All of Kirby Sikes's Comments + Replies

To be clear, those two units are different. 155.8 mW/cm^2, and 0.1 mW/cm^2/nm. So it's not 1,558 times stronger than sunlight overall. Neglecting atmospheric effects, sunlight across all wavelengths is 135 mW/cm^2, so about the same total flux---it's like we compressed the broad spectrum of sunlight to all be a single wavelength. My point is that it's much much more blue-violet light (not much much more light total) than what we usually encounter. Blue-violet from sunlight may be safe for our skin, but that doesn't necessarily imply... (read more)

Right, I will readily believe that for many people with good glove hygiene, it is better to wear gloves than not. But if we're talking about irradiation that encourages everybody to cover up, that's a different question, especially since many people don't own single-use gloves. Would universal use of gloves make spread better or worse? It seems like most experts say worse.

Also, on the question of whether gloves prevent a person from touching their face, it probably can be helpful for some people, but that doesn't mean that it's ... (read more)

2avturchin
A joke: so the best way for air travel would be transport sedated people in boxes. No joke: The plane crew could provide gloves to people inside a plane. This one-time gloves could be covered with virus killing material like coper, which will also protect against UV.

The germicidal flux from the paper is 155.8 mW/cm^2, which is much stronger than sunlight which is about 0.1 mW/cm^2/nm at sea level for short wavelength visible light. I don't know what your threshold for alarming is, but to me that seems high enough that concern is warranted. And I'm not sure that conventional sunscreen would actually help. Based on this overview of sunscreen, it looks like most broad spectrum sunscreens don't do much above 380 nm or so.

Also, It doesn't seem clear to me that the fact that blue light is visibl... (read more)

1Jay Molstad
If your flux is 1,558 times that of sunlight, that's definitely alarming. At that point, the wavelength might not matter very much; you might be dumping enough energy to sterilize surfaces by heating. The paper indicates that the treatment generally works by stimulating porphyrins in bacteria or fungi of interest. Humans can have light sensitivity due to porphyrins, a condition called porphyria, but it's fairly rare. Unless the novel coronavirus has porphyrins in its chemistry, I wouldn't expect to this effect on the virus, as the paper notes. The reported data indicate that the effect is dependent on other elements of the mixture; something else in the solution may break down under the flux and attack the virus. My reasoning was basically similar to this sentence from the paper: An alternative mechanism of inactivation when FCV is suspended in MM may be associated with the LED emission spectrum extending slightly into the UVA region, meaning the virus is exposed to very low-level UVA photons (~390 nm).

It's germicidal by an oxidative stress mechanism, so we should expect it to be carcinogenic (via the indirect DNA damage mechanism), at least at germicidal intensities (normal everyday exposure may be harmless to the skin, I don't know).

Wow, I would not have guessed that light within the visible spectrum would have any germicidal action at all (looks like 405 nm light is germicidal at fluences about 10,000 times as high as germidal UVC).

This brings up an important point which is that sunlight (UVA, UVB, and apparently visible blue-violet too) is somewhat germicidal, and open air treatment during the Spanish Flu had positive patient outcomes, as well as less spread, with nurses and doctors less likely to become infected.

4gjm
Short-wavelength blue light is harmful to humans too. In particular, it's harmful to the eyes. I would be highly unsurprised if it were slightly carcinogenic but I don't know anything about that.

This is exactly the sort of concern that needs to be more rigorously addressed before a solution like widespread far-UVC is implemented.

Agreed that some sort of prioritization of the public spaces most in need of sanitization would be good. The threshold for safety should be lower in cases where the potential benefit is high (and I didn't mention this in the post because it's highly speculative, but I suspect that shorter term occasional exposure may be much safer than constant exposure). Making such a priority list should involve empirical evidence. I agree that airplanes seem like a likely culprit given what we know about mechanism of spread, but it would be good to confirm... (read more)

2avturchin
Yes, the experiments are needed. The main benefit of gloves is that they prevent a person from touching ones' face. If I go outside, I use onetime gloves and clean my hands on return.

I spent a while looking into safety for this idea, and far-UVC has a ways to go before it's established safe enough for public settings---it's only been shown to be non-carcinogenic for one of two relevant DNA damage mechanisms. I've posted a more in depth discussion here.