There was another study from 2011 showing the use of steam bags in microwaves, but localized extreme temperatures might destroy microfiber structures like putting microfiber cloths in a clothes dryer.
In a conventional oven, 75 ℃ / 167 ℉ for 30 minutes is sufficient to inactivate SARS-CoV-2. If someone were worried about packages, mail or objects being contaminated, placing them into the oven like this would probably work if allowed to reach that temp internally for that time.
More recently: a 2017 mask decontamination study from Taiwan that compared a number of commonly-available solutions, using several mask types including N95:
I would suspect if the general population was told to do this we'd have more disruptions due to house fires than from the increased risk of unboxing packages outside of the door, discarding them and then washing your hands and clothes.
If you have a thermometer you can turn the oven off manually as it approaches your target temperature. I do this for warming bread dough. Once you know how long it takes you don't need the thermometer.
People can use a water bath like one of those sous vide machines. You seal the mask in a ziploc bag and weight it down below the surface. That should be a pretty consistent temperature of 75C.
I'm confused by all the disclaimers regarding home ovens. WHY NOT a home oven, what is the scientific reason? I've been baking N95s on a tray in our kitchen oven at 170F for ~20-30 min and reusing. These articles seem to suggest that's a bad idea but do not say WHY. Would love to know WHY.
Perhaps just because of the step where you bring the contaminated N95 into your home kitchen and handle it there, before it enters the oven? This sounds tricky to get right.
It took me a few passes to realize you were not just being comically excited and typing in all caps, but rather, everything you typed is rather pedantically and accurately capitalized.
> Several letterlike symbols are used to indicate units. In most cases, however, such as for SI units (Système International), the use of regular letters or other symbols is preferred.
> In normal use, it is better to represent degrees Celsius “°C” with a sequence of U+00B0 degree sign + U+0043 latin capital letter c, rather than U+2103 degree celsius. For searching, treat these two sequences as identical. Similarly, the sequence U+00B0 degree sign + U+0046 latin capital letter f is preferred over U+2109 degree fahrenheit, and those two sequences should be treated as identical for searching.
It's most likely for round-trip compatibility with another encoding. There are many Unicode codepoints that simply represent combinations of other codepoints. If you don't care about round-tripping, just normalize everything to NFKC or NFKD (the difference being that accented letters like á are one codepoint in NFKC and two codepoints for the base letter and combining mark in NFKD).
What’s the feminine ordinal indicator. I thought it was a degree sign because as a Portuguese speaker I’ve never noticed the feminine ordinal indicator as an easily accessible option. Are both easily accessible on the iOS keyboard?
I just realized I have used the ordinal symbol many times when I should have used the degree sign. Why didn't someone tell me? Oh, I've been making an idiot out of myself.
That depends on the keyboard layout. On the Norwegian keyboard for example, ⌥⇧Q produces the degree symbol, whereas ⌥⇧8 produces U+007B LEFT CURLY BRACKET.
"Conclusions: DO NOT use alcohol and chlorine-based disinfection methods. These will remove
the static charge in the microfibers in N95 facial masks, reducing filtration efficiency. In
addition, chlorine also retains gas after de-contamination and these fumes may be harmful."
Damn..I've been spritzing mine inside and out with 91% OH...time to bake like Snoop Dogg
It still works for killing E Coli (and viruses based on using it on hands).
And you still have at least half of the filtration efficiency. Unsure if that means 90% instead of 95%, or 47.5% instead of 95%, but that's still a gain.
The pressure drop was comparable to the other methods, so you're not going to asphyxiate yourself according to the publication.
Says 56.33% efficiency after OH bath...too much for me. I too have a Breville Air Oven, and will simply collect a few masks and bake. A few percent efficiency drop is more palatable.
It's interesting that they tried UV light and as far as they know it works for sterilization but they're not sure if it would cause the mask to fall apart eventually. Maybe there's an optimal UV frequency/intensity that kills the virus but doesn't hurt the mask.
> In summary bleach and microwaves were failures at point of care because the bleach
gases (skin and respiratory irritants) remained after multiple strategies were used to remove them, the microwave melted the masks and soaking them first led to reduced filtration. EtO, UVGI, and hydrogen peroxide decontamination were safe and effective in the models tested but it is not known if they would retain filtration, material strength,and airflow integrity with repeated use. EtO, UVGI, and hydrogen peroxide limitations include time from decontamination to reuse and available space and materials to decontaminate in an OR setting. 70C /158F heating in a kitchen-type of oven for 30 min,or hot water vapor from boiling water for 10 min, are additional effective
decontamination methods
The bandwidth ends up being pretty large, so just about any UV light does the trick for most DNA types. Though there are many ways that DNA can UV light interact to make viral DNA mostly unreplaceable, the primary interest is in dimerization. There are a few dimers that will form via UV radiation, each with their own absorption spectra.
