Clouds of infectious coronavirus particles created by a cough are up to 23 times smaller when a person wears a mask, study finds

  • Researchers from India calculated how cough clouds evolve as they spread out
  • They compared those coming from a bare face, a surgical mask and an N95 mask
  • Wearing a surgical mask lowered cloud volume seven times and an N95 23 times
  • The team also found that how hard you cough only matters when wearing a mask

Wearing a face mask reduces the size of the clouds of infectious coronavirus particles created by a cough by up to 23 times, a study has found.

Researchers from India calculated how cough clouds evolve as they spread out — and how much various forms of covering can control their spread.

The team found that a surgical facemask lowered the cloud volume by seven times compared with without — while an N95 respirator cut the volume 23-fold.

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Researchers found a surgical facemask lowered the cloud volume by seven times (green line) compared with no mask (red line)— while an N95 respirator cut the volume 23-fold (blue line)

Researchers say there are certain things which can reduce the spread of cough droplets, such as wearing face masks, using handkerchiefs and coughing into one’s elbow (stock)

‘We found that anything that reduces the distance travelled by the cloud… should greatly reduce the region over which the droplets disperse upon coughing,’ said paper author and engineer Rajneesh Bhardwaj of the Indian Institute of Technology.

This, he added, in turn therefore greatly reduces ‘the chances of infection.’ 

According to the team, practices that can lower the distance the cloud travels include wearing face masks, using handkerchiefs and coughing into one’s elbow.

Previous studies have typically focused on the properties of the air — and coughed-out droplets — close to the mouth, considering such factors as the cloud volume, temperature, droplet distribution and humidity.

In their research, however, Professor Bhardwaj and fellow engineer Amit Agrawal set out to determine how these properties change as the cough cloud travels.

By using an analysis based in so-called jet theory, the duo found that the first 5–8 seconds following a cough are vital for suspending infectious droplets in the air — and therefore in the potential to spread coronavirus to other individuals.

After this point, they explained, the cloud tends to disperse.

Alongside the significant reduction in expelled cloud volume brought about by wearing face masks, the researchers also found — surprisingly — that how hard a mask-less person coughs does not affect the volume of the cloud they release.

However, it was important when you wear a mask, they said. Coughing harder leads to faster-travelling droplets as well as more of them.   

The full findings of the study were published in the journal Physics of Fluids.

FACE MASK POLICY IN THE UK

Face masks must be worn on public transport and in many indoor spaces, including shops, shopping centres, indoor transport hubs, museums, galleries, cinemas and public libraries. 

It is currently the law for passengers to wear face coverings in taxis and private hire vehicles, in hospitality venues, like restaurants and bars, other than when you are eating and drinking. Staff in retail and hospitality settings are also legally required to wear face coverings. 

If necessary, the police and Transport for London (TfL) officers have enforcement powers including issuing fines of £200 (halving to £100 if paid within 14 days).

It comes after the World Health Organisation and numerous studies suggested they are beneficial.

As announced, the Government will bring forward changes to mean that for repeat offenders these fines would double at each offence up to a maximum value of £6,400.  

The Prime Minister has also announced tougher enforcement measures, with businesses facing fines or closure for failing to comply with coronavirus rules, meaning there will be consequences for pubs that try to serve you at the bar.

National Police Chiefs’ Council chairman Martin Hewitt said: ‘Individuals, businesses and households all have a responsibility to ensure the virus is suppressed and police will play their part in supporting the public to navigate the measures in place for our safety.

‘Our approach of engaging with people and explaining the regulations in place will remain. The vast majority of situations are resolved following those two stages, with little need for further encouragement or enforcement action to be taken,’ he said.

‘Police will continue to work with their communities and only issue fines as a last resort.

‘Chiefs will be stepping up patrols in high-risk areas and will proactively work with businesses, licensing authorities and local authorities to ensure the rules are being followed.

‘If members of the public are concerned that the law is being broken or they are experiencing anti-social behaviour, they can report this to the police, who will consider the most appropriate response and will target the most problematic behaviour.’  

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