[FRIAM] Masks and Face Shields

[Owen Densmore]

I probably missed it, but: Where can you find reasonably effective masks of
the sort described?

Size appears to be an issue for me as well. I bought a good multilayer,
filter pocket mask. It fits tightly and has a nose wire. But it is too
small from nose to chin. One size does not fit all. I got a large mask and
it does help but it is not as well built as the first mask.

I haven't had much luck finding a website that has multiple sizes, filter
pockets, good descriptions etc. Any suggestions?

   -- Owen

On Wed, Aug 19, 2020 at 4:43 PM uǝlƃ ↙↙↙ <gepropella at gmail.com> wrote:

> This excellent description landed in my spam folder. So it's likely it did
> for others as well. Hopefully, the filters that reroute Frank's emails
> won't be the ones that reroute mine.
>
> The "80% of viral particles from entering your nose and mouth" link in the
> Conversation article was from 2010, but it talks about the 20-1000 nm
> range: https://academic.oup.com/annweh/article/54/7/789/202744
>
> Your link to the built environment website is much more generally
> informative. Thanks.
>
> On 8/17/20 7:43 PM, Frank Chambers wrote:
> > I have been following reports on masks, face shields, and social
> distancing with interest. The analysis is mostly fluid mechanics and
> filtration. My specialty is fluid mechanics and I have conducted research
> on automotive air filtration. I have served on the SAE Air Filter Test Code
> Committee and been an expert witness on air filter testing. To start with,
> the symptomatic who are coughing and sneezing are producing droplets that
> are about 5 microns. The asymptomatic who are expelling droplets while
> breathing, speaking, and singing are expelling droplets which are around 1
> micron. The 6 foot social distancing rule is based on very old research
> about how far 5 micron droplets travel before falling to the floor.
> >
> > I got concerned when I learned about the 1 micron droplets because of a
> rule of thumb used for measurements using optics. Laser Doppler Anemometry
> and Particle Imaging Velocimetry measure turbulent air flow using what are
> called ''seed particles" to reflect laser light. One really measures
> particle velocity, but makes sure that the particles are small enough to
> move with the air. The rule of thumb is that 1 micron particles follow
> laboratory air flows very well. Thus for a face shield, the gross 5 micron
> particles from those with symptoms sneezing impact on the shield, but the 1
> micron particles of the asymptomatic move with the air that is sucked in or
> out by breathing behind the shield. The small particles just flow around
> the corners of the shield. These aerosol particles can remain airborne and
> travel through buildings. Shields only are effective for the larger
> droplets. When Sen. Daschle received his envelope of anthrax powder, the
> particles were about 1 micron. That
> > indicated that it was sent by someone who knew what they were doing.
> >
> > These droplets of mucus surrounding virus particles change size as a
> function of humidity as they evaporate, etc. The importance of asymptomatic
> transmission has been becoming more recognized, but there still are
> questions about how long the aerosols remain viable.
> >
> > On masks, there are different types of N95 masks. The basic standard is
> that they filter particles which are 0.3 microns and larger at 95%
> efficiency. They capture both the 5 micron and 1 micron droplets well The
> N95 masks work very well for medical purposes except for the ones which
> have a bypass valve making it easier to breathe out. These let out the
> virus you are expelling. Surgical masks and homemade masks also work, but
> not as well. They do a good job on larger particles, but are not as good on
> the small ones, though they still are useful, even with filtration
> efficiencies of 40 and 50%. There is a pretty good, very comprehensive
> report on masks. It does, however, give more credence than deserved to the
> study done at Duke which indicated gaiters were worse than nothing. A story
> about this in the Washington Post generated lots of publicity this past
> week. I read the report carefully and they were not even doing standard
> efficiency measurements, ratioing downstream to
> > upstream measurements. They just measured downstream and compared to
> measurements without a mask. One has to be careful, because there are a lot
> of non-peer-reviewed reports coming out from those who are novices at
> filtration. It is easy to mess up, for the filtration efficiency can be a
> strong function of the velocity through the filtration media. If one can’t
> measure flow rate well, one can’t measure filter performance accurately.
> >
> >
> http://built-envi.com/what-kind-of-mask-should-i-be-wearing-to-protect-against-covid-19/
> >
> >
> > Prof. Linsey Marr of Virginia Tech has been writing and been interviewed
> a lot on these topics. I have talked with her and she is pretty good.
> >
> > Frank
> >
> > Frank W. Chambers
> > 2 Sabroso Pl.
> > Santa Fe, NM 87508
> > Home:  (505) 466-1942
> > Cell:  (405) 614-4353
>
>
> --
> ↙↙↙ uǝlƃ
>
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