[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]
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