Face masks should be worn outside when it is windy to thwart the spread of Covid, academics say.
Indian experts say even a slight breeze can increase the chance of infected people spreading the coronavirus.
Researchers at the Indian Institute of Technology Bombay simulated just how far the coronavirus can spread in both calm and windy conditions.
Results showed there was an ‘increased infection risk’ even if there was just a small gust of five miles per hour.
Lead author Professor Amit Agrawal said: ‘We recommend wearing masks outdoors, particularly in breezy conditions.’
Even a slight breeze increases transmission of the virus if an infected person coughs, according to researchers at the Indian Institute of Technology Bombay
Some 89 per cent of Britons said they wore face masks outside the home at the end of August, according to data from the Office for National Statistics. For comparison, in May it was 98 per cent
Face masks have been enforced around the world as one of many curbs to limit the spread of the virus, especially in crowded indoor spaces.
But throughout the pandemic there has been fierce scientific debate about how well the guards work at reducing transmission.
Ministers dropped the legal requirement to wear coverings in England in July, when No10 pushed ahead with ‘Freedom Day’.
But people are encouraged to wear them in crowded places and some businesses — such as Transport for London — still require them.
The new study examined how Covid is transmitted in the air when someone coughs, using an equation designed to measure turbulence.
What are the rules on face coverings?
In England, the legal requirement to wear face masks was lifted on July 19.
But they must will be worn in Scotland, Wales and Northern Ireland in certain venues, such as public transport and shops.
However, the Government says people in England should continue to wear masks when indoors with others who they don’t normally meet.
And its guidance states patients and visitors continue to wear face coverings in all healthcare settings, such as hospitals and GP surgeries.
Masks are no longer required in classrooms in England, but some local authorities have told schools to bring them back to control local outbreaks.
And as part of No10’s ‘Plan B’ to control an expected fourth wave this winter, face coverings could become mandatory if the NHS comes under unsustainable pressure.
Earlier studies modelled a cough using puffs of air but the researchers argued a real cough is more complicated and can swirl ‘like mini whirlpools’.
They examined how a cough spreads in still conditions — comparable to indoors — and in various wind speeds.
The study, published in Physics of Fluids, showed when an infected person coughs outdoors, wind flowing in the same direction can spread the virus faster and further than in calm conditions.
Even a small breeze of five miles per hour (mph) in the same direction someone is coughing increases how far the virus spreads by 20 per cent.
This means social distancing would need to be increased from 1 to 2 metres to up 2.2 metres to be effective, the team found.
‘At 9-11 mph (14-18 kph), spreading of the virus increases in distance and duration,’ the researchers said.
The experts believe wind projects bigger droplets for longer, increasing how long it takes to dilute the viral load in the air.
As the cough jet is spurred on by the wind, infected aerosol droplets — which seems to be the dominant mode of Covid transmission — become ‘trapped’ in the breeze instead of falling quickly to the ground.
Professor Agrawal said: ‘The study is significant in that it points to the increased infection risk that coughing in the same direction as the wind could bring about.
‘The increase in residential time of some of the larger droplets will increase the viral load transmitting through the cough jet and, therefore, the chances of infection.
‘Overall, the study highlights increased chances of infection in the presence of even a light breeze.’
Source: Health & wellbeing | The Guardian