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Modelling shows sneezes and coughs are like “mini atomic bombs” and regularly exceed two metres

Keeping two metres apart might not be far enough to stop the spread of coronavirus from sneezes and coughs, according to a new study.

Researchers at Loughborough University have created a mathematical model which shows that droplets can reach more than 3.5 metres, without a facemask, significantly increasing the distance needed to stay safe.

Dr Emiliano Renzi and student Adam Clarke have published the results in the journal Physics of Fluids.

Using data collected from experiments carried out in his bedroom – due to the first lockdown and closure of some university labs earlier in the summer – Dr Renzi found that the largest droplets consistently travelled further than two metres.

It is due to a phenomenon known as a buoyant vortex - the turbulent motion of hot, dense air that we eject together with the droplets when we cough or sneeze.

The paper also suggests that the trajectories of the droplets are significantly affected by the way people tilt their heads when they cough or sneeze.

Dr Renzi said: “In the majority of our analyses, the predictions made by our model suggest that the largest droplets consistently exceed the horizontal ranges of two metres from the source before settling to the ground.

“In some cases, the droplets are propelled in excess of 3.5 metres by the buoyant vortex, which acts like a mini atomic bomb.

“Therefore, guidelines suggesting two metres physical distancing limits may not be adequate to prevent direct transmission via droplets of large size.

“Our model also shows that the smaller droplets are carried upwards by this mini-vortex and take a few seconds to reach a height of four metres.

“At these heights, building ventilation systems will interfere with the dynamics of the cloud and could become contaminated.”

He added: “Finally, from our analysis it is apparent that tilting the head downward as we cough or sneeze, significantly decreases the range for the majority of droplet sizes.

“We recommend behavioural and cultural changes in populations to direct coughs toward the ground, in addition to wearing face coverings, which could help mitigate the risk of short-range direct transmission of respiratory viruses.”

The paper, Life of a droplet: Buoyant vortex dynamics drives the fate of micro-particle expiratory ejecta, has been published in the journal, Physics of Fluids.

ENDS

Notes for editors

Press release reference number: 20/201

Loughborough is one of the country’s leading universities, with an international reputation for research that matters, excellence in teaching, strong links with industry, and unrivalled achievement in sport and its underpinning academic disciplines.

It has been awarded five stars in the independent QS Stars university rating scheme, named the best university in the world for sports-related subjects in the 2020 QS World University Rankings and University of the Year by The Times and Sunday Times University Guide 2019.

Loughborough is in the top 10 of every national league table, being ranked 7th in the Guardian University League Table 2021, 5th in the Times and Sunday Times Good University Guide 2020 and 6th in The UK Complete University Guide 2021.

Loughborough is consistently ranked in the top twenty of UK universities in the Times Higher Education’s ‘table of tables’ and is in the top 10 in England for research intensity. In recognition of its contribution to the sector, Loughborough has been awarded seven Queen's Anniversary Prizes.

The Loughborough University London campus is based on the Queen Elizabeth Olympic Park and offers postgraduate and executive-level education, as well as research and enterprise opportunities. It is home to influential thought leaders, pioneering researchers and creative innovators who provide students with the highest quality of teaching and the very latest in modern thinking.

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