Study shows Masks with Valves and Face Shields ineffective, allow spread of COVID-19
Researchers from Florida Atlantic University’s College of Engineering and Computer Science, Florida, USA warn the public against the use of face shields alone and face masks with exhalation valves.
According to them, face shields and face masks with exhalation valves may not be as effective as regular face masks when it comes to restricting the spread of aerosolized droplets. Thus, instead of using these alternatives, they said that it is preferable to use a well-constructed, high-quality cloth or surgical masks that are of a plain design.
This is since the widespread public use of the above-mentioned alternatives could potentially have an unfavorable effect on the efforts against the Coronavirus Disease 2019 (COVID-19).
The Study on Face Shields and Face Masks with Exhalation Valves
To test how face shields and masks with valves perform in impeding the spread of aerosol-sized droplets, the researchers – Siddhartha Verma, Manhar Dhanak, and John Frankenfield – have used qualitative visualizations.
In a laboratory setting, they employed flow visualization, using a laser light sheet, a mixture of distilled water, and glycerin to generate the synthetic fog that made up the cough-jet.
They placed a plastic face shield and an N95-rated face mask with a valve on a mannequin, then they visualized the droplets expelled from a mannequin’s mouth while simulating coughing and sneezing. This enabled them to map out the paths of droplets.
Their study is called the “Visualizing droplet dispersal for face shields and masks with exhalation valves” and was published in the Physics of Fluids journal on September 1, 2020.
Face Shields
Although face shields block the initial forward motion of the jet, the expelled droplets move around the visor with ease and it spread out over a large area depending on light ambient disturbances.
“From this latest study, we were able to observe that face shields are able to block the initial forward motion of the exhaled jet, however, aerosolized droplets expelled with the jet are able to move around the visor with relative ease. Over time, these droplets can disperse over a wide area in both lateral and longitudinal directions, albeit with decreasing droplet concentration.”
– Manhar Dhanak, Ph.D., department chair, professor, and director of SeaTech, a co-author of the study
Face mask with Exhalation Port
In the visualizations for the face mask with an exhalation port, on the other hand, a large number of droplets pass through the exhale valve unfiltered. The effectiveness of the mask as a means of source control has been significantly reduced because of its exhalation port or valve.
“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. A driving factor for this increased adoption is better comfort compared to regular masks…
…the inhaled air gets filtered through the mask material, but the exhaled breath passes through the valve unfiltered.”
– Siddhartha Verma Ph.D., lead author of the study, an assistant professor
For More News and Updates
See more news and updates by visiting our Baguio City Guide website on a daily basis or by simply liking and following our official Baguio City Guide Facebook page.
SOURCE
Florida Atlantic University YouTube Channel
How do you feel about this?
