Mine Safety and Health Administration (MSHA), Labor, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Department of Health and Human Services (DHHS).
Proposed rule; notice of hearings.
This proposal announces that the Secretary of Labor and the Secretary of Health and Human Services (the Secretaries) would find in accordance with sections 101 (30 U.S.C. 811) and 202(f)(2) (30 U.S.C. 842(f)(2)) 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. The Secretaries are proposing to rescind a previous 1972 finding, by the Secretary of the Interior and the Secretary of Health, Education, and Welfare, on the validity of such single-shift sampling. Today's proposal addresses the final decision and order in
The Agencies are also announcing that they will hold public hearings on the joint proposed rule within 45 to 60 days of its publication. The hearings will be held in the following locations: Prestonsburg, Kentucky (Jenny Wiley State Park); Morgantown, West Virginia; and Salt Lake City, Utah.
Comments concerning this proposed rule should be submitted on or before August 7, 2000.
The hearing dates, times and specific locations will be announced by a separate document in the
You may use mail, facsimile (fax), or electronic mail to send your comments to MSHA. Clearly identify comments as such and send them—(1) By mail to Carol J. Jones, Director, Office of Standards, Regulations, and Variances, MSHA, 4015 Wilson Boulevard, Room 631, Arlington, VA 22203;
(2) By fax to MSHA, Office of Standards, Regulations, and Variances, 703–235–5551; or
(3) By electronic mail to comments@msha.gov.
Carol J. Jones, Director, Office of Standards, Regulations and Variances; MSHA; 703–235–1910. Copies of this proposed rule in alternative formats may be obtained by calling (703) 235–1910. The alternative formats available are large print, electronic file on computer disk, and audiotape. The proposed rule is also available on the Internet at http://www.msha.gov.
In accordance with sections 101 and 202(f) of the Mine Act (30 U.S.C. 811 and 842(f)), this proposed mandatory standard is published jointly by the Secretaries of the Departments of Labor, and Health and Human Services.
The preamble to this proposed rule on the accuracy of single shift exposure measurements discusses events leading to the proposed rule, health effects of exposure to respirable coal mine dust, degree and significance of the reduction in the number of shifts during which there are overexposures, an analysis of the technological and economical feasibility of this proposed rule, and regulatory impact and regulatory flexibility analyses.
The preamble discussion follows this outline:
For as long as miners have taken coal from the ground, many have suffered respiratory problems due to their occupational exposures to respirable coal mine dust. These respiratory problems, range from mild impairment of respiratory function to more severe diseases, such as silicosis and progressive massive fibrosis (PMF). For some miners, the impairment of their respiratory systems is so severe, they die prematurely. There is a clear dose-response relationship between miners' cumulative exposures (
The Federal Coal Mine Health and Safety Act of 1969 (Coal Act) established the first comprehensive dust standard for underground U.S. coal mines by setting a limit of 2.0 milligrams of respirable coal mine dust per cubic meter of air (mg/m
The Coal Act was subsequently amended by the Federal Mine Safety and Health Act of 1977 (Mine Act), 30 U.S.C. 801
Today, dust levels in underground U.S. coal mines are significantly lower than they were when the Coal Act was passed. Federal mine inspector sampling results during 1968–1969 showed that the average dust concentration in the environment of a continuous miner operator was 7.7 mg/m
The Secretary of Labor and the Secretary of Health and Human Services believe that miners' health can be further protected from the debilitating effects of occupational respiratory disease by limiting their exposures to respirable coal mine dust exceeding the applicable standards. MSHA's improved program to eliminate overexposures on each and every shift includes multiple rulemakings. Through this proposal, MSHA would be able to use single, full-shift respirable coal mine dust samples to more effectively identify overexposures and address them. Other overexposures to respirable coal mine dust would be prevented through finalizing a proposed rule that would require each underground coal mine operator to have a verified mine ventilation plan. MSHA would verify the effectiveness of the mine ventilation plan for each mechanized mining unit (MMU) to controlling respirable dust under typical mining conditions. Furthermore, that proposal would revoke underground operator compliance and abatement sampling. Consequently in underground coal mines, MSHA intends to increase the number of compliance inspections per year, and MSHA would conduct abatement sampling for non-compliance determinations. The notice of proposed rulemaking to promulgate new regulations to require operators to have a verified ventilation plan in underground coal mines is published elsewhere in today's
The issues related to this notice of proposed rulemaking are complex and highly technical. The Agencies have organized this proposal to allow interested persons to first consider pertinent introductory material on the Agencies' 1972 notice and its 1999 recission, and a short overview of the NIOSH mission and assessment of this proposal, as well as those aspects of MSHA's coal mine respirable dust program relevant to this proposal. Following this introductory material is a discussion of the “measurement objective,” or what the Secretaries intend to measure with a single, full-shift measurement, and the use of the NIOSH Accuracy Criterion for determining whether a single, full-shift measurement will “accurately represent” the full-shift atmospheric dust concentration. Next, the validity of
The proposed rule is consistent with Executive Order 12866, the Regulatory Flexibility Act, the Small Business Regulatory Enforcement Fairness Act (SBREFA), the National Environmental Policy Act (NEPA), the Paperwork Reduction Act, the Unfunded Mandates Reform Act, and the Mine Act.
In 1971, the Secretary of the Interior and the Secretary of Health, Education, and Welfare proposed, and in 1972 issued, a joint finding under the Coal Act. The finding concluded that a single, full-shift measurement of respirable dust would not, after applying valid statistical techniques, accurately represent the atmospheric conditions to which the miner is continuously exposed. For the reasons that follow, the Secretaries believe that the 1972 joint finding was incorrect.
Section 202(b)(2) of the Coal Act provided that “each operator shall continuously maintain the average concentration of respirable dust in the mine atmosphere during each shift to which each miner in the active workings of such mine is exposed at or below the applicable respirable dust standard.” In addition, the term “average concentration” was defined in section 202(f) of the Coal Act as follows:
* * * the term “average concentration” means a determination which accurately represents the atmospheric conditions with regard to respirable dust to which each miner in the active workings of a mine is exposed (1) as measured during an 18 month period following the date of enactment of this Act, over a number of continuous production shifts to be determined by the Secretary of the Interior and the Secretary of Health, Education and Welfare, and (2) as measured thereafter, over a single shift only, unless the Secretary of the Interior and the Secretary of Health, Education and Welfare find, in accordance with the provisions of section 101 of this Act, that such single shift measurements will not, after applying valid statistical techniques to such measurement, accurately represent such atmospheric conditions during such shift.
Therefore, 18 months after the statute was enacted, the “average concentration” of respirable dust in coal mines was to be measured over a single shift only, unless the Secretaries found that doing so would not accurately represent mine atmospheric conditions during such shift. If the Secretaries found that a single shift measurement would not, after applying valid statistical techniques, accurately represent mine atmospheric conditions during such shift, then the interim practice of averaging measurements “over a number of continuous production shifts” was to continue.
On December 16, 1969, the U.S. Congress published a Conference Report in support of the new Coal Act. The Report refers to section 202(f) by noting that:
At the end of this 18 month period, it requires that the measurements be over one production shift only, unless the Secretar[ies] * * * find, in accordance with the standard setting procedures of section 101, that single shift measurements will not accurately represent the atmospheric conditions during the measured shift to which the miner is continuously exposed (Conference Report, page 75).
This Report is inconsistent with the wording of the section 202(f), which seeks to apply a single, full-shift measurement to “accurately represent such atmospheric conditions during such shift.” Section 202(f) does not mention continuous exposure. The Secretaries believe that the use of this phrase, “continuously exposed”, is confusing, and to the extent that any weight of interpretation can be given to the legislative history, that the Senate's Report of its bill provides a clearer interpretation of section 202(f) when read together with the statutory language. The Senate Committee noted in part that:
The committee * * * intends that the dust level not exceed the specified standard during any shift. It is the committee's intention that the average dust level at any job, for any miner in any active working place during each and every shift, shall be no greater than the standard. [Standard = 2 mg/m
Following passage of the Coal Act, the Bureau of Mines (MSHA's predecessor Agency within the Department of the Interior) expressed a preference for multi-shift sampling. Correspondence exchanged during that time period of 1969 to 1971 reflected concern over the technological feasibility of controlling dust levels to the limits established, and the potentially disruptive effects of mine closure orders because of noncompliance with the respirable dust limits. Both industry and government officials feared that basing noncompliance determinations on single, full-shift measurements would increase those problems. In June 1971, the then-Associate Solicitor for Mine Safety and Health at the Department of the Interior issued a legal interpretation of section 202(f), concluding that the average dust concentration was to be determined by measurements that accurately represent respirable dust in the mine atmosphere over time rather than during a shift. On July 17, 1971, the Secretaries of the Interior and of Health, Education, and Welfare issued a proposed notice of finding under section 202(f) of the Coal Act. The finding concluded that, “a single shift measurement of respirable dust will not, after applying valid statistical techniques to such measurement, accurately represent the atmospheric conditions to which the miner is continuously exposed” (36 FR 13286).
In February, 1972, the final finding was issued (37 FR 3833). It concluded that:
After careful consideration of all comments, suggestions, and objections, it is the conclusion of the Secretary of the Interior and the Secretary of Health, Education, and Welfare that a valid statistical technique was employed in the computer analysis of the data referred to in the proposed notice [footnote omitted] and that the data utilized was accurate and supported the proposed finding. Both Departments also intend periodically to review this finding as new technology develops and as new dust sampling data becomes available.
The Departments intend to revise part 70 of title 30, Code of Federal Regulations, to improve dust measuring techniques in order to ascertain more precisely the dust exposure of miners. To complement the present system of averaging dust measurements, it is anticipated that the proposed revision would use a measurement over a single shift to determine compliance with respirable dust standards taking into account (1) The variation of dust and instrument conditions inherent in coal mining operations, (2) the quality control tolerance allowed in the manufacture of personal sampler capsules, and (3) the variation in weighing precision allowed in the Bureau of Mines laboratory in Pittsburgh.
The proposed finding, as set forth at 36 FR 13286, that a measurement of respirable dust over a single shift only, will not, after applying valid statistical techniques to such measurement, accurately represent the
As explained in the 1971 proposed finding, the average concentration of all ten full-shift samples (from one occupation) submitted from each working section under the regulations in effect at the time (these were the “basic samples” referred to in the proposed notice of finding) was compared with the average concentration of the two most recently submitted samples, then to the three most recently submitted samples, then to the four most recently submitted samples, etc. In discussing the results of these comparisons, the Secretaries stated that “* * * the average of the two most recently submitted samples of respirable dust was statistically equivalent to the average concentration of the current basic samples for each working section in only 9.6 percent of the comparisons.”
The title of the 1971/1972 notice and the conclusion it reaches are clearly inconsistent. The title states that it is a “Notice of Finding That Single Shift Measurements of Respirable Dust Will Not Accurately Represent Atmospheric Conditions During Such Shift.” However, the conclusion states that, “* * * a single shift measurement * * * will not, after applying valid statistical techniques * * * accurately represent the atmospheric conditions to which the miner is
The Secretaries have determined that section 202(f) would require a determination of accuracy with respect to “atmospheric conditions during such shift,” not “atmospheric conditions
The National Institute for Occupational Safety and Health (NIOSH) was created by Congress in the Occupational Safety and Health Act in 1970. The Act established NIOSH as part of the Department of Health, Education, and Welfare (currently NIOSH is a part of the Department of Health and Human Services) to identify the causes of work-related diseases and injuries, evaluate the hazards of new technologies, create new ways to control hazards to protect workers, and make recommendations for new occupational safety and health standards. Under section 501 of the Mine Act (30 U.S.C. 951), Congress gave specific research responsibilities to NIOSH in the field of coal and other mine health. These responsibilities include the authority to conduct studies, research, experiments and demonstrations, in order “to develop new or improved means and methods of reducing concentrations of respirable dust in the mine atmosphere of active workings of the coal or other mine,” and also “to develop techniques for the prevention and control of occupational diseases of miners * * *”
When the initial finding, issued under section 202(f) of the Coal Act, was published in 1972, both the Secretary of the Interior and the Secretary of Health, Education, and Welfare (the predecessor to the Department of Health and Human Services) indicated that the finding would be reassessed as new technology was developed, or new data became available. The Secretary of Health and Human Services, through delegated authority to NIOSH, has reconsidered the provisions of section 202(f) of the Mine Act (30 U.S.C. 842(f)), reviewed the current state of technology and other scientific advances since 1972, and has determined that the following innovations and technological advancements are important factors in the reassessment of the 1971/1972 joint finding.
In 1977, NIOSH published its “Sampling Strategies Manual,” which provided a framework for the statistical treatment of occupational exposure data (DHEW (NIOSH) Publication No. 77–173; Sec. 4.2.1). Additionally, that year, NIOSH first published the NIOSH Accuracy Criterion, which was developed as a goal for methods to be used by OSHA for compliance determinations (DHEW (NIOSH) Publication No. 77–185; pp. 1–5). In 1980, new mine health standards issued by the Secretary of Labor (30 CFR parts 70, 71, and 90) improved the quality of the sampling process by revising sampling, maintenance, and calibration procedures. Through the mid-nineteen-eighties, MSHA continued to refine and improve its sampling process. In 1984, a fully-automated, robotic weighing system was introduced along with state-of-the-art electronic microbalances. Prior to 1984, filter capsules used in sampling were manually weighed by MSHA personnel using semi-micro balances, making precision weights to the nearest 0.1 mg (100 micrograms). In 1994, the balances were further upgraded, and in 1995 the weighing system was again improved, increasing weighing sensitivity to the microgram level. Also, in 1987, electronic flow-control sampling pump technology was introduced in the coal mine dust sampling program with the use of Mine Safety Appliances FlowLite
With the enactment of the Mine Act, Congress recognized that “the first priority and concern of all in the coal or other mining industry must be the health and safety of its most precious resource—the miner.” Congress further realized that there “is an urgent need to provide more effective means and measures for improving the working conditions and practices in the Nation's coal or other mines in order to prevent death and serious physical harm, and in order to prevent occupational diseases originating in such mines.” With these goals in mind, MSHA is given the responsibility to protect the health and safety of the Nation's coal and other miners by enforcing the provisions of the Mine Act.
In 1970, federal regulations were issued by MSHA's predecessor agency that established a comprehensive coal mine operator dust sampling program for underground mines. The program required the environment of the occupation on a working section exposed to the highest respirable dust concentration to be sampled—the “high risk occupation” concept. All other occupations on the section were assumed to be protected if the high risk occupation was in compliance. Under this program, each operator was required to initially collect and submit ten valid respirable dust samples to determine the average dust concentration across ten production shifts. If the analysis showed the average dust concentration to be within the applicable dust standard, the operator was required to submit only five valid samples a month. If compliance continued to be demonstrated, the operator was required to take only five valid samples every other month. The initial, monthly, and bimonthly sampling cycles were referred to as the “original,” “standard,” and “alternative sampling” cycles, respectively. When the average dust concentration exceeded the applicable standard, the operator reverted back to the standard monthly sampling cycle.
In addition to sampling the high risk occupation at specified frequencies, each miner was sampled individually at different intervals. However, these early individual sample results were not used for enforcement but were provided to NIOSH for medical research purposes. Also required to be sampled every 90 days in underground mines, beginning in 1971, and in surface mines, beginning in 1974, were individuals who had evidence of the development of pneumoconiosis and exercised their option to transfer to a low dust area.
Federal regulations establishing a comprehensive operator dust sampling program for surface coal mines were issued in 1972. Under this program, each miner was sampled initially prior to July 1, 1972, and then either semiannually, if the initial sample exceeded 1.0 mg/m
MSHA revised these regulations in April 1980 (45 FR 23990) to reduce the operator sampling burden, to simplify the sampling process, and to enhance the overall quality of the sampling program. The result was to replace the various sampling cycles in effect in underground and surface coal mines with a bimonthly sampling cycle and to eliminate the requirement that each miner be sampled. Unlike the underground sampling requirements, operators of surface coal mines were required to sample bimonthly only after a “designated work position” (DWP) was established by MSHA. Once established, only one sample is required to be collected each bimonthly period. Under the revised regulations, MSHA could also withdraw the designation of work positions for sampling if samples taken by the operator and by MSHA demonstrated continuing compliance with the applicable dust standard. These are the regulations that currently govern the mine operator dust sampling program at both underground and surface coal mines, and which, in the case of underground mines, continue to be based on the high risk occupation concept, now referred to as the “designated occupation” or “D.O.” sampling concept.
It should be noted that the April 1980 preamble to the final rule, amending the regulations for underground coal mines, explicitly refers to the use of single versus multiple samples as it applies to the operator respirable dust sampling program (45 FR 23997):
Compliance determinations will generally be based on the average concentration of respirable dust measured by five valid respirable dust samples taken by the operator during five consecutive shifts, or five shifts worked on consecutive days. Therefore, the sampling results upon which compliance determinations are made will more accurately represent the dust in the mine atmosphere than would the results of only a single sample taken on a single shift. In addition, MSHA believes the revised sampling and maintenance and calibration procedures prescribed by the final rule will significantly improve the accuracy of sampling results.
At the time of these amendments, MSHA examined section 202(b)(2) of the Coal Act, which was retained unchanged in the 1977 Mine Act. The Agency stated in the preamble to the final rule that:
Although single-[full] shift respirable dust sampling would be most compatible with this single-shift standard, Congress recognized that variability in sampling results could render single-shift samples insufficient for compliance determinations. Consequently, Congress defined “average concentration” in section 202(f) of the 1969 Coal Act which is also retained in the 1977 Act.
MSHA believes that this interpretation merely recognized the two ways of measurement authorized in section 202(f), and expressed the preference on the part of MSHA in 1980 to retain multi-shift sampling in the operator sampling program. The phrase used in the preamble to the final rule reflects that MSHA understood that the 2.0 mg/m
“It had been determined after applying valid statistical techniques, * * * that a single shift sample should not be relied upon for compliance determinations when the respirable dust concentration being measured was near 2.0 mg/m
The preamble provides no further explanation for the statement that single-shift samples should not be relied on when the respirable dust concentration being measured was near 2.0 mg/m
MSHA continues to take an active role in sampling for respirable dust and has recently expanded its sampling to more than once annually at each surface and underground coal mine. During these inspections, MSHA inspectors collect samples on multiple occupations to determine whether miners are being overexposed to respirable coal mine dust; to assess the effectiveness of the operator's dust control program; to quantify the level of respirable crystalline silica (quartz) in the work environment and whether there is a need to adjust the applicable dust standard; and to identify occupations in underground mines, other than the “D.O.”, and occupations in surface mines, that are at risk of being overexposed and should be routinely monitored by the mine operator.
