Katzenbergtunnel A3

Würzburg, Germany


25 AJ 1000 TR jet fans extract smoke in case of fire in tunnel on the A3 motorway


The ultimate nightmare: being stuck in a motorway tunnel after an accident resulting in a fire. Systemair jet fans have been installed in the new North tube of the Katzenberg tunnel on the A3 motorway near Würzburg to extract the smoke to the open air in such a case of fire. This ensures a protected traffic space without smoke and heat for the tunnel users and aids smooth evacuation.

However, the construction conditions for the North pipe of the tunnel on the A3 motorway represent 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 AJ 1000 TR-type 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. The ventilation concept was developed by HBI Haerter GmbH from Heidenheim and realised by GBI Gackstatter Beratende Ingenieure GmbH from Stuttgart.

As a first step, the calculations made by the engineers at HBI 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 per cent 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.

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