Electric cooker an easy, efficient way to sanitize N95 masks, study finds | Hacker News Reader

Electric cooker an easy, efficient way to sanitize N95 masks, study finds

news.illinois.edu

201 pointsjohnny313126 comments

My family has been decontaminating our N95 masks with ozone. I bought a battery-operated O3 generator and if you place it into a tupperware container along with the mask, it will decontaminate it and then you can use it the next day. Yale School of Medicine has done a study on the efficacy of this method. [1]

I prefer this method because it doesn't degrade the mask at all, it needs no disinfecting/harsh chemicals, it penetrates into the pores of the mask completely, and it's near fool-proof.

[1] https://www.medrxiv.org/content/10.1101/2020.05.28.20097402v...

Wow this is actually incredible if this works. However this study was tested bacteria and relate it to covid in the following way:

"an ozone application achieves a high level of disinfection against PsA, a vegetative bacteria that the CDC identifies as more difficult to kill than medium sized viruses such as SARS-CoV-2 (Covid-19)"

Would the implication be that this same method works on covid as well? That is not immediately apparent to me...

It sounds like it's saying "ozone kills the tougher bacteria than Covid at a very high rate".

So directly it says absolutely nothing about Covid but implicitly it does seem to state that it should also kill Covid since it's less tough to kill than the vegetative bacteria. I guess they can't make that statement directly--there's no evidence related to Covid here. I'd ignore it.

But why are they making this proxy argument, why not test with covid directly? Makes me think they did test with covid and it wasn't working.

Maybe the mechanism of death is similar so if it kills a more difficult strain the same mechanism will kill the "easier strain". It doesn't directly state it though, I think it's just speculation. It doesn't belong in a science paper except maybe in a speculative section about the future I guess.

Is the 'difficulty' related to the method at all, or just the amount of effort required?

Can you please link your portable ozone generator? Or at least what the name/brand is?

Is it something like this? https://www.boneview.com/collections/boneview/products/ozone

Hi, this is exactly the same model that I got. Mine has a different branding on but many sellers seem to have re-branded the same white-label model from China. They work well. They generate ozone for 30 min and then for 5 min every hour until the battery runs out. It has a micro USB battery charging port.

You can search for them by using the model number (ST-807A) or by searching for "ozone generator fridge" on your fav shopping sites.

Aliexpress has that exact model quite cost effectively. and a few more w/ higher outputs.

Wow, thanks for this! I just learned that ozone about sterilization and odor elimination from this thread.

Just picked up an ozone generator and looking forward to using it on my masks and shoe cabinet.

Ozone is an extremely harsh disinfectant chemical, and it's dangerous to say it's not. Various regulatory agencies in the USA set prolonged exposure limits at about 0.1ppm. [1] The USA's National Institute for Occupational Safety and Health has set its Immediately Dangerous to Life and Health (IDLH) concentration for ozone as 5ppm.

This study you've linked examines the disinfectant power (against Pseudomonas aeruginosa) of ozone at a concentration of 400ppm. If somebody who's been told that ozone is not a harsh chemical decides to open that airtight container and smell the sanitation, they might get a whiff of ozone so concentrated that doctors around the world will be talking about the resulting injury.

Even if you're careful not to do that, opening the container may cause a significant and harmful elevation of ozone concentration in the room if this is done indoors.

[1] https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-...

[2] https://www.cdc.gov/niosh/idlh/10028156.html

The main thing is consistency, as ovens/cookers are temperature controlled. Other bootleg options are available:

Household clothes driers can get hot enough as well, but not all of them do.

Cars on a hot day can also get to the desired 140-150f+ range.

Many dishwasher sanitize cycles as well

https://www.who.int/csr/sars/survival_2003_05_04/en/

https://dailyhomesafety.com/does-dryer-kill-bacteria-and-ger...

https://heatkills.org/how-hot/

https://www.quora.com/What-temperature-ballpark-does-the-hea...

Question is whether the oven / dryer / dishwasher damages the mask's filter.

Related: can anyone explain why there are still no n95 masks available? It seems like, a few months in, it's surprising that there are none available for non-medical buyers.

Is this perception wrong?

