FEEDBACK Using ultraviolet light to tackle Covid-19 in buildings should be done with care The risk of high frequency UV light Join the conversation We want to hear from you. Talk to us. @CIBSEJournal CIBSE LinkedIn www.cibse.org Subscribe to our newsletter Receive our top stories about building services engineering. Sign up at cibsejournal.com We read with interest your July 2020 article, Light relief,1 on using ultraviolet (UV) light to limit the transmission on Covid-19. We agree that ultraviolet germicidal radiation is a technology with considerable potential for limiting exposure to Covid-19 and have received Innovate UK funding to develop it. As UV light is harmful in a number of ways, our approach is to use occupancy control to ensure no-one is ever directly exposed. Our research in the area leads us to some concerns about the far UV light at the high-frequency end of the ultraviolet spectrum, described in the article as an application that is safe to use in occupied spaces. The view that far UV exposure is safe is based on the assertion that it cannot penetrate human cells which is not based on experiments with human cells, but with hairless mice.2 However, experiments on human volunteers have shown that radiation at 222nm, the wavelength discussed in the article, can cause the skin inflammation called erythema.3 The human experiments used a higher UV dose than would be encountered in the workplace installations proposed, but the fact remains REGISTER FREE to join our live webinar: bit.ly/cibsewebinars A CASE FOR CHANGE: Setting New UK Standards for High Rise Drainage 16 September 2020, 13:00 (BST) Brought to you by: 14 September 2020 www.cibsejournal.com CIBSE September 2020 p14-15 Feedback Partron.indd 14 that, by clearly demonstrating far UV light penetrating human skin, they undermine the basis for stating that far UV exposure is safe. While it is stated that far UV technology needs to pass safety tests, our view is that the safety concerns are significant and it may not be possible to address them all experimentally. Our concerns are: 1. The entire ultraviolet spectrum, including far UV, is classed as carcinogenic by the International Agency for Research on Cancer (IARC).4 The carcinogenic activity is based on lifetime exposure, so the only protection against it is to minimise exposure, which is not compatible with continuous exposure in the workplace. IARCs position is that there is no identifiable safe threshold,5 which makes it impossible to prove the safety of any level of intentional exposure. Any employer who installed it would be placing their employees health at risk and would invite a lawsuit from any employee who develops a skin cancer. 2. The greatest acute danger of UV light is keratitis: damage to the cornea, which overlays the exterior of the eye. While the skin cells are protected by a layer of lipids and dead cells, the live cells of the cornea are more exposed, hence more vulnerable. The paper6 referenced in Light relief contains the assertion that far UV light does not penetrate the cells of the cornea but it does not back up the assertion with any evidence or relevant references. It is stated that the exposure to a far UV installation would not exceed the statutory daily limit, which is calculated to prevent keratitis, but the daily exposure is calculated based on an eight-hour working day7 which, in practice, is often exceeded. 3. High-frequency UV light produces ozone, which is harmful. While peak ozone production is at 185nm, the European Commissions Scientific Committee on Health, Environmental and Emerging Risks states that ozone may be produced at any wavelength below 240nm,8 so continuous use of far UV would cause continuous ozone production. Germicidal UV light is routinely used to control infection and contamination in laboratories, healthcare facilities and food production but, in all those cases, it is installed in such a way that no-one is directly exposed to it. Our view is that UV has a much broader role to play in the built environment, in limiting transmission not only of Covid-19, but also of other airborne viruses, such as influenza and norovirus, but any installation must be designed to prevent direct exposure. We can expect to see an expansion of the use of UV light in workplaces and public places, and we hope CIBSE will take a lead in ensuring safety is not compromised. l References can be viewed at cibsejournal.com David Miles, of Atamate Building Intelligence and the London School of Hygiene & Tropical Medicine, and Dan Cash, of Atamate Building Intelligence CIBSE Journal welcomes readers letters, opinions, news stories, events listings, and proposals for articles. Please send all material for possible publication to: editor@cibsejournal.com or write to: Alex Smith, editor, CIBSE Journal, CPL, 1 Cambridge Technopark, Newmarket Road, Cambridge CB5 8PB, UK. We reserve the right to edit all letters. 21/08/2020 17:08