TOILET VENTILATION | MASS GATHERINGS around 10% all maximum CO2 concentrations were below 800ppm, but the trend line indicates maximum CO2 of more than 2,000ppm might be expected in some toilets at fully occupied events. Conclusions The measurement of CO2 concentration in indoor air does not indicate the risk of long-range transmission of airborne pathogens, but it is a useful way of rapidly assessing the level of ventilation relative to the occupancy of a particular space. Most of the toilets were deemed to be sufficiently ventilated, but a small number were targeted for improvement using the maximum CO2 concentration as a performance metric. The proximity of the toilet to important areas in each venue was a key indicator of performance. This perhaps suggests the ventilation systems in these toilets were undersized and unable to cope with the short periods of very high occupancy. Venue operators should consider ways to better disperse the event attendees around the various toilets in the venue, to avoid overcrowding in any particular toilet. At the Crucible Theatre, for example, venue operators changed some toilets to unisex to reduce overcrowding in the male toilets. The mean average CO2 concentration in 11 toilets was indicative of ventilation that was sufficient relative to the occupancy levels at 96% of the 58 events. Investigation of the maximum CO2 concentrations, however, showed that, at some events, there were intermittent periods of 58 November 2023 www.cibsejournal.com high CO2, which indicated poor ventilation relative to the number of occupants. This mainly occurred during half-time intervals at the snooker and football matches, particularly during the higheroccupancy events, and in toilets closest to auditorium entrances. Key recommendations have been made in the paper (see panel, Key recommendations on p55), including increasing ventilation rates, ensuring supply air is from areas with low occupancy, and allowing different genders to use the same toilets if there is a predominantly male or female audience. CJ References: 1 Dancer et al, 2021; Malki-Epshtein et al, 2023 2 Adzic et al, 2022 The CO2 monitoring study was funded by the Department for Digital, Culture, Media, & Sport, which arranged access to the venues and events. The subsequent analysis was carried out by the Airborne Infection Reduction through Building Operation and Design for SARSCoV-2 (AIRBODS) consortium, funded by the Engineering and Physical Sciences Research Council (EPSRC) grant.