Airborne spread of human coughing droplets with different postures and relative orientation in wards combined with peacetime and epidemic periods

The transmission and deposition of human expiratory droplets are widely acknowledged as a potential pathway for cross-infection within hospital wards. A numerical (CFD) approach validated by experimental testing, is applied to investigate airborne spread of patient expiratory droplet nuclei in a two-bed ward during both peacetime and epidemic periods, utilizing a ceiling downward supplying and bottom exhausting ventilation strategy. The airflow field, spatial and temporal distribution of coughing droplets nuclei, exposure of the healthcare worker (HCW) and another patient are compared based on 10 cases with different postures, relative orientation of patients and ventilation rates. Results reveal that the dispersion range of droplets is maximized when patients are seated and coughing, with an average suspension rate reaching up to 85%. The diffusion of coughing droplets while lying down is significantly influenced by the ventilation rate, showing a 26.6% increase in exhausted rate and a 17.9% decrease in suspension rate when 12 ACH is implemented. When a coughing patient is lying on their side facing to another patient, a substantial amount of coughing droplets quickly occupies the primary breathing zone of the other patient, resulting in a severe risk of cross-infection. Overall, increasing the ventilation rate reduces the concentration of cough-generated droplets in the breathing zone, but the dispersion and removal of indoor pollutants still depend on the exhalation characteristics. These findings enrich the theoretical understanding of indoor pollutant transmission and provide guidance for the further design and optimization of airflow organization in dual-person wards aimed at mitigate the risk of cross-infection.