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
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
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!
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
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/.