Airborne transmission of exhaled droplet nuclei between occupants in a room with horizontal air distribution

This study examines the characteristics of the airborne spread of exhaled droplet nuclei between two persons indoors with horizontal airflow distribution in a full-scale test room. Two breathing thermal manikins were used to simulate an infected and an exposed person. Tracer gas (N2O) was added to the airstream exhaled by the infected manikin. The tracer gas concentrations in the air inhaled by the exposed manikin and in the room ventilation exhaust were continuously monitored using both slow and fast instruments. The independent variables included the separation distance between the simulated persons, the positioning of the persons, the location of the persons in relation to the supply diffuser, the room air temperature, and the installation height and configuration of the air supply and exhaust diffusers. Special attention was paid to exploring the dependence of exposure risk on the distance between the two manikins under different directions of indoor airflow. Air supplied horizontally to the breathing zone intensified the mixing between the exhaled air and the room air, which reduced the exposure risk of persons in close proximity and flattened the risk-distance curves. The highly dynamic dispersion of exhaled air and thus the homogenization of tracer gas concentration in room air considerably reduced the importance of the positioning of the infected and exposed persons. The exposure risk between closely located persons increased when the interaction between the supply flow and the exhaled flow decreased due to an increased supply air temperature, an augmented size of supply air diffuser or decreased height above the floor of the diffusers.