5664 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

DEPARTMENT OF LABOR

Mine Safety and Health Administration

DEPARTMENT OF HEALTH AND

HUMAN SERVICES

Centers for Disease Control and

Prevention

RIN 1219–AA82

Mine Shift Atmospheric Conditions;

Respirable Dust Sample

Correction and Republication

Note: For the convenience of the user,

notice document 97–33934 is being reprinted

in its entirety because of numerous errors in

the document originally appearing at 62 FR

68372–68395, December 31, 1997. Those

wishing to see a listing of corrections, please

call Patricia Silvey, Mine Safety and Health

Administration, 703–235–1910.

AGENCIES: Mine Safety and Health

Administration, Labor, National

Institute for Occupational Safety and

Health, Centers for Disease Control and

Prevention, HHS.

ACTION: Final notice of joint finding.

SUMMARY: This notice announces that

the Secretary of Labor and the Secretary

of Health and Human Services (the

Secretaries) find, in accordance with

sections 101 and 202(f)(2) of the Federal

Mine Safety and Health Act of 1977

(Mine Act), 30 U.S.C. 811 and 842(f)

respectively, that the average

concentration of respirable dust to

which each miner in the active

workings of a coal mine is exposed can

be accurately measured over a single

shift. This notice should be read in

conjunction with the notice published

separately by the Mine Safety and

Health Administration (MSHA)

elsewhere in today’s Federal Register.

The Secretaries are rescinding the

previous finding, which was proposed

on July 17, 1971 and issued on February

23, 1972, by the Secretary of the Interior

and the Secretary of Health, Education

and Welfare.

EFFECTIVE DATE: This notice will be

effective on March 2, 1998.

FOR FURTHER INFORMATION CONTACT:

Patricia W. Silvey, Director, Office of

Standards, Regulations and Variances;

MSHA; 703–235–1910.

SUPPLEMENTARY INFORMATION: In

accordance with section 202(f)(2) and

section 101 of the Mine Act, this notice

is published jointly by the Secretaries of

the Departments of Labor, and Health

and Human Services.

I. Introduction

For as long as miners have taken coal

from the ground, the presence of

respirable dust in coal mines has been

a source of health problems for miners.

Coal workers’ pneumoconiosis, one of

the most insidious of occupational

diseases, is caused by deposits of coal

mine dust in the lung and is known as

‘‘black lung disease.’’ The disability that

may result from these deposits can

range from slightly impaired lung

function to significant decreases in lung

function resulting in breathlessness,

recurrent chest illness, and even heart

failure. In addition, the disease may

progress even after the miner is no

longer exposed to coal mine dust.

The Federal Coal Mine Health and

Safety Act of 1969 (Coal Act)

established the first comprehensive dust

standard for underground U.S. coal

mines by setting a limit of 2.0

milligrams of respirable coal mine dust

per cubic meter of air (mg/m3). The 2.0

mg/m3 standard sets a limit on the

concentration of respirable coal mine

dust permitted in the mine atmosphere

during each shift to which each miner

in the active workings of a mine is

exposed. Congress was convinced that

the only way each miner could be

protected from black lung disease or

other occupational dust disease was by

limiting the amount of respirable dust

allowed in the air that miners breathe.

The Coal Act was subsequently

amended by the Federal Mine Safety

and Health Act of 1977 (Mine Act), 30

U.S.C. 801 et seq. The standard limiting

respirable dust in the mine atmosphere

to 2.0 mg/m3 was retained in the Mine

Act, which also required that ‘‘each

operator shall continuously maintain

the average concentration of respirable

dust in the mine atmosphere during

each shift to which each miner in the

active workings of such mine is exposed

at or below 2.0 milligrams of respirable

dust per cubic meter of air.’’ Section

202(b)(2). (Other provisions in the Mine

Act, sections 205 and 203(b)(2), provide

for lowering the applicable standard

when quartz is present and when

miners with evidence of

pneumoconiosis have elected to work in

a low-dust work environment.)

Today, dust levels in underground

U.S. coal mines are significantly lower

than they were when the Coal Act was

passed. Federal mine inspector

sampling results during 1968–1969

show that the average dust

concentration in the environment of a

continuous miner operator was 7.7 mg/

m3. Current sampling indicates that the

average dust level for that occupation

has been reduced by 83 percent to 1.3

mg/m3. Despite this progress, the

Secretaries believe that occupational

lung disease continues to present a

serious health risk to coal miners. In

November 1995, the National Institute

for Occupational Safety and Health

(NIOSH) issued a criteria document

which concluded that coal miners in

our country continue to be at risk for

developing black lung disease.

The Secretary of Labor believes that

miners’ health can be further protected

from the debilitating effects of black

lung disease by improving their

workplace conditions through more

effective assessment of respirable dust

concentrations during individual, full

shifts. On February 18, 1994, the

Secretary of Labor and the Secretary of

Health and Human Services published a

notice in the Federal Register proposing

to find that the average concentration of

respirable dust to which each miner in

the active workings of a coal mine is

exposed can be accurately measured

over a single shift in accordance with

section 202(f)(2) of the Mine Act (56 FR

8357). Additionally, the Secretaries

proposed to rescind the previous

finding, which was proposed on July 17,

1971 (36 FR 13286) and issued on

February 23, 1972 (37 FR 3833), by the

Secretary of the Interior and the

Secretary of Health, Education and

Welfare.

II. General Discussion

The issues related to this finding are

complex and highly technical. The

Agencies have organized this final

notice to allow interested persons to

first consider pertinent introductory

material on the Agencies’ 1972 notice

and its recision, and a short overview of

the NIOSH mission and assessment of

this finding, as well as those aspects of

MSHA’s coal mine respirable dust

program relevant to this finding.

Following this introductory material is

a discussion of the ‘‘measurement

objective,’’ or what the Secretaries

intend to measure with a single, 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

the sampling process is addressed,

including the performance of the

approved sampler unit, sample

collection procedures, and sample

processing. The concept of

measurement uncertainty is then

addressed, and why sources of dust

concentration variability and various

other factors are not relevant to the

finding. Finally, the notice explains

how the total measurement uncertainty

was quantified, and how the accuracy of

a single, full-shift measurement was

shown to meet the NIOSH Accuracy

Criterion. Several Appendices, which
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5665

contain relevant technical information,

are attached and incorporated with this

notice. The Agencies have additionally

included references to the Appendices

throughout this notice.

A. The 1971/1972 Joint Notice of

Finding

In 1971 the Secretary of the Interior

and the Secretary of Health, Education

and Welfare proposed, and in 1972

issued, a joint finding under the Coal

Act. The finding concluded that a single

shift measurement would not, after

applying valid statistical techniques,

accurately represent the atmospheric

conditions to which the miner is

continuously exposed. For the reasons

that follow, the Secretaries believe that

the 1972 joint finding was incorrect.

Section 202(b)(2) of the Coal Act

provided that ‘‘each operator shall

continuously maintain the average

concentration of respirable dust in the

mine atmosphere during each shift to

which each miner in the active

workings of such mine is exposed at or

below [the applicable respirable dust

standard].’’ In addition, the term

‘‘average concentration’’ was defined in

section 202(f) of the Coal Act as follows:

* * * the term ‘‘average concentration’’

means a determination which accurately

represents the atmospheric conditions with

regard to respirable dust to which each miner

in the active workings of a mine is exposed

(1) as measured during an 18 month period

following the date of enactment of this Act,

over a number of continuous production

shifts to be determined by the Secretary of

the Interior and the Secretary of Health,

Education and Welfare, and (2) as measured

thereafter, over a single shift only, unless the

Secretary of the Interior and the Secretary of

Health, Education and Welfare find, in

accordance with the provisions of section

101 of this Act, that such single shift

measurements will not, after applying valid

statistical techniques to such measurement,

accurately represent such atmospheric

conditions during such shift.

Therefore, 18 months after the statute

was enacted, the ‘‘average

concentration’’ of respirable dust in coal

mines was to be measured over a single

shift only, unless the Secretaries found

that doing so would not accurately

represent mine atmospheric conditions

during such shift. If the Secretaries

found that a single shift measurement

would not, after applying valid

statistical techniques, accurately

represent mine atmospheric conditions

during such shift, then the interim

practice of averaging measurements

‘‘over a number of continuous

production shifts’’ was to continue.

On December 16, 1969, the U.S.

Congress published a Conference Report

in support of the new Coal Act. The

Report refers to section 202(f) by noting

that:

At the end of this 18 month period, it

requires that the measurements be over one

production shift only, unless the Secretar[ies]

* * * find, in accordance with the standard

setting procedures of section 101, that single

shift measurements will not accurately

represent the atmospheric conditions during

the measured shift to which the miner is

continuously exposed [Conference Report,

page 75].

This Report is inconsistent with the

wording of the section 202(f), which

seeks to apply a single, full-shift

measurement to ‘‘accurately represent

such atmospheric conditions during

such shift.’’ Section 202(f) does not

mention continuous exposure. The

Secretaries believe that the use of this

phrase is confusing, and to the extent

that any weight of interpretation can be

given to the legislative history, that the

Senate’s Report of its bill provides a

clearer interpretation of section 202(f)

when read together with the statutory

language. The Senate Committee noted

in part that:

The committee * * * intends that the

dust level not exceed the specified standard

during any shift. It is the committee’s

intention that the average dust level at any

job, for any miner in any active working

place during each and every shift, shall be no

greater than the standard.

Following passage of the Coal Act, the

Bureau of Mines (MSHA’s predecessor

Agency within the Department of the

Interior) expressed a preference for

multi-shift sampling. Correspondence

exchanged during that time period of

1969 to 1971 reflected concern over the

technological feasibility of controlling

dust levels to the limits established, and

the potentially disruptive effects of

mine closure orders because of

noncompliance with the respirable dust

limits. Both industry and government

officials feared that basing

noncompliance determinations on

single, full-shift measurements would

increase those problems. In June 1971,

the then-Associate Solicitor for Mine

Safety and Health at the Department of

the Interior issued a legal interpretation

of section 202(f), concluding that the

average dust concentration was to be

determined by measurements that

accurately represent respirable dust in

the mine atmosphere over time rather

than during a shift. On July 17, 1971,

the Secretaries of the Interior and of

Health, Education and Welfare issued a

proposed notice of finding under

section 202(f) of the Coal Act. The

finding concluded that, ‘‘a single shift

measurement of respirable dust will not,

after applying valid statistical

techniques to such measurement,

accurately represent the atmospheric

conditions to which the miner is

continuously exposed’’ (36 FR 13286).

In February, 1972, the final finding

was issued (37 FR 3833). It concluded

that:

After careful consideration of all

comments, suggestions, and objections, it is

the conclusion of the Secretary of the Interior

and the Secretary of Health, Education, and

Welfare that a valid statistical technique was

employed in the computer analysis of the

data referred to in the proposed notice

[footnote omitted] and that the data utilized

was accurate and supported the proposed

finding. Both Departments also intend

periodically to review this finding as new

technology develops and as new dust

sampling data becomes available.

The Departments intend to revise part 70

of Title 30, Code of Federal Regulations, to

improve dust measuring techniques in order

to ascertain more precisely the dust exposure

of miners. To complement the present system

of averaging dust measurements, it is

anticipated that the proposed revision would

use a measurement over a single shift to

determine compliance with respirable dust

standards taking into account (1) the

variation of dust and instrument conditions

inherent in coal mining operations, (2) the

quality control tolerance allowed in the

manufacture of personal sampler capsules,

and (3) the variation in weighing precision

allowed in the Bureau of Mines laboratory in

Pittsburgh.

The proposed finding, as set forth at 36

F.R. 13286, that a measurement of respirable

dust over a single shift only, will not, after

applying valid statistical techniques to such

measurement, accurately represent the

atmospheric conditions to which the miner

under consideration is continuously exposed,

is hereby adopted without change.

As explained in the 1971 proposed

finding, the average concentration of all

ten full-shift samples (from one

occupation) submitted from each

working section under the regulations in

effect at the time (these were the ‘‘basic

samples’’ referred to in the proposed

notice of finding) was compared with

the average concentration of the two

most recently submitted samples, then

to the three most recently submitted

samples, then to the four most recently

submitted samples, etc. In discussing

the results of these comparisons the

Secretaries stated that ‘‘ * * * the

average of the two most recently

submitted samples of respirable dust

was statistically equivalent to the

average concentration of the current

basic samples for each working section

in only 9.6 percent of the comparisons.’’

The title of the 1971/1972 notice and

the conclusion it reaches are clearly

inconsistent. The title states that it is a

‘‘Notice of Finding That Single Shift

Measurements of Respirable Dust Will

Not Accurately Represent Atmospheric

Conditions During Such Shift.’’
5666 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

1Reference to specific equipment, trade names or

manufacturers does not imply endorsement by

NIOSH or MSHA.

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) requires a determination

of accuracy with respect to

‘‘atmospheric conditions during such

shift,’’ not ‘‘atmospheric conditions to

which the miner is continuously

exposed’’ (37 FR 3833). The statistical

analysis referenced in the 1971/1972

proposed and final findings simply did

not address the accuracy of a single,

full-shift measurement in representing

atmospheric conditions during the shift

on which it was taken. For this and

other reasons set forth in the notice, the

Secretaries hereby rescind the 1972 joint

final finding.

III. NIOSH Mission Statement and

Assessment of the Joint Finding

The National Institute for

Occupational Safety and Health

(NIOSH) was created by Congress in the

Occupational Safety and Health Act in

1970. The Act established NIOSH as

part of the Department of Health and

Human Services to identify the causes

of work-related diseases and injuries,

evaluate the hazards of new

technologies, create new ways to control

hazards to protect workers, and make

recommendations for new occupational

safety and health standards. Under

section 501 of the Mine Act, Congress

gave specific research responsibilities to

NIOSH in the field of coal or other mine

health. These responsibilities include

the authority to conduct studies,

research, experiments and

demonstrations, in order ‘‘to develop

new or improved means and methods of

reducing concentrations of respirable

dust in the mine atmosphere of active

workings of the coal or other mine,’’ and

also ‘‘to develop techniques for the

prevention and control of occupational

diseases of miners * * *.’’

When the initial finding, issued under

section 202(f) of the Coal Act, was

published in 1972, both the Secretary of

the Interior and the Secretary of Health,

Education and Welfare (the predecessor

to the Department of Health and Human

Services) indicated that the finding

would be reassessed as new technology

was developed, or new data became

available. The Secretary of Health and

Human Services, through delegated

authority to the National Institute for

Occupational Safety and Health, has

reconsidered the provisions of section

202(f) of the Mine Act, reviewed the

current state of technology and other

scientific advances since 1972, and has

determined that the following

innovations and technological

advancements are important factors in

the reassessment of the 1971/1972 joint

finding.

In 1977 NIOSH published its

‘‘Sampling Strategies Manual,’’ which

provided a framework for the statistical

treatment of occupational exposure data

[DHEW (NIOSH) Publication No. 77–

173; Sec. 4.2.1]. Additionally, that year,

NIOSH first published the NIOSH

Accuracy Criterion, which was

developed as a goal for methods to be

used by OSHA for compliance

determinations [DHEW (NIOSH)

Publication No. 77–185; pp. 1–5]. In

1980, new mine health standards issued

by the Secretary of Labor (30 CFR parts

70, 71, and 90) improved the quality of

the sampling process by revising

sampling, maintenance, and calibration

procedures. Prior to 1984, filter capsules

used in sampling were manually

weighed by MSHA personnel using

semi-micro balances, making precision

weights to the nearest 0.1 mg (100

micrograms). In 1984, a fully-automated,

robotic weighing system was introduced

along with state-of-the-art electronic

microbalances. In 1994, the balances

were further upgraded, and in 1995 the

weighing system was again improved,

increasing weighing sensitivity to the

microgram level. Also, in 1987,

electronic flow-control sampling pump

technology was introduced in the coal

mine dust sampling program with the

use of MSA FlowLiteTM pumps. 1 These

new pumps compensate for the

changing filter flow-resistance that

occurs due to dust deposited during the

sampling period. The second generation

of constant-flow sampling pumps was

introduced in 1994, with the

introduction of the MSA Escort ELF

pump. The automatic correction

provided by these new pumps improves

the stability of the sampler air flow rates

and reduces the inaccuracies that were

inherent in the 1970–1980s vintage

sampling pumps. One further

improvement was made in 1992 with

the introduction of the new tamperresistant filter cassettes. Because of

these evolving improvements to the

sampling process, a better

understanding of statistical methods

applied to method accuracy, and a

reconsideration of the requirements of

section 202(f) of the Mine Act, the

Secretary of Health and Human Services

has determined that the previous joint

finding should be reevaluated.

