Talleres Zitron, a global leader in tunnel ventilation systems, has played a pivotal role in enhancing the safety and efficiency of Spain’s high-speed rail infrastructure. Their expertise was instrumental in the design and implementation of the comprehensive ventilation system for the Guadarrama Tunnel, a critical component of the Madrid–Asturias high-speed rail line.
by Nicola Cavallo, Area Sales Manager – Talleres Zitron
Ventilation systems for high-speed rail tunnels in Spain are engineered to meet the highest safety and performance standards, especially due to the country’s extensive network of long, deep tunnels through mountainous terrain.
The Guadarrama Tunnel plays a vital role in linking Madrid to key cities across northern and north-western Spain via high-speed rail. It serves as a strategic backbone for improved regional connectivity and reduced travel times across the AVE network.
The Guadarrama Tunnel is equipped with a sophisticated ventilation system designed to ensure passenger safety and optimal air quality under all operating conditions. The system includes emergency ventilation shafts capable of efficiently extracting smoke or air in the event of a fire or other incident. Additionally, the design accounts for the piston effect caused by high-speed trains, maintaining stable airflow and pressure throughout the tunnel.
The Guadarrama Tunnel: a unique engineering challenge
Stretching 28.4 kilometers through the Sierra de Guadarrama, the Guadarrama Tunnel is the longest railway tunnel in Spain and was the fifth longest in the world upon its completion in 2007. This twin-bore tunnel, each with a cross-sectional area of 52 m², was constructed using four tunnel boring machines (TBMs) and serves as a vital link for high-speed trains traveling at speeds up to 310 km/h.
What made this project truly unique was that no intermediate ventilation shafts were included in its design – an exceptional case for a tunnel of such length. This presented extraordinary challenges for smoke control, fresh air supply, and emergency safety, requiring a solution that could deliver long-range, high-capacity airflow from the portals alone. Over the course of the project, several ventilation concepts were evaluated.
The final and most effective solution was the one implemented with Talleres Zitron, based on a Saccardo nozzle longitudinal ventilation system. This approach, refined through Computational Fluid Dynamics (CFD) simulations, ensured that the entire tunnel length could be ventilated effectively from the portals without the need for intermediate shafts.
Innovative ventilation system by Talleres Zitron
Particular care was taken to ensure that all ventilation equipment could withstand the piston effect pressure of 10,000 Pascals generated by high-speed trains travelling at 310 km/h.
The Saccardo nozzles were engineered to inject high-velocity air jets into the tunnel, inducing a high-volume longitudinal airflow capable of clearing smoke and supplying fresh air over the full 28.4 km distance. CFD optimisation determined the ideal injection angle and discharge section, minimizing static pressure losses while maximizing air movement.
To meet operational needs, four ventilation stations were constructed at each tunnel portal, each equipped with three 2-meter-diameter fans powered by 450 kW motors. Two main ventilation rooms with vertical shafts were also built at the portals, each housing three 2-meter-diameter fans with 560 kW motors. An insulated damper system allows each main station to supply air selectively to either the east or west tube.
Emergency ventilation protocol
In the event of an incident, the ventilation system operates according to a protocol established by the control centre:
- The main ventilation station at the affected portal starts delivering a specific airflow generated by two fans (with a third fan in reserve);
- Simultaneously, two fans in the Saccardo nozzle station at the same portal provide additional airflow (also with a third fan in reserve);
- Combined, these airflows achieve a tunnel wind speed of 3 m/s in the incident tube;
- The other fans in that tube remain inactive to avoid disturbing the controlled flow pattern.
In the safe tube, the system switches to pressurization mode. Passengers evacuating from the incident tube enter the safe tube via emergency passageways spaced every 250 meters. The main ventilation station not supplying the incident tube instead supplies the safe tube, maintaining a positive pressure of 50 Pa relative to the fire-affected tube, preventing smoke ingress.
Testing and validation before opening
Before the official opening, full-scale ventilation tests were carried out to confirm the performance of the CFD-based design.
These tests simulated a range of emergency and operational scenarios, including fire events, to measure airflow velocities, pressure differentials, and smoke dispersion over the full tunnel length.
Talleres Zitron actively participated in these trials, providing technical expertise and fine-tuning system parameters. The tests were a complete success, validating both the Saccardo nozzle solution and the absence of intermediate shafts – a first for a tunnel of this scale.
Ensuring safety through overpressure and CFD simulations
The combination of positive pressure in the safe tube, precise longitudinal airflow control, and a robust emergency activation protocol ensures effective smoke management and safe evacuation under the most challenging conditions.
Extensive CFD simulations allowed for optimisation of every design aspect, ensuring compliance with stringent international safety standards.
Conclusion
The Guadarrama Tunnel is not only a feat of civil engineering – it is a global reference in tunnel ventilation without intermediate shafts. Talleres Zitron’s contribution was decisive in making this possible.
The project demonstrated:
- Proven feasibility of long-tunnel ventilation from portals alone – An unprecedented case for a tunnel of this length, now fully validated in real conditions;
- Operational reliability – Redundant fan configurations ensure uninterrupted service;
- Optimised energy efficiency – CFD-driven design reduces pressure losses and power consumption;
- Passenger safety at the core – Pressurisation, high-capacity longitudinal flow, and controlled evacuation paths;
- Robust construction – Equipment designed to resist extreme piston-effect pressures;
- Successful pre-opening testing – Real-world trials confirmed design performance and safety targets.
This achievement reinforces Talleres Zitron’s position as a global leader in tunnel ventilation technology. It stands as proof that, with the right engineering, even the most unconventional tunnel configurations can meet – and exceed – the highest safety and performance standards.
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