Abstract
The airborne concentrations of mineral fiber and quartz dust to which miners are exposed are reported here for four limestone and five dolomite mines. The air samples were collected at fixed monitoring points located in the main work areas. The material comprises 46 samples analyzed by phase contrast microscope (PCM), 90 samples analyzed by scanning electron microscope (SEM), and 50 samples of dust analyzed for quartz content. Fibers (length >5 μm, diameter < 3 μm, and aspect ratio ≥ 3:1) were counted and silicate minerals were identified with an energy-dispersive spectrometer. On the basis of morphology the fibers were classified as perfect fibers, fibrous cleavage fragments, or cleavage fragments. In various work stages the mean fiber concentrations were 0.05 to 0.71 fibers/cc as measured with PCM and 0.06 to 0.34 fibers/cc as measured with SEM. The mean concentrations of the respirable quartz dust (<5 μm) were 0.07 to 0.96 mg/m3. The predominant fibrous silicates were tremolite and wollastonite. Of all the tremolite fibers meeting the counting criteria, 40 percent were cleavage fragments and 30 percent were perfect fibers. The figures for wollastonite were 55 and 35 percent, respectively. The highest fiber concentrations usually occurred at drilling, crushing, automatic sorting, and screening operations. The concentrations of respirable quartz were frequently high at limestone or dolomite crushing. We note that not only the workers but also the users of these mineral products may be exposed to airborne concentrations of fibrous silicates and quartz dust occurring as impurities.