Determination of the retention efficiency of industrial air filters for particle sizes in the submicron range

Particle size distribution up to a maximum diameter of 0.1 μm has been produced in the presence of short-lived tracer Na-24 using an aerosol generator. Industrial air filters with a cross-section of 100 cm² have been exposed to very high particle fluxes such that particulate breakthroughs down to 10^-8 can be assessed by measuring the activity ratio of the air before and after going through the filter. This method, which involves installing an analytical filter (absolute filter) after the test filter, has a high accuracy and makes it possible to determine particle breakthrough under the same conditions of air flow velocity and pressure loss as in industrial processes. In comparison with on-the-spot-methods, e.g. the condensation nucleus counter, the above method includes passage across the entire filter area and excludes secondary aerosols.