I'd just leave things in the sun for a bit. Clouds are transparent to most solar UV too, so just a direct path to the sun is needed. Rotate the objects a few times, maybe take 1.5-2 hours or so.
However, for things that are also UV sensitive, like masks, follow the recommendations when the research has been looked over a bit. Use an oven.
There was a study done using uvc light to disinfect N95 masks and it had negligible effect on filtration rate. It had some effect on strength but that’s only with massive amounts of UVC light. I think you could easily do 50-100 rounds of uvc disinfection without any worries.
Depending on the intensity of light you have and the wattage is the bulb, 7 mins is way too long. If your bulb is very close to the mask 10 seconds is more than enough.
UV-C is basically entirely blocked by the ozone layer and doesn't reach the surface of the earth.
Its extremely dangerous, and can cause eye and skin damage with under 60 seconds of exposure, it is absolutely something you do not want to be anywhere around when active.
I wonder if we could vacuum pack the masks and put them in a sous vide, it would be a lot easier to implement than finding enough ovens for all of the masks.
As for the bleach leaving skin and respiratory irritants, maybe hypochlorous acid (HOCl) might be a good alternative?
Yes, just make sure you still have good fit. If you put an air bubble in to keep the form, you will need to cook longer to compensate for insulating effects.
How is using E. Coli for testing sterilization an accepted protocol? Viruses, even big ones like corona viruses, are much smaller than bacteria. Viruses are very very different than bacteria.They should have tested the sterilization procedure on a virus. Yes, it is harder but lives are at stake.
Escherichia coli is a rod-shaped bacterium. Each bacterium measures approximately 0.5 μm in width by 2 μm in length.
Coronaviruses are large pleomorphic spherical particles with bulbous surface projections.[12] The diameter of the virus particles is around 120 nm.
Citation was requested: Small viruses like corona viruses have a lipid (fatty) envelope, which is easily compromised. Even more so than large viruses which are non-enveloped. Which in turn are easier to compromise than bacteria [1].
There are two goals here: a) determine whether the mask is damaged by the sterilization technique and b) determine whether that technique actually sterilizes.
The E. Coli experiment is for the latter goal. FWIW, E. coli are a pretty standard way for checking sterilization efficacy. They're easy to culture, fairly hardy, and non-pathogenic. Doing a first pass with live SARS-Cov2 would be incredibly foolhardy (what if the sterilization doesn't work?!)
If they used something this size they might resize quickly that N95 isn't suitable, even new ones. Especially for anyone in a high viral load environment.
Weird that alcohol removes the static charge needed for proper filtration, but hot water vapor doesn't. I'm sure someone with a better understanding of electrochemistry could tell us why.
Wouldn't just leaving the mask alone for say 72 hours decontaminate it? Viruses can't survive for that long, so should be safe to reuse the mask after 72 hours?
The oven method only takes 30 minutes. So masks could be sanitized and turned around for reuse much more frequently than leaving the mask “out of commission” for several days would allow.
The report also found acceptable (if a bit lower) sterilization from applying steam from boiling water for just 10 minutes, which would improve turnaround rates even further.
What about other germs, esp from the doctors' own breath? Doctors in OR need sterile masks and hopefully they don't reuse in that setting. But outpatient clinics and testing sites, sure reuse is better than shutting them down due to shortage of respirators.
This is basically what I'm doing with a box of FFP3 masks I bought years ago and partly used. I only need to go out once or twice a week at most, so I can rotate through them and give each mask a good ~14 day rest.
The authors of that article specially mentioned their work on the princess would get badly reported - and it was. There was no live cornovirus found. Their were traces of RNA (ie, after the virus was killed some of its body parts lying around).
It's a half-life thing. If your equipment is sufficiently sensitive, you could find remaining virus for a long time. Especially if the conditions are right.
Right. People like to think of things like 'sick' and 'healthy' but maybe it's more subtle than that. Things aren't 'clean' or 'dirty' w COVID, but somewhere on a long spectrum.
My running joke with the "up to 3 days" figures people keep sharing is that you could get infected "up to 3 miles away" by someone sneezing if the winds/temperatures are just right and you're EXTREMELY unlucky.
It would, but then you need multiple masks per person if each person uses theirs for 1 day. And even that can be a stretch: once they become moist, they're useless.
It's frustrating that my local hospital is facing a critical shortage of masks, begging for donations -- and there is absolutely no way they will implement this.
