Comment by elihu | Hacker News Reader

Comment by elihu | Hacker News Reader

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.

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.

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.

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?

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.

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

Is there a good reference on how to calculate the time based on the wattage W and distance of the bulb D?

Just want to not 254nm does not kill the virus, it requires 222nm UV-C. Only one manufacturer exists in the US for the bulbs AFAIK.

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.

I tried this and was not happy with the results

The mask deformed, got wet, and I do not believe the mask got hot enough - it was cool, including the metal parts.

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