Conference Agenda

The duration and impact of this pandemic has made it possible to develop numerous models in the airborne risk assessment of SARS-CoV-2. Modelling can i) demonstrate building-specific and activity-specific factors to be understood, and potentially modified to reduce risk, ii) be made accessible to non-technical persons and accommodate more sophisticated users as well, iii) permit sensitivity analyses to be simply calculated and iv) provide valuable public health guidance for decision-makers The primarily limitation of these models is their adoption of a completely mixed box model approach to simplify indoor fluid dynamics processes as well as the assumption of reliable input parameters, in particular the viral load emitted by the infected subject. The result of this simplification is a viral exposure concentration that is uniform across the room, instead of a three-dimensional, spatially variable plume with higher exposure concentrations closer to the source of the viral emissions and a high uncertainty of the estimated risk. The importance of these factors will be discussed illustrating the Airborne Infectious Risk Calculator (AIRC) and its validations conducted with retrospective cases, an experimental study in a controlled room and an epidemiological study. The developments of risk assessment together with advanced ventilation for reduction of airborne transmission indoors will be shortly discussed.

Over the past two years people have become acutely aware of the role that the environment plays in transmission of respiratory diseases, and how our interactions in indoor spaces determine the risk of infection. Understanding the routes of transmission is challenging, but measurement and modelling of aerosol and droplet emissions, human activities and indoor airflows can play an important role in identifying mechanisms. This presentation summarises some of our understanding of respiratory emissions, the complexity and challenges in measuring and modelling them and what the implications are for understanding transmission. I will highlight some of the different techniques for understanding transmission, consider how epidemiological approaches need to come together with the physical sciences, microbiology and expertise on human behaviour to unpick the complexity of transmission. I will consider where there are still important gaps in knowledge and how our understanding of respiratory disease transmission has implications for the wider challenge of improving IAQ in buildings and transport systems. I will also highlight some of the challenges in getting complex scientific understanding to policy makers who have a desire to give simple messages for the public.

Current ventilation control strategies for reduction of airborne transmission indoors are mostly based on the assumption of well-mixed indoor air. Most of the models for prediction of infection probability are also based on the assumption of perfect mixing of the room air. Based on the same assumption metabolic CO2 is recommended to be used for prediction of infection probability. However, perfect air mixing in rooms is seldom the case in practice. The non-uniform spread of exhaled virus laden articles and the resulting exposure due to interaction of room airflows and occupant activities is seldom discussed. The importance of these factors on the accuracy of the infection probability prediction will be discussed supported by physical measurements and CFD simulations. The second part of the presentation will focus on future energy efficient ventilation strategies for reduction the risk of airborne cross-infection indoors based on advanced air distribution and considering occupants’ behavior. Examples of advanced air distribution methods taking the advantage of well-defined source location, i.e. exhaled infected air, will be shown. The proper design, implementation and operation of advanced ventilation for reduction of airborne transmission indoors will be shortly discussed.