Depending on the concentration of respirable coal mine dust measured, an MSHA inspector may terminate sampling after the first day if levels are very low, or continue for up to five shifts or days before making a compliance or noncompliance determination. For example, MSHA inspection procedures require inspectors to sample at least five occupations, if available, on each mechanized mining unit (MMU) on the
In response to concerns about possible tampering with dust samples in 1991, MSHA convened the Coal Mine Respirable Dust Task Group (Task Group) to review the Agency's respirable dust program. The Task Group was directed to consider all aspects of the current program in its review, 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 part of the Task Group review, MSHA developed a special respirable dust “spot inspection program” (SIP).
This program was designed to provide the Agency with information on the dust levels to which underground miners are typically exposed. Because of the large number of mines and MMUs (mechanized mining units) involved and the need to obtain data within a short time frame, respirable dust sampling during the SIP was limited to a single shift or day, a departure from MSHA's normal sampling procedures. 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. As a result, MSHA decided 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 individual full-shift sample. If any individual full-shift 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 in the mine atmosphere in order to protect miners.
During the SIP inspections, MSHA inspectors cited violations of the 2.0 mg/m
The procedures issued by MSHA's Coal Mine Safety and Health Division during the SIP were similar to those used by the MSHA Metal/Nonmetal Mine Safety and Health Division and the Occupational Safety and Health Administration (OSHA) when determining whether to cite based on a single, full-shift measurement. That practice provides for a margin of error reflecting an adjustment for uncertainty in the measurement process (
Based on the data from the SIP inspections, the Task Group concluded that MSHA's practice of making noncompliance determinations solely on the average of multiple-sample results did not always result in citations in situations where miners were known to be overexposed to respirable coal mine dust. For example, if measurements obtained for five different occupations within the same MMU were 4.1, 1.0, 1.0, 2.5, and 1.4 mg/m
Thus, 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.
The Task Group also recognized that the results of the first full-shift samples taken by an inspector during a respirable dust inspection are likely to reflect higher dust concentrations than samples collected on subsequent shifts or days during the same inspection. MSHA's comparison of the average dust concentration of inspector samples taken on the same occupation on both the first and second day of a multiple-day sampling inspection showed that the average concentration of all samples taken on the first day of an inspection was almost twice as high as the average concentration of samples taken on the second day. MSHA recognized that sampling on successive days does not always result in measurements that are representative of everyday respirable dust exposures in the mine because mine operators can anticipate the continuation of inspector sampling and make adjustments in dust control parameters or production rates to lower dust levels during the subsequent sampling.
In response to these findings, in November 1991, MSHA decided to permanently adopt the single, full-shift inspection policy initiated during the SIP for all mining types.
In 1991, three citations based on single, full-shift measurements were issued under the SIP to the Keystone Coal Mining Corporation. The violations were contested, and an administrative law judge from the Federal Mine Safety and Health Review Commission (Commission) vacated the citations. The decision was appealed by the Secretary of Labor to the Commission because the Secretary believed that the administrative law judge was in error in
Title II [of the Mine Act] applies to both operator sampling and to MSHA actions to ensure compliance, including sampling by MSHA. Section 202(g) specifically provides for MSHA spot inspections. Nothing in § 202(f) or § 202(g) suggests that § 202(f) applies differently to MSHA sampling. Thus, the 1971 finding, issued for purposes of title II, applies broadly to both MSHA and operator sampling of the mine atmosphere.
The Commission also held that the revised MSHA policy was in contravention of the 1971/1972 finding and could only be altered if the requirements of the Mine Act and the Administrative Procedure Act, 5 U.S.C. 550, were met. Through this proposed notice of rulemaking, MSHA is now attempting to meet those requirements.
On February 3, 1998, MSHA published a corrected notice in the
Under the ISSEP, MSHA followed its existing dust sampling procedures in regard to where and how many samples an inspector collects during a sampling shift at underground and surface coal mines. While the Agency continued its practice of collecting multiple occupational samples at each MMU, the minimum number of occupations monitored was reduced from five to three, focusing only on those occupations at high risk of being overexposed. As part of the ISSEP, inspectors carried with them a control filter when conducting respirable dust sampling. This control filter, which was unexposed, was used to adjust the weight gain obtained on each of the exposed filters. Any change in weight of the unexposed control filter was subtracted from the change in weight of each exposed filter. For the exposed filter to be valid, the control and exposed filter must have been both pre-and post-weighed on the same days. If the control filter was either missing or invalid, the measurement(s) were not used for enforcement purposes and the entity type (
When a single, full-shift measurement exceeded the applicable standard but was less than the CTV, a citation was not to be issued since noncompliance was not demonstrated at a sufficiently high confidence level. Instead, the MMU or other entity type sampled was to be targeted for additional sampling to verify the adequacy of the operator's dust control measures to maintain compliance, with special emphasis directed toward working environments with applicable standards below 2.0 mg/m
The process by which a violation of the applicable standard was to be abated by a mine operator remained unchanged. That is, an operator must first take corrective action to reduce the average dust concentration to within the permissible level, and then sample each production or normal work shift until five valid respirable dust samples are taken. MSHA considers a violation to be abated when the average dust concentration measured by these five valid samples was at or below the applicable standard. Under the ISSEP, MSHA inspectors sampled 1,662 MMUs and other entity types, such as roof bolter DAs and Part 90 miners, in underground mines; and some 860 DWPs and over 3,700 nondesignated work positions at surface mining operations. The Agency issued a total of 309 excessive dust citations based on the results of single, full-shift samples, involving 182 MMUs and 113 other underground entity types, and 14 surface work positions. Of the 1,662 MMUs sampled, 182 or 11 percent were cited, compared to the 27 percent MSHA had projected based on inspector sampling results for 1995. Also, it is important to point out that only 14 of the over 4,500 surface entities sampled were found to be out of compliance. These sampling inspections, which showed a significant decline in the number of cited instances of noncompliance compared to previous experience under the SIP and the earlier projections documented in the 1998 notices, reveal that mine operators are capable of maintaining dust concentrations at or below the applicable standard on every shift.
On February 18, 1994, the Secretary of Labor and the Secretary of Health and Human Services published a proposed
After a notice and comment procedure extending over some three and one-half years, which also included three public hearings, the Agencies published a final corrected notice of finding in the
The National Mining Association (NMA) along with the Alabama Coal Association petitioned the United States Court of Appeals for the 11th Circuit to review the 1998 Notice of Finding (Joint Finding) issued by the Mine Safety and Health Administration (MSHA) and the National Institute for Occupational Safety and Health (NIOSH), and additionally asked for an emergency motion for stay of the Joint Finding pending review. The motion for an emergency stay was denied by the Court.
On appeal NMA argued, among other things, that the agency had not met the requirements of section 101(a)(6)(A) of the Federal Mine Safety and Health Act of 1977 (Mine Act) (30 U.S.C. 811(a)(6)(A)) because it failed to address material impairment of health and economic and technological feasibility. MSHA and the Department of Labor responded that the agencies addressed the positive effect of the notice on miner health, and also concluded in the course of performing the analysis required under the Regulatory Flexibility Act that the economic impact of the Joint Finding was not significant. On September 4, 1998, the United States Court of Appeals for the 11th Circuit issued a decision in the case of
MSHA and NIOSH understand the Court's ruling as requiring the Agencies to comply with all requirements under section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)). Therefore, in response to the Court's ruling, the Secretaries are proposing today to add a new mandatory health standard to 30 CFR part 72. Pursuant to section 202(f) of the Mine Act (30 U.S.C. 842(f)), the 1972 joint notice of finding would be rescinded and a new finding would be made that a single, full-shift measurement will accurately represent atmospheric conditions to which a miner is exposed during such shift. This finding is the basis for the new proposed mandatory health standard.
The Secretaries believe that single, full-shift measurements must be implemented into the MSHA coal mine respirable dust program as quickly as possible in order to better protect miners' health. Therefore, in order to speed the process of reproposing this critical measurement technique, the Secretaries are incorporating the record of the previous 1998 Joint Finding into the record for this proposal and adding appropriate new data and information to support this rulemaking under section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)). The Secretaries have used as much of the original wording as possible from the vacated final finding in this notice of proposed rulemaking. References to previous comments and commenters in the body of this proposal are meant to apply to previous comments received in response to the earlier proposed Joint Finding that was ultimately vacated by the U.S. Court of Appeals for the 11th Circuit.
Since the 1800s, occupational respiratory disease associated with working in a coal mine has been commonly referred to as “Black Lung.” As coal is mined, respirable-sized dust is generated. Depending upon the mine location and its geologic features, silica may also be present in the mine atmosphere. Dust in air that is breathed by miners has the potential to be deposited in their lungs. Some of this dust may be retained. Coal mine dust remaining in the lungs of miners for prolonged periods of time has the potential to result in respiratory diseases, sometimes even after occupational exposure to respirable coal mine dust has stopped. There is a clear and direct relationship between miners' cumulative exposures (
Diseases resulting from long-term retention of coal mine dust in the lung include chronic coal workers' pneumoconiosis (simple CWP), progressive massive fibrosis (PMF), silicosis, and chronic obstructive pulmonary disease (COPD) (
Miners with simple CWP have a substantially increased risk of developing PMF. In the advanced stages of pneumoconiosis (
Factors that are important in the development of simple CWP, PMF and COPD include the type of dust (
In 1998, MSHA estimated that approximately 45,000 miners and
There are complementary data sources, described below, which provide estimates of the prevalence of occupational respiratory disease among coal miners. Together these data demonstrate the progress over the last thirty years in the reduction of occupational respiratory disease among coal miners, as well as the need for further action to reduce occupational lung disease among today's coal miners.
Estimates of the prevalence of simple CWP and PMF among the underground coal miners are gathered from the x-ray program, through which operators are required to provide miners the opportunity to be evaluated periodically for the presence of occupational lung disease, mandated pursuant to Section 203(a) of the Mine Act (30 U.S.C. 843(a)). However, miners are not required to participate. From 1970 to 1995,the prevalence of simple CWP and PMF among miners participating in the mandated x-ray program has dropped from 11 percent to 3 percent (MSHA, Internal Chart, 1998).
In accordance with 30 CFR part 50, those cases of occupational illnesses which both surface and underground coal mine operators learn of must be reported to MSHA. Under this requirement, mine operators reported 224 cases of pneumoconiosis (simple CWP and PMF, combined) in 1998 (Mattos, 1999). Of these, 138 cases occurred among coal miners who worked underground, while the remaining 86 cases occurred among surface coal miners (Mattos, 1999). There were also 14 cases of silicosis, eight in underground mines, reported to MSHA in 1998 in accordance with 30 CFR part 50 (Mattos, 1999). Since miners participate in both these programs at their own discretion, these data do not include the occupational health experience of all coal miners. The prevalence of occupational lung disease among participating miners may significantly differ from the prevalence among non-participants. Thus, the data from these programs may not be representative of the true magnitude of the prevalence of simple CWP and PMF among today's coal miners.
In the 1990s, MSHA conducted a series of one-time medical surveillance programs, in various regions of the country, to develop a more accurate estimate of the prevalence of simple CWP and PMF. Through these special programs, MSHA tried to minimize obstacles which may prevent some miners from either participating in or reporting to operators the results of respiratory diagnostic procedures. Nine geographical cohorts of miners, from around the country, were encouraged to participate in an independent x-ray program (MSHA, Internal Chart, 1999). These cohorts included eight active surface coal mining communities in the states of Pennsylvania, Kentucky and West Virginia, as well as the towns of Poteau, Oklahoma and Gillette, Wyoming. A ninth cohort included underground miners in Kentucky. The process was designed to encourage miner participation by providing for a greater degree of anonymity than may be available under the program provided by Section 203(a) of the Mine Act (30 U.S.C. 843(a)). Across the eight surface cohorts surveyed, the prevalence rate of simple CWP and PMF combined, among participants was 4.8%. The prevalence rate among the participating underground Kentucky miners was 9.2%.
Also, as part of its ongoing effort to “end black lung now and forever,” beginning in October 1999, MSHA implemented a pilot program to provide miners at both surface and underground mines with confidential health screening. Referred to as the “Miners’ Choice Health Screening”, the program addresses the key recommendations of the Secretary's Advisory Committee by (1) increasing participation toward the 85-percent level and (2) expanding the scope of the eligibility to include surface coal miners and surface coal mine independent contractors. The pilot program will operate separately from the existing Coal Workers' X-ray Surveillance Program administered by NIOSH. Since the Miners' Choice Health Screenings' inception, over 7,000 miners have been screened, with the participation rate in most areas exceeding 50 percent. With half of the x-rays taken during the first six months having been processed by NIOSH, preliminary results indicate a prevalence rate of approximately 2.25 percent.
The National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA) are concerned about the prevalence of occupational lung disease among today's miners. Epidemiological studies from the U.S. and abroad have consistently shown that underground and surface coal miners are at risk of developing simple CWP, PMF, silicosis, and chronic obstructive pulmonary disease (NIOSH Criteria Document, 1995).
Coal is a fossil fuel derived from partial degradation of vegetation. Through its combustion, energy is produced which makes coal a valuable global commodity. It has been estimated that over one-third of the world uses energy provided by coal (Manahan, 1994). Approximately 1,800 underground and surface coal mines are in operation in the United States annually producing slightly over a billion short tons of coal (Mattos, 1999).
Coal may be classified on the basis of its type, grade, and rank. The type of coal is based upon the plant material (
Aerosols are a suspension of solid or liquid particles in air (Mercer, 1973); they may be dusts which are solid particles suspended in the air. Coal dust may be freshly generated or may be re-suspended from surfaces on which it is deposited in mines. As discussed below, coal mine dust may be inhaled by miners, depending upon the particle size.
Coal mine dust is a heterogenous mixture, signifying that all coal particles do not have the same chemical composition. The particles are influenced by the type, grade, and rank of coal from which they were generated (Manahan, 1994). Irrespective of differences in coal characteristics, these dusts are water-insoluble, which is important biologically and physiologically. Unlike soluble dusts which may readily pass into the respiratory system and be cleared via the circulatory system, insoluble dusts may remain in the lungs for prolonged periods of time. Thus, a variety of cellular responses may result that could eventually lead to lung disease.
The principal route of occupational exposure to respirable coal mine dust occurs via inhalation. As a miner breathes, coal mine dust enters the nose and/or mouth and may pass into the mid airways (
Coal mine dust has a size distribution that is estimated to range between 1 and 100 micrometer (μm) (1 μm = 10
Particles that are above 10 μm are largely filtered in the nasal passages, although some of these particles may reach the thoracic (or tracheal-bronchial) region of the lung (
For the purposes of this rule, “respirable dust” is defined as dust collected with a sampling device approved by the Secretary of Labor and the Secretary of the Department of Health and Human Services (DHHS) in accordance with 30 CFR Part 74 (Coal Mine Dust Personal Sampler Units). In practice, the coal mine dust personal sampler unit has been used in the U.S. The particles collected with an approved sampler approximate that portion of the dust which may be deposited in the lung (West, 1990; 1992). It does not, however, indicate pulmonary retention (
It is also important to note that silica may be present in the coal seam, within dirt bands in the coal seam, and in rock above and below coal seams. Of the silica found in coal mines, quartz is the form which is found. Thus, quartz may become airborne during coal removal operations (Manahan, 1994). Miners may inhale dust that is a mixture of quartz and coal. MSHA is concerned with the inhalation of quartz since it may be deposited in the lungs of miners and produce silicosis. This is a restrictive lung disease which is characterized by a stiffening of the lungs (West, 1990; 1992). Silicosis has been seen in coal miners (
Respirable dust standard (mg/m
The intent of this formula is to maintain miner exposures to quartz below 0.1 mg/m
Consistently, epidemiological studies have demonstrated miners to be at risk of developing respiratory symptoms, a loss of lung function, and lung disease as a consequence of occupational exposure to respirable coal mine dust. As noted previously, risk factors include type(s) of dust, dust concentration, duration of exposure, age of the miner (often measured as age at time of medical examination), and coal rank.
In earlier stages of pneumoconiosis the term, “simple coal workers’ pneumoconiosis” (simple CWP), has been used, while in more advanced stages, the terms “complicated CWP” and PMF have been used interchangeably. Simple CWP and PMF involve the lung parenchyma and are produced by deposition and retention of respirable coal dust in the lung.
To determine if a miner has simple CWP or PMF, chest x-rays are taken and classified by a certified radiologist or reader. Opacities are identified on chest films and then classified using a scale of 0–3 (
Simple CWP can be associated with a loss of lung function and with premature mortality (Morgan,
Progressive massive fibrosis (PMF) is associated with decreased lung function
During a medical examination, a miner may be questioned by his physician about symptoms such as cough, phlegm production, chest tightness, shortness of breath, and wheezing. Occupational physicians may also conduct pulmonary function tests using spirometry or plethysmography. Pulmonary performance may be assessed via repeated measurements of lung volumes and capacities, such as the forced expiratory volume in one second (FEV
The term, chronic obstructive pulmonary disease (COPD), refers to three disease processes that are often difficult to properly diagnose and differentiate: chronic bronchitis, emphysema, and asthma (Coggon and Taylor, 1998; Garshick,
Chronic Obstructive Pulmonary Disease (COPD) is characterized by airflow limitations, and thus there is a loss of pulmonary function. As in simple CWP or PMF, a miner with COPD may have a variety of respiratory symptoms (
Briefly, in chronic bronchitis and in asthma, there is excess mucous secretion in the mid-lower airways (West, 1990; 1992). In contrast, emphysema is characterized by dilatation (enlargement) of alveoli that are distal to the terminal bronchioles, which leads to poor gas exchange (
The Mine Safety and Health Administration (MSHA) and the NIOSH recognize that respiratory symptoms, loss of lung function, and COPD may impair the ability of a miner to perform his job and may diminish his quality of life. Additionally, miners having such health effects are at increased risk of morbidity (
To better understand the human health effects of exposure to respirable coal mine dust and to more fully characterize the associated risks, it is important to consider data that have been obtained in animal based toxicological studies. To date, sub-acute studies (a study with a duration of 30 days, or less, in which multiple exposures of the same agent are given) and chronic studies (a study with a duration of more than 3-months, in which multiple exposures of the same agent are given) attempted to mimic miners' exposures. Inhalation was generally the route of exposure, although several studies have also employed instillation techniques (
Most recent toxicological studies have been short-term studies, largely focusing on “lung overload” (Snipes, 1996; Oberdorster, 1995; Morrow, 1988, 1992; Witschi, 1990), species-dependent lung responses (Nikula,
The data from Moorman,
Epidemiology studies have consistently demonstrated the serious health effects of exposure to high levels of respirable coal mine dust (
Both early and recent studies have shown that the lung is the major target organ (
Studies following Cochrane (1962) and McLintock
Attfield and Seixas (1995) have demonstrated a relationship between cumulative exposure to respirable coal mine dust and predicted prevalence of pneumoconiosis (
The recent paper of Kuempel,
The data of Attfield and Seixas (1995) and Kuempel,
Recently, Goodwin and Attfield (1998) reported that there were concerns regarding methodological inconsistencies across surveys given during the four rounds of the NSCWP. In particular, they noted the discordance in classification of simple CWP and PMF among readers of chest films. Despite potential discordance, Goodwin and Attfield (1998) have confirmed previous findings of a decline in simple CWP prevalence from 1969 to 1988. Yet, these analyses also demonstrated that simple CWP has not been eliminated. The Round 4 prevalence rates were 3.9 percent for simple CWP category 1 and higher, and 0.9 percent for category 2 and higher. This illustrates the need for continued efforts to reduce dust exposures.
