EDINBURGH: New UK research has found that wearing a face mask could reduce the spread of Covid-19, although choosing one which fits your face will be even more effective.
Carried out by a team from Heriot-Watt University, the University of Edinburgh and NHS Lothian in Scotland, the new study tested seven types of face coverings, including medical-grade and homemade masks, to see how effective they might be at reducing the spread of the viral droplets in our exhaled breath which transmit Covid-19.
The researchers used a technique called Background Oriented Schlieren imaging, which enabled them to measure how far and in what direction exhaled air travels when a person breathes or coughs.
Measurements were taken from people wearing different face coverings while standing or lying down, and also from a mannequin that was connected to a cough-simulating machine.
The findings, which have been posted on the website arXiv without having been peer-reviewed, meaning they have not yet been verified by experts, showed that all of the face masks without an outlet valve reduce the distance that breath traveled forward by at least 90%, potentially limiting the spread of Covid-19.
A type of mask that did come fitted with a valve, a respirator mask, which is often worn by workers exposed to fine dust, was found to also provide protection to the wearer.
However, the fact that the valves on these masks are there to make breathing easier also means they could allow infectious droplets to travel quite far in a forward distance, say the researchers.
The researchers also found that surgical masks and the handmade masks allowed strong jets of air to escape from the back, sides, above and below, even though they limited the amount of exhaled air traveling forward. Even more air escaped if people breathed heavily or coughed.
Only masks that formed a tight seal with the face were found to prevent the escape of viral droplets in our exhaled breath, said the team.
Co-author Dr Cathal Cummins commented on the findings saying, “Even our handmade mask performed very well in preventing the frontal spread of the wearer’s exhaled breath.
While this is positive, wearers of hand-made face masks need to be aware that jets of air can leak out of the sides and back of their masks.
This could be particularly important when using masks on public transport, where sitting behind someone wearing a mask could be more of a hazard than sitting directly facing them.”
“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,” added co-author Dr Felicity Mehendale.
“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.”