Long-range airborne infection analysis of a classroom under different occupancy scenarios

The current real-field studies of long-range airborne infection risk usually assume the space is fully occupied, and does not consider the possible improvement strategies for the space for each potential occupancy scenario. However, consider each potential occupancy is important since occupancy scenarios are often variable in the real-world.

This concern in the ventilation systems design and operation can provide corresponding suggestions to ensure the indoor air quality and minimising the long-range airborne infection risk. This project aims to estimate the long-range airborne infection risk in a typical classroom under different occupancy scenarios, and offer strategies to reduce infection risk to an acceptable threshold with feasible engineering solutions.

The project combines the real-field measurement and simulations. A typical classroom in the School of Architecture, Design and Planning at the University of Sydney is been selected as the study case. All the possible occupancy scenarios are considered with eight influencing factors including ventilation rate, filter efficiency, virus type, mask-wearing, exposure time, the activity of occupants, and the use of additional control measures. Based on the simulation results, we proposed corresponding strategies to mitigate the infection risk in this classroom.

The results show that the occupancy and exposure time are the factors that most affect the infection risk. Strategy of increasing ventilation rate shows the highest efficiency on infection risk reduction, whereas both upgrading the filter and using UVGI show negligible impacts. Wearing masks can also efficiently reduce the infection risk, however the efficacy of this strategy declines when more occupants speak in the class. None of the strategies will completely minimise the long-range airborne infection risk to acceptable level in this classroom under its common occupancy.

Therefore, restricting the occupancy and duration are required during the pandemic. In a longer-term, upgrading the existing mechanical ventilation system to an UFAD-CDR ventilation system can be considered. Besides ensuring the safety and health of occupants, the proposed strategies emphasise the feasibility, and can also be applied in other educational space with similar function and layouts as the study case.