At 57 kilometers in length, the Gotthard Base Tunnel in Switzerland is the world's longest railway tunnel, running under as much as 2,450 meters of mountain rock. Running high-speed trains through two parallel single-track tunnels generates enormous aerodynamic drag and extreme heat, with ambient rock temperatures reaching 46 degrees Celsius. To keep passengers safe during an emergency, engineers designed two multi-functional emergency stations located hundreds of meters below the surface at Sedrun and Faido.
The primary challenge in these deep underground stations is maintaining air pressure balance and controlling smoke movement during a train fire. The emergency ventilation system relies on vertical shafts—most notably the 800-meter-deep Sedrun shaft—equipped with massive industrial exhaust fans capable of moving hundreds of cubic meters of air per second. When an emergency is detected, high-speed train traffic in adjacent tubes creates a piston effect, forcing air through cross-passages.
To prevent toxic smoke from invading the evacuation stations, the ventilation system uses powerful supply fans to over-pressurize the safe escape halls relative to the rail tubes. Simultaneously, giant extraction dampers near the train stoppage point open to pull hot gases up the vertical shaft. The fluid dynamic calculations must account for buoyancy forces from intense heat, air density changes along the 800-meter vertical rise, and transient pressure waves generated by oncoming traffic.
This precise air balance ensures that clean air flows into passenger escape routes while driving lethal fumes straight up through the rock to the Alpine surface above.