Airborne infection risk in classrooms based on environment and occupant behavior measurement under COVID-19 epidemic

ABSTRACT The changes of indoor environment and occupant behavior (OB) are two main causes for the gap between predicted and actual airborne infection risk. To improve the accuracy of COVID-19 airborne infection risk assessment, the environment (CO2 concentration) and OBs (occupant area per person (OA) and activity level (AL)) in three typical classrooms of a primary school in Tianjin, China was selected to conduct the on-site measurement. Based on the measured data, a modified Wells-Riley model was proposed to predict the infection risk, and a risk-controlled ventilation strategy was developed to calculate the ventilation demand. Results indicated that classrooms in the breaking time (B-T) showed a lower indoor CO2 concentration (C in), larger OA, and higher AL than in the teaching time (T-T). The variation tendency of the calculated infection risk increment in T-T was consistent with C in while in B-T was significantly affected by OA and AL, and the maximum fluctuation extent in B-T was two times of that in T-T. Moreover, to avoid the risk spreading in classrooms, a feasible solution of dynamic ventilation control based on the real-time infection risk was proposed, thus facilitating to provide a healthy and sustainable environment for students in classrooms.