Thin seams and small mines are associated with higher exposures to respirable crystalline silica in US underground coal mines.

Objectives: Previous radiologic and histopathologic studies suggest respirable crystalline silica (RCS) overexposure has been driving the resurgence of pneumoconiosis among contemporary US coal miners, with a higher prevalence of severe disease in Central Appalachia. We sought to better understand RCS exposure among US underground coal miners.

Methods: We analysed RCS levels, as measured by respirable quartz, from coal mine dust compliance data from 1982 to 2021.

Results: We analysed 322 919 respirable quartz samples from 5064 US underground coal mines. Mean mine-level respirable quartz percentage and mass concentrations were consistently higher for Central Appalachian mines than the rest of the USA. Mean mine-level respirable quartz mass concentrations decreased significantly over time, from 0.116 mg/m³ in 1982 to as low as 0.017 mg/m³ for Central Appalachian mines, and from 0.089 mg/m³ in 1983 to 0.015 mg/m³ in 2020 for the rest of the USA. Smaller mine size, location in Central Appalachia, lack of mine safety committee and thinner coal seams were predictive of higher respirable quartz mass concentrations.

Conclusions: These data substantially support the association between RCS overexposure and the resurgence of coal workers' pneumoconiosis in the USA, particularly in smaller mines in Central Appalachia.