Thursday, 25 February, 2021


Even face shield, N-95 mask together can't stop coronavirus'

A restaurant employee wears a protective face shield and mask in Moscow Russia Study shows how masks with valves and face shields allow spread of coronavirus
Patty Aguilar | 03 September, 2020, 03:58

The scientists from Florida Atlantic University in the USA used qualitative visualisations to test how face shields and masks with valves perform in impeding the spread of aerosol-sized droplets.

That model showed that face shields-the clear plastic visors that wrap around the face-can block some droplets from a simulated cough, but small droplets can slip around the sides of the visor and spread widely into the surrounding area.

Manhar Dhanak and Siddhartha Verna, both professors of mechanical engineering at Florida Atlantic University in the US, visualized jets of droplets expelled towards a hollow mannequin head fitted with either a face shield or valved face mask.

However, there is an increasing trend of substituting regular cloth masks or surgical masks with masks equipped with exhalation valves and clear face shields.

"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.

"Overall, the visuals presented here indicate that face shields and masks with exhale valves may not be as effective as regular face masks in restricting the spread of aerosolized droplets", the study added.

"Our observations suggest that to minimize the community spread of COVID-19, it may be preferable to use a high-quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves", the researchers concluded in the study. The reusable face shield allows a person to wear them without the fear of feeling claustrophobic and they can be worn all day long while running errands or at work. But the expelled droplets were later spread over a large area by moving around.

Face shields and valved masks - two options many people find more comfortable than cloth face coverings - appear to be less effective at blocking viral particles than regular masks, a new study shows. In some countries, people are not allowed to leave their houses or stay in public places without a mask on.

A concerning flaw in face masks with valves?

It is important to keep the stocks of N95 and surgical masks stable, especially for health workers. While these popular masks clean the air coming in, the air people breathe out is not.

In a mask with a working valve, the pressure inside the masks forces a small disk to open and let air out, but when you inhale the disk fits tightly against the hole and doesn't allow air in.

The FAU study shows how unfiltered aersols escape an N95-rated face mask.

All of these completely defeat the point of wearing a mask to prevent COVID-19 from entering your nose or mouth, or exiting your nose and/or mouth, thereby infecting someone else. Yet, this is true for large respiratory droplets, but may not be as effective on smaller aerosol-sized droplets.

That said, the study also pointed out that these droplets decreased in concentration the further away they hovered - demonstrating the importance of physical distancing. The agency also says you should wash your hands before and after taking it off, and avoid touching your face while removing it.

The CDC also released a guideline, discouraging the use of face shields only as a means to prevent the spread of the coronavirus.

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