Why social distance and wearing mask is important? A new study on cough droplets finds out

The mathematical model designed by the researchers on Covid-19 focusses on the aerodynamics of the droplets to understand how it infects a healthy person.
A woman sneezes as a doctor prepares to take a nasal swab to be tested for the coronavirus in Dharmsala.(AP File Photo)
A woman sneezes as a doctor prepares to take a nasal swab to be tested for the coronavirus in Dharmsala.(AP File Photo)
Updated on Jul 03, 2020 09:11 AM IST
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Hindustan Times, New Delhi | Byhindustantimes.com | Edited by: Amit Chaturvedi

A mathematical model has revealed that respiratory droplets travel between eight to 13 feet before evaporating or escaping, in a new study on the coronavirus disease.

The researchers include scientists from Indian Institute of Science (IISc) in Bengaluru. The research has been published in the journal Physics of Fluids.

Since the beginning of the pandemic, it has been a well-established fact that respiratory droplets are responsible for the transmission of SARS-CoV-2 pathogen which causes Covid-19. These droplets eject when people cough, sneeze or talk.

The mathematical model designed by the researchers focusses on the aerodynamics of the droplets to understand how it infects a healthy person. They compared the droplet cloud ejected by an infected person to the one by a healthy person.

“The size of the droplet cloud, the distance it travels, and the droplet lifetimes are, therefore, all important factors that we calculated using conservation of mass, momentum, energy and species,” said one of the authors Swetaprovo Chaudhuri, from the University of Toronto in Canada. The experiments were conducted in contact-less environment.

She further explained that the model estimates approximately how long droplets can survive, how far they can travel, and which size of droplet survives for how long.

The researchers, however, noted that the actual situation could be complicated by wind, turbulence, air-recirculation or other things.

“Without wind and depending on the ambient condition, we found droplets travel between 8 to 13 feet before they evaporate or escape,” said Abhishek Saha, a co-author, from the University of California, San Diego in the US.

This finding implies that social distancing at perhaps greater than six feet is essential, according to the researchers. The initial size of the longest surviving droplets is in the range of 18-50 microns, meaning masks can indeed help, they said.

These findings, the researchers said, could help inform reopening measures for schools and offices looking at student or employee density.

While noting that the model doesn’t claim to predict the exact spread of Covid-19, researchers noted that it could emerge as a powerful tool in clarifying the role of environment on infection spread through respiratory droplets.

The droplet evaporation or desiccation time is highly sensitive to the ambient temperature and relative humidity, they said.

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