Testing air-filtering systems. I. Procedure for testing high-efficiency air filters on exhaust systems. Appl. Microbiol. 11:394-397. 1963.-A procedure was developed for evaluating high-efficiency filters mounted in exhaust ducts at the National Animal Disease Laboratory. An aerosol of the test organism, Escherichia coli B T3 bacteriophage, was generated in a chamber attached to a ceiling exhaust register in concentrations of at least 1000 viable organisms per ft3 of air. Samples were collected from both the pre-and postfilter areas, and the number of organisms per ft3 of air was determined. The efficiency of the filter was calculated from these figures. A total of 269 highefficiency filters were tested. Of these, 249 had efficiencies of 98 % or greater. The remaining 20, with efficiencies of less than 98 %, were repaired and retested. No filter was accepted with an efficiency of less than 98 %.

A procedure was developed for evaluating high-efficiency filters mounted in exhaust ducts at the National Animal Disease Laboratory. An aerosol of the test organism, Escherichia coli B T 3 bacteriophage, was generated in a chamber attached to a ceiling exhaust register in concentrations of at least 1000 viable organisms per ft 3 of air. Samples were collected from both the pre- and postfilter areas, and the number of organisms per ft 3 of air was determined. The efficiency of the filter was calculated from these figures. A total of 269 high-efficiency filters were tested. Of these, 249 had efficiencies of 98% or greater. The remaining 20, with efficiencies of less than 98%, were repaired and retested. No filter was accepted with an efficiency of less than 98%.

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