Assessment of the mixing air delivery system ability to protect occupants from the airborne infectious disease transmission using Wells–Riley approach

Abstract

Assessment of a mixing air delivery system's ability to protect occupants from airborne infectious disease transmission using the Wells–Riley equation modified for unsteady heterogenic conditions was performed in this study. Experiments were performed in a field environmental chamber equipped with mixing ventilation, while the cough was simulated using a cough machine. Results show that increase of supply flow rate up to 3 ACH rapidly reduces cough-induced inhalation fraction, but an increase above 6 ACH causes minor changes. When the infectiousness of the index case is relatively low, changes in the supply flow rate will not cause any change in the protective effectiveness of the air delivery system, while for the index case of relatively moderate infectiousness, an increase in supply flow rate up to 6 ACH will improve the protective effectivenes. For the index case of high infectiousness, an increase of supply flow rate will reduce the number of secondary cases for the 8-h exposure period. Maximum protective effectiveness depends only on ability of the system to reduce the exposure, but the index case infectiousness at which this is achieved will depend on the exposure period and exposure reduction.