Ultraviolet germicidal irradiation inactivation of airborne fungal spores and bacteria in upper-room air and HVAC in-duct configurations

The efficacy of ultraviolet germicidal irradiation (UVGI) for inactivating airborne fungal spores and bacterial vegetative cells was evaluated under three configurations — intrinsic, upper-room air, and in-duct. Correspondingly, experiments were performed in (1) a pilot-scale chamber (0.8 m3), fitted with four corner UV lamps that irradiated the entire chamber (average UV fluence rate 10.6 ± 0.8 µJ s–1cm–2); (2) a full-scale room (87 m3), fitted with a UVGI system that irradiated the top 30 cm of the room (5 fixtures, 216 W total lamp power, average upper-zone UV fluence rate 26 ± 1 µJ s–1cm–2); and (3) the supply air duct of a heating ventilation and air-conditioning (HVAC) system. Fungal spores of Aspergillus versicolor and vegetative cells of bacterium Mycobacterium parafortuitum were aerosolized continuously such that their numbers and physiologic state were comparable both with and without the UVGI lamps operating. The Z value (UVGI inactivation rate normalized to UVGI fluence rate) was estimated to ...

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