support pad currently in use, in

both exposed and unexposed filter

capsules, could significantly improve

measurement accuracy. This

modification reduced the standard

deviation of weight gains measured for

unexposed filters within batches to 11.6

μg.

MSHA and NIOSH would welcome

further statistical analysis of the datasets

being placed into the public record with

this notice. The Agencies would also

welcome suggestions on how MSHA

might further modify its analytical

procedures to reduce uncertainty in the

amount of dust deposited on an

individual filter.

2. Verification of Method Accuracy

NIOSH’s first independent analysis of

MSHA’s sampling and analytical

method involved MSHA’s 1995 field

study data.21 These data incorporated

certain improvements that NIOSH had

proposed for MSHA’s sampling and

analytical method. As described

elsewhere in this notice, these

improvements were later adopted for all

MSHA inspector samples. From these

data, NIOSH determined, with 95-

percent confidence, that the true CVtotal

for MSHA’s proposed sampling and

analytical method was less than the

target maximum value of 12.8 percent

for dust concentrations of 0.2 mg/m3 or

greater (Wagner, 1995). This

demonstrated that MSHA’s sampling

and analytical method for collecting and

processing single full-shift samples

would meet the NIOSH Accuracy

Criterion whenever the true dust

concentration was at least 0.2 mg/m3.

In the same report NIOSH also

applied an indirect approach for

assessing the accuracy of MSHA’s

sampling and analytical method. The

indirect approach involved combining

separate estimates of weighing

imprecision, pump-related variability,

and variability associated with physical

differences between individual sampler

units. This indirect approach also

indicated that MSHA’s sampling and

analytical method would meet the

NIOSH Accuracy Criterion at

concentrations greater than or equal to

0.2 mg/m3, thereby corroborating the

analysis of MSHA’s field data.

As discussed above, MSHA later

obtained data suggesting that filter

capsules containing Tyvek backup

pads sometimes exhibit spurious

changes in weight. Although the

changes observed were relatively small,

compared to weight gains required for

MSHA’s noncompliance

determinations, this led MSHA to begin

using unexposed control filters in its

enforcement program. As explained in

Appendices A and B, the use of a

control filter adjustment eliminates

systematic errors due to such effects, but

also affects the precision of a single,

full-shift measurement. Consequently,

NIOSH reassessed the accuracy of

MSHA’s sampling and analytical

method, taking into account the effects

of using a control filter capsule (Wagner,

May 28, 1997). After accounting for the

effects of control filter capsules on both

bias and precision, NIOSH concluded,

based on both its direct and indirect

approaches, that a single, full-shift

measurement will meet the NIOSH

Accuracy Criterion at true dust

concentrations greater than or equal to

0.3 mg/m3.

As part of its ongoing commitment to

improving the sampling and analytical

method, MSHA recently compiled data

showing that weight stability of the

filter capsule would be improved by

substituting stainless steel support grids

for the Tyvek support pads currently

in use (Kogut et al., 1999). Therefore,

NIOSH again reassessed the accuracy of

MSHA’s method, this time taking into

account the proposal to switch to

stainless steel support grids (Grayson,

1999a; 1999b). After accounting for the

effects of switching to stainless steel

support grids, and of using unexposed

control filters to adjust for any potential

systematic errors that might remain,

NIOSH once again concluded that a

single, full-shift measurement will meet

the NIOSH Accuracy Criterion at true

dust concentrations greater than or

equal to 0.3 mg/m3.

One previous commenter stated that

the Secretaries ‘‘have not addressed the

‘accuracy’ of a single sample collected

from an environment where the

concentration is unknown.’’ The

purpose of any measurement process is

to produce an estimate of an unknown

quantity. The Secretaries have

concluded that MSHA’s sampling and

analytical method for inspectors meets

the NIOSH Accuracy Criterion for true

concentrations at or above 0.3 mg/m3,

but it is also possible to calculate the

range of measurements for which the

Accuracy Criterion is fulfilled. Since

CVtotal increases at the lower

concentrations, all that is necessary is to

determine the lowest measurement at

which the NIOSH Accuracy Criterion is

met. This is done as follows. If the true

concentration exactly equaled the

lowest concentration at which MSHA’s

sampling and analytical method meets

the Accuracy Criterion (i.e., 0.3 mg/m3),

then no more than 5% of single, fullshift measurements would be expected

to exceed 0.36 mg/m3 (Wagner, May 28,

1997). Conversely, if a measurement

equals or exceeds 0.36 mg/m3, it can be

inferred, with at least 95% confidence,

that the true dust concentration equals

or exceeds 0.3 mg/m3 (Wagner, May 28,

1997). Consequently, the Secretaries

conclude that MSHA’s improved

sampling and analytical method

satisfies the NIOSH Accuracy Criterion

whenever a single, full-shift

measurement is at or above 0.36 mg/m3.

The Secretaries recognize that future

technological improvements in MSHA’s

sampling and analytical method may

reduce CVtotal below its current value.

Also, as additional data are

accumulated, updated estimates of

CVtotal may become available. However,

so long as the method remains unbiased

and CVtotal remains below 12.8 percent,

at a 95-percent confidence level, the

sampling and analytical method will

continue to meet the NIOSH Accuracy

Criterion, and the present finding will

continue to be valid.

XI. Proposed New Finding and

Proposed Rescission of the 1972 Joint

Finding

The Secretaries have concluded that

sufficient data exist for determining the

uncertainty associated with a single,

full-shift measurement; rigorous

requirements are in place, as specified

by 30 CFR parts 70, 71, and 90, to

ensure the validity of a respirable coal

mine dust sample; and valid statistical

techniques were used to determine that

MSHA’s improved dust sampling and

analytical method meets the NIOSH

Accuracy Criterion. For these reasons

the Secretaries would find that a single,

full-shift measurement at or above 0.36

mg/m3 will accurately represent

atmospheric conditions to which a

miner is exposed during such shift.

Therefore, pursuant to section 202(f) (30

U.S.C. 842(f)) and in accordance with

section 101 (30 U.S.C. 811) of the Mine

Act, the 1972 joint notice of finding

would be rescinded.

XII. Feasibility Issues

Section 101(a)(6)(A) of the Mine Act

(30 U.S.C. 811(a)(6)(A)) requires the

Secretary of Labor to set standards

which most adequately assure, on the

basis of the best available evidence, that

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42101

no miner will suffer material

impairment of health or functional

capacity even if such miner has regular

exposure to such hazards dealt with by

such standard over his or her working

lifetime. Standards promulgated under

this section must be based upon

research, demonstrations, experiments,

and such other information as may be

appropriate. MSHA, in setting health

standards, is required to achieve the

highest degree of health and safety

protection for the miner, and must

consider the latest available scientific

data in the field, the feasibility of the

standards, and experience gained under

this and other health and safety laws.

In relation to promulgating health

standards, the legislative history of the

Mine Act states that:

* * * This section further provides that

‘‘other considerations’’ in the setting of

health standards are ‘‘the latest available

scientific data in this field, the feasibility of

the standards, and experience gained under

this and other health and safety laws.’’ While

feasibility of the standard may be taken into

consideration with respect to engineering

controls, this factor should have a

substantially less significant role. Thus, the

Secretary may appropriately consider the

state of the engineering art in industry at the

time the standard is promulgated.

* * * * *

Similarly, information on the economic

impact of a health standard which is

provided to the Secretary of Labor at a

hearing or during the public comment

period, may be given weight by the Secretary.

In adopting the language of section

102(a)(5)(A), the Committee wishes to

emphasize that it rejects the view that cost

benefit ratios alone may be the basis for

depriving miners of the health protection

which the law was intended to insure.

S. Rep. No. 95–181, at 21–22 (1977),

reprinted in 1977 U.S.C.C.A.N. 3421–22.

In American Textile Manufacturers’

Institute v. Donovan, 452 U.S. 490, 508–

509 (1981), the Supreme Court defined

the word ‘‘feasible’’ as ‘‘capable of being

done, executed, or effected.’’ The Court

further stated, however, that a standard

would not be considered economically

feasible if an entire industry’s

competitive structure were threatened.

In promulgating standards, hard and

precise predictions from agencies

regarding feasibility are not required.

A. Technological Feasibility

MSHA, in consultation with NIOSH,

believes that compliance determination

based on an inspector, single, full-shift

exposure measurement would be

technologically feasible for the mining

industry. An agency must show that

modern technology has at least

conceived some industrial strategies or

devices that are likely to be capable of

meeting the standard, and which

industry is generally capable of

adopting. American Iron and Steel

Institute v. OSHA, (AISI–II) 939 F.2d

975, 980 (D.C. Cir. 1991); American Iron

and Steel Institute v. OSHA, (AISI–I)

577 F.2d 825 (3d Cir. 1978) at 832–835;

and Industrial Union Dep’t., AFL–CIO v.

Hodgson, 499 F.2d 467, 478 (D.C. Cir.

1974).

This NPRM would not be a

technology-forcing standard. The single,

full-shift sample rule when promulgated

predominantly affects MSHA’s

procedures since MSHA alone conducts

inspector sampling. After the

promulgation of single, full-shift sample

rule, coal mine operators would

continue to comply with the existing

respirable dust concentration limit of

2.0 mg/m3. Such compliance with the

applicable standard has proven feasible

over the years. Furthermore, single, fullshift samples were found to be

technologically feasible during the prior

effective Interim Single-Sample

Enforcement Policy (ISSEP), March 2,

1998 through September 4, 1998 (see

section V.D. of the preamble detailing

the ISSEP).

B. Economic Feasibility

MSHA, in consultation with NIOSH,

believes that the single full shift sample

(SFSS) rule would be economically

feasible for the coal mining industry.

The coal mining industry would incur

costs of approximately $1.8 million

yearly to comply with the proposed

SFSS rule. Coal mine operators would

also incur approximately an additional

$0.2 million yearly in penalty costs

associated with the additional citations

arising from the proposed SFSS rule.

That the total $2.0 million borne yearly

by the coal mining industry as a result

of the proposed SFSS rule is well less

than 1 percent (about 0.01 percent) of

the industry’s yearly revenues of $19.8

billion provides convincing evidence

that the proposed rule is economically

feasible.

Economic feasibility does not

guarantee the continued existence of

individual employers—‘‘A standard is

not infeasible simply because it is

financially burdensome, * * * or even

because it threatens the survival of some

companies within an industry:’’ United

Steelworkers of America v. Marshall,

647 F.22d 1189, 1265 (D.C. Cir. 1981).

This rule would not threaten the

industry’s competitive structure. After

the promulgation of single, full-shift

sample rule the Agencies expect that

coal mine operators would continue to

comply with the existing respirable dust

concentration limit of 2.0 mg/m3.

Single, full-shift samples were found to

be economically feasible during two

prior effective periods—July 15, 1991

through December 31, 1993, and March

2, 1998 through September 4, 1998—

when noncompliance determinations

were based on the results of MSHA

inspector single samples. No disruption

in mining activity was attributed to

MSHA’s single-sample enforcement

policy during either of these periods.

XIII. Regulatory Impact Analysis

MSHA’s improved program to

eliminate overexposures on each and

every shift includes (1) the

simultaneous implementation of the use

of inspector single, full-shift respirable

coal mine dust samples to identify

overexposures more effectively in both

underground and surface coal mines

(single, full-shift sample), and (2) in

underground coal mines, verified

ventilation plans to maintain miners’

respirable dust exposure at or below the

applicable standard on each and every

shift (plan verification). The plan

verification NPRM is published

elsewhere in today’s Federal Register.

This part of the preamble reviews

several impact analyses which the

Agencies are required to provide in

connection with the single, full-shift

sample proposed rulemaking. Since

single, full-shift sample and plan

verification are complementary NPRMs

intended to be promulgated at the same

time, the detailed presentation of

assumptions and estimates for each are

available in the same Preliminary

Regulatory Economic Analysis

(PREA)(MSHA, December 1999).

Assumptions for single, full-shift

sample requirements are based upon

information provided by MSHA

technical personnel. We encourage the

mining community to provide detailed

comments in this regard to ensure that

single, full-shift sample cost

assumptions and estimates are as

accurate as possible.

A. Costs and Benefits: Executive Order

12866

In accordance with Executive Order

12866, the Agencies have prepared a

detailed PREA of the estimated costs

and benefits associated with the

proposed rule for the underground and

surface coal mining sectors. We have

fulfilled this requirement for the

proposed rule and determined that this

rulemaking is not a significant

regulatory action. The key findings of

the PREA are summarized below.

1. Compliance Costs

The Agencies estimate that the cost of

this NPRM would be approximately

$1.8 million annually, of which all but

42102 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

about $5,200 would be borne by

underground coal mine operators (the

residual $5,200 to be borne by surface

coal mine operators). Table XIII–1

summarizes the estimated compliance

costs by provision, for underground and

surface coal mines, for the following

three mine size categories: (1) those

employing fewer than 20 workers; (2)

those employing between 20 and 500

workers; and (3) those employing more

than 500 workers.

The compliance costs arising from the

single, full-shift sample NPRM would

occur as a result of a slight increase in

the number of MSHA inspector citations

issued to underground and surface coal

mine operators due to the determination

of noncompliance with the respirable

coal mine dust standard being based on

inspector single, full-shift samples

rather than the average of multiple

inspector exposure measurements. The

additional citations due to single, fullshift sample would require mine

operators to undertake the following

actions and to incur associated

compliance costs: take corrective

action(s) in order to get back into

compliance with the applicable

respirable coal mine dust standard;

perform abatement sampling; complete

dust data cards; send abatement samples

to MSHA; post abatement sample

results; write respirable dust plans; and

post or give a copy of dust plans.

In addition to these estimated

compliance costs, mine operators would

incur yearly penalty cost increases of

about $0.2 million. Penalty costs

conventionally are not considered to be

a cost of a rule (and, in fact, are clearly

not a compliance cost) but merely a

transfer payment from a party violating

a rule to the government. Therefore, the

penalty costs are not included as part of

the compliance costs of the proposed

SFSS rule noted above. These penalty

costs are relevant, however, in

determining the economic feasibility of

the proposed SFSS rule.

The derivation of the above cost

figures are presented in Chapter IV of

the PREA that accompanies this rule.

TABLE XIII–1.—SUMMARY OF COMPLIANCE COSTS FOR SINGLE, FULL-SHIFT SAMPLE PROPOSED RULE

Estimated costs by category < 20 emp. > 20 emp.

< 500 > 500 emp. Total

UNDERGROUND COAL MINES

Corrective Actions ............................................................................................ $328,488 $1,266,767 $19,527 $1,614,782

Abatement Sampling ....................................................................................... 38,658 128,264 1,129 168,051

Dust Data Cards .............................................................................................. 717 2,588 37 3,343

Send Sample to MSHA ................................................................................... 1,200 4,331 62 5,593

Post Sample Results ....................................................................................... 241 865 12 1,117

Write Dust Plan ................................................................................................ 151 302 0 453

Post or Give Dust Plan .................................................................................... 3 5 0 8

Total Underground .................................................................................... 369,457 1,403,122 20,769 1,793,348

SURFACE COAL MINES

Corrective Actions ............................................................................................ 366 2,194 0 2,560

Abatement Sampling ....................................................................................... 594 1,394 0 1,989

Dust Data Cards .............................................................................................. 3 13 0 17

Send Sample to MSHA ................................................................................... 6 22 0 28

Post Sample Results ....................................................................................... 4 8 0 12

Write Dust Plan ................................................................................................ 151 453 0 604

Post or Give Dust Plan .................................................................................... 3 8 0 10

Total Underground .................................................................................... 1,127 4,094 0 5,220

UNDERGROUND AND SURFACE COAL MINES

Corrective Actions ............................................................................................ 328,854 1,268,961 19,527 1,617,342

Abatement Sampling ....................................................................................... 39,252 129,658 1,129 170,040

Dust Data Cards .............................................................................................. 720 2,602 37 1,282

Send Sample to MSHA ................................................................................... 1,205 4,353 62 5,621

Post Sample Results ....................................................................................... 245 873 12 1,129

Write Dust Plan ................................................................................................ 302 756 0 1,058

Post or Give Dust Plan .................................................................................... 5 13 0 18

Grand Total ............................................................................................... 370,584 1,407,215 20,769 1,798,568

*Totals may vary due to rounding.