IV. MSHA Mission Statement and

Overview of the Respirable Dust

Program

With the enactment of the Mine Act,

Congress recognized that ‘‘the first

priority and concern of all in the coal

or other mining industry must be the

health and safety of its most precious

resource—the miner.’’ Congress further

realized that there ‘‘is an urgent need to

provide more effective means and

measures for improving the working

conditions and practices in the Nation’s

coal or other mines in order to prevent

death and serious physical harm, and in

order to prevent occupational diseases

originating in such mines.’’ With these

goals in mind, MSHA is given the

responsibility to protect the health and

safety of the Nation’s coal and other

miners by enforcing the provisions of

the Mine Act.

A. The Coal Mine Respirable Dust

Program

In 1970, federal regulations were

issued by MSHA’s predecessor agency

that established a comprehensive coal

mine operator dust sampling program,

which required the environment of the

occupation on a working section

exposed to the highest respirable dust

concentration to be sampled—the ‘‘high

risk occupation’’ concept. All other

occupations on the section were

assumed to be protected if the high risk

occupation was in compliance. Under

this program, each operator was

required to initially collect and submit

ten valid respirable dust samples to

determine the average dust

concentration (across ten production

shifts). If analysis showed the average

dust concentration to be within the

applicable dust standard, the operator

was required to submit only five valid

samples a month. If compliance

continued to be demonstrated, the

operator was required to take only five

valid samples every other month. The

initial, monthly, and bimonthly

sampling cycles were referred to as the

‘‘original,’’ ‘‘standard,’’ and ‘‘alternative

sampling’’ cycles, respectively. When

the average dust concentration exceeded

the standard, the operator reverted back

to the standard sampling cycle.

In addition to sampling the high risk

occupation at specified frequencies,

each miner was sampled individually at

different intervals. However, these early

individual sample results were not used

for enforcement but were provided to

NIOSH for medical research purposes.

MSHA revised these regulations in

April 1980 (45 FR 23990) to reduce the
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5667

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 with a

bimonthly sampling cycle and to

eliminate the requirement that each

miner be sampled. These are the

regulations that currently govern the

mine operator dust sampling program,

and which continue to be based on the

high risk occupation concept, now

referred to as the ‘‘designated

occupation’’ or ‘‘D.O.’’ sampling

concept.

It should be noted that the preamble

to the final rule amending the

regulations in April 1980 (45 FR 23997),

explicitly refers to the use of single

versus multiple samples as it applies to

the operator respirable dust sampling

program.

Compliance determinations will generally

be based on the average concentration of

respirable dust measured by five valid

respirable dust samples taken by the operator

during five consecutive shifts, or five shifts

worked on consecutive days. Therefore, the

sampling results upon which compliance

determinations are made will more

accurately represent the dust in the mine

atmosphere than would the results of only a

single sample taken on a single shift. In

addition, MSHA believes the revised

sampling and maintenance and calibration

procedures prescribed by the final rule will

significantly improve the accuracy of

sampling results.

At the time of these amendments,

MSHA examined section 202(b)(2) of

the Coal Act, which was retained

unchanged in the 1977 Mine Act. The

Agency stated in the preamble to the

final rule that:

Although single-shift respirable dust

sampling would be most compatible with

this single-shift standard, Congress

recognized that variability in sampling

results could render single-shift samples

insufficient for compliance determinations.

Consequently, Congress defined ‘‘average

concentration’’ in section 202(f) of the 1969

Coal Act which is also retained in the 1977

Act.

MSHA believes that this

interpretation merely recognized the

two ways of measurement authorized in

section 202(f), and expressed the

preference on the part of MSHA in 1980

to retain multi-shift sampling in the

operator sampling program. The phrase

used in the preamble to the final rule

reflects that MSHA understood that the

2.0 mg/m3 limit was a single-shift

standard, which was not to be exceeded

on a shift. The preamble referenced the

continuous multi-shift sampling and

single-shift sampling conducted by the

Secretary of the Interior and the

Secretary of Health, Education, and

Welfare, and noted that in the 1971/

1972 proposed and final findings,

It had been determined after applying valid

statistical techniques, * * * that a single shift

sample should not be relied upon for

compliance determinations when the

respirable dust concentration being measured

was near 2.0 mg/m3. Accordingly, the

[Secretaries] prescribed consecutive 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 by

conducting inspections annually at each

surface and underground coal mine.

During these inspections, MSHA

inspectors collect samples on multiple

occupations to determine compliance

with the applicable standard, assess the

effectiveness of the operator’s dust

control program, quantify the level of

crystalline silica (quartz) in the work

environment, and identify occupations

other than the ‘‘D.O.’’ which may be at

risk and should be monitored by the

mine operator.

Depending on the concentration of

dust measured, an MSHA inspector may

terminate sampling after the first day if

levels are very low, or continue for up

to five shifts or days before making a

compliance or noncompliance

determination. MSHA inspection

procedures require inspectors to sample

at least five occupations, if available, on

each mechanized mining unit (MMU)

on the first day of sampling. The

operator is cited if the average of those

measurements exceeds the applicable

standard. However, if the average falls

below the standard, but one or more of

the measurements exceed it, additional

samples are collected on the subsequent

production shift or day. The results of

the first and second day of sampling on

all occupations are then averaged to

determine if the applicable standard is

exceeded. Additionally, when an

inspector continues sampling after the

first day because a previous

measurement exceeds the standard,

MSHA’s procedures call for all

measurements taken on a given

occupation to be averaged individually

for that occupation. If the average of

measurements taken over more than one

day on all occupations is equal to or less

than the applicable standard, but the

average of measurements taken on any

one occupation exceeds the value in a

decision table developed by MSHA

(based on the cumulative concentration

for two or more samples exceeding 10.4

mg/m 3, which is equivalent to a 5-

measurement average exceeding 2.0 mg/

m 3), the operator is cited for exceeding

the applicable standard.

B. The Spot Inspection Program (SIP)

In response to concerns about

possible tampering with dust samples in

1991, MSHA convened the Coal Mine

Respirable Dust Task Group (Task

Group) to review the Agency’s

respirable dust program. As part of that

review, MSHA developed a special

respirable dust ‘‘spot inspection

program’’ (SIP).

This program was designed to provide

the Agency with information on the

dust levels to which underground

miners are typically exposed. Because of

the large number of mines and MMUs

(mechanized mining units) involved

and the need to obtain data within a

short time frame, respirable dust

sampling during the SIP was limited to

a single shift or day, a departure from

MSHA’s normal sampling procedures.

The term ‘‘MMU’’ is defined in 30 CFR

70.2(h) to mean a unit of mining

equipment, including hand loading

equipment, used for the production of

material. As a result, MSHA decided

that if the average of multiple

occupation measurements taken on an

MMU during any one-day inspection

did not exceed the applicable standard

the inspector would review the result of

each individual full-shift sample. If any

individual full-shift measurement

exceeded the applicable standard by an

amount specified by MSHA, a citation

would be issued for noncompliance,

requiring the mine operator to take

immediate corrective action to lower the

average dust concentration in the mine

atmosphere in order to protect miners.

During the SIP inspections, MSHA

inspectors cited violations of the 2.0

mg/m 3 standard if either the average of

the five measurements taken on a single

shift was greater than or equal to 2.1

mg/m 3, or any single, full-shift

measurement exceeded or equaled 2.5

mg/m 3. Similar adjustments were made

when the 2.0 mg/m 3 standard was

reduced due to the presence of quartz

dust in the mine atmosphere.

The procedures issued by MSHA’s

Coal Mine Safety and Health Division

during the SIP were similar to those

used by the MSHA Metal/Nonmetal

Mine Safety and Health Division and
5668 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

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). The

margin of error thus allows citations to

be issued only where there is a high

level of confidence that the applicable

standard has been exceeded.

Based on the data from the SIP

inspections, the Task Group concluded

that MSHA’s practice of making

noncompliance determinations solely

on the average of multiple-sample

results did not always result in citations

in situations where miners were known

to be overexposed to respirable coal

mine dust. For example, if

measurements obtained for five different

occupations within the same MMU were

4.1, 1.0, 1.0, 2.5, and 1.4 mg/m 3, the

average concentration would be 2.0 mg/

m 3. Although the dust concentration for

two occupations exceeds the applicable

standard, under MSHA procedures no

citation would have been issued nor any

corrective action required to reduce dust

levels to protect miners’ health. Instead,

MSHA policy required the inspector to

return to the mine the next day that coal

was being produced and resume

sampling in order to decide if the mine

was in compliance or not in

compliance.

The Task Group also recognized that

the results of the first full-shift samples

taken by an inspector during a

respirable dust inspection are likely to

reflect higher dust concentrations than

samples collected on subsequent shifts

or days during the same inspection.

MSHA’s comparison of the average dust

concentration of inspector samples

taken on the same occupation on both

the first and second day of a 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 shift

inspection policy initiated during the

SIP.

C. The Keystone Decision

In 1991, three citations based on

single, full-shift measurements were

issued under the SIP to the Keystone

Coal Mining Corporation. The violations

were contested, and an administrative

law judge from the Federal Mine Safety

and Health Review Commission

(Commission) vacated the citations. The

decision was appealed by the Secretary

of Labor to the Commission because the

Secretary believed that the

administrative law judge was in error in

finding that rulemaking was required

under section 202(f) of the Mine Act for

the Secretary to use single, full-shift

measurements for noncompliance

determinations. In addition, the

Secretary contended that the 1971/1972

finding pertained to operator sampling

and that the SIP at issue involved only

MSHA sampling. The Commission,

which affirmed the decision of the

administrative law judge, found that:

Title II [of the Mine Act] applies to both

operator sampling and to MSHA actions to

ensure compliance, including sampling by

MSHA. Section 202(g) specifically provides

for MSHA spot inspections. Nothing in

§ 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.

V. Executive Order 12866 and

Regulatory Impact Analysis

MSHA has designated this joint

finding as a significant action; it has

been reviewed by OMB under E.O.

12866. MSHA estimates that the total

annual costs associated with the

implementation of this finding will be

$707,950, of which $446,125 will be

incurred by underground coal mines

and $261,825, incurred by surface coal

operations. MSHA projects that this

finding will result in reductions of

future cases of occupational lung

disease and attendant cost savings.

MSHA has prepared a separate

regulatory impact analysis which is

available to the public upon request.

VI. Procedural History of the Current

Notices

As a result of the innovations and

technological advancements described

earlier, and the decision in Keystone

Coal v. Secretary of Labor, 16 FMSHRC

6 (January 4, 1994), the Secretary of

Labor and the Secretary of Health and

Human Services published a proposed

joint notice in the Federal Register on

February 18, 1994 (59 FR 8357),

pursuant to sections 101 and 202(f)(2) of

the Mine Act. The notice proposed to

rescind the 1971/1972 proposed and

final findings by the Secretaries of the

Interior and Health, Education and

Welfare, and find that a single, full-shift

measurement will accurately represent

the atmospheric conditions with regard

to the respirable dust concentration

during the shift on which it was taken.

Concurrently, MSHA published a

separate notice in the Federal Register

announcing its intention to use both

single, full-shift respirable dust

measurements and the average of

multiple, full-shift respirable dust

measurements for noncompliance

determinations (59 FR 8356). That

notice was published to inform the

mining public of how the Agency

intended to implement its new

enforcement procedure utilizing single,

full-shift samples, and to solicit public

comment on the new procedure.

The comment period on the proposed

joint finding was scheduled to close on

April 19, 1994, but was extended to May

20, 1994, in response to requests from

the mining community (59 FR 16958).

Subsequently, public comments were

received, including comments from both

labor and industry.

On July 6, 1994, in response to

requests from the mining community, a

public hearing was held on both notices

in Morgantown, West Virginia (59 FR

29348). Also, in response to additional

requests from the mining community, a

second hearing was held on July 19,

1994, in Salt Lake City, Utah. To allow

for the submission of post-hearing

comments, the record was held open

until August 5, 1994.

The hearings on the proposed joint

notice were conducted by a joint

MSHA/NIOSH panel. Presenters at the

Morgantown hearing included

international and local representatives

of the United Mine Workers of America

(UMWA), several mine operators, and a

panel presentation from the American

Mining Congress (AMC) and the

National Coal Association (NCA).

Presenters at the Salt Lake City hearing

included the Utah Mining Association,

several mine operators, and another

joint AMC/NCA panel. The joint

MSHA/NIOSH panel received prepared

remarks from the presenters and asked

questions as well. The joint agency

panel also responded to questions from

the presenters.

To ensure that all issues raised were

fully considered, MSHA and NIOSH

conducted a thorough review of existing

data, engaged in an extensive literature
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5669

search, sought an independent analysis

of the scientific validity of single, fullshift measurements, and conducted

additional testing. These efforts resulted

in the collection of a significant amount

of information, which was made a part

of the public record on September 9,

1994 (59 FR 50007). To allow interested

parties the opportunity to review and

comment on the supplemental material,

the Agencies extended the comment

period from September 30 to November

30, 1994.

After the close of the comment period,

the Agencies reviewed all of the

comments, data and other information

submitted into the record. Some of the

commenters raised questions regarding

the accuracy of single, full-shift

measurements and challenged the

Agencies’ estimate of measurement

imprecision inherent in sample

collection and analysis. While

reviewing these issues, the Agencies

concluded that the term ‘‘accurately

represent’’ as used in section 202(f)

needed to be defined because of the

issues which commenters raised. In

response, the Agencies reopened the

record on March 12, 1996, to provide a

criterion for ‘‘accuracy’’, to supply new

data and statistical analytical analyses

on the precision of coal mine respirable

dust measurements obtained using

approved sampling equipment, and to

allow the public to review and submit

comments on the supplemental

information (61 FR 10012). In addition,

the March 12 notice identified certain

refinements in MSHA’s measurement

process as applied to inspector samples.

These modifications, currently in place,

involve the measurement of both preand post-exposure filter weights to the

nearest microgram on a scale calibrated

using the established procedure in

MSHA’s laboratory, and discontinuing

the practice of truncating the recorded

weights used in calculating the dust

concentration (that is, MSHA no longer

ignores digits representing hundredths

and thousandths of a milligram).

The new comment period was

scheduled to close on April 11, 1996,

but was extended until June 10, 1996, in

response to requests from the mining

community. Additionally, on April 11,

1996, the Agencies announced their

intention to conduct a second public

hearing on the content of the March 12

notice (61 FR 16123). On May 10, 1996,

a public hearing conducted by a joint

MSHA/NIOSH panel was held in

Washington, DC. One scheduled

presenter, representing the UMWA,

appeared at this hearing.

Some commenters expressed concern

for the procedures used by the Agencies

in making a new finding, asserting that

MSHA and NIOSH were not complying

with the rulemaking provisions of the

Mine Act. These commenters contended

that the recision of the final finding and

implementation by MSHA of single,

full-shift sampling can only be

effectuated through notice and comment

rulemaking. These commenters argue

that because MSHA failed to appeal the

Keystone case, MSHA was bound by the

Commission decision in that case which

mandated notice and comment

rulemaking to rescind the prior finding

and authorize use of single samples by

the Agency.

MSHA and NIOSH have considered

these comments, but believe that the

process they have chosen to follow is

consistent with the requirement of

section 202(f) of the Mine Act, which

provides that a finding shall be made

‘‘in accordance with the provisions of

section 101’’ of the Mine Act. Section

101 contains the procedural

requirements for promulgation of

mandatory health and safety standards,

including provision for notice and

comment. All interested parties were

given ample opportunity for notice and

comment at every stage of consideration

of the proposed joint finding. The

Agencies are not developing,

promulgating, or revising a mandatory

health standard in this notice, nor is the

2.0 mg/m 3 respirable dust standard

being revised. Moreover, the Agencies

have made a finding that the average

concentration of respirable dust in the

mine atmosphere to which each miner

in the active workings of a coal mine is

exposed during a shift can be accurately

measured with a single, full-shift

sample. This is a scientific finding

contemplated by section 202(f) of the

Mine Act. While one commenter

asserted that the Secretaries were not

following proper notice and comment

procedures in section 101 [e.g., sections

101(a)(1) through (9)], the only example

given by the commenter is the fact that

the notice was published in the

‘‘Notice’’ section, rather than the

‘‘Proposed Rules’’ or ‘‘Rules and

Regulations’’ section of the Federal

Register. Because this is not a

mandatory safety and health standard,

there is no need for the Secretaries to

publish the finding as a proposed rule,

or to address feasibility, for example,

which would be required under section

101(a)(6)(A) when a mandatory safety or

health standard is promulgated. The

Secretaries have properly complied with

all the procedural elements of section

101 which apply to this notice.

