Computational investigation of prolonged airborne dispersion of novel coronavirus-laden droplets

Abstract

We have performed highly accurate numerical simulations to investigate prolonged dispersion of novel coronavirus-laden droplets in classroom air. Approximately 10,900 virus-laden droplets were released into the air by a teacher coughing and tracked for 90 min by numerical simulations. The teacher was standing in front of multiple students in a classroom. To estimate viral transmission to the students, we considered the features of the novel coronavirus, such as the virus half-life. The simulation results revealed that there was a high risk of prolonged airborne transmission of virus-laden droplets when the outlet flow of the classroom ventilation was low (i.e., 4.3 and 8.6 cm/s). The rates of remaining airborne virus-laden droplets produced by the teacher coughing were 40% and 15% after 45 and 90 min, respectively. The results revealed that students can avoid exposure to the virus-laden droplets by keeping a large distance from the teacher (5.5 m), which is more than two times farther than the currently suggested social distancing rules. The results of this study provide guidelines to set a new protection plan in the classroom to prevent airborne transmission of virus-laden droplets to students.

Numerical model for cough‐generated droplet dispersion on moving escalator with multiple passengers

“…To investigate realistic droplet motions, we use the frequency distribution of the diameter of the droplets expelled from the mouth by coughing shown in Figure 5A. This particle distribution was used in the authors' previous study 12 . Figure 5B shows the time variation of cough‐generated droplet radius r based on Equation (10) with a minimum radius.…”

“…Figure 5B shows the time variation of cough‐generated droplet radius r based on Equation (10) with a minimum radius. The total number of droplet particles expelled from the mouth in a cough is 10 900 12 . The number of droplets generated per unit time is proportional to the flow rate.…”

“…This particle distribution was used in the authors' previous study. 12 Figure 5B shows the time variation of cough-generated droplet radius r based on Equation (10) with a minimum radius. The total number of droplet particles expelled from the mouth in a cough is 10 900.…”

“…Various computational models have been reported for numerical simulations of droplets and their airborne propagation routes. Yamakawa et al 12 performed a numerical simulation of airborne droplet dispersion over a long period of time using a classroom model with ventilation and showed that expelled droplets remaining suspended in the air affect the risk of infection. Yu et al 13 simulated the exposure of bioaerosols in offices equipped with mechanical ventilation and air conditioning systems.…”

Ventilation in worker dormitories and its impact on the spread of respiratory droplets

“…The extraction of particles in a room can be based on thresholds defined in different standards, and in one study on outpatient clinic rooms, it was found that lower than standard air changes per hour could lead to increased risks of viral spread ( King et al., 2021 ). 15% of air-borne virus-laden droplets remained in a classroom study even after 90 min due to a low ventilation rate ( Yamakawa, Kitagawa, Ogura, Chung, & Kim, 2021 ).…”