Effects of occupant behavior and ventilation on exposure to respiratory droplets in the indoor environment

To quantify the risk of the transmission of respiratory infections in indoor environments, we systematically assessed exposure to talking-and breathing-generated respiratory droplets in a generic indoor environment using computational fluid dynamic (CFD) simulations. The flow field in the indoor environment was obtained with SST k-omega model and Lagrangian method was used to predict droplet trajectories, where droplet evaporation was considered. Droplets can be categorized into small droplets (initial size <= 30 mu m or <= 10 mu m as droplet nuclei), medium droplets (30-80 mu m) and large droplets (>100 mu m) according to the exposure characteristics. Droplets up to 100 mu m, particular the small ones, can contribute to both short-range and long-range airborne routes. For the face-to-face talking scenario, the intake fraction and deposition fractions of droplets on the face and facial mucosa of the susceptible were up to 4.96%, 2.14%, and 0.12%, respectively, indicating inhalation is the dominant route. The exposure risk from a talking infector decreases monotonically with the interpersonal dis-tance, while that of nasal-breathing generated droplets maintains a relatively stable level within 1.0 m. Keeping an angle of 15 degrees or above with the expiratory flow is efficient to reduce intake fractions to <0.37% for small droplets. Adjusting the orientation from face-to-face to face-to-back can reduce exposure to small droplets by approximately 88.0% during talking and 66.2% during breathing. A higher ventilation rate can reduce the risk of exposure to small droplets but may increase the risk of transmission via medium droplets by enhancing their evaporation rate. This study would serve as a fundamental research for epidemiologist, healthcare workers and the public in the purpose of infection control.

Automated summary

To assess the risk of transmission of respiratory infections in indoor environments, computational fluid dynamics (CFD) simulations were used to study the exposure to respiratory droplets generated by talking and breathing. Different sizes of droplets were categorized, and it was found that small droplets, especially those smaller than 100 μm, contribute to both short-range and long-range airborne transmission. Inhalation was identified as the dominant route of exposure, and adjusting the orientation from face-to-face to face-to-back significantly reduced exposure to small droplets. This research provides fundamental information for infection control and can benefit epidemiologists, healthcare workers, and the general public.