Some commenters referenced section

101(a)(9) of the Mine Act, 30 U.S.C.

811(a)(9), which provides that no

mandatory standard shall reduce the

protection afforded miners by an

existing standard under the Mine Act.

As stated previously, this scientific

finding does not constitute rulemaking

and is not a promulgation of a

mandatory health standard. Rather, it is

a ‘‘finding’’ under the Mine Act,

established in the same manner as the

initial finding, in 1972, the effect of

which is to increase health protection

for miners by allowing single, full-shift

measurements to be used to determine

average concentrations during a single

work shift instead of continuing to rely

solely on averaging the results of several

days of sampling or sampling across

various occupations on the same shift.

In MSHA’s notice published on

February 18, 1994 (59 FR 8356), the

Agency specifically noted that any

change to the substantive procedure for

mine operator respirable dust sampling

governed by MSHA regulations would

require rulemaking by MSHA.

VII. Issues Regarding Accuracy of a

Single, Full-Shift Measurement

Some commenters questioned the

accuracy of single, full-shift

measurements, and challenged the

Secretaries’ assessment of measurement

accuracy. Some commenters questioned

the Secretaries’ interpretation of section

202(b) of the Mine Act, while others

agreed with the interpretation. The

following issues were generally raised:

the measurement objective as defined by

the Mine Act; the definition of the term

‘‘accurately represent’’, as used in

section 202(f); the validity of the

sampling process; measurement

uncertainty and dust concentration

variability; and the accuracy of a single,

full-shift measurement.

A. Measurement Objective

Some comments reflected a general

misunderstanding of what the

Secretaries intend to measure with a

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

measurement objective. For example,

some commenters asserted that the dust

concentration that should be measured

is dust concentration averaged over a

period greater than a single shift. Some

commenters noted that dust

concentrations can vary during a shift

and that dust concentration is not

uniform throughout a miner’s work area.

In order to clarify the intent of the

Secretaries, the explanation that follows

describes the elements of the

measurement objective and how the

measurement objective relates to the

requirements of section 202(f).

To evaluate the accuracy of a dust

sampling method it is necessary to

specify the airborne dust to be

measured, the time period to which the
5670 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

measurement applies, and the area

represented by the measurement. Once

specified, these items can be combined

into a measurement objective. The

measurement objective represents the

goal of the sampling and analytical

method to be utilized.

1. The Airborne Dust to be Measured

Section 202(f) of the Mine Act states

that ‘‘average concentration’’ means

‘‘ * * * a determination [i.e.,

measurement] which accurately

represents the atmospheric conditions

with regard to respirable dust to which

each miner in the active workings of a

mine is exposed.’’ Later in section

202(f), the phrase ‘‘atmospheric

conditions’’ is used to refer to the

concentration of respirable dust.

Therefore, the airborne dust to be

measured is respirable dust. Section

202(e) defines respirable dust as the

dust measured by an approved sampler

unit.

2. Time Period to Which the

Measurement Applies

Section 202(b)(2) provides that each

mine operator ‘‘* * * shall

continuously maintain the average

concentration of respirable dust in the

mine atmosphere during each shift to

which each miner * * * is exposed’’ at

or below the applicable standard. In

section 202(f) ‘‘average concentration’’

is defined as an atmospheric condition

measured ‘‘over a single shift only,

unless * * * such single shift

measurement will not, after applying

valid statistical techniques, accurately

represent such atmospheric conditions

during such shift.’’ For the purpose of

this notice, the Secretaries have

determined that ‘‘atmospheric

conditions’’ mean the fluctuating

concentration of respirable coal mine

dust during a single shift. These are the

atmospheric conditions to which a

sampler unit is exposed. Therefore, the

present finding pertains only to the

accuracy in representing the average of

the fluctuating dust concentration over

a single shift.

3. Area Represented by the

Measurement

The Mine Act gives the Secretary of

Labor the discretion to determine the

area to be represented by respirable dust

measurements collected over a single

shift. As articulated by the United States

Court of Appeals for the 10th Circuit in

American Mining Congress (AMC)

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

the Secretary of Labor may place the

sampler unit in any area or location

‘‘* * * reasonably calculated to prevent

excessive exposure to respirable dust.’’

Because the Secretary of Labor intends

to prevent excessive exposure by

limiting dust concentration at every

location in the active workings, the area

represented by any respirable dust

measurement must be the sampling

location.

Some commenters identified the dust

concentration to be estimated as either

the mean dust concentration over some

period greater than an individual shift,

the mean dust concentration over some

spatially distributed region of the mine,

or a ‘‘grand mean’’ consisting of some

combination of the above. These

comments were based on the false

premise that the measurement objective

in section 202(f) is something other than

the average atmospheric conditions

during a single shift at the sampling

location. It is true that these mean

quantities described by some

commenters cannot be accurately

estimated using a single, full-shift

measurement, but the Secretaries make

no claim of doing so, nor are they

required to make such considerations.

Some commenters argued that

Congress intended that the

measurement objective be a long-term

average. Specifically, some commenters

stated that because coal dust exposure is

related to chronic health effects, the

exposure limit should be applied to dust

concentrations averaged over a miner’s

lifetime. These commenters identified

the measurement objective as being the

dust concentration averaged over a long,

but unspecified, term and argued that a

single, full-shift measurement cannot

accurately estimate this long-term

average.

If the objective of section 202(b) were

to estimate dust concentration averaged

over a lifetime of exposure, then the

Secretaries would agree that a single,

full-shift sample, or even multiple

samples collected during a single

inspection, would not provide the basis

for an accurate measurement. Section

202(b) of the Mine Act, however, does

not mention long-term averaging, rather

it explicitly requires that the average

dust concentration be continuously

maintained at or below the applicable

standard during each shift (emphasis

added). Furthermore, in Consolidation

Coal Company versus Secretary of Labor

8 FMSHRC 890, (1986), aff’d 824 F.2d

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

found that each episode of a miner’s

overexposure to respirable dust

significantly and substantially

contributes to the health hazard of

contracting chronic bronchitis or coal

workers’ pneumoconiosis, diseases of a

fairly serious nature.

Some commenters submitted

evidence that dust concentrations can

vary significantly near the mining face,

and that these variations may extend

into areas where miners are located.

That is, the average dust concentration

over a full shift is not identical at every

point within a miner’s work area. These

commenters submitted several bodies of

data purporting to show significant

discrepancies between simultaneous

dust concentration measurements

collected within a relatively small

distance of one another. Several

commenters maintained that the

measurement objective is to accurately

measure the average concentration

within some arbitrary sphere about the

head of the miner, and that multiple

measurements within this sphere are

necessary to obtain an accurate

measurement. The Secretaries recognize

that dust concentrations in the mine

environment can vary from location to

location, even within a small area near

a miner. As mentioned earlier, the Mine

Act does not specify the area that the

measurement is supposed to represent,

and the sampler unit may therefore be

placed in any location reasonably

calculated to prevent excessive

exposure to respirable dust.

Several commenters suggested that

the measurement objective should be a

miner’s ‘‘true exposure’’ or what the

miner actually inhales. The Secretaries

do not intend to use a single, full-shift

measurement to estimate any miner’s

‘‘true exposure,’’ because no sampling

device can exactly duplicate the particle

inhalation and deposition

characteristics of a miner at any work

rate (these characteristics change with

work rate), let alone at the various work

rates occurring over the course of a shift.

Section 202(a) of the Mine Act,

however, refers to ‘‘the amount of

respirable dust in the mine atmosphere

to which each miner in the active

workings of such mine is exposed’’

measured ‘‘* * * at such locations

* * *’’ as prescribed by the Secretary of

Labor. It is sufficient for the purposes of

the Mine Act that the sampler unit

accurately represent the amount of

respirable dust at such locations only.

Accordingly, the Secretaries define

the measurement objective to be the

accurate determination of the average

atmospheric conditions, or

concentration of respirable dust, at a

sampling location over a single shift.

B. Accuracy Criterion

A ‘‘single shift measurement’’ means

the calculated dust concentration

resulting from a valid single, full-shift

sample of respirable coal mine dust. In

reviewing the various issues raised by

commenters, the Agencies found that

the term ‘‘accurately represent,’’ as used
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5671

in section 202(f) in connection with a

single shift measurement, was not

defined in the Mine Act. Therefore, in

their March 12, 1996 notice, the

Secretaries proposed to apply an

accuracy criterion developed and

adopted by NIOSH in judging whether

a single, full-shift measurement will

‘‘accurately represent’’ the full-shift

atmospheric dust concentration. This

criterion requires that measurements

come within 25 percent of the

corresponding true dust concentration

at least 95 percent of the time [1].

One commenter opposed the

application of the NIOSH Accuracy

Criterion since it ignores environmental

variability. For reasons explained above,

the Secretaries have restricted the

measurement objective to an individual

shift and sampling location. Therefore,

environmental variability beyond what

occurs at the sampling location on a

single shift is not relevant to assessing

measurement accuracy.

For over 20 years, the NIOSH

Accuracy Criterion has been used by

NIOSH and others in the occupational

health professions to validate sampling

and analytical methods. This accuracy

criterion was devised as a goal for the

development and acceptance of

sampling and analytical methods

capable of generating reliable exposure

data for contaminants at or near the

Occupational Safety and Health

Administration’s (OSHA) permissible

exposure limits.

OSHA has frequently employed a

version of the NIOSH Accuracy

Criterion when issuing new or revised

single substance standards. For

example, OSHA’s benzene standard

provides: ‘‘[m]onitoring shall be

accurate, to a confidence level of 95

percent, to within plus or minus 25

percent for airborne concentrations of

benzene’’(29 CFR 1910.1028(e)(6)).

Similar wording can be found in the

OSHA standards for vinyl chloride (29

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

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

chloropropane (29 CFR 1044),

acrylonitrile (29 CFR 1045), ethylene

oxide (29 CFR 1047), and formaldehyde

(29 CFR 1048). Note that for vinyl

chloride and acrylonitrile, the accuracy

criteria for the method is ±35 percent at

95 percent confidence at the permissible

exposure limit.

Some commenters contended that the

NIOSH Accuracy Criterion does not

conform with international standards

recently adopted by the European

Committee for Standardization (CEN)

[2]. Contrary to these assertions, the

NIOSH Accuracy Criterion not only

conforms to the CEN criterion but is, in

fact, more stringent. The CEN criterion

requires that 95 percent of the

measurements fall within ±30 percent of

the true concentration, compared to ±25

percent under the NIOSH criterion.

Consequently, any sampling and

analytical method that meets the NIOSH

Accuracy Criterion will also meet the

CEN criterion.

The NIOSH Accuracy Criterion is

relevant and widely recognized and

accepted in the occupational health

professions. Further, commenters

proposed no alternative criteria for

accuracy. Accordingly, for purposes of

section 202(f) of the Mine Act, the

Secretaries consider a single, full-shift

measurement to ‘‘accurately represent’’

atmospheric conditions at the sampling

location, if the sampling and analytical

method used meets the NIOSH

Accuracy Criterion.

Several commenters suggested that

method accuracy should be determined

under actual mining conditions rather

than in a laboratory or in a controlled

environment. Although the NIOSH

Accuracy Criterion does not require

field testing, it recognizes that field

testing ‘‘does provide further test of the

method.’’ However, in order to avoid

confusing real differences in dust

concentration with measurement errors

when testing is done in the field,

‘‘precautions may have to be taken to

ensure that all samplers are exposed to

the same concentrations’’ [1]. Similarly,

the CEN criterion for method accuracy

specifies that ‘‘testing of a procedure

shall be carried out under laboratory

conditions.’’ To determine, so far as

possible, the accuracy of its sampling

and analytical method under actual

mining conditions, MSHA conducted 22

field tests in an underground coal mine.

To provide a valid basis for assessing

accuracy, 16 sampler units were

exposed to the same dust concentration

during each field test using a specially

designed portable chamber. The data

from these field experiments were used

by NIOSH in its ‘‘direct approach’’ to

determining whether or not MSHA’s

method meets the long-established

NIOSH Accuracy Criterion. (See section

VII.E.2. of this notice).

In response to the March 12, 1996

notice, a commenter claimed that the

supplementary information and

analyses introduced into the public

record by that notice addressed the

precision of a single, full-shift

measurement rather than its accuracy.

According to this commenter, by

focusing on precision, important

sources of systematic error had been

overlooked. The Secretaries agree with

the comment that precision is not the

same thing as accuracy. The accuracy of

a measurement depends on both

precision and bias [1,3]. Precision refers

to consistency or repeatability of results,

while bias refers to a systematic error

that is present in every measurement.

Since the NIOSH Accuracy Criterion

requires that measurements consistently

fall within a specified percentage of the

true concentration, the criterion covers

both precision and uncorrectable bias.

Since the amount of dust present on

a filter capsule used by an MSHA

inspector is measured by subtracting the

pre-exposure weight from the postexposure weight determined in the same

laboratory, any bias in the weighing

process attributable to the laboratory is

mathematically canceled out by

subtraction. Furthermore, as will be

discussed later, a control (i.e.,

unexposed) filter capsule will be preand post-weighed along with the

exposed filter capsules. The weight gain

of the exposed capsule will be adjusted

by the weight gain or loss of the control

filter capsule. Therefore, any bias that

may be associated with day-to-day

changes in laboratory conditions or

introduced during storage and handling

of the filter capsules is also

mathematically canceled out. Moreover,

the concentration of respirable dust is

effectively defined by section 202(e) of

the Mine Act and the implementing

regulations in 30 CFR parts 70, 71, and

90 to be whatever is measured with an

approved sampler unit after

multiplication by the MRE-equivalent

conversion factor prescribed by the

Secretary of Labor. Therefore, the

Secretaries have concluded that the

improved sampling and analytical

method is statistically unbiased. This

means that such measurements contain

no systematic error. It should also be

noted that since any systematic error

would be present in all measurements,

measurement bias cannot be reduced by

making multiple measurements. Other

comments regarding measurement bias

are addressed in Appendix A.

For unbiased sampling and analytical

methods, a standard statistic—called the

coefficient of variation (CV)—is used to

determine if the method meets the

NIOSH Accuracy Criterion. The CV,

which is expressed as either a fraction

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

percent), quantifies measurement

accuracy for an unbiased method. An

unbiased method meets the NIOSH

Accuracy Criterion if the ‘‘true’’ CV is

no more than 0.128 (12.8 percent).

However, since it is not possible to

determine the true CV with 100-percent

confidence, the NIOSH Accuracy

Criterion contains the additional

requirement that there be 95-percent

confidence that measurements by the

method will come within 25 percent of
5672 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

the true concentration 95 percent of the

time. Stated in mathematically

equivalent terms, an unbiased method

meets the NIOSH Accuracy Criterion if

there is 95-percent confidence that the

true CV is less than or equal to 0.128

(12.8 percent).

C. Validity of the Sampling Process

A single, full-shift measurement of

respirable coal mine dust is obtained

with an approved sampler unit, which

is either worn or carried by the miner

directly to and from the sampling

location and is operated portal to portal.

The unit remains operational during the

entire shift or for eight hours, whichever

time is less. A portable, battery-powered

pump draws dust-laden mine air at a

flow rate of 2 liters per minute (L/min)

through a 10-mm nylon cyclone, a

particle-size selector that removes nonrespirable particles from the airstream.

Non-respirable particles are particles

that tend to be removed from the

airstream by the nose and upper

respiratory airways. These particles fall

to the bottom of the cyclone body called

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

particles (of the size that would

normally enter into the lungs) pass

through the cyclone, directly into the

inlet of the filter cassette. This airstream

is directed through the pre-weighed

filter leaving the particles deposited on

the filter surface. The collection filter is

enclosed in an aluminum capsule to

prevent leakage of sample air around the

filter and the loss of any dust dislodged

due to impact. The filter capsule is

sealed in a protective plastic enclosure,

called a cassette, to prevent

contamination. After completion of

sampling, the filter cassette is sent to

MSHA’s Respirable Dust Processing

Laboratory in Pittsburgh, Pennsylvania,

where it is weighed again to determine

the weight gain in milligrams, which is

the amount of dust collected on the

filter. The concentration of respirable

dust, expressed as milligrams per cubic

meter (mg/m3 ) of air, is determined by

dividing the weight gain by the volume

of mine air passing through the filter

and then multiplying this quantity by a

conversion factor (discussed below in

Appendix A) prescribed by the

Secretary.

