Impact of High Altitude Low Pressure Environments on Fire Smoke Propagation in Highway Tunnels

Abstract

The distinct characteristics of high-altitude regions, such as lower atmospheric pressure, reduced air density, diminished oxygen content, and cooler environmental temperatures, significantly influence the nature of tunnel fires. This study employs the Fire Dynamics Simulator (FDS) to simulate highway tunnel fires under five different ambient pressure scenarios. Utilizing dual heat sources of three powers 5MW, 10MW, and 20MW, the investigation delves into the temperature characteristics of smoke within the tunnel and its effect on vertical shaft smoke extraction. Findings reveal consistent longitudinal temperature profiles of smoke along the tunnel ceiling across varying conditions, with relatively higher ceiling temperatures in low-pressure environments. The ceiling's peak temperature in the fire source area varies with the power of the heat source, demonstrating a decrease in the highest longitudinal temperature as ambient pressure diminishes. Smoke temperature profiles at different tunnel locations remain fundamentally consistent, showing increased temperatures in low-pressure settings, with fire source sections exhibiting higher temperatures than non-source sections. At lower heat source powers, substantial temperatures persist at the 2m height level within the fire source area. The maximum smoke temperature differences upstream and downstream of the vertical shaft approximate 100°C, with shaft temperatures also escalating as pressure decreases. In lowpressure environments, the shaft's extraction capacity weakens, enhancing smoke evacuation efficiency. The results from studying tunnel fires in low-pressure environments provide valuable insights for practical tunnel design, evacuation strategies, and firefighting rescue operations.