Face shields and valve masks are ‘ineffective’ claims new study

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CREDIT: Florida Atlantic University

While some health experts have promoted face shields and valve masks to combat the spread of Covid-19, a new study has shown they are ineffective at containing the killer virus.

TO increase public awareness about the effectiveness of face shields and face masks with exhalation valves, researchers from Florida Atlantic University’s College of Engineering and Computer Science used qualitative visualisations to test how they perform in preventing the spread of aerosol-sized droplets.

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For the study, published in the journal Physics of Fluids, researchers used faux sneezes and coughs from a mannequin’s mouth and mapped out the paths of the droplets.

While larger droplets hit the inside of the shield, smaller ‘aerosols’ – which stay airborne for longer periods, particularly indoors – escape to the sides and under the shield.


“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, aerosolised droplets expelled with the jet are able to move around the visor with relative ease,” said professor Manhar Dhanak, Ph.D.

Masks with exhalation ports, if worn by someone who is infected, are likewise “not very effective at protecting others”, he added.


Despite the increased comfort the alternatives offer, the researchers say it “may be preferable to use well-constructed, high quality cloth or surgical masks that are of a plain design”, instead of face shields and masks equipped with exhale valves.

“Widespread public adoption of the alternatives, in lieu of regular masks, could potentially have an adverse effect on ongoing mitigation efforts against Covid-19,” said Siddhartha Verna, Ph.D., lead author and an assistant professor.

“The research conducted by professors Dhanak and Verma on the importance of proper face coverings to stop the spread of Covid-19 has literally illuminated the world,” said Stella Batalama, Ph.D., dean of FAU’s College of Engineering and Computer Science.

“While broad acceptance regarding the need for face coverings has risen steadily, there is an increasing trend of people who are substituting regular cloth or surgical masks.

“This latest research provides important evidence to further support CDC guidelines and inform the public to make better selections in their choice for face coverings for their benefit and for public safety.”




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