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Effect of Ultraviolet Germicidal Lamps on Airborne Microorganisms in an Outpatient Waiting Room

1992; Taylor & Francis; Volume: 7; Issue: 8 Linguagem: Inglês

10.1080/1047322x.1992.10390201

1521-0898

Janet M. Macher, L. E. Alevantis, YongKeun Chang, K.-S. Liu,

Noise Effects and Management

Abstract The effectiveness of 254-nm ultraviolet radiation for inactivating airborne microorganisms (and thereby reducing the spread of respiratory infections such as tuberculosis) was evaluated by collecting air samples in an occupied 90-m3 room equipped with four 15-W wall-mounted germicidal lamps. The indoor concentration of airborne bacteria was positively associated with the number of people present, the concentration of bacteria in the ventilation supply air, and the relative humidity, but was negatively associated with operation of the germicidal lamps and with the number of open windows. A generalized linear model suggested that use of the lamps reduced culturable airborne bacteria by 14 to 19 percent. This degree of air disinfection was calculated to be the equivalent of between 1.5 and 2 air changes per hour (ACHeq). This equivalent ventilation was in addition to the 1 to 2.5 ACH that open windows provided and the 8 ACH that the mechanical ventilation system supplied. The microbicidal effect of the lamps on naturally occurring bacteria in this ventilated and occupied space was approximately one-tenth of the level that was measured for an artificially generated aerosol of Mycobacterium bovis in another study. There are several possible explanations for this smaller than expected effect: (1) the ambient airborne bacteria measured in the current study may have been less sensitive to 254-nm radiation than the M. bovis used in the earlier trial; (2) airborne bacteria may not have remained sufficiently long in the directly irradiated zone near the lamps to receive a bactericidal dose of 254-nm radiation because of the effects on aerosol movement of the open windows and doors, and of the supply air outlet and the exhaust air inlet locations; and (3) although the total wattage from germicidal lamps was higher in this case, low wattage lamps were used, which may not be as effective as higher wattage ones. Users of germicidal lamps should be aware that environmental factors (such as ventilation design and operation, and restrictions on lamp use in order to control occupant exposure) may limit the ability of germicidal lamps to inactivate airborne microorganisms and thus to protect people from airborne infectious agents.