Thoracic size-selective sampling of fibres: performance of four types of thoracic sampler in laboratory tests.

Thecountingoffibresonmembranefilterscouldbefacilitatedbyusingsize-selectivesamplersto excludecoarseparticulateandfibresthatimpedefibrecounting.Furthermore,theuseofthoracic size selection would also remove the present requirement to discriminate fibres by diameter during counting. However, before thoracic samplers become acceptable for sampling fibres, their performance with fibres needs to be determined. This study examines the performance of four thoracic samplers: the GK2.69 cyclone, a Modified SIMPEDS cyclone, the CATHIA sampler (inertial separation) and the IOM thoracic sampler (porous foam pre-selector). The uniformity of sample deposit on the filter samples, which is important when counts are taken on randomfields, was examinedwith twosizes ofspherical particles (1 and 10mm)and aglass fibre aerosol with fibres spanning the aerodynamic size range of the thoracic convention. Counts by optical microscopy examined fields on a set scanning pattern. Hotspots of deposition were detected for one of the thoracic samplers (Modified SIMPEDS with the 10 mm particles and the fibres). These hotspots were attributed to the inertial flow pattern near the port from the cyclonepre-separator.Fortheotherthreethoracicsamplers,thedistributionwassimilartothat on a cowled sampler, the current standard sampler for fibres. Aerodynamic selection was examined by comparing fibre concentration on thoracic samples with those measured on semi-isokineticsamples,usingfibresize(andhencecalculatedaerodynamicdiameter)andnumber data obtained by scanning electron microscope evaluation in four laboratories. The sizeselectioncharacteristicsofthreethoracicsamplers(GK2.69,ModifiedSIMPEDSandCATHIA) appearedverysimilartothethoracicconvention;therewasaslightoversampling(relativetothe convention) for dae < 7 mm, but that would not be disadvantageous for comparability with the cowled sampler. Only the IOM thoracic sampler tended to undersample the fibres relative tothe thoracicconvention.Withthedatadividedintofour classesbasedonfibrelength,thesizeselection characteristics appeared to be unaffected by fibre length for GK2.69, Modified SIMPEDS and CATHIA. Only the IOM thoracic sampler (with the foam selector) showed slightly lower selection for longer length classes of fibres. These results indicate that the tested samplers follow the thoracic sampling convention for fibres, and may be used to improve the quality and reliability of samples that are taken when there is likely to be significant background dust.