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
5688 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

multiple measurements obtained during

the same shift.

B. Why Did MSHA Establish the Coal

Mine Respirable Dust Task Group and

Initiate the Spot Inspection Program?

In 1991 concerns were raised about

the adequacy of MSHA’s program to

control respirable coal mine dust in

underground coal mines. In response to

these issues, MSHA established the Coal

Mine Respirable Dust Task Group (Task

Group) to comprehensively evaluate the

effectiveness of the Agency’s respirable

dust program.

The Task Group was directed to

consider all aspects of the current

program, including the role of the

individual miner in the sampling

program; the feasibility of MSHA

conducting all sampling; and the

development of new and improved

monitoring technology, including

technology to continuously monitor the

mine environment. Among the issues

addressed by the Task Group was the

actual dust concentration to which

miners are exposed. As a result, the

Agency initiated a special respirable

dust ‘‘spot inspection program’’ (SIP),

designed to provide the Agency with

more accurate information on the dust

levels to which miners were exposed,

through sampling, in the underground

coal mine environment.

C. How Was Sampling Accomplished

During the SIP?

Because of the large number of mines

and MMUs involved and the need to

obtain data within a short time frame,

sampling during the SIP was limited to

a single shift or day, a departure from

MSHA’s normal sampling procedures.

As a result, the Agency determined 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 sample

individually. If any individual

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.

The sampling practice under the SIP

was similar to the practice of the Metal/

Nonmetal Health Division of MSHA,

and the Occupational Safety and Health

Administration (OSHA), which use a

single, full-shift measurement for

noncompliance determinations, and

provides for a margin of error to account

for uncertainty in the measurement

process (sampling and analytical error).

This resulted in the issuance of citations

using a single, full-shift measurement

only when there was a high level of

confidence that the applicable standard

was actually exceeded.

Thus, during the SIP inspections,

MSHA inspectors cited violations of the

current 2.0 mg/m3 standard if either the

average of five measurements taken on

a single shift was greater than or equal

to 2.1 mg/m3, or any single, full-shift

measurement was greater than or equal

to 2.5 mg/m3. Similar adjustments were

made when the 2.0 mg/m3 standard was

reduced due to the presence of quartz

(crystalline silica) dust in the mine

environment.

D. What Did the SIP Show About

MSHA’s Sampling Policy?

MSHA’s review of the SIP inspections

showed that 28 percent of 718 MMUs

sampled exceeded the applicable

standard and would have been citable

based on a single, full-shift

measurement, but only 12 percent

would have been citable using the

average of all measurements for the

MMU.

Based on the data from the SIP

inspections, the Task Group concluded

that the Agency practice of determining

noncompliance based solely on the

average of multiple measurements did

not always reveal situations in which

miners were overexposed. For example,

if the measurements obtained for five

different occupations within the same

MMU were 4.1, 1.0, 1.0, 2.5, and 1.4 mg/

m3, the average concentration would be

2.0 mg/m3 and no enforcement action

would be taken, even though the dust

measurements for two of these

occupations significantly exceeded the

applicable standard. While such

individual measurements were not cited

prior to the SIP, they would clearly

demonstrate that some miners were

overexposed. MSHA policy prior to the

SIP however, required the inspector to

return to the mine on the next

production day and resume sampling,

rather than issue a citation at the time

the overexposures were discovered.

E. Why Did MSHA Decide To

Permanently Adopt the SIP Procedures?

The SIP inspections revealed

instances of overexposure that were

masked by the averaging of results

across different occupations. This

showed that miners would not be

adequately protected if noncompliance

determinations were based solely on the

average of multiple measurements. The

process of averaging dilutes a high

measurement made at one location with

lower measurements made elsewhere.

Similarly, averaging a number of fullshift measurements can obscure cases of

overexposure.

Additionally, the Task Group

recognized that the initial full-shift

samples collected by an inspector are

likely to show higher dust

concentrations than succeeding samples

collected on subsequent shifts during

the same inspection. MSHA’s data

showed that the average concentration

of all samples taken on the same

occupation on the first day of an

inspection was almost twice as high as

the average concentration of those taken

on the second day. MSHA recognized

that sampling on successive days after

an inspector first appears could result in

measurements that are not

representative of dust conditions to

which miners are typically exposed.

Unrepresentative measurements would

arise if mine operators anticipated the

continuation of inspector sampling and

made adjustments in dust control

parameters or production rates to reduce

dust levels during the subsequent

monitoring. None of this is specifically

prohibited by MSHA regulations. As a

result of these findings, which indicated

that miners were at risk of being

overexposed, MSHA decided to

permanently adopt use of the single,

full-shift measurement inspection

policy initiated during the SIP. These

procedures were used by MSHA until

the issuance of the decision by the

Federal Mine Safety and Health Review

Commission in the case of Keystone

Coal v. Sec. of Labor, 16 FMSHRC 6

(Jan. 4, 1994). Since that decision,

MSHA has reverted to its previous

practice of basing noncompliance

determinations on the average of

multiple, full-shift measurements.

(Please see the notice of joint finding by

the Secretary of Labor and the Secretary

of Health and Human Services (HHS)

published elsewhere in today’s Federal

Register for an explanation of this

decision.)

III. Why MSHA Is Revising Its

Enforcement Policy

A. What Has Changed To Warrant

Revising the Existing Enforcement

Policy?

During the public hearings held on

the proposed joint finding that a single,

full-shift sample is an accurate

measurement, during the public

meetings held on this enforcement

policy notice, and in other comments

submitted to the Agency, several

commenters questioned why the current

program should be altered. The

commenters asserted that MSHA’s

practice of issuing citations based on the

average of multiple measurements has
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5689

been in effect since the 1970s, that

technology and equipment associated

with sampling remain essentially the

same, and that substantial progress had

been made in lowering respirable dust

levels at U.S. coal mines.

As stated in the final notice of joint

finding published elsewhere in today’s

Federal Register, significant

improvements have in fact been made in

the dust sampling process. Although

MSHA agrees that progress has been

made in reducing average dust

concentrations, the SIP inspections

clearly showed instances of excessive

dust concentrations that would have

been masked by the procedure of

averaging measurements. Specifically,

of the 718 SIP MMUs with valid single,

full-shift measurements, 203 MMUs had

at least one single, full-shift

measurement that was citable, while

only 88 MMUs met or exceeded the

citation threshold based on the average

of multiple measurements. This clearly

shows that under the procedure of

averaging measurements miners would

be at risk of being overexposed and

MSHA would be unable to require

operators to take corrective actions to

protect them.

MSHA believes that a single, full-shift

measurement is more likely to detect

excessive dust concentrations and thus

protect miners than a measurement

average across multiple occupations on

a single shift or across multiple shifts

for a single occupation. MSHA’s

computer simulation which analyzed

data from over 3600 MMU inspections

conducted between October 1989 and

June 1991, showed that 814 MMUs had

citable overexposures based on

individual samples, but only 298 of

these overexposures were citable on the

average of measurements made within

the MMU. Subsequent to the SIP,

between January 1992 and December

1993, MSHA continued making

noncompliance determinations on a

single, full-shift measurement, and 74

percent or 488 of the 658 MMUs cited

by inspectors as having overexposures

were found to be out of compliance

based on a single, full-shift

measurement, requiring mine operators

to take appropriate corrective action.

This experience clearly demonstrates

that citing on a single, full-shift

measurement, as opposed to citing on

the average of measurements taken over

multiple shifts, impacts miners directly,

because it requires mine operators to

take more prompt corrective action once

an overexposure has been identified.

This reduces the risk to miners of

continued exposure to dust

concentrations above the applicable

standard on subsequent shifts.

Furthermore, both NIOSH, in its

recently issued criteria document, and

the Secretary of Labor’s Advisory

Committee on the Elimination of

Pneumoconiosis Among Coal Mine

Workers recommended the use of single,

full-shift measurements for determining

compliance. According to the

Committee report, issued in October

1996, the MSHA practice of not issuing

citations based on single, full-shift

samples ‘‘is not protective of miner

health, moreover, it is inconsistent with

the stated intent of the Coal Act and the

Mine Act, which require that exposure

be at or below the exposure limit for

each shift.’’

B. Why Will MSHA No Longer Rely On

Averaged Measurements of Dust

Concentrations To Determine

Noncompliance?

MSHA’s current enforcement strategy

does not provide the optimal level of

possible health protection. Basing

noncompliance determinations on the

average of different occupational

measurements dilutes a measurement of

high dust exposure with a lower

measurement made at a different

occupational location. Likewise,

averaging measurements obtained for

the same occupation over different

shifts does not ensure that the

concentration of respirable dust is

maintained at or below the applicable

standard during each shift. Section

202(b)(2) of the Mine Act clearly

requires that dust concentrations be

maintained at or below the applicable

standard ‘‘* * * during each shift to

which each miner in the active

workings’’ is exposed.

Some commenters proposed that

MSHA continue to average at least five

separate measurements prior to making

a noncompliance determination. They

stated that abandoning this practice

would reduce the accuracy of

noncompliance determinations.

Specifically, these commenters maintain

that the average of dust measurements

obtained at the same occupational

location on different shifts more

accurately represents dust exposure to a

miner than a single, full-shift

measurement. These commenters

favored the retention of existing MSHA

policy on the grounds that not averaging

measurement results would reduce

accuracy to unacceptable levels. Other

commenters agreed with MSHA that the

averaging of multiple samples dilutes

measurements of dust concentration and

masks specific instances of

overexposure. Some of these

commenters stated that averaging

distorts not only the estimate of dust

concentration applicable to individual

shifts, but also biases the estimate of

exposure levels over a longer term.

According to these commenters, this is

because dust control measures and work

practices affecting dust concentrations

are frequently modified in response to

the presence of an MSHA inspector over

more than a single shift. These

commenters argued that the presence of

the MSHA inspector causes the mine

operator to be more attentive to dust

control than normal.

Section 202(b) of the Mine Act

requires each mine operator to

‘‘continuously maintain the average

concentration of respirable dust in the

mine atmosphere during each shift to

which each miner is exposed’’ at or

below the applicable standard. The

greater the variation in mining

conditions from shift to shift, the less

likely it is that a multi-shift average will

reflect the average dust concentration on

any individual shift. For example,

during one shift, production may be

high and dust concentrations may also

be correspondingly high. However, the

next shift may experience lower

production levels because of equipment

breakdowns or because of unusual

mining conditions. In addition, when a

mine operator knows that the MSHA

inspector is present, more attention may

be given to ensuring that dust control

measures operate effectively, and this

may also affect the concentrations of

respirable coal mine dust found on that

shift. Because of such factors, multishift averaging does not improve the

accuracy of a noncompliance

determination for the sampled shift.

Therefore, MSHA is discontinuing its

policy of relying on averaged dust

concentrations. A more technical

discussion of how averaging

measurements affects accuracy is given

in Appendix A.

C. Why Has MSHA Decided To Base

Noncompliance Determinations Solely

on a Single, Full-Shift Measurement?

One commenter suggested that the

new enforcement strategy proposed in

MSHA’s February 1994 notice,

involving noncompliance

determinations based on either a single

sample or on the average of multiple

samples, placed operators in ‘‘double

jeopardy’’ of being cited—that is, it

provided for two separate evaluations of

whether the applicable standard has

been exceeded. This commenter pointed

out that this enforcement strategy would

reduce the confidence level at which a

noncompliance determination could be

made.

Under the MSHA policy proposed in

the February 1994 notice, measurements

made by an MSHA inspector for
5690 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

different occupational locations would

have been averaged together, not in

order to estimate a hypothetical average

concentration, but rather to ascertain

whether dust concentration was

excessive at any of the sampled

locations. If the average of

measurements across sampling locations

exceeded the applicable standard, then

at least one of the sampling locations

would almost certainly have been out of

compliance on the sampled shift.

Therefore, the commenter was correct in

asserting that noncompliance at each

sampling location would have been

evaluated twice: once using the single

measurement specific to that location;

and, if that test did not result in a

citation, once again using the average of

all available measurements.

MSHA had determined that this

strategy was necessary to provide the

level of health protection to miners

required by the Mine Act, and included

this strategy in the proposed policy

notice to protect against cases of evident

noncompliance that would otherwise go

uncited. For example, if five

occupational measurements of 2.08,

2.28, 2.31, 2.25, and 2.17 mg/m3 were

obtained for an MMU on a 2.0 mg/m3

standard, no enforcement action would

be taken if noncompliance is

determined solely based on a single,

full-shift measurement because no

individual measurement meets or

exceeds the Citation Threshold Value

(CTV), defined in section IV.B. of this

notice. On the other hand, averaging the

measurements results in an average

concentration of 2.22 mg/m3, indicating,

with high confidence, that the

applicable standard was exceeded.

Although MSHA originally proposed

using a combination of both strategies

for determining noncompliance, various

bodies of data show that such

hypothetical occurrences are extremely

improbable in practice. For example,

MSHA’s computer simulation discussed

earlier in this notice showed that,

between October 1, 1989, and June 30,

1991, 298 MMUs would have been

found in noncompliance with the

applicable standard based on averaging

multiple measurements. All 298 MMUs

would also have been found in

noncompliance using the single, fullshift measurement citation criteria.

According to the data from the SIP, only

one noncompliance determination

would have been missed if all averaging

had been discontinued. Similarly,

analysis of more recent inspector

sampling data for 1995 indicates that

miners’ health will not be compromised

by discontinuing all measurement

averaging. In fact, only one additional

case of noncompliance would have been

identified using averaging in addition to

citing on a single, full-shift

measurement. Therefore, MSHA will

not continue to use this combination of

strategies.

As explained in the final notice of

joint finding published elsewhere in

today’s Federal Register, MSHA’s

improved sampling and analytical

method performs in accordance with the

NIOSH Accuracy Criterion whenever a

single, full-shift measurement is at or

above 0.36 mg/m3. The Agency believes

that, in accordance with section 202(f)

of the Mine Act, this enables MSHA to

base noncompliance determinations on

a single, full-shift measurement

whenever that measurement is at or

above 0.36 mg/m3.

IV. The New Enforcement Policy

A. What Is MSHA’s New Enforcement

Policy?

MSHA will continue its current dust

sampling program as it relates to where

and how many samples an inspector

collects during a sampling shift.

Specifically, MSHA will continue to

collect multiple occupational samples

for each MMU. The criterion for making

noncompliance determinations has been

revised and, under the new enforcement

policy, MSHA will use a control filter

capsule to adjust the resulting weight

gain obtained on each exposed filter

capsule. Noncompliance determinations

will be based solely on the results of

individual, full-shift samples, and

MSHA will issue a citation whenever

noncompliance is demonstrated at a

high confidence level. The Agency will

no longer rely on multi-locational or

multi-shift averaging of measurements

to determine noncompliance.

The process by which a violation of

the applicable standard will be abated

by a mine operator will also remain

unchanged. MSHA will consider a

violation to be abated when samples

collected in accordance with 30 CFR

70.201(d) demonstrate that the average

dust concentration in the working

environment of the cited occupation is

at or below the applicable standard.

When a measurement exceeds the

applicable standard but is less than the

CTV, noncompliance is not

demonstrated at a sufficiently high

confidence level to warrant a citation.

However, MSHA will consider whether

to target the MMU or environment for

additional dust sampling. See Appendix

B for further discussion of why MSHA

believes that such measurements

indicate probable overexposure.

B. When Will MSHA Issue a Citation for

a Violation of the Applicable Standard?

MSHA will issue a citation for

noncompliance when a single, full-shift

measurement demonstrates, at a high

level of confidence, that the applicable

standard has been exceeded. Although

MSHA will continue to collect multiple

occupational samples for each MMU,

the Agency will generally issue only one

citation for exceeding the applicable

standard on a single shift on any one

MMU. However, additional citations

may be issued when excessive dust

concentrations are detected for

occupations exposed to different dust

generating sources.

To ensure that citations are issued

only when there is a high level of

confidence that the applicable standard

has been exceeded, MSHA has

developed the Citation Threshold

Values (CTV) below. Each CTV listed is

calculated so that citations are issued

only when the single, full-shift

measurement demonstrates

noncompliance with at least 95 percent

confidence. Citing in accordance with

the CTV table does not constitute a

raising of the applicable standard.

Instead, it reflects the need for MSHA to

ensure a sufficiently high level of

confidence in its noncompliance

determinations. Mine operators are still

required to implement appropriate

controls that will maintain the average

concentration of respirable dust at or

below the applicable standard on all

shifts.

CITATION THRESHOLD VALUES (CTV)

FOR CITING VIOLATIONS BASED ON

SINGLE, FULL-SHIFT MEASUREMENTS

Applicable standard

(mg/m3) CTV (mg/m3)

2.0 ................................. 2.33

1.9 ................................. 2.22

1.8 ................................. 2.11

1.7 ................................. 2.00

1.6 ................................. 1.90

1.5 ................................. 1.79

1.4 ................................. 1.68

1.3 ................................. 1.58

1.2 ................................. 1.47

1.1 ................................. 1.36

1.0 ................................. 1.26

0.9 ................................. 1.15

0.8 ................................. 1.05

0.7 ................................. 0.94

0.6 ................................. 0.84

0.5 ................................. 0.74

0.4 ................................. 0.64

0.3 ................................. 0.53

0.2 ................................. 0.43

C. How Will the CTV Table Be Applied?

Each single, full-shift measurement

used to determine noncompliance will
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5691

be the MRE-equivalent dust

concentration as calculated and

recorded under MSHA’s dust data

processing system. Every valid

measurement will be compared with the

CTV corresponding to the applicable

standard in effect. If any measurement

meets or exceeds that value, a citation

will be issued. However, no more than

one citation will be issued based on

single, full-shift measurements from the

same MMU, unless separate citations

are warranted for occupations exposed

to different dust generating sources.

