According to new research from the West Virginia University School of Medicine, the combination of a disposable surgical mask as an underlayer with a tightly-fitting fabric outer layer significantly improves filtration efficiency and protection.
Earlier this month, the Centers for Disease Control and Prevention recommended that Americans start doubling up on masks. The new guidelines suggest that a cloth mask or gaiter be layered on top of a surgical mask to better protect the wearer and others from COVID-19.
According to new research from the West Virginia University School of Medicine, the combination of a disposable surgical mask as an underlayer with a tightly-fitting fabric outer layer significantly improves filtration efficiency and protection. The overall goal for so many researchers has been to achieve comparable protection as that observed for the industry gold standard N-95-rated respirators which have been in very limited supply since the beginning of the pandemic.
That’s because cloth masks and gaiters tend to fit well but do not filter as well as N-95 masks. Surgical masks, on the other hand, are made of material that excels at filtering, but they don’t fit as tightly against the face.
“If you put a good-fitting mask on top of a good filter, you get the best of both, and that significantly increases the fit and protection of the mask,” said Timothy R. Nurkiewicz, who directs WVU’s Center for Inhalation Toxicology and led the research project.
Another recent study—which the CDC and the National Institute for Occupational Safety and Health conducted—revealed that double masking can filter out up to 96% of droplets inhaled if both the source exhaling the droplets and breather inhaling them are double masked.
But “while very exciting, that study did not use the WVU masks that are distributed when people are COVID-tested at the beginning of the semester,” said Nurkiewicz, the E.J. Van Liere Endowed Professor and chair of the Department of Physiology and Pharmacology.
“One of the goals of their study was reproducibility so it relied on mechanical ventilators—embedded in molded head forms—to ‘inhale’ or ‘exhale,’ instead of humans.
“Because our concern is with the students, the staff and the faculty—and the equipment that we’re handing out—we felt it was important to repeat those studies,” he said. “We wanted to test it in a way that incorporated our masks and actual humans.”
Nurkiewicz and his colleagues recruited four participants to wear three types of masks individually: a disposable surgical mask and the cloth mask and gaiter that WVU distributes to students, faculty and staff members.
The participants also wore the surgical mask under the cloth mask, and the surgical mask under the gaiter.
The researchers performed quantitative fit testing for each type of mask at the WVU Inhalation Facility. To do so, they filled the room with saline droplets, “which we put into the air with something that looks very much like your household humidifier that you would use in winter months,” said Karen Woodfork, a teaching associate professor in the Department of Physiology and Pharmacology who was part of the research team.
Then a machine counted the number of saline droplets inside the mask—next to the wearer’s face—and compared them to the number in the ambient air (outside the mask). That comparison indicated how well the mask filtered out the droplets.
The researchers found that the cloth mask worn over the surgical mask performed the best, with a filtration efficiency of 84%. In other words, out of every 100 droplets in the air, the double mask filtered out 84 of them.
The gaiter worn over the surgical mask performed almost as well, with a filtration efficiency of 81%.
These tests conducted by Nurkiewicz’s team indicate that the CDC’s recommendations are on point: two layers are better than one.
“We’ve all been told that wearing a single mask protects other people from you if you are contagious, but it’s not as effective in protecting you from other people,” Woodfork said. “The research that we’ve done has also borne this out. Single masks do stop those droplets coming out of your mouth from getting into the ambient air, but are not as effective in providing an individual protection from others who are unmasked. Our bottom line is that a double mask provides you with protection for yourself that is significantly better than a single fabric or disposable mask, although it is not a medical-grade N-95 respirator.”
But what if you only have one mask? Is it still worthwhile to wear it?
“Absolutely,” Nurkiewicz said. “We are not mandating double mask wearing. We have previously reported that wearing a single mask is an effective way to contain exhaled droplets and prevent inhalation of droplets. And double masking does not change that observation. It merely strengthens it.”
Doubling up can be particularly valuable if you find yourself in an environment when you want extra protection. Maybe that’s a crowded bus. Maybe that’s a doctor’s waiting room.
Or maybe you’re concerned about the new COVID-19 variants, including the B.1.1.7 variant recently detected in the Morgantown area. The CDC reported that B.1.1.7 spreads more easily and quickly than other variants.
“Double masking is more effective at preventing particles from getting inside the wearer’s respiratory tract,” Woodfork said. “So, if you can block a larger percentage of particles from getting into you, and you’re dealing with a more contagious variant that only needs a few of them to cause an infection, you’re better off with a higher level of filtration from your mask.”
Layering masks can also make sense if you have a preexisting condition or are around other people who aren’t wearing masks themselves.
“Our goal is to educate people about how to double mask—to do the right thing when they need to do it,” Nurkiewicz said.
The “right thing” isn’t always the easy thing, though. Depending on the situation, wearing two masks at once may make breathing feel more difficult than usual.
Nurkiewicz offers reassurance. “What you are experiencing is a change in the way that you breathe. It does require a little bit more force to breathe. Certainly, it’s a small price to pay to get the increased protection. But you’re not robbing your body of oxygen by putting on two masks.”
There’s also no need to worry that carbon dioxide will build up inside your mask, “whether you're wearing one, two, three, four or five masks, gases such as carbon dioxide are not contained by any fabric,” he said.
“One thing we didn’t know at the beginning at the pandemic was how long we would be dealing with this,” he said. “We didn’t know the little things we would start to miss, and how losing those things would affect our daily lives. The immediate benefits of being able to do those things is why double masking has become a very popular topic. It will—in part, at least—contribute to getting us one step closer to normal.”
-WVU-
see/03/04/21
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