Given the current system for monitoring exposures and identifying overexposures in the U.S., miners are at increased risk of developing simple CWP and PMF from a working lifetime exposure to respirable coal mine dust (Kuempel,
The Attfield and Seixas epidemiological study (1995) is the most appropriate to use in estimating the benefit of reduction of overexposures. The authors applied scientific rigor to the collection, categorization, and analyses of the radiographic evidence for the group of 3,194 underground bituminous coal miners who participated in Round 4, 1985–1988, of the National Study of Coal Workers' Pneumoconiosis (NSCWP); this study population excludes 86 miners for whom there was missing exposure data or unreadable x-rays. Radiologic evidence was carefully collected and analyzed by multiple independent, NIOSH certified B readers to identify stages of simple CWP and PMF. In the targeted population of 5,557 miners, the participating miners (3,280) were similar to the non-participants (2,277) with regard to age at the first medical examination and prevalence of simple CWP category 1 or greater. The non-participants had worked slightly longer, yet had lower prevalence of simple CWP category 2 or greater, than the participants. This study describes the differences among current miners and ex-miners (health-related or job-related) in the relationships between the estimated cumulative exposure to respirable coal mine dust and prevalence of simple CWP category 1 or greater. Such data and relationships were not available in other U.S. studies and non-U.S. studies.
A potential limitation in the U.S. studies is the possible bias in the exposure data, which has been the subject of several studies (Boden and Gold, 1984; Seixas
The most complete exposure data available are those for coal miners in the United Kingdom (Hurley,
Bourgkard,
Love,
These investigators found a doubling in the relative risk of developing profusion of simple CWP category 0/1 for every 10 years of work in the dustiest jobs in surface mines. These respirable coal dust exposures were under 1 mg/m
Meijers,
Morfeld,
Starzynski,
Yi and Zhang (1996) conducted a study to measure the progression from simple CWP to PMF or death among a cohort of 2,738 miners with simple CWP who were employed at the Huai-Bei coal mine in China. Relative risks (
Hurley and Maclaren (1987) studied British coal miners who were examined between 1953 and 1978, over 5-year intervals. They have shown that exposure to respirable coal dust increases the risks of developing simple CWP and of progressing to PMF. As seen in their data analysis, these responses were dependent upon dust concentration and coal rank. That is, greater responses were seen at higher dust concentrations and with higher rank coal (
As noted in Table VII–1, there were 16 studies in which the loss of lung function (LLF) was examined in coal miners. Six of these studies also included an evaluation of respiratory symptoms (RS) in the miners. There were five studies describing chronic obstructive pulmonary disease (COPD) in miners.
Henneberger and Attfield (1997; 1996), Kuempel,
Attfield and Hodous (1992) studied U.S. miners who had spent 18 years underground (on average) and who participated in Round 1 (1969–1971) of the NSCWP. They observed that greater reductions in pulmonary function were associated with exposure to higher ranks of coal (
Seixas,
The U.S. findings on respiratory symptoms and loss of lung function in miners have agreed with those of previous British studies by Marine,
Soutar and Hurley (1986) examined the relationship between dust exposure and lung function in British coal miners and ex-miners. The men who were studied were employed in coal mines in the 1950s and were followed up and examined 22 years later. These miners and ex-miners were categorized as smokers, ex-smokers, or nonsmokers. The Forced Expiratory Volume in one second (FEV
Recent studies from China (Wang,
Wang,
As noted above, Bourgkard,
Carta,
Lewis,
There have been two recent mortality studies that have demonstrated a relationship between exposure to respirable coal mine dust and development of COPD. This association was reported by Kuempel,
Kuempel,
Meijers,
As mentioned previously, in addition to this proposed notice of rulemaking, today's
Having reviewed the reported health effects associated with exposure to coal mine dust, MSHA and NIOSH have evaluated the evidence to determine whether the current regulatory strategy can be improved. The criteria for this evaluation is established by the Mine Act under section 101(a)(6)(A) [30 U.S.C. 811(a)(6)(A)] which provides that:
The Secretary, in promulgating mandatory standards dealing with toxic materials or harmful physical agents under this subsection, shall set standards which most adequately assure on the basis of the best available evidence that no miner will suffer material impairment of health or functional capacity even if such miner has regular exposure to the hazards dealt with by such standard for the period of his working life.
Based on Court interpretations of similar language under the Occupational Safety and Health Act, there are three questions that must be addressed: (1) Whether health effects associated with the current pattern of overexposures on individual shifts constitute a material impairment to miner health or functional capacity; (2) whether the current pattern of overexposures on individual shifts places miners at a significant risk of incurring any of these material impairments; and (3) whether the proposed rules would substantially reduce those risks.
The criteria for evaluating the health effects evidence do not require scientific certainty. The need to evaluate risk does not mean that an agency is placed into a “mathematical straightjacket.”
As explained earlier, MSHA's objective in strengthening the requirements for verifying the effectiveness of dust control plans, and in enforcing effective plans through the new enforcement policy proposed in this notice, is to ensure that no miner is exposed to an excessive concentration (
Based on 1999 operator data, there were 704 MMUs (out of 1,251 total) at which dust concentrations for the designated occupation (D.O.) samples exceeded the applicable standard on at least two of the sampling shifts (MSHA, Data file:Operator.ZIP).
These results are based on a large number of shifts (an average of more than 26 at each of the 704 MMUs). Therefore, assuming representative operating conditions on these shifts, the results can be extrapolated to all production shifts, including those that were not sampled, at these same 704 MMUs. With 95-percent confidence, the overall percentage of production shifts on which the D.O. sample exceeded the standard was between 20.6 percent and 22.2 percent for 1999. At the same confidence level, again assuming representative operating conditions, the overall mean excess on noncompliant shifts at these MMUs was between 0.96 mg/m\3\ and 1.12 mg/m\3\. If operators tend to reduce production and/or increase dust controls on sampled shifts, as some commenters to the previous single, full-shift sample rulemaking and the Dust Committee have alleged, then the true values could be higher than even the upper endpoints of these 99-percent confidence intervals.
In 1998, MSHA attempted to enforce compliance on individual shifts. Therefore, to compare the 1999 pattern
Although MSHA found minor differences between individual years, there was no statistically significant upward or downward trend in any of these three parameters over the 1990–1997 time period (see Table VIII–1). In 1999, the percentage of MMUs exhibiting a pattern of recurrent overexposures (Parameter #1) was approximately 56 percent. Also in 1999, for those MMUs exhibiting a pattern of recurrent overexposures, the overall percentage of production shifts on which the D.O. was overexposed (Parameter #2) was approximately 21 percent. In 1999, the average excess above the applicable standard (Parameter #3) for MMUs exhibiting recurrent overexposures was 1.0 mg/m\3\, a significant decrease from prior years. MSHA attributes this decrease to two important changes in the Agency's inspection program, beginning near the end of 1998. These changes, which both resulted in increased inspector presence, were: (1) An increase in the frequency of MSHA dust sampling at underground coal mines; and (2) initiation of monthly spot inspections at mines experiencing difficulty in maintaining consistent compliance with the applicable dust standard.
The available data suggest that unless changes are made to enforce the dust standard on every shift, the same average pattern of overexposures observed in 1999 will persist into the future. Therefore, we conclude that without the proposed changes:
• More than one-half of all MMUs would continue to have a pattern of recurrent overexposures on individual shifts;
• At those MMUs with recurrent overexposures, full-shift average respirable dust concentrations for the D.O. would continue to exceed the applicable standards on about 21 percent of all production shifts;
• Among those shifts on which D.O. exposure exceeds the applicable standards, the mean excess for the D.O. would continue to be approximately 1.0 mg/m
We invite public comment on whether these three parameters, based on operators' regular 1999 bimonthly samples, under-represent or over-represent the frequency and/or magnitude of excessive dust concentrations on all individual shifts—including those that are not sampled.
If all overexposures on individual shifts are eliminated, the reduction in total respirable coal mine dust inhaled by a miner over a working lifetime will depend on the following factors: The average volume of air inhaled on each shift that would otherwise have exceeded the applicable standard, the degree of reduction in respirable dust concentration in the air inhaled on such shifts, and the number of such shifts per working lifetime. If a miner inhales ten cubic meters of air on a shift (U.S. EPA, 1980), reducing the respirable dust concentration in that air by 1.0 mg/m
The Secretaries invite comments on the health benefits expected from reducing the total coal mine dust inhaled over a working lifetime by this amount.
In Section VII, the strengths and weaknesses of various epidemiological studies were presented, supporting the selection of Attfield and Seixas (1995) as the study that provides the best available estimate of material health impairment with respect to CWP and PMF. Two of the distinguishing qualities of this study are the dose-response relationship over a miners' lifetime and the fact that these data best represent the recent conditions experienced by miners in the U.S. Using this relationship, it is possible to evaluate the impact on risk of both simple CWP and PMF expected from bringing dust concentrations down to or below the applicable standard on every shift. This is the only contemporary epidemiological study of simple CWP and PMF providing such a relationship.
Attfield and Seixas used two or three B readers to identify the profusion of opacities using the ILO classification scheme. If three readings were available, the median value was used. If two readings were available, the higher of the two ILO categories was recorded. Eighty radiographs were eliminated because only one reading was available. The most inclusive category of CWP 1+ includes simple CWP, categories 1, 2, 3, as well as PMF. Category CWP 2+ does
Attfield and Seixas (1995) provided logistic regression models for the prevalence for CWP 1+, CWP 2+ and PMF as a function of cumulative dust exposure, expressed as the product of dust concentration measured in the mine atmosphere and duration of exposure at that concentration. These models can be used to estimate the impact on miners' risk of both simple CWP and PMF of reducing lifetime accumulated exposure by eliminating excessive exposures on a given percentage of individual shifts.
At the MMUs being considered (those exhibiting a pattern of recurrent overexposures), bringing dust concentrations down to no more than the applicable standard on each and every production shift would reduce D.O. exposures on the affected shifts by an average of 1.04 mg/m
The Attfield and Seixas models predict the prevalence of CWP 1+, CWP 2+, and PMF for miners who have accumulated a given amount of exposure, expressed in units of mg-yr/m
This 11 per thousand, however, applies only to miners of age 65. The Attfield and Seixas models provide different predictions for each year of age that a miner attains. The predicted benefit turns out to be smaller for younger miners and larger for older miners. This is partly because younger miners will have accumulated less exposure reduction from the proposed changes, and partly because the Attfield and Seixas models depend directly on age as well as on cumulative exposure. The health effects of recurrent overexposures can occur long after the overexposures occurred. Even after a miner retires and is no longer exposed to respirable coal mine dust, the extra risk attributable to an extra 10 mg-year/m
To project the benefits of the two rules expected from eliminating overexposures on individual shifts, MSHA applied the Attfield and Seixas models to a hypothetical population of miners who, on average, begin working at age 20 and retire at age 65, assuming different lifetimes. The risks for three different ages have been presented to show a range of risk depending on the lifetime: 65, 73, and 80 years. During the 45 “working years” between 20 and 65, the lifetime benefit accumulates at a rate of 0.22 mg-yr/m
The expected lifetime for all American males conditional on their having reached 20 years of age, is 73 years (calculated from: U.S. Census March 1997, Table 18; U.S. Census March 1997, Table 119).
• Reduce the combined risk of simple CWP and PMF by at least 18.0 cases per 1000 affected D.O. miners;
• Reduce the combined risk of simple CWP (category 2 and 3) and PMF by at least 9.8 cases per 1000 affected D.O. miners;
• Reduce the risk of PMF by at least 5.1 cases per 1000 affected D.O. miners.
Presented in the first row of Table VIII–2 are the average reductions in risk for simple CWP and PMF combined, and PMF alone, over an occupational lifetime, among affected D.O. miners who live to ages 65, 73, and 80, who have worked at an MMU exhibiting a pattern of recurrent overexposures. Across health outcomes, the benefit due to the predicted reduction in cumulative exposure to respirable coal mine dust, through limiting miners' exposure to no more than the applicable standard on each and every shift, increases with age.
When the dust concentration measured for the D.O. exceeds the applicable standard, measurements for at least some of the other miners may also exceed the standard on the same shift, though usually by a lesser amount. Furthermore, although the D.O. represents the occupation most likely to receive the highest exposure, other miners working in the same MMU may be exposed to even higher concentrations than the D.O. on some shifts. Therefore, in addition to the affected D.O. miners, there is a population of other affected miners who are also expected to experience a significant reduction in risk as a result of eliminating overexposures on their individual shifts.
To estimate how many miners other than the D.O. would be substantially affected, MSHA examined the results from all valid dust samples collected by MSHA inspectors in underground MMUs during 1999 (MSHA, Data file:Inspctor.zip). Within each MMU, the inspector typically takes one full-shift sample on the D.O. and, on the same shift, four or more additional samples representing other occupations.
Combining these results with the 21-percent rate of excessive exposures observed for the D.O. on individual shifts, it is reasonable to infer that, at the MMUs under consideration, an average of 1.2 other miners, in addition to the one classified as D.O., is currently overexposed on at least 21 percent of all production shifts. Over the course of a working year, the reduction in exposure expected for these other miners is 0.17 mg-yr/m
To assess the reduction in risk expected from eliminating all single-shift exposures for faceworkers experiencing lower exposures than the D.O., MSHA again applied the Attfield and Seixas models to miners who begin working at age 20, retire at age 65, assuming various lifetimes: 65, 73, and 80 years. This time, however, the resulting decrease in predicted prevalence was multiplied by 1.2/7 = 0.171, to reflect the fact that the assumed rate of overexposure applies, on average, to about 17 percent of the faceworkers not classified as the D.O.
In the second row of Table VIII–2, we see that over an occupational lifetime, the beneficial average reduction in risk for simple CWP and PMF combined, and for PMF alone, increases with age. However, the magnitude of the risk reduction is smaller for the affected non-D.O.s than the affected D.O.s. This is expected because the estimated probability that a non-D.O. will be overexposed on a given shift is only 17 percent of the corresponding probability for the D.O. Based on this calculation for the MMUs under consideration, the predicted reduction in risk for faceworkers other than the D.O. who live an expected lifetime of 73 years is at least: 2.3 fewer cases of PMF or simple CWP, per thousand affected miners; 1.3 fewer cases of PMF or simple CWP, categories 2 or 3, per thousand affected miners; and 0.7 fewer cases of PMF per thousand affected miners.
Various data, assumptions and caveats were used to conduct the quantitative risk assessment. Therefore, we request any information which would enable us to conduct more accurate analyses of the estimated health benefits of the single, full-shift sample rule and plan verification rule, both individually, and in combination.
The criteria for evaluating the evidence to determine whether these proposed standards improve the regulatory strategy for controlling exposures to respirable coal mine dust are established by the Mine Act pursuant to section 101(a)(6)(A) (30 U.S.C. 811(a)(6)(A))which provides that:
The Secretary, in promulgating mandatory standards dealing with toxic materials or harmful physical agents under this subsection, shall set standards which most adequately assure on the basis of the best available evidence that no miner will suffer material impairment of health or functional capacity even if such miner has regular exposure to the hazards dealt with by such standard for the period of his working life.
Based on Court interpretations of similar language under the Occupational Safety and Health Act, there are three questions that must be addressed: (1) Whether health effects associated with the current pattern of overexposures on individual shifts constitute a material impairment to miner health or functional capacity; (2) whether the current pattern of overexposures on individual shifts places miners at a significant risk of incurring any of these material impairments; and (3) whether the proposed rules would substantially reduce those risks.
The statutory criteria for evaluating the health evidence do not require MSHA and NIOSH to wait for absolute certainty and precision. MSHA and NIOSH are required to use the “best available evidence” (section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)). The need to evaluate risk does not mean that an agency is placed
We have taken steps in our quantitative risk assessment to conduct a balanced analysis using available data. Some of our assumptions were conservative, while others were not.
In identifying the number and percentage of MMUs exhibiting a pattern of recurrent overexposures on individual shifts we choose to include only those MMUs with two or more 1999-operator bimonthly samples in excess of the applicable standard, rather than the population of MMUs with any overexposures.
Another important decision impacting choice in this risk assessment involves the use of the traditional coal miner work schedule of 8-hours per day, 5-days per week, 48-weeks per year. Many of today's miners work longer hours per day, month, and year than the traditional work schedule. These longer work hours increase miners' cumulative exposure to respirable coal mine dust beyond the parameters of exposure used in our estimates of risk. Even so, to the extent that a proportion of miners may have a more limited work schedule (and occupational exposure), either in number of years, weeks per year, or hours per week, their expected health benefit would have to be adjusted downward, all other variables being constant.
Also, because of heavy, physical work, some miners may work at ventilatory rates in excess of the above-cited 10 cubic meters per 8-hour shift; an estimate of this ventilatory rate is 13.5 cubic meters per 8-hour shift (ICRP, 1994). The sub-population of miners with higher breathing rates would inhale more respirable coal mine dust than would otherwise occur given the same environmental exposures, thereby increasing their risks for the development of simple CWP and PMF.
In the Quantitative Risk Assessment, to estimate average reduction in exposure, we chose the best available data sets: 1999 operator bimonthly samples for D.O.s and N.D.O.s., respectively. Currently, both operator bimonthly and inspector samples
Other aspects of our risk assessment methodology reflect more conservative choices including the selection of an occupational lifetime of 45-years. Various factors may affect the consistency of the type and duration of jobs miners hold and hence their associated cumulative exposure levels. For example, some miners who lose their jobs upon mine closure are employed by other mines, sometimes in less-exposed jobs. Some miners may chose to move from job to job over their careers at underground coal mines, sometimes preferring positions away from the mining face. Moreover, if the trend of increasing mechanization continues, there will be fewer miners, and for some of them, their occupational lifetimes will be shorter.
