Field performance of the CATHIA-T sampler and two cyclones against the standard Cowled sampler for thoracic fiber concentrations.

The performance of two thoracic samplers, the GK2.69 cyclone and the CATHIA-T sampler, and the GK3.51 cyclone was investigated in the field against the standard cowled sampler (current NIOSH 7400 method) to determine the effect of thoracic sampling. The CATHIA-T sampler and the GK2.69 cyclone were operated at 7 and 1.6 l min(-1), respectively. The GK3.51 sampler is related to the GK2.69 cyclone, but designed to give a thoracic cut at a flow rate of 3.2 l min(-1). A total of 136 area samples were obtained from a tremolitic talc processing mill and 148 area samples were obtained within a quarry in which metamorphosed volcanic rocks were being crushed for construction stone. Sample slides were prepared using the dimethyl formamide/Euparal technique and relocatable cover slips. NIOSH 7400 'A' counting rules were used to examine fibers. Additionally, counters were asked to record the number of fibers where a fiber meets the 'A' rules and is wider than 3-mum physical diameter in order to estimate the proportion of extra-thoracic fibers. A few slides from each sampler type were randomly selected and fiber widths for those fibers satisfying the counting rules were measured to determine median width ratios of each thoracic sampler to the cowled sampler. Overall, the combined results of this study and the previous study by the same authors (Lee et al., 2008) showed lower fiber concentrations for the CATHIA-T sampler and higher concentrations for the GK2.69 cyclone and the GK3.51 cyclone compared to the standard cowled sampler. The proportion of extra-thoracic fibers (>3-mum physical diameter) on the filters collected with each type of thoracic samplers was comparable to the proportion of such fibers collected with the cowled sampler. The most consistent result over this study and our previous study is that both cyclones gave higher fiber concentrations than the CATHIA-T sampler. However, the estimated width ratios of each cyclone type to the cowled sampler were similar to or equal to 1 indicating no separation of fiber bundles due to cyclone effects. An inverse relationship between the fiber concentration ratios of each thoracic sampler type to the cowled sampler and the relative sample loading rate compared to the cowled sampler was observed. The difference in fiber concentration ratios might be a function of sample loading rather than an effect of thoracic size selection. Therefore, it is not recommended that any of these samplers be used to replace the cowled sampler in measurements intended for comparison with limit values arising from risk assessments developed from cowled sampler measurements without considering this possible effect.