Airborne-mediated microbial diseases such as influenza and tuberculosis represent major public health challenges. A direct approach to prevent airborne transmission is inactivation of airborne pathogens such as Coronavirus, and the airborne antimicrobial potential of UVC ultraviolet light has long been established; however, its widespread use in public settings is limited because conventional UVC light sources are both carcinogenic and cataractogenic.
However there has been a breakthrough, its been proven that far-UVC light (207-222 nm) efficiently inactivates bacteria without harm to exposed mammalian skin.
This is because, due to its strong absorbance in biological materials, far-UVC light cannot penetrate even the outer (non-living) layers of human skin or eye; however, because bacteria and viruses are of micrometer or smaller dimensions, far-UVC can penetrate and inactivate them.
For the first time people can now use far-UVC to safely and efficiently inactivate airborne aerosolized viruses, with a very low dose of only 2 mJ/cm2 at 222-nm light, this was proven to work by inactivating >95% of aerosolized H1N1 influenza virus.
Most scientists and engineers in the UV business now use the units “mJ/cm2” (millijoule per square centimeter) or “J/m2” (joule per square meter) for UV dose (the correct term is “fluence”). The units “J/m2” are used in most parts of the world except for North America, where “mJ/cm2” are used (1 mJ/cm2 = 10 J/m2. The old term “mW-s/cm2” (milliwatt-second per square centimeter) is equivalent to “mJ/cm2”, since a “W-s” is the same as a “J” (joule). Note that 1000 microwatt = 1 milliwatt.
The units “mW/cm2” (for fluence rate or irradiance) are often confused with the units “mJ/cm2” (for fluence or UV dose). The “fluence” (UV dose) is obtained by multiplying the “fluence rate” (or irradiance) (units “mW/cm2”) by the exposure time in seconds.
Continuous very low dose-rate far-UVC light in indoor public locations is a promising, safe and inexpensive tool to reduce the spread of airborne-mediated microbial diseases.
The most commonly used lights have a wavelength of 254 nanometers (nm), which has a relatively short UV wavelength—the so-called “C” category—but can penetrate the skin and eyes, leading to cancers and cataracts. So for the past 4 years, a group led by physicist David Brenner at Columbia University Medical Center in New York City has tested shorter wavelengths, known as “far UVC light” that can’t penetrate the outer layers of the eyes or skin. The researchers found that far UVC eliminated bacteria on surfaces and did not harm lab mice.
The invention increases the safety of both staff, patients and their relatives by reducing the risk of contact with bacteria, viruses and other harmful microorganisms. The concentrated UV-C light emitted has a very strong, yet very safe germicidal effect that removes virtually all airborne viruses and bacteria on the surfaces of a room.
Source:
https://www.rfsafe.com/207-222-nm-uvc-light-can-slow-spread-of-novel-coronavirus-covid-19/