Effectiveness of portable air filtration on reducing indoor aerosol transmission: preclinical observational trials

Lee, Jung Hoon; Rounds, Max; McGain, Forbes; Schofield, Robyn; Skidmore, Grant; Wadlow, Imogen; Kevin, Kevin; Stevens, Ashley; Marshall, Caroline; Irving, Lou; Kainer, Marion; Buising, Kirsty; Monty, Jason

BACKGROUND: While the range of possible transmission pathways of SARS-CoV-2 in various settings has been thoroughly investigated, recently most authorities acknowledged the role of aerosol spread in the transmission of the virus especially in indoor environments where the ventilation is poor. Engineering controls are needed to mitigate aerosol transmission in high risk settings including hospital wards, classrooms, and offices. AIM: To assess the effectiveness of aerosol filtration by portable air cleaning devices with high efficiency particulate air (HEPA) filters used in addition to standard building heating ventilation and air-conditioning (HVAC). METHODS: Test rooms, including a hospital single-patient room, were filled with test aerosol to simulate aerosol movement. Aerosol counts were measured over time with various portable air cleaning devices and room ventilation systems to quantify the overall aerosol clearance rate. FINDINGS: Portable air cleaners were very effective in removing aerosols. In a small control room, the aerosols were cleared five times faster with portable air cleaners than the room with HVAC alone. A single bed hospital room equipped with an excellent ventilation rate (∼14 air changes per hour) can clear the aerosols in 20 minutes. However, with the addition of two air cleaners, the clearance time became three times faster. CONCLUSIONS: Inexpensive portable air cleaning devices should be considered for small and enclosed spaces in health care settings such as inpatient rooms and personal protective equipment donning/doffing stations. Portable air cleaners are particularly important where there is limited ability to reduce aerosol transmission with building HVAC ventilation.