In July 2021, Union Minister of State for Science and Technology, Dr Jitender Singh, 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.
The Ultraviolet-C (UV-C) disinfection technology, developed by CSIR-CSIO (Council of Scientific & Industrial Research-Central Scientific Instruments Organisation), fits into any existing air-ducts and the virucidal dosages using UV-C intensity, and residence time can be optimised according to the existing space. The calibrated levels of UV-C light deactivates the virus in any aerosol particles. It can be used in auditoriums, malls, educational institutions, AC buses, and in railways.
A study, namely, Far-UVC Light (222 nm) Efficiently and Safely Inactivates Airborne Human Coronaviruses, published in the journal Scientific Reports, in June 2020, noted that UV-C radiation can destroy the outer protein coating of the SARS-Coronavirus. The study shows that 222 nm, known as ‘Far-UVC light’ efficiently kills airborne human coronaviruses—alpha HCoV-229E and beta HCoV-OC43. This is different from SARS-CoV-2 virus. However, very limited data is available on the required wavelength and duration needed to inactivate SARS-CoV-2.
Ultraviolet Radiation
Ultraviolet (UV) is a type of radiation naturally emitted by the Sun in a wavelength range of 100–400 nm. It is divided into three bands–UV-C (100—280 nm), UV-B (280–315 nm), and UV-A (315-400 nm). UV-A and UV-B rays are transmitted through our atmosphere and all UV-C is filtered by the ozone layer.
UV-B rays can only reach the outer layer of skin or epidermis and can cause sunburns and the skin cancer. UV-A rays can penetrate the middle layer of skin or the dermis and are known to cause aging of skin cells and indirect damage to cells’ DNA. UV-C radiation emitted from man-made sources has been known to cause skin burns and eye injuries.
Effect of UV-C on Coronavirus
According to an in-vitro study, namely, Effectiveness of 222-nm Ultraviolet Light on Disinfecting SARS-CoV-2 Surface Contamination, conducted by Hiroshima University researchers and published in September 2020 in the American Journal of Infection Control, 99.7 per cent of SARS-CoV-2 viral culture was killed when exposed to 222 nm UV-C irradiation at 0.1 mW/cm2 (milliwatts per square centimetre) for 30 seconds.
Another study, namely, UV-C Irradiation is Highly Effective in Inactivating SARS-CoV-2 Replication, published in Scientific Reports in March 2021, noted that UV-C irradiation was highly effective in inactivating SARS-CoV-2 replication. A complete inactivation at all viral concentrations was observed with 16.9 mJ/cm2 (millijoule per square centimetre). These results are important for the development of novel sterilising methods to contain SARS-CoV-2 infection.
Safety Concern
There are safety concerns regarding the use of UV-C radiation. UV-C radiation (wavelength around 254 nm) is used to disinfect the air in hospitals, laboratories, and in water treatment. But these conventional germicidal treatments are done in unoccupied rooms due to its impact on human health.
Researchers from the Indian Institute of Technology-Kanpur (IIT-K) have also developed a portable disinfectant device, using UV-C radiation (222–254 nm) specifically to disinfect non-living things. The researchers are of the view that UV-C radiation, used in their device, could be harmful to the skin and eyes of the living beings. Therefore, the operator of the device must use spectacles with UV-C radiation protection and use this device safely.
As for the release from the Ministry of Science and Technology, it does not state anything about the wavelength or duration used, but mentioned that the product was tested for more than 99 per cent disinfection.
Another expert, Dan Arnold, who works for UV Light Technology (a company that provides disinfecting equipment to hospitals, pharmaceutical companies across the UK) says, UV-C is really nasty stuff—you should not be exposed to it. It can take hours to get sunburn from UV-B, but with UV-C it takes seconds.
On the other hand, few studies have shown that Far-UVC light (207–222 nm) does not harm mammalian skin, as it has a very limited range and cannot penetrate through the outer dead-cell layer of human skin or the tear layer in the eye. Therefore, it causes no human health hazard. However, David J. Brenner, Director of the Center for Radiological Research (Columbia), opines that viruses and bacteria are much smaller than human cells. So, Far-UVC light can reach their DNA and kill them. In 2018, his team demonstrated that Far-UVC light can help control the spread of airborne-mediated microbial diseases.
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