Dr Eric Westman was helping a nonprofit organization Durham provide free masks to people in need when he decided he needed to find out if the masks would really prevent the spread of the coronavirus.
But it was not simply a matter of searching the internet to see which masks worked best. That was April, and at the time researchers had not tested the variety of home-made masks and makeshift face masks most people wear now, Westman said.
“No one had studied it before,”; he said in an interview. “The situation was new.”
So Westman, an associate professor at Duke University Medical School, asked the Duke physics department if he could try different types of masks and face masks for him.
The results, published Friday in the journal Science Advances, not only helped the nonprofit Cover Durham choose the right masks, Westman said, they also show that testing the effectiveness of face masks is not that difficult.
And to the surprise of Duke researchers, the study also found that some types of veils are worse than not wearing a mask at all.
Martin Fischer took over the task of designing the test. Fischer, who runs the Advance Imaging and Spectroscope facility in Duke, used a method developed by researchers at the National Institutes of Health to measure the tiny droplets of moisture that are expelled from our mouths when we speak. These spots can be carried by a coronavirus from a person who is infected.
Fischer and his team had someone speak to the side of a box, saying “Stay healthy, people,” over and over again, first without a mask and then wearing 15 different types of covers. A laser light passing through the box illuminated the spots in the air, which were then recorded with cell phone videos.
Fischer, who usually works with solid materials, said he was amazed by what he saw.
“It was just an opener to see all those particles that glow in our laser beam,” he said.
With the help of a computer, the team then counted the visible points in the video to determine which overlays allow the most.
Not surprisingly, the fewest (almost zero) points were detected with an N95 fitted mask, those used by doctors, nurses and other healthcare workers in the highest risk environments. A surgical mask was a close second.
Masks made of polypropylene also did very well, but so did different types of two-layer cotton masks. Some of the cotton masks produced less than 20% more particles than someone who had no masks.
Less effective was the bandana, which allows about 50% as much grain as someone who wears no mask at all.
But the worst performer was the guitar, which people wear around their necks and pull their faces up like a mask. The one who tested the Duke team made things worse. Instead of preventing the escape points, he turned the larger points into a small cloud, which hung in the air longer.
“Using such a mask can be counterproductive,” the researchers wrote in their paper. Or, as Westman said Monday, “The idea that something is no better than nothing may not be true.”
The paper refers to the shell as a “neck fleece”, but Martin says it was made of polyester mixed with a little barley, not cotton leaves. He said it seems that the act of pulling the guitar over your face allows the particles to pass.
“You can see that the material was very thin,” he said. “So if you spread it over your mouth, it becomes even thinner.”
Martin notes that Duke researchers tested only one type of neck guitar. In fact, he said, the study was never intended to be a comprehensive test for all masks and mask materials.
“The focus of the study was to develop a simple technique for testing masks so that people could copy and paste themselves,” he said. “This is, as far as we know, the simplest and easiest way to do this. We set this up on a weekend with things we had laid out in the lab.”
With the COVID-19 pandemic showing no signs of disappearing, interest in the Duke study has been high. Martin said he had 130 emails about him as of Monday morning, including requests for interviews from newspapers, wire services, CNN, CBS and the BBC.
An email came from a doctor hoping to repeat the tests in Central Africa. Some came from people who just want the Duke team to try on their masks (Duke does not have the manpower to do so, Martin said).
Westman said all the attention in the study could also underline that a person does not need to cough or sneeze to spread the coronavirus.
“If you do not know that speech can spread particles that can spread the virus, you should know this,” he said. “This was confirmed over and over again in the hundreds of trials we did.”