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Face shields, masks with valves don’t block coronavirus droplets, study finds

Face shields and masks with valves do not fully protect from the transmission of the coronavirus when used, study reveals.

Plastic face shields or masks with valves can spray invisible droplets over a very wide area when they sneeze or cough, making the devices ineffective at preventing the spread of coronavirus when used, according to a report published by the US journal Physics of Fluids.

Researchers at Florida Atlantic University used vertical and horizontal laser sheets to track tiny droplets of distilled water and glycerin as they spread from a hollow mannequin head fitted with a plastic face shield or a mask with a breathing valve on it.

The face shield initially blocks the passage of the droplets as they move forwards, but “the expelled droplets can move around the visor with relative ease and spread out over a large area,” the researchers said.




As for a mask with a valve fitted to make breathing easier, “a large number of droplets pass through the exhale valve unfiltered, which makes it ineffective in stopping the spread of the COVID-19 virus if the person wearing the mask is infected.”

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