Application of blunt sampler theory to the definition and measurement of inhalable dust

From considerations of the air movement near the entrance to a blunt dust sampler, a simple theoretical model has been developed to explain its performance characteristics. This model predicts quantitatively the performance of a simple idealized blunt sampler with a single orifice facing the wind, but for more complicated samplers allows only a qualitative assessment to be made. This can be useful, however, for evaluating practical systems. The head of a live, breathing human subject may also be regarded as a blunt sampler and its performance in this respect assessed qualitatively in terms of the model. Thus the selection characteristic which defines ‘inhalability’ can be placed on a physical footing. Some new measurements of the selection characteristics of a model human head are reported, differing from previously published work in that experiments were carried out in a much larger wind tunnel with the full head and torso. The results suggest that the presence of the torso may have considerable influence on ‘inhalability’ as determined by such experiments. In the light of the experience gained in performing such experiments, the appropriateness of defining ‘inhalability’ in terms of idealized windtunnel-like conditions and the resultant rationale behind the use of ‘static’ samplers for inhalable dust are questioned.