Abstract: In order to explore self-extinction phenomenon of fire in tunnels with different slopes, with America′s Memorial Tunnel as a prototype, a 1/20 reduced-scale model tunnel was constructed based on Froude scaling law and a series of experiments were conducted by using methanol to investigate fire in tunnels under natural ventilation. Then, information of velocity, temperature and oxygen concentration were obtained through data acquisition system. The results show that there is no self-extinction phenomenon in experiments with a slope of 3% and 5%, while it occurs in cases of zero and 1% slope except when heat release rate(HRR) is at 2.8 kW, and the greater HRR is, the shorter self-extinction takes. Existence of tunnel slopes causes hot smoke to form stack effect due to buoyancy, and the larger slope is, the stronger stack effect will be. As tunnels with a slope of 3% and 5% form larger longitudinal wind speed, they restrain self-extinction while in tunnels with a smaller slope, the phenomenon occurs because oxygen concentration near the fire source has fallen to the limit.

Key words: tunnel fire, fire self-extinction, slope, stack effect, natural ventilation