B. Hodge, Biblical Authority Ministries, August 10, 2020
Introduction: Particle Filtration—Size and Percentage
In a culture that has gone berserk for wearing masks because of COVID-19 (SARS-CoV-2), you might actually get yelled at if you are not wearing something around your face. Plenty of people are quick to offer their opinion on masks, but I wanted to write something to educate people on particle filtration—specifically, an obvious one that most people seemed to have forgotten.
But first, let’s look at a few observations to get us started. Some basic particle sizes:
· Pollen 10-40 microns (microms)
· Dust 1-100 microns
· Bacteria 0.3-5 microns
· Viruses 0.005-0.3 microns (most viruses tend to be around 0.02-0.3 microns)
SARS-CoV-2 averages 0.125 microns (varies between 0.06 and 0.14) which is smaller than the average virus by about half. Tested mask filtrations are given below:
· Two-Layer Cotton Weave Masks: 35% of small particles (increases with more layers, some reaching as high as 60%)
· Single Use Face Mask: 95% of particles 3 micron of larger
· Surgical Masks: 95-98% of particles 3 micron or larger
· N95 Mask: 95% of particles 0.3 microns or larger
· N99 Mask: 99% of particles 0.3 or larger
· N100 Mask: 99.7% of particles 0.3 microns of larger
Of course, there are variations of these mask materials but these representations are the main ones you’ll find. Cotton seems to be among the most effective for fabric styles masks; though multiple layers of mixed materials can offer some increased filtration but nothing in the category of the five types of masks listed after dual layered woven cotton.
At an initial glance, you might instantly think masks are pointless—especially at keeping a respiratory virus like COVID-19 out of our lungs (which is where it can become dangerous). Our best masks cannot filter particles less than 0.3 microns and the virus is less than half of that size. So what gives?
Here is what a lot of people don’t realize. The majority of the SARS-CoV-2 airborne viruses (like many other viruses) are attached to larger particles in the air from dust particulates to respiratory droplets (often between 5-10 microns). These particles are much bigger and easier to filter especially with an Single-Use, Surgical, or N95+ mask. Thus, many of the viruses are still getting snagged.
The problem is aerosolized viruses (airborne and unattached to larger droplets). Because they are isolated, they remain their original size and pass through most masks, N95 included, without a problem.
Viruses, like SARS-CoV-2, are largely attached to particles big enough to be filtered. And this is only by a matter of tenths of a micron and many respiratory droplets and dust particles are much larger. So keep in mind that we are only dealing with tenths of a micron in filtration size. And this just now brings me to the point of this article.
I Encourage You To Be Nosey
What many people are missing is the obvious. Virtually everyone alive has a built-in filtration mask that is already attached to their head—your nose! This might be a shock to you, but your nose is a natural, God-designed filter for when you breathe. Our noses obviously filter out big particles that immediately get caught in the hair in your nose (see nose hair has a purpose!).
For instance, I used to bale hay and work with other farmers tossing and gathering the small rectangular hay bales and stuffing them into barns. I knew to constantly breathe through my nose to keep hay dust and larger particles out of my lungs.
Naturally, my nose would run in an effort to keep it operating properly and removing air-borne gunk that was getting caught in my nostril hairs. The mucus would also trap particulates tying to weave through our brilliantly designed nose passages [that force entering air back and forth]. The mucus would also capture particles as they wisp around our mucus coated nose hairs (see mucus has a purpose too!).
Then, there is a narrowing at your nasal cavity. There is also the mucus coated turbinates (superior, middle, inferior). By this point, most micro-particulates have already been filtered. Yet, there is much more. It really is a mind-blowing design (or should I say “nose-blowing” design!).
Efficiency of Nose Filtration
Clearly, these dust particles are larger than viruses. But some dust particles are still rather small being as low as 1 micron. Yet the nose is brilliantly designed to handle that. So how small of a particle can a nose handle efficiently?
Studies have been done on this subject. One such study found that the human nose can effectively filter particulates as small as 0.5 microns! One researcher summed up his study in saying:
“In vivo experiments applying monodisperse or polydisperse aerosols during single or multiple respiratory cycles have shown by using microscopic or laser-optic identification that particles larger than 3 microm have a maximum deposition in the anterior part of the nose (nasal valve). Particles smaller than 3 microm and larger than 0.5 microm are filtered by the nasal mucosa and transported by cilia propulsion to the nasopharynx. The filtration for particles smaller than 0.5 microm is low. They seem to pass easily into the lower respiratory tract.”
This is nearly as effective as an N95 mask! It’s only a matter of approximately two tenths of a micron. And like an N95 mask, you can still grab viruses that are attached to larger particles to filter them via mucus excretion or (as gross as it is) by having it enter your stomach where digestive acids destroy bacteria and viruses. But either way, massive amounts of viruses, bacteria, and micro particulates are filtered out by your nose to prevent them from entering your lungs, which is where a respiratory virus can cause problems.
Of course, not everyone breathes through their nose and therefore, they open up the possibility of unclean air diving directly into their lungs through a bypass in your mouth. And naturally, aerosolized viruses would pass through all protections—whether mouth, nose, or even external masks. There is just no protection for the aerosolized virus and that puts you in the hands of Providence.
The Nose Knows
But the nose is an incredible reusable and self-maintaining natural filter that God designed for us knowing that we would be in a sin-cursed and broken world (Genesis 3). His forethought helps us survive even though we are no longer upheld in a perfect state due to sin. In a sin-broken world, sometimes we get sick and our nose filter loses its effectiveness for a time, I get that.
But overall, the nose is truly an efficient filtration design far beyond what many realize and is effective, when used properly. If you find yourself in a dusty situation, pollen-filled area, or just around people who are sick, it is wise to keep your mouth closed and breathe through your God-given filter. Who knows (pun intended), it might help keep you from getting sick!
 P. Robertson, Comparison of Mask Standards, Ratings, and Filtration Effectiveness, Smart Air, March 15, 2020, https://smartairfilters.com/en/blog/comparison-mask-standards-rating-effectiveness/; M. Godoy, A User's Guide To Masks: What's Best At Protecting Others (And Yourself), NPR, July 1, 2020, https://www.npr.org/sections/goatsandsoda/2020/07/01/880621610/a-users-guide-to-masks-what-s-best-at-protecting-others-and-yourself.
 Many surgical masks still filter 30% of particles at 0.1 micron and depending on the level of surgical mask, they can increase this percentage to 95-98%.
 E. Litke, Fact check: No, N95 filters are not too large to stop COVID-19 particles, USA Today Fact Check, June 11, 2020, https://www.usatoday.com/story/news/factcheck/2020/06/11/fact-check-n-95-filters-not-too-large-stop-covid-19-particles/5343537002/.