Feel free. But it’s right in the literature on N95 masks that use electrostatic filtration that they stop working effectively in hours to filter moist aerosols. There are recommendations on how to “recharge” them, but not a real consensus.
Ultimately, the best mask for people to wear for most uses is the one they wear. The perfect mask that they leave behind is useless, as @anon29537550 points out above.
I’ve cited data (not perfect, published data, though) but you haven’t linked to anything. I’d love to see the data. My less than perfect data outranks your zero data.
Note that 3M has said that their N100 filters for elastomeric respirators can be used until they are hard to breathe through - so electrostatic filtration can be long lasting and resilient. I readily expect that FFRs may loose efficacy over time since they lack check valves that protect the filter from the moisture in exhaled breath, but I’ve not seen the data to confirm it is even remotely as dramatic as you suggest.
And I’d also note that OSHA standards for occupational use of PPE are not well suited for applicability for the general population use of FFRs to reduce overall transmission rates of Covid - where even an FFR with diminished efficacy and/or imperfect fit will still provide a vast improvement over leaky surgical masks (which leak outward up to 76% according to OSHA) and cloth masks.
Also, if the CDC bother to suggest good FFR masks, people might discover that many of them are easier to breathe through and cooler to wear than some crappy cloth masks or cloth masks over surgical masks.
Wait what? I have 3M niosh N95 masks. I wear one close to my face and then a surgical over that. I’m only wearing them for less than an hour at a time when I’m around people and then they are hung from my rear view mirror. I also have some hanging on my fridge for those rare times we need to let someone in the house. Those are weeks old.
I dispose of the surgical mask more often than the N95.
Are we saying my N95 becomes less effective over time? Or is that only when breathing through them?
Only when breathing through them, and they last longer when they have a chance to dry off in between uses. The figures I’m citing are for continuous use.
The IFU for the 3M 8210, for instance doesn’t specify a time period, but says that if it becomes damaged, soiled, or it becomes difficult to breathe, to discontinue use or get a new mask.
The CDC recommends an 8 hour limit. A study from Engineered Science indicates filtration does not decrease after 8 hours under lab conditions, but a study at Louisville testing N95 masks worn by ICU nurses during 12 hour shifts found the masks to be nearly impermeable at end of shift. All the airflow in and out was around the sides. It’s a limited and small study, but it shows the difference between lab conditions and real-world data.
In other words, don’t stop using N95 masks if you have them! They are highly effective, much more so than cloth or surgical masks. Just use them as instructed and be aware of their limitations. They aren’t magic.
There is a debate over whether double masking over an N95 is useful in extending the life of an N95. It’s a technique that was originally used in China and elsewhere during the initial outbreak. If you are using a non-medical N95, adding a surgical mask can give you a water resistant layer. But it may make the mask harder to breathe through, and increase the chance of filter bypass because of the increased mask pressure.
OSHA has found that even valved N95s provide as much source control as cloth masks or surgical masks - in part because the cross section of the valve is no bigger than the cross section of the leaks at the sides of a surgical, and only some of the exhaled air goes out the valve port. The rest goes through the filter media.
The also found that a surgical mask on top of the N95 increased utility as source control, and taping over the valve even more so.
Front line workers re-used N95s much more than you are doing, and in environments much more likely to be saturated with sars cov 2. Aaron Collins showed that at least in his tests electrostatic filtration can stay relatively un-diminished in an FFR for dozens of hours of use. It’s weird that I’ve not seen a better data on that given that reuse of N95s has been a major issue for a year and a half, but neither have I been searching for that data recently.
The inside of the N95 is likely nastier than the outside because of bacteria from your mouth. I don’t know how likely that is to be an issue, nor do I know how likely it is to catch covid by touching the outside of a possibly sars cov 2 contaminated mask.
Both, but the exact numbers are key. Based on Collins tests, the filtration efficacy appears to last dozens of hours of normal consumer use. 3M N95s also have a rated shelf life of 5 years.
If this is the study of Louisville nurses you are referring to they didn’t test the mask filtration at all, and found the nurses could wear the masks for long shifts:
“Conclusion
Long-term use of N95s, when worn alone or with a mask overlay as an outer barrier, did not result in a significant physiologic burden for health care personnel over the course of 2 work shifts.”
Could you provide links or specific, full study titles so we can all be on the same page in terms of the data?
As a card-carrying atheist, I completely understand your reasoning. Aligns with my “Don’t be try not to be a dick.” rule.
How much better less bad could this pandemic have been if TFG just said: “Everyone wear a mask, social distance, wash your hands, and get the shots as the science guides us.” back in Mar. 2020? Not another word out of him on the subject. He’d be POTUS again. Nobel prizes. Millions less dead.
Sigh.
My plan if questioned is to shrug, mutter “OK”, and then ignore. I’ve not been tested, but I rarely go out. My wife had sensed some side-eye, but nothing verbal.
Sadly, I hear this can further enrage some unreasonable types. Hopefully I can keep my cool.
