Appendix G
Mandatory Airborne Dust Standards for U.S. Underground Coal Mines
The laws and regulations that are aimed at protecting the miners from the health hazards associated with exposure to airborne respirable coal mine dust (RCMD) also specify monitoring technology and sampling protocols. Prior to 1969, the enforcement of health and safety standards in the coal mining industry was viewed as primarily a state responsibility, even though in 1865 a bill was introduced in Congress to create a Federal Mining Bureau. In July 1910, Congress established the Bureau of Mines in the Department of Interior by enacting the Bureau of Mines Organic Act, but it contained a specific denial of “any right or authority in connection with inspection or suspension of mining” (Committee on Human Resources, 1978). During subsequent decades, the extent of federal agencies’ involvement in enforcement of mine health and safety standards in the coal mining industry increased through regulatory changes.
From 1970 to 2012, government inspectors collected 750,000 coal mine dust samples in underground mines, and mine operators collected 4.6 million samples during that same period (GAO, 2012). Those numbers reveal the enormous efforts spent by industry, labor, and government to monitor the airborne dust conditions underground. As shown in Figure F-8 in Appendix F of this report, the average airborne RCMD concentrations in underground longwall and continuous-mining sections have been decreasing. However, disappointingly, there has also been an increase in the prevalence of coal workers’ pneumoconiosis in certain mining areas of the country, pointing to the need for further investigations into the effectiveness of the present control strategies.
THE COAL MINE HEALTH AND SAFETY ACT OF 1969
In Title II of the Coal Mine Health and Safety Act of 1969, Congress stated that the purpose of the act is
“to provide to the greatest extent possible, that the working conditions in each underground coal mine are sufficiently free of respirable dust concentrations in the mine atmosphere to permit each miner the opportunity to work underground during the period of his entire adult working life without incurring any disability from pneumoconiosis or any other occupation-related disease during or at the end of such period.”
Specifications in Title II included allowable airborne RCMD concentration in coal mines, sampling technology, procedures determining average RCMD concentrations, allowable quartz content in airborne RCMD, medical examinations (chest x-ray, other tests), and transfer of miners, who show early indications of developing pneumoconiosis, to work areas where the RCMD concentration is lower than the allowable level. In Title IV of the act, Congress created the Black Lung Benefits program to provide benefits to coal miners “who are totally disabled due to pneumoconiosis and to the surviving dependents of miners whose death was due to such disease.”
According to the act, which became effective on June 30, 1970, the average concentration of RCMD in the active sections of underground coal mines was to be maintained at or below 3.0 mg/m3. On December 30, 1972, the standard was reduced to 2.0 mg/m3. The act further stated
that the standard would be reduced further whenever the quartz content in RCMD was greater than 5 percent. The effect of the reduced standard was to keep the quartz concentration at or below 0.1 mg/m3. The significance of achieving these RCMD standard in mines was substantial, as a U.S. Bureau of Mines survey of 29 mines during the period 1968-1969 found average RCMD concentrations in excess of 6 mg/m3 (Shepich, 1983).
The rationale for the allowable RCMD concentrations was provided in a Department of Interior report on the causation of pneumoconiosis (Committee on Education and Labor, 1970). According to that report, the probabilities of developing simple pneumoconiosis and progressive massive fibrosis (PMF) decreased with reduced RCMD exposure. Those probabilities were based on British medical data on dose-response relationships extrapolated to various dust concentrations.
Required Instruments
The Isleworth type 113A (MRE) gravimetric dust sampler was the reference dust sampling instrument for measuring RCMD concentrations with respect to the standard. The device uses a four-channel horizontal elutriator for size classification of the dust sample into respirable and nonrespirable fractions (Tomb et al., 1998). The most commonly used sampling instrument was a personal sampling device that utilizes a cyclone to separate a dust sample into respirable and nonrespirable size fractions.
