Plastic face shields are almost totally ineffective at trapping respiratory aerosols, computer modeling in Japan showed, casting doubt on their effectiveness in preventing the spread of COVID-19.
A simulation using Fugaku, the world’s fastest supercomputer, found that almost 100 percent of airborne droplets of less than 5 micrometers in size escaped through plastic visors of the kind often used by people working in service industries.
Moreover, about half of larger droplets measuring 50 micrometers found their way into the air, according to RIKEN, a government-backed research institute in the city of Kobe.
Photo: Reuters
This week, senior scientists in Britain criticized the government for stressing the importance of handwashing while placing insufficient emphasis on aerosol transmission and ventilation, factors that Japanese authorities have outlined in public health advice throughout the pandemic.
As some countries have attempted to open up their economies, face shields are becoming a common sight in sectors that emphasize contact with the public, such as shops and beauty salons.
Makoto Tsubokura, team leader at RIKEN’s center for computational science, said that the simulation combined air flow with the reproduction of tens of thousand of droplets of different sizes, from under 1 micrometer to several hundred micrometers.
He cautioned against wearing face visors as an alternative to masks.
“Judging from the results of the simulation, unfortunately the effectiveness of face guards in preventing droplets from spreading from an infected person’s mouth is limited compared with masks,” Tsubokura said.
“This is especially true for small droplets of less than 20 micrometers,” he said, adding that all of the much smaller aerosol particles were found to escape through the gap between the face and the face shield.
“At the same time, it somehow works for the droplets larger than 50 micrometers,” he said.
Tsubokura suggested that people who are advised not to wear masks, such as those with underlying respiratory problems and small children, could wear face shields instead, but only outdoors or in indoor settings that are properly ventilated.
Fugaku, which can perform more than 415 quadrillion computations a second, recently found that masks made from non-woven fabric are more effective at blocking the spread of COVID-19 via airborne droplets than those made of cotton and polyester.
The ￥130 billion (US$1.24 billion) supercomputer has also run simulations on how respiratory droplets spread in partitioned office spaces and on packed trains when the carriage windows are open.
Although it will not be fully operational until next year, experts are hoping it will help identify treatments for COVID-19 from about 2,000 existing drugs, including those that have yet to reach the clinical trial stage.
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