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Far UV is a promising technology to kill COVID viruses

Published on 20 Comments on Far UV is a promising technology to kill COVID viruses

Now this is what I'm talking about:

I've written about this before: it's called Far UV, and it's ultraviolet light in a range that's deadly to COVID-19 but harmless to human beings. It's not cheap, but it's a great passive technology that ought to become widespread in crowded indoor spaces. That potentially includes classrooms, arenas, airports, and anyplace else that lots of people gather at a single time.

Note that these units require decent ventilation to work properly. There's further discussion of UV disinfection in the comments to Poppendieck's tweet.

20 thoughts on “Far UV is a promising technology to kill COVID viruses”

      1. mertensiana

        See comments below. There is a definitional problem here. 254nm is outright dangerous. Hospital room disinfection systems that use that wavelength require people to be absent.

        However, it appears that significantly shorter wavelengths are safer. Usually the range from 200-280nm is called UV-C. It seems that "far UV" is now being used informally to describe the far end of that range.

        What's more confusing is that below 200nm there is "vacuum UV" and below 100nm there is "extreme UV". These last two ranges don't pass through air well so they're not particularly relevant here, but they illustrate the need to pay close attention to UV terminology when dealing with it.

        1. painedumonde

          Thank you. I mean it's depriving KD of graphing rates of malignant carcinoma and melanoma, but putting things straight.

        2. golack

          Yeah, the 254 nm line is typical for a germicidal lamp, it is the emission line from Hg, and it is dangerous for humans. Great for bacteria, but needs to be intense for viruses (smaller genome). And 254 nm is damaging to humans--so would need to be confined to air ducts.
          Far UV is not 254, typically it is below 230 nm, in the UV-C range. UVC light has more energy, but turns out is not more damaging to humans because it does not penetrate the top layers of skin, etc.

  2. steve22

    We designed our own UV sterilizer for our N 95 masks. As I recall talking with the engineer far UV is the 222 frequency. 254 is generally considered harmful but I do think there are upper room sterilizers that use 254 and confine it to the upper parts of rooms so place like airports with high ceilings should work well. There were still some safety concerns about 222 and IIRC it takes much longer to kill viruses. (Its been two years so always possible I have this backwards.)

    Steve

    1. Steve_OH

      You have it right. The caption on the tweet is wrong.

      Far UV is 207-222 nm, and is relatively safe. 254 nm UV is the primary wavelength of conventional mercury arc germicidal lamps, and is very hazardous, as it damages DNA (potentially leading to skin cancer, etc.).

      The reason for the difference in risk is because far UV is absorbed in the very outermost layers of skin and other membranes, where the cells are already dead, whereas 254 nm UV penetrates further into living tissue.

      Far-UV does pose a slightly elevated risk of cataract formation and corneal damage, but less than the longer wavelength UV present in sunlight.

  3. kaleberg

    We had a UV water sanitizing system and UV is the standard first line for dealing with dangerous biologicals leaks, so I know UV works pretty well. I gather the biggest risk is welder's eye followed by sunburn, but the risk goes down with the square of distance.

    1. mertensiana

      Those risks vary a lot by wavelength range. Typical UV disinfection systems have traditionally used 254nm UV which is bad news for living tissue.

      The inverse square law is not going to be helpful for real-time sanitizing in the presence of people because effectiveness also goes down as the square of the distance.

  5. Brett

    Does it just kill Covid, or is it effective against all airborne viruses? Because it would be nice if it also tamped down hard on airborne spread of flu and colds.

    1. golack

      It can inactivate basically any virus--as long as the intensity and length of exposure is long enough. That will vary with the virus too.

    1. golack

      Black lights are in the UV-A region, just below 400 nm, typically at 365 nm. They filter out light below 320 nm. UVA light has less energy, and do less damage, then shorter wavelengths, but typically can penetrate further into the skin, eyes, etc., so the damage caused can increase long term chances of cancer.
      UVA lights will cause tanning. UVB lights (shorter wavelengths) cause burning. Tanning beds have more intensity than your typical black light in a room.

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