Quantifying crowding-ventilation effect on respiratory infections

Crowded and poorly ventilated spaces drive outbreaks of respiratory infections like COVID-19, often causing superspreading events. While overcrowding heightens risk, its interplay with space size and ventilation remains underexplored. We introduce a novel framework to assess this risk, using effective clean flow rate, which combines clean airflow (outdoor air, filtration, UVGI) with volume-time air clearance (VTAC), i.e. dilution from indoor air volume per person over time, and intake fraction time, which isolates aerosol exposure risk. Analysis of datasets from jails, earthquake shelters, and dormitories shows modest spaciousness (16-32 m³/person) increases effective clean flow by 8.7 to 17.6 L/s per person in low-ventilation settings (0.5 L/s per person, 1 hour exposure), reducing exposure. Current standards, like ASHRAE 62.1-2022, fall short in crowded spaces, heightening infection risks. Our model predicts infection patterns, showing VTAC limits long-range airborne transmission. These insights call for updated ventilation and spaciousness standards to strengthen public health strategies.