2. Benefits

Occupational exposure to excessive

levels of respirable coal mine dust

imposes significant health risks. These

include the following adverse health

outcomes: simple coal workers’

pneumoconiosis (simple CWP),

progressive massive fibrosis (PMF),

silicosis, and chronic obstructive

pulmonary disease (COPD) (e.g., asthma,

chronic bronchitis, emphysema) (see the

Health Effects section for details).

Cumulative exposure to respirable coal

mine dust is the main determinant in

the development of both simple CWP

and PMF although other factors such as

the percentage of quartz in the

respirable dust and the type of coal also

affect the risk of miners developing

simple CWP and PMF (Jacobsen, et al.,

1977; Hurley, et al., 1987; Kuempel, et

al., 1995; Attfield and Morring, 1992;

Attfield and Seixas, 1995). The true

magnitude of occupationally induced

simple CWP and PMF among today’s

coal miners is unknown, although

prevalence estimates are available from

various surveillance systems. For

example, from 1970 to 1995, the

prevalence of simple CWP and PMF

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42103

22For details, see the Quantitative Risk

Assessment and Significance of Risk sections.

23 If a different definition of ‘‘exhibiting a

recurrent pattern of overexposures’’ were used in

these analyses the estimate of the reduction in risk

and associated benefits would be different. For

example, if the criterion were that four or more D.O.

bimonthly exposure measurements exceeded the

applicable standard then, with 95% confidence, at

least 20 shifts would be overexposures in a year of

384 shifts. Using the four as the criterion, this

would reduce the population for whom we are

estimating benefits, and the estimated number of

prevented cases would decrease by 19%.

24MSHA estimates an MMU average of 384

production shifts per year. Since miner operators

are required to submit five valid designated

operator (D.O.) samples to MSHA every two

months, there would typically be 30 valid D.O.

samples–for each MMU that was in operation for

the full year. If dust concentrations on two or more

of the sampled shifts exceed the standard, then it

follows, at a 95-percent confidence level, that the

standard was exceeded on at least six shifts over the

full year.

25With 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.

26With 95-percent confidence, the mean excess is

at least 0.72 mg/m3

27Since females have a greater life expectancy

than males, the expected benefits would increase if

the proportion of female miners increases

substantially in the future.

among miners, based on the operator

sponsored x-ray program, dropped from

11 percent to 3 percent (MSHA, Internal

Chart, 1998). Also, later rounds of the

National Study for Coal Worker’s

Pneumoconiosis consistently

demonstrated, through prevalence rates

in the range of 2.9–3.9 percent, that

simple CWP and PMF have not been

eliminated.

Through the joint promulgation of

single, full-shift sample and plan

verification rules, miners would be

further protected from the debilitating

effects of occupational respiratory

disease by limiting their exposures to

respirable coal mine dust to no more

than the applicable standard on each

and every shift.22 Reducing respirable

coal mine dust concentrations over a 45-

year occupational lifetime to no more

than the applicable standard on just that

percentage of shifts currently showing

an excess would lower the cumulative

exposure, thereby significantly reducing

the risk of both simple CWP and PMF

among miners. We have estimated the

health benefits of the two rules arising

from the elimination of overexposures

on all shifts at only those MMUs

exhibiting a pattern of recurrent

overexposures on individual shifts.

Based on 1999 operator data, there

were 704 MMUs (out of 1,251) at which

regular (not abatement) designated

occupational (D.O.) samples exceeded

the applicable standard on at least two

of the sampling shifts reported in 1999

(MSHA, Data file: Operator.ZIP).23

MSHA considers these 704 MMUs,

representing more than one-half of all

underground coal miners working in

production areas, to have exhibited a

pattern of recurrent overexposures.

Based on valid D.O. operator samples

collected on a total of 18,569 shifts at

these 704 MMUs, the applicable

standard was exceeded on about on

3,977 of these shifts or 21.4 percent.

At the MMUs being considered (those

exhibiting a pattern of recurrent

overexposures),24 bringing dust

concentrations down to no more than

the applicable standard on each and

every production shift would reduce

D.O. exposures on the affected shifts by

an average of 1.04 mg/m3. 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/m3 over the course

of a working year (i.e., 21 percent of

shifts in one year times 1.04 mg/m3 per

shift). Therefore, over a 45-year working

lifetime, the benefit to each affected

D.O. miner would, on average, amount

to a reduction in accumulated exposure

of approximately 10 mg-yr/m3 (i.e., 45

years times 0.22 mg-yr/m3 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/m3 for each

exposed miner.

When the dust concentration

measured for the D.O. exceeds the

applicable standard, measurements for

at least some of the other miners

working in the same MMU may also

exceed the standard on the same shift,

though usually by a smaller amount.

Furthermore, although the D.O.

represents the occupation most likely to

receive the highest exposure, other

miners working in the same MMU may

be exposed to even higher

concentrations than the D.O. on some

shifts. Therefore, in addition to the

affected D.O. miners, there is a

population of other affected miners who

are also expected to experience a

significant reduction in risk as a result

of eliminating overexposures on their

individual shifts.

To estimate how many miners other

than the D.O. would be substantially

affected, MSHA examined the results

from all valid dust samples collected by

MSHA inspectors in underground

MMUs during 1999 (MSHA, Data file:

Inspctor.zip). Within each MMU, the

inspector typically takes one full-shift

sample on the D.O. and, on the same

shift, four or more additional samples

representing other occupations. On 896

shifts, at a total of 450 distinct MMUs,

the D.O. measurement exceeded the

applicable standard, and there were at

least three valid measurements for other

occupations available for comparison.

There was an average of 1.2 non-D.O.

measurements in excess of the standard

on shifts for which the D.O.

measurement exceeded the standard.25

For non-D.O. measurements that

exceeded the standard on the same shift

as a D.O. measurement, the mean excess

above the standard was approximately

(0.8 mg/m3).26

Combining these results with the 21-

percent rate of excessive exposures

observed for the D.O. on individual

shifts, it is reasonable to infer that, at

the MMUs under consideration, an

average of 1.2 other miners, in addition

to the one classified as D.O., is currently

overexposed on at least 21 percent of all

production shifts. Over the course of a

working year, the reduction in exposure

expected for these affected nondesignated occupational (N.D.O.)

miners, is 0.17 mg-yr/m3 (i.e., 21

percent of one year, times 0.8 mg/m3).

The expected lifetime for all

American males, conditional on their

having reached 20 years of age, is 73

years (U.S. Census March 1997, Table

18; U.S. Census March 1997, Table

119).27 On average, the best estimate of

the lifetime benefit to exposed miners is

expressed by the reduction in

prevalence of disease at age 73. To

project the reduction in risk of simple

CWP and PMF among affected D.O.s

and N.D.O.s, MSHA applied its best

estimate of dose response to a

hypothetical cohort of underground coal

miners who work on an MMU

exhibiting a pattern of recurrent

overexposure, and who, on average,

begin working at age 20, retire at age 65,

and live to age 73. Strengths and

weaknesses of various epidemiological

studies were presented in the Health

Effects section supporting the selection

of Attfield and Seixas (1995) as the

study that provides the best available

estimate of material impairment with

respect to simple CWP and PMF. Two

of the distinguishing qualities of

Attfield and Seixas (1995) are the doseresponse relationship over a miner’s

lifetime and the fact that these data best

represent the recent conditions

experienced by miners in the U.S. Using

this relationship, it is possible to

evaluate the impact on risk of both

simple CWP and PMF expected from

42104 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

28Nine hundred and eighty-four refers to the

number of MMUs operating on February 12, 1999.

The 1,443 number mentioned previously refers to

all MMUs in operation at any time in 1999.

bringing respirable coal mine dust

concentrations down to or below the

applicable standard on every shift. This

is the only contemporary

epidemiological study of simple CWP

and PMF providing such a relationship.

To estimate the benefits (i.e., number

of cases of simple CWP and PMF

prevented) of single, full-shift sample

and plan verification rules combined,

we applied these estimates of risk

reduction to the estimated subpopulations of affected miners. As of

February 12, 1999, there were 984

producing MMUs; 28 applying the

pattern of recurrent overexposures

among MMUs as identified in the

Quantitative Risk Assessment, 56

percent, by mine size, we estimate there

to be 552 affected MMUs (MSHA Table,

November 18, 1999; MSHA Table,

February 12, 1999). Based on MSHA’s

experience, we would expect one D.O.

and seven N.D.O.s for each shift of

production at each MMU. Therefore,

among underground coal miners

working on an MMU, we estimate

12.5% to be designated occupational

miners and 87.5% to be non-designated

occupational miners.

The benefits that would accrue to coal

miners exposed to respirable coal mine

dust and to mine operators, and

ultimately to society at large, are

substantial and take a number of forms.

These proposed rules would reduce a

significant health risk to underground

coal miners, reducing the potential for

illnesses and premature death and their

attendant costs to miners, their

employers, their families, and society.

The joint promulgation of these rules

should realize a positive economic

impact on the Department of Labor’s

(DOL’s) Black Lung Program and

relatedly on mine operators. The Black

Lung Program compensates eligible

miners and their survivors under the

Black Lung Benefits Act. This program

provides monthly payments and

medical benefits (diagnostic and

treatment) to miners who are found to

be totally disabled by black lung

disease, including cases of PMF and

simple CWP. In 1986, DOL’s

Employment Standards Administration

reported that 12% of approved cases of

Black Lung Program were identified as

cases of PMF based on chest

radiographs, while sixty-four percent

had simple CWP based on chest

radiographs (ESA, 1986). For miners

who stopped working in coal mines

after 1969 and for whom the DOL can

establish that the miner worked for the

same operator for at least one calendar

year, and that miner had at least 125

working days in that year, that operator

is financially responsible for the miner’s

Black Lung benefit payment. If a

responsible operator cannot be

identified for an eligible miner, benefit

payments are made by the Black Lung

Disability Trust Fund. To the extent that

these rules reduce overexposures to

respirable coal mine dust, there should

be fewer Black Lung Program cases.

Therefore, over time, the associated

financial outlay by responsible

operators through either insurance

premiums or direct payments of Black

Lung benefits should be lower than

would otherwise occur. The financial

impact could be substantial (see

discussion in Chapter IV, of the PREA).

In 1980, the Black Lung Program

estimated average lifetime payouts for

responsible operators for married

miners of about $248,700 dollars,

assuming a 7-percent annual increase

(ESA, 1980). In fiscal year 1999, 443

claims for Black Lung Benefits were

accepted as new cases; sixty-six percent

(293) are the financial responsibility of

coal mine operators (Peed, 2000).

The most tangible benefit of these

rules is the number of cases of simple

CWP and PMF which would be

prevented. Table XIII–2 presents the

estimated number of cases of simple

CWP and PMF that would be prevented

among the 56 percent of MMUs

currently exhibiting a pattern of

recurrent overexposures. For all

categories of simple CWP and PMF

combined, we estimate 37 fewer of these

cases among affected miners, than

would otherwise occur without the

promulgation of single, full-shift sample

and plan verification rules. Eleven of

these cases would be the most severe

form of coal miners pneumoconiosis,

PMF, and as such these cases could be

interpreted as prevented premature

deaths due to occupational exposure to

respirable coal mine dust. Since simple

CWP predisposes the development of

PMF, it is important that it also be

prevented (Balaan, et al., 1993).

As discussed in the Significance of

Risk sections, MSHA believes this QRA

for simple CWP and PMF strikes a

reasonable balance based on available

data. Yet, our estimates likely

understate the true impact of these rules

since our analyses are restricted to a

sub-population of affected miners, those

working at MMUs exhibiting a pattern

of recurrent overexposures, not the

broader population of coal miners who

would benefit from these rules.

Furthermore, to estimate the average

overexposure which would be

prevented, MSHA had to use data

collected for compliance purposes,

which may not represent typical

environmental conditions and the

associated respirable coal mine dust

exposure in underground coal mines.

The degree to which the exposure

level of respirable coal mine dust on

sampling shifts may not be

representative of typical exposure levels

is affected by the following factors:

(1) There exists a positive relationship

between coal production and generation

of respirable coal mine dust;

(2) Current sampling procedures

permit sampling measurements to be

taken at the mid-range of the

distribution of the level of production—

sampling measurements must be taken

on shifts with production at least 60%

of the average production during the last

30 days and at least 50% of average

production for the last valid set of

bimonthly samples for inspector and

operator samples, respectively;

(3) Miners have reported and MSHA

data have demonstrated lower levels of

production on sampling shifts versus

non-sampling shifts (MSHA, September

1993);

(4) On some sampling shifts, miners

have reported that more engineering

controls may be used than on other

shifts, thus reducing the measured

amount of respirable coal mine dust;

(5) MSHA analyses have

demonstrated, even when controlling

for production, in mines with fewer

than 125 employees, on continuous

mining MMUs, respirable coal mine

dust exposures were much higher

during the unannounced Spot

Inspection Program (SIP) sampling

shifts than on shifts operators

sampled—this is consistent with the

effect of increasing engineering controls

on shifts during which bimonthly

samples are conducted compared to the

level of use of engineering controls used

on shifts for which the operator does not

expect sampling to be conducted given

the same production level (Denk, 1993);

(6) Across mine size, designated area

samples have been found to be larger for

shifts on which unannounced

compliance sampling occurred

compared to operator sampling shifts—

in one study they differed by at least a

factor of 40 percent in large mines and

100 percent in the smallest mines (Ibid.,

pp. 211–212); and

(7) Existing MSHA technical

information indicates that some

reduction in production levels occurs

during some sampling periods on

longwalls (Denk, 1990).

Therefore, at a bare minimum, over an

occupational lifetime (45-years) for

miners who live to age 73 who worked

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42105

29Applying the estimated prevalence rate of 3.0

percent to the estimated population of affected

miners (8,640) results in an estimate of 259 cases

of simple CWP and PMF.

30See detailed discussion in the Significance of

Risk section.

at MMUs exhibiting a pattern of

recurrent overexposures, we estimate at

least 37 fewer cases of pneumoconiosis

(simple CWP and PMF) than would

otherwise occur without the

promulgation of these rules.

Our current quantitative estimate of

benefits demonstrates and qualitative

discussions punctuate that these rules

would have a significant positive impact

on the health of our nation’s coal miners

when promulgated. Yet, due to the

limitations in these data, we believe our

benefit estimate may understate the

number of cases of simple CWP and

PMF which would be prevented over an

occupational lifetime.

MSHA believes that cases of simple

CWP and PMF would also be prevented

among other types of underground

miners, such as roofbolters working in

designated areas (D.A.). Based on MSHA

experience it is reasonable to expect

roofbolter D.A.’s pattern of

overexposures for respirable coal mine

dust to be similar to that for miners with

the highest exposure on a MMU. If so,

we would expect 13 additional cases of

simple CWP and PMF to be prevented.

