Quantification of Bypass Leakage in Filter Holders with Cyclone Elutriators

Abstract

Filter holders are used worldwide for the collection of dust on filters during occupational hygiene measurements. It was anticipated that the filter holders with fixed cyclone elutriators used in Australia and other countries may contribute to an underestimation of dust exposure levels due to bypass leakage. A study was undertaken whereby the bypass leakage in the filter holders was quantified in terms of the resistance measured over the filter area. The filters were also tested using a South African-manufactured filter holder, which was designed to minimize bypass leakage. A statistically significant difference existed (P<0.05) between the results of the two filter holders at the 95% confidence level. The results showed that the evaluation of pressure drop across filters is the most appropriate method to ensure representative dust sampling. Considering that the resistances of filters vary widely within a batch of filters, it would be more appropriate to use a device that reduces or eliminates bypass leakage.