V0058: Colliding respiratory jets as a mechanism of air exchange and pathogen transport during conversations

As the restrictions imposed due to the COVID-19 pandemic are being gradually relaxed and people are resuming their usual activities, the configuration of two unmasked individuals at proximity having a face-to-face conversation poses a risk of transferring a high dose of a pathogen from an infected person to a susceptible one. To study this airflow and exchange between two individuals, we conduct fog flow visualization experiments and direct numerical simulations of colliding respiratory jets mimicking a short conversation. It is found that the vertical offset between the mouths of the speakers is an important parameter governing the propagation and evolution of the respiratory jets. A 'blocking effect' is observed at low offsets, which temporarily protects the susceptible speaker from the pathogen-loaded saliva droplets in the jet from the infected speaker. Whereas at large offsets, the interaction between the jets is minimum. At certain intermediate offsets, jet entrainment and inhaled breath, assist the pathogen-containing jets to propagate towards the susceptible speaker's mouth. Thus, the interaction of the respiratory jets permits air exchange to a varying degree depending upon the effectiveness of the blocking effect and jet entrainment.