For reasons already explained, we believe these choices are appropriate for this risk assessment. We also recognize that use of the most conservative approach at every step of the risk assessment analysis could produce mathematical risk estimates which, because of the additive effect of multiple conservative assumptions, may overstate the likely risk. We believe this QRA for simple CWP and PMF strikes a reasonable balance based on available data. To the extent that we may have underestimated the magnitude of overexposures which would be prevented, we believe the actual benefits to be greater than we have estimated.
It should be noted that reductions in the prevalence of simple CWP and PMF attributable to eliminating individual shift overexposures are not expected to materialize immediately after the overexposures have been substantially reduced or eliminated. Because these diseases typically arise after many years of cumulative exposure, allowing for a period of latency, the beneficial effects of reducing exposures are expected to become evident only after a sufficient time has passed that the reduction in cumulative exposure could have its effect. The total realized benefits would not be fully evident until after the youngest of today's underground coal miners retire.
Finally, even standing alone without simultaneously requiring that mine
While there may be some concern from mine operators that the use of single, full-shift samples could dramatically increase the number of MSHA citations for overexposure to respirable coal mine dust, MSHA's 1998 Interim Single-Sample Enforcement Policy (ISSEP) has demonstrated that mine operators can maintain coal mine dust concentrations at or below the applicable standard.
As discussed in greater detail later in this notice, under ISSEP (May 7, 1998–September 9, 1998), of the 1,662 MMUs sampled, 182 or 11 percent were cited and only 14 of the 4,600 surface entities sampled were found to be out of compliance.
The anticipated increase in MSHA citations due to the use of single full-shift sampling would be the result of identifying overexposures which the current method of sampling masks due to the averaging of samples. Such overexposures and their prospective medical impact on the health of miners has been the subject of a Federal Mine Safety and Health Review Commission case which was affirmed by the Court of Appeals.
In affirming an MSHA citation designated as “significant and substantial” under Section 104(a) of the Mine Act based on a mine operator's bimonthly dust samples which had an average concentration of respirable dust of 4.1 milligrams per cubic meter of air, the Commissioner quoted the administrative law judge who explained in detail the potentially damaging health effects of respirable coal mine dust:
It is clear that the exposure covered by the dust samples which resulted in the citation herein
I conclude that
While
Thus, the same analogy would apply to overexposures identified through single, full-shift exposures. MSHA and NIOSH firmly believe that noncompliance determinations based on single, full-shift measurement will improve working conditions for miners because mine operators will be compelled either to implement and maintain more effective dust controls to minimize the chances of being found in noncompliance by an MSHA inspector, or to take corrective actions to lower those dust concentrations that are shown to be in excess of the applicable standard.
To the extent that the use of single, full-shift samples reduce a miner's cumulative exposure to respirable coal mine dust, as compared to the current method of dust sampling, it reduces a miner's risk of developing occupational respiratory disease. The proposed mandatory standard would provide for fewer drops in each miner's exposure bucket. The health benefit that each miner receives from this rule will vary depending on “how full their bucket is” when the rule is implemented as well as other mediating factors, such as the percentage of quartz and rank of the coal.
Yet, all miners, irrespective of their cumulative exposure to respirable coal mine dust, would benefit by having fewer drops (
Some previous commenters questioned the accuracy of single, full-shift measurements, and challenged the Secretaries' assessment of measurement accuracy. Some commenters questioned the Secretaries' interpretation of section 202(b) of the Mine Act (30 U.S.C.
Some previous comments reflected a general misunderstanding of what the Secretaries intend to measure with a single, full-shift measurement,
To evaluate the accuracy of a dust sampling method, it is necessary to specify the airborne dust to be measured, the time period to which the measurement applies, and the area represented by the measurement. Once specified, these items can be combined into a measurement objective. The measurement objective represents the goal of the sampling and analytical method to be utilized.
Section 202(f) of the Mine Act (30 U.S.C. 842(f)) states that “average concentration” means
* * * a determination [
Section 202(b)(2) provides that each mine operator “* * * shall continuously maintain the average concentra tion of respirable dust in the mine atmosphere during each shift to which each miner *; * * is exposed” at or below the applicable standard. In section 202(f) “average concentration” is defined as an atmospheric condition measured “over a single shift only, unless * * * such single shift measurement will not, after applying valid statistical techniques, accurately represent such atmospheric conditions during such shift.”
Some previous commenters argued that Congress intended that the measurement objective be a long-term average. Specifically, some of these commenters stated that because coal dust exposure is related to chronic health effects, the exposure limit should be applied to dust concentrations averaged over a miner's lifetime. These commenters identified the measurement objective as being the dust concentration averaged over a long, but unspecified, term and argued that a single, full-shift measurement cannot accurately estimate this long-term average.
If the objective of section 202(b) were to estimate dust concentration averaged over a lifetime of exposure, then the Secretaries would agree that a single, full-shift sample, or even multiple samples collected during a single inspection, would not provide the basis for an accurate measurement. Section 202(b) of the Mine Act (30 U.S.C. 842(b)), however, does not mention long-term averaging, rather it explicitly requires that the average dust concentration be continuously maintained at or below the applicable standard during
If exposure is limited on each shift, then this will ensure that a miner's total lifetime exposure will not be excessive. In the context of the proposed finding, the Secretaries have determined that “atmospheric conditions” means the fluctuating concentration of respirable coal mine dust during a single shift. These are the atmospheric conditions to which a miner at the sampling location would be exposed. Therefore, the proposed finding pertains only to the accuracy in representing the average of the fluctuating dust concentration over a single shift.
The Mine Act gives the Secretary of Labor the discretion to determine the area to be represented by respirable dust measurements collected over a single shift. Section 202(a) of the Mine Act (30 U.S.C. 842(a)) refers to “the amount of respirable dust in the mine atmosphere to which each miner in the active workings of such mine is exposed” measured “* * * at such locations * * *” as prescribed by the Secretary of Labor. It is sufficient for the purposes of the Mine Act that the sampler unit accurately represent the amount of respirable dust at such locations only. As articulated by the United States Court of Appeals for the 10th Circuit in
Some previous commenters submitted evidence that dust concentrations can vary significantly near the mining face, and that these variations may extend into areas where miners are located. That is, the average dust concentration over a full shift is not identical at every point within a miner's work area. These commenters submitted several bodies of data purporting to show significant discrepancies between simultaneous dust concentration measurements collected within a relatively small distance of one another. Several previous commenters maintained that the measurement objective is, or should be, to accurately measure the average concentration within some arbitrary sphere about the head of the miner, and that multiple measurements within this sphere are necessary to obtain an accurate measurement.
The Secretaries recognize that dust concentrations in the mine environment can vary from location to location, even within a small area near a miner. As mentioned earlier, the Mine Act does not specify the area that the measurement is supposed to represent, and the sampler unit may therefore be placed in any location, reasonably calculated to determine excessive exposure to respirable dust.
Because the Secretary of Labor intends to prevent excessive exposures by limiting dust concentrations at every location in the active workings, it is sufficient that each measurement accurately represent the respirable dust concentration at the corresponding sampling location only. Limiting the dust concentration at every such location ensures that no miner in the
Several previous commenters suggested that the measurement objective should be a miner's “true exposure” or what the miner actually inhales. The Secretaries do not intend to use a single, full-shift measurement to estimate any miner's “true exposure,” because no sampling device can exactly duplicate the particle inhalation and deposition characteristics of a miner at any work rate (these characteristics change with work rate), let alone at the various work rates occurring over the course of a shift. Limiting the respirable dust concentration at every location in the active workings to which miners are exposed ensures that the respirable dust concentration actually inhaled by any miner is limited.
A number of previous commenters identified the dust concentration to be estimated as either the mean dust concentration over some period greater than an individual shift, the mean dust concentration over some spatially distributed region of the mine, or a “grand mean” consisting of some combination of the above. These comments were based on the premise that the measurement objective should be something other than the average atmospheric conditions during a single shift at the sampling location. It is true that the mean quantities described by some commenters cannot accurately be estimated using a single, full-shift measurement, but the Secretaries make no claim of doing so, nor do they believe that a broader measurement objective would be desirable for enforcement purposes.
The Secretaries believe that MSHA's proposed use of single, full-shift samples for enforcement purposes would eliminate an important source of sampling bias due to averaging, as explained in Appendix A. Under MSHA's existing enforcement procedures, 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. This practice has frequently caused failures to cite clear cases of excessive dust concentration. Therefore, the Secretaries believe that enforcement based on averaging does not provide miners with the greatest level of protection possible under the current exposure limit for respirable coal mine dust.
Some previous 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. Several of these commenters maintained 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 argued that not averaging measurements would reduce accuracy to unacceptable levels.
Other previous commenters agreed with MSHA and NIOSH that the averaging of multiple samples can dilute and mask specific instances of overexposure. Some of these commenters stated that averaging not only distorts 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 currently 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 to which a miner is exposed on any individual shift. Appendix A contains further discussion of this issue.
Accordingly, the Secretaries would define the measurement objective to be the accurate determination of the average concentration of respirable dust at a sampling location over a single shift.
A “single shift measurement” means the calculated dust concentration resulting from a valid single, full-shift sample of respirable coal mine dust. In reviewing the various issues raised by previous commenters, the Agencies found that the term “accurately represent,” as used in section 202(f) (30 U.S.C. 842(f)) in connection with a single shift measurement, was not defined in the Mine Act. Therefore, on March 12, 1996, (61 FR 10012), the Secretaries proposed to apply an accuracy criterion developed and adopted by NIOSH in judging whether a single, full-shift measurement will “accurately represent” the full-shift atmospheric dust concentration. The NIOSH Accuracy Criterion requires that measurements come within 25 percent of the corresponding true dust concentration at least 95 percent of the time (Kennedy,
One previous commenter opposed the application of the NIOSH Accuracy Criterion since it ignores environmental variability. For reasons explained above, the Secretaries have restricted the measurement objective to an individual shift and sampling location. Therefore, environmental variability beyond what occurs at the sampling location on a single shift would not be relevant to assessing measurement accuracy.
For over 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.
OSHA has frequently employed a version of the NIOSH Accuracy Criterion when issuing new or revised single substance standards. For example, OSHA's benzene standard provides: “[m]onitoring shall be accurate, to a confidence level of 95 percent, to within plus or minus 25 percent for airborne concentrations of benzene” (29 CFR 1910.1028(e)(6)). Similar wording can be found in the OSHA standards for vinyl chloride (29 CFR 1917), arsenic (29 CFR 1918), lead (29 CFR 1925), 1,2-dibromo-3-chloropropane (29 CFR 1044), acrylonitrile (29 CFR 1045), ethylene oxide (29 CFR 1047), and formaldehyde (29 CFR 1048). Note that for vinyl chloride and acrylonitrile, the accuracy criterion for the method is ±35 percent at 95 percent confidence at the permissible exposure limit.
Some previous commenters contended that the NIOSH Accuracy Criterion does not conform with international standards recently adopted by the European Committee for Standardization (CEN) (European Standard No. EN 482, 1994). Contrary to these assertions, the NIOSH Accuracy Criterion not only conforms to the CEN criterion but is, in fact, more stringent.
The NIOSH Accuracy Criterion is relevant and widely recognized and accepted in the occupational health professions. Further, previous commenters proposed no alternative criteria for accuracy. Accordingly, for purposes of section 202(f) of the Mine Act (30 U.S.C.842(f)), the Secretaries would consider a single, full-shift measurement to “accurately represent” atmospheric conditions at the sampling location, if the sampling and analytical method used meets the NIOSH Accuracy Criterion.
Several commenters suggested that method accuracy should be determined under actual mining conditions rather than in a laboratory or in a controlled environment. Although the NIOSH Accuracy Criterion does not require field testing, it recognizes that field testing “does provide further test of the method.” However, in order to avoid confusing real differences in dust concentration with measurement errors when testing is done in the field, “precautions may have to be taken to ensure that all samplers are exposed to the same concentrations” (Kennedy,
To determine, so far as possible, the accuracy of its sampling and analytical method under actual mining conditions, MSHA conducted 22 field tests in an underground coal mine. To provide a valid basis for assessing accuracy, 16 sampler units were exposed to the same dust concentration during each field test using a specially designed portable chamber. The data from these field experiments were used by NIOSH in its “direct approach” to determining whether or not MSHA's method meets the long-established NIOSH Accuracy Criterion. (See section X.E.2. of this notice).
In response to the March 12, 1996 notice, a commenter claimed that the supplementary information and analyses introduced into the public record by that notice addressed the precision of a single, full-shift measurement rather than its accuracy. According to this commenter, by focusing on precision, important sources of systematic error had been overlooked. The Secretaries agree with the comment that precision is not the same thing as accuracy. The accuracy of a measurement depends on both precision and bias (Kennedy,
Since the amount of dust present on a filter capsule used by an MSHA inspector is measured by subtracting the pre-exposure weight from the post-exposure weight, any bias present in both weight measurements is mathematically canceled out by subtraction. Furthermore, as will be discussed later, a control (
For unbiased sampling and analytical methods, a standard statistic—called the coefficient of variation (CV)—is used to determine if the method meets the NIOSH Accuracy Criterion. The CV, which is expressed as either a fraction (
A single, full-shift measurement of respirable coal mine dust is obtained with an approved sampler unit, which is either worn or carried by the miner directly to and from the sampling location and remains operational during the entire shift or for eight hours, whichever time is less. A portable, battery-powered pump draws dust-laden mine air at a flow rate of 2 liters per minute (L/min) through a 10-mm nylon cyclone, a particle-size selector that removes non-respirable particles from the airstream. Non-respirable particles tend to be removed from the airstream by the nose and upper respiratory airways. Such particles fall to the bottom of the cyclone body called the “grit pot,” while smaller, respirable particles (of the size that would normally enter into the lungs) pass through the cyclone, directly into the inlet of the filter cassette. This airstream is directed through the pre-weighed filter leaving the particles deposited on the filter surface. This collection filter is enclosed in an aluminum capsule to prevent leakage of sample air around the filter and the loss of any dust dislodged due to impact. The filter capsule is sealed in a protective plastic enclosure, called a cassette, to prevent contamination. After completion of sampling, the filter cassette is sent to MSHA's Respirable Dust Processing Laboratory in Pittsburgh, Pennsylvania, where it is weighed to determine the weight gain in milligrams or the amount of dust collected on the filter surface. The concentration of respirable dust, expressed as milligrams per cubic meter (mg/m3) of air, is determined by dividing the observed weight gain by the volume of mine air passing through the filter and then multiplying this quantity by a conversion factor (discussed in Appendix B) prescribed by the Secretaries.
Some previous comments generally addressed the quality and reliability of the equipment used for sampling.
The validity of the sampling process is an important aspect of maintaining accurate measurements. Since passage of the Coal Act, there has been an ongoing effort by MSHA and NIOSH to improve the accuracy and reliability of the entire sampling process. In 1980, MSHA issued new regulations revising sampling, maintenance and calibration procedures in 30 CFR parts 70, 71, and 90. These regulatory provisions were designed to minimize human and mechanical errors and ensure that samples collected with approved sampler units in the prescribed manner would accurately represent the full-shift, average atmospheric dust concen tration at the location of the sampler unit. These provisions require: (1) Certification of competence of all individuals involved in the sampling process and in maintaining the sampling equipment; (2) calibration of each sampler unit at least every 200 hours; (3) examination, testing, and maintenance of units before each sampling shift to ensure that the units are in proper working order; and (4) checking of sampler units during sampling to ensure that they are operating properly and at the proper flow rate. In addition, significant changes, such as robotic weighing and the use of electronic balances were made in 1984, 1994, and 1995 that improved the reliability of sample weighings at MSHA's Respirable Dust Processing Laboratory. These changes are discussed below in section X.C.3.
All of these efforts improved the accuracy and reliability of the sampling process since the time of the 1971/1972 proposed and final findings. A discussion follows concerning the three elements which constitute the sampling process: sampler unit performance, collection procedures, and sample processing.
In accordance with the provisions of section 202(e) of the Mine Act (30 U.S.C. 842(e)), NIOSH administers a comprehensive certification process under 30 CFR part 74 to approve dust sampler units for use in coal mines. To be approved for use, a sampler unit must meet stringent technical and performance requirements governing the quantity of respirable dust collected and flow rate consistency over an 8-hour period when operated at the prescribed flow rate. As necessary, NIOSH also conducts performance audits of approved sampler units purchased on the open market to determine if the units are being manufactured in accordance with the specifications upon which the approval was issued.
The system of technical and quality assurance checks currently in place is designed to prevent a defective sampler unit from being manufactured and made commercially available to the mining industry or to MSHA. In the event that these checks identify a potential problem with the manufacturing process, established procedures require immediate action to correct the problem.
In 1992, NIOSH approved the use of new tamper-resistant filter cassettes with features that enhanced the integrity of the sample collected. A backflush valve was incorporated into the outlet of the cassette, preventing reverse airflow through the filter cassette, and an internal flow diverter was added to the filter capsule, reducing the possibility of dust dislodged from the filter surface from falling out of the capsule inlet.
Also, in 1999, based on recent MSHA studies, Kogut,
Several previous commenters questioned the quality of the filter cassettes used in the sampling program, expressing concern as to whether the cassettes always meet MSHA specifications. These concerns primarily involve filter-to-foil distance and floppiness of the filters, which are manufacturing characteristics specific to filters and filter capsules, not related to part 74 performance requirements. The Secretaries believe that such characteristics would have no effect on the accuracy of a single, full-shift measurement because, unlike the part 74 requirements, they would not affect the amount of dust deposition.
Previous commenters also questioned the condition of sampling pumps used by MSHA inspectors, stating that many of the pumps are 10 to 20 years old and are not maintained as well as they could be. They claimed that the age and condition of these pumps call into question not only whether the sampling equipment could meet part 74 requirements if tested, but also the accuracy of the measurement.
