As the number of new cases of coronavirus continues to rise nationwide, the recurring message from many public health experts and doctors is simple: wearing masks saves lives.
“We are not defensive against covid-19,” Robert Redfield, director of the Centers for Disease Control and Prevention, said in July. “Blankets of face covering are one of the most powerful weapons we have to slow down and stop the spread of the virus – especially when it is universally used in a community setting.”
But as face masks have become increasingly common in American life, so do questions about effectiveness – and now a group of Duke University researchers are aiming to provide some answers.
In a recently published study, the researchers unveiled a simple method to evaluate the effectiveness of different types of masks, and analyzed more than a dozen different face coverings, ranging from hospital-grade N95 respirators to bandanas. Of the 14 test masks and other covers, the study found that some easily accessible cotton cloth masks are about as effective as standard surgical masks, while popular alternatives, such as neck holes made of thin, stretchy material, may be less than no mask to wear at all. .
“You can really see that the mask is doing something,” said one of the study’s co-authors, Warren S. Warren, a professor of physics, chemistry, radiology and biomedical engineering at Duke. “There’s a lot of controversy and people say, ‘Well, masks do nothing.’ So, the answer is that some do not, but most do. “
The search for a way to determine the effectiveness of various masks began with a request from a professor at Duke Medical School, who worked to provide caring and underserved populations in Durham, NC, with the critical face coverings, according to a news release from the university. Confronted with so many varieties of masks that all claim to have virus-blocking capabilities, the professor sought help – in the university’s physical department.
Introduce Martin Fischer, a chemist and physicist.
Using a simple contraption that uses the power of a laser, which can be easily purchased online for less than $ 200, and a camera from a mobile phone, Fischer created a device that allows his team to support individual particles released from a person’s mouth as they speak. The rest of the set-up includes a box that can be made of cardboard and a lens.
“It’s very simple, does not take up many resources,” Fischer said in a video produced by Duke. “Every research lab has run these things.”
Testing the face coverings was equally complicated, according to the study published Friday in Science Advances, a peer-reviewed journal.
Speakers said the same syllable in the box without mask and then repeated the process again while wearing one. Each face covering was tested 10 times. Inside the device, the airborne particles passed through a bright light produced by the laser that hit the lens and produced visible flashes that were captured by the phone’s camera.
“Even very small particles can do this kind of (light) scattering,” Warren said. “We could use the distribution, and then track individual particles from frame to frame in the film, to actually count the number of particles that were exposed.”
A custom N95 mask, mostly used by hospital workers, was the most effective, Warren said, noting that the mask could “come out no drops at all.” Meanwhile, a breathable neck climber, well liked by tour guides for its light weight, ranked less than the control group without a mask. The gaiter tested by the researchers was described in the study as a ‘neck fleece’ made from a polyester spandex material, Warren said.
“These neck braces are extremely common in many places because they are very comfortable to wear,” he said. “But the exact reason they’re so handy, which is that they do not restrict air, is the reason why they do not do much of a job to help people.”
The high droplet count could be linked to the porous dust of the neck vessel, which breaks up larger particles into many small ones that are likely to hang in the air longer, Fischer said in the video. This effect makes wearing them potentially “counterproductive,” he added.
“It’s not the case that every mask is better than nothing,” he said. “There are some masks that actually hurt or do good.”
Other types of face masks that may fall into that category include bandanas and knit masks, the study found. An N95 mask with an exhalation valve also failed to measure.
“Those relief valves are fantastic as anything you want to do to protect yourself from the outside world because air doesn’t come through them,” Warren said. “If what you are trying to do in this pandemic is to protect the outside world from you, defeat the target completely.”
Warren encourages people to evaluate their face coverage with another basic test.
“If you can see through it if you put it on a light and you can easily blow it through, it’s probably no one to protect.”
However, he stresses that people without access to medical-class masks need not worry.
“We are not like a society that everyone will wear one-off N95 face masks,” he said. “It’s not affordable, and it’s not affordable.” The researchers specifically noted the effectiveness of regular cotton fabric masks, and found that several of the tests performed were similar to surgical masks, which come in second at the N95. Experts with the World Health Organization have recommended that dust masks should ideally have three layers.
Although the study was “not a clinical trial” that included tests of “10,000 patients in seven different languages and all possible circumstances,” Warren said in his general conclusions.
“We are very careful not to claim too much here,” he said. ‘We will not try to prove that our proof is that this is the thread count you need to use on the worksheet for the two-layer cotton mask you make.
“But the broad image of taking home – that masks work in cutting transmission and that some masks you can easily get are better than others – has potential value in protecting everyone and us from this dire situation, he added.
Warren said he and his fellow researchers are now focused on producing a step-by-step instruction manual for making the test device. The team has already been approached by people from foreign countries who have expressed interest, he said.
“It is quite possible for people with a modest amount of scientific training to use this fairly safely and reasonably effectively,” Warren said, noting that he does not recommend that the average person go out and try to construct the device himself. “The idea is that you could have community centers, groups that help test different designs. Especially since we are trying to supply a face of masks to a large number of people who do not have them, you want to supply those who work. “
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