Face masks with valves cannot prevent COVID-19 spread

Credit: CC0 Public Domain

As countries around the world experience a steep surge in COVID-19 infections, face masks have become increasingly accepted as an effective means for combating the spread of the disease when combined with social distancing and frequent hand-washing.

Increasingly people are using clear plastic face shields and masks with exhalation valves instead of regular cloth or surgical masks since they can be more comfortable.

However, in a new study, researchers found these face shields and masks are ineffective in preventing COVID-19 spread.

The research was conducted by a team at Florida Atlantic University and elsewhere.

In the study, the team examined whether face shields and masks with valves are as effective against COVID-19 spread.

They used a hollow manikin head and simulated a cough or sneeze with a pressure impulse from a manual pump.

Tracers composed of droplets of distilled water and glycerin were expelled through the mouth opening, and laser sheets visualized the spatial and temporal development of the ejected flow.

The team focused on the smaller droplets since they can stay suspended for very long times and might contain enough virus particles to transmit COVID-19.

The visualizations showed face shields block the initial forward motion of a simulated jet of a cough or a sneeze, but the expelled droplets can move around the visor with relative ease and spread out over a large area depending on light ambient disturbances.

The visualizations for a mask equipped with an exhalation port illustrate 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 research suggests 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.

Even the very best masks have some degree of leakage. It’s still important to maintain physical distance while wearing them to mitigate transmission.

One author of the study is Siddhartha Verma.

The study is published in Physics of Fluids.

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