TESTING AIR-FILTERING SYSTEMS. I. PROCEDURE FOR TESTING HIGH-EFFICIENCY AIR FILTERS ON EXHAUST SYSTEMS.

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%.