Influence of Bioaerosol Source Location and Ceiling Fan Direction on Eggcrate Upper-room Ultraviolet Germicidal Irradiation

BACKGROUND: Eggcrate upper-room ultraviolet germicidal irradiation (UVGI), an engineering control method for reducing the airborne transmission of infectious diseases, was recently developed as an alternative to conventional upper-room UVGI using conventional louvered fixtures. A UV screen, which is composed of open-cell eggcrate panels supported in a frame designed for a conventional suspended ceiling, was used to minimize UV radiation in the lower room. A ceiling fan, which was blowing upward directly above the microbiological source, provided vertical air exchange between the upper and lower room. This system has been shown to be significantly more effective than conventional upper-room UVGI. STUDY DESIGN: In the present study, the microbiological source location and the airflow direction due to the ceiling fan were varied in order to evaluate their impact on germicidal efficacy. RESULTS: The test results clearly showed that placing an aerosol source directly underneath an upward blowing ceiling fan produces the maximum efficacy. CONCLUSIONS: The likely explanation for this outcome is that the fan sucks the microorganisms emitted by the source into the UV beam before being mixed with the air in the room. This is somewhat analogous to local exhaust ventilation in which the contaminant is removed prior to being mixed with the air in the room. Thus, when possible, the ceiling fan should be blowing upward and directly above the source. However, for experimental testing, the source location should be varied in order to access the range of germicidal efficacies that can be expected.