MSHA believes that this concern is unwarranted, since in 1995, MSHA replaced all pumps in use by inspectors with new constant-flow pumps that incorporate the latest technology in pump design. These pumps provide more consistent flow throughout the sampling period. In addition to using new pumps, inspection procedures require MSHA inspectors to make a minimum of two flow rate checks to ensure that the sampler unit is operating properly. A sample is voided if the proper flow rate was not maintained during the final check at the conclusion of the sampling shift. In fiscal year 1998, only 151 samples or 0.4 percent of the 37,042 inspector samples processed were voided because the sampling pump either failed to operate throughout the entire sampling period or failed to maintain the proper flow rate during the final check. Units found not meeting the requirements of part 74 are immediately repaired, adjusted, or removed from service. Nevertheless, MSHA recognizes that as these pumps age, deterioration of the performance of older pumps could become a concern. However, there is no evidence that the age of the equipment affects its operational performance if the equipment is maintained as prescribed by 30 CFR parts 70, 71, and 90.
Some previous commenters suggested that the accuracy of a dust sample may be compromised when a miner is operating equipment, due to vibration from the machinery. The potential effect of vibration on the accuracy of a respirable dust measurement was recognized by NIOSH in 1981. An investigation, supported by NIOSH, was conducted by the Los Alamos National Laboratory which found that vibration has an insignificant effect on sampler performance (Gray and Tillery, 1981).
MSHA regulations at 30 CFR parts 70, 71, and 90 prescribe the manner in which mine operators are to take respirable dust samples. The collection procedures are designed to ensure that the samples accurately represent the amount of respirable dust in the mine atmosphere to which miners are exposed on the shift sampled. Samples taken in accordance with these procedures are considered to be valid.
Several previous commenters questioned the effects of sampling and work practices on the validity of a sample. Instances were cited where the sampling unit was accidentally dropped, with the potential for the sample to become contaminated. Previous commenters also pointed out that work activities requiring crawling, duck walking, bending, or kneeling could cause the sampling hose to snag. Such activities could also cause the sampling head assembly to be impacted or torn off a person's garment, possibly contaminating the sample. These commenters stated that sampler units are sometimes treated harshly while being worn by miners, mishandled when being transferred from one miner to another, or handled casually at the end of a work shift.
These commenters also maintained that it is impossible for MSHA inspectors or mine operators to continuously observe collection of a sample in order to ensure its validity, and that, for this reason, the reliability and accuracy of the sampling equipment, when used under actual mining conditions, is not the same as when tested and certified in a laboratory. Averaging multiple samples would, according to these commenters, provide some “leeway” in the system, by reducing the impact of an aberrant sample.
While MSHA and NIOSH would agree that it is not possible to continuously observe the collection of each sample, MSHA inspectors are normally in the general vicinity of the sampling location, and therefore would have knowledge of the specific conditions under which samples are taken. In addition, MSHA inspectors are instructed to ask miners wearing the sampler units whether anything that could have affected the validity of the sample occurred during the shift. If so, the inspector would note this on the data card and request that the sample be examined to determine its validity.
Other previous commenters expressed concern that, if special dust control measures are in effect during sampling, a single, full-shift measurement may fail to represent atmospheric conditions during shifts when samples are not collected. The Secretaries believe that this concern is beyond the scope of this new proposal, which, as described in the discussion of measurement objective, deals solely with the accuracy of a measurement in representing atmospheric conditions on the shift being sampled. One previous commenter recommended that MSHA, NIOSH, or the Bureau of Mines (now a part of NIOSH) should evaluate the need for standardizing the MSHA respirable dust sampling procedures. In fact, the procedures for respirable dust sampling have already been standardized under the revised 1980 MSHA regulations codified at 30 CFR parts 70, 71 and 90.
As previously mentioned, as part of the ISSEP discussion, MSHA inspectors are also using unexposed control filters to eliminate any bias that may be associated with day-to-day changes in laboratory conditions or introduced during storage and handling of the filter capsules. A control filter is an unexposed filter that was pre-weighed on the same day as the filter used for sampling. This control filter is used to adjust the weight gain obtained on each exposed filter. Any change in weight of the control filter is subtracted from the change in weight of each exposed filter. MSHA began using control filters on May 7, 1998, with the implementation of the ISSEP, and has continued this practice, even after reverting back to basing noncompliance determinations on an average of multiple samples following the ruling of the 11th Circuit Court of Appeals discussed earlier. The control filter, which is carried by the inspector in a shirt or coverall pocket during the sampling inspection, is plugged to prevent exposure to the mine environment. The experience gained from the use of control filters under ISSEP is discussed in section V.D.
Also, once NIOSH approves the modified design mentioned earlier, MSHA inspectors would use only filters incorporating a stainless steel support wheel. These filters, according to MSHA studies, demonstrated better weighing stability as compared to filters employing Tyvek® material for the support pad.
Sample processing consists of weighing the exposed and control (unexposed) filters, recording the weight changes, and examining certain samples in order to verify their validity. Sample processing also includes electronic transmission of the results to MSHA's MIS center where dust concentrations are computed. The results are then transmitted to MSHA enforcement personnel and to mine operators.
The procedures and analytical equipment, as well as the facility used by MSHA to process respirable coal mine dust samples have been continuously improved since 1970 to maintain a state-of-the-art laboratory. From 1970 to 1984, samples were manually weighed using semimicro balances. This process was automated in 1994 with the installation of a state-of-the-art robotic system and electronic balances, which increased the precision of sample-weight determinations. Weighing precision was further improved in 1994, when both the robotic system and balances were upgraded. Also, beginning in early 1998, all respirable coal mine dust samples were being processed in a new, specially designed clean room facility that maintains the temperature and humidity of the environment at 72 ±2°F and 50 ±5%, respectively. Using a modified HEPA filtration system, the environment is maintained at a clean room classification of 1000 (near optimum for clean room cleanliness).
The full benefit of the 1994 improvements of the weighing system for inspector samples was, however, not attained until mid-1995, when MSHA implemented two modifications to its procedures for processing inspector samples. One modification involved pre- and post-weighing filter capsules to the nearest microgram (0.001 mg) within MSHA's laboratory. Prior to mid-1995, filters had been weighed in the manufacturer's (Mine Safety and Appliances Co.) laboratory before sampling, and then in MSHA's laboratory after sampling. MSHA is currently pre-weighing all such filters in its own laboratory. To maintain the integrity of the weighing process, eight percent of all filters are systematically weighed a second time. If a significant deviation is found, the balance is recalibrated and all filters with questionable weights are reweighed.
The other modification was to discontinue the practice of truncating (to 0.1 mg) the recorded weights used in calculating dust concentrations. This means that MSHA is now using all significant digits associated with the weighing capability of the balance (0.001mg) when processing inspector samples. These modifications improved the overall accuracy of the measurement process.
To eliminate the potential for any bias that may be associated with day-to-day changes in laboratory conditions or introduced during storage and handling of the filters, MSHA is also using control filters in its enforcement program. Any change in the weight of the control filter is subtracted from the measured change in weight of the exposed filter.
Since MSHA began pre- and post-weighing filters to the nearest μg, coal
In 1996, Mine Safety Appliances Company upgraded their equipment used to pre-weigh filter capsules and now uses the same balance as MSHA's Coal Dust Processing Laboratory, thereby permitting weight determinations to be made to the nearest μg.
The requirement that inspector samples be pre- and post-weighed in the same laboratory was developed prior to adopting control filters and was based on the assumption that no control filters were being used. Since use of the control filters adjusts for differences that may exist in laboratory conditions on the days of pre- and post-weighing, it is no longer necessary to pre- and post-weigh the filters in the same laboratory.
To determine the viability of using exposed filters pre-weighed by Mine Safety Appliances Co. and post-weighed by MSHA in establishing the percentage of quartz, the Agency conducted a study to quantify weighing variability between the Mine Safety Appliances Co. and MSHA laboratories (Parobeck,
Using the higher of these two estimates, NIOSH has reassessed the accuracy of MSHA's improved sampling and analytical method, which incorporates a control filter adjustment and employs filter capsules with a stainless steel support pad. NIOSH has concluded that the control filter adjustment will correct for any potential biases due to differences in laboratory conditions, so that it is no longer necessary to pre- and post-weigh filter capsules in the same laboratory (Grayson, 1999b). Therefore, in accordance with NIOSH, MSHA is proposing to change the existing processing procedures for inspector samples from pre- and post-weighing in the same laboratory (with adjustment by a control filter) to pre- and post-weighing of samples to the nearest μ in different laboratories (with continued adjustment by a control filter). The Agencies would welcome comments on this proposed change.
To insure the precision and accuracy of the pre-weight of filters used by inspectors, MSHA plans to institute a program to monitor the daily production of filters weighed to the nearest μg by the manufacturer. The program will conform to MIL–STD–105D, which defines the criteria currently used to monitor the quality of pre-weighed filters used in MSHA's operator sampling program.
All respirable dust samples collected and submitted as required by 30 CFR parts 70, 71, and 90 are considered valid unless the dust deposition pattern on the collection filter appears to be abnormal or other special circumstances are noted that would cause MSHA to examine the sample further. Several previous commenters expressed concern about the potential contamination of samples with “oversized particles.” Such contamination, according to one commenter, can result in aberrational weight gains. These commenters noted that current procedures do not systematically ensure that samples collected by MSHA contain no oversized particles. It was recommended that MSHA analyze, for the presence of oversized particles, any dust sample that exceeds the applicable dust standard. Also suggested for such an analysis was any sample with a weight gain significantly different from other samples taken in the same area.
Standard laboratory procedures, involving visual, and microscopic examination as necessary, are used to verify the validity of samples. Samples with a weight gain of 1.4 milligrams (μg) or more are examined visually for abnormalities such as the presence of large dust particles (which can occur from agglomeration of smaller particles), abnormal discoloration, abnormal dust deposition pattern on the filter, or any apparent contamination by materials other than respirable coal mine dust. Also examined are samples weighing 0.1 mg or less for insufficient dust particle count. Similar checks are also performed in direct response to specific inspector or operator concerns noted on the dust data card to which each sample is attached.
The previous commenters' concerns about the contamination of samples with oversized particles are based on the assumption that all oversized particles, defined as dust particles greater than 10 micrometers (μm) in size, are not respirable and therefore should be totally excluded from any sample taken with an approved sampler unit. However, it has long been known that some particles greater than 10 μ
The Secretaries recognize that there are occasions when oversized particles can properly be considered a contaminant. For example, an excessive number of such particles could enter the filter capsule if the sampling head assembly is accidentally or deliberately turned upside down or “dumped” (possibly causing some of the contents of the cyclone grit pot to be deposited on the collection filter), if the pump malfunctions, or if the entire sampler unit is dropped. When MSHA has reason to believe that such contamination has occurred, the suspect sample is examined to verify its validity.
Contrary to the assertions of some previous commenters, checking for
While rough handling of the sampler unit or an accidental mishap could conceivably cause a sample with a weight gain less than 6 mg to become contaminated, as claimed by some previous commenters, studies show that short-term accidental inclinations of the cyclone will not affect respirable mass measurements made with currently approved sampler units (Treaftis and Tomb, 1974). Sampler units currently used are built to withstand the rigors of the mine environment, and are therefore less susceptible to contamination than suggested by some previous commenters. In any event, the Secretaries believe that the validity checks currently in place, as discussed above, would detect such samples.
Overall variability in measurements collected on different shifts and sampling locations comes from two sources: (1) Environmental variability in the true dust concentration and (2) errors in measuring the dust concentration in a specific environment. The major portion of overall measurement variability reflects real variability in dust concentration on different shifts or at different sampling locations (Nicas,
Variability in the dust concentration is under the control of the mine operator and does not depend on the degree to which the dust concentration can be accurately measured. Measurement uncertainty, on the other hand, stems from the differing measurement results that could arise, at a given sampling location on a given shift, because of potential sampling and analytical errors. Therefore, unlike variability in dust concentration, measurement uncertainty depends directly on the accuracy of the measurement system. Measurement errors generally contribute only a small portion of the overall variability observed in datasets consisting of dust concentration measurements.
Numerous previous commenters identified sources of measurement uncertainty and dust concentration variability that they believed should be considered when determining whether or not a measurement accurately represents such atmospheric conditions. Because the measurement objective is to accurately represent the average dust concentration at the sampling location over a single shift, it does not take into consideration dust concentration variability between shifts or locations. Sources of dust concentration variability would not be considered by the Secretaries in determining whether a measurement is accurate. Consequently, the Secretaries have concluded that the only sources of variability relevant to establishing accuracy of a single, full-shift measurement for purposes of section 202(f) of the Mine Act (30 U.S.C. 842(f)) would be those related to sampling and analytical error.
Filter capsules are weighed prior to sampling. After a single, full-shift sample is collected, the filter capsule is weighed a second time, and the weight gain (g) is obtained by subtracting the pre-exposure weight from the post-exposure weight, which will then be adjusted for the weight gain or loss observed in the control filter capsule. A measurement (x) of the atmospheric condition sampled is then calculated by Equation 1:
The Secretaries recognize that random variability, inherent in any measurement process, may cause
The statistical measure used by the Secretaries to quantify uncertainty in a single, full-shift measurement is the total sampling and analytical coefficient of variation, or CV
Based on a review of the scientific literature, the Secretaries in their March 12, 1996 notice concerning the NIOSH Accuracy Criterion identified three sources of uncertainty in a single, full-shift measurement, which together make up CV
(a) CV
(b) CV
(c) CV
These three components of measurement uncertainty can be combined to form an indirect estimate of CV
These three components are discussed in greater detail, along with responses to specific previous comments, in Appendix B.
Previous commenters also raised issues related to sources of dust concentration variability. Some of these commenters maintain that the Secretaries should include in CV
Exposure variability due to job, location, shift, production level, effectiveness of engineering controls, and work practices will be different from mine to mine. This type of variability has nothing to do with measurement accuracy and depends on factors under the control of the mine operator. The sampler unit is not intended to account for these factors.
Previous commenters stated that CV
Previous commenters stated that CV
Previous commenters expressed concern that respirable dust cyclones are handled in a rough manner in normal use and occasionally turned upside down. According to one commenter, this type of handling would cause more large particles to be deposited on the filter in the mine environment than when used in the laboratory. This commenter knew of no data that could be used to evaluate the error associated with such occurrences and recommended that a study be commissioned to measure the proportion of non-respirable particles on the filters after they are weighed to MSHA standards.
After considering this recommendation, the Secretaries would conclude that the available evidence shows that short-term inclinations of the cyclone, as might frequently occur during sampling, will not affect respirable dust measurements made with approved sampler units (Treaftis and Tomb, 1974). The weight of the sampler head assembly makes it extremely unlikely that a sampler unit could be turned upside down in normal use. Furthermore, with a field study of the type recommended, variability in the field measurements due to normal handling would be confounded with variability due to real differences in atmospheric conditions. Therefore, the Secretaries believe that such a study would not be useful in establishing variability in measurements due to differences in handling of the sampler unit.
Previous commenters asserted that unpredictable, infrequent events, such as a “face blowout” on a longwall (a violent expulsion of coal together with large quantities of coal dust and/or methane gas) or high winds at a surface mine, can cause rapid loading of a filter capsule and thereby distort a measurement to show an excessive dust concentration based on a single, full-shift sample when, they argue, the dust standard had not been exceeded. In fact, if such an occurrence were to cause a measurement above the applicable standard, the dust standard would be violated. No evidence was previously presented to demonstrate that short-term high exposures can overload a dust sampling filter or cause the sampling device to malfunction. Nor was evidence presented to demonstrate that miners are not also exposed to the same high dust concentrations as the sampler unit when such events occur. The Secretaries would conclude that such events are results of the dynamic and ever-changing mine environment—an environment to which the miner is exposed. The sampler unit is designed to measure the atmospheric condition at a specific sampling location over a full shift. If such events occur, the sampler unit will accurately record the atmospheric condition to which it is exposed.
Several previous commenters questioned the 1.38 MRE-conversion factor used in Equation 1. This factor is used to convert a measurement obtained with the type of dust sampler unit currently approved for use in coal mines to an equivalent concentration as measured with an MRE gravimetric dust sampler. The term “MRE instrument” is defined in 30 CFR § 70.2 (i). The conversion factor is necessary because the coal mine dust standard was derived from British data collected with an MRE instrument, which collects a larger fraction of coal mine dust than does the approved dust sampling unit (Tomb,
Some previous commenters contended that variability involved in the data analysis used in establishing the conversion factor should be taken into account in determining CV
One commenter pointed out that in estimating CVtotal, MSHA and NIOSH did not take into account any potential errors associated with silica analysis. The commenter argued that since silica analysis is used to establish reduced dust standards, MSHA and NIOSH had failed to demonstrate “* * * accuracy for all samples ‘across the range of possible reduced dust standards.” '
This commenter confuses the accuracy of a respirable dust concentration measurement with the accuracy of the procedure used to establish a reduced dust standard. MSHA has a separate program in which silica analysis is used to set the applicable respirable coal mine dust standard, in accordance with section 205 of the Mine Act (30 U.S.C. 845), when the respirable dust in the mine atmosphere of the active workings contains more than 5 percent quartz. As shown by Equation 1, no silica analysis is used in a single, full-shift measurement of the respirable dust concentration. Therefore, the Secretaries would not agree with the comment that CV
Several previous commenters pointed out that local factors such as dusty clothing could cause concentrations in the immediate vicinity of the sampler unit to be unrepresentative of a larger area. Dust from a miner's clothing nevertheless represents a potential hazard to the miner. No evidence was previously presented to demonstrate that miners are not also exposed to dust originating from dusty clothing.
Several previous commenters argued that MSHA underestimated CV
MSHA and NIOSH reviewed all of the studies referenced by the previous commenters. The review showed that all of the estimates of measurement variability were from studies carried out prior to improvements mandated by the 1980 MSHA revisions to dust sampling regulations, discussed earlier in “Validity of the Sampling Process” (see Section X.C.). For example, the General Accounting Office (GAO)
One of the previous commenters particularly questioned the value MSHA used in its February 18, 1994 proposed notice of Joint Finding to represent variability in initially setting the pump flow rate. In response to this commenter's suggestion, MSHA conducted a study to verify the magnitude of this variability component. This study simulated flow rate adjustment under realistic operating conditions by including a number of persons checking and adjusting initial flow rate under various working situations (Tomb, September 1, 1994). Results showed the coefficient of variation associated with the initial flow
Intersampler variability, represented by CV
To address previous commenters' concerns that the Agencies had underestimated CV
Prior to the field study, two modifications to MSHA's sampling and analytical method had been considered by MSHA and NIOSH: (1) Measuring both the pre-and post-exposure weights to the nearest microgram (μg) on a balance calibrated using the established procedure within MSHA's Respirable Dust Processing Laboratory; and (2) discontinuing the practice of truncating the recorded weights used in calculating the dust concentration. These modifications were incorporated into the design of the field study.
