Thoracic sampling of fibres.

‘Thoracic’ aerodynamic size selection sampling should collect respirable fibres while excluding coarse
irrelevant material that impedes counting by microscopy. Four samplers (GK2.69, Modified Simpeds,
Cathia, and an IOM foam sampler) were tested to assess their conformity to the thoracic convention,
whether this holds for fibres, and their comparability with the standard (cowled) sampler for fibres.
From tests with spherical particles and an Aerodynamic Particle Sizer, the GK2.69 and Modified Simpeds
comply with the thoracic convention. The other two complied less well, over-sampling (relative to the
convention) particles with aerodynamic diameter dae>10µm.
With isometric particles, the filter deposit appeared uniform for two of the samplers. However, two samplers
(with cyclone separators) showed localised high concentrations near the centre of the filter for coarser particles.
For fibres counted by optical microscopy, distributions across the filter surface appeared adequately uniform for
all samplers. In tests with fibres counted and sized by SEM, the aerodynamic selection depends on dae without
further dependence on fibre length. In work place trials, the thoracic samplers agree well with the cowled
samplers for respirable fibres. Predictably, they gave slightly lower concentrations for non-respirable fibres.
Differences in sample loading were a more important cause of bias in fibre counting (confirming previous
findings). Counting was marginally quicker for the thoracic samples, supporting the supposition that thoracic
sampling would facilitate counting. Thoracic samplers are recommended for sampling fibres where the
concentration of coarse material restricts the volumes that can be sampled with a cowl.
This report and the work it describes were funded by the Health and Safety Executive (HSE) and the
Standards, Measurements and Testing programme of the European Commission (EC). Its contents,
including any opinions and/or conclusions expressed, are those of the authors alone and do not
necessarily reflect HSE policy.