Mine Shift Atmospheric Conditions; Respirable Dust Sample

DEPARTMENT OF LABOR

Mine Safety and Health Administration

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

Mine Shift Atmospheric Conditions; Respirable Dust Sample

AGENCIES: Mine Safety and Health Administration, Labor; National

Institute for Occupational Safety and Health, Centers for Disease

Control and Prevention, Public Health Service, HHS.

ACTION: Notice; reopening of the record; extension of comment period.

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SUMMARY: The Mine Safety and Health Administration (MSHA) and the

National Institute for Occupational Safety and Health (NIOSH) are

reopening the record for their joint notice proposing a finding that

the average concentration of respirable dust to which each miner in the

active workings of a coal mine is exposed can be measured accurately

over a single shift. This finding is being made in accordance with

section 202(f) of the Federal Mine Safety and Health Act of 1977 (Mine

Act). The Agencies are reopening the record to submit a definition of

accuracy, to supply new data and statistical analyses on the precision

of coal mine respirable dust measurements obtained using approved

sampling equipment, and to allow the public time to review and submit

comments on this supplemental information.

DATES: Submit written comments on or before April 11, 1996.

ADDRESSES: Send written comments to the Mine Safety and Health

Administration, Office of Standards, Regulations, and Variances; 4015

Wilson Boulevard, Room 631; Arlington, Virginia 22203. Commenters

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are requested to submit their comments on a computer disk along with an

original hard copy.

FOR FURTHER INFORMATION CONTACT: Ronald J. Schell, Chief, Division of

Health, Coal Mine Safety and Health, 703-235-1358.

SUPPLEMENTARY INFORMATION:

I. Background

On February 18, 1994, the Secretaries of Labor and Health and Human

Services published a notice in the Federal Register (59 FR 8357)

proposing a new finding in accordance with section 202(f) of the

Federal Mine Safety and Health Act of 1977 (Mine Act) that the average

concentration of respirable dust to which each miner in the active

workings of a coal mine is exposed can be accurately measured over a

single shift. This proposed finding would supersede the finding issued

by the Secretaries on July 17, 1971, and affirmed on February 23, 1972,

(37 FR 3833), that a measurement of respirable dust over a single shift

only does not accurately represent the atmospheric conditions to which

a miner is continuously exposed.

MSHA published a notice in the Federal Register (59 FR 8356)

concurrent with publication of the joint notice, announcing its

intention to use both single, full-shift respirable dust measurements

and the average of multiple, full-shift respirable dust samples to

determine noncompliance and to issue citations for violations of the

respirable dust standard.

The comment periods for these notices were scheduled to close on

April 19, 1994; but, in response to requests from the mining community

for additional time in which to prepare their comments, the Agencies

extended the comment period to May 29, 1994 (59 FR 16958).

After the comment period closed, MSHA and NIOSH scheduled two

public hearings. The first public hearing was held on July 6, 1994, in

Morgantown, West Virginia. The second was held on July 19, 1994, in

Salt Lake City, Utah. Both public hearings were well attended by the

mining community.

Based on remarks made at the public hearings and in response to

specific requests from commenters, MSHA supplemented the record with

additional data on September 9, 1994. The record, which had been

scheduled to close on August 5, 1994 (59 FR 38988), was held open for

further comments until September 30, 1994. Subsequently, the mining

community requested additional time beyond the September 30 deadline to

review the supplemental information and prepare comments. In response,

the Agencies published a notice on September 30, 1994, in the Federal

Register (59 FR 50007) extending the comment period until November 30,

1994.

II. Issues

A. Application of the NIOSH Accuracy Criterion

After the close of the comment period, the Agencies reviewed all of

the comments, data, and other information which had been submitted into

the record. Some of the commenters raised questions regarding the

accuracy of single, full-shift measurements, and challenged the

Agencies' estimate of measurement imprecision inherent in the current

sampling and analytical process. In reviewing these issues, the

Agencies concluded that the term ``accurately represent,'' as used in

section 202(f), was not defined in the Mine Act, nor had the Agencies

supplied an adequate definition to apply to the language of the

finding.

Therefore, for purposes of section 202(f), the Secretaries are

proposing to apply an accuracy criterion developed and adopted by NIOSH

in judging whether a single, full-shift measurement will ``accurately

represent'' the full-shift average atmospheric dust concentration.

