By NAOYA KON/ Staff Writer
October 13, 2020 at 07:00 JST
Non-red droplets leak outside a face shield, left, and a nonwoven face mask in a set of simulations of how a wearer’s droplets are spread. (Both images provided by Riken, Toyohashi University of Technology and Kobe University, under cooperation by Kyoto Institute of Technology, Osaka University and Daio Paper Corp.)
Researchers have bad news for people who wear face shields to prevent novel coronavirus infections: The equipment is woefully inadequate in containing droplets that can spread the virus.
And they have the calculations of a supercomputer to back up their findings.
The team of researchers from the Riken national research institute, Kobe University and other institutions used Fugaku, one of the world’s best-performing supercomputers, to simulate the spread of droplets from a wearer of a face mask and a wearer of a face shield.
According to the results released in August, the face shield allowed nearly 100 percent of aerosol particles, which measure 5 micrometers or less, and half of droplets of 50 micrometers to leak.
In comparison, the face mask made of nonwoven fabric leaked about 30 percent of aerosol particles but caught almost all of the larger droplets measuring 50 micrometers or more.
“The nonwoven face mask is the winner in terms of effectiveness in blocking the spray of droplets,” said Makoto Tsubokura, a professor of computational fluid dynamics with Kobe University, who also serves as a Riken team leader.
Medical workers have used face shields to block blood and oral droplets from entering their eyes, nose and mouth.
But the practice of wearing face shields instead of face masks has become more widespread among members of the public.
Face shields are less stifling than masks and allow the lips to show through. This is important for many service industry workers, language teachers, singers and even participants of drinking parties.
Another study showed the dangers of this trend from a health standpoint.
A team of researchers from Florida Atlantic University visualized the spread of droplets from a wearer of a face mask or a face shield.
Their research results, published in September in Physics of Fluids, a scientific journal, showed that a face shield can partially block the spread of droplets emitted straight forward from the wearer’s mouth. But the droplets can escape freely from the right, left and underside of the shield.
In 10 seconds, the droplets were found to have spread 1 meter or so into the surroundings, the study showed.
“Widespread public use of (this and other) alternatives to regular masks could have an adverse effect on mitigation efforts,” the research team warned.
The U.S. Centers for Disease Control and Prevention (CDC) has said a face shield can protect the wearer’s eyes from infection, but the level of protection it provides to people nearby from the droplets of the wearer is unknown.
The CDC does not recommend face shields as a substitute for masks in blocking the spread of the novel coronavirus.
The Osaka Medical Association in June released a statement on the use of face shields in schools and classrooms.
It said face shields are designed to prevent droplets from coughs and sneezes from entering the wearer’s eyes and are not intended to prevent the wearer’s saliva from being sprayed on others.
The statement also cited risks in using face shields, including injuries from hitting a section of plastic, accidents caused by the restricted field of vision, and heatstroke from trapped hot air.
Kazunari Onishi, an associate professor of environmental epidemiology with St. Luke’s International University in Tokyo, called for caution in using face shields.
“Wearing a face shield alone, with no face mask on, is not effective enough for blocking infections,” Onishi said. “Face shields can only block larger droplets. They let go most parts of smaller droplets.”
He added that nothing is known about the size of droplets that can cause COVID-19 infections.
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