There is no unified approach to the virus and states and are fighting each other for the little supply there is

I think price-gouging laws could also have something to do with this. Suppliers have increased their prices in what is essentially protracted inflation from demand. But in most states retailers are not legally allowed to increase price tags which was triggered in March when most states entered a state of emergency/declared disaster [1]. So the results is that retailers have to stop stocking these or they lose money; and the increased demand doesn't fully reach suppliers which means that in turn, manufacturers have also less incentives to increase production.

[1] https://www.natlawreview.com/article/price-gouging-laws-and-...

Please clarify ".. So the results is that retailers have to stop stocking these or they lose money .. "

Citing from https://www.patriotsoftware.com/blog/accounting/price-gougin... > New York's Consumer Protection Law prohibits price gouging during an emergency: What is considered price gouging: 10% or more price increase. When price gouging laws apply: During an emergency. Products or services the law applies to: Necessities.

Say your gross margins on said masks were 50%, you paid $1 per mask and sold them $1.50 plus tax.

Now the same branded masks are $2-3 from the supplier and you cannot legally sell them without losing money.

The market rate for a single N95 mask in the US is approx. $18.

They're not widely available to non-medical buyers because they're still not easily attainable for medical buyers. N95s aren't the easiest thing to manufacturer, so ramping up production to fully satisfy current demand would require a significant investment in time and capital. Companies aren't going to do that without some certainty that they'll actually be able to sell enough of their extra production to cover the initial investment. Nobody has provided them that certainty, so they haven't made the investment. Instead they're (mostly) just maxing out production on whatever equipment they already have.

I work for a hospital and have been heavily involved in our COVID-related supply chain efforts. Six months into this we are still struggling to find a reliable source of high quality N95s. Our standard suppliers are getting us 100-200 per day, but we're using 10 times that every day.

I don't understand why governments haven't made the contracts and guarantees to ensure increased global production over the long-term (not just for Covid-19). We're going to need a much higher rate of production for years to come, yet everybody keeps thinking "Next month! It'll all be over next month!". I'm tired of this shit, and I'm tired of governments thinking so short-sightedly. The EU alone could make a huge difference in this area, but they're so unwilling to actually effect positive change in the world by using their position as a unified region.

Because incompetence?

Or the competent were ousted for not aligning with the team strategy and lowering morale?

“but they're so unwilling to actually effect positive change in the world by using their position as a unified region”

https://en.wikipedia.org/wiki/General_Data_Protection_Regula..., https://en.wikipedia.org/wiki/Restriction_of_Hazardous_Subst... (Both examples of https://en.wikipedia.org/wiki/Brussels_effect)

Thing is: if the long term necessity for increased production of N95 masks were a no-brainer, companies would commit to building facilities. If governments subsidized producers, and it turns out we end up with more masks then we need, people would accuse them of wasting taxpayer money. Making that call is hard, as companies are ramping up production and articles such as the one being discussed could mean much fewer masks are needed.

Also, it seems at least Germany is working on this. https://www.reuters.com/article/us-health-coronavirus-europe...:

“Germany has said it will foot 30% of the investment bill for companies that manage to get production of the coveted filter fabric started before year-end”

> If governments subsidized producers, and it turns out we end up with more masks then we need,

There's no way to end up with more masks than you need. Masks don't expire. If you're worried about the elastic expiring, require designs where the straps are easily replaceable or removable.

And masks are absolutely necessary for the future. Companies can't rely on society recognizing this, which is why they can't blindly commit to building the capacity for it. But that has nothing to do with how necessary masks are for the current situation and for the future. It's just another typical case of market failure, in the sense that a free market won't optimize for the same things you would if your priorities include things like environmental protection and health. This is something that needs to be regulated and subsidized by governments, who are supposed to be protecting us from future risks instead of pretending that there's nothing they ever could've done and nobody could've foreseen a global pandemic.

Also, if a government cares more about looking good than doing the right thing, then it's a bad government.

My company tried donating 120 boxes of 3M N95 masks to our major local hospitals at the beginning of the pandemic. We only asked that the expense would not be charged to patients directly or indirectly. None of the hospitals accepted the masks based on the no indirect billing part.

This is a story worth documenting if there's a paper trail.

I can see why they would refuse to do this. The effort of tracking which masks were donated vs which to charge for, would be significant.

Who’s going to track which patient was treated by staff wearing donated masks, and which were not?

