[Federal Register Volume 61, Number 49 (Tuesday, March 12, 1996)]
[Notices]
[Pages 10012-10014]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-5829]



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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

[[Page 10013]]
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

[[Page 10014]]
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]
BILLING CODE 4510-43-P