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Omaha experts explain the physics behind an N95 mask

Published: Feb. 2, 2022 at 10:29 PM CST
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OMAHA, Neb. (WOWT) - We’re two years into the pandemic, but do you fully understand how some masks work?

When it comes to our masks, many assume they’re like a strainer - stopping most particles from passing through, but some still make it.

University of Nebraska-Omaha physics professor Chris Moore says we need to reframe our thinking to understand how masks, especially N95 and KN95 masks, work.

“We should think about [masks] more as a collection of spider webs, so what we’re really trying to do is capture the particles on the fibers of the mask,” Moore says.

Moore explains that there are two ways to capture those particles. The first, and more obvious way, is mechanically.

“You just make lots of different layers,” he says. “You can start to see where particles are going to hit the fibers themselves and become stuck and trapped on those fibers.”

Moore says this method is good for catching very large particles, which tend to move in straight lines, as well as very small particles that move more randomly around.

To capture those mid-sized particles, Moore says, comes the second method to capture particles. The way N95 and KN95 masks do it - using the electro-static properies they are created with.

Yes, the masks are charged with static.

“N95 masks use permanently charged layers, so, fibers that are made of some sort of polymer that have a permanent charge,” Moore says. “That permanent charge creates an electric field around the fiber, and just like a balloon will stick to a sweater, the particles will be attracted to the fibers in that way.”

UNMC associate professor of pathology and microbiology Josh Santarpia puts it this way:

“The way filters work is they capture particles through a bunch of physical means. . . but another thing that happens in filtration is they are electrostatically attracted,” he says. “Particles carry a little bit of a charge with them and so they’re electrostatically attracted to the fibers so if you add charge to the fibers then you’re just increasing that attraction and the stickiness.”

“It helps increase the filtration efficiency while keeping it breathable,” Santarpia adds.

But this isn’t the only reason why N95 masks are the best on the market, he says.

“In addition to having multiple layers of material and tone of them being the eletro-static one, they’re also fit to your face more closely than surgical masks and most than any of the cloth masks you can find and that helps a lot with maintaining the seal around your face.”

And it’s these same reasons why it is probably best to dispose of those masks after a few uses.

“By design they’re trapping particles, they’re not blocking particles, they’re trapping them,” Moore says. “So of course those particles start to build up and build up and build up on the mask, and that’s what’s going to make it less and less effective with time.”

Right now, Santarpia and Moore say there’s no way to ‘re-charge’ a mask once it’s reached its usage limit. You’re better off just grabbing a new one, they say.

As it stands, the N95 and KN95s are the most protective, but both Moore and Santarpia agree that any mask is better than no mask.

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