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 ↙↙↙ <[email protected]> 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 > > - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . > FRIAM Applied Complexity Group listserv > Zoom Fridays 9:30a-12p Mtn GMT-6 bit.ly/virtualfriam > un/subscribe http://redfish.com/mailman/listinfo/friam_redfish.com > archives: http://friam.471366.n2.nabble.com/ > FRIAM-COMIC <http://friam.471366.n2.nabble.com/FRIAM-COMIC> > http://friam-comic.blogspot.com/ >
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