One previous commenter characterized the field study as being “woefully incomplete” because it was conducted “in a tightly controlled environment * * * not subject to normal environmental variation.” While it is true that the samples within each test were not subject to normal environmental variability, this was because the experiment was deliberately designed to avoid confusing spatial variability in dust concentration with measurement error. However, pumps were handled and flow rates were checked in the same manner as during routine sampling. Furthermore, the sampler units were disassembled and reassembled in the normal manner to remove and replace dust cassettes.
Previous commenters also questioned the value that MSHA used in the February 1994 proposed notice of Joint Finding to represent uncertainty due to potential weighing errors. In September 1994, MSHA submitted into the record an analysis based on replicated weighings for 300 unexposed filter capsules, each of which was weighed once by the cassette manufacturer and twice in MSHA's laboratory (Kogut, May 12, 1994). An estimate of weighing imprecision derived from this analysis was used by NIOSH in its September 20, 1995 assessment of MSHA's sampling and analytical procedure (discussed in more detail later in section X.E.)
In the March 12, 1996 notice concerning the NIOSH Accuracy Criterion, MSHA described the results of an investigation into repeated weighings of the same capsules made over a 218-day period using MSHA's automatic weighing system. It was noted that after approximately 30 days, filter capsules left exposed and unprotected gained a small amount of weight—an average of 0.8 μg (micrograms) per day. Neither NIOSH nor MSHA considered this a problem, since all dust samples are analyzed within 24 hours of receipt and are not left exposed and unprotected. However, more recent data collected to quantify weighing variability between the Mine Safety Appliances Co. and MSHA laboratories showed that filter capsules tend to gain a small amount of weight even when stored in plastic cassettes (Parobeck,
One commenter had previously stated that the Secretaries were addressing only precision, thereby implying that potential biases were being ignored. To eliminate the potential for any bias due to a spurious gain or loss of filter capsule weight, MSHA has used control filter capsules in its enforcement program since April 30, 1998. Any change in weight observed for the control filter capsule will be subtracted from the measured change in weight of the exposed filter capsule. Each control filter capsule will be pre-weighed with the other filter capsules, will be stored and transported with the other capsules, and will be on the inspector's person during the day of sampling. This 1998 modification to MSHA's inspector sampling and analytical procedure will ensure an unbiased estimate of the true weight gain (Wagner, May 28, 1997).
As explained above under the headings of “Sample Processing” and “Quantification of Measurement Uncertainty”, evidence of relatively small weight gains in unexposed filter capsules led MSHA, in 1998, to begin using unexposed control filters to adjust the weight gains measured for exposed filters. Under the new system, respirable coal mine dust samples taken by MSHA inspectors are matched with unexposed control filter capsules. For an inspector sample to be valid, the matching, unexposed control filter capsule must have been weighed on the same two days as the exposed capsule—initially before exposure and then, for a second time, afterwards.
From April 30, 1998 through December 31, 1998, a total of 5,578 such control filter capsules were weighed for the second time in MSHA's laboratory after having been sent out to the field. Although MSHA's new processing system was not fully implemented before April 30, 1998, many of these control filter capsules which were constructed with Tyvek®, along with the corresponding exposed capsules, were initially weighed prior to 1998. The time intervals between first and second weighings ranged from 32 to 608 days. Excluding six filter capsules that were broken, misidentified, improperly labeled, or contaminated, weight gains measured for the remaining 5,572 unexposed filter capsules ranged from a maximum of 420 μg down to a negative 317 μg (
As explained earlier, if an unexposed control filter either shows a weight gain greater than 100 μg or a weight loss greater than 30 μg, then, instead of using it to make any adjustment, MSHA simply voids the corresponding coal mine respirable dust sample. This occurred in 126 cases, leaving 5,446 cases in which the control filter was actually used to adjust a dust sample. For these 5,446 control filters, the mean weight gain measurement was 14.8 μg, and the standard deviation was 19.2 μg. Consequently, weight gains observed in exposed filters were reduced by about 15 μg, on average, through the end of 1998. This corresponds to an average reduction in measured dust concentration of about 0.02 mg/m
Variability in unexposed filter weight gain measurements, as expressed by the standard deviation of 24.6 μg, consists of three components: (1) random weighing errors; (2) spurious but real changes in weight, such as might be due to contamination or outgassing from the plastic filter cassette onto the filter capsule; and (3) effects of any changes in laboratory conditions between the first and second weighings. Each of these three effects also contributes to uncertainty in the amount of coal mine dust accumulated on an exposed filter.
MSHA's purpose in using unexposed control filters to adjust weight gains measured for exposed filters is to eliminate the second and third of these components as sources of measurement uncertainty for the exposed filters. Unfortunately, the control filter adjustment cannot eliminate the first component, comprised of random weighing errors. To the contrary, making the adjustment based on a single control filter doubles the number of weighings required to establish weight gain for an exposed filter. This increases (by a factor of √2) uncertainty due to the random error potentially associated with each weighing. Therefore, there is a tradeoff in applying the control filter adjustment: the adjustment improves accuracy only if it succeeds in reducing uncertainty due to changes in laboratory conditions and spurious changes in filter weight by an amount greater than the increase in uncertainty resulting from the additional weighings required.
Estimates representing the first component (
Control filters, however, fully eliminate the effects of day-to-day variation in laboratory conditions and spurious changes in filter weight only if these effects are consistent for all filters weighed on the same days and sent out to the same field location for the same length of time between weighings. In the absence of evidence to the contrary, MSHA and NIOSH consider this to be a reasonable assumption in the case of laboratory effects: any systematic differences in laboratory conditions between the dates of initial and final weighing should have essentially the same effect on weights recorded for unexposed filter capsules as for exposed filter capsules.
The remaining component of uncertainty, resulting from spurious but real weight changes such as might be caused by outgassing or contamination, is eliminated by the control filter adjustment only to the extent that such effects are consistent for all filters pre-weighed on the same day, sent out to the same field location, and then post-weighed on the same day. MSHA checked this assumption for currently approved filter capsules—
The NHSCP_99 dataset consists of 108 “batches” in which several control filter capsules were first weighed on the same day, taken to the same mine site (but left unexposed), and then all weighed again on the same day in 1999. For example, a batch of six capsules may have been initially weighed on December 19, 1997, left unexposed during a mine visit on February 23, 1999, and then weighed for the second time on March 2, 1999. The NHSCP_99 data set contains information on a total of 564 filter capsules, divided into 108 such batches so that, on average, there were about five unexposed filter capsules per batch. The time interval between initial and final weighings averaged 335 days and ranged from 136 to 694 days. Closely matching results from CNTRL_98, the overall mean weight gain recorded for these unexposed filter capsules was about 14 μg, and the overall standard deviation was about 25 μg.
If changes in weight are indeed consistent for control filters subjected to similar handling and aging effects, then variability in weight gains within batches should not significantly exceed variability attributable to random weighing errors alone. MSHA's statistical analysis of NHSCP_99, however, indicated that variability in weight gains within batches was significantly greater than what can be attributed to random weighing errors under current processing procedures (Kogut,
MSHA then performed a field experiment to determine if modifying the filter capsule would reduce variability due to spurious changes in weight (Kogut,
MSHA's statistical analysis of the MFCS data indicated that substituting a stainless steel support pad for the Tyvek® support pad currently in use, in both exposed and unexposed filter capsules, could significantly improve measurement accuracy. This modification reduced the standard deviation of weight gains measured for unexposed filters within batches to 11.6 μg.
MSHA and NIOSH would welcome further statistical analysis of the datasets being placed into the public record with this notice. The Agencies would also welcome suggestions on how MSHA might further modify its analytical procedures to reduce uncertainty in the amount of dust deposited on an individual filter.
NIOSH's first independent analysis of MSHA's sampling and analytical method involved MSHA's 1995 field study data.
In the same report NIOSH also applied an indirect approach for assessing the accuracy of MSHA's sampling and analytical method. The indirect approach involved combining separate estimates of weighing imprecision, pump-related variability, and variability associated with physical differences between individual sampler units. This indirect approach also indicated that MSHA's sampling and analytical method would meet the NIOSH Accuracy Criterion at concentrations greater than or equal to 0.2 mg/m
As discussed above, MSHA later obtained data suggesting that filter capsules containing Tyvek® backup pads sometimes exhibit spurious changes in weight. Although the changes observed were relatively small, compared to weight gains required for MSHA's noncompliance determinations, this led MSHA to begin using unexposed control filters in its enforcement program. As explained in Appendices A and B, the use of a control filter adjustment eliminates systematic errors due to such effects, but also affects the precision of a single, full-shift measurement. Consequently, NIOSH reassessed the accuracy of MSHA's sampling and analytical method, taking into account the effects of using a control filter capsule (Wagner, May 28, 1997). After accounting for the effects of control filter capsules on both bias and precision, NIOSH concluded, based on both its direct and indirect approaches, that a single, full-shift measurement will meet the NIOSH Accuracy Criterion at true dust concentrations greater than or equal to 0.3 mg/m
As part of its ongoing commitment to improving the sampling and analytical method, MSHA recently compiled data showing that weight stability of the filter capsule would be improved by substituting stainless steel support grids for the Tyvek® support pads currently in use (Kogut
One previous commenter stated that the Secretaries “have not addressed the ‘accuracy’ of a single sample collected from an environment where the concentration is unknown.” The purpose of any measurement process is to produce an estimate of an unknown quantity. The Secretaries have concluded that MSHA's sampling and analytical method for inspectors meets the NIOSH Accuracy Criterion for true concentrations at or above 0.3 mg/m
The Secretaries recognize that future technological improvements in MSHA's sampling and analytical method may reduce CV
The Secretaries have concluded that sufficient data exist for determining the uncertainty associated with a single, full-shift measurement; rigorous requirements are in place, as specified by 30 CFR parts 70, 71, and 90, to ensure the validity of a respirable coal mine dust sample; and valid statistical techniques were used to determine that MSHA's improved dust sampling and analytical method meets the NIOSH Accuracy Criterion. For these reasons the Secretaries would find that a single, full-shift measurement at or above 0.36 mg/m
Section 101(a)(6)(A) of the Mine Act (30 U.S.C. 811(a)(6)(A)) requires the Secretary of Labor to set standards which most adequately assure, on the basis of the best available evidence, that
In relation to promulgating health standards, the legislative history of the Mine Act states that:
* * * This section further provides that “other considerations” in the setting of health standards are “the latest available scientific data in this field, the feasibility of the standards, and experience gained under this and other health and safety laws.” While feasibility of the standard may be taken into consideration with respect to engineering controls, this factor should have a substantially less significant role. Thus, the Secretary may appropriately consider the state of the engineering art in industry at the time the standard is promulgated.
Similarly, information on the economic impact of a health standard which is provided to the Secretary of Labor at a hearing or during the public comment period, may be given weight by the Secretary. In adopting the language of section 102(a)(5)(A), the Committee wishes to emphasize that it rejects the view that cost benefit ratios alone may be the basis for depriving miners of the health protection which the law was intended to insure.
In
MSHA, in consultation with NIOSH, believes that compliance determination based on an inspector, single, full-shift exposure measurement would be technologically feasible for the mining industry. An agency must show that modern technology has at least conceived some industrial strategies or devices that are likely to be capable of meeting the standard, and which industry is generally capable of adopting.
This NPRM would not be a technology-forcing standard. The single, full-shift sample rule when promulgated predominantly affects MSHA's procedures since MSHA alone conducts inspector sampling. After the promulgation of single, full-shift sample rule, coal mine operators would continue to comply with the existing respirable dust concentration limit of 2.0 mg/m
MSHA, in consultation with NIOSH, believes that the single full shift sample (SFSS) rule would be economically feasible for the coal mining industry. The coal mining industry would incur costs of approximately $1.8 million yearly to comply with the proposed SFSS rule. Coal mine operators would also incur approximately an additional $0.2 million yearly in penalty costs associated with the additional citations arising from the proposed SFSS rule. That the total $2.0 million borne yearly by the coal mining industry as a result of the proposed SFSS rule is well less than 1 percent (about 0.01 percent) of the industry's yearly revenues of $19.8 billion provides convincing evidence that the proposed rule is economically feasible.
Economic feasibility does not guarantee the continued existence of individual employers—“A standard is not infeasible simply because it is financially burdensome, * * * or even because it threatens the survival of some companies within an industry:”
This rule would not threaten the industry's competitive structure. After the promulgation of single, full-shift sample rule the Agencies expect that coal mine operators would continue to comply with the existing respirable dust concentration limit of 2.0 mg/m
MSHA's improved program to eliminate overexposures on each and every shift includes (1) the simultaneous implementation of the use of inspector single, full-shift respirable coal mine dust samples to identify overexposures more effectively in both underground and surface coal mines (single, full-shift sample), and (2) in underground coal mines, verified ventilation plans to maintain miners' respirable dust exposure at or below the applicable standard on each and every shift (plan verification). The plan verification NPRM is published elsewhere in today's
Assumptions for single, full-shift sample requirements are based upon information provided by MSHA technical personnel. We encourage the mining community to provide detailed comments in this regard to ensure that single, full-shift sample cost assumptions and estimates are as accurate as possible.
In accordance with Executive Order 12866, the Agencies have prepared a detailed PREA of the estimated costs and benefits associated with the proposed rule for the underground and surface coal mining sectors. We have fulfilled this requirement for the proposed rule and determined that this rulemaking is not a significant regulatory action. The key findings of the PREA are summarized below.
The Agencies estimate that the cost of this NPRM would be approximately $1.8 million annually, of which all but
The compliance costs arising from the single, full-shift sample NPRM would occur as a result of a slight increase in the number of MSHA inspector citations issued to underground and surface coal mine operators due to the determination of noncompliance with the respirable coal mine dust standard being based on inspector single, full-shift samples rather than the average of multiple inspector exposure measurements. The additional citations due to single, full-shift sample would require mine operators to undertake the following actions and to incur associated compliance costs: take corrective action(s) in order to get back into compliance with the applicable respirable coal mine dust standard; perform abatement sampling; complete dust data cards; send abatement samples to MSHA; post abatement sample results; write respirable dust plans; and post or give a copy of dust plans.
In addition to these estimated compliance costs, mine operators would incur yearly penalty cost increases of about $0.2 million. Penalty costs conventionally are not considered to be a cost of a rule (and, in fact, are clearly not a compliance cost) but merely a transfer payment from a party violating a rule to the government. Therefore, the penalty costs are not included as part of the compliance costs of the proposed SFSS rule noted above. These penalty costs are relevant, however, in determining the economic feasibility of the proposed SFSS rule.
The derivation of the above cost figures are presented in Chapter IV of the PREA that accompanies this rule.
Occupational exposure to excessive levels of respirable coal mine dust imposes significant health risks. These include the following adverse health outcomes: simple coal workers' pneumoconiosis (simple CWP), progressive massive fibrosis (PMF), silicosis, and chronic obstructive pulmonary disease (COPD) (e.g., asthma, chronic bronchitis, emphysema) (see the Health Effects section for details). Cumulative exposure to respirable coal mine dust is the main determinant in the development of both simple CWP and PMF although other factors such as the percentage of quartz in the respirable dust and the type of coal also affect the risk of miners developing simple CWP and PMF (Jacobsen,
Through the joint promulgation of single, full-shift sample and plan verification rules, miners would be further protected from the debilitating effects of occupational respiratory disease by limiting their exposures to respirable coal mine dust to no more than the applicable standard on each and every shift.
Based on 1999 operator data, there were 704 MMUs (out of 1,251) at which regular (not abatement) designated occupational (D.O.) samples exceeded the applicable standard on at least two of the sampling shifts reported in 1999 (MSHA, Data file: Operator.ZIP).
At the MMUs being considered (those exhibiting a pattern of recurrent overexposures),
When the dust concentration measured for the D.O. exceeds the applicable standard, measurements for at least some of the other miners working in the same MMU may also exceed the standard on the same shift, though usually by a smaller amount. Furthermore, although the D.O. represents the occupation most likely to receive the highest exposure, other miners working in the same MMU may be exposed to even higher concentrations than the D.O. on some shifts. Therefore, in addition to the affected D.O. miners, there is a population of other affected miners who are also expected to experience a significant reduction in risk as a result of eliminating overexposures on their individual shifts.
To estimate how many miners other than the D.O. would be substantially affected, MSHA examined the results from all valid dust samples collected by MSHA inspectors in underground MMUs during 1999 (MSHA, Data file: Inspctor.zip). Within each MMU, the inspector typically takes one full-shift sample on the D.O. and, on the same shift, four or more additional samples representing other occupations. On 896 shifts, at a total of 450 distinct MMUs, the D.O. measurement exceeded the applicable standard, and there were at least three valid measurements for other occupations available for comparison. There was an average of 1.2 non-D.O. measurements in excess of the standard on shifts for which the D.O. measurement exceeded the standard.
Combining these results with the 21-percent rate of excessive exposures observed for the D.O. on individual shifts, it is reasonable to infer that, at the MMUs under consideration, an average of 1.2 other miners, in addition to the one classified as D.O., is currently overexposed on at least 21 percent of all production shifts. Over the course of a working year, the reduction in exposure expected for these affected non-designated occupational (N.D.O.) miners, is 0.17 mg-yr/m
The expected lifetime for all American males, conditional on their having reached 20 years of age, is 73 years (U.S. Census March 1997, Table 18; U.S. Census March 1997, Table 119).
To estimate the benefits (i.e., number of cases of simple CWP and PMF prevented) of single, full-shift sample and plan verification rules combined, we applied these estimates of risk reduction to the estimated sub-populations of affected miners. As of February 12, 1999, there were 984 producing MMUs;
The benefits that would accrue to coal miners exposed to respirable coal mine dust and to mine operators, and ultimately to society at large, are substantial and take a number of forms. These proposed rules would reduce a significant health risk to underground coal miners, reducing the potential for illnesses and premature death and their attendant costs to miners, their employers, their families, and society.
The joint promulgation of these rules should realize a positive economic impact on the Department of Labor's (DOL's) Black Lung Program and relatedly on mine operators. The Black Lung Program compensates eligible miners and their survivors under the Black Lung Benefits Act. This program provides monthly payments and medical benefits (diagnostic and treatment) to miners who are found to be totally disabled by black lung disease, including cases of PMF and simple CWP. In 1986, DOL's Employment Standards Administration reported that 12% of approved cases of Black Lung Program were identified as cases of PMF based on chest radiographs, while sixty-four percent had simple CWP based on chest radiographs (ESA, 1986). For miners who stopped working in coal mines after 1969 and for whom the DOL can establish that the miner worked for the same operator for at least one calendar year, and that miner had at least 125 working days in that year, that operator is financially responsible for the miner's Black Lung benefit payment. If a responsible operator cannot be identified for an eligible miner, benefit payments are made by the Black Lung Disability Trust Fund. To the extent that these rules reduce overexposures to respirable coal mine dust, there should be fewer Black Lung Program cases. Therefore, over time, the associated financial outlay by responsible operators through either insurance premiums or direct payments of Black Lung benefits should be lower than would otherwise occur. The financial impact could be substantial (see discussion in Chapter IV, of the PREA). In 1980, the Black Lung Program estimated average lifetime payouts for responsible operators for married miners of about $248,700 dollars, assuming a 7-percent annual increase (ESA, 1980). In fiscal year 1999, 443 claims for Black Lung Benefits were accepted as new cases; sixty-six percent (293) are the financial responsibility of coal mine operators (Peed, 2000).
