Effects of exhalation modes and spatial distribution of an infected person on contaminant transmission in a classroom

Abstract

Classrooms pose a huge risk from the cross-infection of respiratory infections. However, quantitative research on the combined effect of the location of the infected individual and exhalation activities on the diffusion and dissemination of contaminants in a classroom is lacking. We elucidated the effects of spatial distribution and exhalation modes of infected individuals, especially when they talk and breath nasally, on dissemination of contaminants under different ventilation modes: mixing (MV) and stratum ventilation (SV), using computational fluid dynamics, and calculated the contaminant removal efficiency (CRE) and personnel infection time (tin). Infected individuals’ exhalation modes and spatial distribution significantly affected indoor exposure risk. Under SV, risk was low (tin > 0.75 h) when infected individuals talk, but significantly higher (tin ≤ 0.75 h) during nasal exhalation. In MV, risk was lower (tin > 0.75 h) when infected individuals were near the outlet, but increased (tin ≤ 0.75 h) when they were further away. CRE revealed that MV was more sensitive to location changes (12.4- and 5.8-fold) than to exhalation mode changes (2.1- and 0.99-fold). Conversely, SV was more sensitive to exhalation mode changes (5.7- and 2.8-fold) than to location changes (3.7- and 1.8-fold), emphasizing the importance of the distribution of infected individuals and exhalation modes in classroom ventilation design.