WORKPLACE VALIDATION OF A LABORATORY EVALUATION TEST OF SAMPLERS FOR INHALABLE AND "TOTAL" DUST

Parallel personal breathing zone sampling of dust with the IOM sampler and the openface 37mm filter cassette has been performed at seven plants where dusting processes take place indoors. The particle size distribution in the breathing zone and the amount of dust collected by passive sampling was also determined. The prevailing orientation of the worker in relation to the dust source was noted. Measured ratios of dust concentrations sampled with the open-face 37mm filter cassette and the IOM sampler were compared with estimated ratios of dust concentrations obtained from the sampled size distributions and published sampling efficiencies of the two samplers determined in a wind-tunnel experiment. The results of the workplace sampling show that at these plants the inhalable size distribution often contained very coarse particles and that the maximum air speed was low, generally less than 0.3ms-1. The worker mainly faced and handled the predominant dust source. The comparison of the sampled and estimated dust concentration ratios of the open-face 37mm filter cassette to the IOM sampler showed that the ratio of sampled dust concentrations were 25% lower than estimated. The present test method employed for dust samplers in wind-tunnels may therefore be improved in order to be even more valid for workplace sampling. The cause of the deviation between the workplace and the wind-tunnel could not be found, but the following major differences between the two cases are probably involved: bias in sampling efficiency between electrically insulating and conducting IOM samplers, lower air speed at workplaces than in wind-tunnel experiments, workers handling the source, dust concentration gradients between the collarbone and the lapel.