For the first time, a high-pressure water mist system has been installed for smoke management purposes in the underground S-Bahn stations Kaiserlei, Ledermuseum, and Marktplatz operated by Deutsche Bahn between Frankfurt am Main and Offenbach Hauptbahnhof - a first for underground stations. The main objective of the project is to significantly extend the time available for external rescue by the fire department by effectively controlling the smoke in the stations.
Challenges of underground stations
The three S-Bahn stations have a common design: an underground track level, above which is an intermediate level containing vending machines, among other things, and connected to the exits to the surface. In the event of a fire, smoke therefore first rises from the track level to the intermediate level before it can escape to the outside. The route to the outside is therefore long and, without further measures, heavily smoke-filled.
Analyses have shown that the available external rescue times – i.e., the time available to the fire department to rescue people – would not be sufficient in an emergency. The specifications for the maximum permissible smoke level and the minimum time available for evacuation of the train stations cannot therefore be reliably guaranteed without additional measures.
Possible fire events could include fires in the station itself, but the greatest risk is posed by fires on trains. If a vehicle catches fire while in the tunnel, train drivers are required to continue to the next station.
High-pressure water mist as an effective solution
Fire tests and detailed analyses confirmed the suitability of the Fogtec high-pressure water mist system for the suburban railway stations described here. By generating extremely small water droplets, a fire is fought, smoke and soot particles are partially bound, and the smoke gas temperatures are significantly reduced. Not only is the volume of smoke reduced, but the spread of smoke is also influenced and slowed down when the high-pressure water mist system is designed appropriately.
Alternative approaches, such as structural or mechanical smoke extraction measures, are either not feasible or considerably more expensive. In addition, these do not actively influence the amount of smoke gas. The decision was therefore clearly in favor of the Fogtec high-pressure water mist system. This is the first application of this technology in underground railway stations.
Technology and logistics in detail
The system was implemented as a stand-alone system in each station.
Due to its small size, the technical infrastructure, such as pumps, power supply, water storage, and main pipe, could be housed in the stations themselves. Part of the system technology is located in the trough area under the platforms. The pumps were lowered into the designated rooms with millimeter precision via former ventilation shafts.
Stainless steel pipes with minimal diameters run along the underside of the station ceiling from the main pipe. These pipes supply water to special high-pressure nozzles. Each station was divided into several extinguishing areas. If the fire alarm system detects a fire, three sections are activated: the section in which the fire was detected and the two adjacent sections. This ensures that the water mist is only released in the areas where the fire is located. As a result, the pipe size and the amount of water required could be kept to a minimum.
The pipes and nozzles were installed under the station ceiling and at the platform edges to enable firefighting from both above and below. In the event of a fire, the section pipes are supplied with water via remotely maintainable valves.
Precision in planning and installation
The installation of the system presented the project team with challenging logistical challenges: Installation work was mainly carried out at night or during breaks in operation, sometimes with complete closures. Tight scheduling of the measures, precise coordination with Deutsche Bahn, and just-in-time material transport by freight train were necessary.
Greater safety for everyone involved
The first-ever installation of a proven high-pressure water mist system in underground stations has made a decisive contribution to increasing safety for passengers, staff, and emergency services at the three stations in Offenbach. The operator was able to significantly reduce closure times for retrofitting and considerably lower investment costs.
The project sets new standards in fire protection for underground transport facilities and demonstrates the possibilities offered by modern Fogtec water mist technology.