Sampling Protocols
Federal regulations issued in 1970 initiated a dust sampling program for mine operators based on the high-risk-occupation concept. Under that concept, individuals in the occupations in the working section of the mine exposed to the highest RCMD concentrations are sampled. The high-risk occupation for each method of mining was identified in the regulation. In addition, Mine Safety and Health Administration (MSHA) inspectors conducted mine inspections and collected RCMD samples to determine compliance with the standards and assess the operator samples. The Government Accountability Office (GAO, 1975) noted the general agreement among the miners, mine operators, union officials, and government agencies that significant reductions had been made in RCMD concentrations in mines. However, the report also identified weaknesses in the dust-sampling program that affect the accuracy and validity of the RCMD results and make it virtually impossible to determine how many mine sections complied with allowable dust concentration. The operator sampling program was revised in 1980 (Raymond et al., 1987) to require mine operators to collect two types of samples during bimonthly sampling periods:
- Designated occupation (DO) samples, which are the same as the previous high-risk-occupation samples, and
- Designated area (DA) samples collected at appropriate locations in the section.
Compliance determinations were based on the average RCMD concentration by five valid RCMD samples taken by the operator during five consecutive normal production shifts or five normal production shifts worked on consecutive days. Compliance was also based on the average of multiple measurements taken by an MSHA inspector over a single shift or on the average of multiple measurements obtained for the same occupation on multiple days. In addition, miners (Part 90 miners) were sampled who had exercised the option to work in areas of mine where the concentration was at or below 1 mg/m3. The sampling results became available to the miner operator, miners, and MSHA about 1 week after the samples were collected due to the need to analyze the samples off site.
SUBSEQUENT RCMD CONTROL PROGRAMS
In May 1991, the Secretary of Labor directed MSHA to form a task force for conducting a review of the administration’s program to control RCMD concentrations and recommend program improvements (MSHA, 1992). The task force examined the developments in the coal industry; explored the roles of labor, industry, and government in the enforcement program; designed and implemented a short-term monitoring program with specific objectives; and explored future technologies for RCMD measurement, monitoring, and control. The review concluded that, even though there were significant reductions in RCMD concentrations since 1969 (Table G-1), MSHA was not conducting the prescribed number of dust sampling inspections nor was it adequately monitoring the operator sampling program.
Recommendations of the task force included the use of continuous monitoring of the mine environment and parameters relevant to control RCMD, development of a personal sampling device capable of measuring short-term exposures and cumulative exposures over a full shift, greater use of more tamper-resistant cassettes, and submission of improved RCMD control plans by operators. Recommendations also addressed topics concerning MSHA inspections, education and training, and the role of miners in improving compliance sampling.
NIOSH Coal Mine Dust Criteria Document
In September 1995, the National Institute for Occupational Safety and Health (NIOSH) published a criteria document (NIOSH, 1995) for occupational exposure to RCMD, which included these recommendations:
- Exposures to RCMD should be limited to 1 mg/m3 as a time-weighted average (TWA) concentration for up to 10 hours per day during a 40-hour workweek, measured according to current MSHA methods.
- The RCMD allowable concentration represents the upper limit of exposure for each worker during each shift. For single, full-shift samples used to determine compliance, no upward adjustment of the limit should be made to account for measurement uncertainties.
- Exposures to respirable crystalline silica should not exceed 0.05 mg/m3 as a TWA concentration for up to 10 hours per day during a 40-hour workweek.
The criteria document provided an extensive analysis of the data from the RCMD sampling program and from the x-ray surveillance program. The criteria document indicated that excess prevalence of coal workers’ pneumoconiosis, PMF, and decreased lung function is expected to be reduced substantially if lifetime average RCMD exposures are reduced from 2 to 0.5 mg/m3. The document also indicated that, at exposures to a mean RCMD concentration of 0.5 mg/m3, miners have a greater than 0.1 percent risk of developing those disease conditions.
Secretary of Labor’s Advisory Committee
A 1996 report (MSHA, 1996) of an advisory committee established by the Secretary of Labor recommended separating and lowering the RCMD and silica standards. The advisory committee recognized the potential uses of continuous-monitoring data for hazard surveillance and compliance monitoring. It recommended that MSHA take full responsibility for all compliance sampling and that the operator-sampling program be continued with substantial improvements to increase its credibility. The advisory committee called for an appropriately balanced strategy of personal (individual miner), occupational (such as DO), and environmental (such as DA) for RCMD sampling for compliance. It recommended major emphasis on personal sampling and single full-shift samples for determining compliance. The advisory committee observed miners’
low participation rate in the medical surveillance program for respiratory effects and recognized the difficulty in resolving the individual’s right to confidentiality and the need for MSHA, NIOSH, operators, and fellow miners to know where and how much disease is occurring.
