Finding the best escape route from underground train stations

Researchers started a fire three times in the underground railway system in Berlin for this project.

Underground railways are indispensable in major German cities. It would be impossible to cope with the entire volume of traffic on the surface. The transport company BVG (Berliner Verkehrsbetriebe) counted more than half a billion passengers on its underground trains alone in 2017. This makes it even more important for people to be protected against dangers – such as fires or poison gas attacks.

The team working on the Orpheus project, short for “Optimization of smoke management and evacuation strategies in underground train stations: experiments and simulations”, focussed on how this could be achieved. “Our aim is to be able to guide people out of underground train stations in the event of an emergency as quickly and safely as possible,” explains Markus Brüne. He works at the RUB in the Working Group Climatology of Extreme Locations headed by Professor Andreas Pflitsch.

Quicker than in real time

In the Orpheus project, the team laid the foundations for a system that could one day simulate how smoke or gas spreads in an underground train station quicker than in real time and thus determine the best escape route for a specific situation. This process is complicated because every station has its own dynamic air flows that can also change depending on external factors.

“The underground railway systems in Germany are in some cases 100 years old and, therefore, most of them do not have any artificial ventilation,” explained Brüne. Air is supplied by the trains that push a wall of air through the tunnel. In addition, the underground system of branching tunnels develops its own climate system, which includes, in particular, its own underlying natural air flows. These air flows become dominant when rail traffic is interrupted in the event of an emergency. In order to ensure that a computer simulation can correctly illustrate how smoke would spread in a station, the air flows need to be taken into account as underlying conditions.

Fire and theatrical smoke in the underground train station

In the Orpheus project, the researchers from Bochum equipped the “Osloer Straße” train station in Berlin with so-called ultrasonic anemometers. These measurement devices recorded the air flows in the station uninterrupted for up to eight years; the data was then fed into the computer model developed at Forschungszentrum Jülich. To test how well the simulation reflected real life, three large experiments were carried out at the station in Berlin. The project team also released a propane gas and measured how the smoke spread.

On the one hand, the researchers used a tracer gas for this purpose so that they could take quantitative measurements of how it spread. While on the other hand, theatrical smoke was released to give an optical impression of how the smoke would spread. “The experiments were very complex,” says Markus Brüne who was present at the station. “And it was of course important not to negatively impact the structure of the station.”

Experiments at night

A major challenge was the fact that the experiments could only be carried out when the transport system was shut down yet a large amount of measurement equipment needed to be set up. “We needed 30 to 40 people to set everything up at 10 p.m. In general, we were able to start the experiment at 1:30 a.m. because at this time there were no more trains running,” explained the researcher. “All of the equipment then needed to be removed again by 3:20 a.m.”

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