The objective of this work was to estimate the percentage of workers by industry that are exposed to defined concentrations of respirable crystalline silica dust. An algorithm was used to estimate the percentage of total workers exposed to crystalline silica in 1993 at concentrations of at least 1, 2, 5, and 10 times the National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) of 0.05 mg/m3. Respirable crystalline silica air sampling data from regulatory compliance inspections performed by the Occupational Safety and Health Administration (OSHA), for the years 1979-1995, and recorded in the Integrated Management Information System (IMIS) were used to estimate exposures. Therefore, this work does not include industries such as mining and agriculture that are not covered by OSHA. The estimates are stratified by Standard Industrial Classification (SIC) codes. This work found that some of the highest respirable crystalline silica dust concentrations occurred in construction (masonry, heavy construction, and painting), iron and steel foundries (casting), and in metal services (sandblasting, grinding, or buffing of metal parts). It was found that 1.8% (13,800 workers) of the workers in SIC 174--Masonry, Stonework, Tile Setting, and Plastering--were exposed to at least 10 times the NIOSH REL. For SIC 162--Heavy Construction, Except Highway and Street Construction--this number is 1.3% (6,300 workers). SIC 172--Painting and Paper Hanging--which includes construction workers involved in sandblasting was found to have 1.9% (3,000 workers) exposed to at least 10 times the NIOSH REL. The industry that was found to have the highest percentage of workers (6%) exposed to at least the NIOSH REL was the cut stone and stone products industry. Conclusion: Not enough is being done to control exposure to respirable crystalline silica. Engineering controls should be instituted in the industries indicated by this work.
Kenneth D. Linch, M.S., National Institute for Occupational Safety and Health, Division of Respiratory Disease Studies, 1095 Willowdale Rd., Morgantown, WV 26505-2888