Limits to the Effectiveness of Ventilation for Reducing Airborne Infection Risk Due to Widely Varying Emissions
Publisher
Chartered Institution of Building Services Engineers (CIBSE)
Proceedings of CIBSE Technical Symposium 26-27 March 2026, Loughborough University, UK
Authors
Christopher Iddon (1) PhD CEng MCIBSE
Benjamin Jones (2) PhD
Liora Malki-Epshtein (1) PhD
1 Department of Civil, Environmental and Geomatic Engineering, University College
London, UK
2 Department of Architecture and Built Environment, University of Nottingham, Notting
ham, UK
Responsible author: [email protected]
Abstract
This research builds on insights gained from analysis of COVID-19 infection risk in mass
gathering events conducted during the UKGovernment’sEventsResearchProgramme
(ERP), combined with clinical data on viable virion emission. Deterministic models
often suggest high effectiveness of airborne transmission mitigation strategies such as
increased ventilation and filtration. However, empirical evidence for these findings is
limited, with Richard Riley noting that “several attempts at control in the community by
air disinfection…all except one were failures.” [1]
In this study, we explore the limits of such mitigation strategies under conditions of
high heterogeneity in quanta emission rates (i.e., wide variation between individuals in
how much virus they release). Using a stochastic (i.e., probabilistic) model simulating
10,000 iterations of an 8-hour exposure in a 50-person office space, we account for
variability in the number and emission strength of potential infectors. Quanta generation
is modelled probabilistically based on clinical data, reflecting the broad range of viable
virion emission and the likelihood of sharing space with an infector.
Results show that mitigation measures reliably reduce inhaled dose, but the absolute
reduction in infection probability is strongly dependent on emission rate. Many sce
narios feature either no infectors or quanta emission levels so low that infection risk
remains negligible. The most significant benefit of mitigation occurs within a narrow
band of emission rates where infection probability is non-zero but moderate.
We conclude that mitigation is most impactful in scenarios that are individually low-risk
but occur frequently. Detecting this effect empirically is difficult due to small effect sizes
and the influence of alternative transmission pathways. In particular, improvements
in poorly ventilated spaces yield substantially greater reductions in infection risk than
equivalent increases in already well-ventilated environments.