Affected D.A.s include D.A.s who work

at the 56 percent of the MMUs under

consideration who are exposed to dust

concentrations similar to the D.O., over

a 45-year occupational lifetime (MSHA

Table, November 1999; MSHA Table,

February 1999).

Also, it is reasonable to expect surface

miners’ health to be further protected by

the promulgation of the SFSS rule alone

since it would identify and require

resolution of overexposures not

previously identified and may thereby

lower some miners’ cumulative

exposure to respirable coal mine dust.

Furthermore, to the extent that

cumulative exposure to respirable coal

mine dust affects other adverse health

outcomes, such as silicosis and chronic

obstructive pulmonary disease, it is

reasonable to expect a reduction in the

number of cases and/or in the severity

of cases for these diseases among

surface and underground coal miners.

Although the effect cannot readily be

quantified, to the extent that these rules

would also reduce the cumulative

exposure to respirable coal mine dust

among some miners working in those

MMUs currently not exhibiting

overexposures, it is reasonable to expect

that we would observe an incremental

benefit among that sub-population of

coal miners. Moreover, to the extent that

the cumulative dust exposure is reduced

for miners working in the ‘‘outby’’ areas,

away from the mining face (i.e., MMU)

where coal is extracted from the coal

seam, they too may realize occupational

health benefits due to the simultaneous

promulgation of these proposals.

Therefore, our best estimate of 37

prevented cases of simple CWP and

PMF, combined, among all affected

miners likely underestimates the true

benefit realized by the coal mining

workforce through the reduction of

overexposures to no more than the

applicable standard on each shift.

Clearly, PMF is associated with

premature death. Since simple CWP

may evolve to PMF, even after

occupational exposure has ceased, it has

the propensity to become a lifethreatening illness. By reducing the total

number of simple CWP and PMF cases

among affected miners from 259 to 222,

over 45 years,29 these standards are

projected to prevent an average of four

cases of simple CWP and PMF for each

5-year interval.

For all those reasons previously

identified, MSHA believes that its

estimate of 37 prevented cases of simple

CWP and PMF over a 45 year working

life understates the true number of cases

of simple CWP and PMF which would

be prevented. This belief is further

supported by the fact that during the

past few years, the Black Lung Benefits

Program has been approving roughly

400 claims each year. These claims

come from individuals whose exposure

for the most part came after the current

standard of 2.0 was established in 1972.

Thus, we believe the consistent

identification, from year to year, of

hundreds of new cases of simple CWP

and PMF per year into the Black Lung

Benefits Program supports our belief

that the true lifetime occupational

health benefits of the proposed rules are

higher than we have estimated. Even

assuming that the number of new claims

would decline in future years simply

due to the continuing decline in the

number of coal miners, MSHA expects

that assuring that future exposures are

maintained below the 2.0 exposure limit

will reduce the number of new cases of

simple CWP and PMF by considerably

more than 1 per year.

In addition to the prevention of

simple CWP and PMF, each of the 8,640

affected miners at MMUs exhibiting a

pattern of recurrent overexposures will

realize some health benefit by limiting

his or her cumulative exposure to

respirable coal mine dust to no more

than the applicable standard on each

and every shift.

The expected number of prevented

cases of simple CWP and PMF would

not be realized for some time even after

the pattern of overexposures has been

minimized or eliminated. This is due, in

part, to the latency (that is, the disease

does not develop immediately after

exposure) of the development of simple

CWP and PMF and the pre-existing

occupational exposure histories of

members of the current coal mining

workforce. Our estimated benefit is

based on the estimated number of

underground coal miners working at the

mine face, 17,280. If the size of this

workforce significantly changed in the

future and the projected pattern of

prevented overexposures remained the

same, the number of cases of prevented

simple CWP and PMF would need to be

adjusted to account for the change.

Finally, even standing alone, without

simultaneously requiring that the

effectiveness of underground mine

ventilation plans be verified (i.e., the

Plan Verification NPRM), the proposed

standard allowing MSHA to use single,

full-shift samples to identify

overexposures requiring corrective

action would provide miners with

health benefits.30 Both the prospect of

being cited for overexposure and the

actual issuance of additional citations

due to this rule would compel mine

operators to be more attentive to the

level of respirable dust in their mines.

Therefore, it is reasonable to expect,

over time, a further decline in the

number of shifts during which the

concentration of respirable coal mine

dust is at or above the applicable

standard. Thus, implementation of the

single, full-shift sample strategy will, in

and of itself, on average, lower miners’

cumulative exposure to respirable coal

mine dust. Since cumulative exposure

to respirable coal mine dust is the main

determinant in the development of both

simple CWP and PMF, the Agencies are

confident that the use of single, fullshift samples, by themselves, even

without the help of a verified dust

control plan, would result in better

health protection to miners.

Various data, assumptions and

caveats were used to conduct the

quantitative risk assessment,

significance of risk discussion, and

benefits analyses. Therefore, we request

any information which would enable us

to conduct more accurate analyses of the

estimated health benefits of the single,

full-shift sample rule and plan

verification rule, both individually, and

in combination.

42106 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

TABLE XIII–2.—OVER A WORKING LIFETIME AMONG AFFECTED MINERS, ESTIMATED NUMBER OF CASES OF CWP A AND

PMF B PREVENTED DUE TO THE IMPLEMENTATION OF SINGLE-SAMPLE AND PLAN VERIFICATION

Type of

miner

Affected

miners, n=

Simple CWP categories

1, 2, 3 or PMF

Simple CWP categories

2 or 3 or PMF

PMF

Reduction in

risk c

Prevented cases,

n=

Reduction in

risk c

Prevented cases,

n=

Reduction in

risk c

Prevented cases,

n=

Affected

Designated

Occupational

Miners d 1,080 18.0/1,000 19.4 9.8/1,000 10.6 5/1,000 5.5

Affected

NonDesignated

Occupational

Miners e 7,560 2.3/1,000 17.4 1.3/1,000 9.8 1/1,000 5.3

Total .. 8,640 na 37 na 20 na 11

aSimple CWP: simple coal workers’ pneumoconiosis.

bPMF: progressive massive fibrosis.

c Reduction in risk per 1,000 affected miners, over a 45-year working lifetime.

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

the D.O.

B. Regulatory Flexibility Certification

and Initial Regulatory Flexibility

Analysis

The Regulatory Flexibility Act

requires MSHA and NIOSH to conduct

an analysis of the effects of the single,

full-shift sample rule on small entities.

That analysis is summarized here; a

copy of the full analysis is included in

Chapter V of the Agencies’ PREA in

support of the proposed rule. The

Agencies encourage the mining

community to provide comments on

this analysis.

The Small Business Administration

generally considers a small entity in the

mining industry to be one with 500 or

fewer workers. MSHA has traditionally

defined a small mine to be one with

fewer than 20 workers, and has focused

special attention on the problems

experienced by such mines in

implementing safety and health rules.

Accordingly, the Agencies have

separately analyzed the impact of the

joint notice proposed rule both on

mines with 500 or fewer workers and on

those with fewer than 20 workers.

Pursuant to the Regulatory Flexibility

Act, MSHA must determine whether the

costs of the joint notice proposed rule

constitute a ‘‘significant impact on a

substantial number of small entities.’’

Pursuant to the Regulatory Flexibility

Act, if an Agency determines that a

proposed rule would not have such an

impact, it must publish a ‘‘certification’’

to that effect. In such a case, no

additional analysis is required (5 U.S.C.

§ 605). In evaluating whether

certification is appropriate, MSHA

utilized a ‘‘screening test,’’ comparing

the costs of the joint notice proposed

rule to the revenues of the affected coal

sector. If the estimated costs are less

than 1 percent of revenues for the

affected entities, then the rule is

assumed not to have a significant

impact on small mine operators.

Table XIII–3 compares, for small

underground and surface coal mines

(using both MSHA’s and SBA’s

definition), MSHA’s estimated total

annual compliance costs of the joint

notice proposed rule to estimated

annual revenues.

TABLE XIII–3.—ESTIMATED YEARLY REVENUES AND COSTS FOR SINGLE, FULL-SHIFT SAMPLE PROPOSED RULE FOR

UNDERGROUND AND SURFACE COAL MINES

[dollars in thousands]

Mine size Estimated

yearly costs a

Estimated revenues b

Costs as percentage of

revenues

Underground Coal Mines

<20 ............................................................................................................................................... $369.0 $249,418 0.1

≤500 c ........................................................................................................................................... 1,770.5 6,883,339 0.03

Surface Coal Mines

<20 ............................................................................................................................................... 1.1 498,935 <0.01

≤500 ............................................................................................................................................. 5.2 10,864,156 <0.01

aEstimated yearly costs are composed of only annual costs. There are no first year costs or annualized costs in the proposed rule.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42107

b Data for revenues derived from: U.S. Department of Labor, Mine Safety and Health Administration, Office of Standards, Regulations and

Variances, based on 1997 Final MIS data (Quarter 1—Quarter 4), CM441, Cycle 1997/84; and U.S. Department of Energy, Energy Information

Administration, Annual Energy Review 1998, DOE/EIA–0384(98), July 1999, p. 203. c Includes mines with fewer than 20 employees.

Table XIII–3 shows that under either

MSHA’s or SBA’s definition of a small

mine, for underground and/or surface

coal mines, the estimated costs would

be significantly less than one percent of

revenues. As a result, MSHA is

certifying that the single, full-shift

sample rule for underground and

surface coal mines would not have a

‘‘significant impact on a substantial

number of small entities,’’ and has

performed no further analyses.

XIV. Other Statutory Requirements

A. Unfunded Mandates Reform Act of

1995

For purposes of the Unfunded

Mandates Reform Act of 1995, this rule

does not include any Federal mandate

that may result in increased

expenditures by State, local, and tribal

governments, or increased expenditures

by the private sector of more than $100

million.

B. Paperwork Reduction Act of 1995

This proposed rule contains

information collections which are

subject to review by the Office of

Management and Budget (OMB) under

the Paperwork Reduction Act of 1995

(PRA95). The proposed SFSS rule has

annual burden hours beginning in the

first year and recurring every year

thereafter. Both underground and

surface coal mines have paperwork

provisions under the proposed SFSS

rule. Underground coal mine operators

would incur 2,985 annual burden hours

and associated costs of $70,822. Surface

coal mine operators would incur 29

annual burden hours and associated

costs of about $1,009. These burden

hours relate to operators performing

abatement sampling, completing dust

data cards, mailing samples to MSHA

for analysis, writing respirable dust

plans, and posting respirable dust plans.

Table XIV–1 shows the burden hours

and associated costs for each SFSS

paperwork provision by mine size for

underground and surface mines.

TABLE XIV–1.—SUMMARY OF MINE OPERATORS’ ANNUAL PAPERWORK BURDEN HOURS AND COSTS ARISING FROM THE

SINGLE, FULL-SHIFT SAMPLE PROPOSED RULE *

Detail

<20 emp. ≥20 emp. ≤500 > 500 emp. Total

Hrs. Costs Hrs. Costs Hrs. Costs Hrs. Costs

UNDERGROUND COAL MINES

Abatement Sampling ........................................ 575 $13,872 2,080 $50,181 30 $724 2,685 $64,776

Dust Data Cards .............................................. 14 716 52 2,589 1 37 67 3,342

Send Samples to MSHA .................................. 48 910 173 3,292 2 47 224 4,250

Write Dust Plan ................................................ 3 149 6 299 0 0 9 448

Post or Give Dust Plan .................................... 0.1 2 0.2 4 0 0 0 6

Total Underground .................................... 640 15,649 2,311 54,364 33 809 2,985 70,822

SURFACE COAL MINES

Abatement Sampling ........................................ 5 $121 10 $241 0 $0 15 $362

Dust Data Cards .............................................. 0.1 6 0.3 12 0 0 0.4 19

Send Samples to MSHA .................................. 0.4 8 0.8 16 0 0 1.2 24

Write Dust Plan ................................................ 3 149 9 448 0 0 12 597

Post or Give Dust Plan .................................... 0.1 2 0.3 6 0 0 0.4 7

Total Surface ............................................ 9 286 20 723 0 0 29 1,009

UNDERGROUND AND SURFACE COAL MINES

Abatement Sampling ........................................ 580 $13,993 2,090 $50,422 30 $724 2,700 $65,138

Dust Data Cards .............................................. 15 722 52 2,602 1 37 68 3,361

Send Samples to MSHA .................................. 48 918 174 3,308 2 47 225 4,273

Write Dust Plan ................................................ 6 299 15 747 0 0 21 1,046

Post or Give Dust Plan .................................... 0 4 1 9 0 0 1 13

Grand Total ............................................... 649 15,935 2,332 57,087 33 809 3,014 73,831

* Totals may vary due to rounding.

MSHA invites public comments and

is particularly interested in comments

which:

1. Evaluate whether the proposed

collection of information (presented

here and in MSHA’s PREA) is necessary

for the proper performance of the

functions of MSHA, including whether

the information will have practical

utility;

2. Evaluate the accuracy of MSHA’s

estimate of the burden of the proposed

collection of information, including the

validity of the methodology and

assumptions used;

3. Enhance the quality, utility, and

clarity of the information to be

collected; and

4. Minimize the burden of the

collection of information on

respondents, including through the use

of appropriate automated, electronic,

mechanical, or other technological

collection techniques or other forms of

42108 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

information technology, e.g., permitting

electronic submissions of responses.

Submission

MSHA and NIOSH have submitted a

copy of this proposed rule to OMB for

its review and approval of these

information collections. Interested

persons are requested to send comments

regarding this information collection,

including suggestions for reducing this

burden, to the Office of Information and

Regulatory Affairs, OMB New Executive

Office Building, 725 17th St., NW, Rm.

10235, Washington, DC 20503, Attn:

Desk Officer for MSHA. Submit written

comments on the information collection

not later than September 5, 2000.

MSHA’s paperwork submission

summarized above is explained in detail

in the PREA. The PREA includes the

estimated costs and assumptions for

each proposed paperwork requirement

related to this proposed rule. A copy of

the PREA is available from MSHA.

These paperwork requirements have

been submitted to the Office of

Management and Budget for review

under section 3504(h) of the Paperwork

Reduction Act of 1995. Respondents are

not required to respond to any

collection of information unless it

displays a current valid OMB control

number.

C. National Environmental Protection

Act

The National Environmental Policy

Act (NEPA) of 1969 requires each

Federal agency to consider the

environmental effects of proposed

actions and to prepare an

Environmental Impact Statement on

major actions significantly affecting the

quality of the human environment.

MSHA has reviewed the proposed

standard in accordance with the

requirements of the NEPA (42 U.S.C.

4321 et seq.), the regulation of the

Council on Environmental Quality (40

CFR Part 1500), and the Department of

Labor’s NEPA procedures (29 CFR Part

11). As a result of this review, MSHA

has preliminarily determined that this

proposed standard will have no

significant environmental impact.

Commenters are encouraged to submit

their comments on this determination.

D. Executive Order 12630: Government

Actions and Interference with

Constitutionally Protected Property

Rights

This proposed rule is not subject to

Executive Order 12630, Governmental

Actions and Interference with

Constitutionally Protected Property

Rights, because it does not involve

implementation of a policy with takings

implications.

E. Executive Order 12988: Civil Justice

Reform

The Agency has reviewed Executive

Order 12988, Civil Justice Reform, and

determined that this rulemaking will

not unduly burden the Federal court

system. The regulation has been written

so as to provide a clear legal standard

for affected conduct, and has been

reviewed carefully to eliminate drafting

errors and ambiguities.

