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Mine Safety: Reports and Key Studies Support the Scientific Conclusions Underlying the Proposed Exposure Limit for Respirable Coal Mine Dust

GAO-12-832R Published: Aug 17, 2012. Publicly Released: Aug 17, 2012.
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What GAO Found

Our evaluation of the reports MSHA used to support its proposal and the key scientific studies on which the reports were based shows that they support the conclusion that lowering the PEL from 2.0 mg/m3 to 1.0 mg/m3 would reduce miners’ risk of disease. The reports and key studies concluded that miners’ cumulative exposure to coal mine dust at the current PEL over their working lives places them at an increased risk of developing CWP, progressive massive fibrosis, and decreased lung function, among other adverse health outcomes. To mitigate the limitations and biases in the data, the researchers took reasonable steps, such as using multiple x-ray specialists to reduce the risk of misclassifying disease and making adjustments to coal mine dust samples where bias was suspected. In addition to addressing the limitations and biases in the data, researchers used appropriate analytical methods to conclude that lowering the existing PEL would decrease miners’ risk of developing black lung disease. For example, in addition to taking steps to precisely estimate a miner’s cumulative exposure, the researchers accounted for several factors in their analyses—such as the age of the miners, the carbon content of the coal (coal rank), and other factors known to be associated with the disease—to better estimate the effect of cumulative exposure to coal mine dust. Further, the other studies we identified generally supported the conclusion that reducing the PEL would reduce miners’ risk of disease.

Why GAO Did This Study

Coal mine dust is one of the most serious occupational hazards in the coal mining industry, and overexposure can cause coal workers’ pneumoconiosis (CWP) and a number of other lung diseases, collectively referred to as black lung disease. CWP has been the underlying or contributing cause of death for more than 75,000 coal miners since 1968, according to the Department of Health and Human Services’ (HHS) National Institute for Occupational Safety and Health (NIOSH), the federal agency responsible for conducting research on work-related diseases and injuries and recommending occupational safety and health standards. Since 1970, the Department of Labor (Labor) has paid over $44 billion in benefits to miners totally disabled by respiratory diseases (or their survivors), including CWP, through the Black Lung Benefits Program.

In October 2010, Labor’s Mine Safety and Health Administration (MSHA)—the federal agency responsible for setting and enforcing mine safety and health standards—proposed revising the existing standard for coal mine dust to lower the permissible exposure limit (PEL) from 2.0 milligrams of dust per cubic meter of air (mg/m3) to 1.0 mg/m3. Several coal mining companies and others have questioned the evidence and analytical methods used to support the proposed PEL. In the Consolidated Appropriations Act, 2012, Congress required that GAO review and report on the data collection, sampling methods, and analyses MSHA used to support its proposal. Although MSHA’s proposed rule includes other provisions, this review focuses on MSHA’s proposal to lower the PEL for coal mine dust from 2.0 mg/m3 to 1.0 mg/m3. To respond to this requirement, we addressed the following question: What are the strengths and limitations of the data and analytical methods MSHA used to support its proposal to lower the PEL for coal mine dust?

For more information, contact Revae E. Moran at (202) 512-7215 or

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Respiratory diseasesOccupational safetyBlack lung diseaseMine safetyCoal miningCoalHealthAppropriationsLabor forceHealth standards