The most tangible benefit of these rules is the number of cases of simple CWP and PMF which would be prevented. Table XIII–2 presents the estimated number of cases of simple CWP and PMF that would be prevented among the 56 percent of MMUs currently exhibiting a pattern of recurrent overexposures. For all categories of simple CWP and PMF combined, we estimate 37 fewer of these cases among affected miners, than would otherwise occur without the promulgation of single, full-shift sample and plan verification rules. Eleven of these cases would be the most severe form of coal miners pneumoconiosis, PMF, and as such these cases could be interpreted as prevented premature deaths due to occupational exposure to respirable coal mine dust. Since simple CWP predisposes the development of PMF, it is important that it also be prevented (Balaan,
As discussed in the Significance of Risk sections, MSHA believes this QRA for simple CWP and PMF strikes a reasonable balance based on available data. Yet, our estimates likely understate the true impact of these rules since our analyses are restricted to a sub-population of affected miners, those working at MMUs exhibiting a pattern of recurrent overexposures, not the broader population of coal miners who would benefit from these rules. Furthermore, to estimate the average overexposure which would be prevented, MSHA had to use data collected for compliance purposes, which may not represent typical environmental conditions and the associated respirable coal mine dust exposure in underground coal mines.
The degree to which the exposure level of respirable coal mine dust on sampling shifts may not be representative of typical exposure levels is affected by the following factors:
(1) There exists a positive relationship between coal production and generation of respirable coal mine dust;
(2) Current sampling procedures permit sampling measurements to be taken at the mid-range of the distribution of the level of production—sampling measurements must be taken on shifts with production at least 60% of the average production during the last 30 days and at least 50% of average production for the last valid set of bimonthly samples for inspector and operator samples, respectively;
(3) Miners have reported and MSHA data have demonstrated lower levels of production on sampling shifts versus non-sampling shifts (MSHA, September 1993);
(4) On some sampling shifts, miners have reported that more engineering controls may be used than on other shifts, thus reducing the measured amount of respirable coal mine dust;
(5) MSHA analyses have demonstrated, even when controlling for production, in mines with fewer than 125 employees, on continuous mining MMUs, respirable coal mine dust exposures were much higher during the unannounced Spot Inspection Program (SIP) sampling shifts than on shifts operators sampled—this is consistent with the effect of increasing engineering controls on shifts during which bimonthly samples are conducted compared to the level of use of engineering controls used on shifts for which the operator does not expect sampling to be conducted given the same production level (Denk, 1993);
(6) Across mine size, designated area samples have been found to be larger for shifts on which unannounced compliance sampling occurred compared to operator sampling shifts—in one study they differed by at least a factor of 40 percent in large mines and 100 percent in the smallest mines (Ibid., pp. 211–212); and
(7) Existing MSHA technical information indicates that some reduction in production levels occurs during some sampling periods on longwalls (Denk, 1990).
Therefore, at a bare minimum, over an occupational lifetime (45-years) for miners who live to age 73 who worked
Our current quantitative estimate of benefits demonstrates and qualitative discussions punctuate that these rules would have a significant positive impact on the health of our nation's coal miners when promulgated. Yet, due to the limitations in these data, we believe our benefit estimate may understate the number of cases of simple CWP and PMF which would be prevented over an occupational lifetime.
MSHA believes that cases of simple CWP and PMF would also be prevented among other types of underground miners, such as roofbolters working in designated areas (D.A.). Based on MSHA experience it is reasonable to expect roofbolter D.A.'s pattern of overexposures for respirable coal mine dust to be similar to that for miners with the highest exposure on a MMU. If so, we would expect 13 additional cases of simple CWP and PMF to be prevented. Affected D.A.s include D.A.s who work at the 56 percent of the MMUs under consideration who are exposed to dust concentrations similar to the D.O., over a 45-year occupational lifetime (MSHA Table, November 1999; MSHA Table, February 1999).
Also, it is reasonable to expect surface miners' health to be further protected by the promulgation of the SFSS rule alone since it would identify and require resolution of overexposures not previously identified and may thereby lower some miners' cumulative exposure to respirable coal mine dust. Furthermore, to the extent that cumulative exposure to respirable coal mine dust affects other adverse health outcomes, such as silicosis and chronic obstructive pulmonary disease, it is reasonable to expect a reduction in the number of cases and/or in the severity of cases for these diseases among surface and underground coal miners.
Although the effect cannot readily be quantified, to the extent that these rules would also reduce the cumulative exposure to respirable coal mine dust among some miners working in those MMUs currently not exhibiting overexposures, it is reasonable to expect that we would observe an incremental benefit among that sub-population of coal miners. Moreover, to the extent that the cumulative dust exposure is reduced for miners working in the “outby” areas, away from the mining face (i.e., MMU) where coal is extracted from the coal seam, they too may realize occupational health benefits due to the simultaneous promulgation of these proposals. Therefore, our best estimate of 37 prevented cases of simple CWP and PMF, combined, among all affected miners likely underestimates the true benefit realized by the coal mining workforce through the reduction of overexposures to no more than the applicable standard on each shift.
Clearly, PMF is associated with premature death. Since simple CWP may evolve to PMF, even after occupational exposure has ceased, it has the propensity to become a life-threatening illness. By reducing the total number of simple CWP and PMF cases among affected miners from 259 to 222, over 45 years,
For all those reasons previously identified, MSHA believes that its estimate of 37 prevented cases of simple CWP and PMF over a 45 year working life understates the true number of cases of simple CWP and PMF which would be prevented. This belief is further supported by the fact that during the past few years, the Black Lung Benefits Program has been approving roughly 400 claims each year. These claims come from individuals whose exposure for the most part came after the current standard of 2.0 was established in 1972. Thus, we believe the consistent identification, from year to year, of hundreds of new cases of simple CWP and PMF per year into the Black Lung Benefits Program supports our belief that the true lifetime occupational health benefits of the proposed rules are higher than we have estimated. Even assuming that the number of new claims would decline in future years simply due to the continuing decline in the number of coal miners, MSHA expects that assuring that future exposures are maintained below the 2.0 exposure limit will reduce the number of new cases of simple CWP and PMF by considerably more than 1 per year.
In addition to the prevention of simple CWP and PMF, each of the 8,640 affected miners at MMUs exhibiting a pattern of recurrent overexposures will realize some health benefit by limiting his or her cumulative exposure to respirable coal mine dust to no more than the applicable standard on each and every shift.
The expected number of prevented cases of simple CWP and PMF would not be realized for some time even after the pattern of overexposures has been minimized or eliminated. This is due, in part, to the latency (that is, the disease does not develop immediately after exposure) of the development of simple CWP and PMF and the pre-existing occupational exposure histories of members of the current coal mining workforce. Our estimated benefit is based on the estimated number of underground coal miners working at the mine face, 17,280. If the size of this workforce significantly changed in the future and the projected pattern of prevented overexposures remained the same, the number of cases of prevented simple CWP and PMF would need to be adjusted to account for the change.
Finally, even standing alone, without simultaneously requiring that the effectiveness of underground mine ventilation plans be verified (i.e., the Plan Verification NPRM), the proposed standard allowing MSHA to use single, full-shift samples to identify overexposures requiring corrective action would provide miners with health benefits.
Various data, assumptions and caveats were used to conduct the quantitative risk assessment, significance of risk discussion, and benefits analyses. Therefore, we request any information which would enable us to conduct more accurate analyses of the estimated health benefits of the single, full-shift sample rule and plan verification rule, both individually, and in combination.
The Regulatory Flexibility Act requires MSHA and NIOSH to conduct an analysis of the effects of the single, full-shift sample rule on small entities. That analysis is summarized here; a copy of the full analysis is included in Chapter V of the Agencies' PREA in support of the proposed rule. The Agencies encourage the mining community to provide comments on this analysis.
The Small Business Administration generally considers a small entity in the mining industry to be one with 500 or fewer workers. MSHA has traditionally defined a small mine to be one with fewer than 20 workers, and has focused special attention on the problems experienced by such mines in implementing safety and health rules. Accordingly, the Agencies have separately analyzed the impact of the joint notice proposed rule both on mines with 500 or fewer workers and on those with fewer than 20 workers.
Pursuant to the Regulatory Flexibility Act, MSHA must determine whether the costs of the joint notice proposed rule constitute a “significant impact on a substantial number of small entities.” Pursuant to the Regulatory Flexibility Act, if an Agency determines that a proposed rule would not have such an impact, it must publish a “certification” to that effect. In such a case, no additional analysis is required (5 U.S.C. § 605). In evaluating whether certification is appropriate, MSHA utilized a “screening test,” comparing the costs of the joint notice proposed rule to the revenues of the affected coal sector. If the estimated costs are less than 1 percent of revenues for the affected entities, then the rule is assumed not to have a significant impact on small mine operators.
Table XIII–3 compares, for small underground and surface coal mines (using both MSHA's and SBA's definition), MSHA's estimated total annual compliance costs of the joint notice proposed rule to estimated annual revenues.
Table XIII–3 shows that under either MSHA's or SBA's definition of a small mine, for underground and/or surface coal mines, the estimated costs would be significantly less than one percent of revenues. As a result, MSHA is certifying that the single, full-shift sample rule for underground and surface coal mines would not have a “significant impact on a substantial number of small entities,” and has performed no further analyses.
For purposes of the Unfunded Mandates Reform Act of 1995, this rule does not include any Federal mandate that may result in increased expenditures by State, local, and tribal governments, or increased expenditures by the private sector of more than $100 million.
This proposed rule contains information collections which are subject to review by the Office of Management and Budget (OMB) under the Paperwork Reduction Act of 1995 (PRA95). The proposed SFSS rule has annual burden hours beginning in the first year and recurring every year thereafter. Both underground and surface coal mines have paperwork provisions under the proposed SFSS rule. Underground coal mine operators would incur 2,985 annual burden hours and associated costs of $70,822. Surface coal mine operators would incur 29 annual burden hours and associated costs of about $1,009. These burden hours relate to operators performing abatement sampling, completing dust data cards, mailing samples to MSHA for analysis, writing respirable dust plans, and posting respirable dust plans. Table XIV–1 shows the burden hours and associated costs for each SFSS paperwork provision by mine size for underground and surface mines.
MSHA invites public comments and is particularly interested in comments which:
1. Evaluate whether the proposed collection of information (presented here and in MSHA's PREA) is necessary for the proper performance of the functions of MSHA, including whether the information will have practical utility;
2. Evaluate the accuracy of MSHA's estimate of the burden of the proposed collection of information, including the validity of the methodology and assumptions used;
3. Enhance the quality, utility, and clarity of the information to be collected; and
4. Minimize the burden of the collection of information on respondents, including through the use of appropriate automated, electronic, mechanical, or other technological collection techniques or other forms of
MSHA and NIOSH have submitted a copy of this proposed rule to OMB for its review and approval of these information collections. Interested persons are requested to send comments regarding this information collection, including suggestions for reducing this burden, to the Office of Information and Regulatory Affairs, OMB New Executive Office Building, 725 17th St., NW, Rm. 10235, Washington, DC 20503, Attn: Desk Officer for MSHA. Submit written comments on the information collection not later than September 5, 2000.
MSHA's paperwork submission summarized above is explained in detail in the PREA. The PREA includes the estimated costs and assumptions for each proposed paperwork requirement related to this proposed rule. A copy of the PREA is available from MSHA. These paperwork requirements have been submitted to the Office of Management and Budget for review under section 3504(h) of the Paperwork Reduction Act of 1995. Respondents are not required to respond to any collection of information unless it displays a current valid OMB control number.
The National Environmental Policy Act (NEPA) of 1969 requires each Federal agency to consider the environmental effects of proposed actions and to prepare an Environmental Impact Statement on major actions significantly affecting the quality of the human environment. MSHA has reviewed the proposed standard in accordance with the requirements of the NEPA (42 U.S.C. 4321
Commenters are encouraged to submit their comments on this determination.
This proposed rule is not subject to Executive Order 12630, Governmental Actions and Interference with Constitutionally Protected Property Rights, because it does not involve implementation of a policy with takings implications.
The Agency has reviewed Executive Order 12988, Civil Justice Reform, and determined that this rulemaking will not unduly burden the Federal court system. The regulation has been written so as to provide a clear legal standard for affected conduct, and has been reviewed carefully to eliminate drafting errors and ambiguities.
In accordance with Executive Order 13045, protection of children from environmental health risks and safety risks, MSHA has evaluated the environmental health or safety effects of the proposed rule on children. The Agency has determined that this proposal would not have an adverse impact on children.
MSHA certifies that this proposed rule does not impose substantial direct compliance costs on Indian tribal governments.
We have reviewed this rule in accordance with Executive Order 13132 regarding federalism, and have determined that it does not have “federalism implications.” The rule does not “have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government.”
The Agencies will hold public hearings on the proposed rule. The hearings will be held in Prestonsburg, Kentucky, (Jenny Wiley State Resort Park); Morgantown, West Virginia; and Salt Lake City, Utah. The hearing dates, times, and specific locations will be announced by a separate document in the
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 main text, MSHA and NIOSH find that 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.
Throughout this appendix, some public comments made to February 18 and June 6, 1994 notices relevant to issues regarding single, full-shift sampling will be cited and addressed to emphasize key findings on accuracy and the effects of averaging dust concentration measurements. Some previous 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
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.
Some previous 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 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, full-shift 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 previous 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 previous 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 basing noncompliance on a single, full-shift measurement.
Furthermore, if the objective were really to estimate average dust concentration throughout some specified zone on a given shift, then it would often 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 previous 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 and NIOSH recognize that a single, full-shift 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.
Some previous 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 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 the measurement objective is to estimate a miner's average dust exposure over a period longer than an individual shift. This assumption is flawed, as shown by the fact that section 202(b) of the Mine Act specifies that each operator will 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 Secretaries recognize 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 previous 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 Secretaries have 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 previous commenter, averaging Monday's exposure measurement with Tuesday's does not improve the estimate of Monday's average dust concentration.
Some previous commenters argued that since the risk of pneumoconiosis depends on cumulative exposure, the measurement 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 previous 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 Secretaries interpret the Mine Act as requiring that dust concentrations be kept at or below the applicable standard on each and every shift. Nevertheless, the Secretaries recognize 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 inspection do not meet this requirement. Therefore, the Secretaries have 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.
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 previous 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 inspection, relative to the dust concentration measured on the final shift of the previous multi-shift inspection. 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
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 single-shift 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 (September 6, 1994b) and also on public comments received in response to the February 18 and June 6, 1994, notices, the Secretaries have 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.
The accuracy of a measurement depends on both precision and bias (Kennedy,
The current U.S. coal mine dust standard is based on studies of British coal miners. In these studies, full-shift dust measurements were made using a sampler employing four horizontal plates which removed the large-sized particles by gravitational settlement (simulating the action of the nose and throat) and collecting on a pre-weighed filter those particles which are normally deposited in the lungs (Goddard,
Two previous commenters noted that the 1.38 conversion factor was derived from a comparison of MRE measurements to measurements obtained using pumps made by two manufacturers: Mine Safety Appliances Co. and Unico. These commenters noted that there was some variability in these comparisons that MSHA and NIOSH did not consider in estimating CV
The study referred to these previous commenters involved collecting side-by-side samples using MRE and cyclone-based samplers (Tomb,
Variability in the operating characteristics of individual sampler units is expressed by CV
Because the conversion factor derived from the inspector data came closer to the theoretical value, the former U.S. Bureau of Mines' Pittsburgh Technical Support Center
One commenter implied that the respirable dust cyclone specifications used by MSHA result in a different particle collection efficiency curve than that specified by the American Conference of Governmental Industrial Hygienists (ACGIH) and the International Organization for Standardization (ISO) for a respirable dust sampler. Other previous commenters questioned whether the 2.0 L/min flow rate used by MSHA was appropriate, since a NIOSH study recommended using a 1.7 L/min flow rate when conforming to the recently adopted ACGIH/ISO specifications for collecting respirable particulate mass.
It is true that MSHA's respirable dust cyclone specifications result in a different particle size distribution than that specified by ACGIH and ISO. However, this fact has no bearing on the conversion to a respirable dust concentration as measured by an MRE sampler, which is the basis of the respirable dust standard. The 1.38 factor used to obtain an MRE-equivalent concentration was derived for a cyclone flow rate of 2.0 L/min. If a flow rate of 1.7 L/min were used, then this would correspond to some other factor for converting to an MRE-equivalent dust concentration. Therefore, the particle size distribution obtained at 2.0 L/min governs the relationship derived between an approved respirable coal mine dust sampler and an MRE sampler. The appropriate dust fraction (
The effects of any other variables on the sampled dust fraction are covered by the 1.38 conversion factor, so long as these effects were present in the data from which the conversion factor was obtained. For example, one commenter expressed concern that nylon cyclones are subject to performance variations due to static charging phenomena. Any systematic effect of static charging on the performance characteristics of the nylon cyclone is implicitly accounted for in the conversion factor, because the same static charging effect would have been present when the comparative measurements were obtained for deriving the relationship between an approved sampler unit and an MRE instrument. Random effects of static charging,
The weight of a dust sample is determined by weighing each filter capsule before and after exposure and then determining the weight gain by subtraction. This weight gain is adjusted by subtracting any change in weight observed for the unexposed, control filter capsule. This practice eliminates potential biases due to any possible outgassing of the plastic cassette or other time-related factors but introduces two additional weighings. The weighing process is designed to control potential effects of temperature, humidity, and contamination. However, because the initial and final weighings of both the exposed and the control filter capsules are each still subject to random error, there is some degree of uncertainty in the computed weight of dust collected on the filter.
