Comparison of some particulate air filter testing methods used in normal and unfavourable conditions

The results of the removal efficiency of HEPA filters obtained by various existing test methods are rather divergent, due to special features of the applied test aerosols, the sampling - and analytical methods etc. Further difficulties arise if the tested filters are operated in various unfavourable conditions, such as: high temperature, humidity, contaminant loading, presence of heavy aerosols etc. Three methods: DOP test, potassium flame - photometric test and the radioisotopic tracer-test developed in our Institute, were intercompared, using various well known filter media, at different air velocity. All the three experiments were carried out in the same equipment using different aerosol generation, sampling and analytical method in it consecutively. The main conclusions were that all the attained filter efficiency values have been found equivalent and they are correlated within the range of experimental errors. The resistance and other properties, i.e. particle size distribution, of the various test aerosols were studied from the point of view of their suitability at high temperature and in humid conditions. It was found that the arc-generated radioactive metal-aerosols proved to be rather successful for filter testing even in unfavourable conditions. They are also very good test-particles to model the filtration of heavy-metal vapours, i.e. alpha-emitting transurane elements