Silicosis, a chronic dust disease of the lung caused by the pulmonary retention of particulate silica (7631869) in the free crystalline state, became epidemic among miners at the turn of the century due to mechanization and the development of pneumatic tools generating increasing amounts of free silica dust. Environmental medical studies in 1913 and 1915 in the Joplin, Missouri lead and zinc mining district showed that two thirds of the miners had silicosis. By the end of the 1930's such controls as wet drilling and ventilation had been instituted. A study of metal mines in 1958 to 1961 showed that only 3.4 percent of the about 14,000 miners examined had x-ray evidence of silicosis; usually the victims had been miners for at least 15 years. An efficient dust sampling device is a battery operated sampling pump that is size selective (respirable) and that may be attached to a miner to collect a day's worth of dust-exposure samples. Recent improvements in quartz analysis methods permit one person with an x-ray diffraction apparatus to make as many as 15 to 20 weighted average quartz exposures daily. There is little, if any, improvement in the rate of silicosis occurrence today. It is not yet known if the miners who contract silicosis do so because of long-term exposure or if the margin of safety of the silica dust standards is inadequate.