ETA:
Can you suggest a good supplier of “good FFR” masks?
One thing this pandemic has taught me: there’s a lot of confusion around masks and health. It should be simplified. Define two masks for general public use. Type 1 = Simple Cloth. Type 2 = N95. CDC sez “MONKEY-COVID-EBOLA-24 is a Pandemic Type 2. Level 2 masks now in effect.”
This simplicity immediately gets masking started at the start where it matters most. Massive stockpiles of these two types ensure availability. Public IP, so no royalties. And we can keep track of expiration dates to ensure they’re used up before going to waste, and to restock as required.
I think the supply chains are less sketchy now, with retailers able to get masks through their normal channels. For KF-94 masks, check out Aaron Collins YouTube videos - he tests masks with a particle counter, and gives the details on where the masks were sourced from.
The last masks I bought were from Home Depot, which once again has a few types of 3M N95s. If they have valves, I tape over them.† I’m more trusting of Home Depot at the moment than Amazon.
There are some other source people like, but I’ve not dealt with them.
† (NIOSH found that even with the valve, N95s are better at source control than surgical masks with leaky sides, but few people know that and give valved N95s the squint eye even as they think nothing of people using crappy cloth masks that are worse at source control.)
Remember also, unless all the people in a room are wearing well fitted N95s, you have a case where one of the less well masked is spreading aerosols, you have two other entry points for the virus on your face…
Yeah, it’s not clear to me exactly how preventative increasing quality of respirator is with reduction in transmission, but so far the evidence I’ve seen is that better respirators are better, even if the corresponding reduction in transmission may not have a completely linear relation with filtration efficacy.
Early on in the pandemic several studies found that wearing eye wear in addition to masks greatly reduced the chance of getting Covid, but the mechanism was unclear. The eye wear could have been catching ballistic droplets (which are still a vector, even if aerosol transmission in the primary vector), or they might have prevented people from unconsciously touching their eyes. I do wear eye wear, and I do also have a full face respirator with P100 filters I can wear in a known high concentration environment. However, your lungs actively suck in a half liter of air with every breath and are in longer contact with more air than your eyes, so respirators are going to be very important. I don’t know if there are studies about how much transmission may be due to aerosol contact with your eyes.
I have a selection of cloth masks, made last spring, with a layer of cotton, a layer of silk, and a layer of poly/cotton, fitted to my face so the sides and chin don’t leak, with a plastic-coated metal strip that keeps the mask so close to my face, my glasses don’t fog up. It’s attached around my head, and is sen so there is space between the mask and my mouth. They all were pre-shrunk, so I can wash them in the hottest water and they don’t pull out of shape.
IMO, these are not crappy, and protect me and you better than badly worn surgical masks.
Given that surgical masks have an outward leakage rate of up to 76% according to NIOSH, that’s a low bar, and a low bar that is unfortunately mis-percieved as a good one.
It’s certainly possible that your combination of layers gives above average fit and filtration, again, not hard given the current average. I’d say it definitely exceeds mandated minimum requirements for the general public. But mostly I think that shows just how poor the current requirements are that lack any kind of tested efficacy standard.
The whole reason we have NIOSH ratings for masks is because unrated masks have unknown efficacy and vary radically in filtration ability, and crappy masks get people injured or sick - especially when people do risk adjustment because they think they are safer by wearing a mask. People might go to more indoor locations and say longer because they think they are protected from Covid, without realizing that their risk adjustment far exceeds the minimal increase in protection from their cloth mask. Which brings us back to your mask. We have no idea how it tests. It’s likely better than most cloth masks, but who knows? Without objective quantitative testing we don’t have any real data one way or another. The only think I think we can say with complete confidence is that it is not N95 level filtration and you would get higher filtration with a rated respirator grade FFR.
We should be pushing for wider use of rated respirator grade masks like Korea does, which made KF-94 (their “civilian grade” masks originally created for dust storms) available to everyone in the country rather than tell people they are on their own and to buy or make masks of utterly unknown efficacy - early in the pandemic, fine, but now? There’s no excuse.
I’ve probably said this elsewhere, but isn’t it time the WHO or UN define a simple standard for at most 3 different masks to match 3 different pandemic levels. With public IP so anyone can make 'em. And good testing to prevent counterfeiting. Maybe some sort of blockchain for authentication?
So much time, effort, headspace is being wasted on the fascinating details about masks. Which is awesome to read. I just want a simple system.
I fully expect this will be XKCDed.
Simplification would be nice, and I’d say you can have that for yourself right now. Just buy Korean KF-94 masks and use them if they feel like you get good fit without any cool air passing along the sides (one study found that participants’ subjective impression of mask leakage corresponded pretty well with actual quantitative mask fit testing).
That’s not a comprehensive, perfect or completely safe in all circumstances suggestion, but it is a simple one, and will give better filtration than the vast majority of people in the US are using.
I am not a doctor or an occupational hygienist. YMMV.
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