The entire world is facing the threat of COVID-19 and the number of people affected by the disease has reached tens of millions. Govts across the globe have issued strict guidelines to reduce the spread of this highly communicable disease. Among all the precautions prescribed by health organizations, face masks are considered the most effective means to combat the virus spread, particularly if used in combination with regular hand hygiene and physical distancing. Wearing of masks across the globe has become the new normal.
There is an increasing trend of substituting regular cloth masks or surgical masks with masks equipped with exhalation valves and clear face shields. However, a new study shows that face shields and masks with valves are ineffective against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Face shield and the N95 respirator mask that has one or two exhale ports or valves, still release infectious droplets into the air.
A new visualization shows why face shields and masks with exhalation valves may not be the best barriers for preventing the spread of COVID-19. Although face shields initially block droplets from a simulated cough, small droplets can easily move around the sides of the visor and eventually spread over a large area, according to the visualization, which is detailed in a study published in the journal Physics of Fluid.
Researchers at Florida Atlantic University used laser light to illuminate the flow of aerosols released when people coughed or sneezed. They used a mannequin to simulate coughing and sneezing while wearing both types of face coverings.
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Their visualizations showed that a large number of potentially infectious droplets were able to escape from the exhale valve on N95s and around the edges of the face shields or visors.
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 Sid Verma, Ph.D., the lead author of the study. “A driving force for this increased adoption is better comfort compared to regular masks. However, face shields have noticeable gaps along the bottom and 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.”
Health departments have already warned residents that N95 masks with valves or openings in the front aren’t safe. The US Centers for Disease Control and Prevention (CDC) does not recommend either of these as alternatives to cloth masks. They recommend using handsewn cloth masks, which are effective in blocking infectious droplets. Surgical masks are also recommended for higher efficacy and protection, but the health agency says that these masks are recommended for health care workers.
The CDC also released a guideline, discouraging the use of face shields only as a means to prevent the spread of the coronavirus. The health agency also said that masks with valves should not be used when a sterile environment is required.