Therefore, when single, full-shift

measurements from two or more

occupations show dust concentrations

in violation of the applicable standard,

as illustrated in the examples below, the

inspector will determine the dust

generation sources and require the

operator to sample the environment of

the occupation most affected by these

sources which is consistent with current

practice. In most cases, this will be the

working environment of the ‘‘D.O.’’

However, if noncompliance is indicated

based on measurements from two or

more occupations on the same MMU

which are exposed to the same dust

generating sources, and which do not

involve the ‘‘D.O.,’’ the occupation with

the highest dust concentration will be

identified in the citation as the affected

working environment. In any case,

when an inspector issues a citation for

violation of the applicable standard

under the new policy, the citation

narrative will identify the specific

environment or occupation to be

sampled by the operator, as well as any

other occupation(s) that exceeded the

CTV.

Several commenters requested that

the application of the CTV table be

clarified. The following examples

illustrate how inspectors will apply the

CTV table and make noncompliance

determinations. Suppose that a

measurement of 2.41 mg/m3 is obtained

for the ‘‘D.O.’’, and measurements of

2.34, 1.54, and 1.26 mg/m3, are obtained

for three other occupations exposed to

the same dust generating sources as the

‘‘D.O.’’ during a single shift on an MMU

required to comply with an applicable

standard of 2.0 mg/m3. Because at least

one of the measurements exceeds the

2.33-mg/m3 CTV (the citation value

when the applicable standard is 2.0 mg/

m3), a citation will be issued for

exceeding the applicable standard on

the shift sampled. Even though two

individual measurements (2.41 and 2.34

mg/m3) exceeded the CTV, one of which

is on the ‘‘D.O.,’’ only one citation will

be issued, specifying the ‘‘D.O.’’ as the

affected working environment because

all occupations were exposed to the

same dust generating sources.

Suppose now that in the previous

example the 2.34-mg/m3 measurement

was obtained for a roof bolter, and the

MMU was ventilated using a doublesplit ventilation system. This means that

the roof bolter, working on a separate

split of air from that of the continuous

miner, is exposed to a different dust

generating source than the ‘‘D.O.’’ and,

therefore, may not be adequately

protected by dust controls implemented

for the ‘‘D.O.’’ Consequently, two

citations would be issued.

As another example, consider an

MMU with measurements of 2.14, 1.92,

1.82, 1.25, and 1.12 mg/m3. Although

none of these measurements meet the

CTV, there is reason to believe that the

MMU is out of compliance, since one of

the measurements exceeds the

applicable standard. However, because

there is a small chance that the

measurement exceeded the applicable

standard because of measurement error,

a citation would not be issued. As

discussed elsewhere in this notice,

additional samples would be necessary

to verify the adequacy of the control

measures under current operating

conditions. Therefore, MSHA would

select this MMU for additional

sampling. As discussed in Appendix B,

even if the first measurement were 1.90

mg/m3 instead of 2.14 mg/m3, because

of measurement error this would not

demonstrate that the mine atmosphere

sampled was in compliance. To confirm

that control measures are adequate,

MSHA would need to take additional

samples.

D. What Is the Potential for a Citation

To Be Issued Due To Measurement

Error?

Some commenters expressed concern

that noncompliance determinations

based on single, full-shift measurements

would result in an unacceptable number

of erroneous citations due to

measurement error. These commenters

expected that MSHA’s new enforcement

policy would result in numerous

erroneous citations.

Based on the analysis in Appendix C,

MSHA has concluded that, because of

the large ‘‘margin of error’’ separating

each CTV from the corresponding

applicable standard, use of the CTV

table provides ample protection against

erroneous citations. For exceptionally

well-controlled environments (e.g., Case

2 of Appendix C), the probability that

any given citation is erroneous will be

substantially less than 5 percent. This

probability is even smaller in

environments which are not well

controlled (e.g., Case 3 of Appendix C).

Therefore, any citation issued in

accordance with the CTV table will be

much more likely the result of excessive

dust concentration rather than

measurement error.

E. What Will Happen When the

Evidence Is Insufficient To Warrant a

Citation?

If the appropriate CTV is not met or

exceeded, MSHA will not issue a

citation. As discussed earlier, this does

not mean that the sampled environment

is necessarily in compliance. Although

in certain cases there may be

insufficient evidence to demonstrate

noncompliance, the measurement may

nonetheless indicate a possible

overexposure. MSHA intends to focus

on cases of measurements above the

applicable standard but below the CTV,

with special emphasis being directed to

working environments required to

comply with applicable standards below

2.0 mg/m3.

If follow-up measurements do not

warrant a citation but suggest that the

dust control measures in use may be

inadequate, MSHA may initiate a

thorough review of the dust control

parameters stipulated in the mine

operator’s approved ventilation or

respirable dust control plan to

determine whether the parameters

should be upgraded.

V. Consequences of the Use of the CTVs

in Conjunction With the Joint MSHA/

NIOSH Finding

A. What is the Impact of MSHA’s New

Enforcement Strategy As Applied Under

the MSHA/NIOSH Joint Finding?

The Agency believes that the

application of the CTVs in conjunction

with the MSHA/NIOSH joint notice of

finding published elsewhere in today’s

Federal Register to single, full-shift

samples collected by MSHA inspectors

provides for more efficient detection of

noncompliance by identifying and

requiring abatement of individual

instances of overexposure which meet

the CTVs. While this issue is more

appropriately addressed in the MSHA/

NIOSH joint notice, the rationale for this

conclusion bears repeating here.

The Mine Act is clear in its intent that

no miner should be exposed to

respirable coal mine dust in excess of

the applicable standard on any shift.

The effect of the joint finding and the

new enforcement strategy set forth here

creates incentives for mine operators to

control dust exposure on a continuing

basis to minimize the chance of being

found in noncompliance during any

MSHA sampling inspection. To prevent

the possibility of any inspector single,
5692 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

full-shift measurement exceeding the

CTV and resulting in a violation, mine

operators will be more likely to keep

dust concentrations at or below the

applicable standard, thereby providing

better protection to miners from

overexposures. This becomes evident

upon closer examination of the

inspector sampling data from the period

when noncompliance determinations

were based on single, full-shift

measurements.

MSHA reviewed inspector MMU

sampling results for FY 1992, the first

full year during which noncompliance

determinations were based on single,

full-shift measurements, and FY 1993,

the last year that the Agency issued

citations based on single, full-shift

measurements. This review showed a

decline in the number of ‘‘D.O.’’ and

nondesignated occupation samples

exceeding 2.0 mg/m3, from 16 percent

and 10 percent in FY 1992 to 13 percent

and 7 percent, respectively, in FY 1993,

suggesting that operators were better

able to maintain dust concentrations

below the applicable standard. MSHA

also conducted a computer simulation

using these data which showed that one

of every four MMU sampling days in FY

1992 would have been found in

noncompliance based on a single, fullshift measurement, compared to one in

five MMU sampling days in FY 1993.

Under the previous enforcement

strategy, which utilized averaging,

inspectors cited violations of the

applicable standard on the average of

multiple measurements taken on a

single shift or on different shifts or days.

Consequently, dust concentrations

could be excessive for some occupations

or work locations, but corrective action

would not be required so long as the

average of the measurements did not

exceed the applicable standard. For

example, averaging occupational

measurements of 3.2, 2.4, 1.5, 1.3 and

1.0 mg/m3 results in an average

concentration of 1.8 mg/m3 for the

sampled MMU where the applicable

standard is 2.0 mg/m3. Despite the fact

that two of the measurements

demonstrate noncompliance with a high

degree of confidence, corrective action

would not have been required because

the average concentration was below the

applicable standard.

As described in this notice and in

conjunction with the MSHA/NIOSH

joint notice, under the new enforcement

policy, whenever an individual

measurement indicates noncompliance

(with a high level of confidence), the

mine operator will be required to take

corrective action to lower the

concentration of respirable dust to

comply with the applicable standard.

Some commenters expressed concern

that MSHA would fail to cite some

instances of noncompliance because of

the high level of confidence required for

a citation. MSHA believes that the new

enforcement strategy as applied in

conjunction with the finding of the

MSHA/NIOSH joint notice will reduce

the chances of failing to cite cases of

noncompliance as compared to the

previous policy of measurement

averaging, while at the same time

ensuring that noncompliance is cited

only when there is a high degree of

confidence that the applicable standard

has been exceeded. According to the

inspector sampling inspections

conducted in 1995, only 132 MMUs

were found to be in violation of the

applicable standard and cited under the

previous enforcement policy of

measurement averaging, compared to

545 MMUs that would have been citable

under the new enforcement policy in

conjunction with the joint notice of

finding using single, full-shift

measurements. This clearly

demonstrates that the new enforcement

policy, in conjunction with the joint

notice, will not compromise miners’

health but would, instead, have

identified 413 additional instances of

overexposure that would have gone

unaddressed under the previous policy

of measurement averaging.

Some commenters proposed that

miners would be even more protected if

noncompliance was cited whenever any

single, full-shift measurement exceeded

the applicable standard by any amount.

That is, it was recommended that

MSHA not make any allowance for

potential measurement errors. MSHA

has considered this recommendation

but has not adopted it in the final policy

because it could result in citations being

issued where compliance with the

applicable standard is more likely than

not. If the mine environment is

sufficiently well controlled, it is more

likely that a particular measurement

exceeds the applicable standard, but not

the CTV, due to measurement error

rather than due to excessive dust

concentration. Furthermore, the

rationale used by these commenters to

justify their proposed citation criterion

breaks down when, as in the case of

multiple samples taken during a given

shift in the same MMU, more than one

measurement is made for a single

noncompliance determination.

Appendix D addresses technical details

relating to this issue.

Some commenters stated that MSHA’s

new citation criteria implemented in

conjunction with the joint notice will

not improve respirable dust levels in the

environment, but will simply result in

MSHA issuing more citations to mine

operators. In these commenters view,

this will foster a continuation of the

adversarial relationship that developed

between mine operators and MSHA over

allegations of widespread tampering

with respirable dust samples.

MSHA firmly believes that basing

noncompliance determinations on a

single, full-shift measurement will

improve working conditions for miners

because it will cause mine operators to

either implement and maintain more

effective dust controls to minimize the

chance of being found in

noncompliance by an MSHA inspector,

or take corrective action sooner to lower

dust concentrations that are shown,

with high confidence, to be in excess of

the applicable standard. The effect of

this new enforcement policy in

conjunction with the MSHA/NIOSH

joint notice will be remedial in nature

because it will address instances of

overexposure that are not addressed

under the current policy of

measurement averaging. For example,

between January 1992 and December

1993, MSHA continued the practice

established under the SIP of making

noncompliance determinations based on

single, full-shift measurements which

demonstrated, with high confidence,

that the applicable standard was

exceeded, and on the average of

multiple measurements. During this

period, MSHA inspectors issued a total

of 658 citations at MMUs. The majority

of these citations (488) were issued

based on the result of a single, full-shift

measurement. Under the existing

enforcement policy, such individual

instances of noncompliance would not

be cited and corrected, but instead

would be factored into an average that

could be at or below the applicable

standard, resulting in no violation and

no corrective action taken by the mine

operator.

Some commenters also contended

that the joint notice of finding, and this

notice of policy, are solely for the

administrative convenience of MSHA’s

mine inspectors. The commenters stated

that allowing inspectors to make

noncompliance determinations on the

basis of a single, full-shift measurement

will eliminate the need for inspectors to

sample on successive days, as is

sometimes required under existing

policy.

MSHA recognizes that there are

administrative advantages related to the

adoption of this new enforcement policy

and the joint notice of finding. By

eliminating the need to sample on

subsequent days, the Agency will be

able to utilize its resources more

efficiently. That is, inspectors will not
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5693

be required to return to a mine to

conduct additional dust sampling, but

the Agency will be able to redirect its

resources to other safety and health

concerns. This result is consistent with

the Mine Act’s objective of protecting

miner safety and health. While

administrative convenience may be a

side benefit of this new enforcement

policy in conjunction with the MSHA/

NIOSH joint notice, the primary reason

for implementing it is to achieve the

intent of Congress that no miner shall be

exposed to dust concentrations above

the applicable standard on any shift.

B. What is the Impact of the New Policy

on Ventilation Plans?

A number of commenters expressed

concern that issuing citations on the

result of a single, full-shift measurement

will cause MSHA to require carefully

developed ventilation plans to be

modified needlessly as part of the

abatement process. These commenters

view such frequent revisions as costly,

disruptive and unnecessary. They

contend that such revisions, if required,

would be made on the basis of

incomplete or invalid information, and

that they would not necessarily decrease

a miner’s dust exposure. Some

commenters believed that some

inspectors would mandate specific

changes without realistically evaluating

their effectiveness, while other

inspectors would not allow operators to

make their own adjustments to the

plans, or provide an opportunity for

them to evaluate the changes in a

rational manner.

When a citation is issued based on a

single measurement, this can indicate

that the control measures in use may no

longer be adequate to maintain the

environment within the applicable

standard. MSHA will consequently

review the adequacy of the ventilation

plan under the current operating

conditions, and will consider the results

of operator bimonthly sampling as well

as operator compliance with the

approved ventilation plan parameters.

Under this approach MSHA would

require plan revisions only after an

examination of all factors has

demonstrated that changes are necessary

to protect miner health. This

enforcement strategy should minimize

unnecessary changes to plans that have

been determined to provide adequate

controls.

MSHA believes that the primary focus

of the federal dust program is to

minimize miners’ overexposures to

respirable dust through the application

of appropriate environmental controls,

which are stipulated in the operator’s

approved mine ventilation plan. After

these controls are evaluated and shown

to be effective under typical mining

conditions, if properly maintained, they

should provide reasonable assurance

that no miner will be overexposed.

Therefore, one of the objectives of

MSHA’s dust sampling is to verify that

the controls stipulated in ventilation

plans continue to adequately control

dust concentrations under existing

operating conditions. In conjunction

with these sampling and other

inspections an inspector checks and

measures the dust control parameters

early in the shift to determine whether

the approved ventilation plan is being

followed. A mine operator’s failure to

follow the parameters stipulated in the

plan will result in the issuance of a

citation, which requires immediate

corrective action to abate the violation.

The type of corrective actions taken to

abate plan violations can vary from

unplugging clogged water sprays to

increasing the amount of ventilating air

delivered to the MMU. However, mere

correction of these deficiencies to

ensure that the ‘‘status quo’’ of the plan

is being maintained may not always be

effective in controlling miners’ exposure

to respirable dust. The required plan

parameters may no longer be effective in

maintaining compliance, and may need

to be upgraded. The determination of

how the plan should be revised is

complicated by the fact that, generally,

most approved plans do not incorporate

all the control measures that were in

place when MSHA sampled.

Consequently, most plan revisions have

simply incorporated into the plan only

those dust controls that were in use

when MSHA sampled, rather than

requiring significant upgrading of the

plan. As an example, an MSHA

inspector might require an increase in

the water pressure stipulated in the plan

from 75 pounds per square inch (psi) to

125 psi to reflect the 125 psi that the

MSHA inspector actually measured. If,

instead, the operator was required to

significantly increase the quantity of air

being delivered to the MMU, this would

be considered a major upgrade. MSHA

recognizes that a determination of

noncompliance should not

automatically necessitate the revision of

a plan. Instead, it should result in a

thorough review of the plan’s continued

adequacy.

When an operator of an underground

mine is cited for excessive dust, 30 CFR

70.201(d) requires the operator to ‘‘take

corrective action to lower the

concentration of respirable dust to

within the permissible concentration.’’

When the citation is based on MSHA

samples, the inspector may request that

the operator describe what type of

corrective action will be taken. The

inspector then determines if the

corrective action is appropriate. If it is

not appropriate in the specific situation,

the inspector may either suggest or

require other corrective action or control

measures. Operators are provided with

the opportunity to make adjustments to

their dust controls and to evaluate their

effectiveness in a rational manner

during the time for abatement set by the

inspector, which is based on the

complexity of the problem, availability

of controls, and the types of changes the

operator intends to make. This

abatement time may be extended by the

inspector based on the operator’s

performance in reducing the dust

concentration in the affected area of the

mine. Typically, the operator then

demonstrates, through sampling, that

the underlying condition or conditions

causing the violation have been

corrected. Failure to take corrective

action prior to sampling that shows

continuing noncompliance may lead to

the issuance of a withdrawal order.

However, this occurs infrequently.

C. Will the New Enforcement Policy

Increase Citations on Individual Shifts,

Even if the So-Called ‘‘Average

Concentration Over the Longer Term’’

Meets the Standard?

Some commenters claimed that even

when the average dust concentration is

well below the applicable standard,

normal variability from shift to shift

results in a substantial fraction of shifts

for which the dust standard is exceeded.

According to these commenters, a

determination of noncompliance is

warranted only if the average dust

concentration to which a miner is

exposed exceeds the standard over a

period of time greater than a single shift,

such as a bimonthly sampling period, a

year, or a miner’s working lifetime.

