Experimental investigation of ventilation and breathing and their effect on the spread of exhaled aerosols between occupants

Airborne transmission of viruses in enclosed spaces is a key factor in infectious disease spread. Mitigating this risk involves utilizing ventilation systems and controlling ventilation rates. Moreover, individual breathing patterns significantly impact the dispersion of airborne particles. In this study, the characteristics of airborne transmission of exhaled droplet nuclei in a controlled climate chamber were investigated under various ventilation modes and breathing patterns. The study was conducted using two thermal manikins to simulate infected and exposed occupants in an office setup. A tracer gas (CO2) was injected into the exhaled air of the infected occupant to mimic particles smaller than 5 μm. The experiments covered nostrils and mouth exhalation combined with two configurations of mixing ventilation: near-floor inlet and near-ceiling inlet, both studied at air change rates (ACH) of 2 h-1 and 4 h-1. The findings revealed that doubling the ACH for near-floor inlet and near-ceiling inlet decreased the intake fraction (IF) in the exposed manikin’s breathing zone (BZ) by 52% and 58%, respectively. Additionally, the breathing pattern was found to have significant effect on IF, wherein mouth-breathing result in 15.2%–35.4% higher IF compared to nose-breathing depending on ACH rate and MV ventilation configuration. Furthermore, switching from from near-ceiling to near-floor inlet configurations reduced the IF by 15%–30% and 4.6%– 15.7% under ACH of 2 h-1 and 4 h-1, respectively.