COVID-19 | UVC LIGHTING UVC might yet be a powerful weapon, but it is not a panacea which is why face coverings, social distancing and hand washing are still necessary systems for germicidal irradiation as part of a multifaceted approach to limiting the transmission of coronavirus; this could include increasing outdoor airflow in a space, upgrading air filters and adding air disinfection equipment, such as UVC. My hope is that the revised WHO position will result in more willingness to use all appropriate engineering controls to reduce airborne exposure, including UVGI, he says. According to Bahnfleth, germicidal UV technology has a long history in the US: In the first half of the 20th century, upper-room systems were used to help control measles outbreaks in schools. The ASHRAE Handbook has two chapters on UVC fundamentals and applications, and the ASHRAE Journal has published articles on applications.2,3,4,5 In addition, he says studies of the effectiveness of upper-room systems have suggested that their ability to inactivate airborne pathogens in a space may be equivalent to as much as 10 air changes per hour of outside air.6,7 It is only my impression, but there seems to be a somewhat greater interest in, and willingness to use, air cleaners as adjuncts to ventilation and particulate filtration in the US, Bahnfleth says. A study in the US by Columbia University is looking at the potential of UVC light, at a wavelength of 222nm, as a means of killing coronaviruses. UV light at this wavelength is known as far-ultraviolet C (far-UVC).8 According to the researchers, the advantage of using light at this wavelength is that it cannot damage human cells, so, potentially, would be safe for use in occupied public spaces to kill pathogens in the air before the occupants breathe them in. To investigate how effective far-UVC light is at killing coronaviruses, a team at Columbia University Irving Medical Center aerosolised two common coronaviruses (the ones that cause coughs and colds), which it then flowed through air in front of a far-UVC lamp. The tests showed that continuous exposure to the far-UVC light in a room inactivated 90% of airborne viruses in about eight minutes, 95% in 11 minutes, 99% in about 16 minutes, and 99.9% in 25 minutes. The team expect far-UVC to have the same impact on SARS-CoV-2. If successful, the research could lead to far-UVC lamps being retrofitted into existing light fixtures in buildings, aircraft and public transport, as part of a holistic approach to limiting coronavirus transmission. Bahnfleth says the research is encouraging and, if far-UVC passes all safety tests for human exposure, it will open up new applications for germicidal ultraviolet. For example, safe germicidal UV could be used to treat occupied spaces, decontaminating both the air and exposed surfaces, displacing conventional upperroom technology. It could open up a market of consumer disinfection products that would be safe to use and could be used for applications such as disinfecting elevator cars, toilet stalls, and other spaces for which it has been hard to identify good decontamination approaches using existing engineering controls, he says. UVC might yet be a powerful weapon against an airborne virus, but it is not a panacea. UV does not prevent someone from being exposed to infectious aerosols emerging from an infected person close by, nor will it prevent people from being exposed to heavier droplets ejected when people nearby cough or sneeze which is why face coverings, social distancing and good hand-washing hygiene are still necessary. However, the benefit of UVC and far-UVC in particular is that, even if researchers develop a vaccine against the virus that causes Covid, UVC technology does not suddenly become redundant. Rather, it will be in place to help inactivate more familiar viruses, such as influenza and measles, helping making public spaces, offices and transport safer and healthier. More importantly, it will be ready for when the next virus pandemic occurs. CJ References: 1 Beggs, C B, Avital, E J, Upper-room ultraviolet air disinfection might help to reduce Covid-19 transmission in buildings, bit.ly/CJAug20UVC1 2 ASHRAE position document, bit.ly/CJAug20Ashrae 3 ASHRAE, Ultraviolet Lamp Systems, 2016 ASHRAE Handbook HVAC systems and equipment 4 ASHRAE, Ultraviolet air and surface treatment, 2019 ASHRAE Handbook HVAC applications 5 Martin, S, Dunn, C, Freihaut, J, Bahnfleth, W, Lau, J, Nedeljkovic-Davidovic, A, 2008, Ultraviolet germicidal irradiation: current best practices. ASHRAE Journal 50(8):28-36. 6 NIOSH, Environmental control for tuberculosis: basic upper-room ultraviolet germicidal irradiation guidelines for healthcare settings, bit.ly/CJAug20NIOSH 7 Article in Public Health Reports from 2003, bit.ly/CJAug20PHR 8 Buonanno, M, Welch, D, Shuryak, I, et al, Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses, Scientific Reports 10, 10285 (2020), bit.ly/CJAug20farUVC 28 August 2020 www.cibsejournal.com CIBSE August 2020 p26-28 UV-C.indd 28 24/07/2020 15:52