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London, May 20: The current physical distancing guidelines of 6 feet may be insufficient to prevent COVID-19 transmission, according to a study which says a mild cough in low wind speeds can propel saliva droplets by as much as 18 feet.

Researchers, including those from the University of Nicosia in Cyprus, said a good baseline for studying the airborne transmission of viruses, like the one behind the COVID-19 pandemic, is a deeper understanding of how particles travel through the air when people cough.

In the study, published in the journal Physics of Fluids, they said even with a slight breeze of about four kilometres per hour (kph), saliva travels 18 feet in 5 seconds.

"The droplet cloud will affect both adults and children of different heights," said study co-author Dimitris Drikakis from the University of Nicosia.

According to the scientists, shorter adults and children could be at higher risk if they are located within the trajectory of the saliva droplets.

They said saliva is a complex fluid, which travels suspended in a bulk of surrounding air released by a cough, adding that many factors affect how saliva droplets travel in the air.

These factors, the study noted, include the size and number of droplets, how they interact with one another and the surrounding air as they disperse and evaporate, how heat and mass are transferred, and the humidity and temperature of the surrounding air.

In the study, the scientists created a computer simulation to examine the state of every saliva droplet moving through the air in front of a coughing person.

The model considered the effects of humidity, dispersion force, interactions of molecules of saliva and air, and how the droplets change from liquid to vapour and evaporate, along with a grid representing the space in front of a coughing person.

Each grid, the scientists said, holds information about variables like pressure, fluid velocity, temperature, droplet mass, and droplet position.

The study analysed the fates of nearly 1,008 simulated saliva droplets, and solved as many as 3.7 million equations.

"The purpose of the mathematical modelling and simulation is to take into account all the real coupling or interaction mechanisms that may take place between the main bulk fluid flow and the saliva droplets, and between the saliva droplets themselves," explained Talib Dbouk, another co-author of the study.

However, the researchers added that further studies are needed to determine the effect of ground surface temperature on the behaviour of saliva in air.

They also believe that indoor environments, especially ones with air conditioning, may significantly affect the particle movement through air.

This work is important since it concerns safety distance guidelines, and advances the understanding of the transmission of airborne diseases, Drikakis said.

Thiruvananthapuram, Mar 23: Amid a spurt in coronavirus cases, Kerala chief minister Pinarayi Vijayan has asked the Centre to give the states authority to give clearances for manufacturing masks, gloves and sanitisers.

In a letter addressed to prime minister Narendra Modi, Vijayan said during the crisis, masks and sanitisers are needed in large numbers.

"As an interim, states must be given authority to give clearances of manufacturing of items related to medical devices, sanitisers, chemicals, etc. which are needed for fighting Covid-19," Vijayan said in the letter.

He also sought permission for the state home department to use drones for the relevant applications related to Covid-19.

"In China and elsewhere in the world, drones have been used extensively in minimising human contact, disinfection, etc. Unfortunately, with the current laws pertaining to the use of drones, none of these is possible in India," the chief minister said.

He also sought permission to access and use facilities available with all central institutions and research labs operating in the state.

The chief minister shared the letter on his Twitter handle.

With 15 new positive cases of Covid-19, the total number of infected persons in Kerala had gone up to 67, including the three who were discharged after recovery last month.