Researchers have found that masks with breathing valves and face shields may not be as effective as regular masks in limiting the spread of aerosol droplets, which transmit the Corona virus through the infected person’s spray.
Scientists from Florida Atlantic University in the United States tested how face shields and valve masks performed in impeding the spread of aerosol droplets, and found that the widespread use of these alternatives to regular masks could have a negative impact on efforts to mitigate the spread of Corona.
For the study, which was published in the journal Physics of FluidsIn a lab environment, the researchers used laser light and a mixture of distilled water to create an artificial mist consisting of the content of cough puffs.
By wearing a plastic face shield and an N95 face mask with a valve, the researchers were able to plot the droplet paths and demonstrate their performance.
The results of the study showed that although face shields prevent the initial forward movement of the spray, the expelled droplets move around the edges with relative ease and spread over a large area.
The researchers said observational photos of a valve-equipped face mask indicate that a large number of drops pass through the unfiltered exhalation valve, which significantly reduces its effectiveness.
The director in charge of this study said in a press interview that this experiment enabled the research team to observe that face shields are able to prevent the initial movement of exhalation, but they cannot prevent the movement of flying drops emitted around the edges.
Then he continued, “With the passage of time, these droplets can spread over a wide area in both the lateral and longitudinal directions, albeit with a decrease in the concentration of the droplets.”
Not only did the researchers notice that the droplets spread forward, but they also found that the droplets spread in the opposite direction.
In this study, N-95 classified face masks were used, but there are other types of masks made of fabric that are commercially available and also have one to two exhalation ports.
The authors of the study said that the exhalation port in N95 masks significantly reduced the effectiveness of the mask, as a large number of droplets passed through the valve without filtering and unimpeded.