VENTILATION | COVID-19 UPWARD TREND In a summary of his winning paper at the CIBSE Technical Symposium, Ventives Tom Lipinski discusses the evidence available for the best methods for ventilating buildings in a Covid-conscious future I t is hard to write about Covid-19 and cover new ground, but one area that seems to have been almost entirely neglected is airflow dynamics. In the pandemic, ventilation was initially ignored as people followed the World Health Organizations (WHO) unfounded fomite theory,1 despite mounting scientific evidence against it.2 When the WHO finally admitted that airborne transfer was a possibility (almost nine months after 239 scientists wrote an open letter urging it to accept the airborne route)3 it continued to insist that aerosol transmission was rare, and fomites were key to the spread of infection.4 Professor Cath Noakes changed her Twitter handle from #hands #face #space to #ventilate to encourage people to start taking ventilation seriously. Still, unanswered questions remained: is it about air changes per hour? Does how we ventilate matter at all? We see air changes per hour (ACH) requirements 10L.s-1 per person, or 15L.s-1, or as much as 210L.s-1 per infected person, for example thrown around with authority, yet we dont see much of a discussion about how breath spreads indoors and whether some ventilation methodologies manage this better than others. Interestingly, this debate took place years ago following SARS-CoV-1, with intriguing outcomes. The fact many super-spreader events happened in settings with good or adequate ventilation should have raised alarm bells immediately. The Skagit Valley Chorale practice that resulted in 53 infections (out of 61 attending) and three deaths, had a modern, forced-air heating and ventilation system installed that was running at 0.7 ACH during the event, designed for occupancy of up to 180.5 The call centre in Seoul, where 94 out of 216 employees were infected, had a functioning, positive pressure HVAC system in place, delivering a recommended airflow rate.6 This inconsistency should have been spotted earlier, but this was happening while the WHO was peddling its unhelpful fomite theory. How do we ventilate? There are two main ventilation methodologies (when We need to take a closer look at how we ventilate buildings, especially with high occupancy. Thinking just in terms of ACH is way too simplistic 62 September 2021 www.cibsejournal.com CIBSE Sep 21 pp62-64 Covid ventilation.indd 62 27/08/2021 13:11