Face shields can absorb COVID-19 airborne particles, simulation shows

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A wind dynamics expert conducted a series of simulation exercises, measuring the effectiveness of face shields against particles found in the air. (FILE PHOTO)

Metro Manila (CNN Philippines, September 7) — A wind dynamics expert conducted a series of simulation exercises, measuring the effectiveness of face shields against particles found in the air.

Engineer Joshua Agar, an assistant professor from the University of the Philippines Institute of Civil Engineering,  said the idea to test the effectiveness of face shields came when he was playing billiards and he started to wonder if theories of wind dynamics can be applied to it.

Agar was able to simulate three scenarios on face shield use, which later on showed there is no guarantee these plastic shields can provide an additional layer of protection.

Scenario 1: High momentum cases with face shield

The simulation features a person in direct contact with an infected person and within one meter from the subject. The infected person directly coughs or sneezes on the other.

Agar noted that this scenario usually happens in hospital settings.

"Papunta siya roon sa faceshield, naredirect siya sa side kaso nagkaroon ng reverse flows po rito nagkaroon po ng mga vortices po," he said. "Nangyari na deposit ngayon doon sumilong ngayon kung ano na introduce po...doon po sumilong kung anong airborne particles sa likod ng face shield, kasama pa 'yung face natin kung wala tayong face mask tataas po ang chances na ma-contract ang virus."

[Translation: The (airborne particles) went to the face shield and despite being redirected on its side, it can also show the reverse flows of wind creating vortices. This means airborne particles have been deposited at the back of face shield and the surface of our face is also involved. If we are not wearing face mask, then that means greater chance of contracting the virus.]

Scenario 2: High momentum cases with face shield at 45 degree angle 

In another scenario, where a person is wearing a face shield but is not directly facing the infected person, Agar said vortices may still be formed, which means air particles can still accumulate on the face shield.

"'Yung flow mapapansin niyo nagkakaroon ng vortices and then nag-reverse po ang air so mas malala po ngayon kung naka-face kayo ng sideways from the source," Agar said.

[Translation: The flow still creates vortices and there's still a reverse flow of wind which means it's worse when you are facing sideways from the source (of infection).]

Scenario 3: Low momentum cases, virus now present in the air 

Agar said wearing face shields can pose even more danger if a person wears them in an area where virus particles are already present in the air.

The US Centers for Disease Control and Prevention or CDC acknowledges the airborne transmission of COVID-19.

"Sabi ng CDC airborne na ang particles...kung nag-walk po kayo across doon sa environment kung nasaan ang virus, nag-act po kayo ngayon as vacuum cleaner," Agar warned.

[Translation: The CDC said the coronavirus is now airborne and if you walked in an environment where it is present in the air, you act like a vacuum cleaner.]

"Hinihigop mo ngayon ang nasa air, so doon po nagsettle ang airborne particles sa likod ng face shield, sa face, so na-aggravate po," he added.

[Translation: You are absorbing the airborne particles which will settle at the back of face shields, on your face, so this aggravates the situation.]

What's next after the simulation exercises?

Agar said he has no plans of publishing his study on face shields, citing lack of funds.

"Medyo masakit po sa bulsa to publish it," he noted. "Siguro ipaubaya nalang o i-refer sa iba and sila nalang mag-pursue."

[Translation: It's expensive to publish it. I would rather refer it to others for them to pursue the study.]

Agar said he is open to collaborate with other experts to study the face shield effect.

The World Health Organization said it is not yet time to scrap the use of face shields - despite lacking evidence on their effectiveness.

Malacañang also said the face shield policy stays for now.