CURRENT DUST STANDARDS
The development of a continuous personal dust monitor (CPDM) that can measure RCMD continuously and in near real time was seen as a key advancement for exposure assessment and RCMD control (Volkwein et al., 2004). In 2010, MSHA and NIOSH published a final rule for approval requirements for the existing RCMD personal samplers, and new approval requirements for the CPDM.
In October 2010, MSHA proposed a rule titled “Lowering Miners’ Exposure to Respirable Coal Mine Dust, Including Continuous Personal Dust Monitors” that included a lowering of the allowable RCMD concentration, full-shift sampling, and redefining “normal production shift,” among other requirements.
Following the publication of the proposed rules, public hearings were held, written comments were submitted, and GAO issued reports on lowering the RCMD standard and single-shift sampling procedures (GAO, 2012, 2014).
TABLE G-1 Underground Dust Exposure Concentrations in 1969 and 1991
| Occupation | 1969a (mg/m3) | 1991b (mg/m3) |
|---|---|---|
| Cutting Machine Helper | 8.4 | 0.8 |
| Continuous Miner Operator | 7.7 | 1.5 |
| Loading Machine Operator | 7.1 | 1.3 |
| Cutting Machine Operator | 6.9 | 1.9 |
| Coal Drill Operator | 6.7 | 1.3 |
| Continuous Miner Helper | 6.5 | 1.3 |
| Loading Machine Helper | 6.0 | 1.4 |
| Shot Firer | 5.9 | --c |
| Timberman | 4.7 | -- |
| Roof Bolter Operator | 4.6 | 1.2 |
| Beltman | 3.7 | 0.9 |
| Section Foreman | 3.2 | 0.8 |
| Scoop Car Operator | -- | 0.9 |
| Supply Man | 3.0 | 1.0 |
| Shuttle Car Operator | 2.7 | 0.9 |
| Boomboy | 2.4 | -- |
| Mechanic | 2.1 | 0.6 |
| Longwall Operator (tail) | -- | 1.7 |
| Longwall Operator (head) | -- | 1.5 |
| Longwall Jack Setter | -- | 1.4 |
bMSHA’s Respirable Dust Spot Inspection Program.
cIndicates that the studies did not include these occupations.
SOURCE: MSHA, 1992.
In 2014, MSHA published a final rule that changed the RCMD standards, measurement technology and sampling protocols (79 Fed. Reg. 24,814, 2014). The major changes include the following:
- RCMD airborne concentration limit is 1.5 mg/m3 for underground mines, and 0.5 mg/m3 for intake air at underground mines and for Part 90 miners (coal miners who have evidence of the development of pneumoconiosis).
- Mine operators are required to use the CPDM to monitor the exposures of underground coal miners in occupations exposed to the highest RCMD concentrations and the exposures of Part 90 miners. Use of the CPDM is optional for nonproduction areas of underground coal mines.
- Normal production shift is redefined such that coal production must be at least 80 percent of the average production over the last 30 production shifts when RCMD samples are collected in the mechanized mining unit.
- The operator must collect RCMD samples for the full shift that a miner works. If a miner works a 12-hour shift, RCMD samples must be taken with an approved sampling device for the entire work shift.
- MSHA inspectors will use single, full-shift samples to determine noncompliance with the RCMD standards.
- Immediate corrective actions to lower RCMD concentrations are required when a single, full-shift operator sample meets or exceeds the excessive concentration value (ECV) for the RCMD standard. ECV ensures that MSHA is 95 percent confident that the applicable standard has been exceeded and allows for the margin of error when measuring the RCMD concentration with an instrument. ECV tables are provided in the regulations for the applicable standard and device.
- Spirometry testing, occupational history, and symptom assessment have been added to the periodic chest radiographic (x-ray) examinations required to be offered by mine operators to underground miners under NIOSH’s existing standards.
- Certified persons who perform RCMD sampling and who maintain and calibrate sampling equipment must complete an MSHA course of instruction and must pass an MSHA examination to demonstrate competency in the tasks needed for RCMD sampling procedures and in maintenance and calibration procedures. MSHA is allowed to revoke a person’s certification for failing to carry out the required sampling or maintenance and calibration procedures in a proper manner.
