Given that the articled discusses 222 nm light being harmless to humans, and acknowledging that 254 nm is known to be dangerous, I am concerned that wide/universal deployment of such systems might lead to situations where poorly constructed or serviced equipment might emit dangerous wavelengths.
According to the article, 222nm would already be stopped by the thin coat of dead cells on the skin. So it shouldn't penetrate far enough to cause any trouble.
> "...led them to conclude that at the current OSHA regulatory standard for continuous 222 nm light exposure that you would see 90% viral inactivation at 8 minutes and 99% inactivation in about 16 minutes."
Something I learnt about disinfection protocols is that they're measured on a logarithmic scale, much like volume (decibels), earthquakes, etc...
So when you see marketing saying things like "kills 99.9% of germs", think of that as "strength 3" because it has three nines.
The article mentions strengths from 1 to 2, which is about as low as it gets and still have "some" effect.
Hospital grade disinfectants are more like 99.99% to 99.999% ("4" and "5" strength), for comparison. Autoclaves and the like can go to "12"!
This is because bacteria grow exponentially, so to remove "one doubling" time, you have to halve the numbers. To remove "two doublings", you have to quarter the numbers, and so forth. In other words, every unit of safety time you want to buy requires an exponential increase in disinfection.
Keep this in mind when shopping for cleaning products! The difference between "99%" and "99.9%" is just "one" doubling time, not a tenfold improvement.
Seems like we should add ~222 UV light to many more home appliances. Home water tanks with lower temperatures, dishwashers with water-free sanitization cycles, refrigerators could include a self-cleaning option, etc. If it holds bacteria and shouldn't, use UV to sanitize.
How about we stop worrying so much about germs unless killing them wholesale is shown to produce a significant increase in health. I am pretty sure bactericides etc. are being pushed by industry for their profit not our wellbeing at all.
Agreed. More sterilization also goes against what we should do per the hygiene hypothesis (https://en.wikipedia.org/wiki/Hygiene_hypothesis, which states that early childhood exposure to germs is necessary for the development of a healthy immune system), especially around children in non-hospitalization situations.
Killing germs is part of modern daily life. You shower, do dishes, brush your teeth, and wash clothes. It's much, much cheaper to shine a UV light onto a surface for a few minutes compared to using soap and other chemicals. UV toothbrushes and toothbrush cleaners are already sold online.
If you're talking cost then maybe. In the right places such as hospitals, very likely. I'm questioning that we should do that indiscriminately in other places such as in homes. We have highly developed immune systems, let's not risk weakening them. And not doing it costs nothing at all.
The Atlantic article that this one links to admits that negative side-effects of UV-C have been known since at least the 40's:
>> But though Wells and other early pioneers of this technology could shine their 254 nm lamps aloft to clean the air floating in the upper portion of rooms, or use the light inside vents or ducts, they couldn’t actually shine them downward, directly onto the occupants of rooms, without ill effect. That’s because, although 254 nm inactivates pathogens, it also causes skin and eye damage at certain doses.
This is a very contradictory tone with the article, which essentially claims UV-C is totally safe for humans. EDIT: The author of the article explicitly acknowledges this.
> That's very much as opposed to (say) 254 nm light, which starts doing damage immediately due to greater penetration into animal tissue.
and that 200-222 is safer because of lower penetration.
> down in that range, the penetration of such light is only a few microns, and it doesn't even get past the dead cells on the surface of the skin and the cornea of the eye!
My bad, thanks for the correction. I am surprised though – I thought higher frequency waves were more dangerous, but clearly that is not universally so.
the article (titled Two-Twenty-Two presumably because it is about this specific wavelength vs the whole UV-C range) does say "222 nm light does not induce DNA damage in mice, even at much higher flux than would be used for disinfection. That's very much as opposed to (say) 254 nm light, which starts doing damage immediately due to greater penetration into animal tissue."
> What's even better than [effective drugs and vaccines] are public health measures that are taken even more broadly and don't require individual actions. In the industrialized world, we took many of these a long time ago, things like providing clean water without pathogens floating around in it. It comes as a shock to us when that layer of defense breaks down, because we're so used to it that we take it as part of the natural order of things.
If disinfection with 222nm light or a similar safety measure becomes so commonplace that we take for granted, that would be a remarkable shift and a small silver lining to the COVID pandemic.
