Dr. Jitendra Singh, Union Minister of State for Science and Technology, recently announced that the government would install Ultraviolet-C or UV-C Disinfection Technology in Parliament to mitigate the possibility of airborne transmission of SARS-CoV-2. Developed by CSIR-CSIO (Central Scientific Instruments Organisation), the UV-C air duct disinfection system can fit into any air-duct. It said calibrated levels of UV-C light is used to deactivate the virus in any aerosol particles, and the system was a perfect fit for malls, auditoriums, AC buses, educational institutions, and railways.
Ultraviolet is the Sun’s natural radiation or light and covers wavelengths in the 100-400 nm range. The light ranges visible for humans is from 380–700 nm. There are three bands for UV — UV-C (100-280 nm), UV-B (280-315 nm) and UV-A (315-400 nm). The Sun transmits both UV-A and UV-B rays through the Earth’s atmosphere, while the ozone layer filters all UV-C. UV-B rays can reach the epidermis or outer layer of the human skin, causing sunburns. It is also associated with causing skin cancer. UV-A rays can penetrate the dermis or the skin’s middle layer to age skin cells and indirectly damage cell DNA. Man-made UV-C radiation is known to have caused eye injuries and skin burns.
Hospitals and laboratories have used UV-C radiation of 254 nm wavelength for decades to disinfect the air. It is also used to treat water. However, these conventional germicidal treatments are usually done in rooms that are unoccupied. A June 2020 paper in Scientific Reports noted that the outer protein layer of SARS-CoV-2 can be destroyed using UV-C radiation. The paper said the 222-nm radiation, also known as far-UVC light, can kill airborne human coronaviruses such as alpha HCoV-229E and beta HCoV-OC43. This, however, is different from SARS-CoV-2, for which very limited data is available on the wavelength and duration required.
Hiroshima University in Japan, which conducted an in-vitro experiment, found that 222 nm UV-C irradiation at 0.1 mW/cm2 killed 99.7% of SARS-CoV-2’s viral culture following a 30-second exposure. In September 2020, the study was published in the American Journal of Infection Control. A March 2021 study in Scientific Reports found that UV-C irradiation effectively inactivated SARS-CoV-2 replication.
On its use on humans, researchers from the Indian Institute of Technology, Kanpur, who developed a small disinfectant device that used UV-C radiation (222-254 nm), said it was developed specifically for non-living things. The device’s UV-C radiation could harm skin and eyes and the operator must use spectacles that protects from UV-C radiation, according to their paper published in June 2020. While the Ministry of Science and Technology did not mention the wavelength of radiation or the duration for which it will be used, it mentioned that tests had shown that the product managed 99% disinfection.
Dan Arnold of UV Light Technology, which offers disinfecting equipment to hospitals and pharmaceutical companies in the UK, said one shouldn’t be exposed to UV-C, and called it “really nasty stuff”. He told bbc.com that while it takes hours to get a sunburn from UV-B, UV-C can do it in seconds.
A few studies have shown, however, that far-UVC light (207–222 nm) does not cause harm to mammalian skin. Director David J. Brenner of the Center for Radiological Research at Columbia University said far-UVC light had a limited range, adding that it could not penetrate through the human skin’s outer dead-cell layer or even the tear layer in eyes and was not a health hazard. However, far-UVC light can reach the DNA of viruses and bacteria and kill them since they are smaller than human cells. Brenner’s team had demonstrated how far-UVC light can control the spread of airborne-mediated microbial diseases in 2018.