Abstract

Over 766 million people have been infected by coronavirus disease 2019 (COVID-19) in the past 3 years, resulting in 7 million deaths. The virus is primarily transmitted through droplets or aerosols produced by coughing, sneezing, and talking. A full-scale isolation ward in Wuhan Pulmonary Hospital is modeled in this work, and water droplet diffusion is simulated using computational fluid dynamics (CFD). In an isolation ward, a local exhaust ventilation system is intended to avoid cross-infection. The existence of a local exhaust system increases turbulent movement, leading to a complete breakup of the droplet cluster and improved droplet dispersion inside the ward. When the outlet negative pressure is 4.5 Pa, the number of moving droplets in the ward decreases by approximately 30% compared to the original ward. The local exhaust system could minimize the number of droplets evaporated in the ward; however, the formation of aerosols cannot be avoided. Furthermore, 60.83%, 62.04%, 61.03%, 60.22%, 62.97%, and 61.52% of droplets produced through coughing reached patients in six different scenarios. However, the local exhaust ventilation system has no apparent influence on the control of surface contamination. In this study, several suggestions with regards to the optimization of ventilation in wards and scientific evidence are provided to ensure the air quality of hospital isolation wards.

Introduction

The study of airborne diseases has recently become increasingly significant with the emergence of severe acute respiratory syndrome, Ebola virus, tuberculosis, coronavirus disease 2019 (COVID-19), and other infectious diseases (Hathway et al. 2011). With the worldwide outbreak of COVID-19 (as of May 10, 2023), there have been 765,903,278 people diagnosed with COVID-19, including 6,927,378 deaths globally (WTO 2023). Some countries or regions succeeded in preventing the spread of the epidemic by managing quarantines and closures, which seriously affected economic growth and the normal operation of whole cities. Over the last 3 years, countries have prioritized preventing and controlling the epidemic. At the beginning of the outbreak, 100,000 people died every day worldwide as a result of COVID-19. It can affect anyone anywhere, especially healthcare workers exposed to environmental existing virus droplets. Therefore, the study of airborne virus diffusion in hospital isolation rooms is significant.

Viral respiratory infections are diffused by contact and droplet transmission, fomite transmission, and other types of transmission (WTO 2020). Contact transmission occurs when a healthy man is in close contact with an infected person (direct contact) or when an infected individual exhausts fomites containing viral droplets (indirect contact) (Morawska and Cao 2020). Viruses spread through the air via droplets or aerosols produced during coughing, sneezing, and talking (Jones and Brosseau 2015). Coughing, which is an intense process of droplet generation over transient time, has recently been the focus of many studies. Small virus droplets expelled into the air can exist as airborne droplets for a long time (Chartier et al. 2009) and can fill the whole room under the effect of an air conditioner (Liu et al. 2020b). Li et al. 2020a, b) investigated the spread of droplets in a tropical outdoor environment and found that at wind speeds of 2 m/s, 100 μm droplets can move up to 6.6 m. Wei and Li (2015) modeled the coughing process as a turbulence jet to investigate the diffusion of droplets and obtained travel distances with different droplet sizes. Lindsley et al. (2016) compared aerosol droplet samples of 61 adult volunteer outpatients through experiments and found that more aerosol droplets containing viruses were released through coughing. Nicas et al.

Conclusion

In this study, the full-scale geometry of the isolation ward in Wuhan Pulmonary Hospital is modeled, and the droplet diffusion process from a coughing event in the ward is simulated. An experiment is conducted to validate the CFD model, and a local exhaust ventilation system is designed to ensure indoor air quality.

(۱) Although the local exhaust ventilation system reduces the number of airborne contaminants, a substantial increase in turbulent air motions may occur. The results show that a negative outlet pressure of 2.5 and 3.5 Pa led to a decrease in evaporated droplets and airborne contaminants remaining indoors, and the negative outlet pressure of 3.0 Pa increases the number of droplets tracked in the ward of the excessively turbulent flow. It is found that the number of droplets remaining indoors on the outlet negative pressure is not linear. The exhaust system can effectively extract contaminants when the negative pressure value is small. However, the negative pressure is increased, and the local exhaust system promotes turbulent transport, leading to a complete breakup of the droplet cluster and enhancing the dispersion of droplets indoors. The mass of the droplets is light, and when the outlet negative pressure value reaches a certain value, droplets can also be effectively removed.