The incidence and progression of pneumoconiosis over nine years in U.S. coal miners: I. Principal findings.

Chest radiographs, taken at a 9-year interval for 1,261 U.S. coal miners, were read for pneumoconiosis side-by-side by six readers in a controlled trial. Incidence and progression of small, rounded opacities were consistent with levels predicted from dose-response curves developed by the British Pneumoconiosis Field Research interpolated at a concentration derived from U.S. compliance levels mandated over the last 9 years. The results imply that the level of pneumoconiosis in U.S. miners is being reduced through application of the current 2 mg/m3 standard. The long developmental period for pneumoconiosis necessitates that further study be undertaken to verify this finding and to determine whether 2 mg/m3 is an appropriate regulatory dust level for the prevention of category 2 or greater simple pneumoconiosis over a 35-year period.