Limiting novel coronavirus spread via coughs
doi:10.1038/nindia.2021.4 Published online 11 January 2021
Airborne respiratory droplets spread the novel coronavirus. Such a spread, however, does not depend on the intensity of coughing.
A mathematical model, developed by researchers from the Indian Institute of Technology in Mumbai shows that a cough cloud slowly traps ambient air as it spreads out after ejection from the mouth of an infected person1.
With time, the droplet concentration inside the cloud reduces significantly. Since the virus requires liquid droplets to survive, the possibility of its spread declines, the researchers explain.
The findings of this research will help devise ways to reduce the chances of infection in a closed space, they say.
The IIT scientists used the mathematical model to study a cough cloud’s spread through most air in an enclosed space without any airflow.
They found that the front of the cough cloud covers the first two metres of its total distance from the source within two seconds of being ejected. Hence, the cloud has the maximum probability of spreading the viral liquid immediately after release.
The analysis suggests that the first five to eight seconds after the commencement of the cough event are crucial for suspending the exhaled droplets in air, and the infected air volume without a mask is around 23 times more than that exhaled during normal coughing.
A mask drastically reduces this volume, considerably cutting down the risk of spreading the infection to other persons in a room. N95 masks, the researchers say, perform much better than surgical masks, decreasing it by as much as 23 times.
1. Agrawal, A. et al. Reducing chances of COVID-19 infection by a cough cloud in a closed space. Phys. Fluids. 32, 101704 (2020)