And if medical staff were working with multiple patients while wearing the same mask, would they have to split the discount for a $1 mask up between patients?

We just wanted our donation to be a donation to patients and staff, not to the business side bottomline. Since n95 masks are practically fungible, it could have easily been credited or treated as a donation to patient bills (as we suggested) whether it be to divide among X random Covid patients or to a single person's ICU bill. The masks value was around $25,000, and who knows what multiple (3-25x ?) the hospital would charge to patients?

The fact is the hospitals gave us no path toward transferring that to patients and not their bottom line. We ended up selling most of our masks to hospitals for that reason, seeing it as the more moral option.

I'm not sure what no indirect billing would even mean. Would they have to track exactly where those 120 boxes were used and subtract some theoretical portion of their bill that would be attributable to the mask expense? No hospital I've worked at would be set up to accomplish that, and 120 boxes isn't nearly enough to warrant trying to set that up. That's barely a day's supply.

Are you guys disinfecting?

If so, which method are you using?

If not, why not?

We are. I want to say we're using UV but I'm not 100% on that.

Just have to spend $10/mask on ebay

$10 per mask seems reasonable in the current environment.

I consistently see them priced for around $18 per mask.

In March, I bought a 2-pack from Tractor Supply for $8.

It took 2 months for me to receive a tactical gas mask, but it also has eye protection, and a variety of filter options.

You can get them, but they are about $18 each.

> Related: can anyone explain why there are still no n95 masks available?

1) The US federal government hasn't stepped in and guaranteed a purchase order to the domestic manufacturers. Companies ramped up for SARS and almost went bust--they learned their lesson. No ramping up unless someone cuts a check.

2) N95 masks require a special type of melt blown material. This material requires high tech manufacturing machines which have long lead times (9-12 months). So, new machines to manufacture this melt blown material are probably just now actually getting installed into manufacturing lines.

Fwiw KN95 (Chinese standard) are available from Costco online for about $2.50 a piece. I assume Costco isn't selling fakes. They have ear loops so the fit isn't as tight as N95 masks and needs some fiddling.

Why would you assume that?

Because multiple governments have found themselves with millions of dollars of fake/noncompliant masks, and last I checked, Costco doesn't have a mask testing facility.

KN94 is the Korean standard. They made their own because the need for a standard arose because of the dust that comes from China. Not sure what KN95 is.

KF94 is a Korean standard. KN95 is a Chinese standard.

Interesting, are you based in the US? N95 masks are still readily available in Singapore and Taiwan.

My wife has been selling NIOSH-approved KN95 [1] masks to folks in the US for the past few months. First she tried to supply them directly to hospitals but ran into a harrowing amount of red tape. Then she listed them on eBay but got banned for “price gouging” despite listing at a lower rate than many of the approved sellers. Now she’s just selling the remaining inventory directly, and completely deterred from trying anything like this again because of all of the obstacles through this process.

Here’s her site FWIW ($128 for a box of 50, $2.56 unit price): https://www.wesupplyppe.com/product-page/KN95-2

[1] https://coronavirus.health.ok.gov/kn95s

Are they really NIOSH approved? NIOSH doesn’t approve KN95 masks[1]. Also, I thought elastic straps have to go around the head instead of the ears to obtain approval.

Can we see the approval certificate?

[1] https://www.cdc.gov/niosh/npptl/usernotices/counterfeitResp....

You are right, I was mistaken, sorry for the misinformation! They went though the NIOSH modified testing protocol, not the official approval process.

They have been tested for respirator filter efficiency only and were found to exceed 99% filter efficiency: https://www.cdc.gov/niosh/npptl/respirators/testing/results/...

But they are explicitly not NIOSH approved and as mentioned have an ear loop design whereas seemingly all approved masks go around the head. Wish I could edit/remove the original posting.

KN95 masks are comparable to n95 masks in their filtration efficiency and you can order them from online stores like Amazon.

The continued scarcity of n95 masks in the US has to do with an incompetent/malicious federal government’s failure/refusal to incentivize massive local production of masks, and a constant increase in demand by hospitals because of the rising number of cases.

The KN95 specification is comparable to the N95 specification. But KN95 masks as a class of real things are often not comparable to N95 masks.

With Amazon's reputation I would be extremely hesitant to order anything health related from them. I'd greatly prefer a store with clear supply lines and no comingling.

