Jet fans extract smoke in motorway tunnels


Smoke test confirms ventilation concept. Smooth activation supports retention of function.


The ultimate nightmare: being stuck in a motorway tunnel after an accident resulting in a fire. The construction conditions for the North pipe of the tunnel on the A3 motorway represented a particular challenge. The slightly S-shaped, 570 metre long tunnel has a 22 m incline in the East to West direction. To deal with these topological and construction conditions, the technical safety system installed in the new tunnel needs a sophisticated design. If there is a fire, the stainless steel jet fans will work for at least 90 minutes at 400°C; but in practice definitely for longer. Achim Wöhrle, Key Account Manager at Systemair says, “With this type of fan we can generally hold out for at least 120 minutes. Our tests confirm this, too.”

The tunnel tube is equipped with 25 AJ 1000 TR-type jet fans, each with a power of 30 kW. They are installed in five groups of five. This enables a total thrust of 900 N (Newtons) to be generated.

As a first step, the calculations made by the engineers were verified in a practical test on the test rig at Systemair in Windischbuch. A smoke test in the tunnel itself – under the watchful eye of the fire service – gave final confirmation of the theoretical and practical assumptions. All 25 fans can also be run in reverse, enabling the system to react to changing meteorological conditions such as rotating wind pressure. Here the fans still run at around 90% capacity.

Normally the jet fans in the Katzenberg tunnel are switched off. The prevailing westerly wind rising from the valley generally ensures the necessary exchange of air. In case of fire, the fans are activated in smooth progression with appropriate speeds, taking into account the natural airflow. This protects the fan equipment and also helps the system function for longer if there is a fire.


Project:          Katzenbergtunnel, motorway A3 near Würzburg, Germany

Concept:        Ventilation of a motorway tunnel

Product:         25 jet fans, type AJ 1000 TR

Total thrust:    900 N

Planning:        HBI Haerter GmbH, Heidenheim, Germany

Implementation: GBI Gackstatter Beratende Ingenieure GmbH, Stuttgart, Germany

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