Owen, the masks from https://rendallco.com/ seem roomier than others I've tried. The "Sentry" feels a bit bigger than the "Ace", though I like both. A bit on the pricey side.
Carl On Mon, Aug 24, 2020 at 9:36 AM Owen Densmore <[email protected]> wrote: > 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/ >> > - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . > 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-comic.blogspot.com/ >
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