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Research published in the scientific journal “Physics of Fluids” indicates that face shields and tube masks are less effective at blocking viral particles than normal masks.
The researchers used a hollow mannequin head with various face coverings. They simulated a cough or sneeze with a pressure increase from a hand pump and used lasers to illuminate the path of the droplets.
“We focus on the smallest droplets as they can be suspended for a long time and can contain enough virus particles to transmit Covid-19,” explained Siddhartha Verma, one of the authors.
Close-up field view of the spread of gout when wearing a face shield to prevent jet stream – Photo: Siddhartha Verma, Manhar Dhanak, John Frankenfield / Disclosure
The test showed that face shields block the initial movement of a simulated cough or sneeze stream, but the expelled droplets can easily move across the visor and spread over a large area.
In the simulation with the valve mask, a cloud of particles can be seen sprouting around the tip of the nose, where the fit is poor. Also, most of the exhaled air passes through the valve unimpeded.
Visualization of the spread of gout when wearing a tube mask to prevent jet stream – Photo: Siddhartha Verma, Manhar Dhanak, John Frankenfield
Tissue, N95, or surgical mask testing was more effective. All the masks blocked a significant amount of particles and appeared to offer adequate protection for the person.
“As students return to schools and colleges, some wonder if it is better to wear face shields, as they are more comfortable and easier to wear for long periods of time. But what if these shields are not that effective? Basically it would put everyone in a tight space with droplets that build up over time, which could lead to infections, “said Verma.
The study suggests that to minimize the spread of the coronavirus in the community, it is preferable to use high-quality cloth masks or simpler surgical masks, rather than face shields and masks equipped with valves. “Even the best masks have some degree of leakage. It is important to maintain a physical distance to mitigate transmission ”, added the author.
Following the publication of the study on face shields, the Government of Canada reported that valve masks are prohibited on flights.
“The use of expiratory valve masks is not recommended because these masks do not protect others from Covid-19 and do not limit the spread of the virus,” says the warning on the official website.
