Study on transport characteristics of saliva droplets produced by coughing in a calm indoor environment

In this paper, the transport characteristics of saliva droplets produced by coughing are examined in a calm indoor environment. Three subjects are studied, with results indicating that more than 6.7 mg of saliva is expelled at speeds of up to 22 m/s during each individual cough, and that saliva droplets can travel further than 2 m. In addition, the dispersion processes of saliva droplets of different diameters expelled during coughing are analyzed using the Lagrangian equation. The results indicate that the transport characteristics of saliva droplets due to coughing change with size. The effects of gravity or inertia on droplets of 30 μm or less are negligible due to their small sizes, and therefore their transport is mostly influenced by the indoor flow field. Droplets of 50–200 μm, which are significantly affected by gravity, fall as the flow-field weakens. Droplets of 300 μm or more, which are affected more by inertia than gravity, fall difficultly. Moreover, the analytical results also indicate that the droplets’ transport is greatly influenced by the spatial relationship between the air-conditioner and the subjects. Finally, based on the experimental and analytical results, droplet infection by saliva droplets due to coughing is examined.