The study investigates the maximum temperature in tunnel fires under forced ventilation conditions, utilizing an innovative 1:10 scale experimental model and numerical simulations to understand fire dynamics better.
Tunnel fires pose a significant risk in infrastructure projects, particularly as construction efforts in underground spaces increase. The rapid expansion of urban areas has compelled countries like China to invest heavily in tunneling projects for transportation and utility purposes. However, these projects bring inherent dangers, as seen in past incidents. For example, in 2023, a fire erupted in the Second Subsea Tunnel construction area in Jiaozhou Bay; in the previous year, a tragic fire at the Housi Tunnel claimed nine lives. In 2019, an incident in the Liangbaosi coal mine excavation tunnel resulted in 11 workers being trapped due to similar hazardous conditions.
The purpose of this study was to fill the knowledge gap regarding maximum temperatures in excavation tunnels, especially under forced ventilation conditions—an essential factor during tunneling operations where fresh air must be continually supplied, and toxic gases expelled. The researchers constructed a scale model to simulate fire behavior and utilized numerical tools to supplement their findings. According to the authors of the article, "The results of the highest temperature in the experimental and FDS simulation results under different fire source conditions have a good fitting performance.." The correlations found between different scenarios indicate the validity of both methods.
One of the innovative aspects of this research is the development of a dimensionless prediction model. When the fire source is located at the end of the tunnel, the study demonstrates a consistent relationship between maximum temperatures and various factors, including the heat release rate and distance from the air duct outlet. The maximum temperature prediction model is designed to enhance the accuracy of safety assessments for tunnel fires, tailoring the ventilation strategy effectively for specific scenarios.
A correction factor was also proposed for the situation where the fire source was situated in the center of the excavation tunnel. This adjustment provides a more accurate forecast of temperature behaviors in confined spaces often encountered during tunneling. Notably, the minimum wind speed necessary for effective ventilation was found to be at least 0.25 m/s, with necessary air volumes calculated to maintain safe conditions.
The study also emphasizes the implications of duct outlet placement on maximum temperature. An optimal layout for ventilation systems is highlighted as crucial, considering both temperature management and airflow volume—"an optimal layout for the ventilation system is important, particularly by considering both the maximum temperature and the ventilation volume," wrote the authors.
This research not only offers critical insights for fire suppression strategies but also addresses broader safety implications in excavation scenarios. By understanding and anticipating the dynamics of tunnel fires, authorities can better prepare for emergencies, ultimately protecting workers' lives and preserving the integrity of critical infrastructure.
As tunneling technology advances and urban underground spaces are utilized more frequently, ongoing research will continue to enhance safety protocols, making elaborate infrastructures safer for everyone involved.
