Since the beginning of the industrial revolution, coal has been the fuel that provided the energy for industry. In the United States, coal production is at near record levels and in 2003 1,972 active mines and about 70,000 working coal miners were engaged in the commercial exploitation of the major U.S. coal deposits in 38 states. After World War II, mechanization in the U.S. coal mining industry brought an end to most pick-and-shovel mining, and resulted in dramatic increases in productivity and consequent sharp and progressive declines in mine employment. However, recent increases in energy prices have led to an increased interest in coal, and current industry figures suggest that coal mine employment is now increasing. (Coal mine employment statistics are available at http://www.msha.gov/stats/statinfo.htm
) To maintain the required high levels of production with a small workforce, modern miners commonly operate powerful and sophisticated mining equipment. Despite extensive mechanization, however, coal mine work often involves strenuous manual labor in cramped and hazardous conditions. The high levels of production that are being achieved in confined spaces present continuing challenges for controlling dust and assuring the safety of miners.