In order to determinethe annountof micro-organism present before and afier the filters ofHVAC systems, 6 system in 5 buildings were monitored every 2 weeks for one year. Measurementswere taken in triplicate and simdtaneously before and afier the titers using a sixstage Andersen sampler. The reduction of total of micro-organisms through the air filtersranged from 20% up to 93% andwas associated with filtration efficiency rating.In most of theHVAC system the total cfu levels were low or very low afier the pre flters and the main titers.The micro-organismswere also analysedby particlesmass (the six stages of the Andersensampler) to determine which micro-orgtisms were small enough to have the potential topenetrate deep into hsnuankings and cause adverse health eflects (stages 4, 5 and 6 of thesampler). These smallersized micro-organisms were significantlyreduced by the filtrationmedia.The results also revealed advantages and disadvantagesbetween HVAC type and designincludingfilter type, maintenance,and moisture damage. During the study, sources of microorganisms contamination werealso identified and mitigation could be performed.
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