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    dudley0

    Nobody Important
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    Mar 19, 2010
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    Of course they are not rushing to open schools just yet.

    I mean, at least not until the teacher's unions say it's cool.
    Both of my kids are teachers, for two different schools. Neither one has been closed. They have had chunks of kids stay home, but never the entire school.

    I don't see why other school systems are not working the problem.
     

    chipbennett

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    Oct 18, 2014
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    I read the same thing, and they actually said one mask gives you 50% protection, two masks 75% protection, and 3 masks would give you 90% protection. Saw it on the Today show yesterday, so it must be true.... :nuts:
    I know we've discussed this here ad nauseum, but these stories and memes are conflating filter efficiency with virus transmission efficacy. Mask filter efficiency is completely irrelevant to prevention of virus transmission if airflow doesn't go through the filter medium. That's why a respirator is different from a face mask.
     

    T.Lex

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    One of the factors that has led me to personally believe in some level of mask efficacy is that it reduces the distance that the particles will go. "Regular" masks are unlikely to completely stop the particles, but can dramatically decrease how far they go, which then reduces the transmission likelihood.

    Now, I'm not a zealot about it. That's just where I net out with it. And my personal opinion doesn't come anywhere near the hurdle for a .gov mandate.

    YMMV
     

    BugI02

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    I read the same thing, and they actually said one mask gives you 50% protection, two masks 75% protection, and 3 masks would give you 90% protection. Saw it on the Today show yesterday, so it must be true.... :nuts:
    That looks like their assumption is each layer is 50% efficient. So one layer 50% protection, two layers 50% plus 1/2 the remaining 50% 0.50 + 0.5(0.50) = 0.5 + 0.25 = 75% efficacy. Three layers then is 0.5 + 0.5(0.5) + 0.5(0.25) = 0.875 which I'm guessing they just call 90%

    Not only is that likely wrong, but I never see anything discussed about a mask after it gets wet/moist with breath and whether that makes infiltration of those postulated large wet virus containing droplets more likely into any breath actually drawn through that layer/those layers. In a damp enough layer, I could see virus-laden droplets coalescing with the moist material and then breathing intake aerosolizing some virus into the intake stream
     

    nonobaddog

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    The moisture from breathing through a real filter material does have an effect. A real N95 filter when it is fresh can capture particles smaller than 0.3 microns at greater than 95% efficiency through diffusion, impingement, etc. However when you run moist breath through that filter enough it starts to lose that capability. That is why the real filters have a wearing time rating. Once you breath through them enough they are no longer good N95 filters. The moisture reduces the ability to capture aerosols and they turn into a regular sieve type material which is less effective against the tiny aerosol virions.
     

    BugI02

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    The moisture from breathing through a real filter material does have an effect. A real N95 filter when it is fresh can capture particles smaller than 0.3 microns at greater than 95% efficiency through diffusion, impingement, etc. However when you run moist breath through that filter enough it starts to lose that capability. That is why the real filters have a wearing time rating. Once you breath through them enough they are no longer good N95 filters. The moisture reduces the ability to capture aerosols and they turn into a regular sieve type material which is less effective against the tiny aerosol virions.
    Early in the pandemic, Battelle ( a private research institute based here) developed a protocol to rejuvenate/re-use N95s. It was pretty simple, IIRC 'x' minutes at I think 158° of dry heat. The devil in the details was the need for really precise temperature control which is next to impossible in a home oven
     

    JettaKnight

    Я з Україною
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    Oct 13, 2010
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    Early in the pandemic, Battelle ( a private research institute based here) developed a protocol to rejuvenate/re-use N95s. It was pretty simple, IIRC 'x' minutes at I think 158° of dry heat. The devil in the details was the need for really precise temperature control which is next to impossible in a home oven
    °C or °F?
     

    BugI02

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    °C or °F?
    I could answer that, or you could think about the construction materials used to make an N95 and figure that out for yourself

    Lets see, which makes more sense, 158 or 316 degrees fahrenheit when plastics are one of the components. Didn't they make you take any chemistry in college? :) :stickpoke:
     

    BugI02

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    Upon further review, it appears their system is more complicated than I thought, and the one approved by the FDA also uses concentrated H2O2 vapor in a contained, autoclave-like vessel.