F. Executive Order 13045: Protection of

Children from Environmental Health

Risks and Safety Risks

In accordance with Executive Order

13045, protection of children from

environmental health risks and safety

risks, MSHA has evaluated the

environmental health or safety effects of

the proposed rule on children. The

Agency has determined that this

proposal would not have an adverse

impact on children.

G. Executive Order 13084 Consultation

and Coordination with Indian Tribal

Governments

MSHA certifies that this proposed

rule does not impose substantial direct

compliance costs on Indian tribal

governments.

H. Executive Order 13132 (Federalism)

We have reviewed this rule in

accordance with Executive Order 13132

regarding federalism, and have

determined that it does not have

‘‘federalism implications.’’ The rule

does not ‘‘have substantial direct effects

on the States, on the relationship

between the national government and

the States, or on the distribution of

power and responsibilities among the

various levels of government.’’

XV. Public Hearings

The Agencies will hold public

hearings on the proposed rule. The

hearings will be held in Prestonsburg,

Kentucky, (Jenny Wiley State Resort

Park); Morgantown, West Virginia; and

Salt Lake City, Utah. The hearing dates,

times, and specific locations will be

announced by a separate document in

the Federal Register. The hearings will

be held under Section 101 of the Federal

Mine Safety and Health Act of 1977.

Appendix A—The Effects of Averaging

Dust Concentration Measurements

MSHA’s measurement objective in

collecting a dust sample is to determine the

average dust concentration at the sampling

location on the shift sampled. As discussed

in the main text, MSHA and NIOSH find that

a single, full-shift measurement can

accurately represent the average full-shift

dust concentration being measured.

Nevertheless, because of sampling and

analytical errors inherent in even the most

accurate measurement process, the true value

of the average dust concentration on the

sampled shift can never be known with

complete certainty. However accurate the

representation, a measurement can provide

only an estimate of the true dust

concentration.

Throughout this appendix, some public

comments made to February 18 and June 6,

1994 notices relevant to issues regarding

single, full-shift sampling will be cited and

addressed to emphasize key findings on

accuracy and the effects of averaging dust

concentration measurements. Some previous

commenters contended that MSHA should

not rely on single samples for making

noncompliance determinations, because an

average of results from multiple samples

would estimate the true dust concentration

more accurately than any single

measurement.

Contrary to the views expressed by these

commenters, averaging a number of

measurements does not necessarily improve

the accuracy of an estimation procedure.

Consider, for example, an archer aiming at

targets mounted at random and possibly

overlapping positions on a long partition.

Each arrow might be aimed at a different

target. Suppose that an observer, on the

opposite side of the partition from the archer,

cannot see the targets but must estimate the

position of each bull’s eye by locating

protruding arrowheads.

Each protruding arrowhead provides a

measurement of where some bull’s eye is

located. If two arrowheads are found on

opposite ends of the partition, averaging the

positions of these two arrowheads would not

be a good way of determining where any real

target is located. To estimate the location of

an actual target, it would generally be

preferable to use the position of a single

arrow. The average would represent nothing

more than a ‘‘phantom’’ target somewhere

near the center, where the archer probably

did not aim on either shot and where no

target may even exist.

The archery example can be extended to

illustrate conditions under which averaging

dust concentration measurements does or

does not improve accuracy. If each

arrowhead is taken to represent a full-shift

dust sample, then the true average dust

concentration at the sampling location on a

given shift can be identified with the location

of the bull’s eye at which the corresponding

arrow was aimed. The accuracy of a

measurement refers to how closely the

measurement can be expected to come to the

quantity being measured. Statistically,

accuracy is the combination of two distinct

concepts: precision, which pertains to the

consistency or variability of replicated

measurements of exactly the same quantity;

and bias, which pertains to the average

amount by which these replicated

measurements deviate from the quantity

being measured. Bias and precision are

equally important components of

measurement accuracy.

To illustrate, arrows aimed at the same

target might consistently hit a sector on the

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42109

lower right side of the bull’s eye. The

protruding arrowheads would provide more

or less precise measurements of where the

bull’s eye was located, depending on how

tightly they were clustered; but they would

all be biased to the lower right. On the other

hand, the arrows might be distributed

randomly around the center of the bull’s eye,

and hence unbiased, but spread far out all

over the target. The protruding arrowheads

would then provide unbiased but relatively

imprecise measurements.

More complicated situations can easily be

envisioned. Arrows aimed at a second target

would provide biased measurements relative

to the first target. Alternatively, if the archer

always aims at the same target, the first shot

in a given session might tend to hit near the

center, with successive shots tending to fall

off further and further to the lower right as

the archer’s arm tires; or shots might

progressively improve, as the archer adjusts

aim in response to prior results.

Averaging reduces the effects of random

errors in the archer’s aim, thereby increasing

precision in the estimation procedure. If the

archer always aims at the same target and is

equally adept on every shot (i.e., if the

arrowheads are all randomly and identically

distributed around a fixed point), then

averaging improves the estimate’s precision

without introducing any bias. Averaging in

such cases provides a more accurate method

of estimating the bull’s eye location than

reliance on any single arrowhead. If,

however, the archer intentionally or

unintentionally switches targets, or if the

archer’s aim progressively deteriorates, then

averaging can introduce or increase bias in

the estimate. If the gain in precision

outweighs this increase in bias, then

averaging several independent measurements

may still improve accuracy. However,

averaging can also introduce a bias large

enough to offset or even surpass the

improvement in precision. In such cases, the

average position of several arrowheads can be

expected to locate the bull’s eye less

accurately than the position of a single

arrowhead.

I. Multi-Locational Averaging

Some previous commenters opposed

MSHA’s use of a single, full-shift

measurement for enforcement purposes,

claiming that determinations based on such

measurements would be less accurate than

those made under MSHA’s existing

enforcement policy of averaging multiple

measurements taken on an MMU. There are

two distinctly different types of multilocational measurement averages that could

theoretically be compiled on a given shift: (1)

the average might combine measurements

taken for different occupational locations and

(2) the average might combine measurements

all taken for the same occupational location.

For MMUs, the averages used in MSHA’s

sampling program usually involve

measurements taken for different

occupational locations on the same shift.

These are averages of the first type. MSHA’s

sampling program has never utilized averages

of the second type. Therefore, those

commenters who claimed that reliance on a

single, full-shift measurement would reduce

the accuracy of noncompliance

determinations, as compared to MSHA’s

existing enforcement policy, are implicitly

claiming that accuracy is increased by

averaging across different occupational

locations.

Averaging measurements obtained from

different occupational locations on an MMU

is like averaging together the positions of

arrows aimed at different targets. The average

of such measurements is an artificial,

mathematical construct that does not

correspond to the dust concentration for any

actual occupational location. Therefore, this

type of averaging introduces a bias

proportional to the degree of variability in

actual dust concentration at the various

locations averaged.

The gain in precision that results from

averaging measurements taken at different

locations outweighs this bias only if

variability from location to location is

smaller than variability in measurement

error. However, commenters opposed to

MSHA’s use of single, full-shift

measurements for enforcement purposes

argued that this is not generally the case and

even submitted data and statistical analyses

in support of this position. Commenters in

favor of noncompliance determinations based

on a single, full-shift measurement agreed

that variability in dust concentration is

extensive for different occupational locations

and argued that MSHA’s existing policy of

measurement averaging is not sufficiently

protective of miners working at the dustiest

locations.

Since an average of the first type combines

measurement from the dustiest location with

measurements from less dusty locations, it

must always fall below the best available

estimate of dust concentration at the dustiest

location. In effect, averaging across different

occupational locations dilutes the dust

concentration observed for the most highly

exposed occupations or dustiest work

positions. Therefore, such averaging results

in a systematic bias against detecting

excessive dust concentrations for those

miners at greatest risk of overexposure.

A somewhat better case can be made for

the second type of multi-locational averaging,

which combines measurements obtained on

the same shift from a single occupational

location. As some previous commenters

pointed out, however, there is ample

evidence that spatial variability in dust

concentration, even within relatively small

areas, is frequently much larger than

variability due to measurement error.

Therefore, the same kind of bias introduced

by averaging across occupational locations

would also arise, but on a lesser scale, if the

average measurement within a relatively

small radius were used to represent dust

concentration at every point in the

atmosphere to which a miner is exposed. A

miner is potentially exposed to the

atmospheric conditions at any valid sampling

location. Consistent with the Mine Act and

implementing regulations, MSHA’s

enforcement strategy is to limit atmospheric

dust concentration wherever miners

normally work or travel. Therefore, the more

spatial variability in dust concentration there

is within the work environment, the less

appropriate it is to use measurement

averaging to enforce the applicable standard

by averaging measurements obtained at

different sampling locations.

Some of the previous comments implied

that instead of measuring average dust

concentration at a specific sampling location,

MSHA’s objective should be to estimate the

average dust concentration throughout a

miner’s ‘‘breathing zone’’ or other area near

a miner. If estimating average dust

concentration throughout some zone were

really the objective of MSHA’s enforcement

strategy, then averaging measurements made

at random points within the zone would

improve precision of the estimate without

introducing a bias. This type of averaging,

however, has never been employed in either

the MSHA or operator dust sampling

programs. MSHA’s current policy of

averaging measurements obtained from

different zones does not address spatial

variability in the area immediately

surrounding a sampler unit. Therefore, even

if averaging measurements from within a

zone were somehow beneficial, this would

not demonstrate that MSHA’s existing

enforcement policy is more reliable than

basing noncompliance on a single, full-shift

measurement.

Furthermore, if the objective were really to

estimate average dust concentration

throughout some specified zone on a given

shift, then it would often be necessary to

obtain far more than five simultaneous

measurements within the zone. This is not

only because of potentially large local

differences in dust concentration. In order to

use such measurements for enforcement

purposes, variability in dust concentration

within the sampled area would have to be

estimated along with the average dust

concentration itself. As some previous

commenters correctly pointed out, doing this

in a statistically valid way would generally

require at least twenty to thirty

measurements. One of these commenters also

pointed out that such an estimate, based on

even this many measurements in the same

zone, could be regarded as accurate only

under certain questionable assumptions

about the distribution of dust concentrations.

This commenter calculated that hundreds of

measurements would be required in order to

avoid these tenuous assumptions. Clearly,

this shows that the objective of estimating

average dust concentration throughout a zone

is not consistent with any viable enforcement

strategy to limit dust concentration on each

shift in the highly heterogeneous and

dynamic mining environment. The large

number of measurements required to

accurately characterize dust concentration

over even a small area merely demonstrates

why it is not feasible to base enforcement

decisions on estimated atmospheric

conditions beyond the sampling location.

MSHA and NIOSH recognize that a single,

full-shift measurement will not provide an

accurate estimate of average dust

concentration anywhere beyond the sampling

location. The Mine Act, however, does not

require MSHA to estimate average dust

concentration at locations that are not

sampled or to estimate dust concentration

averaged over any zone or region of the mine.

42110 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

31Technically, the assumption is that dust

concentrations on all shifts sampled are

independently and identically distributed around

the quantity being estimated.

Instead, the Mine Act requires that a miner

will not be exposed to excessive dust

wherever he/she normally works or travels.

This can be accomplished by maintaining the

average dust concentration at each valid

sampling location at or below the applicable

standard during each shift.

II. Multi-Shift Averaging

Some previous commenters maintained

that in order to reduce the risk of erroneous

noncompliance determinations, MSHA

should average measurements obtained from

the same occupation on different shifts.

These commenters contended that the

average of measurements from several shifts

represents the average dust concentration to

which a miner is exposed more accurately

than a single, full-shift measurement. Other

commenters, who favored noncompliance

determinations based on single, full-shift

measurements, claimed that conditions are

sometimes manipulated so as to produce

unusually low dust concentrations on some

of the sampled shifts. These commenters

suggested that, due to these unrepresentative

shifts, multi-shift averaging can yield

unrealistically low estimates of the dust

concentration to which a miner is typically

exposed. Some of these commenters also

argued that the Mine Act requires the dust

concentration to be regulated on each shift,

and that multi-shift averaging is inherently

misleading in detecting excessive dust

concentration on an individual shift.

Those advocating multi-shift averaging

generally assumed that the measurement

objective is to estimate a miner’s average dust

exposure over a period longer than an

individual shift. This assumption is flawed,

as shown by the fact that section 202(b) of

the Mine Act specifies that each operator will

continuously maintain the average

concentration of respirable dust in the mine

atmosphere during each shift at or below the

applicable standard. Some of those

advocating multi-shift averaging, however,

suggested that MSHA should average

measurements obtained on different shifts

even if the quantity of interest is dust

concentration on an individual shift. These

commenters argued that averaging smooths

out the effects of measurement errors, and

that therefore the average over several shifts

would represent dust concentration on each

shift more accurately than the corresponding

individual, full-shift measurement.

The Secretaries recognize that there are

circumstances, not experienced in mining

environments, under which averaging across

shifts could improve the accuracy of an

estimate for an individual shift. Just as

averaging the positions of arrows aimed at

nearly coinciding targets might better locate

the bull’s eye than the position of any

individual arrow, the gain in precision

obtained by averaging dust concentrations

observed on different shifts could, under

analogous circumstances, outweigh the bias

introduced by using the average to estimate

dust concentration for an individual shift.

This would be the case, however, only if

variability in dust concentration among shifts

were small compared to variability due to

measurement imprecision. It would do no

good to average the location of arrows aimed

at different targets unless the targets were at

nearly identical locations.

To the contrary, several previous

commenters pointed out that variability in

dust concentration from shift to shift tends to

be much larger than variability due to

measurement error and introduced evidence

in support of this observation. Measurements

on different shifts are like arrows aimed at

widely divergent targets. The more that

conditions vary, for any reason, from shift to

shift, the more bias is introduced by using a

multi-shift average to represent dust

concentration for any individual shift. Under

these circumstances, any improvement in

precision to be gained by simply averaging

results is small compared to the bias

introduced by such averaging. Therefore, the

Secretaries have concluded that MSHA’s

existing practice of averaging measurements

collected on different shifts does not improve

accuracy in estimating dust concentration to

which a miner is exposed on any individual

shift. To paraphrase one previous

commenter, averaging Monday’s exposure

measurement with Tuesday’s does not

improve the estimate of Monday’s average

dust concentration.

Some previous commenters argued that

since the risk of pneumoconiosis depends on

cumulative exposure, the measurement

objective should be to estimate the dust

concentration to which a miner is typically

exposed and to identify cases of excessive

dust concentration over a longer term than a

single shift. Other previous commenters

claimed that a multi-shift average does not

provide a good estimate of either typical dust

concentrations or exposures over the longer

term. These commenters claimed that

different shifts are not equally representative

of the usual atmospheric conditions to which

miners are exposed, implying that the

average of measurements made on different

shifts of a multi-day MSHA inspection tends

to systematically underestimate typical dust

concentrations.

The Secretaries interpret the Mine Act as

requiring that dust concentrations be kept at

or below the applicable standard on each and

every shift. Nevertheless, the Secretaries

recognize that, under certain conditions, the

average of measurements from multiple shifts

can be a better estimate of ‘‘typical’’

atmospheric conditions than a single

measurement. This applies, however, only if

the sampled shifts comprise a random or

representative selection of shifts from

whatever longer term may be under

consideration. As shown below, evidence to

the contrary exists, supporting those

commenters who maintained that

measurements collected over several days of

a multi-day MSHA inspection do not meet

this requirement. Therefore, the Secretaries

have concluded that averaging such

measurements is likely to be misleading even

for the purpose of estimating dust

concentrations to which miners are typically

exposed.