Therefore, they consider it ‘‘unfair’’ to

cite operators for exceeding the

applicable standard on individual shifts,

so long as the average over the longer

term meets the applicable standard. For

example, based on historical sampling

data provided by one commenter, the

commenter concluded that, ‘‘* * *

there is at least a 1 in 6 or 17%

probability that any single sample can

show potential overexposure when one

does not exist.’’ These commenters

contend that use of the CTV to

determine noncompliance, based on one

sample collected on a single shift, will

substantially increase the frequency of

‘‘unfair’’ citations, compared to existing

MSHA policy.

MSHA believes that such comments

reflect a misunderstanding of both the
5694 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

requirements of the Mine Act and

MSHA’s longstanding policy with

respect to single, full-shift

noncompliance determinations. It

should be recognized that MSHA has

been basing noncompliance

determinations on the average of

multiple occupation measurements

obtained on the same shift since 1975.

In addition, some of the commenters

confused the average dust concentration

over the course of an individual shift

with the average dust concentration

over some longer term. The joint notice

of finding issued by the Secretaries of

Labor and HHS addresses this issue.

Since the Mine Act requires that dust

concentration be kept continuously at or

below the applicable standard on every

shift, it is appropriate to cite

noncompliance when any single, fullshift measurement at a particular

location demonstrates, with high

confidence, that the applicable standard

has been exceeded on an individual

shift.

Section 201(b) of the Mine Act

mandates that MSHA ensure ‘‘to the

greatest extent possible, that the

working conditions in each

underground coal mine are sufficiently

free of respirable dust concentrations

* * * to permit each miner the

opportunity to work underground

during the entire period of his adult life

without incurring any disability from

pneumoconiosis or any other

occupation-related disease during or at

the end of such a period.’’ Since neither

past nor future exposure levels can be

assumed for any miner, MSHA’s

enforcement strategy must be to limit

the exposure on every shift as intended

by the Mine Act.

D. Will There Be Any Changes in

Operator Bimonthly Sampling?

Several commenters were unclear

about the impact of the joint MSHA/

NIOSH finding and this policy on

operator sampling for compliance and

for abatement of violations. One

commenter suggested that 30 CFR

70.207(a) be revised to allow the

operator to submit one single, full-shift

sample, instead of five samples every

bimonthly period as currently required.

Another commenter suggested that

MSHA assume responsibility for dust

sampling from the mine operators.

MSHA has previously noted that the

change in its enforcement policy

announced through this final notice

affects only how it will determine

noncompliance based on measurements

obtained by MSHA inspectors. There

will be no change in how MSHA

evaluates operator-collected respirable

dust samples for compliance. Under the

regulations currently in effect, the

Agency will continue to average

operator samples taken on multiple

shifts or days to make noncompliance

determinations. MSHA is committed to

revising procedures with respect to

operator-collected respirable dust

samples through the rulemaking process

for consistency with this final finding.

Several commenters expressed

concerns about the credibility of the

operator sampling program because of

alleged operator tampering with

respirable dust samples and alleged

operator manipulation of mine

conditions during dust sampling

periods. As a result, these commenters

felt that mine operators should no

longer have responsibility for sampling

because their sampling results are

unreliable. Another commenter

expressed support for the Agency to

compel coal mine operators to comply

with existing dust standards. Another

commenter voiced concern that a mine

operator could be wrongly cited due to

the loss or mishandling of a single, fullshift sample by MSHA, and claimed that

such occurrences had happened in the

past. Some commenters believe that if

noncompliance can be determined

based on a single, full-shift sample, an

operator should be allowed to abate a

citation with a single, full-shift sample,

particularly if the operator has recently

demonstrated compliance through

bimonthly samples. Another commenter

questioned the impact of the proposed

program on the operator’s program,

specifically, whether MSHA would

require each of the abatement samples

to meet the single, full-shift sample

citation threshold values, in addition to

meeting the dust standard based on the

average of five abatement samples.

Issues concerning operator sampling

are not germane to this enforcement

policy notice, which concerns only the

use of samples collected by MSHA

inspectors. The changes set forth in this

final notice only address how MSHA

will determine noncompliance when

sampling is conducted by federal mine

inspectors. There is no change in how

MSHA evaluates either operatorcollected bimonthly samples or samples

taken to abate a dust citation. MSHA is

committed to revising any procedures

with respect to the operator program

through the rulemaking process for

consistency with this final finding.

Concerning the credibility of the

operator sampling program, MSHA

recognizes that there have been

instances of abuse under the current

operator sampling program. The Task

Group found that the majority of

operators do not engage in such

conduct. MSHA will continue to

monitor the operator sampling program,

increase the frequency of inspector

sampling, and target problem mines for

additional inspections, as appropriate.

MSHA processes over 80,000 samples

annually and it is not unrealistic to

expect some samples to be either lost in

the mail or accidentally misplaced.

MSHA’s experience of processing more

than 7 million dust samples since 1970

indicates that this occurs infrequently.

In the event a sample is lost, the mine

operator is afforded ample opportunity

to submit a replacement sample. If a

citation is issued due to the operator’s

failure to submit the required number of

samples, the affected operator can

present evidence that the required

number of samples had been submitted

and request that MSHA vacate the

citation.

E. How Can MSHA Base a

Noncompliance Determination on a

Single, Full-Shift Sample, When Five

Samples Are Required in Operator

Bimonthly Sampling?

Once a finding has been made that a

single, full-shift measurement will

accurately represent atmospheric

conditions to which a miner is exposed

during such shift, MSHA is bound by

the terms of the Mine Act to make

noncompliance determinations based on

single, full-shift measurements. No

regulatory action is required to

implement this change in MSHA’s dust

sampling program. On the other hand,

the present regulatory scheme for

operator sampling was developed based

on noncompliance determinations being

made by averaging the results of

multiple samples over five successive

shifts or days. In order for MSHA to

incorporate the single, full-shift sample

concept into the operator sampling

program, the Agency must revise the

operator sampling regulations through

notice and comment rulemaking.

F. Do the New Citation Criteria Have

any Impact on Permissible Exposure

Limits?

Some commenters contended that a

policy of citing in accordance with the

CTV table, rather than citing whenever

a measurement exceeds the applicable

standard, effectively increases the

allowable dust concentration limit.

Other commenters stated that the

enforcement of the applicable standard

as a limit on each shift, rather than as

a limit on the average concentration

over some longer time period,

effectively reduces the standard.

Citing in accordance with the stated

CTV neither increases nor decreases the

dust standard. Operators are required to

maintain compliance with the
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5695

applicable standard at all times.

MSHA’s citing of noncompliance only

when there is high confidence that the

applicable standard has been exceeded

does not increase the permissible

concentration limit. Again, mine

operators must maintain compliance

with the applicable standard. MSHA

requires that dust controls maintain

dust concentrations at or below the

applicable standard on all shifts, not

merely at or below the CTV. It is also

MSHA’s intent under this new

enforcement policy that if a

measurement exceeds the applicable

standard by an amount insufficient to

warrant citation—that is, the level does

not meet or exceed the CTV—MSHA

will target that mine or area for

additional sampling to ensure that dust

controls are adequate.

Those commenters who stated that

applying the applicable standard to each

shift will effectively reduce the

respirable dust standard overlooked the

fact that, since 1975, MSHA has taken

enforcement action based on average of

measurements obtained for different

occupations during a single shift. This

new enforcement policy does not

change MSHA’s interpretation of section

202(b) of the Mine Act that dust

concentrations be maintained at or

below the applicable standard on each

shift. The new enforcement policy

merely reflects a change in the technical

criteria used to cite violations of the

applicable dust standard.

Appendix A—The Effects of Averaging

Dust Concentration Measurements

MSHA’s measurement objective in

collecting a dust sample is to determine

the average dust concentration at the

sampling location on the shift sampled.

As discussed in the joint notice of

finding published elsewhere in today’s

Federal Register, a single, full-shift

measurement can accurately represent

the average full-shift dust concentration

being measured. Nevertheless, because

of sampling and analytical errors

inherent in even the most accurate

measurement process, the true value of

the average dust concentration on the

sampled shift can never be known with

complete certainty. However accurate

the representation, a measurement can

provide only an estimate of the true dust

concentration. Some commenters

contended that MSHA should not rely

on single samples for making

noncompliance determinations, because

an average of results from multiple

samples would estimate the true dust

concentration more accurately than any

single measurement.

Contrary to the views expressed by

these commenters, averaging a number

of measurements does not necessarily

improve the accuracy of an estimation

procedure. Consider, for example, an

archer aiming at targets mounted at

random and possibly overlapping

positions on a long partition. Each

arrow might be aimed at a different

target. Suppose that an observer, on the

opposite side of the partition from the

archer, cannot see the targets but must

estimate the position of each bull’s eye

by locating protruding arrowheads.

Each protruding arrowhead provides a

measurement of where some bull’s eye

is located. If two arrowheads are found

on opposite ends of the partition,

averaging the positions of these two

arrowheads would not be a good way of

determining where any real target is

located. To estimate the location of an

actual target, it would generally be

preferable to use the position of a single

arrow. The average would represent

nothing more than a ‘‘phantom’’ target

somewhere near the center, where the

archer probably did not aim on either

shot and where no target may even

exist.

The archery example can be extended

to illustrate conditions under which

averaging dust concentration

measurements does or does not improve

accuracy. If each arrowhead is taken to

represent a full-shift dust sample, then

the true average dust concentration at

the sampling location on a given shift

can be identified with the location of

the bull’s eye at which the

corresponding arrow was aimed. The

accuracy of a measurement refers to

how closely the measurement can be

expected to come to the quantity being

measured. Statistically, accuracy is the

combination of two distinct concepts:

precision, which pertains to the

consistency or variability of replicated

measurements of exactly the same

quantity; and bias, which pertains to the

average amount by which these

replicated measurements deviate from

the quantity being measured. Bias and

precision are equally important

components of measurement accuracy.

To illustrate, arrows aimed at the

same target might consistently hit a

sector on the lower right side of the

bull’s eye. The protruding arrowheads

would provide more or less precise

measurements of where the bull’s eye

was located, depending on how tightly

they were clustered; but they would all

be biased to the lower right. On the

other hand, the arrows might be

distributed randomly around the center

of the bull’s eye, and hence unbiased,

but spread far out all over the target.

The protruding arrowheads would then

provide unbiased but relatively

imprecise measurements.

More complicated situations can

easily be envisioned. Arrows aimed at a

second target would provide biased

measurements relative to the first target.

Alternatively, if the archer always aims

at the same target, the first shot in a

given session might tend to hit near the

center, with successive shots tending to

fall off further and further to the lower

right as the archer’s arm tires; or shots

might progressively improve, as the

archer adjusts aim in response to prior

results.

Averaging reduces the effects of

random errors in the archer’s aim,

thereby increasing precision in the

estimation procedure. If the archer

always aims at the same target and is

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

arrowheads are all randomly and

identically distributed around a fixed

point), then averaging improves the

estimate’s precision without introducing

any bias. Averaging in such cases

provides a more accurate method of

estimating the bull’s eye location than

reliance on any single arrowhead. If,

however, the archer intentionally or

unintentionally switches targets, or if

the archer’s aim progressively

deteriorates, then averaging can

introduce or increase bias in the

estimate. If the gain in precision

outweighs this increase in bias, then

averaging several independent

measurements may still improve

accuracy. However, averaging can also

introduce a bias large enough to offset

or even surpass the improvement in

precision. In such cases, the average

position of several arrowheads can be

expected to locate the bull’s eye less

accurately than the position of a single

arrowhead.

I. Multi-Locational Averaging

Some commenters opposed MSHA’s

use of a single, full-shift measurement

for enforcement purposes, claiming that

determinations based on such

measurements would be less accurate

than those made under MSHA’s existing

enforcement policy of averaging

multiple measurements taken on an

MMU. There are two distinctly different

types of multi-locational measurement

averages that could theoretically be

compiled on a given shift: (1) the

average might combine measurements

taken for different occupational

locations and (2) the average might

combine measurements all taken for the

same occupational location. For MMUs,

the averages used in MSHA’s sampling

program usually involve measurements

taken for different occupational

locations on the same shift. These are

averages of the first type. MSHA’s

sampling program has never utilized
5696 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

averages of the second type. Therefore,

those commenters who claimed that

reliance on a single, full-shift

measurement would reduce the

accuracy of noncompliance

determinations, as compared to MSHA’s

existing enforcement policy, are

implicitly claiming that accuracy is

increased by averaging across different

occupational locations.

Averaging measurements obtained

from different occupational locations on

an MMU is like averaging together the

positions of arrows aimed at different

targets. The average of such

measurements is an artificial,

mathematical construct that does not

correspond to the dust concentration for

any actual occupational location.

Therefore, this type of averaging

introduces a bias proportional to the

degree of variability in actual dust

concentration at the various locations

averaged.

The gain in precision that results from

averaging measurements taken at

different locations outweighs this bias

only if variability from location to

location is smaller than variability in

measurement error. However,

commenters opposed to MSHA’s use of

single, full-shift measurements for

enforcement purposes argued that this is

not generally the case and even

submitted data and statistical analyses

in support of this position. Commenters

in favor of noncompliance

determinations based on a single, fullshift measurement agreed that

variability in dust concentration is

extensive for different occupational

locations and argued that MSHA’s

existing policy of measurement

averaging is not sufficiently protective

of miners working at the dustiest

locations.

Since an average of the first type

combines measurement from the

dustiest location with measurements

from less dusty locations, it must always

fall below the best available estimate of

dust concentration at the dustiest

location. In effect, averaging across

different occupational locations dilutes

the dust concentration observed for the

most highly exposed occupations or

dustiest work positions. Therefore, such

averaging results in a systematic bias

against detecting excessive dust

concentrations for those miners at

greatest risk of overexposure.

A somewhat better case can be made

for the second type of multi-locational

averaging, which combines

measurements obtained on the same

shift from a single occupational

location. As some commenters pointed

out, however, there is ample evidence

that spatial variability in dust

concentration, even within relatively

small areas, is frequently much larger

than variability due to measurement

error. Therefore, the same kind of bias

introduced by averaging across

occupational locations would also arise,

but on a lesser scale, if the average

measurement within a relatively small

radius were used to represent dust

concentration at every point in the

atmosphere to which a miner is

exposed. A miner is potentially exposed

to the atmospheric conditions at any

valid sampling location. Consistent with

the Mine Act and implementing

regulations, MSHA’s enforcement

strategy is to limit atmospheric dust

concentration wherever miners

normally work or travel. Therefore, the

more spatial variability in dust

concentration there is within the work

environment, the less appropriate it is to

use measurement averaging to enforce

the applicable standard by averaging

measurements obtained at different

sampling locations.

Some of the comments implied that

instead of measuring average dust

concentration at a specific sampling

location, MSHA’s objective should be to

estimate the average dust concentration

throughout a miner’s ‘‘breathing zone’’

or other area near a miner. If estimating

average dust concentration throughout

some zone were really the objective of

MSHA’s enforcement strategy, then

averaging measurements made at

random points within the zone would

improve precision of the estimate

without introducing a bias. This type of

averaging, however, has never been

employed in either the MSHA or

operator dust sampling programs.

MSHA’s current policy of averaging

measurements obtained from different

zones does not address spatial

variability in the area immediately

surrounding a sampler unit. Therefore,

even if averaging measurements from

within a zone were somehow beneficial,

this would not demonstrate that

MSHA’s existing enforcement policy is

more reliable than the new policy of

basing noncompliance on a single, fullshift measurement.

Furthermore, if MSHA’s objective

were really to estimate average dust

concentration throughout some

specified zone on a given shift, then it

would be necessary to obtain far more

than five simultaneous measurements

within the zone. This is not only

because of potentially large local

differences in dust concentration. In

order to use such measurements for

enforcement purposes, variability in

dust concentration within the sampled

area would have to be estimated along

with the average dust concentration

itself. As some commenters correctly

pointed out, doing this in a statistically

valid way would generally require at

least twenty to thirty measurements.

One of these commenters also pointed

out that such an estimate, based on even

this many measurements in the same

zone, could be regarded as accurate only

under certain questionable assumptions

about the distribution of dust

concentrations. This commenter

calculated that hundreds of

measurements would be required in

order to avoid these tenuous

assumptions. Clearly, this shows that

the objective of estimating average dust

concentration throughout a zone is not

consistent with any viable enforcement

strategy to limit dust concentration on

each shift in the highly heterogeneous

and dynamic mining environment. The

large number of measurements required

to accurately characterize dust

concentration over even a small area

merely demonstrates why it is not

feasible to base enforcement decisions

on estimated atmospheric conditions

beyond the sampling location.

MSHA recognizes that a single, fullshift measurement will not provide an

accurate estimate of average dust

concentration anywhere beyond the

sampling location. The Mine Act,

however, does not require MSHA to

estimate average dust concentration at

locations that are not sampled or to

estimate dust concentration averaged

over any zone or region of the mine, and

doing so is not part of MSHA’s

enforcement program. Instead, MSHA’s

enforcement strategy is to ensure that a

miner will not be exposed to excessive

dust wherever he/she normally works or

travels. This is accomplished by

maintaining the average dust

concentration at each valid sampling

location at or below the applicable

standard during each shift.

