Optimal distance between jet fans used to extinguish metropolitan tunnel fires: A case study using fire dynamic simulator modeling

Several disastrous tunnel fires have occurred in recent decades; safe evacuation, minimization of damage, and reliable ventilation have received a great deal of attention. Here, we use the Fire Dynamic Simulator (FDS) software to optimize jet fan spacing in an extra-long tunnel: the Zhong Liangshan tunnel of Metropolitan Line 1 in Chongqing, China. The model tunnels were 500, 550, and 600 m in length, with cross-sectional areas of 30.72 m(2); the jet fans were elevated 5.60 m from the floor at different spacings (100, 150, and 200 m). A 5-MW fire burned at 200, 175, and 150 m from the tunnel entrance. We simulated five scenarios using FDS software and compared airflow velocity and temperature curves. We also briefly investigated the effect of the length of an extra-long tunnel. The numerical results revealed that the air temperature always remained well below the 60 degrees C that the human body can withstand during evacuation necessitated by a fire; the air velocity remained nearly constant. We built a 1:15-scale model to validate the simulation; the simulation and experimental curves were in good agreement.