To research the smoke flow patterns and their effects on personnel evacuation during a tunnel fire, a full-scale model of an immersed 150 m tunnel was constructed, taking the Hong Kong-Zhuhai-Macao Bridge immersed tunnel in China as the prototype. A series of fire tests, including pool fires and vehicle fires, were developed to simulate a real fire scenario. The characteristic parameters describing the smoke flow were measured, including smoke layer height, smoke spread velocity, and CO concentration. Their development behaviors and main influence factors were explored, and finally smoke flow patterns were examined. The results showed that smoke stratification appeared, which was measured by smoke layer height. The smoke layer height distribution along the tunnel was found to obey a quartic polynomial trend (goodness of fit 95%). From this, the safety distances were predicted to be 20 m in windy conditions and 80-90 m in still (no wind) conditions. Thus, the longitudinal velocity plays a leading role. Around the fire source or in still conditions, the buoyancy of the smoke is the critical factor driving smoke flow; the influence of other factors is no more than +/- 20%. However, other conditions depended on the ventilation state. CO concentration decreased sharply with increasing distance from the fire source. At a distance of 60 m, CO concentration decayed by 50%.
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