SARS Cov-2 infectiousness decays exponentially, with the time constant a function of temperature and humidity. A two-parameter calculator:

https://www.dhs.gov/science-and-technology/sars-calculator

Sounds like wetting the towel first would be the way to go.

Cooking a wet towel would turn the water to steam, I'm guessing that would be problematic for the mask's durability.

Also, the humidity factor seems counter intuitive to me on that site. I thought the virus survived longer in the air in damp spaces, while sunlight dried out the virus rendering it inert.

Would it be wrong to infer from this that letting a face mask sit in room temperature for a week is almost guaranteed to make it safe for use again?

Not wrong at all. I do 3 days in paper bags. Reasoning for paper is that it breathes more than plastic and the half life of the virus is shorter on paper as well.

Don't just look at single studies. This is a meta-review resource: https://www.n95decon.org/implementation

It's a collaboration among the many people doing research on decontamination that also takes into account the tacit implementation knowledge of those who conducted the studies.

Thanks -- within that review we have this link:

https://www.n95decon.org/files/heat-humidity-technical-repor...

There's a table of mask damage as a function of high temperature exposure time. All tests were well below the 100C cited by OP.

Many N95s are rated for a month (20 days) of 8 hours use. If you're only using them for a few hours a day you can stretch their life by quite a bit.

I’ve been using one for a while. I put it on for 30 minutes or so for only grocery shopping. Then stick it in a paper bag and don’t touch it for 7 days. Repeat.

That's what I've been doing with a pack of N100s and it works fine. The problem is threefold: leaving it in a car out in the sun will quickly melt the glue holding the plastic filter to the mask, after a few uses it just quickly gets contaminated on the inside unless you're obsessive about decontamination before taking the mask off each time, and that month rating is because the plastic fibers used to make the electrostatic filter dry out and crumble, which can also be pretty bad for your lungs.

Why don't you cycle 3-4 of them, wearing a different one each day? Viruses won't survive for longer than 3 days inside, so cycling multiple masks would solve the possible contamination issue.

what conditions are present to make this a constant? just heat and oxygen? moisture?

70F / 21C and 50% RH or something close to that, is how standard "indoor" environmental conditions are tested in general.

In my experience I haven't picked up anything because I wasn't the best about decontamination, but I have picked up something when I wore a surgical mask instead of an N95 mask.

I wonder whether the results change with the pressure cooker.

I had ilizarov apparatus[1] on my legs for over a year(once during age 7 and another during age 15) and my mom used to sterilise the instruments (Scissors, Forceps) used for dressing wounds at home(every alternate day) in pressure cooker(on advice of the doctor).

I presume, pressure cookers are still being used for the sterilisation of instruments[2] in several parts of the world as its still common than an electric cooker.

[1]https://en.wikipedia.org/wiki/Ilizarov_apparatus

[2]https://cdn.ymaws.com/sites/adint.site-ym.com/resource/resmg...

I am sure they perform sterilization effectively, but introduction of water/steam (which is under pressure in a "pressure" cooker) will almost certainly deform a mask like an N95 mask.

I thought electric cooker uses less water in contrast to no water.

My reading of the OP was that no water was to be used, and a towel is placed at the bottom to shield the mask from touching the heating element altogether.

It has a bit of water in the bottom, it effectively steams things.

Do not do this. Pressure cookers exist to accelerate cooking, by raising the boiling point of water above 100C, because pressure resists boiling. All plastics in the mask will deteriorate rapidly.

I have a set of N99 masks that I just rotate over a period of about a week in brown paper bags.

If you don’t have enough masks for that, I imagine a sous vide machine (like the Joule) would work. Just seal the mask in a plastic bag and place under water for the appropriate amount of time. These things hold very precise temperatures.

> I just rotate over a period of about a week in brown paper bags.

Why the brown paper bags? Do these ensure better evaporation?

Wouldn't simply keeping the mask somewhere kill the virus in 3-4 days? Or, what would be the best way to ensure this within 3-4 days without any damage to the mask?

Paper bags are cheap, provide adequate containment, allow moisture to evaporate, and the virus is stable on paper for less time than on plastic.

Mainly this. And I can write the date of last use on the outside of the bag.

