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Face masks effectively limit the probability of SARS-CoV-2 transmission

science.sciencemag.org

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Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#171

Post by tzs »

sschueller wrote: post #17

N95/FFP2 seem to be very effective. I wish the media and government would have spent more time in educating people in things like how N95 masks work and that it isn't like a coffee filter. Even thought the pores are larger than a virus the masks are statically charged causes smaller things to get trapped. Many people don't know this but probably had an interaction with static electricity sometime in school and would…

> Even thought the pores are larger than a virus the masks are statically charged causes smaller things to get trapped.

Even filters that aren't statically charged stop particles that are smaller than the gabs between the fibers. There are actually several mechanisms by which a filter can stop a particle.

1. Big particles don't fit between the fibers of the filter. Think fish in a fish net. This is called sieving.

2. Particles too small for sieving but heavier than the surrounding flow don't make the turns as well as the surrounding flow when the flow goes around the fibers. The particles can get embedded in the fibers. This mechanism is called inertial impaction.

3. The smallest might be too small to actually be affected much by the flow of the surrounding fluid through the filter. The move by diffusion, and many will randomly hit the fibers and get stuck.

4. Particles too big for diffusion but too light for inertial impaction still can run into fibers and get stuck. This is called interception.

5. As you mentioned, some filters have an electrostatic charge which can help trap particles.

The effectiveness of sieving, inertial impaction, and interception all follow S shaped curves that start out low for small particles, then at some point start rising, and then level out. The sieving curve's rise is almost vertical. The rise for inertial impaction is steep but not nearly as steep as it is for sieving. The curve for interception's rise is much more relaxed.

The effectiveness for diffusion goes the other way. Much more effective for very small particles, then above some size drops down and is low from then one.

When you put all these together, you get a curve that is effective at the small end, and at some point as size goes up effectiveness drops, reaching a minimum, and then rises again to reach high effectiveness for particles above some certain size.

The reason 0.3 microns is used for many HEPA filter ratings is that is in the middle of the low part of that U shaped curve, so when you get a filter that removes, say, 99.97% of 3 micro particles, it should actually do better for both larger and smaller particles.

Here's a document that has some diagrams explaining all this, and has some graphs of the efficiency curves for mechanisms #1-4. http://donaldsonaerospace-defense.com/library/files/document...

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#172

Post by rootusrootus »

splitrocket wrote: post #3

Not that this will settle anything. Anecdotally, I've not gotten even a slight cold while being socially distanced while consistently masked.

It has been a pleasant year in that regard. We finally went on a domestic trip to Atlanta a couple weeks ago, after having been fully vaccinated in the middle of April. Guess what we came back with? A cold. Dammit!

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#173

Post by rootusrootus »

XorNot wrote: post #107
neither_color wrote: post #28

Earlier quoted context omitted.

Anecdotally I haven't had a cold in years. I work out 4 days a week and while I wouldn't call it a strict diet I have an upper limit calorie "budget" that I never exceed. While it's certainly possible that masks helped some people avoid all airborne transmissions last year, lots of people were also able to exercise more and make better food choices without the rush of breakfast and lunch commutes.

I made absolutely no changes 1 year, but because my workspace at work was in an alcove next to an air conditioning vent that pulled air from the outside, I completely dodged the office cold because I basically had my own positive pressure environment. It's more likely your lifestyle is simply keeping you away from people and places that experience high levels of foot traffic.

I also wonder if some people just don't have as strong as immune response and so they get barely a sniffle from a typical cold virus.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#174

Post by simpleguitar »

nostrebored wrote: post #158
simpleguitar wrote: post #147

Earlier quoted context omitted.

Not sure what you're getting at. Preprint for this paper was out in Apr 2020: https://pubmed.ncbi.nlm.nih.gov/32240078/

Chinese health authorities not being a credible source of information throughout the pandemic?

I'm not defending what they did, but let's make the facts clear.

Initially (december?) they denied there was human-human transmission, and tried to down play magnitude of the virus.

And once Wuhan was locked down, they down played how harsh it was, cut out the media (with the excuse of not causing panic).

But even before Wuhan locked down, they allowed the release of the virus sequence (Jan 2020), their mitigation efforts in Wuhan (the field hospitals built there, the thousands of doctors sent there, the treatment strategy the doctors used, what worked, what didn't), the air borne transmission, treatment methods, and all of that.

I was following this pretty closely, and the Chinese released very relevant information very early on.

But when Italy got hit, it was like they didn't even bother listening to anything the Chinese already put out. The Italians re-discovered pronation, low oxygen flow intubation, anti blood clot medication, etc.

Blaming the Chinese health authorities for not being credible is fine. But simply discounting everything they said is stupid. And completely ignoring their information even with mounting other evidence because "The Chinese are not credible", is doubly stupid.

It's like the world put on stupid blinders, and just wished that the Chinese were lying and Covid would just disappear magically.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#175

Post by fighterpilot »

alvah wrote: post #142
simpleguitar wrote: post #116

Earlier quoted context omitted.

Absolutely. Considering how long it took CDC and WHO to even acknowledge airborne transmission, even though the Chinese were very clear about it from very early on. https://www.nytimes.com/2021/05/07/opinion/coronavirus-airbo...