II. Multi-Shift Averaging

Some commenters maintained that in

order to reduce the risk of erroneous

noncompliance determinations, MSHA

should average measurements obtained

from the same occupation on different

shifts. These commenters contended

that the average of measurements from

several shifts represents the average

dust concentration to which a miner is

exposed more accurately than a single,

full-shift measurement. Other

commenters, who favored

noncompliance determinations based on

single, full-shift measurements, claimed

that conditions are sometimes

manipulated so as to produce unusually

low dust concentrations on some of the

sampled shifts. These commenters

suggested that, due to these
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5697

1Technically, the assumption is that dust

concentrations on all shifts sampled are

independently and identically distributed around

the quantity being estimated.

unrepresentative shifts, multi-shift

averaging can yield unrealistically low

estimates of the dust concentration to

which a miner is typically exposed.

Some of these commenters also argued

that the Mine Act requires the dust

concentration to be regulated on each

shift, and that multi-shift averaging is

inherently misleading in detecting

excessive dust concentration on an

individual shift.

Those advocating multi-shift

averaging generally assumed that a

noncompliance determination involves

estimating a miner’s average dust

exposure over a period longer than an

individual shift. This assumption is

flawed because section 202(b) of the

Mine Act specifies that each operator

shall continuously maintain the average

concentration of respirable dust in the

mine atmosphere during each shift at or

below the applicable standard. Some of

those advocating multi-shift averaging,

however, suggested that MSHA should

average measurements obtained on

different shifts even if the quantity of

interest is dust concentration on an

individual shift. These commenters

argued that averaging smooths out the

effects of measurement errors, and that

therefore the average over several shifts

would represent dust concentration on

each shift more accurately than the

corresponding individual, full-shift

measurement.

The Secretary recognizes that there

are circumstances, not experienced in

mining environments, under which

averaging across shifts could improve

the accuracy of an estimate for an

individual shift. Just as averaging the

positions of arrows aimed at nearly

coinciding targets might better locate

the bull’s eye than the position of any

individual arrow, the gain in precision

obtained by averaging dust

concentrations observed on different

shifts could, under analogous

circumstances, outweigh the bias

introduced by using the average to

estimate dust concentration for an

individual shift. This would be the case,

however, only if variability in dust

concentration among shifts were small

compared to variability due to

measurement imprecision. It would do

no good to average the location of

arrows aimed at different targets unless

the targets were at nearly identical

locations.

To the contrary, several commenters

pointed out that variability in dust

concentration from shift to shift tends to

be much larger than variability due to

measurement error and introduced

evidence in support of this observation.

Measurements on different shifts are

like arrows aimed at widely divergent

targets. The more that conditions vary,

for any reason, from shift to shift, the

more bias is introduced by using a

multi-shift average to represent dust

concentration for any individual shift.

Under these circumstances, any

improvement in precision to be gained

by simply averaging results is small

compared to the bias introduced by

such averaging. Therefore, the Secretary

has concluded that MSHA’s existing

practice of averaging measurements

collected on different shifts does not

improve accuracy in estimating dust

concentration to which a miner is

exposed on any individual shift. To

paraphrase one commenter, averaging

Monday’s exposure measurement with

Tuesday’s does not improve the

estimate of Monday’s average dust

concentration.

Some commenters argued that since

the risk of pneumoconiosis depends on

cumulative exposure, MSHA’s objective

should be to estimate the dust

concentration to which a miner is

typically exposed and to identify cases

of excessive dust concentration over a

longer term than a single shift. Other

commenters claimed that a multi-shift

average does not provide a good

estimate of either typical dust

concentrations or exposures over the

longer term. These commenters claimed

that different shifts are not equally

representative of the usual atmospheric

conditions to which miners are exposed,

implying that the average of

measurements made on different shifts

of a multi-day MSHA inspection tends

to systematically underestimate typical

dust concentrations.

The Secretary interprets section

202(b) of the Mine Act as requiring that

dust concentrations be kept at or below

the applicable standard on each and

every shift. Nevertheless, the Secretary

recognizes that, under certain

conditions, the average of measurements

from multiple shifts can be a better

estimate of ‘‘typical’’ atmospheric

conditions than a single measurement.

This applies, however, only if the

sampled shifts comprise a random or

representative selection of shifts from

whatever longer term may be under

consideration. As shown below,

evidence to the contrary exists,

supporting those commenters who

maintained that measurements collected

over several days of a multi-day MSHA

inspections do not meet this

requirement. Therefore, the Secretary

has concluded that averaging such

measurements is likely to be misleading

even for the purpose of estimating dust

concentrations to which miners are

typically exposed.

Whether the objective is to measure

average dust concentration on an

individual shift or to estimate dust

concentration typical of a longer term,

the arguments presented for averaging

across shifts all depend on the

assumption that every shift sampled

during an MSHA inspection provides an

unbiased representation of dust

exposure over the time period of

interest.1 To check this assumption,

MSHA performed a statistical analysis

of multi-shift MSHA inspections carried

out prior to the SIP. This analysis,

placed into the record in September

1994, examined the pattern of dust

concentrations measured over the

course of these multi-shift inspections

and compared results from the final

shift with results from a subsequent

single-shift sampling inspection [1].

The analysis found that dust

concentrations measured on different

shifts of the same MSHA inspection

were not randomly distributed. The

later samples tended to show

significantly lower results than earlier

samples, indicating that dust

concentrations on later shifts of a single

inspection may decline in response to

the presence of an inspector.

Furthermore, the analysis provided

evidence that the reduction in dust

concentration tends to be reversed after

the inspection is terminated. These two

results led to the conclusion that

averaging dust concentrations measured

on different shifts of a multi-day MSHA

inspection introduces a bias toward

unrealistically low dust concentrations.

One commenter questioned the

validity of this analysis, stating that

‘‘there is absolutely no basis in the

* * * report for the assertion that the

trend is reversed after the inspection is

terminated.’’ This commenter

apparently overlooked Table 3 of the

report. That table shows a statistically

significant reversal at those mine

entities included in the analysis that

were subsequently inspected under

MSHA’s SIP. Dust concentrations

measured at these mine entities had

declined significantly between the first

and last days of the multi-shift

inspection. It was primarily to address

the commenter’s implication that these

reductions reflected permanent

‘‘adjustments in dust control measures’’

that the analysis included a comparison

with the subsequent SIP inspection. An

increase, representing a reversal of the

previous trend, was observed on the

single shift of the subsequent
5698 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

inspection, relative to the dust

concentration measured on the final

shift of the previous multi-shift inspec

tion. This reversal was found to be

‘‘statistically significant at a confidence

level of more than 99.99 percent.’’

The same commenter also stated that

MSHA ‘‘* * * fails to address the

systematic [selection] bias of the study.

MSHA only does multiple day sampling

when the initial results are higher, but

not out of compliance.’’ It is true that in

order to be selected for revisitation, a

mine entity must have shown relatively

high concentrations on the first shift—

though not, in the case of an MMU, so

high as to warrant a citation on first

shift. Since no experimental data were

available on mine entities randomly

selected to receive multi-shift

inspections, the only cases in which

patterns over the course of a multi-shift

inspection could be examined were

cases selected for multi-shift inspection

under these criteria.

Although the impact of the selection

criteria was not explicitly addressed, it

was recognized that entities selected for

multi-day inspections do not constitute

a random selection of mine entities.

This recognition motivated, in part, the

report’s comparison of the final shift

measurement to the dust concentration

measured during a subsequent singleshift inspection. The magnitude of the

average reversal indicates that most of

the reduction observed over the course

of the multi-shift inspection cannot be

attributed to the selection criteria.

Furthermore, it was not only mine

entities with relatively low dust

concentration measurements that were

left out of the study group. Mine entities

with the highest dust concentration

measurements were immediately cited

based on the average of measurements

taken and excluded from the group

subjected to multi-shift dust

inspections. Therefore, the effect on the

analysis of selecting mine entities with

relatively high initial dust concentration

measurements was largely offset by the

effect of excluding those entities with

even higher initial measurements. In

any event, the magnitude of the average

reduction between first and last shifts of

a multi-shift inspection was

significantly greater than what can be

explained by selection for revisitation

due to measurement error on the first

shift sampled.

The assumption that multiple shifts

sampled during a single MSHA

inspection are equally representative is

clearly violated if, as some commenters

alleged, operating conditions are

deliberately altered after the first shift in

response to the continued presence of

an MSHA inspector and then changed

back after the inspector leaves.

However, if samples are collected on

successive or otherwise systematically

determined shifts or days, the

assumption can also be violated by

changes arising as part of the normal

mining cycle. As one commenter

pointed out, multi-shift averaging

within a single MSHA inspection

potentially introduces biases typical of

‘‘campaign sampling,’’ in which

observations of a dynamic process are

clustered together over a relatively

narrow time span. In order to construct

an unbiased, multi-shift average for each

phase of mining activity, it would be

necessary to collect samples from

several shifts operating under

essentially the same conditions.

Alternatively, to construct an unbiased,

multi-shift estimate of dust

concentration over a longer term, it

would be necessary to collect samples

from randomly selected shifts over a

period great enough to reflect the full

range of changing conditions. Neither

requirement is met by multi-shift MSHA

inspections because (1) the mine

environment is dynamic and no two

shifts are alike and (2) MSHA inspectors

are not there long enough to observe

every condition in their inspection.

Based on the analysis presented by

Kogut [1] and also on public comments

received in response to the February 18

and June 6, 1994, notices, the Secretary

has concluded that it should not be

assumed that multiple shifts sampled

during a single MSHA inspection are

equally representative of atmospheric

conditions to which a miner is typically

exposed. This conclusion undercuts the

rationale for multi-shift averaging

within a single MSHA inspection,

regardless of whether the objective is to

estimate dust concentration for the

individual shifts sampled as it is for

MSHA inspector sampling or for typical

shifts over a longer term as implied by

some commenters. Measurements

collected by MSHA on consecutive days

or shifts of the same inspection do not

comprise a random or otherwise

representative sample from any larger

population of shifts that would properly

represent a long-term exposure or a

particular phase of the mining cycle.

Therefore, there is no basis for assuming

that multi-shift averaging improves

accuracy or reduces the risk of an

erroneous enforcement determination.

Appendix B—Citation Threshold Values

(CTV)

I. Interpretation of the CTV Table

Each CTV was calculated to ensure

that, if the CTV is met or exceeded,

noncompliance with the applicable

standard can be inferred with at least

95-percent confidence. It is assumed

that whatever dust standard happens to

be in effect at the sampling location is

binding, and that a citation is warranted

whenever there is sufficient evidence

that an established standard has been

exceeded. The CTV table does not

depend on how the applicable standard

was established, or on any measurement

uncertainties in the process of setting

the applicable standard.

Some commenters argued that in

order to construct a valid table of CTVs,

MSHA would have to take into account

the statistical distribution of dust

concentrations over many shifts and

locations. One commenter suggested

that stochastic properties of the dust

concentrations, which describe

variability over time in probabilistic

terms, should also be taken into

account. MSHA, however, intends to

use single, full-shift measurements only

in determining noncompliance with the

applicable standard on a particular shift

and at the sampling location consistent

with the measurement objective

described in the MSHA and NIOSH

joint finding published elsewhere in

today’s Federal Register. This is

analogous to using a single

measurement to identify individual

suitcases that are unacceptable because

they weigh more than five pounds. The

efficacy of using a single measurement

to identify unacceptable suitcases

depends on the accuracy of the scale

and the skill of the weigher. It does not

depend on the statistical distribution of

weights among suitcases or on any

stochastic properties of the suitcase

production process. These

considerations would be relevant to

estimating average weight for all

suitcases produced, but they have

nothing whatsoever to do with

determining the weight of an individual

suitcase using a sufficiently accurate

scale. Averaging the weights of several

suitcases would be entirely

inappropriate and extremely

misleading, since the object is to

identify individual suitcases weighing

more than five pounds. Although the

measured weight of an individual

suitcase is liable to contain some error

(so the decision might be uncertain for

a suitcase weighing five pounds and one

ounce), a suitcase weighing seven or

eight pounds could be rejected with

high confidence on the first weighing.

Additional weighings (of the same

suitcase) would be required only for

those suitcases whose initial

measurement was very close to five

pounds.

The CTV table provides criteria for

testing a tentative, or presumptive,
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5699

hypothesis that the true full-shift

average dust concentration did not

exceed the applicable standard (S) at

each of the individual locations

sampled during a particular shift. For

purposes of this test, the mine

atmosphere at each such location is

presumed to be in compliance unless

the corresponding full-shift

measurement provides sufficient

evidence to the contrary. The ‘‘true fullshift average’’ does not refer, in this

context, to an average across different

occupations, locations, or shifts.

Instead, it refers entirely to the dust

concentration at the specific location of

the sampler unit, averaged over the

course of the particular shift during

which the measurement was obtained.

The CTV table is not designed to

estimate or test the average dust

concentration across occupational

locations, or within any zone or mine

area, or in the air actually inhaled by

any particular miner.

Some commenters questioned why

more than one sample might be

required, if the first sample collected

does not exceed the CTV. One of these

commenters argued that in such case,

‘‘compliance has already been

established at a 95% confidence level

based on the first single shift sample.’’

This line of argument confuses

confidence in issuing a citation with

confidence of compliance. It also shows

a basic misunderstanding of how the

citation criteria relate to the requirement

of continuous compliance under section

202(b) of the Mine Act.

The CTV table ensures that

noncompliance is cited only when there

is a 95-percent level of confidence that

the applicable standard has actually

been exceeded. If a single measurement

does not meet the criterion for citation,

this does not necessarily imply probable

compliance with the dust standard—let

alone compliance at a 95-percent

confidence level. For example, a single,

full-shift measurement of 2.14 mg/m3

would not, according to the CTV table,

indicate noncompliance with sufficient

confidence to warrant a citation if S =

2.0 mg/m3. This does not imply that the

mine atmosphere was in compliance on

the shift and at the location sampled.

On the contrary, unless contradictory

evidence were available, this

measurement would indicate that the

MMU was probably out of compliance.

However, because there is a small

chance that the measurement exceeded

the standard only because of

measurement error, a citation would not

be issued. Additional measurements

would be necessary to verify the

apparent lack of adequate control

measures. Similarly, a single, full-shift

measurement of 1.92 mg/m3 would not

warrant citation; but, because of

possible measurement error, neither

would it warrant concluding that the

mine atmosphere sampled was in

compliance. To confirm that control

measures are adequate, it would be

necessary to obtain additional

measurements.

Furthermore, even if a single, fullshift measurement were to demonstrate,

at a high confidence level, that the mine

atmosphere was in compliance at the

sampling location on a given shift,

additional measurements would be

required to demonstrate compliance on

each shift. For example, if S = 2.0 mg/

m3, then a valid measurement of 1.65

mg/m3 would demonstrate compliance

on the particular shift and at the

particular location sampled. It would

not, however, demonstrate compliance

on other shifts or at other locations.

II. Derivation of the CTV Table

Some commenters requested an

explanation of the statistical theory

underlying the CTV table. To

understand how the CTVs are derived

and justified, it is first necessary to

distinguish between variability due to

measurement error and variability due

to actual differences in dust

concentration. The variability observed

among individual measurements

obtained at different locations (or at

different times) combines both: dust

concentration measurements vary partly

because of measurement error and

partly because of genuine differences in

the dust concentration being measured.

This distinction, between measurement

error and variation in the true dust

concentration, can more easily be

explained by first carefully defining

some notational abbreviations.

One or more dust samples are

collected in the same MMU or other

mine area on a particular shift. Since it

is necessary to distinguish between

different samples in the same MMU, let

Xi represent the MRE-equivalent dust

concentration measurement obtained

from the ith sample. The quantity being

measured is the true, full-shift average

dust concentration at the ith sampling

location and is denoted by μi. Because

of potential measurement errors, μi can

never be known with complete

certainty. A ‘‘sample,’’ ‘‘measurement,’’

or ‘‘observation’’ always refers to an

instance of Xi rather than μi.

The overall measurement error

associated with an individual

measurement is nothing more than the

difference between the measurement

(Xi) and the quantity being measured

(μi). Therefore, this error can be

represented as

εi = Xi¥μi.

Equivalently, any measurement can be

regarded as the true concentration in the

atmosphere sampled, with a

measurement error added on:

Xi = μi + εi.

For two different measurements (X1 and

X2), it follows that X1 may differ from

X2 not only because of the combined

effects of ε1 and ε2, but also because μ1

differs from μ2.

The probability distribution of Xi

around μi depends only on the

probability distribution of εi and should

not be confused with the statistical

distribution of μi itself, which arises

from spatial and/or temporal variability

in dust concentration. This variability

[i.e., among μi for different values of I]

is not associated with inadequacies of

the measurement system, but real

variation in exposures due to the fact

that contaminant generation rates vary

greatly in time and contaminants are

heterogeneously distributed in

workplace air.

Since noncompliance determinations

are made relative to individual sampling

locations on individual shifts,

derivation of the CTV table requires no

assumptions or inferences about the

spatial or temporal pattern of

atmospheric dust concentrations—i.e.,

the statistical distribution of μi. MSHA

is not evaluating dust concentrations

averaged across the various sampler

locations. Therefore, the degree and

pattern of variability observed among

different measurements obtained during

an MSHA inspection are not used in

establishing any CTV. Instead, the CTV

for each applicable standard (S) is based

entirely on the distribution of

measurement errors (εi) expected for the

maximum dust concentration in

compliance with that standard—i.e., a

concentration equal to S itself.

