Occupational exposure to dust containing free silica in a ceramics factory

In a ceramics plant employing 225 workers, respirable dust was collected into personal samplers worn by exposed workers. Analysis by X-ray diffraction documented exposures to free silica greater than 50 micrograms/m3-the permissible exposure level or threshold limit value-time weighted average proposed by the U.S. National Institute of Occupational Safety and Health-in 15 of 25 determinations. Excessive exposures were produced by dust with quartz content less than or equal to 8% by weight. If there had been such exposures to free silica-containing dust in the past, X-ray findings compatible with silicosis, described in a group of workers employed for 5 to 23 years prior to this study could be accounted for. The exposures appeared to be due to failure to incorporate established principles for prevention of dust exposure when the plant was designed. Routine determination of free silica content, even at trace and low levels, is necessary to assess the potential hazard for silicosis in dusty workplaces.