Disinfection Using Ultraviolet Radiation – Summarising the WHO Webinar
A webinar hosted by the World Health Organisation brought together expert speakers to discuss the use of ultraviolet light as a disinfection tool. They discussed conventional ultraviolet sterilisation and its limitations, as well as considering the potential Far-UVC has as a low-risk method of disinfection. Some of the key details are summarised here.
Conventional Ultraviolet Radiation (254nm)
Ed Nadel, a Harvard University expert with 40 years of experience working with Germicidal Ultraviolet (GUV) disinfection, discussed the limitations of conventional disinfection methods and the potential Far-UVC has to eliminate these. Most transmission of COVID-19 occurs through person-to-person interaction in settings with no ventilation. Increasing ventilation naturally, by opening a window, or mechanically, with room air cleaners or air conditioning units, is unreliable and only disinfects a limited flow of air. You can never completely rid an environment of a pathogen using these methods, instead a more efficient solution is required.
Traditional GUV lamps treat large volumes of air at once, making them a practical disinfection tool. However, they operate at a wavelength of 254nm which is unsafe for humans, meaning that they can only be used to disinfect the upper room. Whilst upper room disinfection is effective, it relies upon vertical air mixing to produce a reduction in pathogens throughout the entire room, usually achieved with ceiling fans. Far-UVC operates at a shorter wavelength of 222nm making it a safe, viable option for whole room decontamination, eliminating the need for open windows and ceiling fans.
Filtered Far-UVC (222nm)
Far-UVC is a new technology that has emerged over the last decade, emitting radiation at 222nm and not the typical wavelength of 254nm emitted by mercury lamps. Kenny Wood, an expert in Far-UVC, discussed the current research into the technology and what it means for the future of disinfection. A study by Buonanno et al., (2020) shows that Far-UVC effectively inactivates coronaviruses, influenza and bacteria. This is supported by a recent study by Wood et al., (2021) which replicated these findings in a scaled-up room size computer simulation, demonstrating how the technology could be used to disinfect offices, gyms, cafes and more. Ongoing research in Leeds by Eadie et al. aims to reproduce these findings in a real-life setting by introducing aerosolized pathogens into a room and measuring the reduction in pathogens following Far-UVC exposure.
Far-UVC is a behaviour-independent control measure – it is effective despite human actions such as mask wearing, social distancing and vaccine uptake. It can inactivate COVID-19 and all its variants regardless of individual behaviours and practices, making it an important intervention that can reduce illness in workplace and social settings all over the world.
Ewan Eadie has many published and ongoing works investigating the safety of Far-UVC technology. His 2021 study compared the difference between DNA damage caused by sun exposure and Far-UVC radiation, showing that it would take 30,000 hours of Far-UVC exposure to induce the same amount of damage as 10 minutes in the sun. Further research in the same year involved exposing human skin to high doses of filtered Far-UVC light. No visible changes to the skin were observed, proving Far-UVC can be used in a wide range of environments with no risk to human occupants (Eadie et al., 2021). Its shorter wavelength means it cannot penetrate the outer layer of the skin and cause harm, rendering it safe to use in human-occupied spaces.
With 5 million deaths across the world due to COVID-19, and more suffering physically, mentally and financially as a result of the pandemic, it is clear we need an effective solution to combat pathogens and better prepare ourselves for future outbreaks of infection. Far-UVC offers a low risk solution, and is a measure of protection that should be implemented across the globe.
A pilot study in Las Vegas is due to begin in 2022, comparing wastewater samples for COVID-19 in schools with GUV and schools without. Another study due to begin in 2022 in Pretoria, South Africa, will compare the efficacy of conventional upper room, LED upper room and Far-UVC disinfection methods in a real-life environment. These studies aim to provide further supporting literature for the use of Far-UVC as a widespread method of infection control.