EFFECT OF FIRE LOCATION ON TEMPERATURE, VELOCITY,VISIBILITY AND CO CONCENTRATION DISTRIBUTIONS IN UNDER GROUND TUNNEL

摘要

A Numerical study has been undertaken in underground tunnel using Fire Dynamic Simulator (FDS) version 5.5.3. The tunnel is horizontal and completely below ground. It is 300 m long, with a partial circle cross-section. Ventilation devices are mounted by groups of jet fans under tunnel ceiling with 100m distant apart. Emergency doors with 100 m apart are connected to a walkway (cross-passage) for motorists escaping. In the case of longitudinal or transverse ventilation systems, one of the main aspects deals with the preservation of the smoke's natural stratification. It must be preserved in a clean air layer in the lower part of the tunnel, which is crucial in order to facilitate the motorists' evacuation. After motorists evacuating, jet fans start to work at highest speed that is cause to sweep all smoke upstream the fire to downstream to allow fire fighters enter from traffic direction. In the present work two case studies are simulated for 400 seconds in which the smoke reaches to steady state condition with different fire location of Heptane pool with 23 Mw which equivalent to bus or truck fire. Results illustrate the temperature contours at different cross sections upstream and downstream fire location , temperature contours at human level , visibility contours at human level , velocity contours at mid plane and the simulation for motorists escaping from different exits and calculating evacuation time required. This study shows that evacuation time depends on different factors such as agent-agent interactions, agent-wall interactions, the motive force on the evacuating human and the visibility. The local temperature at human occupancy level doesn't exceed the safety limit of 60 C° according to National Fire Protection Association (NFPA 502) and the visibility at human level before operating the jet fans decreases to 20m due to the dropping of the ceiling jet, which was defined as the flow of smoke under tunnel ceiling, extending from the point of fire plume impingement on ceiling, that results in smoke dropping and penetration to reach the human occupancy level.