The volume of the cough cloud produced by a human subject increases over time as the surrounding air is entrained (bottom). Change in volume of the cloud as a function of the distance from the mouth (top). Masks reduce the volume significantly, as can be seen in the inset. Photo credit: Amit Agrawal and Rajneesh Bhardwaj
With the coronavirus affecting more than 30 million people worldwide, researchers have increasingly focused on the extent to which airborne droplets carrying the virus move around and contaminate the air after an infected person coughs.
While scientists have studied the properties of air in the mouth such as volume, temperature, droplet distribution, and humidity, less is known about how these properties change when the cough cloud moves. in the Physics of liquidsFrom AIP Publishing, researchers estimate the evolving volume of the cough cloud and quantify the decrease in its volume in the presence of a face mask.
The scientists found that the cloud volume without a mask is about 7 times larger than with a surgical mask and 23 times larger than with an N95 mask.
“We estimate this volume of air that can help ventilate enclosed spaces and, consequently, reduce the spread of the disease,” said Amit Agrawal, one of the authors.
The researchers also examined the variation in temperature and humidity in the cough cloud as a determinant that influences the droplet distribution in the cloud.
Using an analysis based on jet theory and experimental data from the literature, they found that it is the first 5 to 8 seconds after coughing to suspend the exhaled droplets in the air and, consequently, to spread the disease . After this time, the cloud of cough will typically begin to dissipate.
The scientists found that the cloud volume without a mask is about 7 times larger than with a surgical mask and 23 times larger than with an N95 mask.
“We have found that anything that reduces the distance the cloud covers, like a mask, handkerchief, or coughing into an elbow, greatly reduces the area over which the droplets spread when coughing, and thereby greatly reduces the likelihood of infection should, “said Rajneesh Bhardwaj, another writer.
Interestingly, the researchers found how hard a person coughs, which affects the initial speed and volume of the cough, does not affect the volume in the cough cloud if the person is not wearing a mask, although the initial volume is very important for a person wearing one Mask.
The scientists found that the volume of a cough cloud varies as a cube of the total distance traveled by the cloud with a constant of proportionality from 1 to 150. This formula is helpful in determining the maximum number of people that can be accommodated in an infirmary and the minimum rate at which air must be circulated in a room, elevator, movie theater, car, airplane cabin, or restaurant to maintain freshness and reduce the risk of infection.
Reference: “Reduce chances of COVID-19 Infection through a cloud of cough in a closed room “by Amit Agrawal and Rajneesh Bhardwaj, October 20, 2020, Physics of liquids.
DOI: 10.1063 / 5.0029186
