With all the information about COVID-19 flying about, there are a lot of questions going around about the N95 filter masks, and whether or not they actually will protect you from a disease like COVID-19. So lets step through it and learn a bit about the N95 masks, viruses and how it all works. Lets start off by understand what N95 means:
The N in N95 stands for Not resistant to oil. There are also R95 masks, and P95 masks which are resistant and oil “proof” (or just heavily resistant to oil). If you’re in a situation where there is potential to be oil droplets in the air (perhaps a machine shop or garage), you want to get a P rated filter otherwise the filter efficiency drops of pretty quickly.
For the medical field, this is not really an issue.
And as the chart above says, The 95 in the P95 stands for 95% efficiency, but the big question here is: 95% efficiency for removing what?
Typically, air filters are tested at how well they remove 0.3 micron particles from an air stream. This can be done either by a salt aerosol or DOP aerosol, but basically they aresolize the material and measure the upstream and downstream amount of particles and see how efficient they are at removing the particles.
So why did the entire filter industry just decide that they were going to measure filter efficiency using a 0.3 micron particle? That is a long answer but basically that size is the size particle that is most penetrating.
Basically, if you have a filter where the air must make a tortuous path through the filter, particles that are less than 0.1 micron are so small that they get knocked about easily and kind of vibrating through the air, and have a higher chance of impacting one of the fibers in the filter, and therefore will be intercepted.
Particles that are larger than 1 micron tend to have a hard time navigating through the tortuous course of the filter with the air and will impact onto a fiber and be intercepted. Think a truck trying to do a slalom course.
There is a range of particles that is small enough to be able to move and flow through the path of the filter with the air, but not so small that it gets knocked about easily and will penetrate the filter the most. There is a lot more to go through on that and the MPPS changes when you change fiber diameter, and gets really interesting when you start getting nanofibers but for simplicity sake I think this is a good highlight.
So will an N95 filter protect you from viruses?
The COVID-19 virus is somewhere between 0.08 and 0.16 microns in diameter so very very very small. (SOURCE)
The smallest wavelength of light that we can see is about 0.4 microns. So these viruses are several times smaller than even the smallest wavelengths of light we can see.
And this is where it gets interesting in terms of filtration because you have to ask yourself:
- What is the pathway of transmission?
- Do we need to filter out 0.08 micron particles from the air?
- Is it a cough “particle” or a sneeze “particle” and if so how do we know what sizes those particles are?
From what we know right now (and from what I could find), the biggest pathways of transmission are likely:
- Touching something that was contaminated and then touching your face
- Inhaling a “particle” that is contaminated that was coughed or sneezed
The virus itself is likely not in the air by itself floating around as a 0.08 micron particle, because it’s being transmitted from someones mouth, nose, throat in their saliva. So lets dig in a bit and see if we can find out how big sneeze and cough particles are.
There have been all kinds of studies on size, speed, number etc of particles that get emitted when you cough or sneeze. This study showed that the particle size for sneezes ends up being bimodal in some people and single modal for others (which would be a fascinating study to dive into to see why that is).
This study had people sneeze into a particle analyzer and measured the results of the sizes.
Here is the data:
Quote from the article: “The geometric mean of the droplet size of all the subjects is 360.1 µm for uni-modal distribution and 74.4 µm for bimodal distribution with geometric standard deviations of 1.5 and 1.7, respectively.” So sneeze particles are actually really big compared to even the fiber diameters of the filters.
Cough particles are a bit smaller.
Quote from the article:
“Results indicated the total average size distribution of the droplet nuclei was 0.58–5.42 μm, and 82% of droplet nuclei centered in 0.74–2.12 μm.”
So either way whether it’s a cough or a sneeze, the average particle size is likely to be larger than the MPPS, and we would expect the filter to remove more than 95% of those particles.
So there, now that is something you know; Sneeze particles are likely around 75 micron or 360 micron depending on who is sneezing, and cough particles are somewhere around 1 micron or so. Try not to think about that every time you hear someone cough or sneeze.
So these filters will do a decent job of protecting you from cough and sneeze particles, as you would expect them to have greater than 95% efficiency in removing those particles from the air as they are larger than the most penetrating particle size.
BUT, this will not protect you AT ALL, if you touch a surface and then touch your nose, which is most likely the way people in the general public will get infected. A cough or sneeze can emit tens of thousands of particles, and based on some of the data, the viruses can live for up to 14 days depending on the surface.
This is why it’s people are saying the masks are useless to the general population but hospital staff make such a big deal about not having access to them, because unless you’re a professional that is used to putting them on safely, wearing gloves, and making sure to wash your hands before you touch your face, odds are the masks won’t help you and that you should wash your hands.
And you might be asking: What about the hand made masks I see on Facebook and other social media sites where people are sewing masks and sending them to hospitals; do they offer any protection?
The answer there is mixed. Yes, these masks offer a small amount of protection compared to doing nothing, but not even close to what a standard N95 mask would do.
Believe it or not, this shortage that we’re seeing and the response to make make masks out of common materials was foreseen 10 years ago.
From the study above, which was published in 2010: “A shortage of disposable filtering face-piece respirators can be expected during a pandemic respiratory infection such as influenza A. Some individuals may want to use common fabric materials for respiratory protection because of shortage or affordability reasons. “
The authors went on to do testing on common materials such as T-shirts, towels, sheets etc and compared them to the N95 masks. The results were somewhat disheartening.
The different household materials do offer some protection and reduction (with the Hanes sweatshirt taking the lead), but not even close to the reduction that an N95 mask would do. So the answer is a bit mixed. If there is no other option, these types of masks would be better than nothing, and if you could use one of those masks over an N95 mask, which would make it easier to re-use that would be better than nothing. But they just are not a good replacement for the N95 masks.
And this is why it’s so important for medical professionals to have access to these masks, because they are already trained to wash their hands, and wear gloves, and safely remove them, so for them, in a hospital, the mask prevents their most likely source of transmission.
Their most likely way to get the virus while working is NOT from touching something and then touching their face, like it would be for most of the public, it’s the coughing and sneezing people they are forced to be around. And the masks will protect our health care workers from being infected.
Believe me if you or a loved one has an emergency, you want to make sure we have enough nurses or doctors that aren’t sick in the hospital to take care of them.
Please don’t be blind about this. If you have a stash of masks out there I would urge you to donate them:
https://ppelink.wordpress.com/
https://findthemasks.com/
https://www.donateppe.org/