They could have people manning the ovens in the cafeteria rotating these things in and out, but wether its fear of liability, "not invented here syndrome", or the idea just sounding crazy, it's not going to happen.
I passed it around to some contacts who work there anyway, but I have no hope.
What is the source on this? Sure it has Stanford medicine stamped all over it, but that is no proof. To be clear I'm not saying anything in it is wrong just wondering why it's hosted on Box.
Does this work for surgical masks as well? Are they actually comparable in filtration size to N95? I need to look up all the values...
Edit: from cdc guidelines:
>SARS appears to be transmitted mainly through direct contact with infectious materials (including large respiratory particles), and surgical masks will provide barrier protection against droplets that are considered to be the primary route of SARS transmission. However, surgical masks may not adequately protect against aerosol or airborne particles,
Presumably as coronaviruses SARS and COVID19 are similarly sized, and I don't know that the aerosolization of COVID19 has been confirmed. So at least in a casual setting like stores I imagine masks should reduce the probability of inhaling viral particles.
Every time I left my apartment unit to take out the trash or pickup a delivery, I've thrown all the outerwear I wore into my steam / dry cleaning machine:
It seems to me that a canning pressure cooker would do a faster and better job of sterilizing than an oven. up to 250 + degrees F at twenty pounds pressure. Available at most hardware stores, home depot, fleet farm etc. 22qt size would do a lot of masks
Has no one tested putting it in a plastic bag and boiling it? At the very least they ought to explain why that's a bad idea if it is, because I can't be the only one to think that's the obvious solution.
What about just waiting for the virus to be inactive then reusing the masks? I haven't found any general consensus, but I've read reports of COVID-19 staying infectious on objects ranging from 1 day to 9 days. If a rotation of masks are used, then there would be no need for washing or baking, which also avoids damaging the microfibers or removing the static charge in the masks.
That seems like it'd be much harder to manage. Given the uncertainty about how long the virus takes to inactivate, you'd have people juggling at least a dozen N95 respirators with varying amounts of contamination.
A quick disinfection protocol with greater certainty seems preferable.
It is not whether you can but whether you have a safe and sterile procedure to do so. Wearing mask is symbolic and protect both sides a bit. But as said it is also meant if you touch the germ on the mask etc. you still can be infected. Now how are you going to protect yourselves if you reuse your mask and what procedure involved, if it can be recycled.
If this indeed is the case, anyone with low-temp ovens should immediately be volunteering them up to help sterilize. Hell, I have two of them the Breville countertop convection oven - It'll go as low as 120F steadily, so 158F should be no problem.
Forget home ovens. Hospitals are surrounded by restaurants with big, roomy commercial ovens, most of which are now closed. A functioning government could commandeer those ovens for sterilization.
Heck, pay the restaurant owners rent to use them — now you’ve solved two problems.
Heck, tell the restaurateurs that when we’re done using their ovens we’ll rip them out and install shiny new ones. Problems that can be solved by throwing money at them are good problems to have right now.
Hardware stores have plenty of electric ovens stocked, it's not like people have been or will be panic-buying them.
Hospitals have ovens anyway, the ones in their cafeteria kitchens if nothing else. But even if that weren't the case, they could just send somebody to a local store and buy one. They could have it purchased, installed and operational by the end of the day.
I dunno about typical commercial ovens, but the ovens at a pizza place go up to about 800F. it's unappetizing to think about, but I don't think any pathogens can survive for long at that temperature. the real trick might be keeping the oven at a steady low temp to sterilize the masks. they're not really designed for that.
A lot of regular kitchen ovens can go as low as 100F or 120F. They’re wildly inaccurate and you need to have a baking sheet or other barrier between the mask and any heating elements to block IR.
Source: by far the easiest way to fix crystallized honey is to bake it somewhere in the 120F to 140F range for an hour or two. All the Internet guides saying to use warm water have probably never tried to put a half-full bottle of honey in water, fully submerged to get all the crystals, and without destroying the label. In contrast, all common bottle plastics and labels are just fine in 140F dry air.
I find that the water method results in crystals staying on the sides of the bottle that we’re above water. These serve as nucleation sites to recrystallize the honey faster.
And the label is nice if you have lots of varieties of honey :)
My 3M P95 masks (purchased for 2018 Camp Fire smoke) come in compressed bags. Also if you sous vide using vacuum sealer bags (e.g. Foodsaver) those are a little more stiff.
According to the document, using an autoclave failed.
> Authors found decontamination using an autoclave, 160C dry heat, 70% isopropyl alcohol, and soap and water (20-min soak) caused significant degradation to filtration efficiency.
