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Many countries around the world are experiencing a sharp increase in COVID-19 cases, with the total number of cases globally reaching more than 25.86 million. Face masks have become one of the most effective means of combating the spread of the virus, especially when used in combination with regular hand hygiene and physical distancing.
However, there is a growing trend to replace cloth masks or surgical masks with masks equipped with exhalation valves and transparent face shields. Now, a new study shows that face shields and valve masks are ineffective against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.
In the study published in the journal Fluid physics, A team of researchers from the Florida Atlantic University College of Engineering and Computer Science aimed to determine the effectiveness of face shields alone, as well as masks with exhalation valves.
Although face shields block the initial forward motion of the jet, the ejected droplets move around the visor relatively easily and spread over a large area depending on minor environmental disturbances.
Testing of face shields and valve masks
To arrive at the study findings, the researchers used qualitative visualizations to test how face shields and valve masks work to prevent the spread of aerosols, which are tiny droplets suspended in the air when an infected person sneezes, coughs, talks or breathe.
In the test, the researchers found that although face shields block the initial forward movement of the jet, the ejected droplets can move around the visor and spread over a large area. On the other hand, the displays for masks with exhalation valves showed that a considerable number of droplets pass through the valve unfiltered, thus reducing the effectiveness of the mask.
To see the performance of the face shield, the team used a horizontal laser blade in addition to a vertical laser blade, which shows how the droplets pass through the horizontal plane. The team noted that the face shields prevented the forward spread of the droplets, but the droplets also spread in the opposite direction.
“Our observations suggest that to minimize the spread of COVID-19 in the community, it may be preferable to use a high-quality drape or simply designed surgical masks, rather than face shields and masks equipped with exhalation valves,” the researchers said. . concluded in the study.
Greater comfort
In the midst of the coronavirus pandemic, wearing masks around the world has become the new normal. In some countries, people are not allowed to leave their homes or stay in public places without a mask. Some public vehicles also prohibit passengers from wearing their masks.
The US Centers for Disease Control and Prevention (CDC) recommends the use of hand-sewn cloth masks, which are effective in blocking infectious droplets. Surgical masks are also recommended for greater efficacy and protection, but the health agency says these masks are recommended for healthcare workers. It is important to keep stocks of N95 and surgical masks stable, especially for healthcare workers.
Some people may find it difficult to wear masks all the time, as they find it more difficult to breathe. Since then, many companies have produced masks with exhalation valves. Although these valves are effective for contaminated areas, they may not be recommended for preventing infection. Exhalation valves allow for better breathability and reduce fogging when wearing glasses.
Meanwhile, face shields provide advantages, such as being easier to disinfect and clean, and provide visual communication of facial expression for those with hearing problems, the researchers said.
Although previous studies claim that wearing face shields alone, without a mask, can prevent infections. Shields prevent material ejected from the mouth and nose from spreading when hitting the visor. However, this is true for large respiratory droplets, but may not be as effective for smaller aerosol-sized droplets.
The CDC also released guidance that discourages the use of face shields only as a means to prevent the spread of the coronavirus. The health agency also said that valve masks should not be used when a sterile environment is required.
The best ways to control the spread of the coronavirus are to wear masks in public places, those recommended by health agencies, observe physical distancing, and wash hands regularly. In some countries, they require residents to wear their masks, with face shields, to offer more effective protection.
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