A U.S. Mine Safety and Health Administration proposal to lower allowed coal dust exposure in underground mines is based on adequate evidence, said an Aug. 17 report on the proposal from the Government Accountability Office (GAO).
“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 [permissible exposure limit (PEL)] from 2.0 mg/m3 to 1.0 mg/m3 would reduce miners’ risk of disease,” said the GAO report. “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 [coal workers’ pneumoconiosis (CWP)], progressive massive fibrosis, and decreased lung function, among other adverse health outcomes.”
In proving the validity of their work, the MSHA 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, GAO said. 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.
Coal mine dust is one of the most serious occupational hazards in the coal mining industry, and overexposure can cause 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’ National Institute for Occupational Safety and Health, the GAO noted.
In October 2010, MSHA proposed revising the existing standard for coal mine dust to lower the 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. Earlier this year, 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, the Aug. 17 report focuses on MSHA’s proposal to lower the PEL for coal mine dust from 2.0 mg/m3 to 1.0 mg/m3.
The focus of the GAO work was primarily limited to determining whether the scientific studies MSHA used generally support its conclusion that lowering the exposure to coal mine dust would lower miners’ risk of disease. The GAO noted that its work was not designed to: determine the optimal PEL for coal mine dust; analyze the costs and benefits of the proposed standard; or determine whether the standard would meet MSHA’s legal requirements under the Federal Mine Safety and Health Act of 1977 or other federal laws that govern the rulemaking process.