Study Identifies Face Coverings That Are Most And Least Effective

Henrietta Strickland
August 10, 2020

The quest began when a professor at Duke's School of Medicine was assisting a local group buy masks in bulk to distribute to community members in need.

In the study, the scientists evaluated the effectiveness of 14 different types of masks and other frequently substituted face coverings, using a simple approach in which either one male speaker or, in some cases, four speakers wore each mask while standing in a dark enclosure. "The laser beam is expanded vertically to form a thin sheet of light, which we shine through slits on the left and right of the box".

A computer algorithm then counted the droplets seen in the video to determine how many had leaked through.

They found that the best masks were the surgical N95 masks, which are professionally fitted and mostly used by healthcare workers. First the test was performed with a speaker talking without wearing a mask. So he turned to colleagues in the Duke Department of Physics: Could someone test various masks for him?

In a proof-of-concept study appearing online August 7 in the journal Science Advances, Fischer, Westman and colleagues report that the simple, low-priced technique provided visual proof that face masks are effective in reducing droplet emissions during normal wear. That would be N95 masks without valves, followed by surgical or polypropylene masks.

According to the researchers from Duke University in the United States, the preliminary, proof-of-principle findings suggest that professional-grade N95 masks, surgical or polypropylene masks, and handmade cotton masks may all block much of the droplet-spray produced when wearers speak.

On the other hand, bandanas and neck fleeces such as balaclavas didn't block the droplets much at all.

The scientists also discovered that neck fleeces, or neck gaiters, often worn by runners, were the least effective and actually allowed more respiratory droplets to escape than not wearing a mask at all.

"We were extremely surprised to find that the number of particles measured with the fleece actually exceeded the number of particles measured without wearing any mask", Martin Fischer, one of the study's authors told CNN.

"This was just a demonstration - more work is required to investigate variations in masks, speakers, and how people wear them - but it demonstrates that this sort of test could easily be conducted by businesses and others that are providing masks to their employees or patrons", Fischer noted further.

They relied on a makeshift apparatus consisting of a box, a laser, a lens and a cellphone camera.

The researchers tested how effective each mask was at reducing the number of respiratory droplets transmitted during speech.

"This is a very powerful visual tool to raise awareness that a very simple masks, like these homemade cotton masks, do really well to stop the majority of these respiratory droplets", Fischer said.

Other reports by Click Lancashire

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