Airborne fiber concentrations during splitting open and boxing bags of asbestos

Measured airborne concentrations of asbestos are often unavailable to assess different epidemiologic estimates of past personal exposure levels or concentrations near specific operations involving handling asbestos. The purpose of this study was to assess the potential use of a laboratory study in estimating exposure to asbestos in operations that ceased for many years. The asbestos transfer operations were simulated by splitting and boxing 4.5-kg paper bags of chrysotile asbestos in an enclosed chamber ventilated at 28.2 air changes per hour (ACH). Two recirculation fans achieved chamber air mixing. The airborne concentration of asbestos fibers was determined by sampling air through membrane filters at a rate of 10 l/min and by analysing fibers by phase contrast optical microscopy to determine 15-min average airborne concentrations. Samplers were located at four equidistant locations from the operation. Opening a maximum of seven bags in 15 min was associated with an asbestos-in-air concentration of less than 2 x 10(-6) fibers/m3 (f/m3) in splitting open and boxing and less than 0.85 x 10(-6) f/m3 in boxing of pre-split bags. The measured airborne asbestos concentration exhibited a linear trend with the number of bags opened per 15 min. The empirical results were utilised to model fiber concentrations for various ventilation rates. It was concluded that the distribution of the operation within the workday and the ventilation rate are the two most important variables in the determination of the estimated time-weighted average concentration. Splitting open and boxing 32 bags of asbestos over an 8-h period at a rate of 4 bags/h over an 8-h period results in a calculated time-weighted average exposure of about 1 x 10(-6) f/m3 in a work space with 20 ACH and approximately 7 x 10(-6) f/m3 in a work space with 2 ACH. Splitting open and boxing at a rate of 12 bags/h for 2 h and 45 min yielded calculated concentrations less than one-half of the above mentioned values. These results should serve as a useful benchmark for epidemiologists concerned with the magnitude of exposure in historically dusty industrial tasks.