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.