If control filters are used to eliminate

potential biases, then each εi arises from

a combination of four weighing errors

(pre-and post-exposure for both the

control and exposed filter capsule) and

a continuous summation of

instantaneous measurement errors

accumulated over the course of an eighthour sample. Since the eight-hour

period can be subdivided into an

arbitrarily large number of sub-intervals,

and some fraction of εi is associated

with each sub-interval, εi can be

represented as comprising the sum of an

arbitrarily large number of sub-interval

errors. By the Central Limit Theorem,

such a summation tends to be normally

distributed, regardless of the

distribution of subinterval errors. This

does not depend on the distribution of
5700 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

μi, which is generally represented as

being lognormal.

Furthermore, each measurement made

by an MSHA inspector is based on the

difference between pre- and postexposure weights of a dust sample, as

determined in the same laboratory, and

adjusted by the weight gain or loss of

the control filter capsule. Any

systematic error or bias in the weighing

process attributable to the laboratory is

mathematically canceled out by

subtraction. Furthermore, 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.

Elimination of the sources of systematic

errors identified above, together with

the fact that the concentration of

respirable dust is defined by section

202(e) of the Mine Act to mean the

average concentration of respirable dust

measured by an approved sampler unit,

implies that the measurements are

unbiased. This means that εi is equally

likely to be positive or negative and, on

average, equal to zero.

Therefore, each εi is assumed to be

normally distributed, with a mean value

of zero and a degree of variability

represented by its standard deviation

σ μ i i total = ⋅CV .

Since Xi = μi + εi, it follows that for a

given value of μi, Xi is normally

distributed with expected value equal to

μi and standard deviation equal to σi.

CVtotal, described in the MSHA and

NIOSH joint finding published

elsewhere in today’s Federal Register, is

the coefficient of variation in

measurements corresponding to a given

value of μi. CVtotal relates entirely to

variability due to measurement errors

and not at all to variability in actual

dust concentrations.

MSHA’s procedure for citing

noncompliance based on the CTV table

consists of formally testing a

presumption of compliance at every

location sampled. Compliance with the

applicable standard at the ith sampling

location is expressed by the relation μi

≤ S. Max{μi} denotes the maximum dust

concentration, among all of the

sampling locations within an MMU.

Therefore, if Max{μi} ≤ S, none of the

sampler units in the MMU were

exposed to excessive dust

concentration. Since the burden of proof

is on MSHA to demonstrate

noncompliance, the hypothesis being

tested (called the null hypothesis, or

H0,) is that the concentration at every

location sampled is in compliance with

the applicable standard. Equivalently,

for an MMU the null hypothesis (H0) is

that max{μi} ≤ S. In other areas, where

only one, full-shift measurement is

made, the null hypothesis is simply that

μi ≤ S.

The test consists of evaluating the

likelihood of measurements obtained

during an MSHA inspection, under the

assumption that H0 is true. Since Xi =

μi + εi, Xi (or max{Xi} in the case of an

MMU) can exceed S even under that

assumption. However, based on the

normal distribution of measurement

errors, it is possible to calculate the

probability that a measurement error

would be large enough to fully account

for the measurement’s exceeding the

standard. The greater the amount by

which Xi exceeds S, the less likely it is

that this would be due to measurement

error alone. If, under H0, this probability

is less than five percent, then H0 can be

rejected at a 95-percent confidence level

and a citation is warranted. For an

MMU, rejecting H0 (and therefore

issuing a citation) is equivalent to

determining that μi > S for at least one

value of I.

Each CTV listed was calculated to

ensure that citations will be issued at a

confidence level of at least 95 percent.

As described in MSHA’s February 1994

notice and explained further by Kogut

[2], the tabled CTV corresponding to

each S was calculated on the

assumption that, at each sampling

location:

CV CV mg m

mg m

total CTV

i

≤ = ⋅ 









 + +

0 14 100% 5%) 5%)

3

3

2

2 2 . ( (

μ

The MSHA and NIOSH joint finding

establishes that for valid measurements

made with an approved sampler unit,

CVtotal is in fact less than CVCTV at all

dust concentrations (μi

).

The situation in which measurement

error is most likely to cause an

erroneous noncompliance

determination is the hypothetical case

of μi = S for either a single, full-shift

measurement or for all of the

measurements made in the same MMU.

In that borderline situation—i.e., the

worst case consistent with Ho—the

standard deviation is identical for all

measurement errors. Therefore, the

value of s used in constructing the CTV

table is the product of S and CVCTV

evaluated for a dust concentration equal

to S:

σ = ⋅ 





 S + +

S

0 14 05 05

2

2 2 . (. ) (. )

Assuming a normal distribution of

measurement errors as explained above,

it follows that the probability a single

measurement would equal or exceed the

critical value

c S = + ⋅ 1 64 . σ

is five percent under Ho when CVtotal =

CVCTV. The tabled CTV corresponding

to S is derived by simply raising the

critical value c up to the next exact

multiple of 0.01 mg/m3.

For example, at a dust concentration

(μi) just meeting the applicable standard

of S = 2 mg/m3, CVCTV is 9.95 percent.

Therefore, the calculated value of c is

2.326 and the CTV is 2.33 mg/m3. Any

valid single, full-shift measurement at or

above this CTV is unlikely to be this

large simply because of measurement

error. Therefore, any such measurement

warrants a noncompliance citation.

The probability that a measurement

exceeds the CTV is even smaller if μi>S

for any I. Furthermore, to the extent that

CVtotal is actually less than CVCTV, σ is

actually less than S•CVCTV. This results

in an even lower probability that the

critical value would be exceeded under

the null hypothesis. Consequently, if

any single, full-shift measurement

equals or exceeds c, then Ho can be

rejected at confidence level of at least

95-percent. Since rejection of Ho implies

that μi ≤ S for at least one value of I, this

warrants a noncompliance citation.

It should be noted that when each of

several measurements is separately

compared to the CTV table, the

probability that at least one εi will be

large enough to force Xi ≥ CTV when μi

≤ S is greater than the probability when

only a single comparison is made. For

example (still assuming S = 2 mg/m3),

if CVtotal is actually 6.6%, then the

standard deviation of εi is 6.6% of 2.0

mg/m3, or 0.132 mg/m3, when μi = S.

Using properties of the normal

distribution, the probability that any

single measurement would exceed the

CTV in this borderline situation is

calculated to be 0.0062. However, the
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5701

probability that at least one of five such

measurements results in a citation is 1—

(0.9938)5 = 3.1 percent. Therefore, the

confidence level at which a citation can

be issued, based on the maximum of

five measurements made in the same

MMU on a given shift, is 97%.

The constant 1.64 used in calculating

the CTV is a 1-tailed 95-percent

confidence coefficient and is derived

from the standard normal probability

distribution. At least one commenter

expressed confusion about whether the

CTV table is based on a 1-tailed or a 2-

tailed confidence coefficient. This

commenter claimed that MSHA’s use of

a confidence coefficient equal to 1.64

‘‘clearly establishes a 90% confidence

level’’ rather than 95%. The commenter

apparently confused the CTV for

rejecting a 1-tailed hypothesis (μi ≤ S)

with the pair of critical values for

rejecting a 2-tailed hypothesis (μi = S)

and inferring that μi simply differs from

S in either direction. The criterion for

rejecting the latter hypothesis would be

a measurement either sufficiently above

the applicable standard or sufficiently

below it. In testing for a difference of

arbitrary direction, 1.64 would indeed

yield a pair of 90-percent confidence

limits, with a 5-percent chance of erring

on either side. The purpose of the CTV

table, however, is to provide criteria for

determining that the true dust

concentration strictly exceeds the

applicable standard. Since such a

determination can occur only when a

single, full-shift measurement is

sufficiently high, there is exactly zero

probability of erroneously citing

noncompliance when a measurement

falls below the lower confidence limit.

Consequently, the total probability of

erroneously citing noncompliance

equals the probability that a standard

normal random variable exceeds 1.64,

which is 5 percent.

One commenter alluded to testimony

in the Keystone case (Keystone v.

Secretary of Labor, 16 FMSHRC 6 (Jan.

4, 1994)), suggesting that application of

the CTV to a single measurement

involves an invalid comparison of two

distributions or comparison of two

means. Contrary to much of the

testimony presented in that case, a

determination of noncompliance using

the CTV table is based on the decision

procedure described above. It does not

involve any comparison of probability

distributions or means. Nor does it

involve any statistical distribution of

dust concentrations. It involves only the

comparison of an individual full-shift

measurement to the applicable standard.

There is only one probability

distribution involved in this

comparison: namely, the distribution of

random measurement errors by which

each full-shift measurement deviates

from the true dust concentration to

which the sampler unit is exposed.

Some commenters apparently

misunderstood the effect of potential

weighing errors on the formula for

calculating the CTV corresponding to

different applicable standards. Weight

gain is estimated from the difference

between two weighings of an exposed

filter capsule, adjusted by subtracting

the difference between two weighings of

a control filter capsule. Since weight

gains are small compared to the total

weight of capsules being weighed, any

dependence of weighing error on the

magnitude of the mass being weighed is

canceled in the process of calculating

the difference. Since the standard

deviation of the error in weight gain is,

therefore, essentially constant, the ratio

of that standard deviation to the dust

concentration being measured decreases

with increasing dust concentration. This

causes CVCTV to decrease as the dust

concentration increases. As explained

above, the CTV corresponding to S is

calculated using the value of CVCTV for

dust concentrations exactly equal to S.

Consequently, the CTV corresponding to

a standard of 2.0 mg/m3 is based on a

smaller value of CVCTV than the CTV

corresponding to a standard of 0.2 mg/

m3.

One commenter implied that use of

the CTV table relies on an assumption

that CVtotal declines at concentrations

greater than 2.0 mg/m3 (or S in general).

As explained previously, the CTV

corresponding to different applicable

standards is designed to test the null

hypothesis that S is not exceeded. For

each applicable standard, entries are

based on the probability distribution of

observations expected under that

presumption. Consequently, the

magnitude of CVtotal assumed in

establishing or applying any CTV does

not decrease below the value of CVtotal

calculated for a concentration of 2.0 mg/

m3, since that is the maximum

applicable standard being tested.

Because the probability of wrongly

citing noncompliance is zero when S is

exceeded, measurement uncertainty at

concentrations greater than S is not

relevant to noncompliance

determinations. (It would, however, be

relevant to inferring compliance at a

specified confidence level—i.e., to a test

of the alternative hypothesis that S is

not exceeded.)

III. Validity of the CTV table

Some commenters questioned the

validity of the CTV table and challenged

the formula used to calculate each CTV

listed. Some objected to the use of a

normal distribution and claimed that a

lognormal distribution or nonparametric

assumptions would be more

appropriate. Other commenters objected

specifically to the use of a confidence

coefficient based on a standard normal

probability distribution, rather than a tdistribution. The validity of using √n,

rather than √(n-1), in the formula used

to calculate citation threshold values in

MSHA’s February 1994 notice, was also

questioned. At least one commenter

contended that the formula used to

generate the CTV table is not valid for

use with only one measurement.

Such comments would have some

validity if the CTV table were intended

to test or estimate average concentration

over some spatially distributed region of

a mine or some period greater than the

single shift during which each

measurement is taken. In either case, it

might be necessary and appropriate to

estimate variation in concentration

directly from the measurement samples

obtained. Such an estimate could

conceivably be used in establishing a

site-specific threshold value for citation.

This would, indeed, require a

theoretical minimum of two samples, or

far more for valid practical applications.

Estimating variability from the samples

collected would also require additional

assumptions or nonparametric methods

to reflect the pattern of variation in dust

concentration between locations or

shifts.

The objections raised, however, apply

to a very different task from the one for

which the CTV table is designed. As

explained previously, the CTV table is

not meant to test dust concentration

averaged over any period greater than

the shift during which measurements

were taken. Nor is it meant to test dust

concentration averaged across different

occupational locations or throughout

any spatially distributed region of the

mine. Instead, the CTV table provides

criteria for determining noncompliance

at individual sampling locations on

individual shifts. Neither the spatial nor

temporal distribution of the dust

concentrations is germane to the

intended citation criteria. Although

several measurements may be taken

during a single inspection, MSHA

regards each of these measurements as

relating to the dust concentration

uniquely associated on a given shift

with a separate sampling location. Each

such dust concentration (μi) is the

average for the atmosphere at the

sampling location, accumulated over the

course of the single, full shift sampled.

Since the enforcement objective is to

determine whether μi > S for any

individual I, it is not necessary to

estimate or assume anything about the
5702 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

degree to which μi varies from location

to location or from shift to shift. Nor is

it necessary to assume anything about

the spatial or temporal statistical

distribution of μi. No such assumptions

are built into the CTV table. A normal

distribution is imputed only to εi, the

difference between Xi and μi. Since the

mean across various μi is not being

estimated or tested, it is not necessary

to estimate variability among the μi from

measurements taken during the

inspection. MSHA emphatically agrees

with those commenters who stressed the

impossibility of doing so with a single

measurement.

Those commenters who objected to

MSHA’s use of a normal distribution,

claiming that a lognormal distribution

or nonparametric assumptions would be

more appropriate, apparently confused

the distribution of dust concentrations

over time and between locations with

the distribution of errors that arise when

measuring dust concentration at a

specific time and location. In other

words, they confused the distribution of

μi with the distribution of εi. The

concerns about non-normality stem

from confusion about what quantity is

being estimated.

MSHA does not dispute the fact that

lognormal or nonparametric methods

are often appropriate for modeling

variability in occupational dust

concentrations. MSHA, however, is

explicitly not claiming to estimate any

quantity beyond the average dust

concentration at a particular sampling

location on a single shift. MSHA does

not claim that dust concentrations are

normally distributed from shift to shift,

from occupation to occupation, or from

location to location; nor is any such

assumption built into the CTV table.

Since the object is not to estimate

average concentration over a range of

different locations or shifts, the

statistical distribution of μi is irrelevant,

and application of lognormal or

nonparametric techniques in

constructing citation criteria is both

unnecessary and inappropriate.

In constructing the CTV table, MSHA

used a normal probability distribution

solely to represent a potential

measurement error, εi. This

measurement error causes a

measurement Xi to deviate from μi, the

actual dust concentration at a specific

time and place. As distinguished from

the statistical distribution of dust

concentrations, it is generally accepted

that the distribution of measurement

errors around a given concentration is

normal [3]. This was explicitly

acknowledged by members of the

industry panel in their Morgantown

testimony.

Similarly, criticism directed against

MSHA’s use of a confidence coefficient

derived from the standard normal

distribution instead of the t-distribution

arises from a basic misunder standing of

what is or is not being estimated in the

decision procedure. Contrary to the

remark of one commenter, use of the tdistribution is not justified as a

‘‘compromise’’ between normaltheoretic and nonparametric

assumptions. The

t-distribution arises in statistical theory

when a normally distributed random

variable is divided by an estimate of its

standard deviation. Typically it is

applied to situations in which the mean

and standard deviation are estimated

from the same normally distributed

data, consisting of fewer than about

thirty or forty random data points. If the

estimate of standard deviation is based

on more data, then the confidence

coefficient derived from the tdistribution is approximately equal to

the corresponding value derived from

the standard normal distribution. Use of

the t-distribution is appropriate, for

example, when a group of normally

distributed observations is

‘‘standardized’’ by subtracting the group

mean from each observation and

dividing the result by the group

standard deviation.

Those commenters advocating a

confidence coefficient based on the

t-distribution failed to recognize that

CVCTV was not derived from the

measurements that MSHA inspectors

will use to test for compliance with S.

Use of the t-distribution is not

appropriate when an independently

known or stipulated standard deviation

is used in comparing observations to a

standard [3]. The standard deviation of

measurement errors used in

constructing the CTV table is derived

from prior knowledge, rather than

estimated from a few measurements

taken during an inspection.

Experimental analysis has shown that

CVtotal is less than CVCTV. So long as this

is true, use of a confidence coefficient

derived from the standard normal

distribution is entirely appropriate.

Contrary to the claims of some

commenters, there is no valid basis for

including a so-called [n/(n-1)]1/2

‘‘correction factor’’ in the formula for

establishing a CTV. (The ‘‘n’’ in this

expression would refer to the number of

measurements, if a noncompliance

determination were based on the

average of several measurements.) The

theory behind such a factor does not

apply when, as in the case of the CTV

table, a predetermined or maximum

tolerated variability in measurement

error is used in comparing observations

to a standard [3]. It would apply only if

variability in measurements observed

during each inspection were somehow

used to construct a CTV specific to that

inspection. The variability observed

among multiple samples collected

during an MSHA inspection has little to

do with the accuracy of an individual

measurement and is not used at all in

constructing the CTV table.

Although no explicit reason was given

for the claim by some commenters that

the formula used to generate the CTV

table is not valid for use with a single

measurement, this would follow if

either: (1) the appropriate basis for the

confidence coefficient were a

t-distribution rather than a standard

normal distribution; or (2) it were

necessary to multiply the CTV by [n/(n–

1)]1/2, where n is the number of

measurements on which a

noncompliance determination is based.

In the former case, the standard normal

distribution would not adequately

approximate the t-distribution; and in

the latter case, n = 1 would cause the

so-called correction factor, and hence

the CTV, to be mathematically

indeterminate for determinations based

on a single sample. It has already been

explained, however, that neither of

these considerations are applicable to

the CTV table.

