Drillers and bulldozer operators have experienced exceptionally high exposures to respirable crystalline silica in US surface coal mines

Introduction: Previous studies suggest respirable crystalline silica (RCS) is an important driver of resurgent pneumoconiosis among US coal miners. Although greater attention has been focused on dust exposures in underground coal miners, surface miners are also at risk of severe disease. This study explores RCS exposure in this population.

Methods: We analysed 91 950 respirable quartz samples from 4127 US surface coal mines from 1982 to 2023. We calculated the geometric mean of respirable quartz concentration for each mine-year combination. Then, for each calendar year, we averaged the geometric means across all mines. We used generalised estimating equation models with a natural logarithm link function and Poisson distribution to evaluate the marginal effects of mine characteristic variables on the mass concentration of respirable quartz based on individual dust sample results.

Results: Drillers and bulldozer operators had annual mean respirable quartz exposures as high as 0.58 and 0.32 mg/m3, respectively, while other occupations combined had exposure of 0.08 mg/m³. The mean mine-level respirable quartz mass concentrations decreased substantially over time for all three occupation groups. Drillers or bulldozer operators, mine location in Central Appalachia and lack of a mine safety committee were predictive of higher respirable quartz mass concentrations.

Conclusions: These data demonstrate exceptionally high RCS overexposures among certain groups of surface coal miners, particularly drillers and bulldozer operators in the 1980s and 1990s. Despite recent improvement in RCS levels, these data underscore the importance of continued medical surveillance of current and former surface coal miners.