Face shield, mask with ineffective valves against COVID-19 diffusion: study


However, face shields inhibit the initial forward motion of the jet, the ejected droplets move smoothly along the relative and diffuse over a large area depending on the disturbance of the light ambient. Credit: Florida Atlantic University College of Engineering and Computer Science

If the United States Centers for Disease Control and Prevention (CDC) guidelines are not sufficient to convince you that a face shield alone should not be used to prevent the spread of CO gradient-19, perhaps a new visual study will occur.


To raise public awareness of the effectiveness of facial masks with facial shields as well as exhalation valves, researchers at Florida Atlantic University’s College of Engineering and Computer Science tested using qualitative visualization that aerosols How face shields and masks with valves perform in inhibiting diffusion. -Sized drops. The widespread public use of these options for regular masks could potentially adversely affect mitigation efforts.

For the study, just published in the journal Physics of fluids, The researchers employed a laser light sheet and flow visualization in a laboratory setting using a mixture of distilled water and glycerin to generate the synthetic fog that formed the cuff-jet material. He imagined drops expelled from the mouth of an effigy, simulating coughing and sneezing. By applying a plastic face shield and an N95-rated face mask with a valve, they were able to map the droplet paths and demonstrate how they performed.

The results of the study indicate that although the face gradient blocks the initial forward motion of the jet, the ejected droplets move around the visior with relative and diffuse over a large area depending on the disturbance of the light ambient. Visualizations for face masks equipped with exhalation ports indicate that a large number of droplets pass through the exhaled valve, significantly reducing its effectiveness as a means of source control.

To demonstrate the performance of the face gradient, the researchers used a horizontal laser sheet in addition to a vertical laser sheet, which shows how the droplets cross the horizontal plane. Not only did the researchers observe further propagation of the droplets, they found that the droplets also propagate in the reverse direction. Credit: Florida Atlantic University College of Engineering and Computer Science

“From this latest study, we were able to observe that the face shields are capable of blocking the initial anterior motion of the exhaled jet, however, the aerosolified droplets expelled along the jet rotate around the cap with relative ease. Are capable, ”said Manohar Dhanak. , PhD, Department Chair, Professor, and Director of CTech, who co-authored the paper with Siddharth Verma, PhD, lead author and an assistant professor; And John Frankfeld, a technical professional within FAU’s Department of Ocean and Mechanical Engineering. “Over time, these droplets can spread over a wide area in both lateral and longitudinal directions, albeit with decreasing concentration.”

To demonstrate the performance of the facial gradient, the researchers used a horizontal laser sheet in addition to a vertical laser sheet, which shows how the droplets cross the horizontal plane. Not only did the researchers observe further propagation of the droplets, they found that the droplets also propagate in the reverse direction. In particular, the face shield somewhat impedes the forward motion of the exhaled drops, and the masks with valves do so to an even lesser extent. However, once released into the environment, aerosol-shaped droplets are widely dispersed depending on the disturbance of light ambient.

Face shield, mask with ineffective valve against COVID-19 diffusion

The far-field view of a droplet expands when a face shield is used to interrupt the jet at 2.97 seconds after the initiation of the emitting cough. Credits: Siddharth Verma, Manhar Dhanak, John Frankfield

Like the N-95-rated face masks used in this study, other types of masks such as some fabric-based masks that are commercially available are equipped with one to two exhale ports located on either side of the facemask. The N95-rated face mask with exhale valves used in this study had a small amount of exhaled drops that survived the gap between the top of the mask and the bridge of the nose. In addition, the exhalation port significantly reduced the effectiveness of the mask as a means of source control, as a large number of droplets through the valve became unfiltered and unhealthy.

Face shield or face mask to prevent the spread of COVID-19?

Researchers also tested an N-95 rated face mask with exhalation valves and found that the exhalation port significantly reduced the effectiveness of the mask as a means of source control, as a large number of droplets passed through the valve. Becomes unfiltered and unhealthy. Credit: Florida Atlantic University College of Engineering and Computer Science

“There is a growing trend of people replacing regular cloths or surgical masks with clear plastic face shields who are using masks equipped with exhalation valves,” Verma said. “One driving factor for this increased adoption is better comfort than a regular mask. However, the face shield has noticeable gaps along the bottom and sides, and a one-way valve in the mask with exhaling ports. Is included that restricts airflow when inhaled, but allows free outflow of air. Breathing air is filtered through the mask material, but exposed through the exhalation valve. ”

Researchers say that key passages from this latest study indicate that facial shields and masks with exhalation valves may not be as effective as regular facial masks restricting the spread of aerosolified droplets. Despite the increased comfort that these options offer, they say that it may be better to use well-made, high-quality fabrics or surgical masks that have a plain design rather than a face shield and mask equipped with an exhaled valve. Occur. The widespread public use of alternatives in lieu of regular masks may possibly adversely affect ongoing mitigation efforts against COVID-19.

Droplet visualization occurs when an N95 mask equipped with an exhalation port is used to interrupt the emerging jet. Credits: Siddharth Verma, Manhar Dhanak, John Frankfield

“The research done by professors Dhanak and Verma on the importance of proper face covering to prevent the spread of COVID-19 has truly illuminated the world,” said FAU’s College of Engineering and Computer Science Dean, Stella Batalama. “While there has been a rapid increase in widespread acceptance of the need for face coverings, there is a growing trend of people who are regularly replacing clothing or surgical masks with clear plastic face shields, and by exhalation valves. With equip masks. These latest researches are important evidence. Support CDC guidelines more and inform the public to make better selection in their choice for face coverings for their benefit and for public safety. ”


Can I use a face shield instead of a mask?


more information:
“Squeezing droplet for facial shield and mask with exhalation valve” Physics of fluids, aip.scitation.org/doi/pdf/10.1063/5.0022968

Provided by Florida Atlantic University

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