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Are face shields effective against COVID-19? Wind engineer explains

A wind engineer said face shields may increase risk of exposure to the coronavirus disease 2019 (COVID-19) instead of helping prevent the spread of the virus.

In an episode of "Need To Know," Engr. Joshua Agar from the University of the Philippines said the "aerodynamic consequences" of face shields should be considered as COVID-19 has been confirmed to be airborne.

According to Agar, the presence of a face shield is a factor because  particles of the virus are known to stay in the surrounding air.

"Ang tendency ay nagkakaroon ng negative pressure region doon sa face shields so nag-a-act siya as suction so hinihigop niya kung ano man 'yung nasa air so most likely, pati 'yung virus," he said.

["Face shields tend to create a negative pressure region so it acts as a suction and sucks what is in the air, most likely including the virus."]

Agar added that the direction of air changes around one's head through the formation of vortices or masses of air that are whirlwind-like in between the face and the shield.

These vortices tend to trap air in, hence, the bigger the chances of a person inhaling the virus.

"Okay lang na ikaw 'yung sumasalo sa hangin. Hindi naman sa 'yo made-deposit kung ano 'yung nasa hangin. Made-deposit siya kung saang merong vortices," he said.

["It's ok if you catch the air. Whatever is in it will not be deposited on you, it will be deposited wherever there is vortices."]

"By exposing yourself directly do'n sa hangin, 'di mo ina-allow 'yung sarili mo na ma-expose.”

["By exposing yourself directly to the air, you are not allowing yourself to get exposed (to particles in it)."]

Agar also said face shields also serve as an insulator, which results in higher moisture on a person's face.

"Na-iinsulate 'yung hangin sa loob so iinit pa nang husto 'yung hangin," he said. "The moisture, siya 'yung encouraging factor for the virus to stick into your skin."

["The air gets insulated so it becomes warmer. The moisture is an encouraging factor for the virus to stick into your skin."]

Due to these factors, Agar said people may be more prone to getting infected by the virus.

Meanwhile, a 2014 study by the National Institute for Occupational Safety and Health in the US found that face shields reduced inhalational exposure by 96% of a  healthcare worker in facilities and hospitals, but only right after exposure to a person who coughed. The rest of the particles stay in the air and may still enter the face shield.

However, there is still no complete study about the face shields' effectiveness specifically against COVID-19. Despite this, the Department of Health (DOH) still mandates its use for Filipinos outside their home.

"Any layer of protection is always better than less protection," DOH Sec. Francisco Duque said.

This is backed by a study cited by IATF Technical Advisory Group for COVID-19 member Dr. Anna Ong-Lim, saying that face shields reduce chances of infection.

"There are actually several findings from studies conducted and they indicated that meron pong evidence that eye protection such as face shields actually are able to reduce 78 percent infection."

Other places which have been using face shields are the Oregon state in the United States, Malta, United Kingdom, China, and South Korea.

The use of face shields in these places, however, are not mandated but only recommended. Healthcare workers are only the ones required to use it as part of their personal protective equipment.

—Franchesca Viernes/MGP, GMA News