Method for Estimating Ultraviolet Germicidal Fluence Rates in a Hospital Room

Abstract

Upper-room air UV germicidal irradiation (UVGI) is an effective environmental control measure for mitigating the transmission of airborne infections. Many factors influence the efficacy of an upper-room air UVGI system, including the levels and distribution of radiation. The radiation levels experienced by airborne microorganisms can be estimated by measuring the fluence rate, which is the irradiance from all angles that is incident on a small region of space. The fluence rate can be estimated by use of a radiometer coupled to a planar detector. Measurements in 4 directions at a single point are taken and summed to estimate the fluence rate at that point. This measurement process is repeated at different sites in the room at a single height. In the upper air of a test room, the UV fluence rate varied at least 3-fold, with the maximum rate occurring in the immediate vicinity of the fixtures containing lamps emitting UV radiation. In the area that would be occupied by the patient and/or healthcare personnel, no significant variation occurred in the UV fluence rate for a designated height. There was no significant statistical difference between measurements obtained by different individuals, by using a different alignment, or during 5 observation periods. Lamp failures were detected on multiple occasions. This method is simple, requires no specialized training, and permits regular monitoring of the necessary UV fluence rates needed to sustain the targeted airborne microorganisms' inactivation level. Additionally, this method allowed for the detection of changes in UV fluence rates in the upper air of the simulated hospital room.