A study of workers' exposures to the inhalable and 'total' aerosol fractions in the primary nickel production industry using mannequins to simulate personal sampling

This paper describes a study that was carried out at work sites in the prim ary nickel production industry to investigate the difference between inhala ble and 'total' aerosol exposures by using the mannequin sampling method, a nd to compare the results with those from an earlier study where actual wor kers' personal exposures were assessed in the same way. Experiments were ca rried out at 21 work sites located in mining, milling, smelting, and refini ng works of two primary nickel production companies. During sampling, manne quins were used to simulate the physical presence of workers and the 'expos ures' of these were obtained for strategic positions at selected work sites . The orientations of each mannequin with respect to the wind were rotated through 90 degrees every hour in order to simulate the approximate orientat ion-averaging corresponding to actual workers. Two samplers were placed sid e-by-side on each mannequin: the Institute of Occupational Medicine (TOM) i nhalable aerosol sampler, and the 37-mm plastic cassette widely used as a p ersonal sampler for 'total' aerosol, Each collected sample was analyzed to obtain both overall dust and overall nickel content, A total of 116 such sa mple pairs were collected. The results show that inhalable aerosol exposure levels-for both overall dust and for total nickel content-were consistentl y and significantly higher than the corresponding total aerosol exposure le vels. Weighted least squares linear regression yielded (inhalable/'total') aerosol ratios ranging from 1.38 to 3.90 and 1.20 to 4.01, respectively, fo r overall dust and for total nickel content for different work sites. Compa rison of these results with those from the earlier study of actual workers' personal exposures were in good agreement for most of the work sites studi es. However, the actual intensities of exposure using the mannequin samplin g method were consistently lower than those obtained from actual workers' p ersonal sampling in our earlier study. The consistency of the (inhalable/'t otal') ratios between mannequin and actual personal sampling strongly sugge sts that the characteristics of the aerosol sampled by the two methods, mos t notably the particle size distribution, were the same. This in turn sugge sts that mannequin sampling can be useful in occupational hygiene for deter mining such properties of personal workers' exposures. It certainly provide s a useful and cost effective method for determining factors at work sites in individual industry settings by which to examine the impact of changing exposure assessment from one based on 'total' aerosol to the recommended ne w approach based on inhalable aerosol. (C) 2001 British Occupational Hygien e Society. Published by Elsevier Science Ltd. All rights reserved.