[jefftk]

> Standard germicidal UV-C lights are ~250nm.

The article is about KrCl 222-nm lights, which people want because they're safe [1] to shine on people, unlike Hg 254-nm lights.

[1] Probably -- I'd like to seem some specific additional experiments before widespread deployment.

[lazide]

222nm is not safe to shine on anyone! It will definitely cause skin cancer.

254nm is also not safe.

254nm destroys ozone, interestingly.

240nm and smaller (160nm being the highest producing freq.) produce ozone.

[https://onlinelibrary.wiley.com/doi/full/10.1111/php.13391]

[bsder]

> 222nm is not safe to shine on anyone! It will definitely cause skin cancer.

The whole point of using 222nm is that it doesn't cause effects on either the eyes or the skin. Consequently, you can use it at higher concentrations without worrying about the leakage.

The issue, as I understand it, is simply that we don't have a decent LED monochomatic source. All of the currently available sources have broad spectrums that have to be filtered out.

[hedora]

The claim that 222nm is an effective disinfectant seems to directly contradict the claim that it cannot penetrate skin. In particular, if it bounces off dead skin cells, and the environment contains dust, how can it possibly kill things on the dark side of the dust particles?

On top of that, reasonable disinfectant timeframes are a few minutes to a few hours, tops. Safety timeframes for human exposures need to be measured in decades if this technology catches on. Claims that lethal dosages of 222nm will penetrate typical glops of pathogens in the environment in seconds, but that cancer causing dosages will not penetrate human skin over years are extraordinary.

Extraordinary claims require extraordinary evidence. Are there long term safety trials for this technology? The article claims “reduced damage” in the abstract, implying routine 222 nm exposure is unsafe.

[bsder]

> The claim that 222nm is an effective disinfectant seems to directly contradict the claim that it cannot penetrate skin. In particular, if it bounces off dead skin cells, and the environment contains dust, how can it possibly kill things on the dark side of the dust particles?

It penetrates single cell walls but nothing deeper.

People are mostly interested in 222nm for doing things like sterilizing air circulation and handheld wands. You can put a very high flux without worrying about accidentally exposing someone to a hazardous level of UV light.

People aren't trying to sterilize skin directly (as far as I know), but, even there, it might help healthcare workers. Washing your hands or coating it with alcohol is nasty over time. Being able to hold your hands in a device for 15 seconds and sterilize it rather than having to dump alcohol on them could be an improvement.

[hedora]

"Airborne" viruses are almost always traveling in protective droplets of fluids, sloughed cells, etc, etc. Direct contact with air kills them. So, how does the UV get inside the droplet so that it can reach the pathogen?

[iggldiggl]

Apart from the human safety factor, I'm also curious what it does to other stuff typically found in houses? Even if you were to run the disinfection cycle only while the room is unoccupied, it still affects everything else in the room.

So is the combination of 222 nm + exposure times required for disinfection still enough to cause noticeable bleaching of paints, aging of plastics, etc. etc. over time?

[scotty79]

It's basically because viruses and harmful bacteria are smaller than our dead skin layer. So the light gets into them and destroys their DNA/RNA.

[harvie]

but viruses and bacteria are probably never traveling alone. imagine someone sneezing on table. they will be embeded in pieces of dead skin or tiny droplets of phlegm, saliva, etc... in the linked article they are using it to disinfect surfaces in passenger aircraft. unless it can penetrate a bit, i don't see how it can be effective.

also viruses (eg. HIV, Coronavirii,...) are often killed by oxygen in air, dry out or die in other ways when not floating in bodily fluids.

[jefftk]

The light doesn't need to kill 100% of pathogens to be effective at decreasing risk. I agree that if the pathogen is on a table but under a protective layer the levels of UVC we're talking about aren't going to do anything to it. But the main concern is with airborne viruses which mostly aren't very protected.

[lightedman]

Sadly, not even LEDs are truly monochromatic and typically have a ~20nm spread on either side of the peak. They also exhibit drift in wavelength peak. This is seen at my job, where I run the UV testing and production.

[scotty79]

I don't think it needs to be monochromatic. If the longest wavelength is 222nm, other penetrate skin even less.

[jefftk]

The longest wavelength isn't 222, that's the peak wavelength.

