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An ongoing resurgence of occupational lung disease among coal miners in the United States has been linked to respirable crystalline silica (RCS). To better protect miners, a deeper understanding of key exposure factors is needed. As part of a larger investigation of RCS in 15 coal mines, this paper describes analysis of silica mass content in two types of samples: (1) respirable coal mine dust (RCMD) collected in standardized locations in each mine; and (2) respirable dust generated in the laboratory from primary source materials, including coal and rock strata being mined at the production face, material obtained from the dust collection system on roof bolter machines, and rock dust products being applied by the mine. As expected, results indicate that rock strata drilled for roof bolting or being extracted along with the coal are a major source of RCS in many coal mines—although the coal seam itself can contain significant silica in some mines. While silica content of rock strata encountered in central Appalachian mines is not necessarily higher than in other regions, the sheer abundance of rock being extracted in thin-seam central Appalachian mines can explain the relatively higher silica content typically observed in RCMD from this region.

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Application of fine, inert ‘rock dust’ (RD) to the surfaces in underground coal mines is a common method for mitigating coal dust explosion hazards. However, due to its size, RD has the potential to contribute to the respirable coal mine dust (RCMD) concentration. Though the RD component of RCMD does not appear to pose the sort of health hazards associated with other components such as crystalline silica, understanding its relative abundance may be quite helpful for evaluating and controlling primary dust sources. Given that RD products are frequently comprised of high-purity limestone (i.e., primarily calcite mineral), calcite may serve as a suitable proxy for measuring RD. To estimate the mass percentage of calcite in RCMD samples, this study demonstrates the successful application of direct-on-filter (DOF) Fourier-transform infrared (FTIR) spectroscopy. Incidentally, DOF FTIR has been the focus of recent efforts to enable rapid measurement of crystalline silica in RCMD. Concurrent measurement of other constituents such as calcite is thus a logical next step, which can allow a broader interpretation of dust composition and source contributions.