Airborne transmission of exhaled pollutants during short-term events : quantitatively assessing inhalation monitor points

Abstract

The infection risk assessment associated with the contaminant inhalation can provide a scientific basis for formulating mitigation measures. Previous studies on the breathing zone are primarily based on the assumption of the steady formation and homogeneous property, while it might not be applicable for short-term events. Large-eddy simulation (LES) is employed in the present study, as well as two computational thermal manikins with detailed facial features and transient breathing conditions. Exposure risks in eight commonly used monitor points are compared in short-term events and under steady-state conditions. Three representative physical distances between room occupants are investigated, namely 0.35 m, 1.0 m, and 1.5 m. Based on the statistical difference in the contaminant distribution at a short physical distance, the breathing zone could be identified from the time-averaged concentration field. The results highlight that the previously defined breathing zone ignores unsteady airflow characteristics, significantly impacting the exposure risk estimation in short-term events. Owing to the substantial temporal variation of the contaminant in the identified breathing zone, the instant exposure risk analysis in short-term events should consider its turbulence intensity and concentration fluctuation characteristic. Overall, instead of using the identified breathing zone. Point_A, Point_B, and Point_C should be employed to evaluate infection risk in short-term events. The localized method with direct interference on the respiratory airflow should be recommended in short-term events.