Ultraviolet light has disinfectant properties and can be used to make indoor spaces safe during the pandemic. The Sars-CoV-2 virus, the causative agent of Covid-19, is easily rendered harmless by UV light. If harnessed and used in the right way, UV light can fight the spread of the virus and protect human health as people work, study, and shop indoors.
The virus mainly spreads through person-to-person contact via aerosols and droplets emitted by an infected person. The virus can also be transmitted when people touch their faces soon after touching contaminated surfaces, especially in healthcare settings, retail spaces, and in modes of transport.
UV light can be used to reduce the risk of transmission of viruses, including coronavirus. UV lights can be components of robotic or human-controlled mobile machines that disinfect surfaces. They can also be incorporated in heating, ventilating, and air conditioning systems or positioned within airflows to disinfect indoor air.
What is UV light?
Electromagnetic radiation, which includes radio waves, visible light, and X-rays, is measured in nanometres, or millionths of a millimetre. UV irradiation consists of wavelengths between 100 and 400 nanometres, which lies just beyond the violet portion of the visible light spectrum and are invisible to the human eye. UV is divided into the UV-A, UV-B, and UV-C regions, which are 315-400 nanometres, 280-315 nanometres, and 200-280 nanometres, respectively.
The ozone layer in the atmosphere filters out UV wavelengths below 300 nanometres, which blocks UV-C from the Sun before it reaches Earth’s surface. UV-C contains the most effective wavelengths for killing pathogens. UV-C is also hazardous to the eyes and skin. Artificial UV light sources designed for disinfection emit light within the UV-C range or a broad spectrum that includes UV-C.
How UV kills pathogens
UV photons between 200 and 300 nanometres are absorbed quite efficiently by the nucleic acids in DNA and RNA, and photons below 240 nanometres are also well absorbed by proteins. These essential biomolecules are damaged by the absorbed energy, thereby inactivating the pathogen.
Putting UV to work
For years, hospitals have been using robots like Tru-D and Xenex that emit high-power UV irradiation to disinfect patient rooms, operating rooms, and other areas where bacterial infection can spread. UV light is also used to disinfect medical instruments in special UV exposure boxes.
UV light is being used or tested for disinfecting buses, trains, and planes. Businesses are also considering the technology for disinfecting warehouses and retail spaces.
Overhead UV-C lamps can be installed in indoor spaces and aimed at the ceiling to disinfect the air. Similarly, HVAC systems can have UV light sources to disinfect air as it travels through duct work.
Is Far UV-C safe for humans?
As UV wavelength decreases, the ability of the photons to penetrate into the skin decreases. These shorter-wavelength photons get absorbed in the top skin layer, which minimises DNA damage to the actively dividing skin cells below. At wavelengths below 225 nanometres—the Far UV-C region—UV appears to be safe for skin exposure at doses below the exposure levels defined by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).
Some businesses are installing UV portals that irradiate people as they walk through. While this device may not cause much harm or skin damage in the few seconds walking through the portal, the low dose delivered and the potential to disinfect clothing would also likely not be effective for stemming any virus transmission.
As more studies on Far UV-C reveal that exposure to human skin is not dangerous, and if studies on eye exposure show no harm, it is possible that validated Far UV-C light systems installed in public places could help in controlling virus transmission for Sars-CoV-2 and other potential airborne viral pathogens.
Courtesy: The Statesman, Sept 16, 2020