UV Air Cleaners and Upper-Room Air Ultraviolet Germicidal Irradiation for Controlling Airborne Bacteria and Fungal Spores

In-room air cleaners (ACs) and upper-room air ultraviolet germicidal irradiation (UVGI) are engineering control technologies that can help reduce the concentrations of airborne bacteria and fungal spores in the indoor environment. This study investigated six different types of ACs and quantified their ability to remove and/or inactivate airborne bacteria and fungal spores.Four of the air cleaners incorporatedUVlamp(s) into their flow path. In addition, the efficacy of combining ACs with upper-room air UVGI was investigated. With the ventilation system providing zero or six air changes per hour, the air cleaners were tested separately or with the upperroom air UVGI system in operation in an 87−m³ test room. Active bacteria cells and fungal spores were aerosolized into the room such that their numbers and physiologic state were comparable both with and without air cleaning and upperroom air UVGI. In addition, the disinfection performance of a UV-C lamp internal to one of the ACs was evaluated by estimating the percentage of airborne bacteria cells and fungal spores captured on the air filter medium surface that were inactivated with UV exposure. Average airborne microbial clean air delivery rates (CADRm) varied between 26–981 m³hr⁻¹ depending on the AC, and between 1480–2370 m³hr⁻¹, when using air cleaners in combination with upper-room air UVGI. Culturing, direct microscopy, and optical particle counting revealed similar CADRm. The ACs performed similarly when challenged with three different microorganisms. Testing two of the ACs showed that no additional air cleaning was provided with the operation of an internal UV-C lamp; the internal UV-C lamps, however, inactivated 75% of fungal spores and 97% of bacteria cells captured in the air filter medium within 60 min.

Keywords:

• air disinfection
• bioaerosols
• upper-room air UVGI

ACKNOWLEDGMENTS

The authors thank Millie P. Schafer, NIOSH, for her assistance, and for proposing the study of in-room air cleaning in combination with upper-room air UVGI. The authors also thank Leroy Mickelsen, NIOSH, for his assistance. The authors are grateful to Daniel Veronica, and the Joint Center for Energy Management for providing essential equipment and helping operating the test facility. We are grateful to Jennifer Jeffers for her help with laboratory work, and we acknowledge the help and support of Jay Julos.

This study was supported by funds provided by the Center for Disease Control and Prevention, the National Institute for Occupational Safety and Health, and the Shaklee Corporation.

Notes

^ARetailer.

^BIndependently measured at NIOSH facility (see Ref. 27).

^A Number denotes the number of times that the experiment was repeated.

^B EP, I_UV, and E_UV tested on high setting.

^ARemoval rate determined by direct microscopy unless noted by a “C” or “OPC”, which indicates that culturing or optical particle counter was used.

^BEP, I_UV and E_UV tested on high setting.

^A The ventilation rate provided to the testroom was 0 air changes per hour.

^BEP tested on high setting.