dispersion and concentration of asbestos fibers in an asbestos-cement factory

in this survey, asbestos fiber levels within the breathing zone of employers and in the environment of an asbestos-cement factory were monitored on membrane filter and counted by phase contrast optical microscope considering length/diameter>3:i (asbestos international associational method). the plant was fairly old and utilized both white (chrysotile) and blue (chrocidolite) asbestos. in each workshop, 8-h time-weighted average concentrations (ctw,) or its equivalent were calculated as fiber/ml. average and range of concentrations were determined as well. results indicated that asbestos fibers were dispersed all over the plant and major sources of emission were mills (raw materials and waste products) and finishing. in addition, longer daily shift durations (12-h) increased workers’ exposure levels more than 2 times than that of 8-h shift (α=0.05, t0.95.17). in finishing workshop by comparison of two criteria length/diameter>3:1 (asbestos international association) with length/diameter >5:1 (american society for testing and materials), test statistics on mean showed no significant difference between two counting criteria (α= 0.05, t0.975.9).