Describes a laboratory arrangement used to challenge a glass fibre media filter, a polymer fibre media filter and a two-stage electrostatic precipitator with 100% ambient outside air for one year. States that both of the media filters demonstrated greater than 90% effectiveness on bacteria and fungi bioaerosols. The electronic precipitator demonstrated initial efficiency of 95% or greater, which decreased over time as the device was overloaded. Over the year, no observable microbial growth took place on any of the filters. Subsequent tests on the loaded filters showed that observable microbial growth occurred within a month of continuous exposure to 90% relative humidity.

KEYWORDS: year 1995, Air filters, glass fibre, polymers, electrostatic precipitators, filters, measuring, aerosols, bacteria, fungi, relative humidity