Study finds Tennessee masks as effective as some surgical masks

Jonathan Roberts • May 23, 2020 at 8:00 AM

Tennessee’s novel coronavirus masks may be as effective as some surgical masks, a study by the Knoxville News Sentinel and a professor running a cloth mask testing project at Northeastern University found.

Tennessee’s mask contract was criticized by some state lawmakers and others on social media, as the one-layer fabric material was partially see-through when held up to a light source — bringing into question the effectiveness of the masks, for which Tennessee paid $8.2 million.

Knoxville Rep. Gloria Johnson likened the masks to “chicken wire,” while Bristol Sen. Jon Lundberg — who defended the contract, but had not seen the masks in person — said general concerns about the effectiveness of a mask that’s at least somewhat porous were “valid.”

In a statement to the Press earlier this month, Dean Flener, a spokesperson for Lee’s Unified Command Group, defended the purchase of the masks, saying “neither this mask, nor any other cloth face mask is intended for medical use,” and “it’s also important to note that even when wearing a cloth face mask or covering, Tennesseans still need to observe social distancing and public gathering guidelines when they are out in public.”

The Centers for Disease Control and Prevention recommends that cloth masks be made of multiple layers, something lead researcher and Northeastern engineering professor Amy Mueller said helps increase the filtration efficiency of homemade masks. The CDC also recommends masks be breathable, which Flener pointed to as well when discussing their standards.

According to the test results, the masks — which Tennessee ordered five million of — can effectively filter about 60.5% of particles. The tests were repeated three times, continually counting the number of particles just inside and outside the breathing area to determine filtration efficiency.

Mueller said “we generally tend to be skeptical of (masks) that only have one layer, and that’s just something that previous data has shown — that multiple layers do better,” but that she was “impressed with its filtration efficiency” for only having one layer. Muller also said it’s possible the masks become more effective as they’re washed by puffing up the fibers, and said “if people are worried about a one-layer mask, it’s really easy to add a second layer.”

“Sixty-percent filtration is kind of in the middle of all the range that we’ve seen, it’s obviously not the top,” Mueller said. “I can say as a reference point some of the surgical masks that we’ve tested, if you just wear them right out of the box how they’re designed to be worn, they range in effectiveness from 50-75% because they are also loose fitting.

“That’s a benchmark that tells you you’re in the range of some other options that people would look at and think are effective,” Mueller said, “but I actually think this is a big open question for the public health experts: What percent effectiveness on masks do we need in order for it to be highly impactful to society as a public health protection initiative?”

One study, published in the New England Journal of Medicine, found that if just 60% of the population wears a mask that is at least 60% effective at preventing particles from escaping, a virus or disease could be eliminated. And while the Tennessee masks have a filtration efficiency around that mark, there’s one caveat: Mueller wasn’t testing the masks as public health tools (i.e. how well they prevent particles from escaping), but rather testing them as personal protective equipment (i.e. how well they prevent particles from getting in).

Still, Mueller said it’s “reasonable” to assume the mask would be as good at keeping particles in as it is in keeping them out.

And while some homemade masks can filter up to 90% of particles, Mueller said Tennessee’s masks are trading breathability for filtration efficiency, and that “that's a balance that individuals have to make and that there’s probably not one answer that’s right for everybody.”

Reached by phone Friday afternoon, Lundberg said the masks are a good way to give people access to masks they might not otherwise have. When told about the results, Lundberg said, “I would say then, not only is it proving itself valuable in the short term, but in the long-term it can become even more valuable.”

Johnson said Friday that the results are promising, and hopes the masks are widely used, but expressed concerns about the nature of the no-bid contract given to Renfro.

“I never doubted that they were better than nothing,” Johnson said. “My question is, how effective are they? And how come it’s a no-bid contract?

“Part of the frustration became, ‘we’re not sure how good these masks are, and we spent $8.2 million dollars of Tennessee money on something that we’re not sure works’,” Johnson added. “If it works that’s great, if the science says it’s there I’m glad, I’m definitely glad — but I also want to revisit (the contract).”

For more information on the mask testing project results or its methodology, visit https://www.masktestingatnu.com. 

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