Scientists from Duke University have demonstrated a simple technique designed to test the effects of different mask fabrics and designs to reduce the spread of respiratory droplets when speaking normally,media reported. The study shows that some alternative mask options not only provide little protection, but may be more harmful than not wearing a mask at all.
With the spread of the COVID-19 outbreak, masks have become a mandatory public health necessity in many parts of the world. As the supply of surgical masks and N95 masks has dwindled, these masks have naturally been moved to a medical setting, and the general public is often urged to use anything that can cover their faces when they go out.
Ideally, a homemade mask should have two or three layers, but since there is nothing better, many health authorities around the world recommend alternatives such as scarves, headscarves or neck velvet. Some experts argue: “Any mask or cover is better than none.” “
The originof new research is that Eric Westman of Duke University School of Medicine is trying to find a way to buy masks for a nonprofit organization that helps local high-risk communities. He quickly realized that there were many products on the market, but there was no testing process to verify the efficacy of the masks. “We were trying to decide what type of mask to buy in bulk, and there was very little information about the new material,” Westman said.
So Westman turned to his colleague Martin Fischer, director of Duke University’s Advanced Optical Imaging and Spectroscopy Facility. Using some common laboratory materials, which are available on the market, the researchers developed a cheap and simple system to test how different mask materials effectively block droplets when speaking normally.
“We wanted to develop a simple, low-cost approach that we could share with others in the community to encourage testing of materials, mask prototypes, and accessories,” Fischer explains. “The components of the test instrument are available and easy to assemble, and we have proven that they can provide useful information about the masking effect.”
As a proof-of-concept for testing new technologies, researchers tried out some common masks and mask substitutes. In the test, a speaker wearing a mask repeated the phrase “stay healthy, everybody” for ten seconds, while the laser illuminates any droplets from the mask.
“We’ve shown that when people talk, small droplets are excreted, so disease can be spread by talking without coughing or sneezing,” Fischer said. “We can also see that some masks perform much better than others when it comes to blocking the particles that are being discharged.”
Unsurprisingly, N95 masks are the most effective way to reduce the spread of droplets, while surgical masks are relatively close. However, most of the tests have a strong effect on homemade cotton masks, blocking droplets at a similar rate to what is seen in surgical mask tests.
Unfortunately, not every mask is effective in reducing the spread of droplets. Knitwear and headscarves are significantly weaker in reducing the spread of droplets. But what really surprised the researchers was the results of testing the neck mask.
“The idea that ‘there’s always better than nothing’ doesn’t hold the case,” Westman said of the test results of the neck mask. Westman said the amount of particles emitted through the neck mask was similar to the volume seen in baseline tests that did not wear the mask at all.
“We think this is because velvet and textiles break down those large particles into many small particles. They tend to stay in the air longer and are more likely to be taken away from the air,” he explains.
The study suggests that wearing such masks could eventually be counterproductive, putting a greater risk of transmission than not wearing a mask. But this conclusion is still firmly hypothetical, and the study does not clearly prove that wearing a neck mask exacerbates the spread of the virus. Instead, the study suggests that the phrase “there’s always better than nothing” may not be true.
It is important to note that this type of droplet propagation study only investigates the physical properties of droplets that are excreted from our mouths when we speak. So far, there is no evidence that these studies could be used to draw conclusions about the spread of the virus.
Another limitation of this particular study is that the test device cannot detect the smallest aerosol particles. The commonalities of the materials used in the test, including a smartphone camera as a recording device, meant that small aerosol droplets could not be measured. While the scientific community is not sure whether aerosol emissions are an important form of SARS-CoV-2 transmission, this novel technology only provides data on what mask materials can effectively reduce emissions of larger droplets.
In the case of exhalation valves, the study found that there was little difference between droplet emissions from N95 masks with exhalation valves and non-medical cloth masks. This suggests that while the N95 mask with a breathing valve protects the wearer, it is not particularly safe for those around the wearer because the exhalation valve produces strong outward air flow – a finding that was recently echoed in the updated CDC mask guidelines, urging against wearing a mask with a exhalation valve.
Fischer suggests more work is needed to understand what kind of masks are best in our new COVID-19 reality. In the short term, he hopes the simple method developed by the Duke team could be easily used by mask manufacturers to test the products they are developing.
“It’s just a demonstration — and more work is needed to investigate masks and how people wear them — but it shows that this test can be easily done by businesses and others that provide masks for employees or customers,” Fischer said.
The new study was published in the journal Science Advances.