Developing demand driven ventilation criteria for airborne infection control in congregate spaces

Abstract

This article presents the case that 12 air changes per hour (ACH) does not provide adequate control against the amplification of disease in different indoor congregate settings. It proposes an occupancy and risk-based algorithm for determining ventilation rates for spaces with a high airborne disease transmission risk. The method modifies the Wells-Riley airborne disease transmission model with the indoor space’s local disease amplification rate to estimate a ventilation limit in terms of space, disease, risk and population. This proposed ventilation capacity sizing strategy is subsequently economical, adaptable and application-specific in ways deficient in prescriptive ACH limits. While acknowledging that proximity effects increase individual exposure risk, the modelling conducted shows that far-field exposure is dominant in large congregate settings. It was found that the per-person ventilation demand tends to a definable lower limit as occupancy increases. This reveals how ACH is not a universally comprehensive metric.