Exposure and infection risk from exhaled contaminants at varying occupancy levels: a comparison of ventilation rate recommendations for non-residential spaces

We compared two IAQ standards—EN 16798-1:2019 and ASHRAE 62.1—and four infection control documents: ASHRAE Standard 241, and guidelines from REHVA, WHO, and the Lancet COVID-19 Commission. The objective was to estimate exposure and infection risk for exhaled contaminants across various occupancy levels in classrooms, restaurants, and offices using simplified steady-state mass balance models. Ventilation design methods in these documents rely on five basic principles: occupancy, floor area, air change rates, and formulas considering occupant numbers and room volume. We assessed exposure risk through metrics like ΔCO2 (indoor CO2 above outdoor levels), infection risk probability (P), event reproduction number (R), and quanta independent metrics relative risk reduction (r), and maximum absolute difference (ΔPabs.max). The latter two metrics address variability in virus emission. The infection risk was calculated using SARS-CoV-2 data. We also assessed the methods based on specific fan energy consumption. The latter two metrics address variability in virus emission. Using SARS-CoV-2 data, we calculated infection risk. We also calculated specific fan energy consumption. Our analysis revealed inconsistencies across metrics, with some methods showing no change in infection risk, specific fan energy consumption, ∆CO₂, or risk reduction (r) despite varying occupancy levels. To improve protection, we also proposed two alternative calculation approaches that maintain a constant reproduction number (R) and (ΔPabs.max) regardless of occupancy density.