Far-UVC is safe for humans because a 20-micron layer of dead skin cells full of proteins absorbs all the radiation before it reaches living cells.

7:29of a mechanical story than a chemical or biological story. >> Okay. essentially, you know, it's not good for living cells to be exposed to UVC of any wavelength. Um, you know, but the difference is that humans have a 20 micron thick layer of dead skin cells that are chalk full of proteins that essentially absorb all UVC. And I should say this is unique to far UVC the uh wavelengths of 200 to 235

8:00nanometers principally 222 nmters which is what is most commercially viable right now longer UVC wavelengths um you know 254 nm to 65 nmters which are used in water disinfection these do not have so so significant protein absorption uh so they are I'm not going to say they'll give you cancer relative to UVB they're thought to be less carcinogenic but they are not pleasant to be exposed to. So it's really something that is

8:33unique to the shorter wavelengths uh in the for UVC. So this high protein absorbance it is due to the stratum corneium the outer layer of the skin it absorbs almost everything and what is not absorbed is only is absorbed in only the very upper layers of the skin. uh and those those skin layers uh tend will sl generally slough off and u you know become part of the stratum corneium

9:00within you know typically a couple of days. So um I've never seen a study that showed any significant you know biological activity down at the basil skin cell layer where you would worry about cancer if there was any damage to the DNA there. Now, the story with the eyes is a little bit more complicated, and this is because there isn't a convenient dead skin cell layer or dead

9:27eye cell layer, whatever that might mean to protect us. But eyes are protected in the same way that or they are protected from sunlight. We have eyelids, eyelashes, eyebrows, a brow ridge, and all of these things reduce the effective dose to the eye. So this does mean that you know despite these mechanical protections the eye is more vulnerable. There is the tear layer which has um some lipids and

9:56proteins and that absorbs some of the fur UVC but actually only about 15%. The rest of the incident dose would be absorbed in the epithelium and this is a you know so a relatively lower dose might produce eye pain or discomfort. The positive story there though is that this is still even though these are living cells, they're still full of proteins and the absorption is not to

10:24essentially totally stop after the first few cell layers. So any chance of long-term damage is in my opinion fairly low. Although we haven't, you know, this technology hasn't been around for long enough to do extremely longunning studies. There have been a few long run eye safety studies. Actually, there's a one one-year one and one three-year one going on in I think Japan. But it does mean that the safe effective eye dose is

10:54lower than the safe effective skin dose. We're still figuring out exactly what that is and exactly how to translate that into, you know, industry practice. um we are generally pretty conservative. But the good news is is that it it's sort of like looking into a bright light where and not like looking into an infrared laser where um if you feel any pain that means that you flinch