Mine Safety: Basis for Proposed Exposure Limit on Respirable Coal Mine Dust and Possible Approaches for Lowering Dust Levels
Released: 2014-04-09T00:00:00

Letter

Background

Inhaling excessive amounts of coal mine dust can cause CWP and other debilitating lung diseases, including chronic obstructive pulmonary disease, which encompasses chronic bronchitis and emphysema. According to NIOSH, it usually takes about 10 to 15 years of exposure to coal mine dust to develop CWP, although cases involving fewer years of exposure have been observed. Once contracted, CWP cannot be cured, making it critical to prevent the development of this disease by limiting miners’ exposure to coal mine dust.

MSHA is responsible for protecting miners by enforcing the provisions of the Federal Mine Safety and Health Act of 1977 (Mine Act), as amended. Under this law, MSHA has a number of responsibilities, including setting new safety and health standards and revising existing standards, approving training programs for mine workers, and developing regulations regarding training requirements for rescue teams, among other things.

MSHA also conducts periodic inspections of coal mines and, along with coal mine operators, periodically collects samples of coal mine dust to determine compliance with the exposure limit. MSHA set the current exposure limit for coal mine dust at 2.0 mg/m. This limit applies to the overall level of dust in the mine environment; specifically, it provides that each mine 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 each mine is exposed” at or below that level. To measure the level of dust in the mine environment, MSHA requires that mine operators collect samples of dust in specific areas of the mine and for designated occupations. Designated occupations are those that have the greatest concentration of coal mine dust, as determined through MSHA sampling. then took effect. Pub. L. No. 91-173, § 202(b), 83 Stat. 742, 760-61 (1970). The 1977 Mine Act did not change the 2.0 mg/m. 45 Fed. Reg. 23,990, 24,001 (Apr. 8, 1980) (codified at 30 C.F.R. § 70.100). incurring any disability from… occupation-related disease during or at the end of such period.”

NIOSH shares some responsibility with MSHA for improving mine safety and protecting miners’ health. For example, NIOSH conducts research on the causes of work-related diseases and injuries; researches, develops, and tests new technologies and equipment designed to improve mine safety; and recommends occupational safety and health standards, such as the exposure limit for coal mine dust. NIOSH also administers the Coal Workers’ X-ray Surveillance Program—a medical monitoring and surveillance program designed to detect and prevent lung disease. This program requires mine operators to provide up to three initial chest x-rays for coal miners within specified time frames after their employment begins. Miners then can opt to have periodic chest x-rays approximately every 5 years thereafter. NIOSH uses this program for disease surveillance, which includes tracking trends, setting prevention and intervention priorities, and assessing prevention and intervention efforts. In addition, to estimate the prevalence of lung disease among underground coal miners and to study the relationship between miners’ lung disease and their level of exposure to coal mine dust, NIOSH developed the National Study of Coal Workers’ Pneumoconiosis. In this study, NIOSH collected and analyzed epidemiological data—including findings from chest x-rays, results of lung function tests, and occupational and smoking histories—from a sample of coal miners across all major coalfields in the United States between 1969 and 1988. The data also allowed researchers to link to results of coal mine dust sampling over approximately the same period to estimate dust exposures for individual miners. According to NIOSH, epidemiological studies examining the relationship between coal mine dust and disease must contain a sufficiently large body of data over a time period that is adequate to derive reliable findings.

There are two primary types of underground coal mining in the United States: continuous mining and longwall mining. In continuous mining, a machine called a continuous miner cuts out rooms of coal from the coal bed leaving a series of pillars of coal to help support the mine roof. In addition to the pillars of coal, bolts are driven into the roof of the mine to help support the mine. The extracted coal from the continuous miner is loaded into shuttle cars for transport out of the mine. In longwall mining, a machine called a shearer moves back and forth across a wall of coal. After the coal is cut, a machine crushes it into small pieces and a conveyer belt removes it from the mine. While the shearer cuts the coal and the coal is extracted, the roof is held up temporarily with self- advancing hydraulic supports. While both types of mining produce dust, certain pieces of machinery produce more coal mine dust than others. For example, in continuous mining, the continuous miner, roof bolting machines, and shuttle cars generate the most dust. Major sources of dust in longwall mining include the shearer and crusher.