Whether the objective is to measure

average dust concentration on an individual

shift or to estimate dust concentration typical

of a longer term, the arguments presented for

averaging across shifts all depend on the

assumption that every shift sampled during

an MSHA inspection provides an unbiased

representation of dust exposure over the time

period of interest.31 To check this

assumption, MSHA performed a statistical

analysis of multi-shift MSHA inspections

carried out prior to the SIP. This analysis,

placed into the record in September 1994,

examined the pattern of dust concentrations

measured over the course of these multi-shift

inspections and compared results from the

final shift with results from a subsequent

single-shift sampling inspection (Kogut,

September 6, 1994b).

The analysis found that dust

concentrations measured on different shifts

of the same MSHA inspection were not

randomly distributed. The later samples

tended to show significantly lower results

than earlier samples, indicating that dust

concentrations on later shifts of a single

inspection may decline in response to the

presence of an inspector. Furthermore, the

analysis provided evidence that the

reduction in dust concentration tends to be

reversed after the inspection is terminated.

These two results led to the conclusion that

averaging dust concentrations measured on

different shifts of a multi-day MSHA

inspection introduces a bias toward

unrealistically low dust concentrations.

One previous commenter questioned the

validity of this analysis, stating that ‘‘there is

absolutely no basis in the * * * report for

the assertion that the trend is reversed after

the inspection is terminated.’’ This

commenter apparently overlooked Table 3 of

the report. That table shows a statistically

significant reversal at those mine entities

included in the analysis that were

subsequently inspected under MSHA’s SIP.

Dust concentrations measured at these mine

entities had declined significantly between

the first and last days of the multi-shift

inspection. It was primarily to address the

commenter’s implication that these

reductions reflected permanent ‘‘adjustments

in dust control measures’’ that the analysis

included a comparison with the subsequent

SIP inspection. An increase, representing a

reversal of the previous trend, was observed

on the single shift of the subsequent

inspection, relative to the dust concentration

measured on the final shift of the previous

multi-shift inspection. This reversal was

found to be ‘‘statistically significant at a

confidence level of more than 99.99 percent.’’

The same commenter also stated that

MSHA ‘‘* * * fails to address the systematic

[selection] bias of the study. MSHA only does

multiple day sampling when the initial

results are higher, but not out of

compliance.’’ It is true that in order to be

selected for revisitation, a mine entity must

have shown relatively high concentrations on

the first shift—though not, in the case of an

MMU, so high as to warrant a citation on first

shift. Since no experimental data were

available on mine entities randomly selected

to receive multi-shift inspections, the only

cases in which patterns over the course of a

multi-shift inspection could be examined

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42111

were cases selected for multi-shift inspection

under these criteria.

Although the impact of the selection

criteria was not explicitly addressed, it was

recognized that entities selected for multiday inspections do not constitute a random

selection of mine entities. This recognition

motivated, in part, the report’s comparison of

the final shift measurement to the dust

concentration measured during a subsequent

single-shift inspection. The magnitude of the

average reversal indicates that most of the

reduction observed over the course of the

multi-shift inspection cannot be attributed to

the selection criteria. Furthermore, it was not

only mine entities with relatively low dust

concentration measurements that were left

out of the study group. Mine entities with the

highest dust concentration measurements

were immediately cited based on the average

of measurements taken and excluded from

the group subjected to multi-shift dust

inspections. Therefore, the effect on the

analysis of selecting mine entities with

relatively high initial dust concentration

measurements was largely offset by the effect

of excluding those entities with even higher

initial measurements. In any event, the

magnitude of the average reduction between

first and last shifts of a multi-shift inspection

was significantly greater than what can be

explained by selection for revisitation due to

measurement error on the first shift sampled.

The assumption that multiple shifts

sampled during a single MSHA inspection

are equally representative is clearly violated

if, as some commenters alleged, operating

conditions are deliberately altered after the

first shift in response to the continued

presence of an MSHA inspector and then

changed back after the inspector leaves.

However, if samples are collected on

successive or otherwise systematically

determined shifts or days, the assumption

can also be violated by changes arising as

part of the normal mining cycle. As one

commenter pointed out, multi-shift averaging

within a single MSHA inspection potentially

introduces biases typical of ‘‘campaign

sampling,’’ in which observations of a

dynamic process are clustered together over

a relatively narrow time span. In order to

construct an unbiased, multi-shift average for

each phase of mining activity, it would be

necessary to collect samples from several

shifts operating under essentially the same

conditions. Alternatively, to construct an

unbiased, multi-shift estimate of dust

concentration over a longer term, it would be

necessary to collect samples from randomly

selected shifts over a period great enough to

reflect the full range of changing conditions.

Neither requirement is met by multi-shift

MSHA inspections because (1) the mine

environment is dynamic and no two shifts

are alike and (2) MSHA inspectors are not

there long enough to observe every condition

in their inspection.

Based on the analysis presented by Kogut

(September 6, 1994b) and also on public

comments received in response to the

February 18 and June 6, 1994, notices, the

Secretaries have concluded that it should not

be assumed that multiple shifts sampled

during a single MSHA inspection are equally

representative of atmospheric conditions to

which a miner is typically exposed. This

conclusion undercuts the rationale for multishift averaging within a single MSHA

inspection, regardless of whether the

objective is to estimate dust concentration for

the individual shifts sampled as it is for

MSHA inspector sampling or for typical

shifts over a longer term as implied by some

commenters. Measurements collected by

MSHA on consecutive days or shifts of the

same inspection do not comprise a random

or otherwise representative sample from any

larger population of shifts that would

properly represent a long-term exposure or a

particular phase of the mining cycle.

Therefore, there is no basis for assuming that

multi-shift averaging improves accuracy or

reduces the risk of an erroneous enforcement

determination.

Appendix B—Why Individual

Measurements are Unbiased

The accuracy of a measurement depends

on both precision and bias (Kennedy, et al.,

1995). Precision refers to consistency or

repeatability of results, and bias refers to an

error that is equally present in every

measurement. Since the amount of dust

present on a filter capsule is measured by

subtracting the pre-exposure weight from the

post-exposure weight, any bias present in

both weight measurements is mathematically

canceled out by subtraction. A control filter

capsule is pre- and post-weighed along with

the exposed filter capsules. The weight gain

of each exposed capsule is adjusted by

subtracting the weight gain or loss of the

control filter capsule. Consequently, any bias

due to differences in pre- and post-exposure

laboratory conditions, or to changes

introduced during storage and handling of

the filter capsules, is also mathematically

canceled out. Therefore, since respirable dust

is defined by section 202(e) of the Mine Act

(30 U.S.C. 842(e)) to be whatever is measured

by an approved sampler unit, the Secretaries

have concluded that a single, full-shift

measurement made with an approved

sampler unit provides an unbiased

representation of average dust concentration

for the shift and sampling location sampled.

Some previous commenters, however,

suggested that MSHA’s sampling and

analytical method is subject to systematic

errors that would have the same effect on all

measurements. These comments are

addressed in this appendix.

I. The Value of the MRE Conversion Factor

The current U.S. coal mine dust standard

is based on studies of British coal miners. In

these studies, full-shift dust measurements

were made using a sampler employing four

horizontal plates which removed the largesized particles by gravitational settlement

(simulating the action of the nose and throat)

and collecting on a pre-weighed filter those

particles which are normally deposited in the

lungs (Goddard, et al., 1973). This

instrument, known as the Mining Research

Establishment (MRE) sampler, was designed

to collect airborne dust according to a

collection efficiency curve, developed by the

British Medical Research Council (BMRC) to

approximate the deposition of inhaled

particles in the lung. Because the MRE

instrument was large and cumbersome, other

samplers using a 10-mm nylon cyclone were

developed for taking samples of respirable

dust in U.S. coal mines. However, these

cyclone-based samplers collected less dust

than the MRE instrument. Therefore, a factor

was derived (1.38) to convert measurements

obtained with the cyclone-based samplers to

measurements obtained with the MRE

instrument.

Two previous commenters noted that the

1.38 conversion factor was derived from a

comparison of MRE measurements to

measurements obtained using pumps made

by two manufacturers: Mine Safety

Appliances Co. and Unico. These

commenters noted that there was some

variability in these comparisons that MSHA

and NIOSH did not consider in estimating

CVtotal, and stated that MSHA and NIOSH

should therefore make allowances for any

error or uncertainty in the conversion factor.

It was also noted that the report deriving the

conversion factor showed that Mine Safety

Appliances Co. pumps more closely

approximated MRE concentrations than

Unico pumps, indicating that the 1.38

conversion factor (derived empirically using

both types of pumps) may systematically

overestimate the MRE-equivalent dust

concentration for Mine Safety Appliances Co.

samplers specifically. This commenter

argued that such potential bias in the

conversion factor should be addressed in

order to account for the possibility of a

systematic error in the conversion.

The study referred to these previous

commenters involved collecting side-by-side

samples using MRE and cyclone-based

samplers (Tomb, et al., 1973). The data

showed that multiplying the cyclone sample

concentrations by a constant factor of 1.38

gave values in reasonable agreement with

MRE measurements. Consequently, a

conversion factor of 1.38 was adopted for use

with approved sampler units equipped with

the 10-mm nylon cyclone.

Variability in the operating characteristics

of individual sampler units is expressed by

CVsampler. In response to the comment on

potential bias, MSHA and NIOSH reviewed

the original report recommending the 1.38

MRE conversion factor. This report contained

both an empirical determination, using sideby-side comparison data collected in

underground coal mines, and a theoretical

determination of the conversion factor. Two

sets of field data were collected: one set was

collected by mine inspectors who visited 200

coal mines across the U.S.; the other set was

collected by investigators from MSHA’s

Pittsburgh laboratory at 24 coal mines. Linear

regression was used to analyze both sets of

data, with the slope of the regression line

representing the conversion factor. The

theoretical determination suggested that the

conversion factor should be close to a value

of 1.35. Analysis of the district mine

inspector data resulted in a conversion factor

of 1.38, while analysis of the laboratory

investigator data suggested a greater

conversion factor of 1.45.

Because the conversion factor derived from

the inspector data came closer to the

theoretical value, the former U.S. Bureau of

Mines’ Pittsburgh Technical Support Center

42112 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

32Prior to mid-1995 there were two additional

sources of uncertainty in the weight gain recorded

for MSHA inspector samples. First, filter capsules

were routinely weighed in different laboratories

before and after exposure, without use of blank

filters or control filters, thus subjecting them to

interlaboratory variability. Second, the pre- and

post-exposure weights were both truncated down to

the nearest exact multiple of 0.1 mg, below the

weight actually measured, prior to recording weight

gain and calculating dust concentration.

(in the Department of Interior) recommended

that 1.38 be the value adopted for any

approved sampler unit operating at 2.0 L/min

and equipped with a 10-mm nylon cyclone.

This recommendation was subsequently

accepted. The 1.38 conversion factor was not,

as implied by the commenters, meant to

represent the average value to be used with

two different types of sampler unit, one of

which is no longer in use. Instead, based

largely on the theoretical value, it was meant

to represent the appropriate value to be used

with any approved sampler unit operating at

2.0 L/min and equipped with a 10-mm nylon

cyclone. No data or analyses were submitted

to suggest that this conversion factor, which

has been accepted and used for over twenty

years, should be any other value.

II. Conforming to the ACGIH and ISO

Standard

One commenter implied that the respirable

dust cyclone specifications used by MSHA

result in a different particle collection

efficiency curve than that specified by the

American Conference of Governmental

Industrial Hygienists (ACGIH) and the

International Organization for

Standardization (ISO) for a respirable dust

sampler. Other previous commenters

questioned whether the 2.0 L/min flow rate

used by MSHA was appropriate, since a

NIOSH study recommended using a 1.7 L/

min flow rate when conforming to the

recently adopted ACGIH/ISO specifications

for collecting respirable particulate mass.

It is true that MSHA’s respirable dust

cyclone specifications result in a different

particle size distribution than that specified

by ACGIH and ISO. However, this fact has no

bearing on the conversion to a respirable dust

concentration as measured by an MRE

sampler, which is the basis of the respirable

dust standard. The 1.38 factor used to obtain

an MRE-equivalent concentration was

derived for a cyclone flow rate of 2.0 L/min.

If a flow rate of 1.7 L/min were used, then

this would correspond to some other factor

for converting to an MRE-equivalent dust

concentration. Therefore, the particle size

distribution obtained at 2.0 L/min governs

the relationship derived between an

approved respirable coal mine dust sampler

and an MRE sampler. The appropriate dust

fraction (i.e., the fraction corresponding to

the 1.38 conversion factor) is sampled so long

as the specified 2.0 L/min flow rate is

maintained.

III. Effects of Other Variables

The effects of any other variables on the

sampled dust fraction are covered by the 1.38

conversion factor, so long as these effects

were present in the data from which the

conversion factor was obtained. For example,

one commenter expressed concern that nylon

cyclones are subject to performance

variations due to static charging phenomena.

Any systematic effect of static charging on

the performance characteristics of the nylon

cyclone is implicitly accounted for in the

conversion factor, because the same static

charging effect would have been present

when the comparative measurements were

obtained for deriving the relationship

between an approved sampler unit and an

MRE instrument. Random effects of static

charging, i.e., effects that vary from sample to

sample, are included in CVtotal.

Appendix C—Components of CV total

I. Weighing Uncertainty

(a) Derivation of CVweight

The weight of a dust sample is determined

by weighing each filter capsule before and

after exposure and then determining the

weight gain by subtraction. This weight gain

is adjusted by subtracting any change in

weight observed for the unexposed, control

filter capsule. This practice eliminates

potential biases due to any possible

outgassing of the plastic cassette or other

time-related factors but introduces two

additional weighings. The weighing process

is designed to control potential effects of

temperature, humidity, and contamination.

However, because the initial and final

weighings of both the exposed and the

control filter capsules are each still subject to

random error, there is some degree of

uncertainty in the computed weight of dust

collected on the filter.

For both the control and the exposed filter

capsule, the error in the weight-gain

measurement results from combining two

independent weighing errors. For example,

suppose that the true pre- and post-exposure

weights of a filter capsule are W1 = 392.275

mg and W2 = 392.684 mg, respectively. The

true weight gain (G) would then be:

G =−= W W mg. 2 1 0.409

If, due to weighing errors, pre- and postexposure weights were measured at w1 =

392.282 mg and w2 = 392.679 mg,

respectively, then the measured weight gain

(g) would be:

gw w =−= 2 1 0 397 . mg.

The error (e) in this particular weight-gain

measurement, resulting from the combination

of a 7 μg error in w1 and a5 μg error in w2,

would then be:

e = g G

 w W

 = w 

 = 5 

2 2

2

−

= − ( ) − − ( )

( ) − − − ( )

− − =−

w W

W wW

g

1 1

2 11

32 7 12 μ

Imprecision in the true weight gain is

expressed by Qe, the standard deviation of e.

When a weight-gain measurement (g) is

converted to an MRE-equivalent

concentration (in units of mg/m3) based on

a 480-minute sample at 2.0 L/min, both the

actual weight gain (G) and the weight-gain

error (e) are multiplied by the same factor:

138

480 2 1

1000

1

3 3

. .438

 min liters

min

 m

 liters ⋅ ⋅

= m

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42113

Therefore, the standard deviation of the

propagated weighing error component in a

single, full-shift measurement (x = g·1.438/

m3) is 1.438σe mg/m3, assuming no

adjustment for weight change in the control

filter capsule.

