A group of academics within our School is leading a collaborative, interdisciplinary team which have assessed a range of face coverings to test whether they could potentially help limit the spread of Covid-19.

The team made a series of findings that could aid policymakers producing guidance on the wearing of masks to help combat the virus, which can be spread in small droplets of water in people’s breath.

Those involved in the research included academics, researchers, students and technical staff from the School of Engineering alongside NHS staff, the University of Edinburgh’s Medical School, School of Physics, Edinburgh Innovations and mathematicians at Heriot-Watt University.

Method

The researchers used a technique called Background Oriented Schlieren imaging that enables scientists to measure the distance and direction travelled by air expelled when a person breathes or coughs.

Measurements were taken from people wearing different face coverings while standing or lying down, and from a manikin connected to a cough-simulating machine.

The team tested seven types of face covering – including medical-grade and home-made masks – and found that they could all potentially help limit the spread of Covid-19.

Findings

Researchers found that all face coverings without an outlet valve reduce the forward distance travelled by a deep breath out by at least 90 per cent. However, some of the masks enabled strong jets of air to escape from the back and sides, they found.

A type of mask commonly worn by workers exposed to fine dust – called a respirator mask – was shown to provide protection to the wearer. However, the valves on these masks that made breathing easier could potentially allow infectious air to spread considerable distances in front, the study suggested.

Surgical masks and the tested hand-made masks were found to limit the forward flow of a breath out, but also generate far-reaching leakage jets to the side, behind, above and below. Heavy breathing and coughing, in particular, were shown to generate intense backward jets.

Only masks that form a tight seal with the face were found to prevent the escape of virus-laden fluid particles, the team says. Researchers found that full-face shields worn without masks enabled the release of a strong downward jet.

Risk areas

The team also discovered that a regular medical procedure known as extubation – the removal of a breathing tube used during anaesthesia and when patients are on a ventilator – may increase the risk of spreading Covid-19.

Simulations showed that the coughing that regularly accompanies extubation caused people nearby to be enveloped in the patients’ exhaled air. This puts clinicians and others at high risk of exposure to the virus, the team said.

Conclusions

The School's Dr Ignazio Maria Viola, who coordinated the project, commented: “I have generally been impressed by the effectiveness of all the face coverings we tested. However, we discovered that some face coverings allow the emergence of downward or backward jets that people are not aware of and that could be a major hazard to others around them.”

Dr Felicity Mehendale, a surgeon at the Centre for Global Health at the University of Edinburgh’s Usher Institute, said: “It was reassuring to see the hand-made mask worked just as well as the surgical mask to stop the wearer’s breath flowing directly forwards. This suggests that some hand-made masks can help to prevent the wearer from infecting the public. But, the strong backward jets mean you need to think twice before turning your head if you cough while wearing a mask; and be careful if you stand behind or beside someone wearing a mask.”

The research findings are now available in a preprint paper, which can be accessed below.

Find out more

• Read the research preprint paper: Face Coverings, Aerosol Dispersion and Mitigation of Virus Transmission Risk
• Find out more about VOILAb: Dr Ignazio Maria Viola's research group in the School of Engineering
• Watch the ITV news report

The research has also appeared in the Guardian, the Daily Mail, Sky News, STV News, the Herald, the Metro, the Independent, The Times, and other broadcast and print media.