Wouldn’t that jeopardize the filtration ability of these masks by affecting the fields of the electrets under heat?

absolutely. don't do this please. The filter is able to filter out particles smaller than 0.3um by using weak electrostatic forces. baking it will make the mask less effective. if you can just have a few masks that you rotate through... the best would be a 3 day rotation.

there's a good reason the CDC doesn't say to do this.

anyway .3 micron particles are the hardest for a mask to filter out because they are small and tend to go in a straight line more than the smaller particles. the filtration effectiveness of the mask is a u shaped curve with a trough in the region of the .3 micron particle sizes.

I bought one of these UV sanitizer boxes to sanitize my N95s: https://www.amazon.co.uk/gp/product/B085XZPLVS/ref=ppx_yo_dt...

I'm still not totally certain how well it really works, but I know it works better than those UV wands (you need at least a few minutes of exposure).

It's also neat for a few other things that it's probably healthy to sterilize a bit more frequently (e.g. keys, phone, toothbrush heads).

Yup, my wife went all out and got one of those UV sanitizer boxes[1] too along with the Under Armour face masks[2]. Their instructions say to wash it but it's convenient to just place in a box. We have also been cleaning other items in there including baby toys.

[1] https://lumolite.com/

[2] https://www.underarmour.com/en-us/p/ua-sportsmask/1368010.ht...

Underarmour.com:

> Polyurethane open-cell foam lets air through ...

And virus particles.

I can understand how UV light can sterilize hard surfaces like a cell phone, but how does it sterilize multi-layer fabrics where the virus may be shaded from the UV light by the fabric?

Their website states and shows that face masks are items you can sanitize. They also have a testimonial from a health care worker that uses it for masks. Neither go into details but their FAQ page says "UV-C light only sanitizates surfaces it can reach" so that is a fair question you are asking they should address.

And that is called the shadow effect. The UV-C doesn't much make it into the plastic statically-charged inner layer of the mask.

In May I built a 5-ft long 24x24" cross-section sealed plywood box with a small (6x6") MERV13 filtered inlet opening and an auto-detailing fogger filled with 3% hydrogen peroxide at one end. A center chamber with a web of small hooks on a wire frame for the N95 masks, mirror (plexiglass) glued on the walls of the center chamber to bounce the UV-C around and an 18" long Blade UV-C (254nm) lamp that peers in through a slot on the top of the chamber. On the far end I used a ~30cfm duct fan to pull the the hydrogen peroxide fog through the chamber and masks and a flexible duct to take the exhaust outside my garage. I used UV-C dosimeter disks to tune the amount of time needed for proper UV-C exposure (about 5 mins or so). I put the masks in it, turn on the Blade UV-C lamp, turn on the fogger and let it go for about an hour. I then turn off the fogger and let the fan pull fresh air through for another hour or so. It's not pretty but I think it is effective.

My wife thinks I am crazy.

Already had this on hand for sanitizing CPAP/BiPAP supplies and so it's been getting extra use during covid season this year.

An autoclave is what the electrical cooker is being used to emulate. A pressure cooker is a better option if you'll be on the road, camping, or otherwise without electricity. Researchers in Canada already proved several months ago that N95 masks could be sanitized this way:

https://news.ycombinator.com/item?id=22761264

Unfortunately the referenced NewsArticle does not link to the ScholarlyArticle https://schema.org/ScholarlyArticle :

"N95 Mask Decontamination using Standard Hospital Sterilization Technologies" (2020-04) https://www.medrxiv.org/content/10.1101/2020.04.05.20049346v... :

> We sought to test the ability of 4 different decontamination methods including autoclave treatment, ethylene oxide gassing, ionized hydrogen peroxide fogging and vaporized hydrogen peroxide exposure to decontaminate 4 different N95 masks of experimental contamination with SARS-CoV-2 or vesicular stomatitis virus as a surrogate. In addition, we sought to determine whether masks would tolerate repeated cycles of decontamination while maintaining structural and functional integrity. We found that one cycle of treatment with all modalities was effective in decontamination and was associated with no structural or functional deterioration. Vaporized hydrogen peroxide treatment was tolerated to at least 5 cycles by masks. Most notably, standard autoclave treatment was associated with no loss of structural or functional integrity to a minimum of 10 cycles for the 3 pleated mask models. The molded N95 mask however tolerated only 1 cycle. This last finding may be of particular use to institutions globally due to the virtually universal accessibility of autoclaves in health care settings.

