Comparison of the Aerosol Photometer and Light Scattering Airborne Particle Counter (LSAPC) Methods for Installed Filter System Leak Testing

The installed filter system leak test method for cleanrooms and clean zones is described in ISO 14644-3, Cleanrooms and associated controlled environments—Part 3: Test method. Portions of the methods in ISO 14644-3 were adapted from IEST-RP-CC034.4[Schaumburg, Illinois, US: Institute of Environmental Science and Technology], which provides a set of recommended procedures for leak testing HEPA and ULPA filters in situ (in the field) with the aerosol photometer test method and the light scattering airborne particle counter (LSAPC) test method. Leak testing is performed to confirm that the final high efficiency air filter system is properly installed by verifying the absence of bypass leakage in the installation, and that the filters are free of defects (small holes and other damage in the filter medium, frame, seal and leaks in the filter bank framework). This study was conducted to compare the aerosol photometer and LSAPC methods. Testing in the study consisted of creating artificial leaks in the filter system, measuring the upstream and downstream concentrations with the aerosol photometer and with the LSAPC, and comparing the filter leak penetration results. Comparison testing was applied to the procedure for the installed terminal panel filter system leakage scan test (stationary measurement) and the procedure for evaluating overall leakage of high-airflow box-type filters mounted in a duct or air-handling unit (AHU) (overall leakage test). It was found that the aerosol photometer and the LSAPC gave similar results for filter leakage within experimental error. The comparison of the leakage scan tests (stationary measurement) showed that the penetration calculated for the channel ≥ 0.3 μm of the LSAPC with an air flow rate of 1cu ft/min (CFM) (28.3 l/min) was very similar to the penetration measured with the aerosol photometer for a leakage level >0.01 % of the upstream concentration. The comparison result of the overall leakage test showed that overall total penetration values, obtained after dilution of artificial calibrated leaks in the filter media, were identical, within the measurement uncertainty, for particles ≥0.3 μm whether the sampling rate of the LSAPC was 1 CFM (28.3 l/min) or 50 l/min. Several recommendations are provided. In particular, for filters mounted in a duct or AHU where the filter function is critical, the recommended method is the leakage scan test method, using a grid sampling method in a plane downstream of the filter (as agreed between customer and supplier).