Airborne Infection Probability in Relation of Room Air Distribution: an Experimental Investigation

The objective of this study was to investigate the importance of room air distribution in airborne cross-infection. Tracer gas measurements were performed in a field lab arranged as an office with two breathing thermal manikins. The room was ventilated with a mixing air distribution operating at a constant supply airflow rate of 60 L/s (4 ACH) under different air discharge scenarios: 2-way, 3-way and 4-way. Room air temperature was kept at 22.0±0.2°C. Respiratory-generated airborne pathogens were simulated by N2O dosed into the exhaled air of the manikin acting like an infected person. The N2O concentration was measured in the inhaled air of the second manikin (simulating susceptible person), exhaust and occupied zone. Measured values were used to calculate infection probability by modified Wells-Riley method. The infection probability in the occupied zone depended on the air discharge scenario. The highest infection probability of 2.9-3.9% was obtained in the inhaled air of the exposed manikin in all experimental cases. The results reveal that room air distribution is of major importance for airborne cross-infection. Therefore, during ventilation design and operation, air distribution should be carefully considered in practice. Infection probability calculated using original Wells-Riley method was underestimated compared to values obtained through measurements.