Mapping full-range infection transmission from speaking, coughing, and sneezing in indoor environments and its impact on social distancing

Infectious respiratory diseases have posed significant threats to public health in the past decades. However, the full-range transmission in indoor environments remains unclear. In this study, we used the computational fluid dynamics (CFD) method with the large eddy simulation (LES) model, validated by particle image velocimetry (PIV) experiments, to explore the full-range transmission in an indoor space. The penetration of airborne droplets was divided into five power-law phases: accelerating jet (< 0.04–0.1 s, 0.3 m), decelerating jet (< 0.2–0.6 s, 0.7 m), puff (< 20 s, 2.2–3.8 m), mixing (< 360 s), and well-mixed phases (> 360 s). The maximum travel distance versus droplet diameter indicated “V” shapes, with minimum distances of 0.5–1.3 m for 100 µm droplets. The virus concentration decreased exponentially with distance and sustained high values within 2.8 m as a cone shape. The safe distance with an infection risk threshold of 10 % varied from 1 to 4 m, depending on viral load, dwell time, and mask. Here, we suggest social distances of 1, 1.8, and 4 m for the mask and asymptomatic cases, a short duration of viral loads < 10⁷ #/mL, and a short duration of viral loads of 10^8–9 #/mL or long duration, respectively.