Covid-19 cough clouds determine viral load in closed spaces: Study

Prashasti Awasthi Mumbai | Updated on October 21, 2020

According to new research published in the journal Physics of Fluids, the Covid-19 cough cloud volume without a mask is about seven times larger than with a surgical mask and 23 times larger than with an N95 mask.

The study came as the researchers aimed to estimate the growing volume of cough clouds and intended to quantify the reduction in its volume after the use of face masks.

One of the authors of the study said in a statement: “We estimate this volume of the air, which may help to design ventilation of closed spaces and consequently reduce the spread of the disease.”

The researchers also studied the variation in temperature and humidity in the cough cloud as the determinant that impacts the droplet distribution in the cloud.

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Suspension of particles

The researchers found that it is the first five- eight seconds after coughing that determine the suspension of the exhaled droplets in the air and the spread of the disease. After this, the cough cloud typically starts to disperse.

Rajneesh Bhardwaj, one of the authors, said: “We found that anything that reduces the distance travelled by the cloud, such as a mask, handkerchief, or coughing into an elbow, should greatly reduce the region over which the droplets disperse upon coughing and therefore the chances of infection.”

The researchers also noted that the intensity of someone’s coughing, which determines the initial velocity and volume of cough, does not affect the volume in the cough cloud when the person is not wearing a mask. Although the initial volume is pivotal for a person wearing a mask.

The scientists determined the volume of a cough cloud varies as a cube of the total distance traveled by the cloud with the proportionality constant being 1 to 150.

This model will be helpful in determining the maximum number of people that can be accommodated in a hospital ward, and the minimum rate at which air in a room, elevator, cinema hall, car, aircraft cabin, or restaurant needs to be circulated to maintain freshness and reduce the chance of infection, the study speculated.

Published on October 21, 2020

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