With new cases of COVID-19 climbing quickly upwards, an increasing number of governments and businesses are mandating the wearing of face coverings in public places.
Just this week, for example, the University of Minnesota and the cities of Edina and Rochester announced such requirements.
Health officials at the Centers for Disease Control and Prevention (CDC) recommend that everyone over the age of 2 wear some form of cloth face covering in public settings to help keep COVID-19 respiratory droplets from reaching others.
But just how effective are those cloth coverings? From previous studies, we know the ability of medical-grade face masks — the ones used by doctors and nurses in hospitals and other medical settings — to mitigate the spread of respiratory droplets. But little research has been done to determine the effectiveness of the myriad types of cloth-based face coverings that most of us wear when we venture into public spaces.
A new study, published Tuesday in the journal Physics of Fluids, may offer some guidance. For the study, a team of researchers from Florida Atlantic University devised a way of creating visualizations of emulated coughs and sneezes. They gave a mannequin’s head a circular opening — a “mouth” — and a hollowed-out interior space that mimicked the shape of an adult’s nasal passages. The head was also mounted at a height of 5 feet, 8 inches to approximate that of a person. Then, using a pump and a mixture of water and glycerin, the researchers made the mannequin deliver a rather simplified “cough,” capturing the ensuing spray of droplets visually with the aid of a laser light sheet.
With this device, the researchers tested the protective effects of four types of non-medical face coverings: a single-layer bandana-style covering, a non-stitched mask made from folding up a cotton handkerchief or similar material (as described in a video by the U.S. surgeon general), a mask stitched by hand from two layers of cotton quilting fabric and a non-sterile cone-style mask available in most pharmacies.
Differences in droplet distances
When the mannequin wore no mask, droplets were able to travel up to 12 feet within about 50 seconds. In addition, the small tracer droplets remained suspended in the air for up to three minutes.
These findings suggest, say the study’s authors, that the CDC 6-foot social-distancing guidelines may need to be updated.
The cloth coverings helped mitigate the spread of the droplets, but with varying success. The bandana decreased the droplets’ traveling distance to 3 feet, 7 inches, while the folded homemade mask cut it down to 1 foot, 3 inches.
The cone-style mask limited the droplet spread even further, to a distance of about 8 inches. But the stitched two-layer cotton mask was the most protective, limiting the droplet spread to 2.5 inches.
All the coverings mitigated the forward motion of droplets, but some tracer droplets were propelled through each type of mask. Tracer droplets also escape from the edges of the masks, particularly the top edges.
The researchers point out that the thread count of the fabric was not a factor, as the bandana had the highest thread count, but provided the lowest level of protection.
Social distancing is essential
Of course, this is just one study. The findings need to be duplicated and confirmed, perhaps with other types of “coughing devices” and mask materials.
Still, the overall take-home message is clear: Any kind of facial covering offers some protection in keeping COVID-19 pathogens from spreading, and some coverings offer more protection than others.
The study’s findings also underscore the urgent and continuous need for social distancing.
“It’s important to understand that face coverings are not 100 percent effective in blocking respiratory pathogens, which is why it’s imperative that we use a combination of social distancing, face coverings, handwashing, and other recommendations from healthcare officials until an effective vaccine is released,” said Siddhartha Verma, the study’s lead author and an assistant professor of ocean and mechanical engineering at Florida Atlantic University, in an interview with Healthline.
“Promoting widespread awareness of effective preventative measures is crucial given the high likelihood of a resurgence of COVID-19 infections in the fall and winter,” he and his colleagues add in their study.