Ceiling fixtures emitting a safe form of ultraviolet light called far-UVC would be very efficient at killing airborne coronaviruses, according to a study by researchers at Columbia University. “A very low exposure to far-UVC light killed well over 99.9% of the exposed virus,” lead researcher Dr. David Brenner told Reuters.
This is a dangerous assumption, justified by one of two competing ideas. I have worked with these sources. In germicidal applications, the lights are mounted in enclosures that contain the material, or air, to be irradiated. In this context, UVC is safe. There is no more danger from air that has been irradiated when blown through an enclosure than there is from irradiated food, which is nil.
Brenner’s creative wiggle room may be in the phrase, “very low exposure.” There is a standard reply to that. UVC is in the broad class of ionizing radiation, which includes blue light, all UV, X-rays, and gamma rays. Two ideas compete about the existence of an intensity threshold for radiation damage to occur:
- Radiation intensity below some threshold is harmless, or even salutary — radiation hormesis.
- There is no threshold; any level of ionizing radiation is harmful.
These competing ideas are in complete contradiction with each other. No middle position has yet been elucidated. The specious certainty that low level UVC is harmless may stem from the weak ability of UVC to penetrate the cornea. A quote from WHO (What is UV) helps. (In lab wavelength jargon, “far” is equivalent to “short”):
If Brenner has his way, UVC, to which there is no natural exposure, is to be introduced at low levels into public spaces, without the confinement of sterilizing enclosures.
I doubt this will happen. But Reuters should take care with the word “safe”. We already read of people drinking bleach. The equivalent can be anticipated with “safe” UV. LED UV flashlights are cheap and widely available for mineralogy and curing adhesives.
The Reuters article could instigate the use by the uneducated of commonly available UV lights that can cause eye damage and promote cancer.