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Statement of Need: The use of diesel-powered equipment in underground mines has increased significantly and rapidly during the past decade. MSHA estimates that approximately 13,000 miners are occupationally exposed to diesel exhaust emissions in underground mines. ^PSeveral epidemiological studies have shown a positive carcinogenic risk associated with exposure to diesel exhaust. Other reported health effects associated with exposure to diesel exhaust include dizziness, drowsiness, headaches, nausea decreased visual acuity, and forced expiratory volume. In addition, studies by MSHA and the former Bureau of Mines show that miners working in underground mining operations that use diesel equipment are probably the most heavily exposed workers of any occupational group. Based on the levels of diesel particulate measured in underground mining operations and the evidence of adverse health effects associated with exposure to diesel exhaust, MSHA is concerned about the potential health risk to miners. The proposed rule would control exposure of miners to diesel particulate matter by requiring the installation of high-efficiency filters on diesel powered equipment to trap diesel particulates before they enter the mine atmosphere.

Alternatives: In the fall of 1995, MSHA held a series of public workshops to gather suggestions for possible approaches to limit miners' exposure to diesel particulate. In addition, over the past 10 years, MSHA and the former Bureau of Mines have conducted research on methodologies for the measurement and control of diesel particulate in the mining environment. This research has demonstrated that the use of low sulfur fuel, good engine maintenance, exhaust after-treatment, new engine technology, and optimized application of ventilating air all play a role in reducing miners' exposure to diesel exhaust particulate matter. ^PMSHA considered establishing a PEL for diesel particulate, but found that technology for measuring it in the presence of coal mine dust is not currently feasible. MSHA encourages the mining community to continue to voluntarily use protective measures to address exposure to diesel exhaust. In addition, the proposal provides for MSHA technical assistance to operators and a phased-in period for compliance.

Anticipated Costs and Benefits: MSHA estimates that the per year compliance costs are just over $10 million, of which underground coal mine operators would incur about $10 million and manufacturers of diesel engines and equipment would incur about $30,000. ^PThe proposed rule would reduce a significant health risk to underground miners, reducing the potential for acute sensory irritations and respiratory symptoms, lung cancer, and premature death, along with the attendant suffering and costs thereof to their employees, their families, and society.

Risks: Several epidemiological studies have found that exposure to diesel exhaust presents potential health risks to workers. In addition, laboratory tests have shown diesel exhaust to be carcinogenic in rats, as well as toxic and mutagenic. These potential adverse health effects range from headaches and nausea to respiratory disease and cancer. In the confined space of the underground mine environment, occupational exposure to diesel exhaust may present a greater hazard due to ventilation limitations and the presence of other airborne contaminants, such as toxic mine dusts or mine gases. The Agency believes that the health evidence forms a reasonable basis for exploring possible methods to reduce miners' exposure to diesel particulate.