Measurement of Breath Velocity and Volume on Speaking, and Performance of Local Exhaust System as Prevention Measure of Infection

Abstract

This study proposes a novel approach combining a local exhaust ventilation system (LEV) and a whole underfloor air distribution system (WUFAD) in the consulting room. This study assumes that two persons (doctor and patient) are sitting face to face and talking without a mask in a simple room regarded as a consulting room. To model people talking, exhaled air velocity and volume from talking were required, so we estimated velocity speed using an ultrasonic anemometer and volume using a PET bag and mask. Then CFD steady analyses were carried out, setting various parameters (hood height, hood flow rate, horizontal hood position, and ACH) using the breath experiment results. Capture efficiency and contribution distribution for the hood (SVE5: scale for ventilation efficiency 5) for tracer gas have been calculated. Infection risk for the doctor also has been calculated using the Wells-Riley model. The estimation’s results showed that exhaled air velocity was 0.30m/s and volume was 5.2L/min from talking. The CFD results showed that hood flow rate significantly affected capture efficiency. SVE5 showed that ACH greatly influenced the hood’s effective area. The infection risk for the doctor revealed that the combination of the LEV and WUFAD could protect doctors from infection risk under low supply conditions: 60 m3/h/person (6 ACH).