Home-made masks with multiple layers provide more protection from virus droplets

Fabric face masks with more layers provide more protection from COVID-19 virus say NSW researchers

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UNSW researchers compared one and two layer home-made masks with 3 ply surgical masks.

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Has the issue of whether or not to wear a mask to prevent the spread of COVID-19 and if so what sort, got you confused? Well you're not alone.

It's an argument that's raged across the world for months but as cases have escalated more and more cities and countries have advocated voluntary or even compulsory mask use.

Here in Australia, Victoria has introduced compulsory mask wearing in public in Melbourne and the Mitchell shire and in regional areas where social distancing is not possible, to help stop the spread of the deadly disease.

Well now Australian researchers have done the research and the results, published in the journal Thorax, are clear.

Scientists at the University of NSW compared one and two layer home-made masks with 3 ply surgical masks and found a surgical mask is the most effective at blocking droplets and aerosols from talking, coughing and sneezing. But if you can't get hold of one, a cloth mask is the next best thing, and the more layers the better.

Viral droplets are released when talking, coughing or sneezing.

Viral droplets are released when talking, coughing or sneezing.

Viral droplets are generated during coughing, sneezing, or speaking. And face masks are thought to protect healthy people from inhaling infectious droplets as well as reducing the spread from those who are already infected.

You can be infected with the coronavirus, but not show symptoms. So you cannot identify an infected person just by looking at them. And you may be infected (and infectious) but not know it.

But worldwide shortages of personal protective equipment during the pandemic have led some health agencies, such as the US Centers for Disease Control (CDC), to recommend the use of home-made cloth face coverings as an alternative to surgical face masks.

Several types of material have been suggested for these, but based on little or no evidence of how well they work.

The team of NSW researchers therefore compared the effectiveness of single and double-layer cloth face coverings (175 g/m cotton fabric, with a thread count of 170/ inch) with a 3-ply surgical face mask (Bao Thach) at reducing droplet spread.

The single layer covering was made from a folded piece of cotton T shirt and hair ties; the double layer covering was made using the sew method, as set out by CDC:

https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/how-to-make-cloth-face-covering.html

The researchers used a tailored LED lighting system and a high-speed camera to film the dispersal of airborne droplets produced by a healthy person with no respiratory infection, during speaking, coughing, and sneezing while wearing each type of mask.

The video recording showed that the 3-ply surgical face mask was the most effective at reducing airborne droplet dispersal, although even a single layer cloth face covering reduced the droplet spread from speaking.

But a double layer covering was better than a single layer in reducing the droplet spread from coughing and sneezing, the recording showed.

This is just one case, added to which several other factors contribute to the effectiveness of cloth face masks, note the researchers. These include the type of material used, design and fit, as well as the frequency of washing.

Nevertheless, based on their observations, a home made cloth mask with at least two layers is preferable to a single layer mask, they say, adding: "Guidelines on home-made cloth masks should stipulate multiple layers."

And they emphasise: "There is a need for more evidence to inform safer cloth mask design, and countries should ensure adequate manufacturing or procurement of surgical masks."

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