"even though the Chinese were very clear about it from very early on" I'm not sure this adds as much credibility as you seem to think. See (for example) - propaganda videos of people dropping dead in the street in Wuhan in early 2020.

True, but there was many other reasons to think masks would work. Its demonstrated efficacy in other coronaviruses and the cultural evolution of dense Asian countries to use masks as a way to combat virus transmission. The WHO and CDC behaved liked total idiots, setting the burden of proof way too high for what should've been a pragmatic, common sense decision made with some uncertainty. Not atypical of bureaucrats to miss such a layup.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#176

Post by solarengineer »

mattm wrote: post #153
function_seven wrote: post #113

Earlier quoted context omitted.

> On the other hand, "observational data show that regions or facilities with a higher percentage of the population wearing masks have better control of the coronavirus disease 2019 (COVID-19) (7–9)." So how to explain these contrasting results and apparent inconsistencies? My hypothesis regarding surgical mask prevalence and how it correlates with better virus control: People who wear masks--however effective they m…

"Some people with swine flu travelled on a plane from New York to China, and many fellow passengers got infected. Some researchers looked at whether passengers who wore masks throughout the flight stayed healthier. The answer was very much yes. They were able to track down 9 people who got sick on the flight and 32 who didn’t. 0% of the sick passengers wore masks, compared to 47% of the healthy passengers. Another wa…

What is astounding to a lot of us in South East Asia is the reluctance of the West in learning from our lessons. How many deaths and personal trauma experiences do people in general need to go through in order to learn from others?

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#177

Post by simpleguitar »

xkcd-sucks wrote: post #165
panarky wrote: post #135

Earlier quoted context omitted.

> The effectiveness of masks, however, is still under debate Effective for the mask wearer, or effective for others in the vicinity of the mask wearer? It's well established that cheap cloth masks and procedure masks don't protect the mask wearer very much. The rationale for cheap masks is that they drastically reduce the spread of particles from the wearer to everyone else nearby . If your goal is to protect yoursel…

I wear "n95" masks while sanding drywall, obviously trying to make the fit as good as possible, and still my boogers end up with tons of plaster in them. I would assume these particles to be bigger than any virion.

A properly fit N95 should block out all dust. If you are getting plaster in your nose, try different types of masks (folding), or a half-face respirator.

One of the justification for not advising N95s to the public was the fact that most people don't know how to properly wear one. As if they couldn't be trained in a few weeks, or duration of the pandemic.

Also, N95s filter out particles smaller than .3 microns (the 95% part). You can look it up, but it has something to do with the electrostatic media and physics. It definitely does not work like a sieve. (https://www.usatoday.com/story/news/factcheck/2020/06/11/fac...)

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#178

Post by boplicity »

andreygrehov wrote: post #155
rsj_hn wrote: post #75

Earlier quoted context omitted.

Indeed this is the money paragraph: "The effectiveness of masks, however, is still under debate. Compared to N95/FFP2 respirators which have very low particle penetration rates (around ~5%), surgical and similar masks exhibit higher and more variable penetration rates (around ~30-70%) (2, 3). Given the large number of particles emitted upon respiration and especially upon sneezing or coughing (4), the number of respi…

> observational data show that regions or facilities with a higher percentage of the population wearing masks have better control of the coronavirus disease Which is also not entirely true. There are quite a lot of regions (data from worldometer, statista) that have a better control of the virus despite people not giving a crap about face masks. For instance, Florida has 1600 deaths/M vs 3000 deaths/M in New Jersey.…

I don't understand this myth about Florida. It has fared very badly in the pandemic. You're three times as likely to have died in Florida from COVID, as opposed to in Canada. It sits in the middle of the States, in terms of death rates, which overall have been among the worst in the world. Compare your example to an area where people really take masking serious, such as Hong Kong, and then maybe you'll have a valid comparison.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#179

Post by simpleguitar »

nimish wrote: post #144
tgsovlerkhgsel wrote: post #39

This entire study seems to be centered around a theoretical, mathematical model, and I didn't see any attempt to actually validate that model. Basically, the authors seem to assume that the virus behaves according to their formulas, and show that under their assumptions, face masks work, but don't actually prove that their assumptions match reality - or did I miss something?

Nope. It's circular. We need actual tests in the wild, not models.

During an interview with some of the doctors sent into Wuhan in their wave, they claimed none of the 10 thousand or so doctors sent in became infected. They used strict PPE protocol, including N95 masks.

Given what we know about the covid transmission now, it was absolutely the N95s that prevented these doctors from getting infected.

Re: Face masks effectively limit the probability of SARS-CoV-2 transmission

#180

Post by randomopining »

anonymousiam wrote: post #35

Here's the manufacturer's (3M) label: WARNING: This respirator helps protect against certain particulate contaminants but does not eliminate exposure to or the risk of contracting any disease or infection. Misuse may result in sickness or death. For proper use, see supervisor, or User Instructions. https://multimedia.3m.com/mws/media/1837275O/3m-9132-healthc...

“Does not eliminate” aka it may reduce probability.

Imagine the brain of people that don’t understand simple probability lol.

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