During the COVID-19 pandemic in 2021, researchers monitored air quality in marquees and semi-outdoor venues at UK mass gatherings to understand ventilation and airborne infection risk — work that directly informed how such events could safely reopen. 🧵

The study found that most marquee spaces were well ventilated relative to occupancy (mean CO₂ <800 ppm). Short spikes to ~1200 ppm occurred during peaks in crowding — showing that occupancy and density drive air quality.

The research showed that semi-outdoor marquees aren’t automatically well-ventilated. When side panels were closed in wet or cold weather, or mechanical systems reduced, CO₂ levels rose sharply — highlighting how operation and crowding directly affect air quality.

There are currently no ventilation standards for semi-outdoor temporary structures — a major gap in regulation. The paper argues these spaces should be included in future building guidance and pandemic preparedness plans.