Some commenters stated that a single

measurement cannot accurately be used

to detect excessive dust concentrations,

even if the noncompliance

determination applies only to a specific

shift and location. These commenters

implied that due to random, temporary

fluctuations in dust concentration, a

single measurement is inherently

unstable and misleading. Such

arguments fail to differentiate a full-shift

sample from a ‘‘grab sample,’’ which is

typically a sample collected over only a

few minutes or seconds and used to

estimate average conditions over an

entire shift. In contrast to a grab sample,

each full-shift dust sample is collected

continuously over the full period to

which the measurement applies. An 8-

hour dust sample consists of 480 1-

minute grab samples, or an arbitrarily

large number of even shorter grab

samples. A full-shift dust sample can be

viewed as measuring average

concentration over the entire shift by

averaging together all of these shorter

subsamples. Although short-term

fluctuations in dust concentration, as

well as random changes in flow rate and

collection efficiency, may cause many of

the subsamples to poorly represent

average concentration over the entire

shift, random short-term aberrations

tend to cancel one another when the

subsamples are combined. Therefore, a
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5703

full-shift dust sample does not suffer

from lack of sample size.

Appendix C—Risk of Erroneous

Enforcement Determinations

I. What Constitutes Compliance or

Noncompliance?

To simplify the following discussion,

let μ denote the average dust

concentration to which a sampler unit is

exposed on a given shift, let S denote

the applicable standard, and let X

denote a valid, full-shift measurement of

μ. Also, let c be the CTV in the table

corresponding to S so that a citation is

issued when X ≥ c. Section 202(b)(2) of

the Mine Act requires that the average

dust concentration during each shift be

maintained at or below the applicable

standard wherever miners normally

work or travel. This means that, on any

given shift, the average dust

concentration (μ) at any valid sampling

location must not exceed the applicable

standard (S).

Since the CTVs listed always exceed

S it can happen that a full-shift

measurement (X) falls between S and c.

In such instances, MSHA will not issue

a citation. This does not, however,

imply that MSHA considers the mine

atmosphere sampled to have been in

compliance with the Mine Act or that

cases of marginal noncompliance are

tolerable. MSHA’s use of the CTVs is

not motivated by any tacit acceptance of

marginal noncompliance. Rather, it is

motivated by the necessity to avoid

unsustainable violations. When X falls

between S and c, this provides some

evidence that μ > S; but the evidence is

insufficient to warrant a citation.

Although μ > S constitutes a violation,

X greater than S but less than the CTV

does not provide compelling evidence

that μ > S. This is because, in a

sufficiently well-controlled mining

environment, X is more likely to slightly

exceed S due to measurement error than

due to μ > S. In fact, as demonstrated

in Appendix D, citing when X > S but

X < c could result in citations when the

probability of compliance (μ ≤ S) on the

shift and location sampled is greater

than 50 percent. Use of the CTV table is

necessary in order to avoid citing in

such cases.

There are two sorts of conclusions

that might be drawn from the results of

a single MSHA inspection: those

relating to the individual shift sampled

and those relating to some longer time

period, such as the full interval between

MSHA inspections. Therefore, in

evaluating the probability of erroneous

enforcement determinations, it is

essential to distinguish between (1)

compliance or noncompliance with the

applicable standard on the shift

sampled and (2) compliance or

noncompliance with the full

requirement of the Mine Act as it

applies to every shift over a longer term,

such as the period between MSHA

inspections.

If μ > S on some proportion of shifts,

say P < 1, then the mine does not

comply with the applicable standard on

some individual shifts and, therefore,

does not comply with the Mine Act over

the longer term. At the same time, the

mine is in compliance with the

applicable standard (at the location

sampled) on a complementary

proportion, equal to 1—P, of individual

shifts. If an MSHA inspection happens

to fall on one of those shifts that is out

of compliance, then a correct

determination with respect to the

individual shift would also be correct

with respect to the longer term. If, on

the other hand, the MSHA inspection

happens to fall on a shift that is in

compliance, then it would be a mistake

to assume compliance on subsequent

shifts and vice versa. Although MSHA

interprets the Mine Act as requiring μ ≤

S on each shift and at each sampling

location to which miners in the active

workings are exposed, the immediate

objective of an MSHA dust inspection

can only be to determine compliance or

noncompliance for the shift and

location sampled. Therefore, MSHA

does not consider a compliance or

noncompliance determination to be

erroneous if it is correct with respect to

the individual shift and location but

incorrect with respect to other shifts or

locations.

II. Uncertainty in the Standard-Setting

Process

In response to the March, 12, 1996

MSHA/NIOSH Federal Register notice,

a commenter claimed that a

noncompliance determination based on

a single, full-shift measurement could

be erroneous if the applicable standard

was improperly established due to

measurement errors associated with

silica analysis. It was, therefore,

suggested that uncertainty in the

standard-setting process should be

factored into the risk of erroneous

enforcement decisions. MSHA agrees

that, like any measurement process, the

sampling and analytical method used to

quantify the silica content of a

respirable dust sample in order to set

the applicable standard is subject to

potential measurement errors.

Therefore, MSHA uses an analytical

procedure that meets the requirement of

a NIOSH Class B analytical method.

Applicable standards are set based on

results of silica analysis using the most

up-to-date laboratory equipment.

The Secretary, however, considers the

accuracy of the standard-setting process

to be a separate issue from the accuracy

of noncompliance determinations based

on a single-full-shift measurement, once

the applicable standard has been set.

The present notice relates only to the

enforcement of the applicable standard

in effect at time of the sampling

inspection. Therefore, the following

discussion treats any applicable

standard in effect at the time of

sampling as binding and evaluates the

risk of erroneous determinations relative

to that standard.

III. Measurement Uncertainty and Dust

Concentration Variability

Variability in dust concentration

refers to the differing values of μ on

different shifts or at different locations.

For a given value of μ, measurement

uncertainty refers to the differing

measurement results that could arise

because of different potential

measurement errors. If μ ≤ S,

measurement error can cause an

erroneous citation. Similarly, if μ > S,

then measurement error can cause an

erroneous failure to cite.

The ‘‘margin of error’’ separating each

CTV from the corresponding applicable

standard does not eliminate the

possibility of erroneous enforcement

determinations due to uncertainty in the

measurement process. A determination

based on comparing X to the CTV could

be erroneous in either of two ways with

respect to the individual shift sampled:

(1) the comparison could erroneously

indicate noncompliance on the shift (i.e,

X ≥ c but μ ≤ S) or (2) the comparison

could erroneously fail to indicate

noncompliance on the shift (i.e, X < c

but μ > S). The margin of error built into

the CTV table reduces the probability of

erroneous citations but increases the

probability of erroneous failures to cite.

MSHA recognizes that in determining

how large the margin of error should be,

there is a tradeoff between the

probabilities of these two mistakes—i.e.,

if the chance of erroneously failing to

cite is reduced, then the chance of

erroneously citing is increased, and vice

versa. MSHA has constructed the CTV.

table so as to ensure that citations will

be issued only when they can be issued

at a high level of confidence. As will be

shown below, doing this provides

assurance that for any given citation, μ

is more likely than not to actually

exceed S. In contrast, if there were no

margin of error, citations more likely

than not to be erroneous could

occasionally be issued. Examples of this

are given in Appendix D.
5704 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

2Appendix D addresses cases in which a

noncompliance determination is based on the

maximum of several measurements.

3A vertical bar is used to denote conditional

probability. Prb {A | B} denotes the conditional

probability of event A, given the occurrence of

event B. For any events A and B,

Prb{A|B}=Prb{A and B}/Prb {B}=Prb{B|A}•Prb

{A}/Prb{B}

In the discussion below, the risk of

erroneous citations and erroneous

failures to cite is quantified for

noncompliance determinations based on

the CTV table. To illustrate points in the

theoretical discussion, three different

mining environments will be used as

examples. These environments

exemplify different degrees of dust

concentration variability and dust

control effectiveness. The first example

(Case 1) is based on historical mine data

provided by commenters in connection

with these proceedings. The second and

third examples (Case 2 and Case 3) are

hypothetical and are designed to reflect

extremely well-controlled and poorly

controlled mining environments,

respectively. In these three examples, it

will be assumed that μ is lognormally

distributed from shift to shift. This is a

standard assumption for airborne

contaminants in an occupational setting

[3]. The three cases considered are

characterized as follows:

Case

Dust concentration (mg/m3)

Arithmetic

mean,

E{μ}

Arithmetic

Std.

Dev.,

SD{μ}

Geometric

mean

Geometric

Std.

Dev.

Prb

{μ>S}

(percent)

1 ................................................................................................................................................................ 1.66 0.70 1.53 1.50 25.4

2 ................................................................................................................................................................ 1.20 0.24 1.18 1.22 0.4

3 ................................................................................................................................................................ 2.20 1.32 1.89 1.74 45.8

In addition to the variability in dust

concentrations described by the

arithmetic and geometric standard

deviations of μ, full-shift measurements

contain a degree of uncertainty

described by CVtotal, the coefficient of

variation for measurements of the same

dust concentration. In calculating the

probability of erroneous determinations

for the three example cases, it will also

be assumed that the applicable standard

is S = 2.0 mg/m3 and that the coefficient

of variation in full-shift measurements

taken at a given value of μ is:

CV

Liters m

Liters

total CV CV

e

= pump sampler

⋅ ⋅

⋅

























+ ( ) + ( )

138 1000 2

2 480

3 2

2 2 . min min

σ

μ

Where σe = 9.12 μg is the standard

deviation of error in weight gain, as

determined from MSHA’s 1995 field

investigation of measurement precision

[4]; 1.38 is the MRE-equivalent

conversion factor for measurements

made with an approved sampler unit;

the first quantity being squared is

CVweight; CVpump = 4.2% and CVsampler =

5%, as explained in Appendix B.II of

the joint MSHA and NIOSH notice of

finding published elsewhere in today’s

Federal Register.

It should be noted that the ‘‘total’’ in

CVtotal refers to total measurement

uncertainty and is not meant to include

the effects of variability in dust

concentration.

Because it employs a higher value for

CVsampler (reflecting variability amongst

used rather than new 10-mm nylon

cyclones), this composite estimate of

CVtotal is slightly greater and perhaps

slightly more realistic than that obtained

directly from MSHA’s 1995 field

investigation. It declines from 11.3% at

dust concentrations of 0.2 mg/m3 to no

more than 6.6% at concentrations of 2.0

mg/m3 or greater. At all dust

concentrations within this range, it falls

well below the 12.8% maximum value

permitted for a method meeting the

NIOSH Accuracy Criterion [5]. It is also

smaller than the value, CVCTV, used to

construct the CTV table. As explained in

Appendix B, this ensures that any

citation issued will be warranted at a

confidence level of at least 95 percent.

To simplify the discussion below on

risk of erroneous citations and

erroneous failures to cite, it is necessary

to introduce some additional notation

and to focus on just one measurement

collected during each inspection.2 This

could be the ‘‘D.O.’’ sample in a MMU,

or the measurement collected for a

designated area. Let ε = X¥μ represent

the measurement error in a valid

measurement. For reasons explained in

Appendix B, ε is assumed to be

normally distributed with zero mean

and standard deviation equal to σ =

μ•CVtotal. Consequently, X is normally

distributed with mean equal to μ and

standard deviation equal to σ. This

normal distribution of X around μ

reflects uncertainty in the measurement

of a given dust concentration. On any

given shift, the probability distribution

of X is determined by the value of μ for

that shift and sampling location.

Therefore, the probability of citation on

a given shift is conditional on μ and is

denoted by Prb{X≥c | μ .}3

Since μ varies from shift to shift,

variability in dust concentration is

represented by the probability

distribution of μ. Let E {μ} denote the

expected (i.e., arithmetic mean) dust

concentration over some longer term of

interest, such as the interval between

MSHA inspections; and let SD{μ}

denote the standard deviation of μ over

the same period. Although the value of

μ on any individual shift is unknown,

Prb{X≥c} can be calculated using the

probability distribution of μ. In

particular, if the probability is known

that μ fulfills a specified condition, such

as μ ≤ S or μ > S, then

Prb{X≥c} = Prb{X≥c | μ ≤S} •Prb{μ≤S}+Prb{X≥c | μ >S} •Prb{μ>S}.

Over a sufficiently long term, with

respect to any particular sampling
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5705

4P defines this likelihood exactly only if shifts

are randomly selected for MSHA inspection and there is no adjustment of conditions in response to

the inspection.

location, Prb{μ>S} and Prb{μ≤S} can be

identified, respectively, with the

proportion of noncompliant shifts, P,

and the proportion of compliant shifts,

1¥P. P is sometimes called the

noncompliance fraction and more or

less defines the likelihood that the

applicable standard is or is not

exceeded on the particular shift

inspected.4

If the statistical distribution of μ can

be adequately represented by a

probability density function, denoted

f(μ), then Prb{μ>S} and Prb{μ≤S} can

also be calculated by integrating f(μ)

over the desired range. The probability

that μ falls in any interval, say between

a and b, is given by:

Prb a b f d

a

b

{ } < ≤ = ∫ μ μ μ ( ) .

It follows that:

Prb

Prb X > c

X c a b

f d

f d

a

b

a

b { } > < ≤ =

{ }⋅ ∫

∫

μ

μ μ μ

μ μ

( )

( )

IV. Risk of Erroneous Citation

Some commenters argued that a

citation for noncompliance is warranted

only if the average dust concentration to

which a miner is exposed exceeds the

applicable standard over a period of

time greater than a single shift, such as

a bimonthly sampling period, a year, or

a miner’s lifetime. Therefore, these

commenters called it ‘‘unfair’’ to cite

individual shifts on which the

applicable standard is exceeded, so long

as the average over this longer term

meets the applicable standard. For

example, based on the historical

sampling data provided by a commenter

and employed here as Case 1, one

commenter concluded that ‘‘* * * there

is at least a 1 in 6 or 17% probability

that any single sample can show

potential overexposure [using the CTV

table] when one does not exist.’’

Further, these commenters maintained

that basing citations on a single, fullshift measurement would substantially

increase the frequency of unfair

citations, compared to existing MSHA

policy.

Using the notation introduced above,

these commenters have confused μ with

E(μ) and confounded the

noncompliance fraction P with the

probability of erroneous citation. For

example, the 17-percent figure

mentioned above includes all cases in

which X ≥ c, regardless of whether μ >

S on the shift sampled. In the discussion

accompanying the data, commenters

argue that since E(μ) is approximately

1.66 mg/m3, or less than 1.85 mg/m3 at

a high confidence level, ‘‘* * * [cases

of X ≥ c] show potential overexposure

when one does not exist.’’ This

statement depends on the unwarranted

assumption that miners exposed to

these conditions have been exposed to

similarly distributed dust

concentrations in the past and that they

will be exposed to similarly distributed

concentrations in the future. These

commenters’ own analysis indicates that

the dust concentration has not been kept

below the standard on each shift.

Therefore, a citation is warranted under

the Mine Act.

To more fully explore what is going

on in Case 1, suppose, as these

commenters suggest, that dust

concentrations over the period observed

are lognormally distributed from shift to

shift, with E{μ} = 1.66 mg/m3 and a

geometric standard deviation of about

1.5 mg/m3. Under this assumption, μ >

2.0 mg/m3 on more than 25 percent of

all shifts, and μ > 2.33 mg/m3 on 15

percent. These percentages pertain to

actual dust concentrations and have

nothing to do with measurement error

or accuracy of an individual

measurement. Therefore, a 2.0 mg/m3

dust standard would be violated on 25

percent of all production shifts. The

applicable standard would be violated

by an amount greater than 0.33 mg/m3

on 15 percent. Since 2.33 is the CTV for

a single measurement, this 15 percent

actually represents shifts sufficiently far

out of compliance that they would

probably be cited if inspected.

Nevertheless, the commenters’ analysis

includes such shifts in the 17 percent

claimed as cases subject to erroneous or

unfair citation.

The expected value of the

noncompliance fraction (P) in Case 1 is

25 percent. Therefore, close to 25

percent of all single shift measurements

made under the conditions of Case 1

would be expected to exceed the

standard. Only 17 percent of the single

full-shift measurements taken, however,

exceeded the CTV and would have

warranted citations. Using the estimate

of CVtotal described above, 15 percent of

all single shift measurements would be

expected to do so. Therefore, contrary to

the commenters’ conclusion, Case 1

does not demonstrate a high probability

of erroneously identifying

overexposures. Instead, it illustrates an

effect of the high confidence level

required for citation: the margin of error

built into the CTV reduces the

probability of citing whatever shift

happens to be selected for inspection

from about 25 percent to 15 percent.

Although the applicable standard is

violated on 25 percent of the shifts,

there is only a 15 percent chance that

any particular measurement meets the

citation criterion.

To correctly and unambiguously

quantify the risk of ‘‘unfair’’ citations, it

is necessary to identify three distinct

ways of interpreting the risk of

erroneous noncompliance

determinations. This risk can be defined

alternatively as:

(1) the probability of citing when the

mine atmosphere sampled is actually in

compliance, Prb{X≥c|μ≤S};

(2) the probability that the mine

atmosphere on a shift randomly selected

for inspection is in compliance but is

nevertheless cited, Prb{μ≤S and X≥c}; or

(3) the probability that a given citation

is erroneous,

Prb{μ≤S|X≥c}.

These three different probabilities

apply to three different base

populations. Although the different

interpretations of risk give rise to

quantitatively different probabilities, the

expected total number of erroneous

citations, denoted Nα, remains constant

if each probability is multiplied by the

size of the population to which it

applies. To obtain Nα, the first

probability must be multiplied by the

number of valid measurements made

when μ ≤ S, the second by the total

number of valid measurements, and the

third by the total number of citations

issued—i.e., valid measurements for

which X ≥ c.