Since a control filter capsule will is used

to eliminate potential bias, the weight gain

measured for the exposed filter (g) is adjusted

by subtracting the change in weight (which

may be positive or negative) observed for the

control filter capsule (g′). Therefore, the

adjusted measurement of dust concentration

is

x gg ' ' .438 . = − ( )⋅1 3 / m

Any change in weight observed for the

control filter capsule is subject to the same

measurement imprecision due to random

weighing errors, represented by σe, as the

weight gain measurement for an exposed

filter. In addition to the weight-gain error for

the exposed filter whose measured weight

gain is g, x′ will also contain a weight-gain

error contributed by the measured change in

weight of the control filter capsule (g′). Using

a standard propagation-of-errors formula, the

imprecision is represented by

σσ σ σ ee e e

22 2 += = ⋅ 2 2

Therefore, the standard deviation of the

propagated weighing error component in the

adjusted measurement is 1.438σe√2 mg/m3.

To form an estimate of CVweight when

control filter capsules are used, the estimated

value of 1.438σe is multiplied by √2 and

expressed as a percentage of the true dust

concentration being measured (X):

CV

X weight e = ⋅ ⋅ 1 2 100% 3 .438 ( ) σ

Since σe is essentially constant with respect

to dust concentration, CVweight decreases as

the dust concentration increases.

(b) Values Expressing Uncertainty Due to

Random Errors in Weight-Gain

Measurements

Table C–1 summarizes 13 different

estimated values for σe. Six of these values

were mentioned during earlier proceedings

related to this notice, and two additional

values for σe are derived in this appendix

from data introduced during these earlier

proceedings. Three other values for σe are

derived from data and statistical analyses

placed into the record along with the Federal

Register notices published by MSHA and

NIOSH on February 3, 1998 (Parobeck, et al.,

1997; Wagner, May 28, 1997). The remaining

two values of σe are derived in an analysis

being placed into the record in connection

with the present Federal Register notice

(Kogut, et al., 1999). The 13 values listed in

Table C–1 are not inconsistent, but as

explained below, represent estimates of

weight-gain imprecision during different

historical periods or under different sample

processing procedures. Eleven of these values

are based on weight gains measured for

capsules employing a Tyvek; filter support

pad. Two are based on capsules with

stainless steel support pads.

TABLE C–1.—STANDARD DEVIATION OF ERROR IN WEIGHT GAIN (σe)

Description Reference σe (μg)

MSHA’s historical estimate of upper bound ..................................................................... 59 FR 8356; Kogut, September 6, 1994a .. 97.4

1981 measurement assurance estimate;† older technology, truncation of weights ........ Parobeck, et al., 1981; Bartley, September

7, 1994.

81

300 unexposed tamper-resistant capsules pre- and post-weighed in different labs;† no

truncation.

Kogut, May 12, 1994 .................................. 29

Inspector samples processed between late 1992 and mid 1995;† capsules pre- and

post-weighed in different labs with truncation; estimate adjusted for differences between labs.

Appendix C ................................................. 51.7

NMA data obtained from samples collected by Skyline Coal, Inc.† ................................ Appendix D ................................................. 76

Value used in NIOSH ‘‘indirect approach’’ based on repeated measurements on same

day and in same lab;† derived from Kogut.

61 FR 10012; Kogut, May 12, 1994 ........... 5.8

1995 MSHA field study;† capsules pre-weighed, assembled, and post-weighed by

MSHA.

Kogut, et al., 1997; Wagner, 1995 ............. 9.1

1996 measurement assurance estimate † ....................................................................... 61 FR 10012; Tomb, February 16, 1996 ... 6.5

75 unexposed capsules recalled from MSHA field offices † ............................................ Wagner, May 28, 1997 ............................... 8.2

50 replicate weighings of 16 unexposed filter capsules † ................................................ Parobeck, et al., 1997 ................................ 10.3

50 replicate weighings of 16 unexposed filter capsules † ................................................ Parobeck, et al., 1997 ................................ 11.2

2,640 unexposed ‘‘quality control’’ capsules pre-weighed by MSHA, assembled by

MSA, and subsequently post-weighed by MSHA †.

Kogut, et al., 1999 ...................................... 11.3

300 unexposed capsules pre-weighed by MSHA, assembled by MSA, carried during

MSHA inspection, and subsequently post-weighed by MSHA‡.

Kogut, et al., 1999 ...................................... 11.6

†Tyvek support pad.

‡ stainless steel support pad.

MSA Mine Safety Appliances Co.

In MSHA’s February 1994 notice, 1.438σe

(identified as ‘‘variability associated with the

pre- and post-weighing of the filter capsule’’)

was presented as 0.14 mg/m3, or 7 percent of

2.0 mg/m3, as described in Kogut (September

6, 1994a). It follows that the value of σe

42114 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

33To construct a 90-percent confidence interval

for σe, based on the Skyline data, the 15-μg

‘‘standard error of the estimate’’ must be multiplied

by a confidence coefficient of 1.64.

implicitly assumed in MSHA’s February

1994 notice (obtained by dividing 0.14 by

1.438) was 0.0974 mg (97.4 μg). Seven

percent of 2.0 mg/m3 had been used by

MSHA from the inception of its dust

enforcement program to represent an upper

bound on weighing imprecision in a dust

concentration measurement.

After publication of the February 1994

notice, several other candidate values for σe

were placed into the public record. In 1981,

based on data collected to implement a

measurement assurance program in MSHA’s

weighing laboratory, σe was estimated using

a method developed by the NBS to be 0.0807

mg (80.7 μg) (Parobeck, et al., 1981). The

published NBS estimate reflected weighing

technology in place at the time the article

was published (1981), as well as the practice

(no longer in effect for MSHA inspector

samples) of truncating both the pre- and postexposure weights down to an exact multiple

of 0.1 mg. This estimate was used to calculate

CVweight by Bartley (September, 1994).

Some previous commenters misread or

misunderstood the published NBS estimate.

One of these previous commenters claimed

that ‘‘the only published report of the

weighing error in MSHA’s laboratory * * *

was 0.16 mg of variation, which would

convert to a concentration of 0.20 mg/m3

compared to the 0.14 mg/m3 * * * MSHA

and NIOSH used.’’ This is incorrect, since the

standard deviation of weight-gain errors

(including the effect of truncation) is actually

identified as 0.0807 mg in the Appendix to

Parobeck, et al., (1981). The 0.16-mg figure

quoted by the commenter is presented in that

paper as defining a 2-tailed 95-percent

confidence limit, for use in establishing

process control limits. It is derived by

multiplying σe by 2.0. As explained above,

the published value of σe = 0.0807 mg is

multiplied by 1.438 m¥3 to propagate an

MRE-equivalent concentration error of 0.116

mg/m3. Contrary to the commenters’

assertion, this is less—not more—than the

quantity (0.14 mg/m3) assumed in the

February 1994 notice.

In September 1994, a more recent analysis

was placed into the public record, based on

repeated weighings of 300 unexposed filter

capsules, each of which was weighed once in

the Mine Safety Appliances Co. laboratory

and twice in MSHA’s laboratory using

current equipment (Kogut, May 12, 1994).

Based on this analysis, σe was estimated to

be 29 μg for pre- and post-weighings on

different days at different laboratories, or 5.8

μg for pre- and post-weighings on the same

day within MSHA’s laboratory. The 5.8-μg

value was used as part of the NIOSH

‘‘indirect approach’’ in its 1995 accuracy

assessment (Wagner, 1995). Neither of these

two estimates, however, reflects the effects of

truncation or of a mean difference of about

12 μg discovered between weighings in the

two laboratories. Combining these two

additional effects with the 29-μg estimate

results in an adjusted estimate of σe = 51.7

μg for weighings made in different

laboratories and truncated to a multiple of

0.1 mg. MSHA and NIOSH regard this 51.7-

μg value to be the best available estimate of

σe for inspector samples processed between

late 1992, when the current style of (tamperresistant) cassette was introduced, and mid1995, changes in inspector sample processing

were implemented.

Some previous commenters suggested that

the estimates of σe, placed into the record in

September 1994, did not adequately account

for potential errors in the weighing process

as it existed at that time. One of these

previous commenters asserted that truncation

error was an additional source of uncertainty

that had not been accounted for. As

explained above, however, σe accounts for

uncertainty deriving from both the pre- and

post-exposure weighings. Both the 80.7-μg

NBS estimate and the 97.4-μg value assumed

in the February 1994 notice included the

effects of truncating weight measurements to

0.1 mg. Truncation effects are also included

in the 51.7-μg estimate.

Some previous commenters expressed

special concern over the accuracy of preexposure filter capsule weights as measured

by Mine Safety Appliances Co. One

commenter expressed ‘‘grave concern’’ with

regard to the 12-μg systematic difference in

weights found between Mine Safety

Appliances Co. and MSHA weighings of the

same unexposed capsules, as described in

MSHA’s 1994 analysis (Kogut, May 12, 1994).

These concerns became moot, at least with

respect to MSHA’s inspector sampling

program, when MSHA began pre- and postweighing all inspector samples at MSHA’s

laboratory. Furthermore, any potential bias

resulting from differences in laboratory

conditions on the days of pre- and postexposure weighings should now be

eliminated by the use of control filter

capsules. However, contrary to this

commenter’s interpretation, the analysis

submitted to the record in September 1994

resulted in a substantially lower estimate of

σe than that assumed in the February 1994

notice—even after adjustment for the 12-μg

systematic difference observed between

weighing laboratories. The 51.7-μg estimate

discussed above includes this adjustment.

MSHA and NIOSH also analyzed data

submitted by the NMA in connection with

these proceedings. An important result of

that analysis, described in Appendix D, was

an estimate of σe equal to 76 μg ± 15 μg.33

This estimate is not significantly different,

statistically, from either the 97.4-μg value

assumed in the February 1994 notice, the

80.7-μg NBS estimate, or the 51.7-μg value

estimated for samples collected between late

1992 and mid-1995. Since the NMA data

were obtained from samples collected by

Skyline Coal, Inc. prior to 1995, the

Secretaries believe these data confirm the

51.7-μg value of σe applicable to the Skyline

samples. The estimate of σe obtained from the

Skyline data is, however, significantly greater

than the value estimated for weight-gain

measurements under MSHA’s current

inspection program. This is explained by the

fact that when the Skyline samples were

collected, all samples were weighed in

different laboratories before and after

sampling, and the weights were truncated to

0.1 mg. before calculating the weight gain.

Both truncation of weights and the practice

of pre- and post-weighing samples in

different laboratories were discontinued for

inspector samples in mid-1995. Under

MSHA’s revised procedures for processing

inspector samples, filter capsules were

weighed both before and after sampling in

MSHA’s laboratory. Furthermore, MSHA

began to use weights recorded to the nearest

μg in calculating dust concentrations.

Therefore, the 5.8-μg estimate of σe described

above, applying to pre- and post-exposure

weighings in the same laboratory using

current equipment and no truncation, was

used by NIOSH to calculate CVweight as part

of the NIOSH ‘‘indirect’’ evaluation of CVtotal,

placed into the public record on March 12,

1996.

Based on the results of MSHA’s 1995 field

study, σe was estimated to be 9.12 μg (Kogut,

et al., 1997). The filter capsules involved in

this study were used to collect respirable coal

mine dust samples in an underground mine

between pre- and post-exposure weighings in

MSHA’s laboratory, potentially subjecting

them to unknown sources of variability in

weight gain not covered by the laboratory

estimates. Substituting the estimated value of

σe = 9.12 μg into Equation 3 results in a

corresponding estimate of CVweight that

declines as the sampled dust concentration

increases—ranging from 9.3 percent at dust

concentrations of 0.2 mg/m3 to less than one

percent at concentrations greater than 2.0

mg/m3. This estimate of CVweight applies to

the procedure utilizing control filter

capsules.

An updated estimate of σe = 6.5 μg was also

calculated using the published NBS

procedure for filter capsules processed with

the current equipment and procedures for

inspector samples. This estimate, derived

from weighing the same group of 55

unexposed filter capsules 139 times over a

218-day period, was described in material

placed into the public record on March 12,

1996 (Tomb, February 16, 1996). The 6.5 μg

estimate applies to filter capsules pre- and

post-weighed robotically on different days

within MSHA’s laboratory, but it does not

reflect any potential effects of removing the

capsule from the laboratory and exposing it

in the field between weighings.

The estimate of imprecision in measured

weight gain derived from MSHA’s 1995 field

study discussed earlier (9.1 μg), falls only

slightly above the 6.5-μg laboratory estimate.

This suggested that the process of handling

and actually exposing the filter capsule in a

mine environment does not add appreciably

to the imprecision in measured weight gain.

In February 1997, 75 unexposed filter

capsules that had been pre-weighed in

MSHA’s laboratory and distributed to MSHA

district offices were recalled and reweighed.

After adjusting for variability attributable to

the date of initial weighing (i.e., variability

that would be eliminated by use of a control

filter capsule), these data provided an

estimate of σe equal to 8.2 μg (Wagner, May

28, 1997). This estimate, based on weighings

separated by a span of about four to five

months, corroborated the 9.1-μg estimate

obtained from MSHA’s 1995 field study.

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42115

An MSHA report placed into the public

record with the December 31, 1997 Federal

Register notices described results from an

experiment in which 32 filter capsules were

each weighed on 50 different days,

alternating between the MSHA and Mine

Safety Appliances Co. laboratories. Sixteen of

these capsules employed a Tyvek filter

support pad of the type approved under 30

CFR part 74. The remaining sixteen were of

the modified type, in which the Tyvek

support pad was replaced by a stainless steel

support pad. The residual variance

associated with an individual weight

measurement was found to be 53.5 μg2 for

filter capsules employing a Tyvek support

pad and 62.9 μg2 for capsules employing a

stainless steel support pad (Parobeck, et al.,

1997, Table 3.) These figures represent the

squared residual variability not ‘‘explained’’

by repeated handling, elapsed time, changes

in laboratory conditions, or other terms of the

model used in the report. The other sources

of variability reported (i.e., those ‘‘explained’’

by the model) are all eliminated by the use

of a control filter. Therefore, since

measurement of a weight gain requires two

measurements of weight, the corresponding

estimates of σe are (2·53.5)1/2 = 10.3 μg for

Tyvek-supported filters and (2·62.9)1/2 =

11.2 μg for stainless steel.

The final two values for σe presented in

Table C–1 of this appendix are based on filter

capsules pre-weighed in MSHA’s laboratory,

sent to Mine Safety Appliances Co. for

assembly into standard plastic cassettes, and

then later weighed a second time in MSHA’s

laboratory. This is currently the normal

practice for filter capsules used by MSHA

inspectors. Both of these values, summarized

below, are derived in a statistical analysis

being placed into the public record along

with this notice (Kogut, et al., 1999, Table A–

2). In that analysis, ‘‘σn’’ represents the

portion of uncertainty in a weight gain

measurement that a control filter correction

cannot be expected to eliminate. This

includes both weighing imprecision and

spurious but unsystematic changes in weight,

such as might be due to random

contamination. Therefore, in the present

context, σe can conservatively be identified

with σn.

In 1998, to maintain quality control for the

production of filter capsules used in MSHA’s

enforcement program, 2,640 unexposed filter

capsules were weighed at MSHA’s laboratory

before and after assembly by Mine Safety

Appliances Co. All of these capsules

employed a Tyvek filter support pad. The

estimated value for σn (here identified with

σe) associated with these capsules was 11.3

μg.

