Wearing double-layer masks may not significantly improve efficiency

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Wearing double-layer masks may not significantly improve efficiency

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Study says face shape affects mask fit, wearing double-layer masks may not significantly improve efficiency. 

In an updated guidance in early 2022, the Centers for Disease Control and Prevention (CDC) said that loose cloth masks are the least effective at preventing the spread of COVID-19, while N95 and KN95 masks provide the most protection.

Still, more than two years after the pandemic began, the characteristics of masks for optimal protection are still not fully understood.

In Fluid Physics , published by AIP Press , researchers at Florida State University and Johns Hopkins University use principal component analysis (PCA) along with a fluid dynamics simulation model to show the correct fit of all types of masks The importance of fit and how face shape affects the optimal fit.

The study suggests that wearing two layers of an ill-fitting mask may not significantly improve the effectiveness of the mask and create a “false sense of security”.

More layers means the mask is less porous, causing more airflow to be forced out of the mask’s perimeter voids (sides, top, and bottom), and the mask is less secure. Double-layer masks can improve filtration efficiency only with good mask fit, but can also cause breathing difficulties.

The researchers simulated moderate coughing airflow from the mouth of an adult male wearing a cloth mask with elastic bands around his ears. They calculated the maximum volumetric flow rates through the front and perimeter gaps of the mask at different levels of material porosity.

To obtain a more realistic three-dimensional face shape and size, the researchers used PCA, which integrates head data from 100 adult males and 100 adult females retrieved from head scan data at the University of Basel in Switzerland. PCA condenses a large set of variables while retaining most of the information.

Their model shows how the slight asymmetry typical of all facial structures affects correct mask fit. For example, a mask may fit better on the left side of the face than on the right side.

“The asymmetry of the face is almost imperceptible to the eye, but is evident in the cough airflow through the mask,” said co-author Tomas Solano of Florida State University. “For this particular case, the only unfiltered leakage observed was through the top. However, leakage through the bottom and sides of the mask is also possible for different face shapes.”

Creating “designer masks” that are customized to each person’s face is not practical at scale.

Nonetheless, PCA-based simulations can be used to design better masks for different populations, revealing general differences in the facial structure of men and women or children and the elderly and the associated airflow through the masks.

Wearing double-layer masks may not significantly improve efficiency

(source:internet, reference only)

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