I'd think an autoclave/pressure cooker/rice steamer would have a much lower risk of melting plastic fibers in masks since they're physically limited to lower temperatures than a typical oven.
I'm skeptical about that. You can easily put a bunch of masks in an oven at one time. There is no complication at all to that approach and no questions of coverage or distance (did your water vapor get all over the mask properly and at a high enough temp). The oven is fire and forget, pull after 30 minutes.
From a virological POV, yes. But masks conform to the wearer's face. There's a clip and it can only bend so many times. Not sure if the filter itself also conforms over time.
Users are tested for fit, but that test is based on new masks.
Not an expert, but I'd be wary of using a microwave at least for the plastic type filters. If the plastic filter fibers absorb microwaves, it might turn out that the smaller fibers get melted without affecting the bulk structure enough to easily notice.
Was interesting reading all the 1-star reviews on AMZ complaining the packaging wasn't sterile (a bread tie,wtf) then complain the straps didn't fit their ears...
My point is that so-called "fact checking" here was incorrect.
> Dr. Ho Pak-leung, a microbiologist and director of the Centre for Infection at the University of Hong Kong, described the video in the misleading post as “fake news” in an email to AFP on January 30.
In a mask shortage the question of whether masks can be sterilized and reused should never have been dismissed out of hand.
We have medical professionals working without masks as we speak due to the shortage.
Many of our trusted experts have been feeding us misinformation exacerbating the problem.
> 4C Air confirmed all the proposed treatments have killed corona viruses. Labs have no way to test COVID-19 directly and as an accepted protocol, E. Coli is used for testing. We asked what methods can be used to decontaminate the facial mask for reuse safely and without loss to filtration efficiency. 4C Air confirms using 70 degree C hot air in an oven (typical kitchen-type of oven will do) for 30min, or hot water vapor are additional effective decontamination methods.
Keep reading:
"4C Air confirmed all the proposed treatments have killed corona viruses. Labs have no way to test COVID-19 directly and as an accepted protocol, E. Coli is used for testing. We asked what methods can be used to decontaminate the facial mask for reuse safely and without loss to filtration efficiency. 4C Air confirms using 70 degree C hot air in an oven (typical kitchen-type of oven will do) for 30min, or hot water vapor are additional effective decontamination methods. Please see Table 2"
Is there a temperature range that viruses generally die off within? Assuming yes, it would seem a bit peculiar to have to test a specific virus with a specific temperature, no?
Viruses come in many shapes and forms. One of the major features of viruses is whether they have a viral envelope (derived from the host plasma membrane lipid bilayer) or a protein capsid shell.
The structure of capsids can make them more or less hearty.
Luckily for us, Covid-19 and coronaviruses in general have viral envelopes. These are easy to disrupt with soap and susceptible to the environment.
Polio, on the other hand, was damned near impossible to be rid of. Capsids can be resilient.
Other major features are the nucleic acid family (RNA or DNA), encoding (single or doubly stranded, multiple senses), and these impact mutation rate and what host or viral machinery is used. RNA doesn't survive as long as DNA, but that doesn't matter if the virus is in a good environment.
I'm not asking, because I don't trust that this is the best information we have. I am asking, because I want to understand more about how certain the people who understand the subject are about this recommendation.
I thought we (as a computer science-centric population) valued learning over credentials?
I didn't mean to come off as agressively taking a stance, which is /why/ I wrote that I don't know anything about this topic.
They carefully caveated their results, and we all know this isn't peer-reviewed or replicated--although it has been informally reviewed by other scientists.
But it is also very safe to say that serious scientists don't put forth studies that someone completely uncredentialled can poke a hole in with two minutes of thought.
So, I tried reading quite a bit of the comments, and the whole article before commenting.
I might have misunderstood the wording:
"4C Air confirmed all the proposed treatments have killed corona viruses. Labs have no way to test COVID-19 directly and as an accepted protocol, E. Coli is used for testing."
I understood this as: There has been no testing using corona viruses (because there's no way to do so currently?), but instead they're benchmarking with E. coli.(because this has some sort of similar attributes)
But what it's saying is(?): Testing has been done on E.coli AND corona viruses, but there's no standardized protocol for corona viruses, which is why they're focusing on the E.coli aspect.
Please do not assume malintent, even though I know these are stressful times, and we'd do well to let important information surface to the general population, I think a part of that is to understand the limitations of that information as well.
In a conventional oven, 75 ℃ / 167 ℉ for 30 minutes is sufficient to inactivate SARS-CoV-2. If someone were worried about packages, mail or objects being contaminated, placing them into the oven like this would probably work if allowed to reach that temp internally for that time.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3078131/