[This is a follow-on to my earlier post on a lay person’s perspective of far-UVC]

I’ve had a LOT of thoughts lately about 222 nm far-UVC, which is a highly effective pathogen-killer that many, including myself, believe is an amazing weapon in our battle against SARS-CoV-2 and other airborne microbial threats.

“222 nm far-UVC isn’t ready for prime-time, because <X, Y, and Z>”

I’ve heard this and similar thoughts from a few different sources of late, and my well-considered reply, specifically related to many, and I dare say most, consumer use cases, is: “Bollocks.”

Well, more accurately, it would be, “While 222 nm may not be appropriate or practical for EVERY use case, for the majority of them the benefits of well-considered use of this technology vastly outweighs the likely risk by orders of magnitude.”

Is there a lot we still have to figure out? Hell, yeah! But we know enough now to get started on that, and it’s the perfect time, as the high price of far-UVC now gives time for air quality experts and early adopter consumers to figure out best practices before the real flood of consumers comes as prices come down.

So, the risks. The two main risk concerns for 222 nm far-UVC are 1) potential overexposure and 2) the light creating ozone and particulates – “indoor smog” – through its interaction with contaminants in the air in poorly ventilated indoor spaces.

Exposure Concerns

With regard to potential overexposure, the current Threshold Limit Values (TLV) for skin and eyes for 222 nm are 479 mJ/cm2 and 160 mJ/cm2 over a period of 8 hours (a typical work shift), respectively, per the American Conference of Governmental Industrial Hygienists (ACGIH). What’s a TLV? Basically the amount of exposure during an 8 hour period that “does not create an unreasonable risk of disease or injury.” Note that these are guidelines, not standards; that doesn’t mean you should toss them out the window, but I believe it’s an important distinction. At this point, there aren’t any “standards” for 222 nm UV exposure.

Note that the ACGIH TLV for skin not long ago was a mere *22* mJ/cm2. But extensive testing led them to raise it to 479 mJ/cm2, which is still arguably conservative. Testing has included exposure of up to 1,000 mJ/cm2 on animal and human skin, and 600 mJ/cm2 on animal eyes, with “no adverse effects,” according to this 2021 Defense Systems Information Analysis Center presentation by Boeing, which draws on the results of a number of studies. The briefing also noted that increasing dosage of 222 nm light did not damage DNA in mammalian cells, as did longer UV wavelengths (254 nm was referenced in the briefing).

My point here isn’t to encourage anyone to be a moron and ignore the TLVs, but to put the potential risk posed by 222 nm overexposure (per TLV guidelines) in a larger context. So many people seem to be terrified that they or people around them exposed a bit too much to 222 nm will spontaneously combust or suddenly erupt in body-wide cancers. This just isn’t the case.

Are there people who may be sensitive to 222 nm? Without doubt, although I’m not aware of any studies quantifying how many. But like with a great many things, those folks are at the far ends of the bell curve. It’s like with vaccines: choose a vaccine, any vaccine, and there will be people who are sensitive to it or have a bad reaction. That doesn’t make the vaccine – or 222 nm light – bad, it means we all have to be observant for anyone who may have a reaction and do everything possible in that particular situation to mitigate.

Indoor Smog

With regard to indoor smog (ozone + potentially harmful particulates) created by 222 nm light in poorly ventilated spaces, all that means is that those particular use cases have to be more thoroughly examined for possible mitigations. Just as with exposure concerns, it does NOT mean that we should just toss 222 nm technology out the window!

Let’s take the use case of a relative in an elder care home where the air in your loved one’s room seems “stale” (hard to precisely define, but you know it when you breathe it) – that likely means it’s “poorly ventilated” (something else we don’t really have a clear standard for). You may or may not be able to do anything about the ventilation, depending on the facility’s rules, but you could certainly (if the facility allows) add a properly sized HEPA filter

But there’s a problem: the staff doesn’t mask (!!), and they come in close proximity to your loved one, exhaling aerosols potentially laden with virus. Near field transmission is a huge problem that the HEPA in the room may not be able to solve. A far-UVC device, on the other hand, most likely in the 12-20W range (depending mainly on room size), could help add another layer of protection by zapping much/most of that virus before it can reach your loved one.

But wait! Now you’re worried about ozone and particulates, too! Argghhhh! Well, the HEPA should be taking out most of the particulates, and to minimize ozone, you might have staff (or your loved one) only switch on the far-UVC device when someone enters, and turn it off when they leave. That would also likely eliminate any potential concerns about overexposure.

