Viral Penetration of High Efficiency Particulate Air (HEPA) Filters
APPLIED RESEARCH ASSOCIATES INC TYNDALL AFB FL
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High Efficiency Particulate Air HEPA filters are the primary technology used for particulate removal in many individual and collective protection applications. HEPA filters are commonly thought to be impenetrable to particulate matter, but in fact they are only 99.97 efficient at collecting the most penetrating particle 0.2 micrometer. While this is an impressive collection efficiency, HEPA filters may be vulnerable to certain types of threats Viruses are submicron in size and most have very small minimum infections doses MID. Therefore, an appropriate viral challenge will yield penetration that exceeds the MID, for many of the threat agent viruses. Nonetheless, the overall particle size agglomerated viruses andor viruses attached to inert carriers will determine the capture efficiency by HEPA filters. Aerosolized viruses are commonly thought to exist as agglomerates, which would increase the particle size and render them more prone to capture. However many of the threat agent viruses can be highly agglomerated and still exist as submicron particles. Furthermore the stability of aggregates is not well understood, and they may break apart during filtration. We have demonstrated in our laboratory that biological aerosols of MS2 coli phage, a common viral simulant, can penetrate both Carbon HEPA Aerosol Canisters CHAC and flat sheet HEPA material. The penetration is linear over time, thus viral penetration exceeding the MID is expected to occur in minutes following a viral challenge. We are currently investigating the particle size of the MS2 coli phage aerosol and our aim is to shift the particle size to see what effect it has on penetration. Furthermore, we are evaluating the penetration characteristics of a mammalian virus, which may better represent the threat agent viruses.
- Pumps, Filters, Pipes, Tubing, Fittings and Valves
- Air Pollution and Control