- Along with valve masks, face shields are becoming more prevalent
- Researchers set out to prove that face shields alone are not effective in limiting the spread of droplets
- While face shields offer additional protection, they are not effective without a cloth mask
As the economy slowly reopens, masks have become compulsory to limit the spread of coronavirus droplets. But besides cloth masks, other options such as masks with valves and face shields have become prevalent.
In a previous article, Health24 looked at the effectiveness of valve masks and found that, even though they might protect the user, they do little to protect other people from droplets that escape through the built-in vents.
Now, in an effort to establish the effectiveness of these valve masks and face shields, researchers from Florida Atlantic University's College of Engineering and Computer Science used qualitative visualisations to test how face shields and masks with valves perform in limiting the spread of aerosol-sized droplets, according to a news release.
Significant amount of droplets escape from both
The study, published in the journal Physics of Fluids, was done by using flow visualisation in a laboratory setting. This was done by setting up a laser light sheet and using a mixture of distilled water and glycerine to create synthetic fog. This was then placed in a cough-jet to simulate droplets expelled from a mannequin’s mouth when coughing.
The results showed that, while the face shield protected the user against droplets being propelled forward, it did little to stop expelled droplets moving out from around the visor.
Face shields impede the forward motion of exhaled droplets to a certain extent, as do masks with valves, but to a lesser extent. The problem is, however, that once released into the environment, the aerosol-sized droplets are widely dispersed, according to the news release.
The valve face masks also showed that a large number of droplets escaped through the valve when the user exhaled, which does little to protect other people against droplets that could potentially carry SARS-CoV-2.
Cloth masks still most effective
The researchers conducted this study to create public awareness about the effectiveness of different varieties of masks.
"There is an increasing trend of people substituting regular cloth or surgical masks with clear plastic face shields as well as using masks that are equipped with exhalation valves," said Siddhartha Verma, PhD, lead author and an assistant professor. "A driving factor for this increased adoption is better comfort compared to regular masks. However, face shields have noticeable gaps along the bottom and the sides, and masks with exhalation ports include a one-way valve which restricts airflow when breathing in, but allows free outflow of air. The inhaled air gets filtered through the mask material, but the exhaled breath passes through the valve unfiltered."
The key takeaway from this research is that cloth masks remain the most effective at lowering transmission through droplets, while valve masks and face shields used without any additional cloth mask, do little to protect others against droplets.
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