MSHA Did Not Use Recent CWP Trend Data as a Basis for Its Proposed Exposure Limit on Coal Mine Dust, Which Was Appropriate

Appropriately, MSHA did not use NIOSH’s surveillance data as the basis for its proposed new coal mine dust limit, although the data served to inform MSHA’s decision to take action. In the preamble to its proposed rule, MSHA cited an increase in the prevalence of CWP among underground coal miners based on NIOSH surveillance data, which may have led many to believe that these data were part of the basis for MSHA’s proposed change in the exposure limit. The surveillance data showed that the prevalence of CWP, which declined substantially between 1970 and the late 1990s, increased for several years in the early 2000s before declining again between 2005 and 2009. According to MSHA and NIOSH officials, information about the increasing prevalence of CWP based on the surveillance data was mentioned in the preamble to the proposed rule to show that black lung disease still exists among active underground coal miners, thus helping to compel MSHA to take action to reduce miners’ exposure to dust, in accordance with its duties under the Mine Act. However, as we reported in August 2012, the data MSHA used to support its proposal were from two reports, which relied on six epidemiological studies, not the surveillance data. In addition, in a 1996 notice in the Federal Register, well before the increase in the prevalence of CWP shown by the surveillance data, MSHA stated its intent to respond to a 1995 NIOSH recommendation to lower the exposure limit for coal mine dust by developing a proposed rule. dust because of some important limitations of the data. For example, because the data do not include individual miners’ past exposures to coal mine dust, they cannot be used to estimate disease risk for individual miners. Based on principles of epidemiology and statistical modeling, measures of past exposures to coal mine dust are critical to assessing the relationship between miners’ cumulative coal mine dust exposure and their risk of developing CWP. Also, because there is no active selection of miners by researchers and participation in the surveillance program is voluntary, miners who choose to participate may differ in unknown ways from those who choose not to participate, which could result in an overestimation or underestimation of the prevalence of disease. This methodological limitation is known as participation bias, and there are many ways it could affect the prevalence of disease indicated by the surveillance data. For example, the prevalence of CWP could be underestimated because some miners may decline further x-ray screenings once CWP is detected. Alternatively, the prevalence of CWP could be overestimated because miners may be more likely to participate after years of dust exposure, when they believe they are at risk of developing CWP.

Experts Identified Various Approaches that Could Reduce Overall Coal Mine Dust Levels, as Well as Individual Miners’ Exposure to Dust

Experts Identified Various Engineering Controls That Could Help Reduce Overall Coal Mine Dust Levels

Experts identified various engineering controls that could further reduce the overall level of coal mine dust, but they said reductions would likely be incremental. Since 1968, the mining industry has achieved significant reductions in the level of dust in underground coal mines. Average dust levels declined from about 7 mg/m in 1968 to below 2 mg/mreplace contaminated air with fresh air, which also helps reduce the level of coal mine dust in the air.

The experts also described ways that operators use water to prevent dust from being generated in mining operations. For example, operators spray water on the surface of the coal and on the machines’ cutting surfaces as the coal is being cut to reduce the amount of dust generated. In some cases, operators also infuse water into the coal prior to cutting, but the experts reported limited success with that approach. Operators also use hygroscopic salts on mine floors to help maintain the moisture content of the mine floor, which in turn absorbs coal mine dust. The experts said that, with the increased productivity of mines in recent years, the water quantity and pressure for sprays may need to be increased. From 1978 to 2007, the amount of coal produced per work hour has more than tripled. The experts cautioned, however, that using too much water could have adverse impacts, such as causing conveyor belts to slip, which would affect production.

The experts pointed to a number of factors that could limit mine operators’ use of engineering controls aimed at reducing coal mine dust in the mine environment. The experts said that fundamental differences between continuous mining and longwall mining operations render some technological approaches useful for one type of mining, but not both. For example, while scrubbers were cited as an effective tool for reducing dust in continuous mining operations, the experts cautioned that they may not be as effective for mines that require a lot of ventilation, such as longwall mines, because the amount of air flowing through the mine can overwhelm the scrubber. An expert noted that one way to reduce dust levels is to operate only one continuous mining machine at a time in a section of a mine instead of more than one. However, he estimated that this could significantly decrease the productivity of the mine and increase the cost of producing the coal. Another expert noted that controlling dust in a cost-effective manner requires some flexibility.

