FAU College of Engineering and Computer Science Visualization study illustrates why face shields alone don’t work.
If the US Centers for Disease Control and Prevention (CDC) guidelines aren’t enough to convince you that face shields alone shouldn’t be wont to stop the spread of COVID-19, then maybe a new latest visualization study will.
To increase public awareness about the effectiveness of face shields alone also as face masks with exhalation valves, researchers from Florida Atlantic University’s College of Engineering & Computer science (CS) used qualitative visualizations to check how face shields and masks with valves perform in impeding the spread of aerosol-sized droplets. Widespread public use of those alternatives to regular masks could potentially have an adverse effect on mitigation efforts.
For the study, just published within the journal Physics of Fluids, researchers employed flow visualization during a laboratory setting employing a laser light sheet and a mix of water and glycerin to get the synthetic fog that made up the content of a cough-jet. They visualized droplets expelled from a mannequin’s mouth while simulating coughing and sneezing. By placing a plastic face shield & N95-rated mask with a valve, they were ready to map the paths of droplets and demonstrate how they performed.
Results of the study show that although face shields block the initial straight forward-motion of the jet, the expelled droplets move round the visor with relative ease and opened up over an outsized area counting on light ambient disturbances. Visualizations for the mask equipped with an exhalation port indicate that an outsized number of droplets undergo the exhale valve unfiltered, which significantly reduces its effectiveness as a way of source control.
“From this latest study, we were ready to observe that face shields are ready to block the initial straight forward-motion of the exhaled jet, however, aerosolized droplets expelled with the jet are ready to move round the visor with relative ease,” said Manhar Dhanak, Ph.D., department chair, professor, and director of SeaTech, who co-authored the paper with Siddhartha Verma, Ph.D., lead author and an assistant professor; and John Frankenfeld, a technical professional, all within FAU’s Department of Ocean and engineering . “Over time, these droplets can disperse over a good area in both lateral and longitudinal directions, albeit with decreasing droplet concentration.”
To demonstrate the performance of the face shield, researchers used a horizontal laser sheet additionally to a vertical laser sheet revealing how the droplets cross the horizontal plane. Not only did the researchers observe forward spread of the droplets, they found that droplets also spread in reverse direction. Notably, face shields impede straight motion of the exhaled droplets to some extent, and masks with valves do so to a good lesser extent. However, once released into the environment, the aerosol-sized droplets get dispersed widely based on light ambient disturbances.
Like the N-95-rated mask utilized in this study, other sorts of masks like certain cloth-based masks that are available commercially also come equipped with one to 2 exhale ports, located on either side of the facemask. The N95-rated mask with the exhale valve utilized in this study had alittle amount of exhaled droplets that escaped from the gap between the top of mask and therefore the bridge of the nose. Moreover, the exhalation port significantly reduced the effectiveness of the mask as a way of source control, as large amount of droplets skilled the valve unfiltered and unhindered.
“There is an increasing trend of individuals substituting regular cloth or surgical masks with clear plastic face shields also as using masks that are equipped with exhalation valves,” said Verma. “A driving factor for this increased adoption is best comfort compared to regular masks. However, face shields have noticeable gaps along bottom and therefore the sides, and masks with exhalation ports include a one-way valve which restricts airflow when inhaling , 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 researchers say that the key takeaway from this latest study illustrates that face shields and masks with exhale valves might not be as effective as regular face masks in restricting the spread of aerosolized droplets. Despite the increased comfort that these alternatives offer, they assert it’s going to be preferable to use well-constructed, top quality cloth or surgical masks that are of a simple plan design, rather than face shields and masks equipped with exhale valves. Widespread public adoption of the alternatives, in lieu of normal masks, could potentially have an adverse effect on ongoing mitigation efforts against COVID-19.
“The research conducted by professors Dhanak & Verma on the importance of proper face coverings to prevent the spread of COVID-19 has literally illuminated the worldwide ,” said Stella Batalama, Ph.D., dean of FAU’s College of Engineering and computer Science. “While broad acceptance regarding the necessity for face coverings has risen steadily, there’s an increasing trend of individuals who are substituting regular cloth or surgical masks with clear plastic face shields, and with masks equipped with exhalation valves. This latest research provides important evidence to further support CDC guidelines and inform the general public to form better selections in their choice for face coverings for his or her benefit and for public safety.”