Pneumoconiosis in workers exposed to silicon carbide

Two men who had been exposed only to silicon carbide for many years in a factory manufacturing refractory bricks developed bilateral reticulonodular densities, as shown on chest radiograms, and complained of dyspnea. An open lung biopsy of one of them showed a large amount of black material in the fibrosed alveolar septums. Studies by X-ray diffraction revealed that the silicon carbide to which they were exposed did not contain quartz; X-ray powder diffraction analysis of the lung tissue revealed at least 6 different silicon carbides, traces of tungsten carbide, and an insignificant amount of quartz. Line-width analysis of the pattern suggested that the lung contained foreign material, with a significant number of particles smaller than 0.1 micron. The etiologic role of silicon carbide for tissue fibrosis is discussed.