Experimental study on fire suppression in ultrawide subsea immersed tube tunnels using high-pressure water mist

Given the confined and elongated configuration of ultrawide subsea immersed tube tunnels, fires can lead to a rapid spread of flames and smoke, posing a substantial threat to the structural integrity of the tunnel and the safety of personnel. Traditional fire protection designs are often not ideal for cooling and controlling fires in such environments. Therefore, developing effective fire prevention and control technologies specifically suited to subsea tube tunnels is of great practical importance for ensuring tunnel safety and facilitating personnel evacuation. The main objective of this study is to evaluate the fire suppression and cooling effects of high-pressure mist in subsea immersed tube tunnels. To simulate real-life conditions, a full-scale 1:1 experimental model of a subsea tunnel was constructed, with the width, height, and length being 18.0, 6.6, and 25.0 m, respectively. This study aims to evaluate the combustion behavior, temperature distribution, and cooling efficiency of high-pressure water mist under different heat release rates.

Gasoline was used as the fuel source in experiments conducted at three heat release rates: 2.5, 5.0, and 10.0 MW. Key parameters, including the flame height, temperature variation curves, and the cooling effects of high-pressure water mist, were measured throughout the experiments. The experimental setup was designed to closely replicate real fire scenarios in subsea tunnels, ensuring accurate and reproducible results. During the experiments, high-precision temperature sensors and imaging devices were used to continuously record and analyze the temperature distribution and flame characteristics.

The experimental results showed significant differences in the flame characteristics and temperature distribution across different heat release rates. For example, the maximum flame heights under 2.5, 5.0, and 10.0 MW heat release rates were 4.5, 6.0, and 6.6 m, respectively. Without high-pressure water mist for fire suppression, the highest ceiling temperatures reached 180℃, 310℃, and 528℃, respectively, posing a certain threat to the structural integrity of the tunnel. Upon activation of the high-pressure water mist, ceiling temperatures in all fire scenarios dropped significantly, falling below 300℃, thereby effectively reducing the risk of structural damage. Furthermore, for the 2.5 MW heat release rate, the activation of the high-pressure water mist rapidly reduced the temperature in the burning area to below 150℃. While complete suppression of flames was more challenging in higher-power fire scenarios, the water mist significantly lowered the ceiling temperature and the temperature in the burning area. This slowed the fire progression, providing valuable time for personnel evacuation and firefighting efforts.

The experimental results confirm the effectiveness of high-pressure water mist in controlling fires within subsea immersed tube tunnels, particularly in reducing ceiling temperatures and minimizing structural damage risks. The use of high-pressure water mist in such tunnels can effectively reduce temperatures and mitigate the impact of fires on tunnel structures, providing technical support for improving fire safety. Overall, this research provides valuable insights for enhancing fire safety strategies in subsea immersed tube tunnels and provides practical recommendations for designing fire prevention and control systems.