The dimensions of airborne fibres collected at various stages of fibre processing in mines and mills producing crocidolite, amosite and chrysotile asbestos were measured by using light optical and electron microscopy. Airborne fibres of different asbestos types had markedly different size and shape distributions. For a given asbestos type, airborne fibres collected at various stages of processing differed in their size distributions but the differences were considerably less than between fibre types. Most of the airborne fibres to which miners and millers were exposed were short, thin and thus respirable. The proportions of long fibres in the air of crocidolite and chrysotile mines and mills were small compared to those in amosite mining and milling environments. The physical parameters which best differentiated crocidolite fibres from other asbestos fibre types were aspect ratio, which was higher, and proportions of long thin fibres (0.06 - 0.2 (mu)m in diameter and > 5 (mu)m in length). Median mass of amosite fibres was more than 108 and 13 times higher than the median mass of chrysotile and crocidolite fibres respectively. Median true diameter of amosite fibres was approximately 4 and 3 times higher than median true diameters of chrysotile and crocidolite fibres respectively. Median true length of amosite fibres was more than 4.5 and 1.9 times higher than median true lengths of chrysotile and crocidolite fibres respectively. / The differences in size and shape of airborne fibres have important implications for setting of work environmental standards and explaining differences in health risks associated with different fibre types.

No description available.