In tunnel fire, smoke is a great threat to successful emergency escapes, and its spreading patterns at high altitude tunnel may differ. Therefore, the impact of ambient pressure on the stability of smoke layers and maximum smoke temperature under ceiling in ventilated tunnels were investigated in this study. Results show that the temperature of smoke layer is negatively correlated with the longitudinal velocity and ambient pressure. Besides, the influence of longitudinal velocity at different ambient pressures on the shear velocity between the smoke and air layers was further studied. Using Richardson number (Ri) and Froude number (Fr), smoke flow can be classified into three patterns, namely stable and obvious smoke stratification (Ri>3.2 or Fr < 0.38), a stable smoke layer but with blurred interface (2.3 < Ri < 3.2 or 0.38 < Fr < 0.53) and a completely unstable smoke stratification (Ri < 2.3 or Fr > 0.53). Furthermore, a model has been developed to predict maximum smoke temperature under the tunnel ceiling, which agrees well with previous studies at standard atmospheric pressure. The results of the present work provide information for tunnel structure protection and safe evacuation in fire accidents at different ambient pressures.

在隧道火灾中，烟雾对成功的紧急逃生构成巨大威胁，并且其在高海拔隧道中的传播方式可能会有所不同。因此，研究了通风管道中环境压力​​对烟层稳定性和天花板下最高烟气温度的影响。结果表明，烟层温度与纵向速度和环境压力呈负相关。此外，进一步研究了在不同环境压力下纵向速度对烟气层与空气层之间剪切速度的影响。使用Richardson数（Ri）和Froude数（Fr），烟流可分为三种模式，即稳定的烟气分层和明显的烟气分层（Ri > 3.2或Fr）。 <0.38），稳定的烟层但界面模糊（2.3 <  Ri  <3.2或0.38 <  Fr  <0.53）和完全不稳定的烟气分层（Ri  <2.3或Fr  > 0.53）。此外，已经开发了一个模型来预测隧道顶棚下的最高烟气温度，这与以前在标准大气压下的研究非常吻合。本工作的结果为在不同环境压力下发生火灾时隧道结构的保护和安全疏散提供了信息。