Inexpensive, accessible device provides visual evidence that masks block drops

Duke Eric Westman was one of the first champions of masking as a means of curbing the spread of coronavirus, and worked with a local nonprofit to provide free masks to at-risk and under-served populations in the greater Durham community. .

But he needed to know if the makers of blocking claims masks were true, to ensure that he did not supply ineffective masks that spread viruses along with false security. That he turned to colleagues in the Duke Department of Physics: Could anyone test different masks for him?

Martin Fischer, Ph.D., in chemistry and physics, stepped up. As director of the Advanced Light Imaging and Spectroscopy facility, he normally focuses on exploring new optical contrast mechanisms for molecular imaging, but for this task he MacGyvered a relatively inexpensive device made from ordinary lab material that can be easily purchased online. The set-up consisted of a box, a laser, a lens and a camera for mobile phones.

In a proof-of-concept study that will appear online in the journal on August 7th Science Advances, Fischer, Westman, and colleagues report that the simple, low-cost technique provided visual evidence that face masks are effective in reducing droplet emissions during normal wear.

“We have confirmed that when people talk, small droplets are expelled so that disease can be spread by talking, without coughing or wheezing,” Fischer said. “We could also see that some face coatings performed much better than others in blocking expelled particles.”

Notably, the researchers reported, the best face coverings were N95 masks without valves – the hospital-grade covers used by health care workers. Surgical and polypropylene masks also performed well.

But hand-made cotton face coat provided good coverage, eliminating a substantial amount of the spray from normal speech.

On the other hand, bandanas and neck fleeces like balaclavas do not block the drops at all.

“This was just a demonstration – more work is needed to investigate variations in masks, speakers and how people wear them – but it proves that this type of test could easily be performed by companies and others who supply masks to their employees. or patrons, ”Fischer said.

“Wearing a mask is a simple and easy way to reduce the spread of COVID-19,” Westman said. “About half of infections come from people who have no symptoms, and often do not know they are infected. They can spread the virus unconsciously like coughing, sneezing and just talking.

“If everyone wore a mask, we could stop up to 99% of those drops before they reach anyone else,” Westman said. “In the absence of a vaccine or antiviral drug, it is the only proven way to protect others than yourself.”

Westman and Fischer said it is important that companies provide masks to the public and employees have good information about the products they supply to ensure the best protection possible.

“We wanted to develop a simple, low-cost method that we could share with others in the community to encourage testing of materials, prototypes and masks for masks,” Fischer said. “The test device components are accessible and easy to assemble, and we have shown that they can provide useful information on the effectiveness of masking.”

Westman said he immediately put the information to use: “We were trying to make a decision on what type of face covering to buy in volume, and not much information was available about these new materials being used.”

The masks he intended to buy for the “Cover Durham” initiative?

“They were not good,” Westman said. “The idea that ‘everything is better than nothing’ does not apply.”