Stanford researchers confirm N95 masks can be sterilized in oven

More recently: a 2017 mask decontamination study from Taiwan that compared a number of commonly-available solutions, using several mask types including N95:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5638397/

Surprisingly, the method that worked best was...

> "Place the test masks in a traditional electric rice cooker using dry heat for 3 minutes (149~164°C, without adding water)."

Apparently dry heat was much better at preserving the structural integrity of the different masks, compared to chemicals or steam.

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.

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.

Do we need the steam bags to pack the n95 respirators? Or is it okay to just put inside the oven.

TIL U+2103 DEGREE CELSIUS and U+2109 DEGREE FAHRENHEIT.

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.

What about ozone? I've been thinking of putting them in a box and ozonating them.

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.

https://en.wikipedia.org/wiki/Pyrimidine_dimer

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.

My N95 mask smells like burnt plastic after 7 minutes under UVC (254 nm), I wonder if that means the mask is damaged.

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?

It says in the article that (end of page 4)

"4C Air confirmed all the proposed treatments have killed corona viruses."

E. coli are much heartier than viruses and harder to kill. If they kill bacteria they will definitely kill viruses.

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.

Just guessing that the static charge comes from a coating which is soluble in alcohol but not water.

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.

IIRC, there were still traces of the virus on the diamond princess 15 days after it was cleared out. So it might be able to last longer.

No, SARS-CoV-2 is thought to have a half-life of about 72 hours on some surfaces but some virus particles can survive much longer.

(edit: that's not right, the half life is shorter with the virus still infectious on a surface for 72 hours or so)

https://www.youtube.com/watch?v=JNQUHc8wbRc

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.

I was thinking the same. Or keeping it in very dry environment that desicate the virus?

Coronavirus survived for over a week on that empty cruise ship.

Origin https://aim.stanford.edu/covid-19-evidence-service/

Surgical masks have an air gap, so are not comparable to N95 masks at all in that regard. They are solving different problems.

The temperature would be too high and would damage the microfibers

Here's a study on the surface lifetime of SARS-Cov-2: https://www.nejm.org/doi/10.1056/NEJMc2004973

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.

Dangerous and it degrades them.

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.

I'm really curious if you'd get the same results if you put the mask in a bag and sous vided it.

People could do that on their stove with a pot of water and a thermometer.

A $50 electric oven is probably enough for a few hospitals. No need to go searching it.

Food dehydrators may also work well for this. They usually range around 90-140f.

Many of them have stackable horizontal racks which may make it possible to 6-12 at a time.

edit: s/vertical/horizontal/

Food dehydrators can go lower temperature.

The ozone layer filters out most of the UVC light which is needed to destroy the virus / bacteria.

Is there a way to configure an autoclave to work at such low temperatures?

Water vapor from boiled water seems much easier

They included UV Light in the study. It is comparable to the hot oven.

UV light might damage the mask itself. Radiation will work but that's not readily available like an autoclave or oven.

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.

The article mentions microwaves melting the masks.

Microwaves work by heating the water in food. They don't work properly on paper.

The dryer is a much better alternative.

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.

A steamer on a stove seems like a safer bet.

There is a metal clip on the respirator for fitting.

check the last article I submitted.

Well, apparently source Stanford App uses Box, link appeared in Reddit: https://stanfordmedicine.app.box.com/v/covid19-PPE-1-1

No, I've done this with my mask (n95, same one I use for wood working) four times now and it appears to be fine.

It's covered in the article. Sanitisers cause the mask to lose effectiveness due to loss of static charge in the microfibres.

Slide 5 says it's fine.

I'd doubt it's sterilized though. Fungal spores will survive this process. But it'll kill viruses: high heat is often good enough.

Keep in mind that N95 is made from polypropylene, which is an autoclavable plastic.

Sterilization is overkill anyway: N95s aren't sterilized from the factory in the first place.

The fact check is obviously incorrect. But note that this research also considers "baking" in oven at 70 celsius for 30 min, and other tests.

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.

How is that the same? This is steaming

Yeah the fact check is about steaming (which is totally unrelated and closer to autoclaving, which doesn't work)

Critically?

> 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 don't cherry pick here.

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?