Face shields ineffective at trapping aerosols, says Japanese supercomputer

[nitpicker]

https://www.theguardian.com/world/2020/sep/22/face-shields-ineffective-trapping-aerosols-japanese-supercomputer-coronavirus

Face shields ineffective at trapping aerosols, says Japanese supercomputer

Justin McCurry in Tokyo

Tue 22 Sep 2020 07.19 BSTLast modified on Tue 22 Sep 2020 07.34 BST

Plastic face shields are almost totally ineffective at trapping respiratory aerosols, according to modelling in Japan, casting doubt on their effectiveness in preventing the spread of coronavirus. A simulation using Fugaku, the world’s fastest supercomputer, found that almost 100% of airborne droplets of less than 5 micrometres in size escaped through plastic visors of the kind often used by people working in service industries.
(snip)

In addition, about half of larger droplets measuring 50 micrometres found their way into the air, according to Riken, a government-backed research institute in the western city of Kobe.

This week, senior scientists in Britain criticised the government for stressing the importance of hand-washing while placing insufficient emphasis on aerosol transmission and ventilation, factors that Japanese authorities have outlined in public health advice throughout the pandemic.
(snip)

Makoto Tsubokura, team leader at Riken’s centre for computational science, said the simulation combined air flow with the reproduction of tens of thousand of droplets of different sizes, from under 1 micrometre to several hundred micrometres.

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 told the Guardian.

“This is especially true for small droplets of less than 20 micrometres,” 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 micrometres.”

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.
(snip)

[LisaL]

1. I am not surprised.

Face shields work for large droplets, such as if somebody sneezes or coughs in your face. Otherwise since they are not forming a seal with the face, they won't stop aerosols from getting to you.

[hlthe2b]

2. Wearing them WITH a face mask to reduce possible ocular exposure is reasonable. It is too damned bad

Last edited Tue Sep 22, 2020, 10:59 AM - Edit history (1)

we can't have a united public health voice as that could have stopped/reduced both the face mask backlash and the total misunderstanding of what face shields can and can not do. I saw an elderly couple wearing nothing more than a face shield in a fairly crowded grocery store and in a community with mandatory face mask regulation. It saddened me, but I hope the fact they were mostly surrounded by customers wearing actual face masks may save this ill-informed and at-risk couple.

[LisaL]

3. Yep, they should be worn with the mask, not instead of the mask.

NT

[BigmanPigman]

7. That's what I read yesterday too.

I read mask AND goggles or mask AND face shield.

[jimfields33]

8. I've seen many in grocery stores wearing face shields

I didn’t think it was bad at all until reading this article. I hope they get this information before going to another store. This was weeks ago before I found instacart. Love it!!!!

[FBaggins]

4. Little need for a supercomputer

That isn't what they're designed for.

It's hard to imagine why they thought it needed to be evaluated. They also aren't useful against poison gas attacks or secondhand smoke.

[LisaL]

5. Because some people suggested wearing them instead of masks?

NT

[tanyev]

6. It's been a while back, but I remember an article about waitstaff in Sweden who tested positive.

They had all been wearing face coverings of some sort, but everyone who tested positive had been wearing shields only, no mask.


ETA: I'm seeing a lot of shields only in video and photos from back to school stories. Students and teachers. Not good.

[sl8]

9. Related: "Visualizing droplet dispersal for face shields and masks with exhalation valves"

https://aip.scitation.org/doi/10.1063/5.0022968

Visualizing droplet dispersal for face shields and masks with exhalation valves

(Video, text, pdf at link)