Three-dimensional masks are most effective against large breath drops

If you are going to buy a face mask to protect yourself and others from COVID-19, make sure it is a three-dimensional mask. You may have heard this suggestion already, but researchers have now found an additional reason why triangular masks are safer than other single – layered or double – layered alternatives.

Although this advice was originally based on studies that showed that three layers prevent small particles from passing through the pores of mascara, researchers have now shown that three-masked surgical masks lateral is also most effective in preventing large droplets from coughing or sneezing from getting atomized into smaller droplets. These large droplets can pass through the single- and double-fold masks and atomize into much smaller droplets, which is especially crucial as these tiny droplets (often called aerosol) are able to stay in the air for longer periods. Researchers studied surgical masks with one, two, and three layers to reveal this behavior.

The researchers described their findings in Advances in science on 5 March.

The team notes that single-layer and double-layer masks provide protection in preventing some of the melting volume of the original drop and are much better than wear without a mask at all. They hope that their decisions on appropriate pore mascara size, material thickness, and healing could be used by manufacturers to achieve the most effective mask designs.

Using a droplet generator and a high-speed camera, the team of engineers from the University of California San Diego, Indian Institute of Science and the University of Toronto suddenly discovered large respiratory droplets containing virus-reporting (VEP) particles. atomization when they hit a single-layer mask, and many of these VEPs pass through that layer. Think of it as a drop of water breaking into smaller drops while pushing it through a sieve. For a 620 micron droplet – the size of a large droplet from coughing or sneezing – a single-layer surgical mask limits only about 30 percent of the droplet size; a double-layer mask performs better, limiting about 91 percent droplet size; although a three-layer mask has very little droplet pressure.

“While it is expected that large solid particles in the 500-600-micron range should be stopped with a single-layer mask with an average pore size of 30 microns, we show that this is not true for melt droplets,” he said. Abhishek Saha, professor of mechanical and aerospace engineering at UC San Diego and co-author of the paper. “If these larger respiratory droplets, which happen to cough or sneeze, have enough distance, when they land on one layer of this material it will get scattered and squeezed through the smallest pores in the mask.”

This is a problem. Droplet physics models have shown that while these large droplets are expected to fall to the ground very quickly due to gravity, these droplets will now be smaller, 50-80 microns coming through. first and second layer of mask lying in the air, where they can spread to humans at greater distances.

The team of engineers – which also includes Swetaprovo Chaudhuri Professors from the University of Toronto, and Saptarshi Basu from the Indian Institute of Science – were well acquainted with this type of experiment and analysis, although they were used to ‘study of aerodynamics and physics of droplets for applications involving propulsion, combing, or thermal shower systems. They turned their attention to the physics of respiratory droplet last year when the COVID-19 pandemic broke out, and since then, they have been studying the transport of these respiratory droplets and their roles in the spread of type 2 infections. Covid-19.

“We do a lot of droplet impact tests in our labs,” Saha said. “For this study, a special generator was used to extract a relatively fast droplet. The droplet was then allowed to land on a piece of mask material – that could be a single-row, double, or triple, depending on what; we do a test. At the same time, we use a high-speed camera to see what happens to the droplet. “

Using the droplet generator, they will be able to change the size and speed of the droplet to see how that affects the flow of the droplet.

Going forward, the team plans to investigate the role of various mask materials, as well as the effect of wet or wet mask, on material repellency.

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