The experts did not quantify the cost of some of the technologies used in reducing dust levels because dust control is not the only purpose of some of the technologies, and future technologies have not been developed enough to fully determine their costs. However, they did identify primary cost drivers. For example, mines that contain high levels of gas must ventilate significant amounts of fresh air, which also helps lower coal mine dust levels. They also noted that while NIOSH has done some of the major research on dust control, overall, industry research on dust control technologies has declined. One expert made the point that research is directly proportional to the economic health of the coal industry. When the industry is contracting economically, manufacturers may not be willing to devote resources to research and development. While specific costs were difficult to assign, the primary drivers the experts identified for lowering dust levels were the cost of maintaining equipment; the cost of purchasing new or additional equipment, materials, and labor; and the cost of providing training.

Experts Noted Options That Could Reduce Individual Miners’ Exposure to Dust

The experts identified options that could reduce individual miners’ exposure to respirable coal mine dust, specifically, personal protective equipment and administrative controls. However, they noted that these options would not help mines reduce the overall level of coal mine dust in the mine environment, and therefore would not help mine operators comply with MSHA’s exposure limit. Personal protective equipment includes items such as respirators and air stream helmets. Respirators filter the air that an individual miner breathes and air stream helmets actively filter and push air across a miner’s face. While respirators and air stream helmets could reduce the amount of coal dust to which individual miners are exposed, the experts noted that miners have concerns that these devices limit communication between miners and thus could raise safety issues. The experts also said that personal dust monitors could be used to reduce individual miners’ exposure to dust because they provide workers with real time data on dust levels in the area of the mine in which they are working. This information allows workers to adjust their position in the mine to reduce their exposure to coal mine dust. Although personal dust monitors have no effect on dust levels in the mine, the experts noted that they may provide data that could be used by mine operators to identify problem areas in the mines and to change work practices to reduce miners’ exposure to coal mine dust. One of the experts told us personal dust monitors cost about $13,000 to $18,000 per unit, which could be a significant expense if all miners were outfitted with them.

The experts also noted that administrative controls could limit miners’ exposure to coal mine dust, although they do not control the overall level of dust in the mine. These controls include rotating workers more frequently from positions that are exposed to higher levels of dust, cutting the coal using a remote control device, and changing the sequence by which coal is cut. Experts said that rotating workers to other positions could help reduce their exposure to dust, but this could also require changes to the current collective bargaining agreement at unionized mines because the jobs that involve highest exposure to dust may also pay more. This approach may also increase costs for mine operators because, for example, the collective bargaining agreement might require them to continue to pay workers a higher rate of pay when they rotate to a lower paying position. The experts also said that some mines use remote control devices to keep miners farther away from the source of dust. Controlling the mining machine from a greater distance than is currently done may require high resolution imaging equipment. One expert said that this is especially true for mining operations where geologic conditions change frequently, requiring miners to make judgments about where to move the machinery. According to the experts, another way to limit exposure to individual miners in continuous mining is by modifying the sequence in which coal is mined. The experts explained that this approach reduces the number of miners who are downwind from the dust generated by the continuous mining machine. However, this type of change could result in decreased productivity in the mine.

Agency Comments

We provided a draft of this report to the Secretaries of Labor and Health and Human Services for review and comment. Both agencies generally concurred with the findings of the report, but provided no formal written comments. The agencies did, however, provide technical comments, which we incorporated as appropriate.

We are sending copies of this report to the appropriate congressional committees and the Secretaries of Labor and Health and Human Services. In addition, the report is available at no charge on the GAO website at http://www.gao.gov. If you or your staff have any questions about this report, please contact me at (202) 512-7215 or moranr@gao.gov. Contact points for our Offices of Congressional Relations and Public Affairs may be found on the last page of this report. GAO staff who made key contributions to this report are listed in appendix II.

