COVID-19 | UVGI LEADING LIGHT Ultraviolet germicidal irradiation has been used for many years to mitigate the spread of measles and tuberculosis. It can effectively inactivate the Covid-19 virus too, but a lack of guidelines makes modelling the equipment a complex task. Liza Young reports W ith the emergence of Covid-19 a virus spread by aerosols there has been growing interest in the use of ultraviolet (UV) light to disinfect air in buildings. Ultraviolet germicidal irradiation (UVGI) is a disinfection method that uses shortwavelength ultraviolet C (UV-C) light to kill or inactivate microorganisms by destroying nucleic acids and disrupting their DNA and RNA. Although not a new technology, having been pioneered in 1930s America by William F Wells to reduce the transmission of measles among schoolchildren, Covid-19 has sparked renewed interest in UVGI as a possible countermeasure to the virus. Researchers from industry and academia have found evidence that suggests SARSCoV-2, when suspended in air, is reasonably easy to inactivate using UV light at 254nm. Clive Beggs, emeritus professor at Leeds Beckett University, has been researching UV air disinfection to reduce Covid-19 transmission in buildings, and his research paper has recently been published by PeerJ, the biological, medical and environmental sciences journal. The question, he says, is not whether UV works we know it does but whether we can deliver the dose thats necessary to prevent the transmission of infection? When considering UVGI air disinfection, he adds, it is important to evaluate its likely performance in the context of the space, which will depend on occupancy levels, room geometry and the ventilation system. UVGI devices can be divided into three main application classifications: upperroom, in-duct, and room air cleaners. All have benefits, but there is a distinct lack of guidelines for their design and installation, says Beggs. There is also a need for manufacturers to undertake robust microbiological testing and fully characterise the UV fields (UV light beam produced by the lamps) created by their devices. UVGI room air cleaners These standalone devices are located within a room and use UV-C lamps mounted in a container with a fan. Air enters the device and is drawn by the fan over a UV lamp before being blown back out into the space, says Beggs, who was a HVAC design engineer before specialising in air disinfection and the transmission of diseases in hospitals. Although room air cleaners are efficient at disinfecting the air that enters the device, they are only as good as the fan. If youve got a small device with a small fan, all the air that www.cibsejournal.com November 2020 33 CIBSE Nov 2020 pp33-35 UVGI.indd 33 23/10/2020 16:12