| Abstract
| - This study evaluated the efficacy of an upper-room airultraviolet germicidal irradiation (UVGI) system for inactivatingairborne bacteria, which irradiates the upper part of aroom while minimizing radiation exposure to persons in thelower part of the room. A full-scale test room (87 m3),fitted with a UVGI system consisting of 9 louvered walland ceiling fixtures (504 W all lamps operating) was operatedat 24 and 34 °C, between 25 and 90% relative humidity,and at three ventilation rates. Mycobacterium parafortuitumcells were aerosolized into the room such that theirnumbers and physiologic state were comparable bothwith and without the UVGI system operating. Airbornebacteria were collected in duplicate using liquid impingersand quantified with direct epifluorescent microscopy andstandard culturing assay. Performance of the UVGI systemdegraded significantly when the relative humidity wasincreased from 50% to 75−90% RH, the horizontal UV fluencerate distribution was skewed to one side compared tobeing evenly dispersed, and the room air temperature wasstratified from hot at the ceiling to cold at the floor. Theinactivation rate increased linearly with effective UV fluencerate up to 5 μW cm-2; an increase in the fluence rateabove this level did not yield a proportional increase ininactivation rate.
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