Some comments generally addressed

the quality and reliability of the

equipment used for sampling. Specific

concerns were expressed about the

quality of filter cassettes and the

reliability, due to their age and

condition, of sampling pumps used by

MSHA inspectors. Other commenters

questioned the effect of sampling and

work practices on the validity of a

sample.

The validity of the sampling process

is an important aspect of maintaining

accurate measurements. Since passage

of the Coal Act, there has been an

ongoing effort by MSHA and NIOSH to

improve the accuracy and reliability of

the entire sampling process. In 1980,

MSHA issued new regulations revising

sampling, maintenance and calibration

procedures in 30 CFR parts 70, 71, and

90. These regulatory provisions were

designed to minimize human and

mechanical error and ensure that

samples collected with approved

sampler units in the prescribed manner

would accurately represent the fullshift, average atmospheric dust

concentration at the location of the

sampler unit. These provisions require:

(1) Certification of competence of all

individuals involved in the sampling

process and in maintaining the

sampling equipment; (2) calibration of

each sampler unit at least every 200

hours; (3) examination, testing, and

maintenance of units before each

sampling shift to ensure that the units

are in proper working order; and (4)

checking of sampler units during

sampling to ensure that they are

operating properly and at the proper

flow rate. In addition, significant

changes, such as robotic weighing using

electronic balances were made in 1984,

1994, and 1995 that improved the

reliability of sample weighings at

MSHA’s Respirable Dust Processing

Laboratory. These changes are discussed

below in section C.3.

All of these efforts improved the

accuracy and reliability of the sampling

process since the time of the 1971/1972

proposed and final findings. A

discussion follows concerning the three

elements which constitute the sampling

process: sampler unit performance,

collection procedures, and sample

processing.

1. Sampler Unit Performance

In accordance with the provisions of

section 202(e) of the Mine Act, NIOSH

administers a comprehensive

certification process under 30 CFR part

74 to approve dust sampler units for use

in coal mines. To be approved for use,

a sampler unit must meet stringent

technical and performance requirements

governing the quantity of respirable dust

collected and flow rate consistency over

an 8-hour period when operated at the

prescribed flow rate. NIOSH also

conducts annual performance audits of

approved sampler units purchased on

the open market to determine if the

units are being manufactured in

accordance with the specifications upon

which the approval was issued.

The system of technical and quality

assurance checks currently in place is

designed to prevent a defective sampler

unit from being manufactured and made

commercially available to the mining

industry or to MSHA. In the event these

checks identify a potential problem with

the manufacturing process, the system

requires immediate action to identify

and correct the problem.

In 1992, NIOSH approved the use of

new tamper-resistant filter cassettes

with features that enhanced the integrity

of the sample collected. A backflush

valve was incorporated into the outlet of

the cassette, preventing reverse airflow

through the filter cassette, and an

internal flow diverter was added to the

filter capsule, reducing the possibility of

dust dislodged from the filter surface

falling out of the capsule inlet.

Several commenters questioned the

quality of the filter cassettes used in the

sampling program, expressing concern

about whether the cassettes always meet

MSHA specifications. These concerns

primarily involve filter-to-foil distance

and floppiness of the filters, which are

manufacturing characteristics not

related to part 74 performance

requirements. The Secretaries believe

that such characteristics have no effect

on the accuracy of a single, full-shift

measurement because, unlike the part

74 requirements, they would not affect

the amount of dust deposition.

Commenters also questioned the

condition of sampling pumps used by

MSHA inspectors, stating that many of

the pumps are 10 to 20 years old and are

not maintained as well as they could be.

They claimed that the age and condition

of these pumps call into question not

only whether the sampling equipment

could meet part 74 requirements if

tested, but also the accuracy of the

measurement.

This concern is unwarranted. In 1995,

MSHA replaced all pumps in use by

inspectors with new constant-flow

pumps that incorporate the latest

technology in pump design. These

pumps provide more consistent flow

throughout the sampling period. In

addition to using new pumps, MSHA

inspectors are required to make a

minimum of two flow rate checks to

ensure that the sampler unit is operating

properly. The sample is voided if the

proper flow rate was not being

maintained during the final check at the

conclusion of the sampling shift. Units

found not meeting the requirements of

part 74 are immediately repaired,

adjusted, or removed from service.

Nevertheless, MSHA recognizes that as

these pumps age, deterioration of the

performance of older pumps could

become a concern. However, there is no
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5673

evidence that the age of the equipment

affects its operational performance if the

equipment is maintained as prescribed

by 30 CFR parts 70, 71, and 90.

Some commenters suggested that the

accuracy of a dust sample may be

compromised when a miner is operating

equipment, due to vibration from the

machinery. The potential effect of

vibration on the accuracy of a respirable

dust measurement was recognized by

NIOSH in 1981. An investigation,

supported by NIOSH, was conducted by

the Los Alamos National Laboratory

which found that vibration has an

insignificant effect on sampler

performance [4].

2. Sample Collection Procedures

MSHA regulations at 30 CFR parts 70,

71, and 90 prescribe the manner in

which mine operators are to take

respirable dust samples. The collection

procedures are designed to ensure that

the samples accurately represent the

amount of respirable dust in the mine

atmosphere to which miners are

exposed on the shift sampled. Samples

taken in accordance with these

procedures are considered to be valid.

Several commenters questioned the

effects of sampling and work practices

on the validity of a sample. Instances

were cited where the sampling unit was

accidentally dropped, with the potential

for the sample to become contaminated.

Commenters also pointed out that work

activities requiring crawling, duck

walking, bending, or kneeling could

cause the sampling hose to snag. Such

activities could also cause the sampling

head assembly to be impacted or torn off

a person’s garment, possibly

contaminating the sample. These

commenters stated that sampler units

are sometimes treated harshly while

being worn by miners, mishandled

when being transferred from one miner

to another, or handled casually at the

end of a work shift.

These commenters maintained that it

is impossible for MSHA inspectors or

mine operators to continuously observe

collection of a sample in order to ensure

its validity, and that, for this reason, the

reliability and accuracy of the sampling

equipment, when used under actual

mining conditions, is not the same as

when tested and certified in a

laboratory. Averaging multiple samples

would, according to these commenters,

provide some ‘‘leeway’’ in the system,

by reducing the impact of an aberrant

sample.

While MSHA and NIOSH agree that it

is not possible to continuously observe

the collection of each sample, MSHA

inspectors are normally in the general

vicinity of the sampling location, and

therefore have knowledge of the specific

conditions under which samples are

taken. In addition, MSHA inspectors are

instructed to ask miners wearing the

sampler units whether anything that

could affect the validity of the sample

had occurred during the shift.

Other commenters expressed concern

that, if special dust control measures are

in effect during sampling, a single, fullshift measurement may fail to represent

atmospheric conditions during shifts

when samples are not collected. The

Secretaries believe that this concern is

beyond the scope of this notice, which,

as described in the discussion of

measurement objective, deals solely

with the accuracy of a measurement in

representing atmospheric conditions on

the shift being sampled. One commenter

recommended that MSHA, NIOSH, or

the Bureau of Mines (now a part of

NIOSH) should evaluate the need for

standardizing the MSHA respirable dust

sampling procedures. In fact, the

procedures for respirable dust sampling

are already standardized under the

revised 1980 MSHA regulations codified

at 30 CFR parts 70, 71 and 90.

MSHA inspectors will also begin

using control filter capsules to eliminate

any bias that may be associated with

day-to-day changes in laboratory

conditions or introduced during storage

and handling of the filter capsules. A

control filter capsule is an unexposed

filter capsule that was pre-weighed on

the same day as the filter capsules used

during a sampling inspection. These

control filter capsules will be carried by

the inspector, but will remain plugged

and not be exposed to the mine

environment.

3. Sample Processing

Sample processing consists of

weighing the filter capsules, recording

the weight gains, and examining certain

samples in order to verify their validity.

Sample processing also includes

electronic transmission of the results to

MSHA’s computer center where dust

concentrations are computed. The

results are then distributed to MSHA

enforcement personnel and to mine

operators.

(a) Weighing and recording

procedures. One commenter cited a

personal experience in which anomalies

were noted in the pre-exposed weights

recorded by the dust cassette

manufacturer. The commenter was

concerned that such anomalies

indicated poor quality control in the

manufacturer’s weighing process,

implying that this would cause a

significant number of single, full-shift

measurements to be inaccurate.

The procedures and analytical

equipment used by MSHA to process

respirable coal mine dust samples have

improved since 1970. From 1970 to

1984, samples were manually weighed

using semimicro balances. In 1984, the

process was automated with a state-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 balance were

upgraded.

The full benefit of the 1994

improvements of the weighing system

for inspector samples was, however, not

fully attained until mid-1995, when

MSHA implemented two modifications

to its procedures for processing

inspector samples. One modification

involved measuring both the pre- and

post-exposed weights to the nearest

microgram (0.001 mg) on a balance

calibrated using the established

procedure within MSHA’s laboratory.

Prior to mid-1995, filter capsules had

been weighed in the manufacturer’s

laboratory before sampling, and then in

MSHA’s laboratory after sampling.

MSHA is now pre-weighing all such

filter capsules in its own laboratory,

which will significantly reduce the

potential for anomalous pre-exposed

weights of filter capsules used by

inspectors. To maintain the integrity of

these pre-exposed weights, eight percent

of all capsules are systematically

weighed a second time. If a significant

deviation is found, the balance is

recalibrated and all filter capsules with

questionable weights are reweighed.

The other modification was to

discontinue the practice of truncating

the recorded weights used in calculating

dust concentration. This means that

MSHA no longer ignores digits

representing hundredths and

thousandths of a milligram when

processing inspector samples. These

modifications improved the overall

accuracy of the measurement process.

To eliminate the potential for any bias

that may be associated with day-to-day

changes in laboratory conditions or

introduced during storage and handling

of the filter capsules, MSHA will use

control filter capsules in its enforcement

program. Any change in weight of the

control filter capsule will be subtracted

from the change in weight of the

exposed filter capsule.

(b) Sample validity checks. All

respirable dust samples collected and

submitted as required by 30 CFR parts

70, 71, and 90 are considered valid

unless a questionable appearance of the

filter capsule or other special

circumstances are noted that would
5674 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

cause MSHA to examine the sample

further. Several commenters expressed

concern about the potential

contamination of samples with

‘‘oversize particles.’’ Such

contamination, according to one

commenter, can result in aberrational

weight gains. These commenters noted

that current procedures do not

systematically ensure that samples

collected by MSHA contain no oversize

particles. It was recommended that

MSHA analyze, for the presence of

oversize particles, any dust sample that

exceeds the applicable dust standard.

Also suggested for such an analysis was

any sample with a weight gain

significantly different from other

samples taken in the same area.

Standard laboratory procedures,

involving visual, and microscopic

examination as necessary, are used to

verify the validity of samples. Samples

weighing 1.4 milligrams (mg) or more

are examined visually and

microscopically, as necessary, for

abnormalities such as the presence of

large dust particles (which can occur

from agglomeration of smaller particles),

abnormal discoloration, abnormal dust

deposition pattern on the filter, or any

apparent contamination by materials

other than respirable coal mine dust.

Also examined are samples weighing

0.1 mg or less for insufficient dust

particle count. Similar checks are also

performed in direct response to specific

inspector or operator concerns noted on

the dust data card to which each sample

is attached.

The commenters’ concerns about the

contamination of samples with oversize

particles are based on the assumption

that all oversize particles, defined as

dust particles greater than 10

micrometers in size, are not respirable

and therefore should be totally excluded

from any sample taken with an

approved sampler unit. In fact, it has

long been known that particles greater

then 10 micrometers in size can be

inhaled, and that some of these particles

can reach the alveoli of the lungs [5].

According to the British National Coal

Board, ‘‘particles as large as 20 microns

(i.e. micrometers) mean diameter may

be deposited, although most ‘‘lung dust’’

lies in the range below 10 microns

diameter’’ [6]. Furthermore, it is known

that, due to the irregular shapes of dust

particles, the respirable dust collected

by the MRE instrument (the dust

sampler used by the British Medical

Research Establishment in the

epidemiological studies on which the

U.S. coal dust standard was based) may

include some dust particles as large as

20 micrometers [6]. Moreover, MSHA

studies have shown that nearly all

samples taken with approved sampler

units, even when operated in the

prescribed manner, contain some

oversize particles [7]. Since section

202(e) of the Mine Act defines

concentration of respirable dust to be

that measured by an approved sampler

unit, and because the approved sampler

unit will collect some oversize particles,

the Secretaries do not consider a sample

to be ‘‘contaminated’’ because it

contains some oversize particles.

The Secretaries recognize that there

are occasions when oversize particles

can properly be considered a

contaminant. For example, an excessive

number of such particles could be

introduced into the filter capsule if the

sampling head assembly is accidentally

or deliberately turned upside down or

‘‘dumped’’ (possibly causing some of

the contents of the cyclone grit pot to be

drawn into the filter capsule), if the

pump malfunctions, or if the entire

sampler unit is dropped. When MSHA

has reason to believe that such

contamination has occurred, the suspect

sample is examined to verify its

validity.

Contrary to the assertions of some

commenters, checking for oversize

particles is not standard industrial

hygiene practice. Nevertheless, MSHA

checks any dust sample suspected of

containing an excessive number of

oversize particles. MSHA’s laboratory

procedures require any sample

exhibiting an excessive weight gain

(over 6 mg) or showing evidence of

being ‘‘dumped’’ to be examined for the

presence of an excessive number of

oversize particles. Samples identified by

an inspector or mine operator as

possibly contaminated are also

examined. If this examination indicates

that the sample contains an excessive

number of oversize particles according

to MSHA’s established criteria, then that

sample is considered to be invalid, and

is voided and not used. In fiscal year

1996, only 83 samples or 0.4 percent of

the 20,331 inspector samples processed

were found to contain an excessive

number of oversize particles and thus

were not used.

While rough handling of the sampler

unit or an accidental mishap could

conceivably cause a sample weighing

less than 6 mg to become contaminated,

as claimed by some commenters, studies

show that short-term accidental

inclinations of the cyclone will not

affect respirable mass measurements

made with currently approved sampler

units [8]. Sampler units currently used

are built to withstand the rigors of the

mine environment, and are therefore

less susceptible to contamination than

suggested by some commenters. In any

event, the Secretaries believe that the

validity checks currently in place, as

discussed above, will detect such

samples.

D. Measurement Uncertainty and Dust

Concentration Variability

Overall variability in measurements

collected on different shifts and

sampling locations results from the

combination of errors associated with

the measurement of a particular dust

concentration and variability in dust

concentration. Variability in dust

concentration refers to the differing

atmospheric conditions experienced on

different shifts or at different sampling

locations. Measurement uncertainty, on

the other hand, refers to the differing

measurement results that could arise, at

a given sampling location on a given

shift, because of potential sampling and

analytical errors.

Numerous commenters identified

sources of measurement uncertainty and

dust concentration variability that they

believed should be considered when

determining whether or not a

measurement accurately represents such

atmospheric conditions. Because the

measurement objective is to accurately

represent the average dust concentration

at the sampling location over a single

shift, it does not take into consideration

dust concentration variability between

shifts or locations. Sources of dust

concentration variability will not be

considered by the Secretaries in

determining whether a measurement is

accurate. Consequently, the Secretaries

have concluded that the only sources of

variability relevant to establishing

accuracy of a single, full-shift

measurement for purposes of section

202(f) of the Mine Act are those related

to sampling and analytical error.

1. Sources of Measurement Uncertainty

Filter capsules are weighed prior to

sampling. After a single, full-shift

sample is collected, the filter capsule is

weighed a second time, and the weight

gain (g) is obtained by subtracting the

pre-exposure weight from the 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/

m 3);

1.38 is a constant MRE-equivalent

conversion factor;
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5675

2The 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.

g is the observed weight gain (mg)

after adjustment for the control filter

capsule;

v is the estimated total volume of air

pumped through the filter during a

typical full shift.

The Secretaries recognize that random

variability, inherent in any

measurement process, may cause x to

deviate either above or below the true

dust concentration. The difference

between x and the true dust

concentration is the measurement error,

which may be either positive or

negative. Measurement uncertainty

arises from a combination of potential

errors in the process of collecting a

sample and potential errors in the

process of analyzing the sample. These

potential errors introduce a degree of

uncertainty when x is used to represent

the true dust concentration.

