Factors influencing effectiveness of ultraviolet germicidal irradiation for inactivating airborne bacteria: air mixing and ventilation efficiency.

As a result of the recent resurgence in tuberculosis incidence, there has been increased interestin using ultraviolet germicidal irradiation (UVGI) of room air to reduce exposures toinfectious agents. This paper presents results of experimental studies investigating how airmixing and ventilation influences the efficacy of UVGI for inactivating airborne bacteria.Tracer gasSFGand tracer particles generated by nebulization of a- salt solution were injected into a full-scale room. The particles simulate an aerosol carrying an infectious agent generated by persons coughing or sneezing. The tracer gas was used to study the roomairflow patterns. The concentration of the gas and particles was, measured over time with a gas chromatography and an optical particle counter. Using these data, the air mixing andventilation efficiency were characterized. The results showed that the room air was notnecessarily well mixed and the ventilation efficiency were not necessarily close to unity underhigher air-exchange rates (6 air changes per hour), depending on the thermal conditionswithin the room.