(Guidelines for Air Sampling and Analytical Method Development and

Evaluation. DHEW (NIOSH) Publication No. 95-117 (1995)).

The NIOSH Accuracy Criterion requires that a sampling and

analytical method be sufficiently accurate so that measurements by the

method will come within 25 percent of the corresponding true dust

concentration at least 95 percent of the time. Adopting this criterion

provides a basis for determining whether a single, full-shift sample by

MSHA's sampling and analytical method accurately measures the

respirable coal mine dust concentration to which a miner is exposed

during the shift in which the sample is collected.

For nearly 20 years, the NIOSH Accuracy Criterion has been used by

NIOSH and others in the occupational health professions to validate

sampling and analytical methods. This accuracy criterion was devised as

a goal for the development and acceptance of sampling and analytical

methods capable of generating reliable exposure data for contaminants

at or near the Occupational Safety and Health Administration's (OSHA)

permissible exposure limits. The Secretaries believe that the NIOSH

Accuracy Criterion is relevant for this proposed finding.

Accordingly, for purposes of section 202(f) of the Mine Act, the

Secretaries would consider a single, full-shift measurement to

``accurately represent'' a specified mine atmosphere if the sampling

and analytical method used meets the NIOSH Accuracy Criterion. MSHA and

NIOSH specifically solicit comments on the use of the NIOSH Accuracy

Criterion to evaluate measurement accuracy.

B. Sampling and Analytical Accuracy

To address commenters' concerns that the Agencies had

underestimated measurement imprecision inherent in the currently used

sampling and analytical method, MSHA conducted a field study to

directly estimate the overall measurement precision attainable when

dust samples are collected with currently approved coal mine dust

sampling equipment and analyzed using state-of-the-art analytical

techniques. The study involved simultaneous field measurements of the

same coal mine dust cloud using sampling pumps incorporating constant

flow control technology. An automated weighing system, capable of

weighing the sample collection filters to the nearest microgram

(g) (0.001 milligram (mg)), was used for determining the pre-

and post-exposure weights.

Using a specially designed, portable dust chamber, 22 tests were

conducted at various locations in an underground coal mine. Each test

consisted of collecting 16 dust samples simultaneously and at the same

location. No adjustments in the flow rate were made beyond what would

routinely have been done by an MSHA inspector. The filter capsules were

weighed to the nearest g in MSHA's Respirable Dust Weighing

Laboratory in Pittsburgh, Pennsylvania, before and after exposure.

Based on the results of this study, MSHA estimates that, for dust

samples collected over a 480-minute period, overall measurement

imprecision (as measured by the coefficient of variation) decreases

from 7.8 percent at dust concentrations of 0.2 mg/m\3\ to about 4.3

percent at concentrations greater than 2.0 mg/m\3\. These results apply

to dust samples collected using pumps with flow control technology and

filter capsules weighed to the nearest g, both before and

after exposure, on a balance calibrated according to the established

procedure within MSHA's Respirable Dust Weighing Laboratory.

NIOSH evaluated the accuracy of the sampling and analytical method

used by MSHA, using both a direct and indirect

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approach. Under the direct approach, NIOSH independently analyzed the

results of MSHA's field study and obtained estimates of measurement

imprecision consistent with those calculated by MSHA. The NIOSH

evaluation demonstrates that the sampling and analytical method, as

employed during the field study, meets NIOSH's Accuracy Criterion at

concentrations greater than or equal to 0.13 mg/m\3\. The indirect

approach involved combining independently derived estimates, previously

placed into the public record, of intra-laboratory weighing

imprecision, pump-related variability, and variability associated with

physical differences between individual sampler units. This indirect

approach indicated that the NIOSH Accuracy Criterion can be met at

concentrations greater than or equal to 0.11 mg/m\3\.

C. Refinements in MSHA's Measurement Process

To ensure that the NIOSH Accuracy Criterion is met over a wide

range of dust concentrations, NIOSH has recommended two modifications

to MSHA's sampling and analytical method, which have now been adopted.

These modifications involve (1) measuring both the pre- and post-

exposure weights to the nearest g on a balance calibrated

using the established procedure within MSHA's laboratory; and (2)

discontinuing the practice of truncating the recorded weights used in

calculating dust concentration. This means that MSHA will no longer

ignore digits representing hundredths and thousandths of a milligram.

