Video shows why wearing face shields alone won’t prevent the spread of COVID-19
Face shields may be considered more comfortable than masks during the coronavirus pandemic, but experts say comfort shouldn’t trump protection.
Now, a new visualization from Florida Atlantic University shows just how ineffective face shields and masks with valves are at preventing respiratory droplets from escaping your mouth.
“There is an increasing trend of people substituting regular cloth or surgical masks with clear plastic face shields as well as using masks that are equipped with exhalation valves,” study lead author Siddhartha Verma, an assistant professor at FAU’s College of Engineering and Computer Science, said in a news release.
“A driving factor for this increased adoption is better comfort compared to regular masks. However, face shields have noticeable gaps along the bottom and the sides, and masks with exhalation ports include a one-way valve which restricts airflow when breathing in, but allows free outflow of air.”
The study was published Tuesday in the journal Physics of Fluids.
The Centers for Disease Control and Prevention says that face shields are primarily used for eye protection, and that they do not “currently recommend” their use “as a substitute for masks.” The agency cites a lack of evidence to support their effectiveness in preventing viral spread.
In the FAU study, researchers used a manual pump to simulate coughs and sneezes from a mannequin’s mouth with synthetic fog made of distilled water and glycerin. They beamed a horizontal and vertical laser light to capture how respiratory droplets move with a face shield and a valved mask.
The results show that face shields do in fact block the forward motion of droplets from coughs and sneezes, but they still found their way out into the open through the top, bottom and sides, according to the study. After the initial release, the aerosolized droplets float at their own will depending on the environment, and can expel as far as 3 feet.
Masks with valves prevented droplet spread “to an even lesser extent,” the researchers said in the release. “A large number of droplets pass through the exhale valve unfiltered, which significantly reduces its effectiveness as a means of source control.”
The researchers suggest that face shields and valved masks not be used as an alternative to traditional surgical, cloth or N95 masks during the coronavirus pandemic.
This story was originally published September 1, 2020 at 5:30 PM with the headline "Video shows why wearing face shields alone won’t prevent the spread of COVID-19."
