Occupational exposure to respirable crystalline silica among US metal and nonmetal miners, 2000-2019

BackgroundIn metal and nonmetal (M/NM) mines in the United States, respirable crystalline silica (RCS) exposures are a recognized health hazard and a leading indicator of respiratory disease. This study describes hazardous exposures that exceed occupational exposure limits and examines patterns of hazardous RCS exposure over time among M/NM miners to better inform the need for interventions. MethodsData for this study were obtained from the Mine Safety and Health Administration (MSHA) Open Government Initiative Portal for the years 2000-2019, examining respirable dust samples with MSHA-measured quartz concentration >1%. Descriptive statistics for RCS were analyzed for M/NM miners by year, mine type, sector, commodity, occupation, and location in a mine. ResultsThis study found the overall geometric mean (GM) for personal exposures to RCS was 28.9 mu g/m(3) (geometric standard deviation: 2.5). Exposures varied significantly by year, mine type, sector, commodity, occupation, and location in a mine. Overall, the percentages of exposures above the MSHA permissible exposure limit (PEL for respirable dust with >1% quartz, approximately 100 mu g/m(3) RCS) and the National Institute for Occupational Safety and Health RCS recommended exposure limit (REL, 50 mu g/m(3)) were 11.8% and 27.3%, respectively. GM exposures to RCS in 2018 (45.9 mu g/m(3)) and 2019 (52.9 mu g/m(3)) were significantly higher than the GM for all years prior. The overall 95th percentile of RCS exposures from 2000 to 2019 was 148.9 mu g/m(3), suggesting a substantial risk of hazardous exposures above the PEL and REL during the entire period analyzed. ConclusionsThe prevalence of high exposures to RCS among M/NM miners continues in the past 20 years and may be increasing in certain settings and occupations. Further research and intervention of the highest exposures are needed to minimize the risks of acquiring silica-induced respiratory diseases.