The statistical measure used by the

Secretaries to quantify uncertainty in a

single, full-shift measurement is the

total sampling and analytical coefficient

of variation, or CVtotal. CVtotal quantifies

the magnitude of probable sampling and

analytical errors and is expressed as

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

percentage (e.g., 5 percent) of the true

concentration. For example, if a single,

full-shift measurement (x) is collected in

a mine atmosphere with true dust

concentration equal to 1.5 mg/m 3, and

the standard deviation of potential

sampling and analytical errors

associated with x is equal to 0.075 mg/

m 3, the uncertainty associated with x

would be expressed by the ratio of the

standard deviation to the true dust

concentration: CVtotal = 0.075/1.5 = 5

percent.

Based on a review of the scientific

literature, the Secretaries in their March

12, 1996 notice, identified three sources

of uncertainty in a single, full-shift

measurement, which together make up

CVtotal:

(1) 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

the filter cassettes to and from the mine,

and weighing the exposed and control

filter capsules after sampling (postweighing).

(2) CVpump—variability in the total

volume of air pumped through the filter

capsule. This covers variability

associated with calibration of the pump

rotameter,2 variability in adjustment of

the flow rate at the beginning of the

shift, and variation in the flow rate

during sampling. It should be noted that

variation in flow rate during sampling

was identified as a separate component

of variability in MSHA’s February 18,

1994, notice. Here, it is included within

CVpump.

(3) CVsampler—variability in the

fraction of dust trapped on the filter.

This is attributable to physical

differences among cyclones. This

component was introduced in the

material submitted into the record in

September 1994.

These three components of

measurement uncertainty can be

combined to form an indirect estimate

of CVtotal by means of the standard

propagation of errors formula:

CV CV CV CV total weight pump sampler = + + 2 2 2 ( ) 2

These three components are discussed

in greater detail, along with responses to

specific comments, in Appendix B.

2. Sources of Dust Concentration

Variability

Numerous commenters also raised

issues related to sources of dust

concentration variability. Some of these

commenters maintain that the

Secretaries should include in CVtotal

additional components representing the

effects of shift-to-shift variability and

variability related to location (spatial

variability). These comments reflect a

misunderstanding of the measurement

objective as intended by the Mine Act

(see section VII.A. of this notice).

Exposure variability due to job,

location, shift, production level,

effectiveness of engineering controls,

and work practices will be different

from mine to mine, and is under the

control of the mine operator. The

sampler unit is not intended to account

for these factors.

(a) Spatial variability. Several

commenters stated that CVtotal should

account for spatial variability, or the

differences in concentration related to

location. The Secretaries agree that dust

concentrations vary between locations

in a coal mine, even within a relatively

small area. However, real variations in

concentration between locations, while

sometimes substantial, do not contribute

to measurement error. As stated earlier,

the measurement objective is to

accurately measure average atmospheric

conditions, or concentration of

respirable dust, at a sampling location

over a single shift.

(b) Shift-to-shift variability. Several

commenters stated that CVtotal should

take into account the differences or

variations in dust concentration that

occur shift to shift. Although the

Secretaries agree that dust

concentrations vary from shift to shift,

the measurement objective is to measure

average atmospheric conditions on the

specific shift sampled. This result is

consistent with the Mine Act, which

requires that concentrations of

respirable mine dust be maintained at or

below the applicable standard during

each shift.

3. Other Factors Considered

(a) Proportion of oversize particles.

Several commenters expressed concern

that respirable dust cyclones are

handled in a rough manner in normal

use and occasionally turned upside

down. According to one commenter,

this type of handling would cause more

large particles to be deposited on the

filter in the mine environment than

when used in the laboratory. This

commenter knew of no data that could

be used to evaluate the error associated

with such occurrences and

recommended that a study be

commissioned to measure the

proportion of non-respirable particles

on the filters after they are weighed to

MSHA standards.

After considering this

recommendation, the Secretaries have

concluded that the available evidence

shows that short-term inclinations of the

cyclone, as might frequently occur

during sampling, will not affect

respirable dust measurements made

with approved sampler units [8]. The

weight of the sampler head assembly

makes it extremely unlikely that a
5676 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

3Many of the recommendations in the GAO

report were later adopted and implemented by

MSHA.

sampler unit could be turned upside

down in normal use. Furthermore, with

a field study of the type recommended,

variability in the field measurements

due to normal handling would be

confounded with variability due to real

differences in atmospheric conditions.

Therefore, the Secretaries believe that

such a study would not be useful in

establishing variability in measurements

due to differences in handling of the

sampler unit.

(b) Anomalous events. Several

commenters asserted that unpredictable,

infrequent events, such as a ‘‘face

blowout’’ on a longwall (a violent

expulsion of coal together with large

quantities of coal dust and/or methane

gas) or high winds at a surface mine, can

cause rapid loading of a filter capsule

and thereby distort a measurement to

show an excessive dust concentration

based on a single, full-shift sample

when, they argue, the dust standard had

not been exceeded. In fact, if such an

occurrence were to cause a

measurement above the applicable

standard, the dust standard would in

fact be violated. No evidence was

presented to demonstrate that 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 conclude that such events

are results of the dynamic and everchanging mine environment—an

environment to which the miner is

exposed. The sampler unit is designed

to measure the atmospheric condition at

a specific sampling location over a full

shift. If such events occur, the sampler

unit will accurately record the

atmospheric condition to which it is

exposed.

(c) Conversion factor used in the dust

concentration calculation. Several

commenters questioned the 1.38 MREconversion 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 [9]. The 1.38 constant has

been established by the Secretaries as

applying to the currently approved dust

sampler unit described in 30 CFR part

74.

Some commenters contended that

variability involved in the data analysis

used in establishing the conversion

factor should be taken into account in

determining CVtotal. This suggestion

demonstrates a misunderstanding of the

difference between measurement

imprecision and measurement bias. The

1.38 factor applies to every sampler unit

currently approved under part 74. Since

the same conversion factor is applied to

every measurement, any error in the

value used would cause a measurement

bias but would have no effect on

measurement imprecision. Since

Congress defined respirable dust in

section 202(e) of the Mine Act as

whatever is collected by a currently

approved sampler unit, a measurement

incorporating the 1.38 factor is unbiased

by definition. Further discussion is

provided in Appendix A on why use of

the 1.38 factor does not introduce a bias.

Appendix A also addresses comments

relating to other aspects of the 1.38

conversion factor; comments regarding

the fact that MSHA’s sampler unit does

not conform to other definitions of

respirable dust; and questions

concerning the effect of static charge on

sampler unit performance.

(d) Reduced dust standards. One

commenter pointed out that in

estimating CVtotal, MSHA and NIOSH

did not take into account any potential

errors associated with silica analysis.

The commenter argued that since silica

analysis is used to establish reduced

dust standards, MSHA and NIOSH had

failed to demonstrate ‘‘* * * accuracy

for all samples ‘across the range of

possible reduced dust standards.’ ’’

This commenter confuses the

accuracy of a respirable dust

concentration measurement with the

accuracy of the procedure used to

establish a reduced dust standard.

MSHA has a separate program in which

silica analysis is used to set the

applicable respirable coal mine dust

standard, in accordance with section

205 of the Mine Act, when the

respirable dust in the mine atmosphere

of the active workings contains more

than 5 percent quartz. As shown by

Equation 1, no silica analysis is used in

a single, full-shift measurement of the

respirable dust concentration.

Therefore, the Secretaries do not agree

with the comment that CVtotal should

include a component representing

potential errors in silica analysis.

(e) Dusty clothing. Several

commenters pointed out that local

factors such as dusty clothing could

cause concentrations in the immediate

vicinity of the sampler unit to be

unrepresentative of a larger area. Dust

from a miner’s clothing nevertheless

represents a potential hazard to the

miner. No evidence was presented to

demonstrate that miners are not also

exposed to dust originating from dusty

clothing.

E. Accuracy of a Single, Full-Shift

Measurement

1. Quantification of Measurement

Uncertainty

Several commenters argued that

MSHA underestimated CVtotal in its

February 18, 1994 notice and suggested

alternative estimates ranging from 16 to

50 percent. These commenters cited

several published studies and submitted

five sets of data in support of these

higher estimates. Statistical analyses of

the data were also submitted.

MSHA and NIOSH reviewed all of the

studies referenced by the commenters.

The review showed that all of the

estimates of measurement variability

were from studies carried out prior to

improvements mandated by the 1980

MSHA revisions to dust sampling

regulations, discussed earlier in

‘‘Validity of the Sampling Process.’’ For

example, the General Accounting Office

(GAO) 3 and the National Bureau of

Standards (NBS, now the National

Institute of Standards and Technology)

studies were conducted in 1975. The

National Academy of Sciences report,

which analyzed the same data as the

NBS and GAO reports, was issued in

1980. The review further showed that

the measurement variability quantified

in these studies included effects of

spatial variability—a component of

variability the Secretaries deliberately

exclude when determining the accuracy

of a sampling and analytical method as

discussed in section D.2.(a).

Additionally, since past studies

frequently relied on combining

estimates of variability components

obtained from different bodies of data,

some of them also suffered from

methodological problems related to

combining individual sources of

uncertainty. For example, in 1984, a

NIOSH study identified several

conceptual errors in earlier studies that

had led to double-or even triplecounting of some variability

components [10].

Although all the data and analyses

submitted by commenters included

effects of spatial variability, one of these

data sets, consisting of paired sample

results, contained sufficient information

to indicate that weighing imprecision
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5677

was less than what MSHA had assumed

in its February 18, 1994 notice.

However, without an independent

estimate of spatial variability applicable

to these samples, it is not

mathematically possible to utilize this

data set to estimate variability

attributable to the sampler unit or the

volume of air sampled. A second data

set consisted only of differences in dust

concentration between paired samples,

making it impossible to use it even for

evaluating weighing imprecision. The

remaining three data sets included

effects of shift-to-shift variability,

which, like spatial variability, is not

relevant to the measurement objective.

Therefore, none of these data could be

used to estimate overall measurement

imprecision. Further details are

provided in Appendix C.

One of the commenters particularly

questioned the value MSHA used in its

February 18, 1994 notice to represent

variability in initially setting the pump

flow rate. In response to this

commenter’s suggestion, MSHA

conducted a study to verify the

magnitude of this variability

component. This study simulated flow

rate adjustment under realistic operating

conditions by including a number of

persons checking and adjusting initial

flow rate under various working

situations [11]. Results showed the

coefficient of variation associated with

the initial flow rate adjustment to be

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 have concluded that the

component of uncertainty associated

with the combined effects of variability

in flow rate during sampling and

potential errors in calibration is actually

less than 3 percent. As explained in

Appendix B, these two sources of

uncertainty can be combined to estimate

CVpump. After reviewing the available

data and the comments submitted, the

Secretaries have concluded that the best

estimate of CVpump is 4.2 percent.

Additional details regarding CVpump,

along with the Secretaries’ responses to

comments, are presented in Appendix

B.

Intersampler variability, represented

by CVsampler, accounts for uncertainty

due to physical differences from

sampler to sampler. Most of the

commenters ignored this source of

uncertainty. As explained in Appendix

B, the Secretaries have adopted a 5-

percent estimate of CVsampler.

To address commenters’ concerns that

the Agencies had underestimated CVtotal,

MSHA conducted a field study to

directly estimate the overall

measurement precision attainable when

dust samples are collected with

currently approved sampler units and

analyzed using state-of-the-art analytical

techniques. The study involved

simultaneous field measurements of the

same coal mine dust cloud using

sampling pumps incorporating constant

flow technology. Using a specially

designed portable dust chamber, 22 tests

were conducted at various locations in

an underground coal mine. Each test

consisted of collecting 16 dust samples

simultaneously and at the same

location. No adjustments in the flow

rate were made beyond what would

routinely have been done by an MSHA

inspector.

Prior to the field study, two

modifications to MSHA’s sampling and

analytical method had been considered

by MSHA and NIOSH: (1) Measuring

both the pre-and post-exposure weights

to the nearest microgram (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 commenter characterized the

field study as being ‘‘woefully

incomplete’’ because it was conducted

‘‘in a tightly controlled environment

* * * not subject to normal

environmental variation.’’ While it is

true that the samples within each test

were not subject to normal

environmental variability, this was

because the experiment was deliberately

designed to avoid confusing spatial

variability in dust concentration with

measurement error. However, pumps

were handled and flow rates were

checked in the same manner as during

routine sampling. Furthermore, the

sampler units were disassembled and

reassembled in the normal manner to

remove and replace dust cassettes.

Commenters also questioned the

value that MSHA used in the February

1994 notice to represent uncertainty due

to potential weighing errors. In

September 1994, MSHA submitted into

the record an analysis based on

replicated weighings for 300 unexposed

filter capsules, each of which was

weighed once by the cassette

manufacturer and twice in MSHA’s

laboratory [12]. An estimate of weighing

imprecision derived from this analysis

was used by NIOSH in its September 20,

1995 assessment of MSHA’s sampling

and analytical procedure (discussed in

more detail later).

In the March 12, 1996 joint notice,

MSHA described the results of an

investigation into repeated weighings of

the same capsules made over a 218-day

period using MSHA’s automatic

weighing system. It was noted that after

approximately 30 days, filter capsules

left exposed and unprotected gained a

small amount of weight—an average of

0.8 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 MSA and MSHA laboratories

showed that filter capsules tend to gain

a small amount of weight even when

stored in plastic cassettes [13]. To check

this result, 75 unexposed filter cassettes

that had been distributed to MSHA’s

district offices were recalled and the

filter capsules were reweighed. On

average, the weight gain was about 40 μg

over a time period of roughly 150 days.

Statistical analyses of these data

performed by MSHA and NIOSH

confirmed the previous result [13,14].

While the cause has not been

established, it is hypothesized that at

least some of the observed weight gain

may be the result of outgassing from the

plastic cassette onto the filter capsule. If

uncorrected, any systematic change in

weight not due to coal mine dust would

introduce a bias in dust concentration

measurements.

One commenter had previously stated

that the Secretaries were addressing

only precision, thereby implying that

potential biases were being ignored. To

eliminate the potential for any bias due

to a spurious gain or loss of filter

capsule weight, MSHA will use control

filter capsules in its enforcement

program. Any change in weight

observed for the control filter capsule

will be subtracted from the measured

change in weight of the exposed filter

capsule. Each control filter capsule will

be pre-weighed with the other filter

capsules, will be stored and transported

with the other capsules, and will be on

the inspector’s person during the day of

sampling. This modification to MSHA’s

inspector sampling and analytical

procedure will assure an unbiased

estimate of the true weight gain [14].

2. Verification of Method Accuracy

With its field study, MSHA exceeded

the usual requirements for determining

the accuracy of a sampling and

analytical method, as described by

NIOSH [1] and the European

Community [2]. Both of these require

only a laboratory determination of

method accuracy. NIOSH’s independent

analysis of the study data determined,

with 95-percent confidence, that the
5678 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

true CVtotal for MSHA’s sampling and

analytical method is less than the target

maximum value of 12.8 percent for

concentrations ranging from 0.2 mg/m3

to greater than 2 mg/m3 [3]. In other

words, NIOSH demonstrated that, with

two recommended modifications,

MSHA’s sampling and analytical

method for collecting and processing

single, full-shift samples would meet

the NIOSH Accuracy Criterion at dust

concentrations greater than or equal to

0.2 mg/m3.

NIOSH also applied an indirect

approach for assessing the accuracy of

MSHA’s sampling and analytical

method. The indirect approach involved

combining independently derived

estimates, previously placed into the

public record, of intra-laboratory

weighing imprecision, pump-related

variability, and variability associated

with physical differences between

individual sampler units. This indirect

approach also indicated that MSHA’s

sampling and analytical method meets

the NIOSH Accuracy Criterion at

concentrations greater than or equal to

0.2 mg/m3, thereby corroborating the

analysis of MSHA’s field data.

These NIOSH analyses predate

MSHA’s more recent data indicating a

correctable weight gain bias (discussed

above). As explained in Appendices A

and B, the use of control filter capsules

will eliminate this bias but also affect

the precision of a single, full-shift

measurement. Consequently, NIOSH

reassessed the accuracy of MSHA’s

sampling and analytical method, taking

into account the effect of using a control

filter capsule on the measurement

process [14]. After accounting for the

effects of control filter capsules on both

bias and precision, NIOSH concluded,

based on both its direct and indirect

approaches, that a single, full-shift

measurement will meet the NIOSH

Accuracy Criterion at dust

concentrations greater than or equal to

0.3 mg/m3.