In 1999, MSHA performed a special

Modified Filter Capsule Study (MFCS) in

which the Tyvek filter support pad was

replaced by a stainless steel support pad. The

purpose of the MFCS was to quantify the

impact of such a substitution on the accuracy

of respirable coal mine dust measurements.

Based on an analysis of weight gains

measured for 300 modified filter capsules, σn

(here identified with σe) was estimated to be

11.6 μg. All of these capsules were initially

weighed in MSHA’s laboratory, assembled

into cassettes by Mine Safety Appliances Co.,

distributed to MSHA inspectors, carried but

not exposed during a mine inspection, and

then weighed for a second time in MSHA’s

laboratory. The 11.6 μg value represents the

combined effects of weighing imprecision

and random contamination during assembly,

distribution, and field use. It therefore

provides a conservative estimate of σe for

filter capsules employing stainless steel

support pads.

(c) Negative Weight-Gain Measurements

Some previous commenters pointed out

that MSHA routinely voids samples when the

measured pre-exposure weight of a filter

capsule is greater than the measured postexposure weight. According to these

commenters, such occurrences reflect an

unacceptable degree of inaccuracy in weightgain measurements. One commenter asserted

that such cases are ‘‘of particular significance

when only one sample is relied upon.’’ This

commenter attributed such occurrences

solely to errors in the capsule pre-weight and

implied that they should not be expected to

occur under MSHA’s quality assurance

program. It was, therefore, implied that

negative weight-gain measurements are not

consistent with the degree of uncertainty

being attributed to weighing error.

Prior to implementation of the 1995

processing modifications, a significant

fraction of samples with less than 0.1 mg of

true weight gain (i.e., G < 0.10 mg) could be

expected to exhibit negative weight gains

(i.e., g ≤ ¥0.1 mg). Contrary to the

commenter’s implication, however, negative

weight-gain measurements do not arise

exclusively from positive pre-exposure

weighing errors (i.e., w1 > W1). They can also

arise, with equal likelihood, from negative

post-exposure weighing errors (i.e., w2 < W2).

What is required for a negative weight gain

(w2 < w1) is that e < ¥G. Since the true

weight gain (G) is always greater than or

equal to zero, this means that a negative

weight gain is observed when e is sufficiently

negative. Under standard assumptions of

normally distributed errors, σe fully accounts

for the probability of such occurrences.

Naturally, this probability becomes smaller

as G increases and also as σe decreases.

The occasional negative weight-gain

measurements that have been observed are

consistent with values of σe estimated for

previous processing procedures. Table C–2

contains the probability of a negative weightgain measurement for true weight gains (G)

ranging from 0.0 mg to 0.08 mg, assuming σe

= 51.7 μg and the previous practice of

truncation, which has now been

discontinued for inspector samples. Since the

purpose here is to evaluate the probability of

negative weight gains under MSHA’s

previous processing procedures, it is also

assumed that no control filter capsules are

used to adjust weight gains.

TABLE C–2.—PROBABILITY OF NEGATIVE WEIGHT-GAIN MEASUREMENT,

ASSUMING TRUNCATION AND σe =

51.7 μG

True weight gain G =

W2¥W1 (mg)

Estimated probability of negative

measurement, %

0.00 ................................. 12.9

0.01 ................................. 8.4

0.02 ................................. 5.1

0.03 ................................. 2.8

0.04 ................................. 1.5

0.05 ................................. 0.7

0.06 ................................. 0.4

0.07 ................................. 0.2

0.08 ................................. 0.1

Note: Tabled probabilities (in percent)

were obtained from a simulation of 35,000

weight-gain measurements at each value of G,

assuming normally distributed weighing

errors and the now discontinued practice of

measurement truncation.

One commenter suggested the use of a test

based on the frequency of negative weightgain measurements to check the magnitude of

the MSHA/NIOSH estimate of CVtotal. As

proposed by the commenter, the test of CVtotal

would consist of comparing the observed

proportion of samples voided due to a

negative recorded weight gain to the

proportion expected, given CVtotal equal to

the MSHA/NIOSH estimate. If the observed

proportion were to exceed the expected

proportion, then this would constitute

evidence that CVtotal was being

underestimated.

The commenter miscalculated the expected

proportion, because he mischaracterized the

MSHA/NIOSH estimate of CVtotal as constant

over the continuum of dust concentrations.

The MSHA/NIOSH estimate of CVtotal

increases as dust concentrations decrease.

This would cause a higher proportion of

negative results than what the commenter

projected under the MSHA/NIOSH estimate,

regardless of what statistical distribution of

dust concentrations is assumed. The

commenter’s projection also neglected to take

into account the effects of truncating pre- and

post-exposure weights to multiples of 0.1 mg.

Although this practice has now been

discontinued for MSHA inspector samples, it

is a factor in the available historical data.

In principle, if the statistical distribution of

true dust concentrations were known, the

expected proportion of samples voided for

negative weight gain could be recalculated to

reflect both a variable CVtotal and, when

applicable, truncation of recorded weights.

However, under the commenter’s proposal,

deriving the expected proportion of negative

measurements would involve not only CVtotal,

but also an estimate of the distribution of true

dust concentrations. Such an estimate would

rely on the tenuous assumption that a

mixture of dust concentrations in different

environments is closely approximated by a

lognormal distribution far into the lower

tail—i.e., even at concentrations extremely

near zero. Furthermore, valid estimation of

the lognormal parameters, applicable to dust

concentrations near zero, would be

42116 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

complicated by measurement errors,

especially those resulting in negative or zero

values. Depending on the data used,

truncation effects could also confound the

analysis.

Before truncation was discontinued,

negative weight-gain measurements were

caused by various combinations of pre- and

post-exposure weighing and truncation error.

Before MSHA began adjusting weight gains

using an unexposed control filter, differences

in laboratory conditions on the two weighing

days and/or unexplained but real systematic

weight losses over time may also have

contributed to the observed frequency of

negative weight gains. Now that truncation

has been removed as a source of error in

weight-gain measurements for inspector

samples, and control filters are used to

correct for systematic changes, the frequency

of negative weight gains observed historically

is largely irrelevant. Significant negative

weight-gain measurements—i.e., those that

cannot be explained by normal weighing

imprecision—are expected to occur less

frequently than in the past.

(d) Comparing Weight Gains Obtained From

Paired Samples

Some previous commenters maintained

that ‘‘although there may be slight differences

between how the samples are dried * * *’’

differences between the weight gain observed

in MSHA samples and simultaneous samples

collected nearby (and processed at an

independent laboratory) indicated a greater

degree of weighing uncertainty than what

was being assumed. In response to the

Secretaries’ request for any available data

supporting this position, results from paired

dust samples were provided by two coal

companies.

In comparing measurements obtained from

paired samples, there are several important

considerations that some previous

commenters did not take into account. First,

if two different sampler units are exposed to

identical atmospheres for the same period of

time, the difference between weight-gain

measurements g1 and g2 arises, in part, from

two independent weight-gain measurement

errors, e1 and e2. If uncertainty due to each

of these errors is represented by σe, then the

difference between g1 and g2 has uncertainty

due to weighing error equal to σe√2.

Consequently, weight gains measured in the

same laboratory, on the same day, for

different filter capsules exposed to identical

atmospheres can be expected to differ by an

amount whose standard deviation is 1.41σe.

Furthermore, if the two exposed capsules

are processed at different laboratories, the

difference in weight gains contains an

additional error term arising from differences

between laboratories. Evidence was

presented that this term (in the notation of

Kogut, May 12, 1994) is far more significant

than the intra-lab, intra-day weighing error in

MSHA’s laboratory. Moreover, the additional

uncertainty introduced by use of a third

laboratory also depends on unknown

weighing imprecision within that laboratory,

which may differ from that maintained by

MSHA’s measurement assurance process.

(See Appendix D for analysis of paired

sample data submitted by NMA).

However, the most important consideration

in comparing weight gains from two different

samples is that under real mining conditions,

the atmospheres sampled may not be

identical—even if the sampler units are

located near one another. Differences in

atmospheric dust concentrations over

relatively small distances have been

documented (Kissell, et al., 1993). Such

differences would be expected to produce

corresponding differences in weight gain that

are unrelated to the accuracy of a single, fullshift measurement as defined by the

measurement objective explained earlier in

this notice.

II. Pump Variability

The component of uncertainty due to

variability in the pump, represented by

CVpump, consists of potential errors associated

with calibration of the pump rotameter,

variation in flow rate during sampling, and

(for those pumps with rotameters) variability

in the initial adjustment of flow rate when

sampling is begun. The Secretaries believe

that CVpump adequately accounts for all

uncertainty identified by previous

commenters as being associated with the

volume of air sampled.

In deriving the Values Table published in

MSHA’s February 1994 notice, MSHA used

a value of 5 percent to represent uncertainty

associated with initial adjustment of flow

rate at the beginning of the shift and another

value of 5 percent to represent flow rate

variability. The 5-percent value for variability

in initial flow rate adjustment was estimated

from a laboratory experiment conducted by

MSHA in the early 1970s, while the value for

flow rate variability was based on the

allowable flow rate tolerance specified in 30

CFR part 74. This part requires that the flow

rate of all sampling systems not vary by more

than ±5 percent over a full shift with no more

than two adjustments. MSHA did not include

a separate component of variability for pump

rotameter calibration because it was already

included in the 5-percent value used to

represent flow rate variability.

Based on a review of published results by

Bowman et al. (1984), the Secretaries

concluded that the component of uncertainty

associated with the combined effects of

variability in flow rate during sampling and

potential errors in calibration is less than 3

percent. Therefore, as proposed in the March

12, 1996 notice, the Secretaries are now

estimating uncertainty due to variability in

flow rate to be 3 percent.

Because MSHA could not provide the

experimental data supporting the 5-percent

value used to represent uncertainty

associated with the initial adjustment of flow

rate, one commenter recommended that

MSHA conduct a new experiment. In

response to that request, MSHA conducted a

study to establish the variability associated

with the initial flow rate adjustment. The

study, placed into the public record on

September 9, 1994, attempted to emulate

realistic operating conditions by including a

variety of sampling personnel making

adjustments under various conditions.

Results showed the coefficient of variation

associated with the initial adjustment to be

3 ± 0.5 percent (Tomb, September 1, 1994).

The Secretaries consider this study to

provide the best available estimate for

uncertainty associated with the initial

adjustment of a sampler unit’s flow rate.

Therefore, as proposed in the March 12, 1996

notice, the Secretaries are now estimating

uncertainty due to variability in the initial

adjustment to be 3 percent.

One previous commenter expressed

concern regarding how representative

MSHA’s study on initial flow rate adjustment

was of actual sampling conditions. The

Secretaries consider the conditions under

which the study was conducted to have

adequately mimicked conditions under

which the flow rate of a coal mine dust

sampling system is adjusted. This was more

rigorous than the original study, from which

MSHA estimated the 5-percent value

assumed in the February 12, 1994 notice. The

tests were conducted in an underground

mine, using both experienced and

inexperienced persons to make the

adjustments. Also, the only illumination was

supplied by cap lamps worn by the person

making the adjustments. Tests were

conducted for adjustments made in three

different physical positions: standing,

kneeling and prone. Inspection personnel

participating in the study provided guidance

as to the methods typically used by

inspection personnel in adjusting pumps. In

fact, environmental conditions under which

the test was conducted were generally more

severe than those normally encountered by

inspection personnel, since initial

adjustment of the pumps normally occurs on

the surface just before the work shift begins.

The same commenter also questioned why

only the variability associated with initial

adjustment of the flow rate was estimated

and not the variability associated with

subsequent adjustments during the shift. This

is because the variability associated with the

subsequent flow rate adjustments of an

approved sampler unit is already included in

the 3-percent value estimated for variability

in flow rate over the duration of the shift.

Since variability in the initial flow rate

adjustment is independent of calibration of

the pump rotameter and variability in flow

rate during sampling, these two sources of

uncertainty can be combined through the

standard propagation of errors formula:

CVpump = + ( . 3%) 3% 4 2% ( ) = 2 2

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42117

34Section 74.3(13) requires that flow rate in an

approved sampler unit deviate from 2.0 L/min by

no more than 5 percent over an 8-hour period, with

no more than 2 readjustments after the initial

setting. However, this is a maximum deviation, and

the uncertainty associated with pump flow rate, as

quantified by its coefficient of variation, is 3

percent.

This estimate accords well with a more

recent finding based on 186 measurements in

an underground mine, using constant flowcontrol pumps (Kogut et al., 1997). That

study estimated CVpump = 4.0 percent and

concluded that CVpump was unlikely to

exceed 4.4 percent.

Three previous commenters stated that

there are reports of sampling pumps being

calibrated and used at altitudes differing by

as much as 3,000 feet and that, for many

pumps, this could result in more than a 3-

percent change in flow rate per 1,000 feet of

altitude. MSHA recognized this as a potential

problem as early as 1975. As a result, MSHA

conducted a study to ascertain the effect of

altitude on coal mine dust sampler

calibration (Treaftis, et al., 1976). The study

showed that both pump performance and

rotameter calibration were affected by

changes in altitude but that an approved

Mine Safety Appliances Co. sampling system,

calibrated and adjusted at an altitude of 800

feet to a flow rate of 2.0 L/min, would meet

the requirement of 30 CFR 74.3(11) when

sampling at an altitude of 10,000 feet, even

if no adjustment were made to the pump. The

study also provided equations for adjusting

the calibration mark on the pump rotameter

so that, when sampling at an altitude

different from the one at which the rotameter

was calibrated, the appropriate flow rate

would be obtained. These procedures are

used by MSHA inspectors in instances where

the sampling altitude is significantly

different from the altitude where the

sampling system is calibrated.

Some previous commenters questioned the

ability of the older Mine Safety Appliances

Co. Model G pumps to meet the same flow

rate specifications as new pumps. MSHA has

discontinued the use of these older pumps in

its sampling program and will be using only

flow-control pumps. More recent MSHA

studies show that these pumps continue to

meet the flow rate requirement of 30 CFR

74.3(11) at altitudes up to 10,000 feet (Gero,

et al., 1995). As a result, the flow-control

pumps currently used by inspectors can be

calibrated at one altitude and used at another

altitude with no additional adjustments made

to the pumps. Furthermore, all sampler units

used to measure respirable dust

concentrations in coal mine environments

are required to be approved in accordance

with the regulatory requirements of 30 CFR

part 74, which require flow rate consistency

to be within ± 0.1 L/min of the 2.0 L/min

flow rate.34 MSHA’s experience over the past

20 years has demonstrated that flow rate

consistency of older sampling systems will

continue to meet the requirements specified

in part 74, provided the systems are regularly

calibrated and maintained in approved condi

tion. To ensure that sampling systems

continue to meet the specification of part 74,

MSHA’s policy requires calibration and

maintenance by specially trained personnel

in accordance with MSHA Informational

Report No. 1121 (revised).

III. Intersampler Variability

Intersampler variability, represented by

CVsampler, accounts for uncertainty due to

physical variations from sampler to sampler.

Most of the previous commenters ignored

this source of uncertainty. One commenter,

however, stated that 10-mm nylon cyclones

are subject to performance variations due to

static charging phenomena (discussed in

Appendix B).

Intersampler variability was investigated

by Bowman, et al., (1984), Bartley, et al.

