[conspire] A more-effective face mask as a DIY project

[Rick Moen]

Quoting Paul Zander (paulz at ieee.org):

> I well remember the mixed messaging of the early days.  The news said
> don't wear N95. I looked at the box I had bought a couple years back
> when we had too many days with smoke filled skies.   In that same
> time, an email list for engineers tried to over-analyze N95.  The
> spec was written to keep out dust particles of a certain size.  But
> COVID-19 virus was smaller.  Maybe N95 couldn't stop the virus.  Now
> we understand that most of the problem is droplets of water and
> virus.  N95 is good, so are many kinds of fabric.

"Good" is relative.

Early on, I cited in online discussions the typical size of a virus, 
during discussions of face coverings.  For the record, particularly
small viruses are about 30 nanometres in diametre.  the SARS-CoV-2 virus
is about 0.1 micrometres in diametre (about 3x larger).  Bacteria, being
prokaryotes (much smaller than eukaryotes), are around 2x-20x larger still.

But, basically, any virus is unbelievably small, one of the reasons they
couldn't even be imaged until invention of the electron microscope.

An N95 respirators is a design whose tested units blocked 95% of very
small (0.3 micrometre) particles, when properly fitted.  This means they
cut greatly the amount of bacteria and (even) viruses making it through
-- at the serious cost of them being hot, uncomfortable, obstructive to
one's breathing, and useless if badly fitted (sealed to one's face).

If it were necessary, in order to give humans meaningful protection from
dangerous pathogens, to block sub-micrometre particles, we'd be pretty
much already dead.  Fortunately, it isn't (unless you are working in a
COVID-19 ward, or are immunosuppressed/immunocomprmised).

Key to understanding why is to understand the key concept of viral titre
(aka viral burden):  It's a metric of how many viral particles are in
so-and-so mL of a fluid.  In short, infection doesn't work like in the
lab scenes early in _The Andromeda Strain_, where the moment the filter
aperature between to test chambers became big enough for a single cell
to waft through, the rhesus monkey seized up from an accelerating
infection and died.

This isn't the Andromeda Strain, just a somewhat novel coronavirus.
If we were able to fully study the progression of moderate-to-serious
infections, we'd probably find that the initial exposure was typically
to a great many virus particles all at once, overwhelming immune
response.  If we were able to track such things for an individual over
time, we'd doubtless find that the individual suffers tiny incursions of
potentially truly dangerous pathogens plus influenza strains and
rhinoviruses on an ongoing basis, and the immune system catches them and
mops them up.

The theory of operations of things like surgical masks is to slow down
and (with some luck) catch and stop moist droplets in motion in the air,
that might be carrying tiny pathogens.  In this, they mostly work on the
wearer's exhalations, catching _those_ and slowing them down.  The
wearer still breathes in (and to a degree, out) moist air along the
edges with basically no impediment, and air (that with luck has a lot of
the moisture caught) breathed straight through the mask material.  

When walking around indoor spaces, the better the ventilation, the less
crowding, and the less elapsed time you spend, there, the less potential
virus titre exposure.

The shop-towel materials tested by the Suay Community Mask Coalition
effort, with the Portacount Pro machine set to measure particles down to
0.02 - 1 micrometres, the best shop-towel materials filtered out 87% of
particles.  That's _almost_ N95 grade -- and I can say that these sewn
masks are comfortable to wear over many hours, don't unduly impede
breathing, and are easy to get on and off.

That's why, especially in a pandemic situation that is already terrible
here and California and will be even worse in about a fortnight, I
considered making them for me and my family to be a top priority:  
E.g., today, I needed to go shopping in four stores, and believed myself
to be much, much better protected wearing my prototype Suay mask than I
was with the series of throwaway surgical masks I've been getting by
with.