A re-evaluation of radiological evidence from a study of U.S. strip coal miners

In 1972, the U.S. Public Health Service examined 1438 workers employed at seven bituminous and one anthracite U.S. strip coal mines. One conclusion from the study was that workers without previous dust exposures were not at risk of category 2 or higher pneumoconiosis from their strip coal mining environment. Because of recent concerns for silicosis among strip coal miners, the radiographs were reinterpreted and the data re-evaluated. In addition, data from respirable coal mine dust samples collected from 1972 to 1979 in all surface coal mines were analyzed. The results showed that category 2 or higher pneumoconiosis was prevalent among strip coal miners with experience in an underground coal mine. Among those without underground coal mine experience, category 2 or higher was prevalent among anthracite strip miners, but not among bituminous strip miners. Average respirable coal mine dust exposures in the anthracite mine were less than 1 mg/m3 prior to 1975 and, coupled with the radiographic findings, suggest further study of the efficacy of the 2 mg/m3 U.S. Federal surface coal mine dust standard in anthracite coal mines.