Evaluation of gravimetric sampler bias, effect on measured concentration, and proposal for the use of harmonised performance based dust sampler for exposure assessment

Abstract

The last three years has brought about alarming news of re-identification of coal worker’s pneumoconiosis (CWP) or ‘black lung” in Australia after reporting nearly being absent for over five decades. While, the CWP statistics in South Africa (SA) are unverifiable, but certainly CWP has not been eliminated. These events have re-kindled the need for better understanding of the dust monitoring, performance of sampling devices, and compliance determination. Over the last half century, gravimetric sampling has been the fundamental means for dust exposure monitoring using recognised respirable size-selective standards. In both South Africa and Australia, the gravimetric sampling technique in coal mines has been followed since 1988 and 1983 respectively using samplers of original Higgins-Dewell (HD) type design. This paper provides the evaluation results of currently used South African and Australian gravimetric samplers compared against the original UK SIMPEDS ‘true reference’ sampler. The results consistently suggested that the South African and Australian cyclones do not conform to the required size selective curve or even the ‘true’ reference sampler. The results show that the currently used SA and Australian samplers showed a D50 sampling bias as high as 59 and 47% respectively against the size-selective curve. Similarly, under the controlled laboratory coal dust test conditions measuring the same coal mine dust level in a chamber, the South African, Australian and UK standard SIMPEDS sampler were 7.87, 9.79 and 6.71 mg/m3 respectively, which aligned with the sampling bias. The differences can in part be attributed to the ‘un-auditable’ inherent design and manufacturing quality, or unverifiable data on size-selective sampling curve. This finding has significant implications towards exposure data collected over the last 25 years and their subsequent use in the arrival of the dose-response curves. Therefore, it is strongly recommended that the harmonised use of ‘true reference’ SIMPEDS cyclone that meets the ISO (1995) criteria uniformly across the industry would benefit the exposure assessment and compliance determination.