The Risk-Benefit Ratio

EU MDR's Benefit-Risk Ratio: Making Your Clinical Evaluations Safety-Focused
From “EU MDR’s Benefit-Risk Ratio: Making Your Clinical Evaluations Safety-Focused”

The elder care home example illustrates something that I see consistently being lost in much of the discussion of 222 nm far-UVC: the difference between specific use cases, many of which can be tailored or mitigated, versus a broad-brush, “Welp, there’s some risk here, so we can’t/shouldn’t/mustn’t use it.” [Note: I’ll be talking more about “uses cases” in another installment.]

Further, in almost every discussion on the topic of potential risk, we immediately veer into the realm of “If it’s not 100% risk-free, it’s unusable, not ready for prime-time. Sorry.”


Look, we DO have to take risk seriously, we DO have to act responsibly to mitigate/avert risk, but the fact is that we accept risk – in some cases a LOT of risk – every single day. And virtually all of the things that I can think of that pose risk in our daily lives don’t have anywhere near the KNOWN health benefits as 222 nm far-UVC.

Here are just a few examples of risks in our daily lives:

  • Your car. Aside from you running into someone or someone running into you or running off the road, every time you sit in your car you’re breathing in gunk from plastics and synthetic materials, brake and tire dust, gasoline and diesel fumes when you fill up, etc., etc.
  • Air travel. Checked the news lately?
  • Tobacco. I don’t think I have to go into this one.
  • Alcohol. Same here.
  • All the chemical crap in so much of our food and drinks.
  • Roundup! Ick.
  • Photocopiers – who’d a thunk it? They’re actually pretty horrible.
  • Every single thing in your home that has some sort of warning label carries risk. Hell, even the simplest tool around, a hammer – a direct descendant of the rock – carries risk!

You know what else carries risk? Unrelenting exposure to a brain-eating bat virus that’s killed tens of millions of people and disabled millions more in only three years, and is still running rampant across the globe. THAT carries a LOT of risk, and not employing every tool we have to reduce transmission of SARS-CoV-2 and other pathogens is, frankly, nuts.

Again, we shouldn’t accept risk without due consideration, but the truth is WE ACCEPT RISK ALL THE TIME. The difference is that in the case of 222 nm far-UVC, the deck is stacked high and heavy on the benefit side, with a lot less potential risk than we accept from so many other things in our lives.

I also suspect that most consumer use cases involve limited use of far-UVC in any given instance, which right there would mitigate much of the potential risk of overexposure or smog: at the dentist or doctor, when you have guests or are visiting friends, at business events, or hell, even at a restaurant. But even if your use case requires the lamp to be on for an extended period or constantly, avoiding overexposure and mitigating any risks from ozone or particulates, in most situations, is likely possible with some thought and ingenuity.

Commercial uses cases are likely going to be somewhat different, as proper coverage of large spaces needs to be calculated in relation to mechanical ventilation and filtration, occupancy, etc. Still, this can – and should – be done. I submit that the same risk-benefit ratio (very low – very high) applies.

I’ll also say this, and I know there will be some who will vehemently disagree, but if I need to make a risk-benefit choice between some degree of limited/temporary overexposure or ozone and protecting myself or others (such as my wife) from exposure to the virus, I’m choosing the latter. Every time. I’m not trying to minimize any health impacts of potential risks, but I’m FAR more worried about what happens to me (or others) from COVID infection. 

And remember: SARS-CoV-2 isn’t the only pathogen out there we have to worry about, and it likely won’t be the worst in the years to come, but 222 nm can help kill them all. We need this technology. It’s not THE tool, it’s not THE solution, but it’s an amazing tool that we need to add to our toolbox to fight these bugs. And more manufacturers are entering the market with a more diverse choice of devices, and there are some indications prices may be starting to come down a bit (but they still won’t be cheap). Now’s the time.

Next time we’ll talk about how to define use cases (from a lay person’s perspective) and go over some ideas about how to choose a device(s) that will hopefully best suit your needs.

Let’s Talk Some More About 222 nm Far-UVC

2 thoughts on “Let’s Talk Some More About 222 nm Far-UVC

  • June 8, 2023 at 1:10 pm

    I don’t understand how UV can zap pathogens at a distance from the light source. Doesn’t it require air to be drawn towards the light, like a filter? The killing power presumably diminishes with the cube of the distance from the source.

    • July 2, 2023 at 12:23 am

      222 nm light is extremely effective at killing virus, bacteria, and fungal spores, but distance, power, and time (for log reduction and exposure) are all interrelated and interdependent. And energy falls off by distance according to the inverse square law.

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