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]
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.
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.
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.
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?
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.
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.
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.
> 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.
*Source: https://www.ehime-iinet.or.jp/ehime_e/corp/toyo/ronbun/image...
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.
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...
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.
Presumably what’s going on is that longer wavelength UVC from welding is extremely dangerous.