Abstract
Current methods for evaluating the performance and reliability of high-efficiency air cleaning systems use forward light-scattering photometers and DOP aerosol. This method is limited to measuring protection factors of 104 or 105 and has poor sensitivity to particles less than 3µm. More accurate determination of system performance could be made by measuring two filter stages with a single test. Because of the large protection factors of a two-stage system, it is necessary to use high challenge aerosol concentrations and long downstream sampling times. Concentrations were measured using an intra-cavity laser light-scattering aerosol spectrometer which is capable of detection of single particles ranging in size from 0.07 to 3.00 µm diameter. The results of several tests with challenge aerosols of both NaCI and DOP yielded protection factors ranging from 1.4×107 to 3.0×109 for two HEPA filters in series.