Science

'Even Face Shield, N-95 Mask Together Can't Stop COVID-19'

'Even Face Shield, N-95 Mask Together Can't Stop COVID-19'”

"The larger droplets, they will get stopped, but the smaller droplets, they follow the air streams very well, so they can basically flow around the visor very easily and then they are released into the environment", said Siddhartha Verma, Ph.D., a professor at Florida Atlantic University and one of the study's authors.

While the study allowed the researchers to compare the relative effectiveness of various masks and face shields, the methods used did not quantify the volume or size of the particles that escaped.

In experiments that visualized the likely travel patterns of "respiratory droplets", researchers found that plastic face shields are poorer barriers than standard masks.

However, a new study has demonstrated that face shields alone aren't good enough to keep droplets from a cough away from our faces - they sneak under and around the shield.

The U.S. Centers for Disease Control and Prevent recommends cloth face masks for the public and not the surgical and N95 masks needed by health care providers.

'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 with clear plastic face shields, and with masks equipped with exhalation valves, ' said Dr Stella Batalama, dean of FAU's College of Engineering and Computer Science, in a statement.

The key takeaway illustrates that face shields and masks with exhale valves may not be as effective as regular face masks in restricting the spread of aerosolised droplets.

For this study, Verma and his colleagues used a hollow mannequin head and simulated a cough or sneeze with a pressure impulse from a manual pump.

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Researchers also found that valve masks allowed a large number of particles to escape and that some of the nonmedical vented masks used had faulty valves. Valved masks, with one-way vents created to allow breath to escape while blocking germs from entering, can feel more breathable and prevent the mask from getting moist as quickly.

The research is unlikely to be the final word on face shields. "Shields are not able to do that".

Marr said work in her own lab also shows that face shields offer nearly no protection against aerosolised particles believed to play an important role in the spread of illness. So those walking in front or behind them could also catch the droplets.

"The main objective of face shields, when used by healthcare workers (in conjunction with masks), is to protect them from incoming sprays and splatters".

While face shields do block large splatters from a cough or sneeze, smaller particles get caught in air flows and never hit the plastic, slipping below it instead. "Air can't pass through the face shield - it has to bend and go around the shield", Marr said.

The researchers concluded that despite the comfort that both types of protection offer, high-quality cloth or medical masks of plain design are preferential in helping to prevent the spread of the virus.

"Our face shields not only help people to feel safe and allow them to breathe more freely, but experts have also stated that face shields are a safer, more comfortable, and more effective deterrent to Covid-19".

"These masks with valves are not meant for acting as source control", Verma said.



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