Spatial distribution of human respiratory droplet residuals and exposure risk for the co-occupant under different ventilation methods

Since the severe acute respiratory syndrome (SARS) epidemics in 2003, more attention is given to ventilation effects on airborne infection control. Questions remain on whether the three typical air distribution methods can have significant differences in reducing the infections between occupants in a space. This study adopts a novel modeling approach by including respiratory thermal manikins in the computational fluid dynamics domain to directly assess the inhalation dose of infectious droplets. Both the initial momentum of a coughing jet and the consequent droplet dispersion due to room airflow are simulated in detail. The preliminary results indicate that including the co-occupant in the modeling domain can present a more reliable exposure. The droplets movements are very complicated, and the whole exposure process can be roughly separated as two stages-a direct exposure at first and a later indirect exposure. The effects of the stratified air distribution systems on the co-occupant's inhalation of infectious droplets cannot easily be concluded. Although the inhaled dose is lowest under displacement ventilation for smaller droplets, under-floor air distribution can achieve the lowest inhalation for larger droplets.