Ventilation, Air Filtration and Universal Masking to Reduce Exposure to Respiratory Aerosols in a Simulated Classroom

WILLIAM LINDSLEY, Raymond Derk, Jayme Coyle, Francoise Blachere, Stephen Martin, Jr., Kenneth R. Mead, Donald Beezhold, John Noti, National Institute for Occupational Safety and Health

     Abstract Number: 26
     Working Group: Aerosol Science of Infectious Diseases: What We Have Learned and Still Need to Know about Transmission, Prevention, and the One Health Concept

Abstract
SARS-CoV-2 can be spread by aerosols expelled by infected people when they cough, talk, sing, or exhale. Exposure to these aerosols while indoors can be reduced by increasing ventilation rates, using portable air cleaners, and wearing face masks. To study the effectiveness of these interventions singly and in combination with each other, we placed a NIOSH respiratory aerosol source simulator in a conference room to simulate a person who was exhaling infectious aerosols. We then placed a breathing simulator 6 feet (1.8 m) in front of the source simulator to represent a speaker such as a teacher exposed to these respiratory aerosols, and placed two breath simulators 3 feet (0.9 m) and 6 feet (1.8 m) to either side of the source simulator to simulate other participants such as fellow students who also were potentially exposed to these aerosols. Aerosol concentrations were measured at the mouths of the speaker and participants to determine their aerosol exposure. We found that increasing the room ventilation rate from 2 air changes/hour (ACH) to 6 ACH reduced the aerosol exposure of the speaker and participants by an average of 37%, while adding two portable HEPA air cleaners in the center of the room with a combined filtration rate of 5 ACH reduced the average exposure by 65%. Placing cloth face masks on all the simulators reduced the average exposure by 72%. A combination of increasing ventilation from 2 ACH to 6 ACH and universal masking reduced exposure by 87%, while combining universal masking with the HEPA air cleaners reduced exposure by 90%. Our results show that increased ventilation, portable air cleaners, and universal masking can all reduce exposure to indoor respiratory aerosols, and that a combination of these methods is more effective than any single intervention.