[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.

[daniel_reetz]

Perhaps 222nm is absorbed primarily by dead skin cells - but why is skin the only tissue mentioned? It says nothing about damage to corneal and conjunctival tissues. Eye damage is a major hazard for humans with UV light in particular. "Very low risk" simply doesn't track. "Reduced risk" might.

[jefftk]

Eyes, like skin, have a layer of dead cells, and sufficiently short wavelengths can't get through. If you shine enough 222-nm into eyes they'll get dry and uncomfortable, but we're talking about much lower levels.

Here's an example of some of the research here, where they shined 222 nm vs 254 nm into rat eyes and looked for corneal damage. While 254 had some harmful effects 222 was fine: https://www.tandfonline.com/doi/abs/10.1080/10715762.2019.16...

[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.