During the COVID-19 coronavirus pandemic, there has been some controversy around the wearing of masks or face coverings. We were alternately told to wear them and not wear them. But does wearing a face covering reduce transmission of the virus? A new study seeks to answer that question.
In the interest of resolving the mask question using science instead of opinion and conjecture, clinicians from Britain’s National Health Service at Lothian and engineers from Heriot-Watt University and the University of Edinburgh teamed up to study the question. They tested the effectiveness of seven different types of face coverings as ways to reduce transmission of viruses, COVID-19 in particular. Face coverings tested ran the gamut from medical grade to purely home-made.
In short, the result was pretty universal. Every type of mask tested reduced the transmission of the COVID-19 virus. The longer answer is more interesting, however.
Using a technique known as Background Oriented Schlieren, the team tested all the masks and found that a face covering which spans the mouth and nose reduces the forward travel distance of an exhaled breath by more than 90 percent.
Background Oriented Schlieren is a technique which allows researchers to measure both distance and direction of expelled air traveling from a person when they cough or breathe. Measurements were taken from people standing and lying down as well as from a mannequin connected to a cough simulation machine.
While all masks significantly reduced transmission of expelled breath in both quantity and distance, not all masks were created equal. Even given this reality, every face covering which did not employ an outlet valve reduced forward distance of expelled breath by more than 90 percent.
While you might think surgical masks would do the best job of keeping expelled breath from escaping, they fared only about as well as hand-made masks. Both types allowed considerable leakage to the sides, behind, below and above. Called “leakage jets,” these plumes of expelled air can carry virus droplets. Heavy breathing and coughing in surgical and hand-made masks resulted in intense backward leakage jets.
Respirator masks, commonly worn by construction and other workers who are exposed to fine dust, provided protection to the wearer. But the valves on this type of mask that improve breathing for the wearer can allow infectious air to spread to the front for a considerable distance, according to the study.
Full face shields, such as those worn in some emergency medicine environments, enabled the release of strong downward leakage jets. Only by employing them with surgical or similar masks could this be reduced significantly.
The only masks that prevented the escape of breath and respiratory droplets were those that allowed a tight seal on the face. These would be successful at preventing virus droplets from escaping in significant amounts.
The research team believes that their findings can aid public health authorities and policymakers in producing guidelines regarding the wearing of masks to help stem the spread of the COVID-19 coronavirus.
The research team found something else that may give medical personnel and public health authorities pause. Extubation, or the removal of the breathing tube employed during anesthesia and when patients are ventilated, may increase the risk of spreading COVID-19.
When a breathing tube is removed, patients cough, sometimes violently. This can expel large quantities of respiratory droplets, which surround the people nearby. This puts the clinicians and those they come in contact with to be at high risk of exposure to COVID-19, according to the study.
Regarding the relative performance of various mask types, the researchers had mostly positive things to say after completion of their work.
Dr. Cathal Cummins, an assistant professor in the Department of Mathematics and Institute for Infrastructure & Environment from Heriot-Watt University , who co-authored the work, said: “Even our hand-made 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.”
Dr. Ignazio Maria Viola, of the University of Edinburgh’s School of Engineering, who coordinated the project, said: “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.”
Mind you, this doesn’t settle every question about masks and wearing face coverings. Many people are still wondering things like “if I wear a mask, why do I still have to social distance?” and “can I skip the mask when nobody else is around?”
My take on this is simple. While I don’t want to wear a mask when I go out, I will. Not because it’s some ordinance or some governor’s decree from on high. And not because I believe a mask can stop all infection spread.
I’ll wear a face covering because it allows me to show respect to others who may be very concerned about spread, who may be at-risk for severe symptoms or even death should they contract the virus and for those who simply feel more confident when masks are worn by others around them.
I know the arguments against wearing face coverings. I go without one whenever someone else’s rights and mine don’t clash to create discomfort or unnecessary risk. I hope you’ll consider doing the same.
Keep the faith and keep after it!
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Journal Reference – Face Coverings, Aerosol Dispersion and Mitigation of Virus Transmission Risk. arXiv:2005.10720v1 [physics.med-ph] arxiv.org/abs/2005.10720