For both the control and the exposed filter capsule, the error in the weight-gain measurement results from combining two independent weighing errors. For example, suppose that the true pre- and post-exposure weights of a filter capsule are W
The error (e) in this particular weight-gain measurement, resulting from the combination of a 7 μg error in w
Imprecision
Therefore, the standard deviation of the propagated weighing error component in a single, full-shift measurement (x = g·1.438/m
Since a control filter capsule will is used to eliminate potential bias, the weight gain measured for the exposed filter (g) is adjusted by subtracting the change in weight (which may be positive or negative) observed for the control filter capsule (g′). Therefore, the adjusted measurement of dust concentration is
To form an estimate of CV
Table C–1 summarizes 13 different estimated values for σ
In MSHA's February 1994 notice, 1.438σ
After publication of the February 1994 notice, several other candidate values for σ
Some previous commenters misread or misunderstood the published NBS estimate. One of these previous commenters claimed that “the only published report of the weighing error in MSHA's laboratory * * * was 0.16 mg of variation, which would convert to a concentration of 0.20 mg/m
In September 1994, a more recent analysis was placed into the public record, based on repeated weighings of 300 unexposed filter capsules, each of which was weighed once in the Mine Safety Appliances Co. laboratory and twice in MSHA's laboratory using current equipment (Kogut, May 12, 1994). Based on this analysis, σ
Some previous commenters suggested that the estimates of σ
Some previous commenters expressed special concern over the accuracy of pre-exposure filter capsule weights as measured by Mine Safety Appliances Co. One commenter expressed “grave concern” with regard to the 12-μg systematic difference in weights found between Mine Safety Appliances Co. and MSHA weighings of the same unexposed capsules, as described in MSHA's 1994 analysis (Kogut, May 12, 1994). These concerns became moot, at least with respect to MSHA's inspector sampling program, when MSHA began pre- and post-weighing all inspector samples at MSHA's laboratory. Furthermore, any potential bias resulting from differences in laboratory conditions on the days of pre- and post-exposure weighings should now be eliminated by the use of control filter capsules. However, contrary to this commenter's interpretation, the analysis submitted to the record in September 1994 resulted in a substantially lower estimate of σ
MSHA and NIOSH also analyzed data submitted by the NMA in connection with these proceedings. An important result of that analysis, described in Appendix D, was an estimate of σ
Both truncation of weights and the practice of pre- and post-weighing samples in different laboratories were discontinued for inspector samples in mid-1995. Under MSHA's revised procedures for processing inspector samples, filter capsules were weighed both before and after sampling in MSHA's laboratory. Furthermore, MSHA began to use weights recorded to the nearest μg in calculating dust concentrations. Therefore, the 5.8-μg estimate of σ
Based on the results of MSHA's 1995 field study,
An updated estimate of
The estimate of imprecision in measured weight gain derived from MSHA's 1995 field study discussed earlier (9.1 μg), falls only slightly above the 6.5-μg laboratory estimate. This suggested that the process of handling and actually exposing the filter capsule in a mine environment does not add appreciably to the imprecision in measured weight gain.
In February 1997, 75 unexposed filter capsules that had been pre-weighed in MSHA's laboratory and distributed to MSHA district offices were recalled and reweighed. After adjusting for variability attributable to the date of initial weighing (
An MSHA report placed into the public record with the December 31, 1997
The final two values for
In 1998, to maintain quality control for the production of filter capsules used in MSHA's enforcement program, 2,640 unexposed filter capsules were weighed at MSHA's laboratory before and after assembly by Mine Safety Appliances Co. All of these capsules employed a Tyvek® filter support pad. The estimated value for
In 1999, MSHA performed a special Modified Filter Capsule Study (MFCS) in which the Tyvek® filter support pad was replaced by a stainless steel support pad. The purpose of the MFCS was to quantify the impact of such a substitution on the accuracy of respirable coal mine dust measurements. Based on an analysis of weight gains measured for 300 modified filter capsules,
Some previous commenters pointed out that MSHA routinely voids samples when the measured pre-exposure weight of a filter capsule is greater than the measured post-exposure weight. According to these commenters, such occurrences reflect an unacceptable degree of inaccuracy in weight-gain measurements. One commenter asserted that such cases are “of particular significance when only one sample is relied upon.” This commenter attributed such occurrences solely to errors in the capsule pre-weight and implied that they should not be expected to occur under MSHA's quality assurance program. It was, therefore, implied that negative weight-gain measurements are not consistent with the degree of uncertainty being attributed to weighing error.
Prior to implementation of the 1995 processing modifications, a significant fraction of samples with less than 0.1 mg of true weight gain (
What is required for a negative weight gain (w
The occasional negative weight-gain measurements that have been observed are consistent with values of
Tabled probabilities (in percent) were obtained from a simulation of 35,000 weight-gain measurements at each value of G, assuming normally distributed weighing errors and the now discontinued practice of measurement truncation.
One commenter suggested the use of a test based on the frequency of negative weight-gain measurements to check the magnitude of the MSHA/NIOSH estimate of CV
The commenter miscalculated the expected proportion, because he mischaracterized the MSHA/NIOSH estimate of CV
In principle, if the statistical distribution of true dust concentrations were known, the expected proportion of samples voided for negative weight gain could be recalculated to reflect both a variable CV
Before truncation was discontinued, negative weight-gain measurements were caused by various combinations of pre- and post-exposure weighing and truncation error. Before MSHA began adjusting weight gains using an unexposed control filter, differences in laboratory conditions on the two weighing days and/or unexplained but real systematic weight losses over time may also have contributed to the observed frequency of negative weight gains. Now that truncation has been removed as a source of error in weight-gain measurements for inspector samples, and control filters are used to correct for systematic changes, the frequency of negative weight gains observed historically is largely irrelevant. Significant negative weight-gain measurements—
Some previous commenters maintained that “although there may be slight differences between how the samples are dried * * *” differences between the weight gain observed in MSHA samples and simultaneous samples collected nearby (and processed at an independent laboratory) indicated a greater degree of weighing uncertainty than what was being assumed. In response to the Secretaries' request for any available data supporting this position, results from paired dust samples were provided by two coal companies.
In comparing measurements obtained from paired samples, there are several important considerations that some previous commenters did not take into account. First, if two different sampler units are exposed to identical atmospheres for the same period of time, the difference between weight-gain measurements g
Furthermore, if the two exposed capsules are processed at different laboratories, the difference in weight gains contains an additional error term arising from differences between laboratories. Evidence was presented that this term (in the notation of Kogut, May 12, 1994) is far more significant than the intra-lab, intra-day weighing error in MSHA's laboratory. Moreover, the additional uncertainty introduced by use of a third laboratory also depends on unknown weighing imprecision within that laboratory, which may differ from that maintained by MSHA's measurement assurance process. (See Appendix D for analysis of paired sample data submitted by NMA).
However, the most important consideration in comparing weight gains from two different samples is that under real mining conditions, the atmospheres sampled may not be identical—even if the sampler units are located near one another. Differences in atmospheric dust concentrations over relatively small distances have been documented (Kissell,
The component of uncertainty due to variability in the pump, represented by CV
In deriving the Values Table published in MSHA's February 1994 notice, MSHA used a value of 5 percent to represent uncertainty associated with initial adjustment of flow rate at the beginning of the shift and another value of 5 percent to represent flow rate variability. The 5-percent value for variability in initial flow rate adjustment was estimated from a laboratory experiment conducted by MSHA in the early 1970s, while the value for flow rate variability was based on the allowable flow rate tolerance specified in 30 CFR part 74. This part requires that the flow rate of all sampling systems not vary by more than ±5 percent over a full shift with no more than two adjustments. MSHA did not include a separate component of variability for pump rotameter calibration because it was already included in the 5-percent value used to represent flow rate variability.
Based on a review of published results by Bowman
Because MSHA could not provide the experimental data supporting the 5-percent value used to represent uncertainty associated with the initial adjustment of flow rate, one commenter recommended that MSHA conduct a new experiment. In response to that request, MSHA conducted a study to establish the variability associated with the initial flow rate adjustment. The study, placed into the public record on September 9, 1994, attempted to emulate realistic operating conditions by including a variety of sampling personnel making adjustments under various conditions. Results showed the coefficient of variation associated with the initial adjustment to be 3 ± 0.5 percent (Tomb, September 1, 1994). The Secretaries consider this study to provide the best available estimate for uncertainty associated with the initial adjustment of a sampler unit's flow rate. Therefore, as proposed in the March 12, 1996 notice, the Secretaries are now estimating uncertainty due to variability in the initial adjustment to be 3 percent.
One previous commenter expressed concern regarding how representative MSHA's study on initial flow rate adjustment was of actual sampling conditions. The Secretaries consider the conditions under which the study was conducted to have adequately mimicked conditions under which the flow rate of a coal mine dust sampling system is adjusted. This was more rigorous than the original study, from which MSHA estimated the 5-percent value assumed in the February 12, 1994 notice. The tests were conducted in an underground mine, using both experienced and inexperienced persons to make the adjustments. Also, the only illumination was supplied by cap lamps worn by the person making the adjustments. Tests were conducted for adjustments made in three different physical positions: standing, kneeling and prone. Inspection personnel participating in the study provided guidance as to the methods typically used by inspection personnel in adjusting pumps. In fact, environmental conditions under which the test was conducted were generally more severe than those normally encountered by inspection personnel, since initial adjustment of the pumps normally occurs on the surface just before the work shift begins.
The same commenter also questioned why only the variability associated with initial adjustment of the flow rate was estimated and not the variability associated with subsequent adjustments during the shift. This is because the variability associated with the subsequent flow rate adjustments of an approved sampler unit is already included in the 3-percent value estimated for variability in flow rate over the duration of the shift.
Since variability in the initial flow rate adjustment is independent of calibration of the pump rotameter and variability in flow rate during sampling, these two sources of uncertainty can be combined through the standard propagation of errors formula:
This estimate accords well with a more recent finding based on 186 measurements in an underground mine, using constant flow-control pumps (Kogut
Three previous commenters stated that there are reports of sampling pumps being calibrated and used at altitudes differing by as much as 3,000 feet and that, for many pumps, this could result in more than a 3-percent change in flow rate per 1,000 feet of altitude. MSHA recognized this as a potential problem as early as 1975. As a result, MSHA conducted a study to ascertain the effect of altitude on coal mine dust sampler calibration (Treaftis,
Some previous commenters questioned the ability of the older Mine Safety Appliances Co. Model G pumps to meet the same flow rate specifications as new pumps. MSHA has discontinued the use of these older pumps in its sampling program and will be using only flow-control pumps. More recent MSHA studies show that these pumps continue to meet the flow rate requirement of 30 CFR 74.3(11) at altitudes up to 10,000 feet (Gero,
Intersampler variability, represented by CV
Intersampler variability was investigated by Bowman,
During the public hearings, several previous commenters indicated they had data showing that MSHA and NIOSH had underestimated the overall magnitude of uncertainty associated with a single, full-shift measurement. These data and accompanying analyses were submitted to the record and evaluated by MSHA and NIOSH. Some of the data sets consisted of paired samples, where two approved sampler units were placed nearby one another and operated for a full shift. One of the resulting samples was analyzed in MSHA's laboratory and the other by an independent laboratory. These data were represented as showing that single, full-shift measurements cannot be used to accurately estimate dust concentrations. Other data sets submitted consisted of unpaired measurements collected from miners at intervals over varying spans of time. These data sets were represented as showing that exposures vary widely between shifts and between occupations.
The American Mining Congress and National Coal Association [AMC and NCA have since merged into the National Mining Association, (NMA)] submitted at the request of MSHA and NIOSH a data set consisting of 381 pairs of exposure measurements. These measurements had been obtained from the “designated occupations” on two longwall and six continuous mining sections belonging to Skyline Coal, Inc. Two sampling units were placed on each participating miner and operated for the full shift. After sampling, one sample cassette was sent to MSHA for analysis while the other was analyzed at a private laboratory. All samples were reported to be “portal to portal” samples as required by MSHA regulations. Using these data, the NMA estimated an overall CV of 16 percent. Based on this 16-percent estimate, the NMA suggested that MSHA had underestimated measurement uncertainty in its February 1994 notice by 60 percent at dust concentrations of 2.0 mg/m
The NMA estimate of 16 percent for overall CV includes not only sampling and analytical error, but also variability arising from two additional sources: (1) Spatial variability between the locations where the two samples were collected; and (2) interlaboratory variability introduced by the fact that a third laboratory was involved in weighing exposed filter capsules.
Since the two dust samples within each pair submitted were not collected at precisely the same location, differences observed between paired samples in the Skyline data are partly due to spatial variability. The Secretaries fully recognize and acknowledge that, as suggested by the Skyline data, spatial variability in mine dust concentrations can exist, even within a relatively small area such as the so-called breathing zone of a miner. Consistent with general industrial hygiene practice, however, the Secretaries do not consider such variability relevant to the accuracy of an individual dust concentration measurement.
The NMA expressed sampling and analytical error as a single percentage relative to the average of all dust concentrations that happened to be observed in the data analyzed. Contrary to the NMA analysis, sampling and analytical error cannot be expressed as a constant percentage of the true dust concentration. Because σ
Even if the effects of spatial variability and the third laboratory are ignored, and the overall CV is interpreted as an average over the range of concentrations encountered, the 16-percent value reported by the NMA makes no allowance for the paired covariance structure of the data. Therefore, MSHA and NIOSH consider the 16-percent value to be erroneous, even under NMA's assumptions.
MSHA and NIOSH re-analyzed the Skyline data in order to check whether these data were consistent with the value of σ
To estimate SAE* as a function of dust concentration from the data provided, a least-squares regression analysis was performed on the square of the difference between natural logarithms of dust concentrations x
The least squares estimate of σ
Mountain Coal Company submitted a data set consisting of the difference (expressed in mg/m
Mountain Coal Company provided only the differences between measurements within each pair and not the concentration measurements themselves. Since CV
Jim Walter Resources, Inc. submitted a data set consisting of exposure measurements collected from all miners working on two longwall sections. Measurements were collected from each miner on five consecutive days. This procedure was repeated during five sampling cycles over a two-year period. During each sample cycle the five measurements for each miner were averaged and compared to the respirable dust standard. According to Jim Walter Resources, Inc., the sampling plan “eliminates the effect of the variability of the environment and minimizes the error due to the coefficient of variation of the pump because
In its submission, Jim Walter Resources, Inc. apparently assumed that the quantity being measured is average dust concentration across a number of shifts, rather than dust concentration averaged over a single shift at the sampling location. The Secretaries agree that dust concentrations do vary from shift to shift and from job to job, as these data illustrate. This variability, however, is largely under the control of the mine operator and should not be considered when evaluating the accuracy of a single, full-shift measurement.
The NMA submitted data consisting of recently collected and historical measurements collected from the designated occupations (continuous miner operator for continuous mining sections and either the headgate or tailgate shearer operator for longwall mining sections) for three continuous mining sections and five longwall mining sections. According to the NMA analysis, there is a 17-percent probability that these mines would be cited, even though the long-term average is less than the respirable dust standard.
The NMA failed to recognize that the quantity being measured is dust concentration averaged over a single shift at the sampling location. The Secretaries agree that exposures do vary from shift to shift, as these data illustrate. This variability, however, is largely under the control of the mine operator and should not be considered when evaluating the accuracy of a single, full-shift measurement.
Jim Walter Resources, Inc. submitted data collected from several longwall faces. For each longwall, seven dust samples were collected, using sampler units placed on the longwall face at least 48″ from the tailgate at the MSHA 061 designated location. Pumps were successively turned off in one hour increments, resulting in samples covering progressively longer time periods over the course of the shift, from one to eight hours. This was repeated on a number of days at each longwall.
Many of the samples showed either the same or less weight gain than the previous sample (collected over a shorter time period) within a sequence. In the cover letter and written comments accompanying these data, it was claimed that the weight gains observed for samples within each sequence should progressively increase, irrespective of variations in air flow and production levels, and that the patterns observed exemplify
MSHA and NIOSH have concluded that these data cannot be used to estimate or otherwise evaluate measurement accuracy for the following reasons: First, a highly sensitive and accurate sampling device would be expected to produce variable results when exposed to even slightly different environments. Since the samples within each sequence of seven were not collected at exactly the same point, they are subject to spatial variability in dust concentration. It is well known that dust concentrations can vary even within small areas along a longwall face. Therefore, variability in sample results is attributable not only to measurement errors but also to variations in dust concentration due to spatial variability.
Second, even on a production shift, variations in air flow and production levels over the course of the shift can result in periods within the shift during which the true dust concentration to which a sampler is exposed is low or near zero. If a sampler unit is exposed to a relatively low dust concentration during the final hour in which it is exposed, any difference between that sample and the previous sample will tend to be dominated by spatial variability. In such cases the increase in weight accumulated during the final hour would be statistically insignificant as compared to variability in dust concentration at different locations. Without detailed knowledge of the airflow and production levels as they varied over each shift, it is impossible to determine how many cases of this type would be expected. However, approximately one-half of such samples would be expected to exhibit less weight gain than the previous sample.
Further, because sample weights were truncated to 0.1 mg at the time these data were collected, and because expected weight gains of less than 0.1 mg are not uncommon over a one-hour period, there would be no apparent increase in recorded weight gain in many cases where the two sample results actually differed by a positive amount. Therefore, some unknown number of cases showing no difference in successive weight gains are attributable to truncation effects. Truncation has now been discontinued for samples collected under MSHA's inspection program.
Finally, as has been shown in Appendix C, a certain percentage of negative weight-gain measurements at low dust concentrations is consistent with the weighing imprecision experienced at the time these samples were collected. However, since these data were not collected in a controlled environment, it is impossible to determine what that percentage should be. Because the weight gain for each sample is determined as the difference between two weighings, comparison of weight gains between two samples involves a total of four independent weighing errors. Therefore, variability attributable purely to weighing error in the difference between weight gains in two successive samples is greater (by a factor equal to “2) than variability due to weighing error in a single sample. Furthermore samples collected over less than a full shift are subject to more variability due to random fluctuations in pump air flow and cyclone performance than samples collected over a full shift. Both of these considerations increase the likelihood that a sample will exhibit less weight gain than its predecessor, as compared to the likelihood of recording a negative weight gain for a single, full-shift sample.
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Accordingly, it is proposed by the Department of Labor, Mine Safety and Health Administration, to amend chapter I of title 30 of the Code of Federal Regulations as follows:
1. The authority citation for part 72 continues to read as follows:
30 U.S.C. 811, 813(h), 957, 961.
2. Section 72. 500 is added to subpart E of part 72 to read as follows:
The Secretary may use a single, full-shift measurement of respirable coal mine dust to determine average concentration on a shift if that measurement accurately represents atmospheric conditions to which a miner is exposed during such shift.