The influence of human movement on transport of airborne infectious particles in hospital premises

In hospital premises, where the requirement of controlling cross infection is demanding, the impact of human movement on transport of airborne infectious particles (AIPs) is rarely investigated. In this study, the impacts of human movement on distribution of AIPs in two highly infectious hospital environments, i.e. airborne infection isolation room (AIIR) and operating theatre (OT) are investigated numerically. In the case of AIIR, the influence of different walking speeds on the distribution of respiratory droplets is investigated by adopting Lagrangian method for tracing the motion of droplets, dynamic mesh model for describing human walking, and Eulerian RANS model for solving airflow. In the case of OT, the impact of surgeon bending movement on distribution of bacteria-carrying particles (BCPs) is dynamically simulated by applying the similar numerical method as in the AIIR case, except that the drift-flux model is used for modelling BCPs distribution. The adopted models are first successfully validated against literature data. The results show that, in the case of AIIR walking speed could effectively change the overall numbers of suspended droplets and faster walking speed is more favorable to reduce the overall numbers of suspended droplets. In the case of OT, 45o bending posture for performing operation and bending back movement of the surgeon can cause the concentration of BCPs within the surgical critical zone exceeding the recommended 10 cfu/m3, while for the 2-second bending over process as well as the 30-second standing upright posture for rest the concentration of BCPs within the surgical critical zone can be generally less than 10 cfu/m3. Therefore, lack of considering the influence of human movement in hospital premises may ignore some important phenomena related to nosocomial infection and consequently misinterpret the nosocomial infection risk. More in-depth studies in this area should be done in the future.