The ScholarlyArticle referenced by and linked to by the OP NewsArticle is "Dry Heat as a Decontamination Method for N95 Respirator Reuse" (2020-07) https://pubs.acs.org/doi/full/10.1021/acs.estlett.0c00534 . Said article does not reference "N95 Mask Decontamination using Standard Hospital Sterilization Technologies" DOI: 10.1101/2020.04.05.20049346v2 . We would do well to record that (article A, seemsToConfirm, Article B) as third-party linked data (only if both articles do specifically test the efficacy of the given sterilization method with the COVID-19 coronavirus)

I don't want to appear a naysayer, but everyone should be aware that N95 masks usually aren't effective at the intended level because of the lack of a fit test and training by the non-professional users.

See:

https://news.ycombinator.com/item?id=23957506

Generally,the instant pot requires at least 1 cup of water when running, according to the manual.

How does this work without water ?

You can put another container inside the instant pot to hold the masks. That is how you make things like cheese cake in them.

But steam may ruin the masks, and the instructions on sanitizing don't mention water.

I'm also wondering, IIRC rice cookers rely on the temperature of the pot not exceeding 100C until all the water has evaporated (which is why getting the correct rice/water amount is important). Without any water in the container I would expect the pot to quickly exceed 100C and shut off.

Mine certainly seems to provide no way to maintain such a temperature, I'd guess it'd just switch to "keep warm" and AFAIK that's nowhere near 100C (maybe 60~70).

the cheap rice cookers use a temperature switch that triggers after it reaches a bit over 100C yes.

What do more expensive cookers use? A timer sounds more simplistic than a temperature sensor, are they mixing the temperature information with something else?

they use some more advanced logic than just on or off until it boils off the water

https://lifehacker.com/why-some-rice-cookers-are-20-and-othe...

There's no reason you can't run these pots without water (in theory). I don't think you'd damage the heating elements themselves. This is an issue for heating wire like NiChrome where if you put a high current through it, it'll melt. The elements in a slow cooker could probably handle a much higher current than you would normally use. And obviously the elements themselves can withstand the nominal operating current. I'm assuming a slow cooker/crock pot, not a rice cooker. The one I have at home is very very simple, electrically. Rice cookers are a bit more complicated and might be more finnicky because they have to go through some fairly accurate states within a short amount of time (and make assumptions about the level of rice/water in the cooker).

It probably depends if your pot has a thermostatic control or not. Some pots might damage their coating if there is no "load" to sink the heat into. Fancier units might shut off if they detect that they're being run empty. Cheaper pots might put out enough heat that if nothing is in them, they'll damage the non-stick. But if your pot is designed to hit a set temperature, it should be OK regardless of whether there's anything in it.

Anecdote - our milk frother (a cheap Lavazza Mi Moda) has fill levels for heat/foam, but is also clearly thermostatic. The second time you run it (say if you make two cups back to back), it takes much less time to indicate it's finished when it starts from warm. My guess is that it's designed to heat the milk up to a preset temperature (measured using the wall of the chamber) and then it ramps up the whisk for a preset period of time.

I really doubt cheap slow cookers use PID loops to control the temperature. They're normally "bang bang" relay driven - they hit a set temperature and the elements turn off. When the temp decreases they turn on again. Perhaps if there's no load in the cooker they'll keep over/undershooting.

You might be able to put a piece of something like cast iron in there to heat up initially, then when the unit is up to 100C, take it out and replace with the towel/masks. My guess would be you want to avoid an initial thermal runaway more than anything else. Also if you're using a crock pot for covid sterilisation, maybe you don't want to use it for food!

Would that not depend on the type of Instant pot you have? There are so many now

Many of a Sautee mode used to brown meat, I dont think you need a 1 cup of water for that? or the ones with the Air Fry attachments...

The ones requiring water are pressure cookers, and not suitable for this purpose (steam, high pressure + high temperature will cook your mask). I think the article is discussing a multi-cooker with a 'slow cook' setting, and using the 'instant pot' term to mean multicookers in general rather than the 'Instant Pot' brand name cookers.

How does this compare to just letting the mask sit for several days?

Cooking the mask ensures that microorganisms on it will die and not pose a risk to the wearer. A mask sitting around for several days can still harbor them in some cases.

