Study, published in journal Physics of Fluids, finds that surgical masks can reduce volume of spread of cough cloud by seven times, compared to no mask
Representation image of a man wearing an N95 mask
Have you been questioning the need of wearing face-mask amid pandemic? A study by researchers at the Indian Institute of Technology, Powai, shows how important it is. The study finds out, while the cloud of cough remains effective till about 8 seconds before dissipating irrespective of whether the person is masked or not, surgical masks reduce the volume by seven times compared to having no mask.
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By analysing the equations of flow for the cough, the researchers found that a large volume of ambient air slowly gets trapped inside the cloud as it spreads outwards. With time, the droplet concentration inside the cloud thus reduces significantly from its initial concentration. Since the virus requires liquid droplets to survive, the possibility of its spread declines. They also 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 emitted. Hence, the cloud has the maximum probability of spreading the viral liquid immediately after release. The study was published in the journal, Physics of Fluids.
The calculations also enabled the researchers to quantify the effect of masks precisely. Masks reduce the net distance covered by the cloud by blocking it before its spread, earlier experiments had revealed. The researchers now compared the effect of surgical masks and clinical N95 masks on the volume of the cloud. While the cloud remains effective till about 8 seconds before dissipating irrespective of whether the person is masked or not, surgical masks reduce the volume by seven times compared to having no mask. N95 masks perform much better, decreasing it by as much as 23 fold. This quantitative estimate sheds a clear light on why masks have been so effective in curbing the spread. “In case a person is not using a mask while coughing, it is possible to reduce the spread by simply blocking the mouth with a palm or an elbow,” says Prof Amit Agrawal, one of the authors of the study.
Infected airborne respiratory droplets play a significant role in the spread of the Coronavirus. The widespread use of respiratory masks has curbed the spread of the virus and brought down the number of people affected by the disease. But, as the pandemic rages, general fatigue in following the behavioural restrictions has set among the public. Festive gatherings continue to be celebrated, and governments across the world have had a difficult time convincing people to adhere to the safety guidelines. In such a scenario, according to researchers, this study finding can help in understanding the nature of the spread of the virus and make arrangements accordingly.
Sharing the importance of the study, Prof Rajneesh Bhardwaj, another author added, “Such a study will help us determine the maximum number of people that can be safely accommodated in a hospital ward.”
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The reduction of spread of cough cloud by N95 masks
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