Study of spatial-temporal distribution of speech droplets: an experimental measurement in conference room

This study conducted experimental measurements of continuous speech-generated droplets simulated by a water mist generator in a conference room, to investigate the characteristics of indoor droplet dispersion and distribution. Spatial-temporal distribution characteristics of droplets at varying distances and directions were analyzed in both the presence and absence of air-conditioned air supply. Results show that the droplet concentration gradually increases over time and ultimately attains a stable state with no air conditioning. Droplets in front of the speaker decay as the distance increases. Droplets at 1.5 m did not significantly attenuate compared to 0.5 m, implying that the commonly recommended social safe distance of 1-1.5 m merits further scrutiny. This study offers a robust quadratic fit to the spatial and temporal distributions in droplet concentrations in front of the speaker, which can be used as a reference method for estimating droplet propagation. When the air conditioning system is operational, the influence of the conditioned airflow on droplet dispersion becomes dominant, resulting in distinct periodic variations in droplet concentration. Distance and direction do not significantly influence droplet concentration, and localized spaces may exhibit droplet accumulation. The peak concentration can be up to 2-3 times higher than in the absence of air conditioning.