Risk assessment of cough droplets in both static and dynamic indoor environments with different ventilation strategies

In real-life scenarios, occupants typically alternate between sitting and walking in a room. The wake induced by human movement affects the local airflow, enhances local mixing effects, and increases airborne propagation laterally and across long distances. This study aimed to provide a comprehensive comparison of the impact of human movement on the dispersion of coughed droplets in an office under four ventilation strategies (i.e. Mixed Ventilation (MV), Displacement Ventilation (DV), Stratum Ventilation (SV) and Stratum Displacement Ventilation (SDV)). The improved Wells-Riley model was used to calculate the risk of infection for susceptible individuals in both static and dynamic indoor environments under different ventilation strategies. The results showed that different ventilation strategies, as well as the presence or absence of human movement, significantly affected the diffusion of droplets. When there was no human movement or human movement occurred close to the air supply, the risk of infection for susceptible individuals was lowest under SDV, 5.03 × 10⁻⁶ and 21.44 × 10⁻⁶, respectively. The risk of infection for susceptible individuals during the infection stage was almost linearly related to exposure time when human beings moved away from the air supply, and all four ventilation methods presented a high risk of infection. The SDV has the best performance, followed by DV, SV, and finally MV for reducing the risk of indoor cross infection. These results can provide a reference for epidemic control in both static and dynamic indoor environments.