Numerical investigation of the transmission route of infectious particles produced by human
Keywords:droplet dispersion, Lagrangian method, coughing, breathing, particle fate
This study aims to investigate the major factors to influence the respiratory transmission occurred by infectious particles from a human in an indoor environment. Identifying the critical factors of respiratory transmission is important for taking a countermeasure to control its spread. However, it is difficult to track large numbers of infectious particles generated by a human and floating in a room by the experimental method. Therefore, the transient jet airflow by human cough was numerically reproduced, and the trajectories of particles were investigated using the Lagrangian method. In the numerical analysis, two persons sitting and facing each other in a small office room were considered assuming that one person produced infectious particles by cough, and another was exposed to the infection. The trajectory of the dispersed infectious particles was calculated to confirm the proportion of particles that were directly inhaled by a person, attached to the human body surface, adhered to the floor, removed by ventilation, and suspended in the air. Also, the size of particles (1, 5, 10, 20, 40, and 80 μm) produced by the infector, the ventilation rate (6 m3 h−1⋅person−1, equivalent to air changes per hour is 0.5 h−1), and the distance between individuals (0.9 m (3 ft) and 1.8 m (6 ft)) were investigated as an influential major factor to affect the spread of transmission. As a result, it was confirmed that the effects of gravity and inertia increased with larger particles, resulting in a greater rate of adhered particles to the floor. On the other hand, when the size of particles was smaller, they were able to be removed more effectively by increasing the ventilation rate. Further, when the individuals were spaced 1.8 m apart, particles larger than 20 μm had no significant effect on droplet transmission. However, the smaller particles less than 10 μm were highly likely to be inhaled directly and cause droplet transmission. Therefore, for smaller particles less than 10 μm, practical measures to avoid infections such as social distancing is necessary.
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