Experiments at UNC-CH put CDC double-masking guidance to the test

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RALEIGH, N.C. (WNCN) – Earlier this month, the CDC’s new guidance said two masks were better than one.

UNC Chapel Hill scientists put that guidance to the test in their own labs.

“I had my skepticism whether I would actually benefit to have two of these masks — one over the other,” said Dr. Phillip Clapp, an aerosol toxicology expert in the Center for Environmental Medicine, Asthma, and Lung Biology, and assistant professor of pediatrics at the UNC School of Medicine.

To test it out, Clapp had a test subject enter a 10 foot by 10 foot chamber. It was filled with harmless particles. Clapp then tested how much made it into masks using different layering combinations.

Typically, a surgical mask or cloth mask alone can blocks about 40 percent of particles.

The experiment at UNC Chapel Hill found:

  • Two surgical masks blocked 15% more particles
  • A surgical mask over a cloth mask blocks 10% more particles
  • Cloth over a surgical mask blocks 40% more particles

CBS 17 asked if any combination of double masking would create the same level of protection as an N95 mask. Those types of masks are still hard to find.

“We haven’t seen, except for under one scenario, a surgical mask or a procedure mask reach the threshold of an N95,” Clapp said.

But scientists say we may not need a mask that blocks 100 percent of dangerous particles.

“We don’t know how much of the SARS-CO-V2 you actually need to filter out in order to prevent infection to yourself,” said Dr. Emily Sickbert-Bennet, director of infection prevention at the UNC Medical Center and associate professor of infectious diseases at the UNC School of Medicine.

Fit over everything

Sickbert-Bennet said without layering, a mask altered to fit more tightly to the face could block 20 percent more particles. Adding a gaiter over a surgical mask, creating a tighter mask, also greatly increased protection.

Dr. Clapp says the material used for surgical masks are very protective. They just don’t fit well.

“As I’m turning my face and talking, you’re seeing gaps open up on the corners of the mask and the nose,” said Clapp.

Those gaps are where you lose protection. It’s why layering a fitted cloth on top helps close those entry points.

But Sickbert-Bennet said wearing a mask you are comfortable in while covering the nose and mouth is the most important thing.

“You and the person you are interacting with both having a mask on, is the most important double masking there is,” said Sickbert-Bennet.

What to look for in a surgical mask

Surgical masks can be found everywhere from you local dollar store to Amazon. More expensive doesn’t necessarily mean more protective. Clapp said even within the same manufacturer, he found differences in ear loops and mask size.

When purchasing a surgical mask look for the following features:

  • Three layers
  • An inner layer made from polypropylene
  • Splash resistant
  • ASTM certification (while not crucial, this rating offers medical level protection)

Improving what you already have

Because fit is one of the most important attributes, the CDC encourages the use of a mask fitter or a brace. These are accessories that are placed over the mask to make for a snug fit. The CDC said they could help to reduce air leakage from around the edges of the mask.

The CDC said regardless of mask materials, fitters could improve filtration by up to 90 percent.

If you don’t have access to one of these, you may be able to make use of old hoisery.

The CDC said a fitter or brace alternative would involve placing a piece of sheer nylon hosiery material around the neck and pulling it up over a mask to create a tighter fit.

The CDC encouraged the “knot and tuck” method to ensure your surgical mask is not leaking or taking in as little viral particles as possible. Watch the video above for a tutorial on how to do this.

  • Knot the ear loops of a 3-ply face mask where they join the edge of the mask
  • Fold and tuck the unneeded material under the edges





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