One commenter claimed that the

Secretaries ‘‘have not addressed the

‘accuracy’ of a single sample collected

from an environment where the

concentration is unknown’’. The

purpose of any measurement process is

to produce an estimate of an unknown

quantity. Since the Secretaries have

concluded that MSHA’s sampling and

analytical method for inspectors meets

the NIOSH Accuracy Criterion for true

concentrations ranging from 0.3 mg/m3

to greater than 2 mg/m3, it is possible to

calculate the range of measurements for

which the Accuracy Criterion applies.

Since CVtotal increases at the lower

concentrations, it is important to

determine the lowest measurement at

which the NIOSH Accuracy Criterion is

met. If the true concentration exactly

equaled the lowest concentration at

which MSHA’s sampling and analytical

method meets the Accuracy Criterion

(i.e., 0.3 mg/m3), no more than 5% of

single, full-shift measurements would

be expected to exceed 0.36 mg/m3 [14].

Conversely, if a measurement equals or

exceeds 0.36 mg/m3, it can be inferred,

with at least 95% confidence, that the

true dust concentration equals or

exceeds 0.3 mg/m3 [14]. Consequently,

the Secretaries conclude that MSHA’s

improved sampling and analytical

method satisfies the NIOSH Accuracy

Criterion whenever a single, full-shift

measurement is at or above 0.36 mg/m3.

As a result of the prior analyses,

MSHA’s existing inspector sample

processing procedures were changed to

reflect the modifications that were

incorporated into MSHA’s field study.

MSHA is now pre- and post-weighing

inspector samples in the same

laboratory, and reporting the pre- and

post-exposure weights of inspector

samples to the nearest microgram (μg).

As a result of NIOSH’s latest analysis,

MSHA will now require its inspectors to

use control filter capsules during

sampling. In addition, MSHA is now

using only constant-flow control pumps

in the inspector sampling program.

MSHA believes that exclusive use of

constant-flow pumps, as in the field

study, further enhances the quality of

the Agency’s sampling program.

The Secretaries recognize that future

technological improvements in MSHA’s

sampling and analytical method may

reduce CVtotal below its current value.

Also, as additional data are

accumulated, updated estimates of

CVtotal may become available. However,

so long as the method remains unbiased

and CVtotal remains below 12.8 percent,

at a 95-percent confidence level, the

sampling and analytical method will

continue to meet the NIOSH Accuracy

Criterion, and the present finding will

continue to be valid.

VIII. Finding

The Secretaries have concluded that

sufficient data exist for determining the

uncertainty associated with a single,

full-shift measurement; rigorous

requirements are in place, as specified

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

ensure the validity of a respirable coal

mine dust sample; and valid statistical

techniques were used to determine that

MSHA’s improved dust sampling and

analytical method meets the NIOSH

Accuracy Criterion. For these reasons

the Secretaries find that a single, fullshift measurement at or above 0.36 mg/

m3 will accurately represent

atmospheric conditions to which a

miner is exposed during such shift.

Therefore, pursuant to section 202(f)

and in accordance with section 101 of

the Mine Act, the 1972 joint notice of

finding is hereby rescinded.

Appendix A—Why Individual

Measurements are Unbiased

The accuracy of a measurement

depends on both precision and bias

[1,3]. Precision refers to consistency or

repeatability of results, and bias refers to

an error that is equally present in every

measurement. Since the amount of dust

present on a filter capsule is measured,

for MSHA inspector samples, by

subtracting the pre-exposure weight

from the post-exposure weight observed

in the same laboratory, any bias in the

weighing process attributable to the

laboratory is mathematically canceled

out by subtraction. A control filter

capsule will be pre- and post-weighted

along with the exposed filter capsules.

The weight gain of each exposed

capsule will be adjusted by subtracting

the weight gain or loss of the control

filter capsule. Consequently, any bias

introduced during storage and handling

of the filter capsules is also

mathematically canceled out. Therefore,

since respirable dust is defined by

section 202(e) of the Mine Act to be

whatever is measured by an approved

sampler unit, the Secretaries have

concluded that a single, full-shift

measurement made with an approved

sampler unit provides an unbiased

representation of average dust

concentration for the shift and sampling

location sampled. Some commenters,

however, suggested that MSHA’s

sampling and analytical method is

subject to systematic errors that would

have the same effect on all

measurements. These comments are

addressed in this appendix.

I. The Value of the MRE Conversion

Factor

The current U.S. coal mine dust

standard is based on studies of British

coal miners. In these studies, full-shift

dust measurements were made using a

sampler employing four horizontal

plates which removed the large-sized

particles by gravitational settlement

(simulating the action of the nose and

throat) and collecting on a pre-weighed

filter those particles which are normally

deposited in the lungs [6]. This

instrument, known as the Mining

Research Establishment (MRE) sampler,

was designed to collect airborne dust

according to a collection efficiency

curve, developed by the British Medical

Research Council (BMRC) to

approximate the deposition of inhaled
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5679

particles in the lung. Because the MRE

instrument was large and cumbersome,

other samplers using a 10-mm nylon

cyclone were developed for taking

samples of respirable dust in U.S. coal

mines. However, these cyclone-based

samplers collected less dust than the

MRE instrument. Therefore, a factor was

derived (1.38) to convert measurements

obtained with the cyclone-based

samplers to measurements obtained

with the MRE instrument.

Two commenters noted that the 1.38

conversion factor was derived from a

comparison of MRE measurements to

measurements obtained using pumps

made by two manufacturers [Mine

Safety Appliances Co. (MSA) and

Unico]. These commenters noted that

there was some variability in these

comparisons that MSHA and NIOSH did

not consider in estimating CVtotal, and

noted that MSHA and NIOSH should

therefore make allowances for any error

or uncertainty in the conversion factor.

It was also noted that the report deriving

the conversion factor showed that MSA

pumps more closely approximated MRE

concentrations than Unico pumps,

indicating that the 1.38 conversion

factor (derived empirically using both

types of pumps) may systematically

overestimate the MRE-equivalent dust

concentration for MSA samplers

specifically. This commenter argued

that such potential bias in the

conversion factor should be addressed

in order to account for the possibility of

a systematic error in the conversion.

The study referred by these

commenters involved collecting side-byside samples using MRE and cyclonebased samplers [9]. The data showed

that multiplying the cyclone sample

concentrations by a constant factor of

1.38 gave values in reasonable

agreement with MRE measurements.

Consequently, a conversion factor of

1.38 was adopted for use with approved

sampler units equipped with the 10-mm

nylon cyclone.

Variability in the operating

characteristics of individual sampler

units is expressed by CVsampler. In

response to the comment on potential

bias, MSHA and NIOSH reviewed the

original report recommending the 1.38

MRE conversion factor. This report

contained both an empirical

determination, using side-by-side

comparison data collected in

underground coal mines, and a

theoretical determination of the

conversion factor. Two sets of field data

were collected: one set was collected by

mine inspectors who visited 200 coal

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

collected by investigators from MSHA’s

Pittsburgh laboratory at 24 coal mines.

Linear regression was used to analyze

both sets of data, with the slope of the

regression line representing the

conversion factor. The theoretical

determination suggested that the

conversion factor should be close to a

value of 1.35. Analysis of the district

mine inspector data resulted in a

conversion factor of 1.38, while analysis

of the laboratory investigator data

suggested a greater conversion factor of

1.45.

Because the conversion factor derived

from the inspector data came closer to

the theoretical value, the former U.S.

Bureau of Mines’ Pittsburgh Technical

Support Center (in the Department of

Interior) recommended that 1.38 be the

value adopted for any approved sampler

unit operating at 2.0 L/min and

equipped with a 10-mm nylon cyclone.

This recommendation was subsequently

accepted. The 1.38 conversion factor

was not, as implied by the commenters,

meant to represent the average value to

be used with two different types of

sampler unit, one of which is no longer

in use. Instead, based largely on the

theoretical value, it was meant to

represent the appropriate value to be

used with any approved sampler unit

operating at 2.0 L/min and equipped

with a 10-mm nylon cyclone. No data or

analyses were submitted to suggest that

this conversion factor, which has been

accepted and used for over twenty

years, should be any other value.

II. Conforming to the ACGIH and ISO

Standard

One commenter implied that the

respirable dust cyclone specifications

used by MSHA result in a different

particle collection efficiency curve than

that specified by the American

Conference of Governmental Industrial

Hygienists (ACGIH) and the

International Organization for

Standardization (ISO) for a respirable

dust sampler. Other commenters

questioned whether the 2.0 L/min flow

rate used by MSHA was appropriate,

since a NIOSH study recommended

using a 1.7 L/min flow rate when

conforming to the recently adopted

ACGIH/ISO specifications for collecting

respirable particulate mass.

It is true that MSHA’s respirable dust

cyclone specifications result in a

different particle size distribution than

that specified by ACGIH and ISO.

However, this fact has no bearing on the

conversion to a respirable dust

concentration as measured by an MRE

sampler, which is the basis of the

respirable dust standard. The 1.38 factor

used to obtain an MRE-equivalent

concentration was derived for a cyclone

flow rate of 2.0 L/min. If a flow rate of

1.7 L/min were used, then this would

correspond to some other factor for

converting to an MRE-equivalent dust

concentration. Therefore, the particle

size distribution obtained at 2.0 L/min

governs the relationship derived

between an approved respirable coal

mine dust sampler and an MRE sampler.

The appropriate dust fraction (i.e., the

fraction corresponding to the 1.38

conversion factor) is sampled so long as

the specified 2.0 L/min flow rate is

maintained.

III. Effects of Other Variables

The effects of any other variables on

the sampled dust fraction are covered by

the 1.38 conversion factor, so long as

these effects were present in the data

from which the conversion factor was

obtained. For example, one commenter

expressed concern that nylon cyclones

are subject to performance variations

due to static charging phenomena. Any

systematic effect of static charging on

the performance characteristics of the

nylon cyclone is implicitly accounted

for in the conversion factor, because the

same static charging effect would have

been present when the comparative

measurements were obtained for

deriving the relationship between an

approved sampler unit and an MRE

instrument. Random effects of static

charging, i.e., effects that vary from

sample to sample, are included in

CVtotal.

Appendix B—Components of CVtotal

I. Weighing Uncertainty

(a) Derivation of CVweight

The weight of a dust sample is

determined by weighing each filter

capsule before and after exposure and

then determining the weight gain by

subtraction. This weight gain is adjusted

by subtracting any change in weight

observed for the unexposed, control

filter capsule. This practice eliminates

potential biases due to any possible

outgassing of the plastic cassette or

other time-related factors but introduces

two additional weighings. The weighing

process is designed to control potential

effects of temperature, humidity, and

contamination. However, because the

initial and final weighings of both the

exposed and the control filter capsules

are each still subject to random error,

there is some degree of uncertainty in

the computed weight of dust collected

on the filter.

For both the control and the exposed

filter capsule, the error in the weightgain measurement results from

combining two independent weighing

errors. For example, suppose that the

true pre- and post-exposure weights of
5680 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

4Prior to mid-1995 there were two additional

sources of uncertainty in the weight gain recorded

for MSHA inspector samples. First, filter capsules

were routinely weighed in different laboratories

before and after exposure, subjecting them to

interlaboratory variability. Second, the pre- and

post-exposure weights were both truncated down to

the nearest exact multiple of 0.1 mg, below the

weight actually measured, prior to recording weight

gain and calculating dust concentration.

a filter capsule are W1=392.275 mg and

W2=392.684 mg, respectively. The true

weight gain (G) would then be:

G=W2¥W1=0.409 mg.

If, due to weighing errors, pre- and

post-exposure weights were measured at

w1=392.282 mg and w2=392.679 mg,

respectively, then the measured weight

gain (g) would be:

g=w2¥w1=0.397 mg.

The error (e) in this particular weightgain measurement, resulting from the

combination of a 7 μg error in w1 and

a ¥5 μg error in w2, would then be:

e=g¥G=(w2¥w1)¥(W2¥W1)=(w2¥W2)

¥(w1¥W1)=¥5¥7=¥12 μg.4

Imprecision in the true weight gain is

expressed by σe, 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 1

3 3

. .438

480 min 2 liters

min

1 m

1000 liters ⋅ ⋅

= m

Therefore, the standard deviation of

the propagated weighing error

component in a single, full-shift

measurement (x=g1.438/m 3 ) is 1.438σe

mg/m 3, assuming no adjustment for

weight change in the control filter

capsule.

Since a control filter capsule will be

used to eliminate potential bias, the

weight gain measured for the exposed

filter (g) will be adjusted by subtracting

the change in weight (which may be

positive or negative) observed for the

control filter capsule (g′). Therefore, the

adjusted measurement of dust

concentration is

x g g m ′ = − ( )′ ⋅1 3 .438 .

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 in g-g′ is

represented by

σ σ σ σ e e e e

2 2 2 + = = 2 2.

Therefore, the standard deviation of

the propagated weighing error

component in the adjusted

measurement is 1.438σe√2 mg/m 3.

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 Weight-Gain

Uncertainty

Table 1 summarizes six different

values of σe that have been mentioned

during the proceedings related to this

notice and two additional values for σe

derived in this appendix from data

introduced during these proceedings. A

ninth value for σe is derived from newly

acquired data being placed into the

record along with this notice [14]. The

nine values listed in Table 1 are not

inconsistent, but as explained below,

represent estimates of weight-gain

imprecision during different historical

periods or under different sample

processing procedures.

TABLE 1.—STANDARD DEVIATION OF ERROR IN WEIGHT GAIN

DESCRIPTION Reference σe (μg)

MSHA’s historical estimate of upper bound ............................................................................................ 59 FR 8356, [15] ........... 97.4

1981 Measurement Assurance Estimate (older technology, truncation of weights) ............................... [16,17] ............................ 81

Experiment on 300 unexposed, tamper-resistant filter capsules (pre- and post-weighing in different

labs; no truncation).

[12] ................................. 29

Inspector samples processed between late 1992 and mid 1995 (truncation of weights; pre- and postexposure weighing in different labs; adjusted for differences between labs).Appendix B .................... 51.7

NMA Data (obtained from samples collected by Skyline Coal, Inc.) ...................................................... Appendix C .................... 76

Value used in NIOSH ‘‘indirect approach’’ (pre- and post-exposure weighing on same day and in the

same lab; derived from Kogut [12]).

61 FR 10012, [12] ......... 5.8

MSHA Field Study ................................................................................................................................... [18,3] .............................. 9.1

1996 Measurement Assurance Estimate ................................................................................................ 61 FR 10012, [19] ......... 6.5

1997 field data (75 unexposed capsules) ............................................................................................... [14] ................................. 8.2

In MSHA’s February 1994 notice,

1.438σe (identified as ‘‘variability

associated with the pre- and postweighing of the filter capsule’’) was

presented as 0.14 mg/m3, or 7 percent of

2.0 mg/m3, as described in Kogut [15].

It follows that the value of σe 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) [16]. The published

NBS estimate reflected weighing

technology in place at the time the

article was published (1981), as well as

the practice (no longer in effect for

MSHA inspector samples) of truncating

both the pre- and post-exposure weights

down to an exact multiple of 0.1 mg.

This estimate was used to calculate

CVweight by Bartley [17], in September

1994.

Some commenters misread or

misunderstood the published NBS

estimate. One of these commenters

claimed that ‘‘the only published report

of the weighing error in MSHA’s
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5681

5To construct a 90-percent confidence interval for

σG, based on the Skyline data, the 15-μg ‘‘standard

error of the estimate’’ must be multiplied by a

confidence coefficient of 1.64.

laboratory * * * was 0.16 mg of

variation, which would convert to a

concentration of 0.20 mg/m3 compared

to the 0.14 mg/m3 * * * MSHA and

NIOSH used.’’ This is incorrect, since

the standard deviation of weight-gain

errors (including the effect of

truncation) is actually identified as

0.0807 mg in the Appendix to Parobeck

et al. [16]. The 0.16-mg figure quoted by

the commenter is presented in that

paper as defining a 2-tailed 95-percent

confidence limit, for use in establishing

process control limits. It is derived by

multiplying σe by 2.0. As explained

above, the published value of σe =

0.0807 mg is multiplied by 1.438 to

propagate an MRE-equivalent

concentration error of 0.116 mg/m3.

Contrary to the commenters’ assertion,

this is less—not more—than the

quantity (0.14 mg/m3) assumed in the

February 1994 notice.

In September 1994, a more recent

analysis was placed into the public

record, based on repeated weighings of

300 unexposed filter capsules, each of

which was weighed once in the MSA

laboratory and twice in MSHA’s

laboratory using current equipment [12].

Based on this analysis, 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 postweighings 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 [3]. 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 (tamper-resistant) cassette was

introduced, and mid-1995, when the

most recent changes in inspector sample

processing were implemented.

