Study shows how masks with valves and face shields allow spread of virus

Shoppers wear masks as a precaution against the transmission of the novel coronavirus as they walk past a shop window on Oxford Street in London on July 14, 2020. – Face masks will be compulsory in shops and supermarkets in England from next week, the government said on July 14, in a U-turn on previous policy. (Photo by JUSTIN TALLIS / AFP)

WASHINGTON D.C., United States (AFP) — People wearing plastic face shields or masks fitted with a valve 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 on their own, a simulation model shows.

In a report published Tuesday in 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.

A handout picture released by the Jordanian Royal Palace on August 16, 2020 shows Jordanian King Abdullah II (C-R) accompanied by his wife Queen Rania (C-L), as they and their entourage are clad in masks due to the COVID-19 coronavirus pandemic, while inaugurating a new emergency hospital in the capital Amman. (Photo by Yousef ALLAN / Jordanian Royal Palace / AFP)

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

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 prevent the spread of the virus.