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Mine Shift Atmospheric Conditions; Respirable Dust Sample [03/12/96]

Volume 61, Number 49, Page 10012-10014

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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 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 (<greek-m>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 <greek-m>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/m3 to about 4.3 percent at concentrations greater than 2.0 mg/m3. These results apply to dust samples collected using pumps with flow control technology and filter capsules weighed to the nearest <greek-m>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 indirectapproach. 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/m3. 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/m3.

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 <greek-m>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/m3.

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 <greek-m>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 <greek-m>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 <greek-m>g. Since this value includes a component of day-to-day variability, it is statistically consistent with the 5.8 <greek-m>g estimate used by NIOSH in its ``indirect'' evaluation. (The 5.8 <greek-m>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 <greek-m>g), falls only slightly above the 6.5 <greek-m>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 <greek-m>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 <greek-m>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/m3 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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