Modern fire protection in underground facilities

In order to ensure the safety of passengers in the event of a fire in an underground facility, special measures are required. The Kölner Verkehrs-Betriebe AG (KVB) and the Studiengesellschaft für Tunnel und Verkehranlagen GmbH (STUVAtec) have demonstrated in close and constructive cooperation at the Nord-Süd Stadtbahn in Cologne how modern fire protection can look like in such plants.

Possible fires in tunnels, subway stations and underground facilities are a challenge for fire safety experts. Because in the underground, special conditions prevail: Fire and fire gases tend to move upwards in the direction of the thermal system, exactly in the direction in which endangered people must escape.

50 years of experience in consulting and research
The requirements for fire protection in underground and light rail tunnels are fundamentally defined in the tram construction and operating regulations (BOStrab) and their associated technical rules. Decisive, however, is the adaptation to the respective building situation. Here, the experts of STUVAtec in Cologne have in-depth knowledge from almost 50 years of experience in consulting and research on questions of fire protection in underground facilities. Together with the KVB executives, they also implemented extensive fire protection measures for passengers during the construction of the new Nord-Süd Stadtbahn in Cologne, while at the same time creating the best possible conditions for the use of rescue services at stops and track tunnels.

Intensive dialogue with building owner and building planner
The work of STUVAtec usually begins with an evacuation calculation and a fire simulation for the relevant underground facility. The evacuation calculation results in the time span until all persons have reached the open air. The fire simulation determines the duration within which the breathing air in the stop is used up and a safe stay for persons is no longer guaranteed. This calculation is done by a mathematical-numerical computer simulation (CFD simulation, Computational Fluid Dynamics) based on the present stop designs. From the juxtaposition of these two determined periods, it becomes clear whether the users within the self-rescue phase can reach a - at least temporarily - safe area and subsequently the open air. If the simulations show that this is not possible, it must be considered which structural or plant engineering measures can be implemented in order to achieve the specified protection goals. At this point STUVAtec enters into an intensive dialogue with the client and the building designer. It is worked out constructively, which possibilities are conceivable under the concrete circumstances and which of them can be integrated architecturally. In the North-South light rail Cologne, for example, it was desired in the further planning process to reduce the number of extendable smoke curtains provided in the course of the planning approval, since these require a high level of maintenance and are thus cost-intensive. This reduction was compensated on the one hand by fire-resistant glazing of the staircases (Fig. 1) and on the other by the use of solid smoke aprons.

Extendible smoke curtains, which are installed concealed and only move to their designated position in case of fire, usually require lateral guide rails to minimize the construction-related leakage areas. Since the arrangement of pillars with integrated guide rails was not possible in all places, a solution had to be found, to form the gap of two abutting smoke curtains as small as possible. This was achieved in close cooperation with the manufacturer by optimizing the smoke hoods in order to be able to guide the smoke curtain cloths close enough (Figure 2). In addition, with a newly developed hinge for this purpose a connection of adjacent ballast rails was made possible. This hinge allows for a slight movement of the two connected smoke curtains in the vertical and horizontal directions to compensate for possible asynchronisms during extension. At the same time it prevents the adjacent smoke curtains from diverge.

Engineering and economical solution in view

With the publication of the Technical Rules for Fire Protection in Underground Facilities (TRStrab BS) in June 2014, the creation of a fire protection concept and the fire protection upgrade is also mandatory for existing systems. This task is more demanding than with new construction, because the retrofit has to work with the boundary conditions of the existing system. In this case the STUVAtec will also start with an evacuation calculation and a fire simulation first. If the defined protection goals are not achieved, the STUVAtec first examines the possibilities that can be implemented with relatively simple means. Only if these are insufficient it will be necessary to implement more extensive measures with interventions in the bodyshell. On the one hand, an attempt can be made to maintain the low-smoke layer for a longer time. This happens, for example, through the installation of additional smoke curtains or the enclosure of staircases with fire-resistant glazing and fire doors. On the other hand, a shortening of the evacuation time can make sense by allowing people to flee faster. This can be achieved for example by improving the signage. The STUVAtec always has an engineering and economic solution in mind for the operator. However, the prerequisite is always the fulfillment of the overall safety level and the approval of the Technical Supervisory Authority. Corresponding holistic fire protection concepts for new and existing light rail stops as well as safety concepts for the associated track tunnels were also developed by STUVAtec for the projects "Combi solution Karlsruhe", "Wehrhahn line Düsseldorf" and "Mobility hub Augsburg". In addition, STUVAtec, certified by Deutsche Bahn, has developed fire protection concepts for the 2nd S-Bahn trunk line Munich and Stuttgart 21 as well as many other DB facilities.