The CTV table limits the probability

of erroneously citing defined by the first

two interpretations to a maximum of

less than five percent. However, in a
5706 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

well-controlled mining environment,

where citations are rarely warranted, the

third probability can be larger than the

first two. Since the burden of proof rests

with MSHA to demonstrate

noncompliance, it is essential that α° be

kept well below 50 percent. As will be

shown by example, the use of the CTV

table accomplishes this goal.

Each of the three different

probabilities related to erroneous

noncompliance determinations will

now be explained in detail. Calculations

for all examples are performed under

the assumptions (1) that μ is

lognormally distributed and (2) that ε is

normally distributed with mean equal to

zero and standard deviation equal to

μ•CVtotal.

1. α = Prb{X≥c|μ≤S}

The first risk to be considered is the

probability of citing noncompliance

when the mine atmosphere sampled is

actually in compliance. This probability

represents the proportion of those

measurements made when μ ≤ S that

result in X ≥ c. In other words,

α=Prb{X≥c|μ≤S} is the probability that,

due to measurement error, a citation is

issued under the condition that μ ≤ S.

This is the probability associated with

what is commonly designated Type I

error for testing the null hypothesis: μ

≤ S on the shift sampled.

Essentially, α is the expected (i.e.,

mean) probability of citation over all

those shifts sampled that are at or below

the applicable standard. The relative

frequency distribution of μ over those

shifts is described by its probability

density function, f(μ). Therefore, α can

be calculated as follows:

α

μ = μ μ { } ≥

− ( ) ∫

Prb X c

P

f d

S

1 0

If μ did not vary, then α would be

directly related to the confidence level

at which the null hypothesis could be

rejected when X ≥ c. That confidence

level, which applies to citations issued

in accordance with the CTV table, is

defined as the minimum possible value

of 1¥Prb{X≥c|μ}, subject to the

restriction that μ ≤ S. There is a subtle

but extremely important distinction

between this and 1¥α. Among all those

shifts on which μ ≤ S, Prb{X≥c|μ} is

maximized when μ = S. Therefore, the

minimum possible value of 1¥α, arises

when μ = S on every shift. The resulting

confidence level for concluding μ > S

when X ≥ c is equal to 1¥Prb{X≥c|μ=S}.

For the value of CVtotal described above

(i.e., 6.6% when μ = S = 2.0 mg/m3), this

works out to a confidence level of 0.99,

or 99%.

Although MSHA interprets the Mine

Act as requiring μ ≤ S on each shift at

any location to which a miner in the

active workings is exposed, citations for

noncompliance are intended to apply

only to the shift and location sampled.

Therefore, MSHA makes no assumption

regarding the relative frequency

distribution of μ from shift to shift. This

is consistent with the concept of

defining the confidence level according

to the scenario most susceptible to an

erroneous determination under the null

hypothesis. However, the resulting

confidence level for citing when X ≥ c

really applies only to the hypothetical

case most susceptible to erroneous

citation.

In reality, so long as μ falls below S

on some shifts, α will be smaller than

0.01. The further μ falls below the

applicable standard, and the more shifts

on which this occurs, the less likely it

becomes that measurement error alone

(ε) will be great enough to cause X ≥ c

on a shift randomly selected for

inspection. For example, if S = 2.0 mg/

m3, then c = 2.33 mg/m 3.

Therefore, if μ = 1.8 mg/m3, a citation

would be issued only if ε ≥ c¥μ. An ε

≥ 0.53 mg/m3 (resulting in X ≥ 2.33 mg/

m3) amounts to a measurement error

greater than 29 percent of the true dust

concentration. If the sample is valid,

then the probability of such an

occurrence (given that CVtotal = 6.6% at

μ = 1.8 mg/m3) is less than 4 per

million. This illustrates the general

point that Prb{X≥c|μ} can be far less

than 0.01 when μ < S.

Since Prb{X≥c|μ} is smaller the

further μ falls below S, Prb{X≥c|μ≤S}

depends on the probability distribution

of μ. This probability distribution is

expressed by the relative frequency with

which μ assumes each possible dust

concentration at or below S. If μ falls

substantially below the applicable

standard on many shifts, then many of

the corresponding values of Prb{X>c|μ}

averaged into the calculation of α

should be much smaller than 0.01, as

shown by the foregoing example.

Consequently, in a mining environment

where the dust concentration is usually

well below the applicable standard, α

can reasonably be expected to fall

substantially below its maximum

possible value.

The number of erroneous citations

expected (Nα), is obtained by first

multiplying the total number of

production shifts during the period of

interest by the expected proportion of

these shifts for which μ ≤ S. This

proportion is 1 ¥ P. The result is the

number of production shifts expected to

be in compliance at the sampling

location. This must then be multiplied

by α to calculate Nα.

In Case 1, which is based on real

sampling data (submitted by

commenters), E{μ} is 1.66 mg/m 3 and

SD{μ} is 0.70 mg/m 3. As mentioned

earlier, P is expected to be 0.25 in this

case. This distribution results in a

negligible probability of citing when the

mine atmosphere sampled is in

compliance: α = 0.00012. If 10,000

production shifts are sampled in this

type of environment, 7500 of these

would be expected to be in compliance

at the sampling location. Approximately

one of these 7500 samples (i.e., 7500•α)

would be erroneously cited.

In Case 2, which is meant to represent

a more controlled mining environment,

less than one percent of the shifts are

expected to exceed the standard: P =

0.0037. Furthermore, μ can be expected

to fall below the geometric mean of 1.18

mg/m 3 on about half of the shifts.

Therefore, α is even smaller than in the

first case: α = 0.0000079. Out of 10,000

sampled shifts, 9963 would be expected

to be in compliance. Since 9963 •α is

less than 0.1, it is unlikely that any of

these shifts would be cited erroneously.

Case 3 is meant to represent a poorly

controlled mining environment, in

which E{μ} exceeds the applicable

standard and the coefficient of variation

in shift-to-shift dust concentrations is a

relatively high 60% (i.e., 1.32 ÷ 2.20).

The geometric mean, however, falls

slightly below the applicable standard,

so μ is expected to fall below the

applicable standard on more than 50%

of the shifts. The noncompliance

fraction is expected to be P = 0.46. Also,

because of the high shift-to-shift

variability, μ is not very close to its

geometric mean on most shifts, and a

fairly large percentage of shifts can be

expected to experience μ well below the

standard. The probability of citing when

the mine atmosphere is in compliance

is: α = 0.00015. If 10,000 of shifts in this

environment are sampled, then 5400 of

these shifts would be expected to

comply with the applicable standard at

the sampling location. As in Case 1, an

erroneous citation would be expected

on about one of these shifts.

2. α* = Prb{μ≤S and X≥c}

The probability of erroneous citation

can also be defined unconditionally.

The second way of interpreting this risk

represents the proportion of all

measurements expected to result in an

erroneous citation. Let α* = Prb{μ≤S

and X≥c} be the probability that a shift

and/or mine atmosphere randomly

selected for inspection is in compliance

but, because of measurement error, is

nevertheless cited. For an erroneous
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5707

citation to occur, two events must take

place: first, the atmosphere sampled

must be in compliance (μ≤ S); second,

a measurement error must occur of

sufficient magnitude that a citation is

issued (X ≥ c). The probability that a

randomly selected shift will be in

compliance is Prb{μ≤S} = 1–P. The

probability of citation, given compliance

on the sampled shift, has already been

quantified above as Prb{X≥c|μ≤S} = α.

The probability that both events occur is

the product of these two probabilities—

i.e.,

Prb{μ≤S and X≥c} = Prb{μ≤S} •

Prb{X≥c|μ≤S}

Therefore, α*=(1–P) •α.

If the applicable standard is exceeded

on all shifts, it is exceeded on the shift

sampled, so there is no chance of

erroneously citing that shift: i.e., P = 1,

so α*=(1–1)•α=0. At the opposite limit,

if the applicable standard is never

exceeded, then P = 0 and α* = α.

Between these two extremes, α*

decreases as the noncompliance fraction

P increases, so that α* is always less

than α. To get the number of erroneous

citations, α* is simply multiplied by the

number of shifts sampled. This always

gives an identical result for Nα as that

obtained from multiplying the number

of compliant shifts by α.

In Case 1, P = 0.25. Therefore, the

probability of erroneously citing a

randomly selected shift is α* = 0.75•α

= 0.00009, or about nine in 100,000. If

10,000 shifts are sampled, then 10,000

•α* gives the same number of erroneous

citations as α multiplied by the 7500

compliant shifts expected in this case.

In the relatively well-controlled

environment exemplified by Case 2,

dust concentrations on most shifts

generally fall well below the standard.

Only occasional excursions approaching

or (rarely) exceeding the standard occur,

so P is near zero. Therefore, α* is only

slightly smaller than α. Since P =

0.0037, α* = 0.9963 •α. In this

environment, the chance of erroneously

citing a randomly selected shift is less

than one in 100,000.

In Case 3, the noncompliance fraction

is much greater: P = 46%. Therefore, α*

is substantially smaller than α. In this

environment the probability of

erroneously citing a randomly selected

shift is α* = 0.00008, or about eight in

100,000.

3. α° = Prb{μ≤S|X≥c}

Finally, the risk of an erroneous

citation can be interpreted as the

probability, given a measurement of

sufficient magnitude to warrant citation

(X ≥ c), that the dust concentration

measured actually complies with the

standard (μ≤S). Let α° = Prb{μ≤S|X≥c}

denote this probability, which

represents the expected proportion of all

citations issued because of measurement

error. If any particular citation, based on

a valid single, full-shift measurement, is

selected for scrutiny, then α° is the

probability that this citation is

erroneous. Using the definition of

conditional probability:

α μ

μ

α

μ μ

α

α μ μ

α

α μ

o = ≤ ≥ { }

= { } ≤ ≥

{ } ≥

= { } ≥ ≤ + ≥ { }

= + ≥ { }⋅ { }

= + ⋅ ≥ { }

Pr

Pr

Pr

*

Pr Pr

*

* Pr Pr

*

* Pr

b S X c

b S and X

b X c

b X c and b X c and 

b X c b

P b X c

c

S > S

> S > S

> S

Prb{X≥c|μ>S} represents the power of

the citation criterion to identify cases of

noncompliance when they actually

occur. This probability is calculated as

follows:

Prb

Prb X

X c S

c

P

f d

S

{ } ≥ > = { } ≥ ∞

∫ μ

μ ( ) μ μ

When the distribution of dust

concentrations is such that the

applicable standard is rarely exceeded

(i.e., when P is near zero), the

denominator in the expression for α°

namely

Pr { } * Pr { }, b X c P b X c S ≥ = + ⋅ ≥ > α μ

is only slightly greater than the

numerator, α*. This implies that α° is

not constrained to be smaller than α or

α*. Since this situation arises in

environments where the applicable

standard is rarely exceeded, such

citations will not often be issued.

However, when one is issued, the

probability that it is erroneous can

exceed α.

For example, in the relatively wellcontrolled environment exemplified by

Case 2, α* is 0.00000788, P is 0.00370,

and Prb{X≥c|μ>S} = 0.133. Therefore, in

this example, α° = 0.0158, or about 1.6

percent. That is to say, 1.6 percent of the

citations issued under these

circumstances will be erroneous. This is

considerably greater than α, which was

earlier shown to equal only 0.00079

percent. However the expected

proportion of measurements resulting in

citation, given by Prb{X≥c}, is only

0.000498, or 0.050%. Therefore, out of
5708 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

10,000 shifts sampled, it is expected

that only five would be cited. Since on

average only 1.6% of these five citations

would be erroneous, it is unlikely that

the 10,000 samples would result in any

erroneous citations.

Case 2 represents an environment in

which the noncompliance fraction is

less than one percent. In contrast, the

noncompliance fraction in Case 3 is

nearly 50%: P = 0.458. For this case, α

= 0.000147, α* = 0.0000799, and α° =

0.000227. The calculated value of

Prb{X≥c} is 0.3513, so approximately 35

percent of all measurements would

result in citation. Only about 0.027% of

these citations, however, would be

erroneous. Therefore, out of 10,000

shifts sampled in such an environment,

3513 citations could be expected; and

only about one of these citations

(3513α•°) would be expected to be

erroneous.

In Case 2, the probability (α°) that a

given citation is erroneous is relatively

high (though low enough to sustain a

citation), but the probability of citing

noncompliance in such an environment

is very low. In Case 3, the probability of

citation is more than 700 times higher,

but α° is commensurately lower than in

Case 2. Comparison of Cases 2 and 3

illustrates the general principle: as the

noncompliance fraction P increases, the

probability of citation increases but the

probability that a given citation is

erroneous decreases.

It is important to note that even in the

well-controlled environment of Case 2,

the probability that a given citation is

erroneous (α°) remains substantially

below five percent and far below 50

percent. Although environments even

more well controlled could give rise to

somewhat greater values of α°, the

probability of citing in such

environments would be even smaller

than the probability in Case 2. If a

citation is issued because X > c, then the

probability that μ > S is simply 1 ¥ α°.

This shows that in any particular

instance where a citation based on a

single, full-shift measurement is

reasonably likely to be issued according

to the CTV table, there would be

compelling evidence that μ > S.

V. Risk of Erroneous Failure to Cite

Use of the CTV implies that citations

will be issued only when they can be

issued with high confidence that the

applicable standard has actually been

exceeded on the shift sampled. On the

other hand, failure to meet or exceed the

CTV does not in itself imply compliance

at a similarly high confidence level—

even on the shift sampled, let alone

continuously over any longer term.

Because of limited resources, MSHA

inspections are relatively infrequent and

serve only to identify instances in

which the rest of the dust control

program has been ineffective. They

cannot be relied upon to ensure

continuous compliance.

It should be remembered, however,

that MSHA does not rely exclusively on

sampling by inspectors to ensure

compliance. The MSHA inspection is

only one element of the Agency’s

comprehensive health protection

program, which includes mandatory

implementation and maintenance by

operators of effective dust control

methods to control dust levels where

miners normally work or travel. It also

provides for periodic evaluation by

mine operators of the quality of mine air

and of the effectiveness of the operator’s

dust control system through operator

bimonthly sampling. If they are not

detected during an MSHA inspection,

poorly controlled environments, which

are out of compliance with the dust

standard in a substantial fraction of

instances, are likely to be detected

during some other phase of the MSHA’s

enforcement program.

It should also be remembered that

MSHA’s new enforcement policy

eliminates an important source of

sampling bias due to averaging, as

explained in Appendix A. Under the

existing policy, measurements made at

the dustiest occupational locations or

during the dustiest shifts sampled are

diluted by averaging them with

measurements made under less dusty

conditions. As shown by the SIP data,

this practice has frequently caused

failures to cite clear cases of excessive

dust concentration.

1. β = Prb{X<c|μ>S}

The complement of power, the

probability of detecting cases of

noncompliance when they occur, is the

probability of erroneously failing to

detect such cases. Let β = Prb{X<c|μ>S}

be the probability that a citation will not

be issued when the true dust

concentration being measured exceeds

the standard. This is the probability of

what is commonly called Type II error

for testing the null hypothesis that μ ≤

S. Since β = 1 ¥ Prb{X≥c|μ>S}, the

power of the citation criterion,

formulated earlier as Prb{X≥c|μ>S}, can

be used to calculate β. The expected

number of erroneous failures to cite, Nβ

is obtained by multiplying β by the

number of shifts for which μ > S.

It is true that due to the high

confidence level required for citation, β

is greater than it would be if a citation

were issued whenever X > S. In fact,

setting the CTV to any value greater

than S results in Prb{X<c|μ} potentially

greater than 50 percent when a single

dust concentration exceeding the

standard is being measured. For

example, if μ = 2.12 mg/m3 and S = 2.0

mg/m3, then the CTV is c = 2.33 mg/m3.

Since the probability distribution for X

is centered on μ, any individual

measurement is more likely to fall

below the CTV than to exceed it. The

probability of erroneously failing to cite

in this instance, based only on a single

measurement, would be

Prb{X<2.33|μ=2.12} = 93 percent.

Citing in accordance with the CTV

table does not, however, necessarily

result in β > 50%. When more than one

measurement is made during a single

shift in the same general area of a mine,

such as in the same MMU, the dust

concentrations are correlated. This

increases the chances that if μ exceeds

the standard at one of the sampled

locations, at least one of the

measurements will meet the citation

criteria. More importantly for the

present discussion, however, the value

of β depends on the distribution of μ

even when only a single measurement is

considered on each shift.

This is because the magnitude of β

depends on the average magnitude of

Prb{X<c|μ} over all those instances in

which μ > S. Although Prb{X<c|μ}

exceeds 50 percent when μ < c, it does

not exceed 50 percent when μ > c.

Poorly controlled environments are

likely to experience a significant

number of shifts during which μ

exceeds not only S but also the CTV. If

these shifts ‘‘outweigh’’ those shifts on

which S < μ ≤ c, then this will result in

β < 50 percent.

On those shifts for which μ > S,

Prb{X<c|μ} exceeds 50% only when μ

falls between S and c. In contrast, the

range of potential values of μ>c is

essentially unlimited, and Prb{X<c|μ}

approaches zero as μ increases.

Therefore, β is less than 50% whenever

the distribution of μ is such that

Prb{μ>c} > Prb{S<μ≤ c}. In a poorly

controlled environment, μ is more likely

to exceed the CTV than to fall into the

relatively narrow interval between S

and the CTV.

