Building safely upwards TU Braunschweig investigates concepts for buildings without a second escape route

In many German cities, the demand for housing is growing. One response to this is so-called redensification: building gaps are closed and existing buildings are extended upwards. However, fire safety regulations, which stipulate two escape routes, often present a major hurdle. That is why a research team of scientists from Technische Universität Braunschweig, Magdeburg-Stendal University of Applied Sciences and Rottenburg University of Applied Sciences is investigating how to make stairwells safer as the sole escape route. To this end, a controlled fire was set in a 12-metre-high stairwell at the Centre for Fire Research. The Braunschweig fire brigade was also called in to assist.

Multi-storey buildings must have two independent escape routes: one via the stairwell and a second one via a location accessible to the fire brigade, such as a balcony or a window. In many cities, however, parked vehicles, dense tree cover or overhead lines from public transport block the areas where fire brigade ladders can be set up. If the fire brigade cannot use its equipment, an additional structural escape route or safety stairwell is required. In existing buildings, neither of these options is often technically or economically feasible. The result is that potentially valuable extensions, especially in timber construction, are rejected due to fire safety obstacles.

A stairwell, an escape route

This is where the scientists in the “ALREKO” project come in. They are investigating what measures can be taken to improve stairwells so that they can serve as the only escape route, with a comparable risk profile to buildings with a second escape route via fire brigade ladders. The same applies to adding storeys to existing buildings.

“This offers considerable potential for timber construction, which is particularly suitable for this type of building project. It enables extensions that would not be possible under the current conditions,” says Professor Jochen Zehfuß, Head of the Fire Protection Department at the Institute for Building Materials, Solid Construction and Fire Protection (iBMB) at TU Braunschweig.

The research team aims to develop alternative escape route concepts that can be implemented economically and attractively in multi-storey residential buildings. They are focusing on technical solutions that can effectively protect the stairwell from smoke and fire without significantly affecting the building’s structure or incurring high costs. These solutions include fire doors, intelligent smoke extraction and extinguishing technology.

Fire tests in a twelve-metre stairwell

For the full-scale testing series, a four-storey stairwell, approximately twelve metres high, was added to the fire station at the Centre for Fire Research at TU Braunschweig. Two doors on each floor connect the stairwell directly to an adjacent room in the multi-storey fire house, where the fire was started on the ground floor.

To gain meaningful insights into smoke propagation, the researchers installed two different door variants on the second and third floors. In addition to a special fire door, they installed a tightly closing extra door.

When the extinguishing system fails

The researchers set up four different scenarios in their series of experiments, ranging from stairwells with non-combustible surfaces and closed or open doors, to wooden staircases with or without extinguishing systems. These scenarios were designed to demonstrate how structural conditions affect the spread of fire and smoke in existing buildings. The scientists also considered what the consequences of extinguishing system failure would be. Could fire-optimised doors provide sufficient protection in the event of a fire in the stairwell?

These fire tests are of great importance to the fire service. Fire services from several large cities (Berlin, Hamburg, Frankfurt and Magdeburg) are participating in the experiments, with the Braunschweig fire service providing support and keeping emergency personnel on standby.

“If the fire brigade cannot provide a second escape route with ladders, the stairwells must be designed in such a way that they offer a safe escape route in the event of a fire, so that the risk to residents does not increase,” emphasises Torge Malchau, Head of the Braunschweig fire brigade.

Project data

The ALREKO (Alternative Escape Route Concept) project involves Technische Universität Braunschweig, Institute for Building Materials, Solid Construction and Fire Protection (Prof. Dr.-Ing. Jochen Zehfuß), Magdeburg-Stendal University of Applied Sciences (Prof. Dr.-Ing. Björn Kampmeier) and Rottenburg University of Applied Sciences (Prof. Dipl.-Ing. Ludger Dederich). The ALREKO project has received funding totalling 500,000 euros from the Agency for Renewable Resources (the project management agency of the Federal Ministry of Food and Agriculture) and industry.

About the Centre for Fire Research (ZeBra)

The Centre for Fire Research offers ideal conditions for the research team’s investigations in the ALREKO project. With its 12-metre-high facade test rig and large calorimeter for open-air fire tests on electric vehicles, buses and high-voltage storage systems, ZeBra is unique in Europe. Here, fires can be simulated, measured in detail and analysed on a real scale, with a heat release rate of up to 20 megawatts. For comparison, conventional cars release around five megawatts of heat in a fire.