Appendix I: Objectives, Scope, and Methodology

The objectives of our review were to: (1) determine the extent to which the Mine Safety and Health Administration (MSHA) used recent coal workers’ pneumoconiosis (CWP) trend data as a basis for its proposed exposure limit on coal mine dust, and (2) obtain experts’ views on ways to lower the level of dust in coal mines, including their associated advantages, disadvantages, and cost.

To address our first objective, we reviewed MSHA’s Notice of Proposed Rulemaking, including the proposed exposure limit and related documents, updated the literature search from our prior report, and interviewed officials from MSHA and the National Institute for Occupational Safety and Health (NIOSH) to identify recent data on the prevalence of coal worker respiratory diseases. Two GAO research methodologists and one public health specialist reviewed information gathered about CWP trend data, to assess its strengths and limitations, and reviewed a recent study by NIOSH researchers on the usefulness of these data for estimating disease prevalence. We also reviewed our prior report and the analyses that supported it, and interviewed MSHA and NIOSH officials to determine what role, if any, recent CWP trend data had in developing the proposal to lower the exposure limit. We examined whether these data would have been appropriate for MSHA to use in developing its proposed exposure limit using principles of social science research and epidemiology.

For our second objective, we worked with the National Academies to convene a group of experts to obtain their views on these issues. To prepare for our discussions with experts, we reviewed NIOSH and other studies on the ability of currently available and alternative technologies to control coal mine dust. We also reviewed the technological and economic feasibility assessments MSHA used to develop its proposed exposure limit. The group included experts from all of the major stakeholder groups: NIOSH researchers, academics, other technical experts, individuals from companies that manufacture mining equipment, and individuals who represent coal mine operators and workers. In identifying the experts, the National Academies compiled a preliminary list of 53 experts who represented 17 universities, 7 coal companies or coal associations, 5 equipment manufacturers, 1 mine workers’ association, and 2 government agencies. The nominees were grouped by sector and field of expertise, and were vetted by 10 individuals working in the public, private, and academic sectors who have expertise in coal mining or a related field. Feedback from these individuals, along with biographical information about the experts, was used to prioritize the experts within each sector and field of expertise. Using this information, we invited 17 experts to participate in a 1-day panel discussion, although 1 person subsequently cancelled. The resulting 16 experts included 3 representatives of mine operators, 1 representative of underground coal miners, 3 representatives of equipment manufacturers, 6 academics, and 3 representatives of federal government agencies.

To ensure that there were no unforseen biases or conflicts of interest, each panelist reported to the National Academies his or her investments, sources of earned income, organizational positions, relationships, and other circumstances that could affect, or could be viewed to affect, his or her view on the topic of methods for reducing the level of respirable dust in underground coal mines. We asked the experts to discuss the technological and other options available for lowering the level of dust in coal mines below the existing permissible exposure limit and the costs, advantages, and disadvantages of these technologies. We did not ask the experts about the proposed new limit. In addition to the 16 panelists, we allowed 5 observers to sit in on the panel discussion. The observers included representatives of mining equipment manufacturers, coal mine operators, and one government agency.

We conducted this performance audit from July 2013 to April 2014 in accordance with generally accepted government auditing standards. Those standards require that we plan and perform the audit to obtain sufficient, appropriate evidence to provide a reasonable basis for our findings and conclusions based on our audit objectives. We believe that the evidence obtained provides a reasonable basis for our findings and conclusions based on our audit objectives.

Appendix II: GAO Contacts and Staff Acknowledgments

Contact

Revae Moran, (202) 512-7215 or moranr@gao.gov.

Staff Acknowledgments

In addition to the contact listed above, individuals making key contributions to this report were Mary Crenshaw (Assistant Director), Nabajyoti Barkakati, Russell Burnett, Sarah Cornetto, Andrea Dawson, Timothy Guinane, Kristy Kennedy, Kathy Leslie, Sheila McCoy, Sara Pelton, Tim Persons, Martin Scire, Sushil Sharma, Walter Vance, Kathleen van Gelder, and Shana Wallace.