NIOSH's independent analysis of the study data confirmed that, with the

two recommended modifications, MSHA's sampling and analytical method

for collecting and processing single, full-shift samples would meet the

NIOSH Accuracy Criterion at all respirable dust standards greater than

or equal to 0.2 mg/m\3\.

Accordingly, MSHA's existing inspector sample processing and data

entry procedures have been changed, and the Agency is now reporting the

pre- and post-exposure weights of inspector samples to the nearest

g. In addition, MSHA is now using only constant flow control

pumps in the inspector sampling program. MSHA believes that exclusive

use of constant-flow pumps, as in the field study, will further enhance

the quality of the Agency's sampling program.

D. Precision of Respirable Coal Mine Dust Weighings

As part of MSHA's ongoing measurement assurance program, MSHA also

investigated the precision of weighings made to a g with

MSHA's automatic weighing system on a group of filter capsules. This

involved weighing the same unexposed filter capsules 139 times over a

218-day period. Statistical imprecision in the difference between two

consecutive weighings of the same capsule was calculated in accordance

with procedures developed by the National Bureau of Standards (NBS) for

the MSHA weighing laboratory in 1981 (`Measurement Assurance Program

for Weighings of Respirable Coal Mine Dust Samples''; Journal of

Quality Technology, 13(3):157-165, (July 1981)). Using the NBS

procedure, imprecision in the measured difference between two weighings

on different days was estimated to be 6.5 g. Since this value

includes a component of day-to-day variability, it is statistically

consistent with the 5.8 g estimate used by NIOSH in its

``indirect'' evaluation. (The 5.8 g estimate, which applies to

the standard deviation of the difference between two weighings within

the same laboratory on the same day, was derived from an analysis of

comparative weighings made on 300 unexposed cassettes. The results of

the analysis along with the data on comparative weighings were placed

into the public record on September 9, 1994.)

Moreover, the estimate of imprecision in measured weight gain

derived from the new field study discussed earlier (9.1 g),

falls only slightly above the 6.5 g laboratory estimate. This

suggests that the process of handling and actually exposing the dust

cassette in a mine environment does not add appreciably to the

imprecision in measured weight gain.

While investigating the precision of weighings made to a

g, MSHA observed that a gain in the weight of the unexposed

filter capsules had occurred over the course of the 218-day period.

Analysis of the weighing data showed that the filter capsules increased

in weight at the average rate of approximately 0.8 g per day,

beginning after approximately 30 days of unprotected exposure to the

laboratory environment. An investigation into possible causes failed to

establish the reason for the observed weight gain.

This weight gain was observed only for filter capsules that were

left completely exposed and unprotected in the laboratory environment

over an extended period of time, a situation never encountered in

actual practice. MSHA also weighed filters that were more than three

years old, which had been kept in their original cassettes with both

the inlet and outlet ports capped. These showed no evidence of weight

gain. Both MSHA and NIOSH conclude that the weight gains observed in

the 218-day laboratory investigation are irrelevant to the accuracy of

the sampling and analytical process used in MSHA's respirable coal mine

dust sampling program. This is because, in conjunction with the MSHA

respirable coal mine dust program, all dust samples analyzed by the

Pittsburgh Weighing Laboratory are processed within 24 hours after

arriving in the laboratory.

E. Documentation

Documentation of the analyses conducted by MSHA and NIOSH, as well

as the field data used to derive the new estimates of measurement

imprecision, are available from the MSHA Office of Standards,

Regulations, and Variances. The Agencies are publishing this notice to

re-open the record and to seek public comment on this new information.

III. Request for Comments

The Agencies specifically request comments on the following:

1. The use of the NIOSH Accuracy Criterion as the basis for

finding that a single, full-shift measurement will accurately represent

the respirable dust concentration to which a miner is exposed during

such shift; and

2. The experimental field data, which NIOSH has concluded

demonstrate that MSHA's sampling and analytical method meets the NIOSH

Accuracy Criterion at dust concentrations of 0.2 mg/m\3\ and above.

Dated: March 6, 1996.

J. Davitt McAteer,

Assistant Secretary for Mine Safety and Health.

Dated: March 6, 1996.

Linda Rosenstock,

Director, National Institute for Occupational Safety and Health.

[FR Doc. 96-5829 Filed 3-7-96; 4:12 pm]

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