Can increase of the supply flow rates cause reduction of the exposure to cough released droplets when total volume systems are used?

Abstract

Exposure attributable to cough released droplets was investigated in a field environmental chamber (FEC) designed with three total volume air delivery systems (Mixing, Displacement and Underfloor system). A cough machine reproducing size distribution and velocity of human cough droplets was used to inject droplets into the FEC at 1, 2, 3 and 4 m from the target breathing thermal manikin placed at the middle of the FEC. Exposure to cough droplets was determined by measuring the droplet concentration in the breathing zone of the thermal manikin. Results for cough release in front of the manikin indicate that increase of the supply flow rate from 6 to 12 ACH causes increase of the exposure when mixing system is used, but decrease when displacement and underfloor systems were used. These results show that exposure to cough released droplets highly depended on the airflow patterns generated in the indoor environment which can result in unexpected exposure increase with the increase of supply flow rate.