Abstract
Results of a two-year study of dust conditions in Pennsylvania coal mines, including 24 anthracite and 14 bituminous coal mines are presented. Determinations of airborne concentrations, particle size distribution, and free silica content were made on more than 1400 samples. Dust in anthracite mines had, in general, more free silica and smaller particle size. Mechanized mines were not significantly different from non-mechanized mines in dust production. Exceptions to these generalizations are discussed.