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Ask HN: Irradiation to reuse surgical masks?

25 points by vermorel ↗ HN
High-quality surgical masks require nonwoven fabric that appears to be in short supply at WW level. Reusing masks is typically a big no-no due to obvious reasons. Autoclaving them is not an option either as it would damage the fabric. However, what about reusing the (somewhat) extensive food irradiation facilities to reuse masks faster? Viruses are notoriously resistant to the usual kGy doses used for food, but my (uneducated) guess is that it's a matter of dosage, RNA is a complex fragile molecule. Is there any blocking element that would prevent mask reuse after suitable irradiation?

24 comments

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sloaken
Great idea, I love it. Only reason I can think of is fear of lawsuit. "they reused a mask and I caught xyzzy" - of course there is no proof that was the source, but nuisance lawsuits are common.
m-ee
Health care workers are already reusing masks due to short supply
pacamara619
You seem to be forgetting that the rest of the world is not as litigious as people from the United States.
Gustomaximus
Add to that the emergency nature of the choice is reuse or have nothing. I suspect lawsuit risk at least today is limited.
toomuchtodo
Are there any gamma emitting devices at hospitals that could repurposed for this? Such as those used for cancer therapy? Or imaging devices (CT scanners)?
vermorel
I doubt it. Those devices are not designed to pour lots of kGy into stuff. Food irradiation typically involve some kind of lead-covered mini-tunnel with the radioactive source in the middle. Definitively not an expert, but I suspect the radioactive sources used for food irradiation to be two to four orders of magnitude stronger than what is used for therapy.
yummypaint
Dosage for food is like a 1000 Gy, for therapy on people its more like 1-10. A medical 60Co source could still reproduce the same effect by putting the masks right against the aperture and increasing exposure time. No idea if this would destroy viruses, though.
vermorel
I have found literature on this, look for "Sterways Process". It seems that it starts to be safe virus-wise somewhere around 35kGy.
saurik
The studies show you can UV-C them (it reduces the physical strength of the mask but not the filtration ability, and can be done many many cycles: I think I saw at least 20); have you actually tried searching for how to sterilize masks yet?
nikolay
UV does not kill coronavirus.
Doxin
Do you have a source for that? I'd be very surprised at the existence any organism that's entirely impervious to UV. Especially something like a virus that doesn't have active repair machinery (or any machinery altogether) when it's out and about.
viggity
I bought a few UV-C lamps for this very purpose. I'm sorry I can't find the research I found, but it said that UVC does indeed work, but lowers the efficacy such that it's not worth it more than 5 times (although, I think'd rather re-use a UVC N-95 mask than make one out of paper towels or a home sewn one).

The same research said isopropyl alcohol was a terrible idea as it kills the electrostatic nature of the filter. It said a light bleach solution worked best and could be re-used indefinitely.

A DIFFERENT study showed that soaking in a saltwater solution (NaCl) and letting it dry was extremely effective. As droplets hit the micro salt crystals the a very small solution forms, then recrystalizes as it dries. The crystalization essentially rips the virus apart. https://www.businessinsider.com/mask-coated-in-salt-neutrali...

There are some anti-viral masks that use citric acid, AFAICT for the same reason. bulk Citric acid can be bought in the canning aisle at any grocery store as it is needed to make jams. Although I imagine salt is even easier to find

http://ryanpharmacy.com/curad-antiviral-face-mask/

burfog
Autoclaving is fine. Pick the hottest non-damaging temperature.

The plan in some places is to put a mask in a paper bag, write the date on it, and leave it in a warm place for two weeks. This does require that every worker have two weeks worth of masks, plus spares to replace masks that get really splattered.

vermorel
Not sure about that. Electrostatic properties of the nonwoven fabric must be preserved. Tough pathogen likes spores must be eradicated as well. Then, the "warm place" must be kept sterile, or it's going to become the infection vector. The solution must be scalable.
burfog
Coronaviruses do not make spores. Even new masks are not sterile. Paper bag storage scales with the number of employees; each employee needs personal space for 14 small paper bags such as lunch bags.
rubidium
What about just letting it sit out in the sun for a couple days? Sunlight and warmth kills the virus. Would it have a negative material effect?
vermorel
Covid-19 isn't the only pathogen around, there are many tougher pathogens. I suspect a few days of sunlight won't be enough for those.
Gibbon1
I don't know what the answer is but it's a materials problem. Almost all medical stuff gets sterilized after manufacturing and packaging. The common ways are gamma radiation, ETO gas, steam. Less common are ebeam and Chlorine Dioxide.

There is no golden process. Materials especially polymers have limits to how many times they can be sterilized. Different materials/different processes.