Frequency of Sampling
Operators must collect all samples quarterly on consecutive shifts. The sampling frequency for the DOs and other designated occupations (ODOs) is 15 shifts per quarter, and the frequency for DAs and Part 90 miners is 5 shifts per quarter. DOs and ODOs cannot be sampled concurrently. Corrective action is required when one operator full-shift sample meets or exceeds the ECV. Noncompliance is considered to occur when three samples meet or exceed the ECV or the average of the 15 samples meets or exceeds the ECV. Data from CPDM must be transmitted within 24 hours to MSHA.
When sampling is done by MSHA, the instrument used is the personal gravimetric sampler (CMDPSU). The collected sample is used to determine compliance with the RCMD standard and the allowable limit for quartz concentration in RCMD.
Since February 2016, CPDM must be used for operator sampling and since August 2016, the RCMD concentration limit for underground coal mines has been 1.5 mg/m3. Tables G-2 and G-3 summarize quarterly operator-sample data from April 2016 to March 2017 for the designated occupation and other designated occupation, respectively (Meikle, 2017). It is evident from the reported data that noncompliance was rare and the average RCMD concentration was well below the mandated level.
| Valid CPDM Dust Sample Counts by Type Longwall Designated Occupation Sampling Results for a 4 Quarter Period April 2016 - March 2017 |
Valid CPDM Dust Sample Counts by Type Continuous Miner Designated Occupation Sampling Results for a 4 Quarter Period April 2016 - March 2017 |
||||||||
|---|---|---|---|---|---|---|---|---|---|
| Quarter | Total Number of Samples | Number of Samples Non-Compliant | Compliance % | Average Concentration (mg/m3) | Quarter | Total Number of Samples | Number of Samples Non-Compliant | Compliance % | Average Concentration (mg/m3) |
| 1 | 639 | 3 | 99.5% | 0.999 | 1 | 6553 | 4 | 99.9% | 0.712 |
| 2 | 626 | 2 | 99.7% | 0.866 | 2 | 6745 | 11 | 99.8% | 0.664 |
| 3 | 581 | 8 | 98.6% | 0.903 | 3 | 7051 | 21 | 99.7% | 0.651 |
| 4 | 628 | 2 | 99.7% | 0.861 | 4 | 7409 | 22 | 99.7% | 0.688 |
| Total | 2474 | 15 | 99.4% | 0.907 | Total | 27758 | 58 | 99.8% | 0.679 |
SOURCE: Meikle, 2017.
| Valid CPDM Dust Sample Counts by Type Longwall Other-Designated Occupation Sampling Results for a 4 Quarter Period April 2016 - March 2017 |
Valid CPDM Dust Sample Counts by Type Continuous Miner Other-Designated Occupation Sampling Results for a 4 Quarter Period April 2016 - March 2017 |
||||||||
|---|---|---|---|---|---|---|---|---|---|
| Quarter | Total Number of Samples | Number of Samples Non-Compliant | Compliance % | Average Concentration (mg/m3) | Quarter | Total Number of Samples | Number of Samples Non-Compliant | Compliance % | Average Concentration (mg/m3) |
| 1 | 518 | 2 | 99.6% | 0.835 | 1 | 5402 | 11 | 99.8% | 0.694 |
| 2 | 503 | 1 | 99.8% | 0.716 | 2 | 6248 | 8 | 99.9% | 0.610 |
| 3 | 505 | 4 | 98.8% | 0.789 | 3 | 6372 | 15 | 99.8% | 0.647 |
| 4 | 635 | 0 | 100.0% | 0.732 | 4 | 7226 | 12 | 99.8% | 0.635 |
| Total | 2161 | 7 | 99.7% | 0.768 | Total | 25248 | 46 | 99.8% | 0.647 |
SOURCE: Meikle, 2017.
Of the 86,941 CPDM samples submitted to MSHA in 2016, about 24 percent of the samples were voided (or invalidated) (NMA, 2017). About 45 percent of the samples were voided because an insufficient amount of coal production occurred during the shift the sample was taken. CPDM malfunction was responsible for about 55 percent of the voided samples. Some of those problems were associated with temperature selection, battery life, and CPDM software.
SUMMARY
The current monitoring technology and sampling protocols are significantly different from the ones that were specified in the rules and regulations stemming from the 1969 coal act. The CPMD had been under development for more than two decades to address a long-recognized need for the real-time assessment of airborne RCMD underground. The use of the CPDM for personal sampling is demonstrated as being effective for obtaining regulatory compliance data.
REFERENCES
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