KrCl excimer lamps produce a relatively narrow spectrum as is: https://pubs.acs.org/doi/10.1021/acsphotonics.2c00041

If it turns out we need it to be even narrower, we could put filters on them.

[jefftk]

I don't see anything in your link about 222nm causing skin cancer? It's short enough that it shouldn't be getting through the outermost layer of skin, which is dead.

[lazide]

Welders have plenty of experience to contradict it. UV-C is usually blocked by the atmosphere, and most people don't get exposed to it directly - so it rarely comes up. But if you're sitting next to a UV-C generator, don't.

It cleaves DNA the same as UV-B, and there is no reason to think it isn't cancer causing. There are a number of areas that can get exposed that have very thin epidermis, or none at all (eyes), though eyes would get retinal keratosis not cancer.

That said, hopefully no one is spending enough time close to a high enough power UV-C source for this to REALLY be a problem.

Welding Cite - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5640727/]

Notably, while having a higher skin cancer risk despite being inside a lot (shop welders, not shipyard welders), the vast majority of welders in that sampled population will have been wearing heavy protective clothing continuously. There was a noticeable increase in risk of skin cancer on the neck, which is one of the few areas that is not always adequately covered.

Anecdotally, I knew folks who didn't wear proper full coverage PPE when welding and welded a lot (auto body repair in one case, farm equipment repair in another), and both died in their early 40's from multiple malignant melanomas. One of them, it was 10+ all at once, and he died in less than a year. No one was surprised, unfortunately. They were ALWAYS sunburned from it, and they didn't spend a huge amount of time outside otherwise. That is a pretty broad spectrum source though.

UV-C As Potentially Mutagenic/Causing Damage not caught by normal replication suppression mechanisms - [https://pubmed.ncbi.nlm.nih.gov/9951833/]

UV-C will also have no problem converting all sorts of organic chemicals into interesting, and often more toxic versions (albeit killing any organisms relying on their original structure in the process), same as UV-B or UV-A.

[the8472]

welding light is broad-spectrum, so it's not relevant when comparing to a narrow-peak light source.

> UV-C As Potentially Mutagenic/Causing Damage not caught by normal replication suppression mechanisms - [https://pubmed.ncbi.nlm.nih.gov/9951833/]

p53-/- human keratinocyte cell line means that those were in vitro experiments which don't account for the wavelength-dependent penetration depth, which is the point of discussion here.

[jefftk]

None of your links are about 222nm; they're all about longer wavelengths or mixes that include longer wavelengths.

[daniel_reetz]

Let's be clear here. Nothing outside of some extremely filtered high end equipment is producing exactly and only 222nm light, and no cancer study is isolating exactly and only 222nm light. Except in extreme cases all light sources have some bandwidth. Most UV generators produce tens to hundreds of nm of bandwidth. A common MIG or TIG welder produces plenty of 222nm light in a broad distribution* of UV. UV lamps for curing applications have used arcs to generate deep UV for ages. Lack of a particular study for a particular 1nm band is not a meaningful signal.

*Source: https://www.ehime-iinet.or.jp/ehime_e/corp/toyo/ronbun/image...

[jefftk]

I agree welding is very broad spectrum, including both 222-nm and many other frequencies, and also dangerous. But these KrCl excimer 222-nm products generate light through a completely different mechanism and produce a far narrower spectrum. See https://pubs.acs.org/doi/10.1021/acsphotonics.2c00041 and specifically this chart https://pubs.acs.org/cms/10.1021/acsphotonics.2c00041/asset/...

We do know a lot about how dangerous different frequencies are, and when you combine the "risk to humans" curve with the "emissions by wavelength" curve you get very low risk.

I do still think we should run additional experiments here before rolling this out broadly for hours-a-day usage, but from what we know so far it looks very good.

[red-iron-pine]

Anecdote of one but...

Have an uncle who is / was (recently retired) a welder. He worked everywhere, did all sorts of welding, and even got certified to do underwater stuff -- which he did for 2 years and GTFO out of as soon as he made enough $$$$

He got skin cancer on his next and on his right elbow. Cuz that's where the gloves and other PPE clothing had gaps, esp. when he leaned certain ways or use his right hand to move the torch.

[amluto]

And yet Far-UVC seems quite safe for people.

Presumably what’s going on is that longer wavelength UVC from welding is extremely dangerous.