Is UVC light safe?
It is unlikely that UVC from artificial sources presents an acute or long-term hazard to human skin. ... UVC exposure is unlikely to cause acute or long-term damage to the skin but can cause severe acute damage to the eye and should not be permitted at all from any tanning device.”
UVC radiation refers to wavelengths shorter than 280 nm. These wavelengths are entirely absorbed by our atmosphere and no natural UVC radiation reaches the surface of the earth. These wavelengths are available to us through artificial sources, such as UVC mercury lamps. The intensity from point sources like UVC LAMPs falls off as 1 over distance squared, and once it gets past the scattering length, it falls off exponentially. This means that 1) the further away from the UVC source from a human, the lesser dose he is exposed to, and 2) the absorption length of UVC radiation in human skin is extremely short so that almost no UVC radiation can reach the living cells in the skin; all the absorption occurs in the dead cell layers.