    However:


    https://www.sciencedaily.com/releases/2020/05/200505164638.htm

    N95 masks contain a layer of "meltblown" polypropylene fibers that form a porous, breathable network. To help capture smaller particles that could slip through the holes, the fibers are electrostatically charged. The U.S. Centers for Disease Control and Prevention has recommended several methods for disinfecting N95 masks, such as heating, ultraviolet (UV) radiation and bleach treatment, but so far they have not been tested extensively, especially for multiple rounds of disinfection. Yi Cui and colleagues wanted to compare five of the methods that could reasonably be used within a hospital setting to see how mask materials hold up to repeated disinfections.

    In this study, instead of analyzing N95 masks -- which should be reserved for health care workers -- the researchers examined pieces of the meltblown fabric used to make these masks. They treated the material with a particular disinfectant and compared its ability to filter aerosol particles (resembling respiratory droplets, but lacking coronavirus) before and after disinfection. The team found that spraying the fabric with an ethanol or chlorine bleach solution drastically reduced the filtration efficiency after only one treatment, from about 96% to 56% (ethanol) or 73% (bleach). A single steam treatment maintained filtration, but five steam treatments led to a sharp decline in efficiency. UV radiation allowed up to 20 cycles of disinfection; however, administering the exact dose of UV that kills the virus without damaging mask materials could be problematic, the researchers note. The best disinfection method appeared to be heating. For example, heating at 185 F for 20 minutes allowed the fabric to be treated 50 times without loss of filtration efficiency. But frequently donning and removing N95 masks could affect fit, which also impacts performance, the researchers point out.
     

    NKBJ

    at the ark
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    I had chemistry class. But I learned about plastic by building models and blowing them up with fire crackers and Mom's cleaning fluid.
     

    smittygj

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    Nov 11, 2010
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    I personally can't stand to wear a mask any longer than I have to. If I wear it more than 10 or 15 minutes, I start to gag. Heck I was labeled as CPAP intolerant during my two sleep studies due to the fact that as soon as I fell asleep, I ripped off the mask. So in this country where it is required to wear everywhere in public, needless to say, I don't spend too much time in public. I can be in and out of the grocery store over here in less than 5 minutes!
     

    nonobaddog

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    Mar 10, 2015
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    Early in the pandemic, Battelle ( a private research institute based here) developed a protocol to rejuvenate/re-use N95s. It was pretty simple, IIRC 'x' minutes at I think 158° of dry heat. The devil in the details was the need for really precise temperature control which is next to impossible in a home oven
    I read about one group that was regenerating the N95 filtration by placing the material between two plates and applying a voltage. I don't remember the voltage they found that worked or even if it was AC or DC. I think they concluded the process worked but was too tedious to be practical.
     

    T.Lex

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    We here in Indiana continue do really well on the numbers. Like, REALLY well.

    Nationally, though, the same can't be said. We're still in exponential growth of deaths (~108 days to double) and the CFR remains at ~1.67% +/- 1%. Its been there for about a fortnight. (No, not the battle royale game.)

    Also, we're about a fortnight away from hitting 500k deaths from the virus. That's a grim milestone.

    But, the serious/critical number continues to decrease. So, that suggests an improvement on the drag on the health care system.

    It also isn't really clear yet if the various variants will really pose any additional problems. Not that we can do much about it anyway.

    I remain personally hopeful that by the summer (ok maybe late summer), things will be pretty close to 2019-normal.
     

    BugI02

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    Jul 4, 2013
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    We here in Indiana continue do really well on the numbers. Like, REALLY well.

    Nationally, though, the same can't be said. We're still in exponential growth of deaths (~108 days to double) and the CFR remains at ~1.67% +/- 1%. Its been there for about a fortnight. (No, not the battle royale game.)

    Also, we're about a fortnight away from hitting 500k deaths from the virus. That's a grim milestone.

    But, the serious/critical number continues to decrease. So, that suggests an improvement on the drag on the health care system.

    It also isn't really clear yet if the various variants will really pose any additional problems. Not that we can do much about it anyway.

    I remain personally hopeful that by the summer (ok maybe late summer), things will be pretty close to 2019-normal.
    Just came back from worldometers, and The Magic Mask Kingdom Japan is coming up to meet us on our way down. Up from CFR of 1.36% to almost 1.43% in two weeks
     

    T.Lex

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    Mar 30, 2011
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    Just popped up that the South African variant has been discovered in South Carolina.

    Buckle up, buttercup.
     
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