(1994), and Kogut, et al. (1997). Bowman, et

al. designed a precision experiment to

determine the contribution to CVtotal from

differences between individual coal mine

dust sampler units. Based on their

experiment, they reported CVsampler = 1.6

percent, which included variation in both the

10-mm nylon cyclone and the Mine Safety

Appliances Co. Model G pump. They

concluded that this low degree of component

variability indicates there is excellent

uniformity in the mechanical components of

dust sampler units. Bartley, from his

experimental investigation of eight 10-mm

nylon cyclones, estimated CVsampler to be no

more than 5 percent for aerosols with a size

distribution typical of those found in coal

mine environments. Based on an analysis

involving 32 different sampler units, Kogut,

J., et al., (1997) found that CVsampler was

unlikely to exceed 3.1 percent. Unlike

Bartley’s study, however, this analysis relied

on new cyclones, which might be expected

to exhibit less variability than older, heavily

used cyclones. Therefore, NIOSH used the

more conservative estimate of 5 percent, with

an upper 95-percent confidence limit of 9

percent, in its ‘‘indirect approach’’ for

estimating CVtotal and evaluating method

accuracy (Wagner, 1995).

Appendix D—Data Submitted by

Previous Commenters

During the public hearings, several

previous commenters indicated they had data

showing that MSHA and NIOSH had

underestimated the overall magnitude of

uncertainty associated with a single, full-shift

measurement. These data and accompanying

analyses were submitted to the record and

evaluated by MSHA and NIOSH. Some of the

data sets consisted of paired samples, where

two approved sampler units were placed

nearby one another and operated for a full

shift. One of the resulting samples was

analyzed in MSHA’s laboratory and the other

by an independent laboratory. These data

were represented as showing that single, fullshift measurements cannot be used to

accurately estimate dust concentrations.

Other data sets submitted consisted of

unpaired measurements collected from

miners at intervals over varying spans of

time. These data sets were represented as

showing that exposures vary widely between

shifts and between occupations.

I. Paired Sample Data Submitted by the

NMA

The American Mining Congress and

National Coal Association [AMC and NCA

have since merged into the National Mining

Association, (NMA)] submitted at the request

of MSHA and NIOSH a data set consisting of

381 pairs of exposure measurements. These

measurements had been obtained from the

‘‘designated occupations’’ on two longwall

and six continuous mining sections

belonging to Skyline Coal, Inc. Two sampling

units were placed on each participating

miner and operated for the full shift. After

sampling, one sample cassette was sent to

MSHA for analysis while the other was

analyzed at a private laboratory. All samples

were reported to be ‘‘portal to portal’’

samples as required by MSHA regulations.

Using these data, the NMA estimated an

overall CV of 16 percent. Based on this 16-

percent estimate, the NMA suggested that

MSHA had underestimated measurement

uncertainty in its February 1994 notice by 60

percent at dust concentrations of 2.0 mg/m3.

The NMA estimate of 16 percent for overall

CV includes not only sampling and analytical

error, but also variability arising from two

additional sources: (1) Spatial variability

between the locations where the two samples

were collected; and (2) interlaboratory

variability introduced by the fact that a third

laboratory was involved in weighing exposed

filter capsules.

Since the two dust samples within each

pair submitted were not collected at precisely

the same location, differences observed

between paired samples in the Skyline data

are partly due to spatial variability. The

Secretaries fully recognize and acknowledge

that, as suggested by the Skyline data, spatial

variability in mine dust concentrations can

exist, even within a relatively small area such

as the so-called breathing zone of a miner.

Consistent with general industrial hygiene

practice, however, the Secretaries do not

consider such variability relevant to the

accuracy of an individual dust concentration

measurement.

The NMA expressed sampling and

analytical error as a single percentage relative

to the average of all dust concentrations that

happened to be observed in the data

analyzed. Contrary to the NMA analysis,

sampling and analytical error cannot be

expressed as a constant percentage of the true

dust concentration. Because σe is constant

with respect to dust concentration, CVweight

declines with increasing dust concentration,

as explained in Appendix C. The value of

CVtotal assumed by MSHA and NIOSH for the

period when the Skyline samples were

collected (i.e., prior to 1995) is approximately

7.5 percent when the true dust concentration

(μ) is 2.0 mg/m3 and approximately 16.2

percent when μ=0.5 mg/m3. This is based on

applying Equations 2 and 3 to σe=51.7 μg,

CVpump=4.2 percent, and CVsampler=5 percent.

Even if the effects of spatial variability and

the third laboratory are ignored, and the

overall CV is interpreted as an average over

the range of concentrations encountered, the

16-percent value reported by the NMA makes

no allowance for the paired covariance

structure of the data. Therefore, MSHA and

NIOSH consider the 16-percent value to be

erroneous, even under NMA’s assumptions.

MSHA and NIOSH re-analyzed the Skyline

data in order to check whether these data

were consistent with the value of σe (i.e., 51.7

42118 Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules

μg) estimated for the time when the Skyline

samples were collected. To distinguish the

NMA interpretation of sampling and

analytical error (including spatial variability)

from the Secretaries’ interpretation

(excluding spatial variability), SAE will

denote sampling and analytical error

according to the Secretaries’ interpretation,

and SAE* will denote sampling and

analytical error according to the NMA

interpretation. If CVspatial denotes the

component of SAE* attributable to spatial

variability for each measurement, it follows

that

SAE CV CV total spatial

∗ = + ( ) ⋅ 2 2 1

2

To estimate SAE* as a function of dust

concentration from the data provided, a leastsquares regression analysis was performed on

the square of the difference between natural

logarithms of dust concentrations x1 and x2

observed within each pair. Let μ* denote the

true mean dust concentration, not only over

the full shift sampled, but also over the two

locations sampled. The expected value (E{·})

of each squared difference forms the ordinate

of the regression line at each value of the

abscissa (1/μ*)2:

E Ln X Ln X SAE

CV CV

CV CV CV CV

CV CV CV

a a

total spatial

pump sampler weight spatial

pump sampler spatial e

1 2

2 2

2 2

22 2 2

22 2 2

0 1

2

2

2

2

2 21

1

{ } ( ) ( ) − ( ) ≈ ( )

= + ( )

= + ++ [ ]

= ++ ( ) + ( )

= + ( )

∗

∗

∗

.438 /

/

σ μ

μ

Since no control filter capsules were used in

processing the Skyline dust samples, CVweight

does not, in this analysis, contain the √2

factor shown in Equation 3 of Appendix C.

The intercept of the regression line is:

a0=2(CV2

pump+CV2sampler+CV2spatial), and the

slope is a1=2(1.438σe) 2. To carry out the

regression analysis, μ* was approximated by

(x1+x2)/2. Regression estimates of the

parameters a0 and a1 were used to generate

corresponding estimates of e and CV2

spatial.

The least squares estimate of σe obtained

from this analysis is 76.0 μg, with standard

error of ±15 μg. This is not significantly

different, statistically, from the 51.7-μg value

estimated for the time period when the

Skyline samples were collected. Assuming

CVpump = 4.2 percent and CVsampler = 5

percent, the value of CVspatial obtained from

the least squares estimate of a0 is 19.7

percent, with standard error of ± 2.9 percent.

II. Paired Sample Data Submitted by

Mountain Coal Company

Mountain Coal Company submitted a data

set consisting of the difference (expressed in

mg/m3) between paired samples collected

from miners over roughly a one-year period.

Two sampler units were placed on each

participating miner (presumably one on each

collar or shoulder) and operated for roughly

a full shift. One sample cassette was sent to

MSHA for analysis (post-weighing) while the

other was analyzed at a private laboratory.

Mountain Coal Company provided only the

differences between measurements within

each pair and not the concentration

measurements themselves. Since CVtotal

varies with dust concentration, and the dust

concentrations were not provided, it was

impossible to form a valid estimate of

measurement variability from these data, or

to determine what part of the observed

differences could be attributed to weighing

error and what part to spatial variability or

variability attributable to operation of the

pump and physical differences between

sampler units.

III. Exposure Data Submitted by Jim Walter

Resources, Inc.

Jim Walter Resources, Inc. submitted a data

set consisting of exposure measurements

collected from all miners working on two

longwall sections. Measurements were

collected from each miner on five

consecutive days. This procedure was

repeated during five sampling cycles over a

two-year period. During each sample cycle

the five measurements for each miner were

averaged and compared to the respirable dust

standard. According to Jim Walter Resources,

Inc., the sampling plan ‘‘eliminates the effect

of the variability of the environment and

minimizes the error due to the coefficient of

variation of the pump because all miners

[original emphasis] are sampled for five

shifts,’’ and these data ‘‘show the variability

of the sample pump and of the worker’s

exposure to respirable dust.’’

In its submission, Jim Walter Resources,

Inc. apparently assumed that the quantity

being measured is average dust concentration

across a number of shifts, rather than dust

concentration averaged over a single shift at

the sampling location. The Secretaries agree

that dust concentrations do vary from shift to

shift and from job to job, as these data

illustrate. This variability, however, is largely

under the control of the mine operator and

should not be considered when evaluating

the accuracy of a single, full-shift

measurement.

IV. Exposure Data Submitted by the NMA

The NMA submitted data consisting of

recently collected and historical

measurements collected from the designated

occupations (continuous miner operator for

continuous mining sections and either the

headgate or tailgate shearer operator for

longwall mining sections) for three

continuous mining sections and five longwall

mining sections. According to the NMA

analysis, there is a 17-percent probability that

these mines would be cited, even though the

long-term average is less than the respirable

dust standard.

The NMA failed to recognize that the

quantity being measured is dust

concentration averaged over a single shift at

the sampling location. The Secretaries agree

that exposures do vary from shift to shift, as

these data illustrate. This variability,

however, is largely under the control of the

mine operator and should not be considered

when evaluating the accuracy of a single,

full-shift measurement.

V. Sequential Exposure Data Submitted by

Jim Walter Resources, Inc.

Jim Walter Resources, Inc. submitted data

collected from several longwall faces. For

each longwall, seven dust samples were

collected, using sampler units placed on the

longwall face at least 48′′ from the tailgate at

the MSHA 061 designated location. Pumps

were successively turned off in one hour

increments, resulting in samples covering

progressively longer time periods over the

course of the shift, from one to eight hours.

This was repeated on a number of days at

each longwall.

Many of the samples showed either the

same or less weight gain than the previous

sample (collected over a shorter time period)

within a sequence. In the cover letter and

written comments accompanying these data,

it was claimed that the weight gains observed

for samples within each sequence should

progressively increase, irrespective of

variations in air flow and production levels,

and that the patterns observed exemplify

Federal Register / Vol. 65, No. 131 / Friday, July 7, 2000 / Proposed Rules 42119

‘‘the variability of sample results with today’s

equipment and weighing techniques.’’

MSHA and NIOSH have concluded that

these data cannot be used to estimate or

otherwise evaluate measurement accuracy for

the following reasons: First, a highly

sensitive and accurate sampling device

would be expected to produce variable

results when exposed to even slightly

different environments. Since the samples

within each sequence of seven were not

collected at exactly the same point, they are

subject to spatial variability in dust

concentration. It is well known that dust

concentrations can vary even within small

areas along a longwall face. Therefore,

variability in sample results is attributable

not only to measurement errors but also to

variations in dust concentration due to

spatial variability.

Second, even on a production shift,

variations in air flow and production levels

over the course of the shift can result in

periods within the shift during which the

true dust concentration to which a sampler

is exposed is low or near zero. If a sampler

unit is exposed to a relatively low dust

concentration during the final hour in which

it is exposed, any difference between that

sample and the previous sample will tend to

be dominated by spatial variability. In such

cases the increase in weight accumulated

during the final hour would be statistically

insignificant as compared to variability in

dust concentration at different locations.

Without detailed knowledge of the airflow

and production levels as they varied over

each shift, it is impossible to determine how

many cases of this type would be expected.

However, approximately one-half of such

samples would be expected to exhibit less

weight gain than the previous sample.

Further, because sample weights were

truncated to 0.1 mg at the time these data

were collected, and because expected weight

gains of less than 0.1 mg are not uncommon

over a one-hour period, there would be no

apparent increase in recorded weight gain in

many cases where the two sample results

actually differed by a positive amount.

Therefore, some unknown number of cases

showing no difference in successive weight

gains are attributable to truncation effects.

Truncation has now been discontinued for

samples collected under MSHA’s inspection

program.

Finally, as has been shown in Appendix C,

a certain percentage of negative weight-gain

measurements at low dust concentrations is

consistent with the weighing imprecision

experienced at the time these samples were

collected. However, since these data were not

collected in a controlled environment, it is

impossible to determine what that percentage

should be. Because the weight gain for each

sample is determined as the difference

between two weighings, comparison of

weight gains between two samples involves

a total of four independent weighing errors.

Therefore, variability attributable purely to

weighing error in the difference between

weight gains in two successive samples is

greater (by a factor equal to ‘‘2) than

variability due to weighing error in a single

sample. Furthermore samples collected over

less than a full shift are subject to more

variability due to random fluctuations in

pump air flow and cyclone performance than

samples collected over a full shift. Both of

these considerations increase the likelihood

that a sample will exhibit less weight gain

than its predecessor, as compared to the

likelihood of recording a negative weight

gain for a single, full-shift sample.

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XVI. Regulatory Text

List of Subjects in 30 CFR Part 72

Coal, Health standards, Mine safety

and health, Underground mines,

Miscellaneous.

Dated: May 31, 2000.

Alexis M. Herman,

Secretary, Department of Labor.

Dated: May 31, 2000.

Donna E. Shalala,

Secretary, Department of Health and Human

Services.

Accordingly, it is proposed by the

Department of Labor, Mine Safety and

Health Administration, to amend

chapter I of title 30 of the Code of

Federal Regulations as follows:

PART 72—[AMENDED]

1. The authority citation for part 72

continues to read as follows:

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

2. Section 72. 500 is added to subpart

E of part 72 to read as follows:

§ 72.500 Single, full-shift

measurement of respirable coal mine

dust.

The Secretary may use a single, fullshift measurement of respirable coal

mine dust to determine average

concentration on a shift if that

measurement accurately represents

atmospheric conditions to which a

miner is exposed during such shift.

[FR Doc. 00–14075 Filed 7–6–00; 8:45 am]

BILLING CODE 4510–43–P

DEPARTMENT OF LABOR

Mine Safety and Health Administration

30 CFR Parts 70, 75 and 90

RIN 1219–AB14

Verification of Underground Coal Mine

Operators’ Dust Control Plans and

Compliance Sampling for Respirable

Dust

AGENCY: Mine Safety and Health

Administration (MSHA), Labor.

ACTION: Proposed rule; notice of

hearings.

SUMMARY: MSHA is proposing to revoke

existing operator respirable dust

sampling procedures under parts 70 and

90, and to implement new regulations

that would require each underground

coal mine operator to have a verified

mine ventilation plan. Under this

proposal, MSHA would verify the

effectiveness of the mine ventilation

plan for each mechanized mining unit

(MMU) in controlling respirable dust

under typical mining conditions. MSHA

would collect full-shift respirable dust

samples, called ‘‘verification samples,’’

to demonstrate the adequacy of the dust

control parameters specified in the mine

ventilation plan in maintaining the

concentration of respirable coal mine

and quartz dust at or below 2.0 mg/m3

and 100 μg/m3, respectively. The

adequacy of these parameters would be

demonstrated on shifts during which

the amount of the material produced is

at or above the ‘‘verification production

level’’ (VPL) or the tenth highest

production level recorded in the most

recent 30 production shifts.