Some commenters suggested that the

estimates of 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 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 postexposure 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 commenters expressed special

concern over the accuracy of preexposure filter capsule weights as

measured by MSA. One commenter

expressed ‘‘grave concern’’ with regard

to the 12-μg systematic difference in

weights found between MSA and MSHA

weighings of the same unexposed

capsules, as described in MSHA’s 1994

analysis [12]. These concerns are moot,

at least with respect to MSHA’s

inspector sampling program, since all

inspector samples are now pre- and

post-weighed at MSHA’s laboratory.

Furthermore, any potential bias

resulting from differences in laboratory

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

eliminated by the use of control filter

capsules. However, contrary to this

commenter’s interpretation, the analysis

submitted to the record in September

1994 resulted in a substantially lower

estimate of 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 C, was an estimate of σe equal

to 76 μg ± 15 μg.5 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.

Truncation of weights, and also the

practice of pre- and post-weighing

samples in different laboratories, were

discontinued for inspector samples in

mid-1995. Under MSHA’s revised

procedures for processing inspector

samples, filter capsules are weighed

both before and after sampling in

MSHA’s laboratory. Furthermore, the

results recorded and used in calculating

dust concentrations are expressed to the

nearest μg. 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 [18]. In this study, the filter capsules

were used to collect respirable coal

mine dust samples in an underground

mine between pre- and post-exposure

weighings in MSHA’s laboratory,

potentially subjecting them to unknown

sources of variability in weight gain not

covered by the laboratory estimates.

Substituting the estimated value of 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 [19]. 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 the

MSHA’s 1995 field study discussed

earlier (9.1 μg), falls only slightly above

the 6.5 μg laboratory estimate. This

suggests that the process of handling

and actually exposing the filter capsule

in a mine environment does not add

appreciably to the imprecision in

measured weight gain.
5682 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

In February 1997, 75 unexposed filter

capsules that had been pre-weighed in

MSHA’s laboratory and distributed to

MSHA district offices were recalled and

reweighed [13]. After adjusting for

variability attributable to the date of

initial weighing (i.e., variability that

would be eliminated by use of a control

filter capsule), these data provide an

estimate of σe equal to 8.2 μg [14]. This

estimate, which is based on weighings

separated by a span of about four to five

months, corroborates the 9.1 μg estimate

obtained from MSHA’s 1995 field study.

(c) Negative Weight-Gain Measurements

Some commenters pointed out that

MSHA routinely voids samples when

the measured pre-exposure weight of a

filter capsule is greater than the

measured post-exposure weight.

According to these commenters, such

occurrences reflect an unacceptable

degree of inaccuracy in weight-gain

measurements. One commenter asserted

that such cases are ‘‘of particular

significance when only one sample is

relied upon.’’ This commenter

attributed such occurrences solely to

errors in the capsule pre-weight and

implied that they should not be

expected to occur under MSHA’s

quality assurance program. It was,

therefore, implied that negative weightgain 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 2 contains the

probability of a negative weight-gain

measurement for true weight gains (G)

ranging from 0.0 mg to 0.08 mg,

assuming 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 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

.01 8.4

.02 5.1

.03 2.8

.04 1.5

.05 0.7

.06 .4

.07 .2

.08 .1

NOTE: Tabled probabilities (in percent) were

obtained from a simulation of 35,000 weightgain measurements at each value of G, assuming normally distributed weighing errors

and the now discontinued practice of measurement truncation.

One commenter suggested the use of

a test based on the frequency of negative

weight-gain measurements to check the

magnitude of the MSHA/NIOSH

estimate of CVtotal. As proposed by the

commenter, the test of CVtotal would

consist of comparing the observed

proportion of samples voided due to a

negative recorded weight gain to the

proportion expected, given CVtotal equal

to the MSHA/NIOSH estimate. If the

observed proportion were to exceed the

expected proportion, then this would

constitute evidence that CVtotal was

being underestimated.

The commenter miscalculated the

expected proportion, because he

mischaracterized the MSHA/NIOSH

estimate of CVtotal as constant over the

continuum of dust concentrations. The

MSHA/NIOSH estimate of CVtotal

increases as dust concentrations

decrease. This would cause a higher

proportion of negative results than what

the commenter projected under the

MSHA/NIOSH estimate, regardless of

what statistical distribution of dust

concentrations is assumed.

The commenter’s projection also

neglected to take into account the effects

of truncating pre- and post-exposure

weights to multiples of 0.1 mg.

Although this practice has now been

discontinued for MSHA inspector

samples, it is a factor in the available

historical data.

In principle, if the statistical

distribution of true dust concentrations

were known, the expected proportion of

samples voided for negative weight gain

could be recalculated to reflect both a

variable CVtotal and, when applicable,

truncation of recorded weights.

However, under the commenter’s

proposal, deriving the expected

proportion of negative measurements

would involve not only CVtotal, but also

an estimate of the distribution of true

dust concentrations. Such an estimate

would rely on the tenuous assumption

that a mixture of dust concentrations in

different environments is closely

approximated by a lognormal

distribution far into the lower tail—i.e.,

even at concentrations extremely near

zero. Furthermore, valid estimation of

the lognormal parameters, applicable to

dust concentrations near zero, would be

complicated by measurement errors,

especially those resulting in negative or

zero values. Depending on the data

used, truncation effects could also

confound the analysis.

Before truncation was discontinued,

negative weight-gain measurements

were caused by various combinations of

pre- and post-exposure weighing and

truncation error. Since truncation, and

especially interlaboratory variability,

have now been removed as sources of

error in weight-gain measurements for

inspector samples, negative weight-gain

measurements are expected to occur less

frequently than in the past.

(d) Comparing weight gains obtained

from paired samples

Some commenters maintained that

‘‘although there may be slight

differences between how the samples

are dried * * *,’’ differences between

the weight gain observed in MSHA

samples and simultaneous samples

collected nearby (and processed at an

independent laboratory) indicated a

greater degree of weighing uncertainty

than what was being assumed. In

response to the Secretaries’ request for

any available data supporting this

position, results from paired dust

samples were provided by two coal

companies.

In comparing measurements obtained

from paired samples, there are several

important considerations that some

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
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5683

each of these errors is represented by se,

then the difference between g1 and g2

has uncertainty due to weighing error

equal to se√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 1.41•se.

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 (σσ in the notation of [12])

is far more significant than the intra-lab,

intra-day weighing error in MSHA’s

laboratory. Moreover, the additional

uncertainty introduced by use of a third

laboratory also depends on unknown

weighing imprecision within that

laboratory, which may differ from that

maintained by MSHA’s measurement

assurance process. (See Appendix C for

analysis of paired sample data

submitted by NMA).

However, the most important

consideration in comparing weight

gains from two different samples is that

under real mining conditions, the

atmospheres sampled may not be

identical—even if the sampler units are

located near one another. Differences in

atmospheric dust concentrations over

relatively small distances have been

documented [20]. Such differences

would be expected to produce

corresponding differences in weight

gain that are unrelated to the accuracy

of a single, full-shift measurement as

defined by the measurement objective

explained earlier in this notice.

II. Pump Variability

The component of uncertainty due to

variability in the pump, represented by

CVpump, consists of potential errors

associated with calibration of the pump

rotameter, variation in flow rate during

sampling, and (for those pumps with

rotameters) variability in the initial

adjustment of flow rate when sampling

is begun. The Secretaries believe that

CVpump adequately accounts for all

uncertainty identified by commenters as

being associated with the volume of air

sampled.

In deriving the Values Table

published in MSHA’s February 1994

notice, MSHA used a value of 5 percent

to represent uncertainty associated with

initial adjustment of flow rate at the

beginning of the shift and another value

of 5 percent to represent flow rate

variability. The 5-percent value for

variability in initial flow rate

adjustment was estimated from a

laboratory experiment conducted by

MSHA in the early 1970s, while the

value for flow rate variability was based

on the allowable flow rate tolerance

specified in 30 CFR part 74. This part

requires that the flow rate of all

sampling systems not vary by more than

±5 percent over a full shift with no more

than two adjustments. MSHA did not

include a separate component of

variability for pump rotameter

calibration because it was already

included in the 5-percent value used to

represent flow rate variability.

Based on a review of published

results [10], the Secretaries concluded

that the component of uncertainty

associated with the combined effects of

variability in flow rate during sampling

and potential errors in calibration is less

than 3 percent. Therefore, as proposed

in the March 12, 1996 notice, the

Secretaries are now estimating

uncertainty due to variability in flow

rate to be 3 percent.

Because MSHA could not provide the

experimental data supporting the 5-

percent value used to represent

uncertainty associated with the initial

adjustment of flow rate, one commenter

recommended that MSHA conduct a

new experiment. In response to that

request, MSHA conducted a study to

establish the variability associated with

the initial flow rate adjustment. The

study, placed into the public record on

September 9, 1994, attempted to

emulate realistic operating conditions

by including a variety of sampling

personnel making adjustments under

various conditions. Results showed the

coefficient of variation associated with

the initial adjustment to be 3 ± 0.5

percent [11]. The Secretaries consider

this study to provide the best available

estimate for uncertainty associated with

the initial adjustment of a sampler unit’s

flow rate. Therefore, as proposed in the

March 12, 1996 notice, the Secretaries

are now estimating uncertainty due to

variability in the initial adjustment to be

3 percent.

One commenter expressed concern

regarding how representative MSHA’s

study on initial flow rate adjustment

was of actual sampling conditions. The

Secretaries consider the conditions

under which the study was conducted

to have adequately mimicked conditions

under which the flow rate of a coal mine

dust sampling system is adjusted. This

was more rigorous than the original

study, from which MSHA estimated the

5-percent value assumed in the

February 12, 1994 notice. The tests were

conducted in an underground mine,

using both experienced and

inexperienced persons to make the

adjustments. Also, the only illumination

was supplied by cap lamps worn by the

person making the adjustments. Tests

were conducted for adjustments made

in three different physical positions:

standing, kneeling and prone.

Inspection personnel participating in

the study provided guidance as to the

methods typically used by inspection

personnel in adjusting pumps. In fact,

environmental conditions under which

the test was conducted were generally

more severe than those normally

encountered by inspection personnel,

since initial adjustment of the pumps

normally occurs on the surface just

before the work shift begins.

The same commenter also questioned

why only the variability associated with

initial adjustment of the flow rate was

estimated and not the variability

associated with subsequent adjustments

during the shift. This is because the

variability associated with the

subsequent flow rate adjustments of an

approved sampler unit is already

included in the 3-percent value

estimated for variability in flow rate

over the duration of the shift.

Since variability in the initial flow

rate adjustment is independent of

calibration of the pump rotameter and

variability in flow rate during sampling,

these two sources of uncertainty can be

combined through the standard

propagation of errors formula:

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

This estimate accords well with a

more recent finding based on 186

measurements in an underground mine,

using constant flow-control pumps [18].

That study estimated CVpump = 4.0

percent and concluded that CVpump was

unlikely to exceed 4.4 percent.

Three commenters stated that there

are reports of sampling pumps being

calibrated and used at altitudes differing

by as much as 3000 feet and that, for

many pumps, this could result in more

than a 3-percent change in flow rate per

1000 feet of altitude. MSHA recognized

this as a potential problem as early as

1975. As a result, MSHA conducted a

study to ascertain the effect of altitude

on coal mine dust sampler calibration

[21]. The study showed that both pump

performance and rotameter calibration

were affected by changes in altitude but

that an approved MSA sampling system,

calibrated and adjusted at an altitude of

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
5684 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

6Section 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.

different from the one at which the

rotameter was calibrated, the

appropriate flow rate would be

obtained. These procedures are used by

MSHA inspectors in instances where

the sampling altitude is significantly

different from the altitude where the

sampling system is calibrated.

Some commenters questioned the

ability of the older MSA Model G

pumps to meet the same flow rate

specifications as new pumps. MSHA

has discontinued the use of these older

pumps in its sampling program and will

be using only flow-control pumps. More

recent MSHA studies show that these

pumps continue to meet the flow rate

requirement of 30 CFR 74.3(11) at

altitudes up to 10,000 feet [22]. As a

result, the flow-control pumps currently

used by inspectors can be calibrated at

one altitude and used at another altitude

with no additional adjustments made to

the pumps. Furthermore, all sampler

units used to measure respirable dust

concentrations in coal mine

environments are required to be

approved in accordance with the

regulatory requirements of 30 CFR part

74, which require flow rate consistency

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

min flow rate.6 MSHA’s experience over

the past 20 years has demonstrated that

flow rate consistency of older sampling

systems will continue to meet the

requirements specified in part 74,

provided the systems are regularly

calibrated and maintained in approved

condition. To ensure that sampling

systems continue to meet the

specification of part 74, MSHA’s policy

requires calibration and maintenance by

specially trained personnel in

accordance with MSHA Informational

Report No. 1121 (revised).

III. Intersampler Variability

Intersampler variability, represented

by CVsampler, accounts for uncertainty

due to physical variations from sampler

to sampler. Most of the commenters

ignored this source of uncertainty. One

commenter, however, stated that 10-mm

nylon cyclones are subject to

performance variations due to static

charging phenomena (discussed in

Appendix A).

Intersampler variability was

investigated by Bowman et al. [10],

Bartley et al. [17], and Kogut et al. [18].

Bowman et al. designed a precision

experiment to determine the

contribution to CVtotal from differences

between individual coal mine dust

sampler units. Based on their

experiment, they reported CVsampler = 1.6

percent, which included variation in

both the 10-mm nylon cyclone and the

MSA Model G pump. They concluded

that this low degree of component

variability indicates there is excellent

uniformity in the mechanical

components of dust sampler units.

Bartley, from his experimental

investigation of eight 10-mm nylon

cyclones, estimated CVsampler to be no

more than 5 percent for aerosols with a

size distribution typical of those found

in coal mine environments. Based on an

analysis involving 32 different sampler

units, Kogut et al. found that CVsampler

was unlikely to exceed 3.1 percent.

Unlike Bartley’s study, however, this

analysis relied on new cyclones, which

might be expected to exhibit less

variability than older, heavily used

cyclones. Therefore, NIOSH used the

more conservative estimate of 5 percent,

with an upper 95-percent confidence

limit of 9 percent, in its ‘‘indirect

approach’’ for estimating CVtotal and

evaluating method accuracy [3].

Appendix C—Data Submitted by

Commenters

During the public hearings, several

commenters indicated they had data

showing that MSHA and NIOSH had

underestimated the overall magnitude of

uncertainty associated with a single,

full-shift measurement. These data and

accompanying analyses were submitted

to the record and evaluated by MSHA

and NIOSH. Some of the data sets

consisted of paired samples, where two

approved sampler units were placed

nearby one another and operated for a

full shift. One of the resulting samples

was analyzed in MSHA’s laboratory and

the other by an independent laboratory.

These data were represented as showing

that single, full-shift measurements

cannot accurately be used to estimate

dust concentrations. Other data sets

submitted consisted of unpaired

measurements collected from miners at

intervals over varying spans of time.

These data sets were represented as

showing that exposures vary widely

between shifts and between

occupations.

I. Paired Sample Data Submitted by the

NMA

The American Mining Congress and

National Coal Association [AMC and

NCA have since merged into the

National Mining Association, (NMA)]

submitted at the request of MSHA and

NIOSH a data set consisting of 381 pairs

of exposure measurements. These

measurements had been obtained from

the ‘‘designated occupations’’ on two

longwall and six continuous mining

sections belonging to Skyline Coal, Inc.

Two sampling units were placed on

each participating miner and operated

for the full shift. After sampling, one

sample cassette was sent to MSHA for

analysis while the other was analyzed at

a private laboratory. All samples were

reported to be ‘‘portal to portal’’ samples

as required by MSHA regulations. Using

these data, the NMA estimated an

overall CV of 16 percent. Based on this

16-percent estimate, the NMA suggested

that MSHA had underestimated

measurement uncertainty in its

February 1994 notice by 60 percent at

dust concentrations of 2.0 mg/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 B. The value of CVtotal

assumed by MSHA and NIOSH for the

period when the Skyline samples were

collected is approximately 7.5 percent

when the true dust concentration (μ) is

2.0 mg/m 3 and approximately 16.2

percent when μ = 0.5 mg/m 3. This is

based on applying Equations 2 and 3 to
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5685

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 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 2

total + CV2spatial)1/2.

