Using Far-UVC Light To Kill Airborne Human Coronaviruses

[Pratyeka]

Er... isn't this the exact paper that I cited in the very first post of this thread?

Sorry, I picked the wrong thread, and I don't know how to delete my post.

 

[James Demers]

I'm not sure how path lengths have anything to do with ozone production

With a weak absorber like O2, a photon needs a lot of encounters with the molecule to have a fair probability of being absorbed. You get that passing through miles of atmosphere, but not in passing across a room.

Far-UV-C doesn't penetrate to skin cells' DNA, but that happens because it gets absorbed and deposits its considerable energy in the outermost layers of the skin. That will surely lead to photochemcal damage, but it's dead skin that's going to be shed anyhow, so overall, it's "safe". The cornea is another matter - it can repair itself, but there's no sacrificial layer, so at best we're talking about reversible damage, quite possibly with considerable discomfort. Eyeglasses or goggles would be highly advisable, but at least they don't have to be specialized UV filters.
Keep in mind that the proposed use, as a preventative measure, calls for constant, all-day exposure.
This raises the question of everything else in the room: Metals will be unaffected, but fabrics, paints, plastics, and surface finishes of all kinds will suffer from prolonged exposure. This, I think, is what makes far-UV-C illumination impractical in most environments. At best, you could circulate the room's air through an enclosed irradiator, reducing but not entirely eliminating airborne pathogens. Whether or not it affords effective protection from SARS-CoV-2, I bet you could get rich selling such units.

 

[DaveE]

This is a good interview with one researcher of Far UVC sterilization:
https://www.microbe.tv/twiv/twiv-666/

 

[Eric Bretschneider]

With a weak absorber like O2, a photon needs a lot of encounters with the molecule to have a fair probability of being absorbed. You get that passing through miles of atmosphere, but not in passing across a room.

Far-UV-C doesn't penetrate to skin cells' DNA, but that happens because it gets absorbed and deposits its considerable energy in the outermost layers of the skin. That will surely lead to photochemcal damage, but it's dead skin that's going to be shed anyhow, so overall, it's "safe". The cornea is another matter - it can repair itself, but there's no sacrificial layer, so at best we're talking about reversible damage, quite possibly with considerable discomfort. Eyeglasses or goggles would be highly advisable, but at least they don't have to be specialized UV filters.
Keep in mind that the proposed use, as a preventative measure, calls for constant, all-day exposure.
This raises the question of everything else in the room: Metals will be unaffected, but fabrics, paints, plastics, and surface finishes of all kinds will suffer from prolonged exposure. This, I think, is what makes far-UV-C illumination impractical in most environments. At best, you could circulate the room's air through an enclosed irradiator, reducing but not entirely eliminating airborne pathogens. Whether or not it affords effective protection from SARS-CoV-2, I bet you could get rich selling such units.

The layer of tears over the cornea is mostly water which is itself a strong absorber of far UV-C (i.e. 222 nm). Its not exactly a sacrificial layer, but it is readily replenished.

There also isn't a lot of information on the effect of far UV-C light on surfaces and materials. It isn't exactly a common wavelength. Those sources that do emit significant amounts (welding arc, deuterium lamps, etc.) are broad band emitters, so you have to sort out what wavelengths have an effect.