
Stanford researchers confirm N95 masks can be sterilized in oven - notRobot
https://m.box.com/shared_item/https%3A%2F%2Fstanfordmedicine.box.com%2Fv%2Fcovid19-PPE-1-1
======
anonsubmit2671
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.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3078131/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3078131/)

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

~~~
basilgohar
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.

~~~
saagarjha
I just copied the DuckDuckGo Unicode Instant Answer
([https://duck.co/ia/view/unicode](https://duck.co/ia/view/unicode)) ;)

------
wideasleep1
"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

~~~
Scoundreller
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.

~~~
wideasleep1
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.

------
elihu
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

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

~~~
remote_phone
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.

~~~
koolba
Can I disinfect other things like mail or a cardboard box with a UV light?

Alternatively, would leaving things under the sun have a similar effect and,
if so, how long would it take?

~~~
throwaway2048
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.

~~~
nfpfish
UVC is safest actually. Short wavelength is absorbed by dead skin cells. Never
gets to live.

------
ancorevard
FYI. Dr. Larry Chu is an absolutely brilliant person. This should be
considered as solid evidence and recommendation.

------
rfgasser
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.

There are 1000 nm in 1 um.

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

~~~
cmbailey
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].

[1] [https://www.infectioncontroltoday.com/environmental-
hygiene/...](https://www.infectioncontroltoday.com/environmental-
hygiene/understanding-physiology-healthcare-pathogens-environmental-
disinfection)

------
ravenstine
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.

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

------
petilon
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?

~~~
swsieber
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.

~~~
Scoundreller
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.

~~~
thedudeabides5
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.

~~~
Scoundreller
Yup, it's continuous, not discrete.

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.

~~~
WalterBright
There's also a distinct probability that your pencil will suddenly levitate an
inch then drop back. I'm not kidding.

~~~
Scoundreller
Next you’ll try to convince me that the moon can pull stuff from the earth
towards it.

~~~
saagarjha
There's a small probability it'll stop doing that ;)

------
nsxwolf
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.

------
MivLives
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.

~~~
ancorevard
Origin [https://aim.stanford.edu/covid-19-evidence-
service/](https://aim.stanford.edu/covid-19-evidence-service/)

~~~
MivLives
Fantastic! Thank you for linking this.

------
twomoretime
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.

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

------
alephnan
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:

[https://www.lg.com/us/styler-steam-closet](https://www.lg.com/us/styler-
steam-closet)

It's relatively effective according to this article

------
Cantbekhan
The dutch are doing it with hydrogen peroxide in their official
recommendations [https://www.rivm.nl/en/documenten/reuse-of-
ffp2-masks](https://www.rivm.nl/en/documenten/reuse-of-ffp2-masks)

------
woodchuck1
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

------
nohat
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.

~~~
tartoran
The temperature would be too high and would damage the microfibers

------
sizzle
Anyone know if this method works with the disk filters you put on the half
face mask?

[https://www.3m.com/3M/en_US/company-
us/all-3m-products/~/3M-...](https://www.3m.com/3M/en_US/company-
us/all-3m-products/~/3M-Particulate-Filter-2091-07000-AAD-P100-100-EA-
Case/?N=5002385+3294780267&rt=rud)

------
shard
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.

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

------
ngcc_hk
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.

------
einpoklum
From the fine article:

> IMPORTANT NOTICE

> Do not use anything in your home to disinfect contaminated

> equipment. Please do not heat your masks in a home oven!

------
charliewallace
Alternative method - how about putting the masks in a box with an ozone
generator? Comments?

~~~
swader999
Dangerous and it degrades them.

------
kposehn
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.

~~~
smacktoward
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.

~~~
ringshall
I doubt you'd want what is essentially medical waste burning off inside a
commercial food oven.

~~~
smacktoward
As opposed to peoples’ home ovens?

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.

~~~
catalogia
Why is there presumed to be an oven shortage at all?

~~~
Aeolun
Much more need for an average oven every day than face masks, or ventilators.

~~~
catalogia
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.

------
opendomain
I got a digital toaster over to try this at home, but the lowest temp I can
set is 200 degrees F. Can I still use it (with a shorter period)?

------
mdani
Wondering if direct sunlight would be as effective as UV light?

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

------
notRobot
Tl;DR: 70C /158F heating in a kitchen-type of oven for 30min, or hot water
vapor from boiling water for 10 min, are effective decontamination methods.

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

~~~
notRobot
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.

------
WalterBright
I'm curious why UV light couldn't be used, or even X-ray machines, or one of
those "gamma knife" machines.

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

------
koolba
Is the resulting mask totally sterilized that it could be used without issue
by a different person?

~~~
Scoundreller
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.

------
10Meadowood
Does anyone know if this applies to the N95 masks with a cool vent?

------
mk6
Is there a method if an oven is not available? In a bag in a microwave?

~~~
tiredwired
The article mentions microwaves melting the masks.

------
raleighm
Flagged this in hope of a more reliable source than a PDF in Box.

~~~
wideasleep1
Well, apparently source Stanford App uses Box, link appeared in Reddit:
[https://stanfordmedicine.app.box.com/v/covid19-PPE-1-1](https://stanfordmedicine.app.box.com/v/covid19-PPE-1-1)

------
syspec
Will the rubber bands on them melt at that temperature

~~~
aethertap
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.

------
jaequery
anyone know the effects of spraying sanitizers all over the mask after use?

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

------
maallooc
Sterilize? Sure. But after it the mask won’t be able to filter on N95 level.

~~~
Scoundreller
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.

~~~
wideasleep1
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...

------
metreo
Has this been checked on Snopes.com?

------
bjoyx
This was "fact checked" weeks ago as false (lol)

[https://factcheck.afp.com/novel-coronavirus-health-
experts-w...](https://factcheck.afp.com/novel-coronavirus-health-experts-warn-
against-steaming-face-masks-reuse-after-misinformation-chinese)

~~~
ancorevard
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.

------
gshdg
Critically, this was tested with E. Coli, NOT a coronavirus. This method has
not been proven effective for the current epidemic.

~~~
toptal
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?

~~~
echelon
Not at all!

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.

~~~
NegatioN
So we're accepting E.coli as a benchmark here, because we're pretty sure it
destroys the viral envelope?

Why is this more than a guesstimate? It strikes me as odd to test for virus
disinfection by using a bacteria, but I am a complete noob in this field.

~~~
compiler-guy
You did read the author's qualifications, did you not?

Consider your qualifications, ('I am a complete noob in this field.') compared
to theirs.

Amy Price, DPhil (Oxon) ... earned her Doctorate in Evidence Based Health Care
at The University ofOxford.

Larry Chu, MD, MS (Epidemiology) ....

If anyone understands the science, and the limitations of their study, it is
themselves and they caveated their conclusions carefully.

Is it peer reviewed? No. But it is the best science we have at the moment.

A noob in the field isn't going to find a hole in two minutes that two serious
professionals haven't thought about.

~~~
NegatioN
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.

~~~
compiler-guy
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.

