1. The mask has to actually filter out the virus.
The mask is called N95 and not “N let’s see what can and can’t get through the mask.” N95 means that the mask can filter out at least 95% of particles of all sizes from the air. That includes something less than 0.1 microns in size and something as large as a watermelon. Note, if watermelons are flying through the air, it helps to duck as well.
Basically, the mask needs keep the virus from reaching your nose and mouth, which is why wearing panty hose over your head like a gangster isn’t going to do the trick. “Something like panty hose is too porous,” explained Sundaresan Jayaraman, PhD, the Kolon Professor at the Georgia Institute of Technology School of Materials Science & Engineering. “That’s the case with many types of fabric. Even when you use several layers of fabric, it may have too many holes.” He added that one layer of a handkerchief or bandana is only going to filter out less than 10% of particles.
Polypropylene is a commonly used material for N95 masks. To get through a filter made out of interlaced layers of polypropylene fibers, small particles have to wind through a rather tortuous path and as a result tend to get stuck, as described by a National Academies of Science, Engineering, and Medicine (NASEM) report that Jayaraman helped author. Think about getting through the filter material as getting through the entire crowd at a BTS concert. However, creating a tortuous path isn’t the only way that polypropylene makes it difficult for viruses to pass.
2. The mask should have more than one filtering mechanism.
If you are trying to keep someone from getting into the nightclub that you call your body, you would want multiple ways to keep him or her from entering. That way if one mechanism fails, the others are there. The NASEM report described three general mechanisms that N95 masks have to pull particles from the air stream: inertial impaction, diffusion, and electrostatic attraction. Inertial impaction sounds like a dance move or a dental procedure. But it is when the tortuous path makes it difficult for particles that are 1 μm and larger to continue on their straight paths. Such particles are too large to weave through the mask fibers and end up running into one the fibers.
The second mechanism, diffusion, helps keep particles that are 0.1 μm and smaller from proceeding. The design of the mask filter creates a situation in which these very small particles move in random directions, colliding with each other and with filter fibers. When these particles are bouncing against each other as if they were in a mosh pit, it less likely that they will get though the maze.
The third mechanism, electrostatic attraction, sounds like something someone would say on a Tinder conversation. The filter material for N95 doesn’t just physically block viruses and other small particles. As the song goes, you can’t see it, it's electric. During the manufacturing process, the fibers receive an electric charge. As Jayaraman described, “this electrostatic charge then attracts the virus so that it gets stuck on the fibers.” This is one case where forced attraction is a good thing.
3. The mask shouldn’t suffocate you.
Lots of materials could keep the virus out like cement or Saran Wrap. There’s one slight problem with such materials though. You have to be able to breathe, which is why you have your nose in the first place. Breathing resistance is not a movement against breathing, but instead how difficult a mask makes it to breathe. “You have to make sure the breathing resistance is not too high for a mask,” said Jayaraman. “Wrapping your face with Saran wrap may keep viruses out but the breathing resistance would be too high. The same would be true for many layers of fabric.” Low enough breathing resistance is important both for the inhale as well as the exhale. if air can’t get back out through the mask, it could blow up like a balloon.
4. The mask has to fit and form a seal with your face.
Wearing a mask that filters out the virus but does not form a tight seal with your face can be like locking the front doors of your car but not the back. Any gaps between the mask and your face can allow the virus to sneak into your nose or mouth. That’s why you should be fit-tested for a N95 mask before actually using it.
Here is a video from the Occupational Safety and Health Administration (OSHA) on fit testing:
As the video shows, one method of fit testing is for you to put on the mask and then have someone spray one of the following around you:
Smelling bananas can be nice when you are in a bakery. However, not in this case. If you end up smelling one of the first three or coughing from the fourth, the mask is not keeping out what it’s supposed to keep out of your nose.
Designing a mask that can fit everyone’s face is not necessarily that easy. Don’t ever let anyone tell you that you’re not special because your face probably has its own special shape and contour. There’s little more leeway with designing underwear than with designing N95 respirators because underwear doesn’t necessarily have to form a tight seal with your butt.
5. The mask should be reasonably comfortable to wear.
OK, the phrase “slip into something more comfortable” usually doesn’t mean put on a N95 mask. If a date ends with N95 masks on, something probably has gone wrong. There will always be some level of discomfort wearing such a mask. Nevertheless, the mask can’t be too uncomfortable. The edges of the mask can’t be so sharp or abrasive that they cause substantial irritation, sores, or cuts. The mask can’t be so tight that you feel like your head is going to explode.
6. The mask shouldn’t shed.
The song “Pieces of Me” shouldn’t apply to your mask. Anything that breaks off or sheds from your mask such as fibers and little particles can go straight up your nose and potentially down into your lungs. And that’s not good.
7. The mask must be durable enough.
Health care settings aren’t exactly rom-coms. Things rarely go perfectly. They can be quite chaotic with unexpected splashing of liquids. Plus, you breathe out water vapor from your mouth and also may spit while you talk. If you believe that you don’t spit at least occasionally when talking then you probably believe that you don’t fart either. The mask has to be reasonably resistant to all of these possibilities and maintain its integrity and filtering capabilities at least for a while.
8. The airstream and filtering portion of the mask need to be large enough.
This can be like making a highway too narrow. A too narrow passageway may not only increase breathing resistance but also lead water droplets to coalesce. Coleascing water droplets can make the filter wet and thus decrease its effectiveness.
All of this being said, N95 respirators are not the only option to protect health care workers from SARS-CoV2 in the air. For example, reusable elastomeric respirators may provide superior protection compared to N95 masks. A drawback is that they can make you “look like Darth Vader,” in the words of Jayaraman. But as long as you don’t say “feel the power of the Dark Side” or “I am your father,” this may not be such a bad thing. So while any new design of a respirator should have the qualities mentioned above, it doesn’t have be exactly the same as a N95 respirator. Who knows, one good thing that could come out of the COVID-19 coronavirus pandemic may be some new respirator designs.
Again, there are a lot of well-meaning people out there trying to address the N95 mask shortage. However, masks that are not designed to provide appropriate levels of filtering, porosity, and comfort are not replacements for N95 respirators. If health care workers mistakenly believe that DIY masks will provide the same level of protection that N95 respirators do, if the availability of such masks convinces hospitals and health care systems that they do not need to urgently pay for legitimate N95 respirators, or if such masks somehow prevent policy makers from taking more urgent action to rectify the shortage with real OSHA-compliant masks, then such DIY masks could end up doing more harm than good.
It’s heartwarming to see so many people trying to cover the shortage of N95 respirators. Protecting health care professionals should be paramount. Just make sure that the limitations of any DIY mask are clearly covered or rather uncovered for everyone to clearly see. And that the design of any masks trying to serve as replacements for N95 respirators clearly cover the scientific principles that need to be covered.