To estimate SAE* as a function of dust

concentration from the data provided, a

least-squares regression analysis was

performed on the square of the

difference between natural logarithms of

dust concentrations x1 and x2 observed

within each pair. Let 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(X1)¥Ln(X2)) 2} ≈ 2(SAE*) 2

= 2(CV 2

total+CV 2spatial)

= 2[CV 2

pump+CV 2sampler+CV 2

weight+CV 2

spatial]

= 2(CV2

pump+CV 2sampler+CV 2spatial)+

2(1.438σe/μ*)2

=a0+a1(1/μ*) 2

Since no control filter capsules were

used in processing the Skyline dust

samples, CV weight does not, in this

analysis, contain the √2 factor shown in

Equation 3 of Appendix B. The intercept

of the regression line is

a0=2(CV2

pump+CV2+sampler+CV 2 spatial),

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 σe and CV 2 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/m 3) between paired

samples collected from miners over

roughly a one-year period. Two sampler

units were placed on each participating

miner (presumably one on each collar or

shoulder) and operated for roughly a

full shift. One sample cassette was sent

to MSHA for analysis (post-weighing)

while the other was analyzed at a

private laboratory.

Mountain Coal Company provided

only the differences between

measurements within each pair and not

the concentration measurements

themselves. Since CVtotal varies with

dust concentration, and the dust

concentrations were not provided, it

was impossible to form a valid estimate

of measurement variability from these

data, or to determine what part of the

observed differences could be attributed

to weighing error and what part to

spatial variability or variability

attributable to operation of the pump

and physical differences between

sampler units.

III. Exposure Data Submitted by Jim

Walter Resources, Inc.

Jim Walter Resources, Inc. submitted

a data set consisting of exposure

measurements collected from all miners

working on two longwall sections.

Measurements were collected from each

miner on five consecutive days. This

procedure was repeated during five

sampling cycles over a two-year period.

During each sample cycle the five

measurements for each miner were

averaged and compared to the respirable

dust standard. According to Jim Walter

Resources, Inc., the sampling plan

‘‘eliminates the effect of the variability

of the environment and minimizes the

error due to the coefficient of variation

of the pump because all miners [original

emphasis] are sampled for five shifts,’’

and these data ‘‘show the variability of

the sample pump and of the worker’s

exposure to respirable dust.’’

In its submission, Jim Walter

Resources, Inc. apparently assumed that

the quantity being measured is average

dust concentration across a number of

shifts, rather than average dust

concentration averaged over a single

shift at the sampling location. The

Secretaries agree that dust

concentrations do vary from shift to

shift and from job to job, as these data

illustrate. This variability, however, is

largely under the control of the mine

operator and should not be considered

when evaluating the accuracy of a

single, full-shift measurement.

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 ‘‘the variability of

sample results with today’s equipment

and weighing techniques.’’
5686 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

MSHA and NIOSH have concluded

that these data cannot be used to

estimate or otherwise evaluate

measurement accuracy for the following

reasons: First, a highly sensitive and

accurate sampling device would be

expected to produce variable results

when exposed to even slightly different

environments. Since the samples within

each sequence of seven were not

collected at exactly the same point, they

are subject to spatial variability in dust

concentration. It is well known that dust

concentrations can vary even within

small areas along a longwall face.

Therefore, variability in sample

results is attributable not only to

measurement errors but also to

variations in dust concentration due to

spatial variability.

Second, even on a production shift,

variations in air flow and production

levels over the course of the shift can

result in periods within the shift during

which the true dust concentration to

which a sampler is exposed is low or

near zero. If a sampler unit is exposed

to a relatively low dust concentration

during the final hour in which it is

exposed, any difference between that

sample and the previous sample will

tend to be dominated by spatial

variability. In such cases the increase in

weight accumulated during the final

hour would be statistically insignificant

as compared to variability in dust

concentration at different locations.

Without detailed knowledge of the

airflow and production levels as they

varied over each shift, it is impossible

to determine how many cases of this

type would be expected. However,

approximately one-half of such samples

would be expected to exhibit less

weight gain than the previous sample.

Further, because sample weights were

truncated to 0.1 mg at the time these

data were collected, and because

expected weight gains of less then 0.1

mg are not uncommon over a one-hour

period, there would be no apparent

increase in recorded weight gain in

many cases where the two sample

results actually differed by a positive

amount. Therefore, some unknown

number of cases showing no difference

in successive weight gains are

attributable to truncation effects.

Truncation has now been discontinued

for samples collected under MSHA’s

inspection program.

Finally, as has been shown in

Appendix B, a certain percentage of

negative weight-gain measurements at

low dust concentrations is consistent

with the weighing imprecision

experienced at the time these samples

were collected. However, since these

data were not collected in a controlled

environment, it is impossible to

determine what that percentage should

be. Because the weight gain for each

sample is determined as the difference

between two weighings, comparison of

weight gains between two samples

involves a total of four independent

weighing errors. Therefore, variability

attributable purely to weighing error in

the difference between weight gains in

two successive samples is greater (by a

factor equal to √2) than variability due

to weighing error in a single sample.

Furthermore samples collected over less

than a full shift are subject to more

variability due to random fluctuations

in pump air flow and cyclone

performance than samples collected

over a full shift. Both of these

considerations increase the likelihood

that a sample will exhibit less weight

gain than its predecessor, as compared

to the likelihood of recording a negative

weight gain for a single, full-shift

sample.

References

1. Kennedy, E.R., T.J. Fischbach, R. Song,

P.M. Eller, and S.A. Shulman. Guidelines for

Air Sampling and Analytical Method

Development and Evaluation. U.S.

Department of Health and Human Services,

Public Health Service, National Institute for

Occupational Safety and Health, DHHS

(NIOSH) Publication No. 95-117.

2. European Standard No. EN 482:

Workplace atmospheres—General

requirements for the performance of

procedures for the measurement of chemical

agents. European Committee for

Standardization (CEN), 1994.

3. Wagner, G.R. Letter of October 13, 1995,

from Gregory R. Wagner, M.D., National

Institute for Occupational Safety and Health,

to Ronald J. Schell, Chief, Division of Health,

Coal Mine Safety and Health, Mine Safety

and Health Administration.

4. Gray, D.C. and M.I. Tillery. Cyclone

vibration effects. Am Ind Hyg Assoc J,

42(9):685–688, 1981.

5. Lippmann, M. and R.E. Albert. The

Effect of Particle Size on the Regional

Deposition of Inhaled Aerosols in the Human

Respiratory Tract. Am Ind Hyg Assoc J,

30:257–275, 1969.

6. Goddard, B., K. Bower, and D. Mitchell.

Control of Harmful Dust in Coal Mines.

National Coal Board, 6–12, 1973.

7. Tomb, T.F. Memorandum of August 31,

1981, from Thomas F. Tomb, Chief, Dust

Division, Pittsburgh Health Technology

Center, MSHA, to William Sutherland, Chief,

Division of Health, Coal Mine Safety and

Health, MSHA, Subject: Evaluation of

Criterion Used to Select Respirable Coal Mine

Dust Samples for Examination for Oversize

Particles.

8. Treaftis, H.N. and T.F. Tomb. Effect of

Orientation on Cyclone Penetration

Characteristics. Am Ind Hyg Assoc J,

35(10):598–602, 1974.

9. Tomb, T.F., H.N. Treaftis, R.L. Mundell,

and P.S. Parobeck. Comparison of Respirable

Dust Concentrations Measured With MRE

and Modified Personal Gravimetric Sampling

Equipment. BuMines RI 7772, 1973.

10. Bowman, J.D., G.M. Breuer, S.A.

Shulman, and D.L. Bartley. Precision of Coal

Mine Dust Sampling. U.S. Department of

Health and Human Services, Public Health

Service, Centers for Disease Control, National

Institute for Occupational Safety and Health,

NTIS No. PB–85–220–721, 1984.

11. Tomb, T.F. Memorandum of September

1, 1994, from Thomas F. Tomb, Chief, Dust

Division, Pittsburgh Safety and Health

Technology Center, MSHA, to Ronald J.

Schell, Chief, Division of Health, Coal Mine

Safety and Health, MSHA, Subject:

Determination of the Precision of Setting the

Rotameter Ball to a Calibration Mark on

Personal Respirable Dust Sampling Pumps.

12. Kogut, J. Letter of May 12, 1994, from

Jon Kogut, MSHA, to David Bartley, Division

of Physical Sciences and Engineering,

NIOSH.

13. Parobeck, P., J. Kogut, T. Tomb, and L.

Raymond. Investigation of Weighing

Variability Between MSHA and MSA

Laboratories. Internal MSHA Report 1997.

14. Wagner, G.R. Letter of May 28, 1997,

from Gregory R. Wagner, M.D., Acting

Associate Director for Mining, National

Institute for Occupational Safety and Health,

to Ronald J. Schell, Chief, Division of Health,

Coal Mine Safety and Health, MSHA.

15. Kogut, J. Memorandum of September 6,

1994, from Jon Kogut, Mathematical

Statistician, Denver Safety and Health

Technology Center, MSHA, to Ronald J.

Schell, Chief, Division of Health, Coal Mine

Safety and Health, MSHA, Subject: Coal Mine

Respirable Dust Standard Noncompliance

Determinations.

16. Parobeck, P., T. Tomb, H. Ku, and J.

Cameron. Measurement Assurance Program

for Weighings of Respirable Coal Mine Dust

Samples. J Qual Tech, 13(3):157–165, 1981.

17. Barley, D.L. Letter of September 7,

1994, from David L. Bartley, Research

Physicist, Division of Physical Sciences and

Engineering, NIOSH, to Ronald J. Schell,

Chief, Division of Health, Coal Mine Safety

and Health, MSHA.

18. Kogut, J., T.F. Tomb, P.S. Parobeck, A.J.

Gero, and K.L. Suppers. Measurement

Precision With the Coal Mine Dust Personal

Sampler. Internal MSHA Report, 1995.

19. Tomb, T.F. Memorandum of February

16, 1996, from Thomas F. Tomb, Chief, Dust

Division, Pittsburgh Safety and Health

Technology Center, MSHA, to Ronald J.

Schell, Chief, Division of Health, Coal Mine

Safety and Health, MSHA, Subject:

Investigation to Determine the Precision of

MSHA’s Automatic Weighing System for

Weighing Respirable Coal Mine Dust

Samples.

20. Kissell, F.N. and R.A. Jankowski. FixedPoint and Personal Sampling of Respirable

Dust for Coal Mine Face Workers. Paper in

Proceedings of the 6th US Mine Ventilation

Symposium. Society of Mining, Metallurgy,

and Exploration, Inc (SME), Littleton, CO,

281–186, 1993.

21. Treaftis, H.N., T.F. Tomb, and H.F.

Carden. Effect of altitude on personal

respirable dust sampler calibration. Am Ind

Hyg Assoc J, 37(3):133–138, 1976.

22. Gero, A.J., P.S. Parobeck, K.L. Suppers,

B.P. Apel, and J.D. Jolson. The Effect of
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5687

Altitude, Sample Port Inlet Loading, and

Temperature on the Volumetric Flow Rate of

the MSA Escort Elf Constant Flow Rate

Pump. Pres. at Second International

Conference on the Health of Miners,

Pittsburgh, PA, November 11–13, 1995.

Dated: December 19, 1997.

J. Davitt McAteer,

Assistant Secretary for Mine Safety and

Health.

Dated: December 19, 1997.

Linda A. Rosentock,

Director, National Institute for Occupational

Safety and Health.

Note: For the convenience of the user,

notice document 97–33934 is being reprinted

in its entirety because of numerous errors in

the document originally appearing at 62 FR

68372–68395, December 31, 1997. Those

wishing to see a listing of corrections, please

call Patricia Silvey, Mine Safety and Health

Administration, 703–235–1910.

[FR Doc. 97–33934 Filed 12–30–97; 8:45 am]

BILLING CODE 4160–18–P 4510–43–P

DEPARTMENT OF LABOR

Mine Safety and Health Administration

Coal Mine Respirable Dust Standard

Noncompliance Determinations

Correction and Republication

Note: For the convenience of the user,

notice document 97–33937 is being reprinted

in its entirety because of numerous errors in

the document originally appearing at 62 FR

68395–68420, December 31, 1997. Those

wishing to see a listing of corrections, please

call Patricia Silvey, Mine Safety and Health

Administration, 703–235–1910.

AGENCY: Mine Safety and Health

Administration, Labor.

ACTION: Notice; final policy.

SUMMARY: This notice announces the

Mine Safety and Health

Administration’s (MSHA) final policy

concerning the use of single, full-shift

respirable dust measurements to

determine noncompliance and issue

citations, based on samples collected by

MSHA, when the applicable respirable

dust standard is exceeded. This notice

should be read in conjunction with the

notice published elsewhere in today’s

Federal Register jointly by the

Department of Labor and the

Department of Health and Human

Services.

EFFECTIVE DATE: This policy is effective

March 2, 1998.

FOR FURTHER INFORMATION CONTACT:

Ronald Schell, Chief, Division of Health,

Coal Mine Safety and Health; MSHA;

703–235–1358.

SUPPLEMENTARY INFORMATION:

I. About This Notice

This notice provides information

about MSHA’s new enforcement policy

for the use of single, full-shift respirable

dust measurements obtained by

inspectors to determine noncompliance

with the respirable dust standard

(applicable standard) under the MSHA

coal mine respirable dust program. A

question and answer format has been

used to explain the background for the

enforcement policy, the reasons for the

policy change, and the specific elements

of the new policy. In addition, several

appendices are attached to and

incorporated with this final notice

which address technical issues

concerning the new enforcement policy.

II. Background Information

A. How Has MSHA Sampled Coal Mines

for Noncompliance in the Past?

Prior to October 1975, noncompliance

determinations were based on the

average of full-shift measurements

collected from individual occupations

on multiple shifts. MSHA interprets a

full shift for underground coal mines to

mean the entire shift worked or 8 hours

in duration or whichever time period is

less (30 CFR 70.201(b)). The need to

reduce the Agency’s administrative

burden attributable to inspector

sampling prompted MSHA to revise its

underground health inspection

procedures and redirect the Agency’s

enforcement resources away from

sampling and toward assessing the

effectiveness of mine operators’

respirable dust control programs.

Since October 1975, MSHA has

determined noncompliance with the

applicable standard based on the

average of measurements obtained for

different occupations during the same

shift of a mechanized mining unit

(MMU), or on the average of

measurements obtained for the same

occupation on successive days. 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.

MSHA inspectors routinely sample

multiple occupations to determine

compliance with the applicable

standard, assess the effectiveness of

mine operators’ dust control programs,

determine whether excessive levels of

quartz dust are present, and verify the

designation of the ‘‘high risk

occupation’’ (now referred to as the

‘‘designated occupation’’ or ‘‘D.O.’’—the

occupation on a working section

exposed to the highest respirable dust

concentration) to be sampled by mine

operators.

Under the sampling procedures in

place between 1975 and 1991, MSHA

inspectors would collect full-shift

measurements from the working

environment of the ‘‘D.O.’’ and four

other occupations, if available, on the

first day of sampling each MMU. The

mine operator was cited if the average

of all measurements obtained during the

same shift exceeded the applicable

standard by at least 0.1 milligram of

respirable dust per cubic meter of air

(mg/m3). If one or more measurements

exceeded the applicable standard but

the average did not, the Agency’s

practice was to continue sampling for

up to four additional production shifts

or days. If the inspector continued

sampling after the first day because a

previous measurement exceeded the

applicable standard, noncompliance

determinations were based on either the

average of all measurements taken or on

the average of measurements taken on

any one occupation. Thus, if the average

of measurements taken over more than

one day on all occupations was less

than or equal to the applicable standard,

but the average of measurements taken

on any one occupation exceeded the

value set by MSHA (based on the

cumulative concentration for two or

more measurements exceeding 10.4 mg/

m3, which is equivalent to a 5-

measurement average exceeding 2.0 mg/

m3), the operator was cited for

exceeding the applicable standard.

In some instances, MSHA inspectors

sampled for a maximum of five

production shifts or days before making

a noncompliance determination.

However, most citations issued prior to

1991 were based on the average of

multiple measurements on different

occupations collected during a single

shift. To illustrate, MSHA conducted a

computer simulation using data from

3,600 MMU inspections conducted

between October 1989 and June 1991.

This simulation showed that a total of

293 MMUs would have met the criteria

to be found in noncompliance with the

applicable standard based solely on the

average of multiple measurements. Two

hundred forty-two of those

noncompliance determinations, or 83

percent, met the citation criteria based

on sampling results from the first day of

MSHA sampling, rather than from

multi-day sampling. Only 51 MMUs, or

17 percent, were citable based on the

average of measurements collected over

multiple shifts or days. These statistics

clearly show that the citation criteria

were met based not only on the average

of measurements taken during several

shifts, but also on the average of