[Silicon carbide, occupational exposure, proposed MAC values].

Occupational exposure to dust silicon carbide production and exploitation of its products was evaluated. Individual dosimetry was used to measure concentrations of total and respirable dusts; concentration of respirable mineral fibres was measured by means of light microscopy; the distribution of fiber length was analysed by employing a laser FM-7400; morphology of dust molecules was analysed in light and electron microscopes; x-ray diffraction and infrared spectrometry was used to identify dust mineral composition. Concentrations of total dust at workposts involved in silicon carbide production ranged between 5.0 and 14.0 mg/m3 (mean = 10.3 mg/m3); concentration of respirable fraction between 0.1 and 1.9 mg/m3 (mean = 1.1 mg/m3); and concentration of respirable mineral fibres between 0.42 and 1.04 f/cm3 (mean = 0.64 f/cm3). In the plants where SiC products were used the mean concentrations of total dust and respirable mineral fibres were about two times lower, and the concentrations of respirable fraction about five times lower. In the workpost air the presence of carborundum, mullite and cristobalite was revealed. A proposed MAC value for SiC dust (nonfibrous) containing less than 2% of free crystalline silica accounts for 10 mg/m3 for total dust.