TOILET VENTILATION | MASS GATHERINGS LIFTING THE LID Research has shown that the surge in use of toilets during intervals at large-scale events leads to an increased risk of virus transmission. Analysis of CO2 levels at three venues enabled researchers to understand the issue and suggest how to ush out the problem This is a summary of conference paper Measurement of ventilation effectiveness and indoor air quality in toilets at mass gathering events presented at the AIVC Conference in Copenhagen, Denmark The authors are: Ben Roberts and Malcolm Cook, Loughborough University; Filipa Adzic, Liora Malki-Epshtein and Chris Iddon, Department of Civil, Environmental and Geomatic Engineering at UCL; E. Abigail Hathway, Department of Civil and Structural Engineering University of Sheffield; and Benjamin Jones, the Department of Architecture and Built Environment at University of Nottingham A t the height of the Covid pandemic, the UK government commissioned research on the potential for Covid transmission in sports arenas and other venues attracting large crowds. The studies, carried out in 2021 as part of the Events Research Programme, aimed to establish whether it was safe to lift restrictions at massgathering events. Ventilation and air quality was monitored at Wembley Stadium in London, the Crucible Theatre in Sheffield, and the O2 Arena in London, including bars, arrival/departure areas and toilets. Researchers measured the CO2 concentration as a proxy for ventilation effectiveness. Toilets (sanitary accommodation) were identified as an area of potential high risk for the transmission of airborne pathogens1, because they are densely and continuously occupied for short 54 November 2023 www.cibsejournal.com durations throughout events, such as theatre intervals, half-time at sports matches or just after the event finishes. This increases the risk of both short-range and long-range airborne transmission2. Results showed that while the average air quality in toilets was good at most events, there were peaks in CO2 concentration of up to 3,431ppm when occupancy was presumed high. This indicates that the risk of exposure to exhaled breath, which may contain virusladen aerosols, is higher in toilets (although occupancy is much lower). Person-to-person transmission of pathogens is compounded in toilets by faecal particles entering the air by flushing toilets (Best et al, 2012; Cai et al, 2022; Knowlton et al, 2018). A possible faecaloral SARS-CoV-2 transmission route has been identified (Guo et al, 2021) leading to toilets being considered a contact hub for community transmission of SARS-CoV-2 (Dancer et al, 2021). Ventilation that introduces uncontaminated air into a space is an important mechanism to reduce longrange transmission of airborne pathogens, but in transiently occupied spaces the ventilation rates may not be adequate to introduce enough uncontaminated air during the brief period of dense occupancy to dilute or remove airborne pathogens (Dancer et al, 2021). The aim of the work reported in this paper was to measure the ventilation effectiveness of outdoor air in toilets at mass gatherings. The research The concentration of CO2 in the indoor air was measured in 11 toilets at three different venues at 58 live events (Table 1). A snooker match at the Crucible Theatre and a football fixture at Wembley Stadium were played in two halves. This meant there were three periods when toilets were densely occupied pre-event, midevent interval, and post-event although attendees were able to occupy the toilet at any time during the event. The Brit Awards event at the O2 Arena