FYI From the GAO report: Lab Air Filters
Posted by nonbafks on August 11, 2008
We also found that the study did not consider other safety issues specific to FMD. For example, the study did not look at the likely loads that air filtration systems have to deal with, especially in the case of pigs infected with FMD virus—which, through normal expiration, excrete very large amounts of virus-laden aerosols. Properly fitted and maintained high-efficiency particulate air (HEPA) filters are a key factor in all modern biocontainment facilities and have a record of being highly effective in keeping aerosolized pathogens, including viruses, contained. Nevertheless, they do not represent an absolute barrier. The typical standard for such filters is that they must operate with an efficiency of at least 99.97 percent.32 Often the highest level-containment laboratories use two HEPA filters in series, in addition to prefiltration systems, to gain increased efficiency. However, we found no indication that the study examined specific filtration issues with the FMD virus or that it questioned the efficiency of such systems specifically in relation to a high-volume challenge of virus, a concern that, while remote, should not have been dismissed, given the very low dose of FMD virus required for animals to become infected.33
32Institute of Environmental Sciences and Technology, IEST-RP-CC001.3 and MIL-STD-282 Method 102.9.1, are typical standards applied for HEPA filtration. It has been shown that because of the unique design of HEPA filters, they are least efficient around the 0.3 micron particle size and the efficiency benchmark of 99.97 is applied at that particle size.
33Few, if any, empirical studies examin the true efficiency of HEPA filtration against a specific challenge of FMD virus. One expert in airborne transmission of FMD virus told us that while it is theoretically possible for transmission through HEPA filters to occur, to his knowledge there has never been a documented case.
Source: Page 20 GAO-08-821T
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