Exploring agglomeration of respirable silica and other particles in coal mine dust

A better understanding of respirable dust particle characteristics is needed to advance exposure monitoring and prevent health effects. In coal mines and other occupational environments, understanding respirable silica is especially important. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) enables particle-level dust analysis, but interpretation of data can be challenging when samples include agglomerated particles (i.e., particulates consisting of multiple independent particles attached together). On the other hand, a failure to recognize agglomerates or account for them in analysis risks oversimplification in exposure assessment. This research explores possible effects of agglomerates on respirable coal mine dust classification by SEM-EDX, with a specific focus on silica. Analysis was conducted both on respirable samples (collected with a typical apparatus including a cyclone size selector) and on respirable-sized particulates identified in passive samples. Results demonstrate that silica is often contained in respirable-sized agglomerates, though the typical respirable sampling apparatus appears to break up some of those agglomerates. For agglomerates that do persist, they may influence SEM-EDX results-possibly increasing apparent size distributions and/or "hiding" some of their constituents, including silica.