Wikipedia:Reference desk/Archives/Science/2021 April 26

= April 26 =

N95 / KN95 masks
This is a comment on "It wasn't until this year that I was able to buy my second ever pack of N95s in the U.S." in the question above.


 * "The U.S. Centers for Disease Control and Prevention (CDC) recommends fabric masks for the general public. The CDC says that N95 masks should be reserved for health care providers... Because N95 masks have been in short supply, the CDC has said they should be reserved for health care providers. Health care providers must be trained and pass a fit test before using an N95 mask... Some N95 masks, and even some cloth masks, have valves that make them easier to breathe through. Unfortunately, these masks don't filter the air the wearer breathes out. For this reason, they've been banned in some places."
 * --How well do face masks protect against coronavirus?, Mayo Clinic


 * "Not all N95 respirator masks are created equal. In fact, you may unknowingly be wearing one that does more harm than good when it comes to preventing the spread of COVID-19. That was the warning the San Francisco Department of Public Health sent via Twitter last week. It said, in part, 'the ones with the valves or openings on the front are NOT safe, and may actually propel your germs further'."
 * --A Certain Type of N95 Mask May Do More Harm Than Good, San Francisco Department of Public Health, quoted by Healthline


 * "Both [epidemiologist] Rutherford and [infectious disease specialist] Chin-Hong cautioned against N95 masks with valves (commonly used in construction to prevent the inhalation of dust) because they do not protect those around you. These one-way valves close when the wearer breathes in, but open when the wearer breathes out, allowing unfiltered air and droplets to escape. Chin-Hong said that anyone wearing a valved mask would need to wear a surgical or cloth mask over it. 'Alternatively, just wear a non-valved mask,' he said. San Francisco has specified that masks with valves do not comply with the city's face covering order."
 * --Still Confused About Masks? Here’s the Science Behind How Face Masks Prevent Coronavirus, The University of California San Fransisco

--Guy Macon (talk) 18:03, 26 April 2021 (UTC)


 * I'm not clear what your question is. --OuroborosCobra (talk) 18:12, 26 April 2021 (UTC)


 * It's an answer to something posted yesterday in another answer, put into a new section because it is a completely different topic. This isn't Jeopardy!. There is no absolute rule that everything has to be in the form of a question. Sometime we answer other answers. --Guy Macon (talk) 00:03, 27 April 2021 (UTC)


 * Guy, how about moving this to a subsection of the original question so it doesn't look like a new question? --184.147.181.129 (talk) 20:46, 26 April 2021 (UTC)


 * No thanks. The words "This is a comment on..." at the top of this section are perfectly clear, and this is section is not in any way related to the medical oxygen shortage in India. --Guy Macon (talk) 00:03, 27 April 2021 (UTC)


 * FWIW the warning about valved masks was from quite early in the pandemic. Later CDC findings said valved masks are as good as surgical masks at preventing the wearer fromsspreading virus.  I have some valved masks and simply glued a piece of surgical mask over the valve just in case.  It didn't impair exhalation in any way that I could notice. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 22:19, 26 April 2021 (UTC)


 * To those who think that all refdesk discussions must be in the form of a quuestion: congratulations: we now have a proper question:


 * See Facepiece filtering respirators with exhalation valve shouldnot be used in the community to limit SARS-CoV-2 diffusion in Infection Control & Hospital Epidemiology


 * So, who is right? The government agency or the peer reviewed medical journal? --Guy Macon (talk) 00:03, 27 April 2021 (UTC)


 * Here is a good overview of the entire topic of face masks: An evidence review of face masks against COVID-19
 * Here is an interesting analysis published in Physics of Fluids: Visualizing droplet dispersal for face shields and masks with exhalation valves
 * Key quote: "Visualizations for a mask equipped with an exhalation port indicate that a large number of droplets pass through the exhale valve unfiltered, which significantly reduces its effectiveness as a means of source control. Our observations suggest that to minimize the community spread of COVID-19, it may be preferable to use high quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves."
 * Here is a video of the experiment: https://aip.scitation.org/doi/video_original/10.1063/5.0022968/5.0022968.mm.original.v3.mp4
 * --Guy Macon (talk) 00:23, 27 April 2021 (UTC)


 * Quoting CDC, especially the one from the Trump era, for pandemic advice makes me not trust whatever else a person says. I'd have been using Clorox wipes and looking into plasma therapy and remdisivir instead of wearing masks from March forward. It wasn't until this year that the CDC recommending double-masking surgical masks or respirators. You can keep your cloth coverings; I saw one for $8 at Macy's. I'll buy my KN95 when N95 wasn't available and now N95s. No one related to me has been infected, AFAIK, in China or in the U.S., and I've only used one bottle of Clorox wipes so far.
 * The CDC is now preparing to relax recommendations for outdoor masking. Again, you go ahead and do that. Fool me once, shame on you. Fool me twice, shame on me.
 * The CDC is still not taking aerosol transmission seriously, so their recommendations are pretty worthless to me. I know respirators with valves are frowned upon, but where they are not forbidden (my municipality has rules against valves, for example), I will wear them, because they're so freaking comfortable. Sorry, your health is not as important as mine or my family's. That said, I've used only a handful of valves so far, but I feel no qualm using it on the street, because other people are wearing nothing or cloth coverings, which do very little to limit aerosols. I'm no worse than them, and actually more responsible in other ways. Imagine Reason (talk) 00:52, 27 April 2021 (UTC)
 * Reducing community spread to get the pandemic under control is important for everyone's health. --Lambiam 06:37, 27 April 2021 (UTC)