Evaluation of Air Filters with Submicron Viral Aerosols and Bacterial Aerosols

Abstract

Abstract Velocity, aerosol particle size, aerosol charge, and exposure to high humidity were found to affect the performance of air filters. Filter papers and the DOP scan-tested filter units (HEPA filters) fabricated from these papers were evaluated with submicron T1 bacteriophage aerosols having a number median diameter (NMD) of 0.12 micron and with Bacillus subtilis var niger spore aerosols with a NMD of 1 micron. Penetration of submicron phage aerosols through filter papers increased markedly with an increase in velocity. Neutralizing phage aerosol with bipolar air ions resulted in 2- to 5-fold increases in penetration. Penetration of bacterial spore aerosols through the filter papers was essentially zero. Phage aerosol penetration through HEPA filters averaged 0.00095%. Spore aerosol penetration was 0.00005%. Exposure to high humidity (>95%) resulted in roughly a 3-fold increase in HEPA penetration. HEPA filters can be expected to provide excellent protection against submicron viral aerosols as well as against bacterial areosols, but the installations must be commensurate with the high performance of this type of filter for full efficiency.