UVGI Design Basics for Air and Surface Disinfection

Lethal to microorganisms, ultraviolet radiation in the range of 2250 to 3020 angstroms is used in a variety of disinfection applications, a process referred to as ultraviolet germicidal irradiation (UVGI). Since the first UVGI system was successfully implemented for disinfecting the municipal water system in Marseilles, France, in 1909, the disinfection of medical equipment using UVGI has been a common and reliable practice. But unlike waterand equipmentdisinfection applications, the disinfection of air streams using UVGI has a history of varying success and unpredictable performance. The first laboratory studies on UVGI of air in the 1920s showed such promise that the elimination of airborne disease seemed possible. In 1936, Hart used UVGI to sterilize air in a surgical operating room. In 1937, the first application of UVGI for a school ventilation system dramatically reduced the incidence of measles, with subsequent applications enjoying similar success. Experiments by Riley and O’Grady resulted in the elimination of tuberculosis (TB) bacilli from hospitalward exhaust air. A plethora of designs that were more imitative than engineered followed these early applications. The result was a mixture of successes and failures. This experience is reflected in various guidelines that decline to sanction the use of UVGI as a primary system. A 1954 study on the use of UVGI showed a failure to reduce disease in London schools. Although limited data are available to determine the causes of earlier design failures, the apparent cloning of UVGI systems without regard to operating conditions probably doomed many installations from the start. A review of current industry practices indicates that information on the design of UVGI systems lacks the detail necessary for engineers to ensure performance. This article addresses the factors that determine the design UVGI Design Basics