For example, in Case 1 the probability

that μ exceeds c = 2.33 is 14.9 percent,

whereas the probability that μ falls

between S and c is only P ¥ 14.9 = 10.5

percent. Therefore, in this environment,

the probability of erroneously failing to

cite an instance of μ > S works out to

be somewhat less than 50 percent: β =

1 ¥ Prb{X≥c|μ>S} = 0.404, or 40.4%.

For worse offenders, β is considerably

smaller. In Case 3, Prb{μ>c} = 35.2%,

whereas Prb{S<μ≤c} is 10.6%. In this

case, even though dust concentrations

below the applicable standard are
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5709

expected on a majority of shifts (as

indicated by the geometric mean), β is

calculated to be only 23.3%. Stated

another way, if MSHA were to select

10,000 shifts in this environment, an

expected 4580 of those shifts would be

out of compliance. It is expected that on

76.7% of those 4580 shifts a single

measurement would be sufficiently

large to warrant citation.

There are inherent tradeoffs, not only

between β and α, but also between β and

the probability that a given citation is

erroneous, α° = Prb{μ≤S|X≥c}.

Decreasing the CTV in order to reduce

β forces both α and α° to increase. Even

if α remains below 50 percent, the effect

on α° can be so great as to render some

citations clearly unsustainable. In

particular, setting the CTV at or near S

could result in citations more likely

than not to be erroneous. Circumstances

in which this can occur are discussed in

Appendix D. Use of the CTV, on the

other hand, ensures that any given

citation based on X ≥ c is more likely

than not to represent a case of actual

noncompliance (i.e., μ > S).

Failure to issue a citation based on a

single, full-shift measurement collected

during an MSHA inspection does not

imply failure to detect and correct a

noncompliant condition in the context

of MSHA’s entire enforcement program.

Those commenters expressing concern

over the potential magnitude of β have

largely ignored other means MSHA uses

to protect miners from excessive dust

concentrations relative to the longer

term. As stated earlier in this notice,

MSHA’s health protection program

provides for the implementation and

maintenance by mine operators of

effective methods to control dust

concentrations where miners normally

work or travel, as well as for periodic

evaluation of the quality of mine air to

which miners may be exposed and the

effectiveness of the operator’s dust

control program through operator

bimonthly sampling. Furthermore,

MSHA intends to continue its longstanding practice of collecting

additional measurements when the

standard is exceeded by an amount

insufficient to warrant citation at a high

confidence level.

VI. Summary and Conclusions

Use of the CTV table is based on

MSHA’s need for sufficient evidence to

issue a citation and show, by a

preponderance of the evidence, that a

violation occurred. The burden rests

with MSHA to show that the applicable

standard has in fact been violated on the

particular shift cited. Accordingly, the

CTV table is designed so that the risk of

erroneously not citing is subordinated to

the risk of erroneously issuing a

citation. However, the probability of

erroneously failing to cite a case of

noncompliance at a given sampling

location is less than 50 percent when

the applicable standard is exceeded on

a significant proportion of shifts at that

location.

Three cases were used to illustrate the

risk of erroneous enforcement

determinations over a broad range of

environmental conditions. The results

calculated for each of the three cases

considered are summarized in the

following table.

Case

Probability (percent) Average number of erroneous determinations

(per 10,000 sampled

shifts) Prb{X>S} Prb{X≥c} α α* α° β

Nα Nβ

1 ................................... 25.51 15.14 0.0121 0.00903 0.060 40.4 0.9 1,026

2 ................................... 0.53 0.05 .000791 .000788 1.581 86.7 .1 32

3 ................................... 45.69 35.17 .0147 .00799 0.0227 23.3 .8 1,067

Based on this analysis, it can be

concluded that application of the CTV

table provides ample protection against

erroneous citations. The probability (α)

of issuing a citation when the mine

atmosphere sampled is actually in

compliance is constrained to fall below

a maximum of five percent. This

maximum defines the 95-percent

confidence level claimed for any

citation issued. The expected proportion

(α*) of all valid samples resulting in an

erroneous citation is constrained not to

exceed α. In practice, both α and α* are

expected to fall far below five percent in

a broad range of mining environments.

Furthermore, even in an exceptionally

well-controlled environment, where μ is

very unlikely to exceed the applicable

standard on any particular shift, the

probability (α°) that a given citation is

erroneous will also fall substantially

below five percent. If a measurement

exceeds the CTV, the probability that

the standard has actually been exceeded

is (1–α°). Therefore, any citation issued

in accordance with the CTV table will

be based on clear and compelling

evidence that the standard has been

exceeded on the particular shift

sampled.

Although it is increased by the margin

of error built into the CTV table, the

probability (β) of erroneously failing to

cite noncompliance using a single

measurement is expected to be

significantly less than 50 percent in

mining environments where μ > S on a

substantial percentage of shifts. For the

example considered of a poorly

controlled mining environment (Case 3),

β was calculated to be about 23 percent.

This means that on any given shift for

which μ > S, there would be a 77-

percent chance that X would exceed the

CTV, thereby warranting a citation.

Despite the high confidence level

required for single-sample citations, β is

considerably less than 50 percent even

in the better-controlled environment

exemplified by Case 1. Although citing

whenever X > S would increase the

probability of detecting conditions of

excessive dust concentration, Appendix

D shows that doing so instead of using

the CTV table could result in citations

under conditions of probable

compliance. As shown by the small

values of α° in the table above, use of

the CTV table makes it very unlikely

that this would happen.

Moreover, poorly controlled

environments are likely to be detected

and cited during some other phase of

MSHA’s enforcement program even if

they are not immediately cited on a

particular MSHA sampling inspection.

Regardless of the value of β, it can safely

be concluded that the risk of failing to

detect excessive dust is lower under

MSHA’s new enforcement policy than

under existing procedures, in which

measurements of high dust

concentration are diluted by averaging.

Appendix D—Consequences of

Eliminating the Margin of Error

Several commenters objected to the

emphasis placed on avoiding erroneous

citations and took issue with MSHA’s

intention to cite noncompliance only

when indicated at a high confidence

level. These commenters proposed that

it is unfair to limit citations to cases in
5710 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

which a measurement (X) meets or

exceeds some critical value (c) greater

than the applicable standard (S). They

argued that such an approach unfairly

exposes miners to a far higher

probability of wrongly failing to cite

than the maximum probability specified

for wrongly citing. Their

recommendation was to divide the

burden equally between proving

noncompliance and ensuring

compliance. They maintained that if X

exceeds S by an arbitrarily small

amount, noncompliance is more likely

than compliance and that under such

circumstances a citation should be

issued.

Using notation explained in

Appendix C, X = μ +ε, where ε is a

random, normally distributed

measurement error whose standard

deviation is σ=μ•CVtotal.CVtotal is given

by the formula presented in Appendix

C. A citation based on a single, full-shift

measurement applies specifically to the

shift and location sampled, and hence to

a distinct value of μ. For the citation to

be upheld, the preponderance of

evidence must indicate that μ > S at one

or more of the sampling locations on the

cited shift.

Those commenters who maintained

that a citation should be issued

whenever X > S all assumed (1) that a

citation could withstand legal challenge

so long as noncompliance is more likely

than compliance, even if the probability

of compliance is nearly 50 percent; and

(2) that if X > S, then noncompliance is

more likely than compliance. Aside

from the question of the legal validity of

the first assumption (which equates

preponderance of evidence with any

probability greater than 50 percent), the

second assumption is not always true.

Specifically, the second assumption

fails to hold in relatively well-controlled

environments or in cases where more

than one measurement is used to check

for noncompliance. Commenters making

this assumption confused Prb{X>S|μ≤S}

with Prb{μ≤S|X>S} and also failed to

consider citations based on the

maximum of several measurements.

I. Well-controlled Environments

In a relatively well-controlled

environment, where μ is generally

below the applicable standard, the

probability that X > S due to a large

value of ε can exceed the probability

that X > S due to μ > S. If X < c and

sampling records indicate that the

environment is relatively wellcontrolled, the preponderance of

evidence may support μ ≤ S on the

particular shift sampled.

For example, suppose a citation is

based on a single, full-shift

measurement that barely exceeds S=2.0

mg/m3, but dust sampling records for

the environment indicate a pattern of

dust concentrations resembling Case 2

in Appendix C. That is to say, the

statistical distribution of μ is lognormal,

with arithmetic mean and standard

deviation of 1.2 mg/m3 and 0.24 mg/m3,

respectively. As in Appendix C, let f(μ)

denote the lognormal probability

density function. Then the probability

that μ≤S, given a single full-shift

measurement that falls between S and c,

is:

Prb

Prb S

Prb

Prb

Prb

μ

μ

μ μ μ

μ μ μ

{ } ≤ < ≤ = { } < ≤ ≤

{ } < ≤

=

{ } < ≤ ƒ( )

{ } < ≤ ƒ( )

=

=

∫

∫

∞

S S X c

S X c and 

S X c

S X c d

S X c d

S

0

0

0 00252

0 00481

0 52%

.

.

. .

In other words, when X falls between

S and c in this environment, there is a

52-percent chance that the standard has

not actually been exceeded. It is more

likely that X>S due to a large

measurement error than because μ itself

has exceeded the applicable standard. It

would be unreasonable to cite

noncompliance in such situations. By

citing when and only when X≥c, the

probability that μ≤S is reduced to

α°=1.5%, as shown for Case 2 in

Appendix C.

II. Multiple Samples

Proponents of citing whenever X>S

based their argument on a premise of

symmetry: since potential measurement

errors (ε) are symmetrically distributed

around μ, they assumed that citing

when X=S would result in equal

probabilities of erroneously citing and

erroneously failing to cite. From this,

they argued that if X>S by an arbitrarily

small amount, the probability of

erroneously failing to cite would exceed

the probability of erroneously citing.

The symmetry argument for citing

whenever X>S fails to hold if, on a

single inspection, more than one

measurement is compared to the

standard. In MSHA’s dust inspection

program, several measurements are

routinely made on the same shift,

within the same MMU. MSHA intends

to use each of these measurements

individually to determine

noncompliance at the MMU. However,

as described in the notice to which this

Appendix is attached, no more than one

citation will be issued based on single,

full-shift measurements from the same

MMU. The commenters advocating

issuance of a citation whenever X>S all

endorsed such single-sample

determinations. Since any of several

measurements could warrant a citation

against the MMU, the citation will be

based, in most cases, on the maximum

measurement taken in the MMU during

the shift. If each of several

measurements is compared directly to

the applicable standard, then the

symmetry assumed for citing whenever

X>S breaks down. The mistake of

wrongly citing occurs when any one of

the measurements exceeds the

applicable standard because of a

sufficiently large measurement error,

but the mistake of wrongly failing to cite

occurs only when each and every

measurement is at or below the

standard. Each additional measurement

reduces the probability of erroneously

failing to cite while increasing the

probability of erroneously citing.
Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices 5711

A few examples will be used to

demonstrate how the premise of

symmetric error probabilities breaks

down when more than a single

measurement is taken. These examples

demonstrate that noncompliance

determinations made by comparing so

few as two measurements directly to the

S can result in citations issued at a

confidence level substantially below 50

percent.

Using I to index different valid

measurements for the same MMU, let

max{Xi} denote the maximum

measurement, and let max{μi} denote the

maximum true dust concentration. Note

that due to potential measurement

errors, the maximum dust concentration

does not necessarily correspond to the

maximum measurement. For example,

max{Xi} might be X3 even though

max{μi}=μ2. Since the object is to

examine the consequences of citing

whenever any of several measurements

exceeds S by any amount, it will be

assumed in these examples that the

citation criterion is max{Xi}>S rather

than max{Xi}>c.

As in Appendix C, let α be the

probability of citing under conditions of

compliance, and let β be the probability

of erroneously failing to cite. Then:

α μ β μ = > ≤ ≤ > Prb{max{X and = Prb{max{X i i } |max{ } } } |max{ } }. S S S S i i

For simplicity, suppose S=2.0 mg/m3. The following quantities will be used in the calculations:

μ (mg/m3) CVtotal (percent)

σ=μ•CVtotal

(mg/m3)

Prb{X>2.0|

μ}

(percent)

Prb{X≤2.0|

μ}

(percent)

1.90 ................................................................................................................................... 6.602 0.1254 21.3 78.7

1.99 ................................................................................................................................... 6.596 0.1385 47.1 52.9

2.00 ................................................................................................................................... 6.595 0.1319 50.0 50.0

2.01 ................................................................................................................................... 6.595 0.1326 53.0 47.0

If exactly one measurement is taken

and μ=1.99 mg/m3, then σ=0.1385 mg/

m3. Using the standard normal

probability distribution for ε/σ,

α μ

ε

σ

= > = { }

= − >  − 









= > 











=

Pr . .

Pr .

.

. .

.

Pr .

.

b X

b X

b

2 0 1 99

1 99

0 1385

2 0 1 99

0 1385

0 0722

471%.

On the other hand, if μ=2.01 mg/m3,

then σ=.1319 mg/m3; so

β μ

ε

σ

= ≤ = { }

= − ≤  − 









= ≤ − 











=

Pr . .

Pr .

.

. .

.

Pr .

.

b X

b X

b

2 0 2 01

2 01

0 1326

2 0 2 01

0 1326

0 0754

47 0%.

It is this approximate equality of α

and β, for values of μ symmetrically

falling below or above S=2.0 mg/m3 that

motivates the premise of symmetric

error probabilities.

Suppose now that two measurements

are taken, and a citation is issued if

either X1 or X2 exceeds S=2.0. Suppose

further that μ1=1.99 and μ2=1.90. Then:

α μ μ

μ μ

= > = =

= − ≤ = ⋅ ≤ =

= − ⋅

=

Pr {max{ } . . }

Pr { . . } Pr { . . }

( . ) ( . )

b X S and

b X b X

i 1 2

1 1 2 2

1 99 1 90

1 2 0 1 99 2 0 1 90

1 0 531 0 789

58%.

Since a citation is justified if μi > S

for any I, the greatest probability of

wrongly not citing in a comparable case

of noncompliance is obtained when

μ1=2.01 and μ2 is held at 1.90. In that

case:

β μ μ

μ μ

= { } { } ≤ = =

= ≤ = { }⋅ ≤ = { } = ⋅

=

Pr max . .

Pr . . Pr . .

( .470) ( . )

b X S

b X b X

i 1 2

1 1 2 2

2 01 1 90

2 0 2 01 2 0 1 90

0 0 787

37%.

 and 

This example illustrates the point that

α can exceed β by a substantial amount

when as few as two measurements are

directly compared to the applicable

standard. If μ2 were actually 1.99, then

the discrepancy would be even greater:

α=72% and β=25%. Notice,

furthermore, that in both cases, α would

be greater than 50%. The confidence

level at which a citation is issued

depends on the maximum possible

value of α. Therefore, when one

measurement out of two marginally

exceeds S, the confidence level at which

a citation can be issued is less than 28%

(i.e., 100%¥72%). Such a citation

would be difficult to defend if

challenged.
5712 Federal Register / Vol. 63, No. 22 /Tuesday, February 3, 1998 / Notices

If five measurements are made, as is

routinely done during MSHA

inspections of an MMU, then citing

whenever max{Xi}>S is even less

defensible. The confidence level for a

citation based on the maximum of five

measurements is defined by the value of

α when μi=S for all five values of I.

Under these circumstances, the

probability that at least one of the five

measurements would exceed the

applicable standard is:

α μ = { } { } > =

= −

=

Pr max

( . )

b X S S for all i i i

1 0 5

97%.

5

Therefore, the confidence level at

which a citation could be issued is only

3%. At the same time, the probability

that none of the five measurements will

exceed S is β=(0.5)5=3%, so the

probability that a citation would be

issued is 97%.

III. Conclusion

MSHA, along with other federal

agencies, recognizes that in issuing

citations, the burden rests with the

Agency to show that a violation of the

applicable standard occurred. Use of the

CTV table will severely limit the risk of

an erroneous citation, even when the

true dust concentration being measured

is exactly equal to or slightly below the

applicable standard. If a single

measurement falls between S and the

CTV, then the measurement does not

necessarily provide sufficient evidence

of μ>S to support a citation.

Consequently, MSHA cannot justify

issuing a citation whenever a

measurement exceeds the applicable

standard by an arbitrarily small amount.

Although citing whenever X>S would

result in a smaller probability (β) of

erroneously failing to cite, and hence in

a greater level of protection for the

miner, doing so would result in

citations that may not withstand legal

challenge. However, as stated earlier in

the notice, if the measurement exceeds

the applicable standard but not the CTV,

MSHA intends to target environments

for additional sampling to confirm that

dust control measures in use are

adequate. These follow-up inspections,

in conjunction with operator dust

sampling and MSHA monitoring of

operator compliance with approved

dust control parameters, should further

help to protect miners from excessive

dust concentration.

References

1. 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: Multi-day

MSHA Sampling of Respirable Coal Mine

Dust.

2. 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.

3. Leidel, N.A. and K.A. Busch. Statistical

Design and Data Analysis Requirements.

Patty’s Industrial Hygiene and Toxicology,

Third Edition, Vol. 3, Part A, Chapter 10,

1994.

4. 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.

5. 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.

Dated: December 19, 1997.

J. Davitt McAteer,

Assistant Secretary for Mine Safety and

Health.

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.

[FR Doc. 97–33937 Filed 12–30–97; 8:45 am]

BILLING CODE 4510–43–P