I see that in general, but if we're wearing N95s specifically to protect against the coronavirus then several days seems like it should be (a) enough and (b) not as hard on the mask?

This is what I do. I just place it in a plastic bag and don't use it for about a week. I have enough to let me use one each day and quarantine the used mask for a week.

What's the plastic bag for? Seems like a good way to promote bacterial and fungal growth.

I'm using open plastic bags for avoiding touching the mask itself. I figure there's enough air circulation when I let the bag sit open on a shelf. Granted a paper bag could be better.

Happened to have bought a towel warmer with UV sanitation pre-pandemic. There are some early reports that heat and UV neutralize the virus.

None of this is necessary for non-healthcare workers, since the virus will die off on a fabric mask in a few hours.

1) Not a single study has demonstrated that viable Sars-Cov-2 virus survives on porous materials in the real world

2) Even before Covid, it was known for decades (common medical knowledge) that human coronaviruses and flu viruses do not remain viable on porous materials for more than several hours.

That this common knowledge is not so common knowledge among the public is a failure of public health communication. The one or two alarmist studies showing that the virus "survives" X number of days don't reflect the real world because 1) the researchers literally directly douse or soak the surface with a huge viral load, and 2) the researchers usually only look for viral genetic material, not whether the virus can infect cells. Viability != detecting viral genetic material (same story for people - we shed viral genetic material long after we stop being contagious).

There is a reason the CDC has always said surface transmission is rare: https://www.nytimes.com/2020/05/22/health/cdc-coronavirus-to...; there have been no documented cases of surface transmission: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-si... Fortunately some in the media are catching on to the hygiene (security) theater: https://www.theatlantic.com/ideas/archive/2020/07/scourge-hy...

Citations for 1) and 2):

Most studies use unrealistic starting doses: https://www.thelancet.com/pdfs/journals/laninf/PIIS1473-3099...

Other human coronaviruses don't survive long on porous surfaces (gone by 6 hours): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7134510/. A hospital randomly collected patient and real surface swabs (including non-porous surfaces) for original SARS, a minority were PCR positive, none of the swabs were infectious (viral culture): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7134510/. Same story for flu (virus can be detected for days, but inactive and not viable after a few hours): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3222642/.

I could only find this study on Sars-Cov-2 that cultured the virus (still used a huge viral dose in a lab setting, not the real world). Even though they were able to culture the virus, only 1% of virus remains after 6 hours on a surgical mask, several orders of magnitude less for cotton clothing: https://www.medrxiv.org/content/10.1101/2020.05.07.20094805v...

This long post was originally meant to be a reply to someone asking for a citation; it's yet another example of how much effort is required to combat misinformation.

"Interim Recommendations for U.S. Households with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19)" https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-si... :

> On the other hand, transmission of novel coronavirus to persons from surfaces contaminated with the virus has not been documented. Recent studies indicate that people who are infected but do not have symptoms likely also play a role in the spread of COVID-19. Transmission of coronavirus occurs much more commonly through respiratory droplets than through objects and surfaces, like doorknobs, countertops, keyboards, toys, etc. Current evidence suggests that SARS-CoV-2 may remain viable for hours to days on surfaces made from a variety of materials. Cleaning of visibly dirty surfaces followed by disinfection is a best practice measure for prevention of COVID-19 and other viral respiratory illnesses in households and community settings

My big concern is modifying the electrostatic properties of the fibers which is how much larger fibers stop much smaller particles (order of 10x-100x). It looks like moderate heat and no humidity in this study didn't have those effects. Hoping this can be peer reviewed soon!

Can someone explain why you can’t just have three masks, and circulate through them? We’ve been told that the virus dies after 3 days just sitting there. Why do I need to decontaminate it ad in TFA? I don’t get it.

There are other things other than SARS-CoV-2 that can get trapped in those masks that ought to be decontaminated by some means.

Such as? Anything I wouldn't be inhaling in normal circumstances anyway?

I rotate 10 masks, wear each of them 20m/day at most. Drop out of rotation if smelly (only happened once with serious sweating).

