Evolution of the fire combustion and propagation of smoke plume in the high-altitude area is likely to perform different features compared to those fires burned in flatlands. Currently, limited experiments have been conducted to analyze the fire and smoke behavior in the high-altitude tunnels. Motivated by such knowledge gap, the present work conducted a set of burning tests at the altitude of 3200 m. The flame spreading characteristics, as well as the propagation of smoke plume, were studied. Meanwhile, comparison with the data derived from urban tunnel fires was made to quantify the influence of tunnel altitude. Results suggest that the longitudinal ventilation speed has vital influence on the flame behavior and smoke movement. Burning rate of heptane pool fires firstly decreases and then increases with the wind velocity. The peak drop of burning rate caused by the wind cooling effect exceeds 70 %. At a certain ventilation speed, the flame titled angle at high-altitude area is found to be smaller than that predicted for the fires in flatlands. As the ventilation velocity increases, plume bifurcation results in a sharp decrease of ceiling temperature. The maximum temperature is found to decrease at a very low speed when the ventilation velocity is within 0.40 m/s ∼ 1.10 m/s. Thermal stratification loses its stability due to the strong wind while the corresponding temperature rise at human height is still below the safety limit. According to the comparison with literature models, more exploration regarding tunnel fires in the high-altitude area shall be conducted since the existing formulae may lose their effectiveness if applying to such conditions.
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