Fundamental factors affecting upper-room ultraviolet germicidal irradiation - part I. Experimental.

The objective of this research was to study the factors that relate to the effectiveness of upper-room ultraviolet germicidal irradiation for inactivating airborne microorganisms. The work was conducted in a room-sized chamber designed and furnished for investigations of this nature. Nebulized Serratia marcescens, Bacillus subtilis spores, and vaccinia virus were used as test aerosols. Most data were collected from steady-state experiments comparing the number of viable organisms in the chamber air remaining with UV lamps turned on to the number with UV lamps turned off, but some decay experiments were conducted to compare the two methods. UV power level had a strong influence but was fully effective only in the presence of air mixing that produced vigorous vertical air currents. A conclusion of the study is that an upper-room ultraviolet installation is a complex system that requires careful integration of UV luminaires, UV power, and room ventilation arrangements.