I would not use this method for N95 masks with plastic exhalation valves due to potential melting of the latter.

direct sunlight kills everything eventually

Another way to clean masks is to put them in a bowl of hot water (at least 70°C) and add detergent. Let it sit for a few minutes and you‘re good to go.

this will damage n95 masks

if your concern is corona, there's no need to do any of this for most people, most of the time (i.e., not a front-line worker). the likelihood of getting live corona on the mask is pretty low, and any corona that does get on the mask will die naturally overnight. certain situations like going to a party might warrant it, but in that case, just throw the mask away and use a new one next time.

if you're more worried about other bacteria and viruses, it's a little more relevant, but not much for most of us. despite the endless news coverage, it's just not worth worrying about unless you're often in elevated risk situations, like being a medical worker. just wash your hands occasionally (particularly after situations like going to the bathroom or handling raw meat).

You make a lot of claims here about how to properly protect oneself, and as matters as important as this one, citations should be considered strictly necessary.

And the reasons people ask for citations is what you are saying is very misleading. The CDC estimates that 45% of US Adults fall into these increased risk categories. So no, it's not just people fighting off cancer it's almost half the country.

> We estimated that 45.4% of US adults are at increased risk for complications from coronavirus disease because of cardiovascular disease, diabetes, respiratory disease, hypertension, or cancer. Rates increased by age, from 19.8% for persons 18–29 years of age to 80.7% for persons >80 years of age, and varied by state, race/ethnicity, health insurance status, and employment.

1. https://wwwnc.cdc.gov/eid/article/26/8/20-0679_article

Am I reading this right, does this mean that 45% of the country has a serious pre-existing medical condition?

> A greater percent of men (47%) have high blood pressure than women (43%)

https://www.cdc.gov/bloodpressure/facts.htm

none of that makes any difference. basically no one needs to disinfect masks, including those at elevated risk (emergency personnel and hospitals facing shortages the likeliest exceptions). just wear your mask at appropriate times (indoors when you can't distance from strangers for extended periods of time). regular folk don't need to do more than that.

What did the parent comment say about people fighting cancer?

I've heard you can use 151-proof grain alcohol in lieu of rubbing alcohol (which has disappeared entirely from store shelves for months) in order to sanitize things. Apparently if you mix it with vegetable glycerin you can create your own ersatz hand sanitizer?

I was thinking you could create your own rubbing alcohol by mixing water, sugar, and yeast, distill it over your stove, and then combine it with aloe vera to create hand sanitizer, but that's probably less preferable than using store-bought ingredients that are more consistent.

I’m not a medical professional, but since 151 is basically 75% ethanol, and ethanol is sold as a cleaner/disinfectant when pure, i assume it would work well.

Please don't disinfect an N95 or N100 mask with alcohol (of any sort). It will dissolve the plastic fibers of the filter.

How do you know this?

https://smartairfilters.com/en/blog/sanitizing-masks-with-al...

Thanks very much for that link (and the links contained in it.)

I'm using 75% ethanol in a spray to "sterilize" (for SARS2 only, it's a fragile virus).

Even if the efficiency drops after spraying (which is not the same as soaking), I think it's still better than just a cloth or surgical mask.

The link to making high efficiency masks

https://groups.oist.jp/nnp/diy-face-mask

in the link you provided is quite interesting. The concept of HV electrostatic blowing of polyethylene is new to me - I wondered how N95 masks were made. I note that in the cotton candy machine experiments they reduced the voltage to 50V, lol.

I'm going to reserve judgement on the physics behind making electrostatically charged fibers and the question of how long they retain the charge. That's an interesting area to investigate! For example:

https://www.tandfonline.com/doi/abs/10.1080/00022470.1974.10...

Ethanol and isopropyl alcohol don't dissolve polypropylene, so the efficiency loss must be due to some other effect.

If the small fibers in the N95 mask have charge embedded in manufacturing, i.e. they are electrets, perhaps the removal of surface charge by alcohol (or screening by adsorbed alcohol?) is only temporary, and if the masks were tested a couple of days later, perhaps their efficiency might have recovered?

https://search.proquest.com/docview/236317922

I would appreciate it if the Federal administration put some effort into upping production of N95 masks for everyone - I've used them for years as dust masks, and now they are not readily obtainable. I still have a small stash, which we reuse and spray down with Everclear 151 after use.

If you're going to DIY hand sanitizer you may want to follow this WHO guidance: https://www.who.int/gpsc/5may/Guide_to_Local_Production.pdf

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