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Well Protected Under the Mountain

In order to achieve the highest level of safety in a tunnel, potential dangers need to be identified as early as possible. Integrated technical solutions assist in this process: Video and radar systems combined with fire protection and evacuation systems guarantee the seamless detection of incidents and a rapid reaction. A leading example of a well-protected tunnel is the recently opened Gotthard Base Tunnel in the Alpes.

FeuerTRUTZ International: Well Protected Under the Mountain
Fig. 1: The safety technology in the Gotthard Base Tunnel includes an integrated fire detection system with thermal imaging cameras, smoke detectors and a heat detection system. (Photo: Siemens)

By Jürgen Poslovski. The tunnels in Europe are becoming safer. At a European level, lessons have been learnt from sometimes serious fires in the past and statutory regulations for tunnel safety have been significantly tightened. For this reason, the EU Tunnel Directive was approved by the EU Commission in 2004. It defines the minimum safety requirements for tunnels in the Trans-European road network. In Germany, these regulations were implemented in the Guidelines for the equipping and operation of road tunnels (RABT) that was amended in 2006.
The EU Tunnel Directive requires electricity, measurement and control circuits to be designed so that in the event of a partial failure, e.g. due to a fire, other undamaged parts of the system are left unimpaired. In addition, the level of fire resistance for the operating facilities in the tunnel must be suitable for maintaining their required safety functions in the event of a fire.

The Gotthard Base Tunnel

  • Length of tunnel: 57.1 km
  • Electrical system: 15 kV, 16.7 Hz
  • Top speed: 250 km/h
  • Trains/day: 200 to 260 freight trains, 65 passenger trains
  • Transport capacity (freight trains): 40 million tonnes/year
  • Vehicle speed: Freight trains: 100 to 160 km/h, passenger trains: 200 to 250 km/h
  • Total mass of rock excavated: 28.2 million tonnes
  • Construction cost (status June 2010): 12 billion CHF

Always stay in the picture with video technology

The greatest danger for persons and infrastructure in a tunnel is a fire. It is only rarely that malfunctions in the technical infrastructure are responsible for a fire; vehicles are almost always the cause of tunnel fires. A small engine fire with smoke can develop into an open fire within a few minutes. If fuel has also escaped, there are possibly only seconds until it develops into a full-scale fire resulting in extreme temperatures and the release of poisonous smoke gases.
In order to identify any potential danger as quickly as possible, modern video systems provide an ideal solution. They enable the seamless detection of incidents and make it possible e.g. to identify the development of smoke in a tunnel fire. These systems reveal their full potential in combination with up-to-date fire protection and evacuation systems.

Automatic fire detection systems speed up alarm management

Speed is of the essence in the event of a fire. Where is the source of the fire? How big is the fire? In what direction is it moving? These questions need to be answered immediately. It is only then possible to initiate the right rescue measures. This means that an automatic fire detection system for tunnels must be capable of precisely localising the source of the fire and automatically allocating an alarm zone. Air flows must not be able to adversely impact the detection results in this process. Furthermore, it is necessary for the system to also identify the direction in which the fire is spreading.
If the system detects a fire, the security centre must respond as quickly as possible. The entire alarm management system depends on correct and quick detection by the fire detection system. In the event of a confirmed alarm, the tunnel extinguishing system needs to be triggered, automatic traffic management steps initiated, the tunnel ventilation system controlled according to the source of the fire and the evacuation of people in the tunnel managed via voice alarms. At the same time, the fire service and other intervention forces must be alerted. The information provided by the automatic fire detection system will then enable the emergency services to rapidly initiate a tactical plan and clearly identify the direction of attack.

Video and radar monitoring systems are combined in the Gotthard Base Tunnel

FeuerTRUTZ International: Well Protected Under the Mountain
Fig. 2: Thousands of kilometres of fibreglass cables ensure fast data transmission between the safety systems in the Gotthard Base Tunnel. (Photo: Siemens)

The Gotthard Base Tunnel was planned in Switzerland due to the high volume of traffic in the Alps. It opened on 1 June 2016 after a 17 year construction period. It is to date the longest rail tunnel in the world at a distance of more than 57 km. Following a test phase, regular scheduled services will start from December 2016. After final commissioning of the tunnel, up to 260 freight trains and 65 passenger trains will use the route on a daily basis – at up to 250 km/h for the high-speed trains (see infobox).
At the heart of the safety measures in the Gotthard Base Tunnel lie fire protection and fire management. Therefore, the operators decided to install an integrated fire detection system. The crucial factor is that the entire tunnel from the entrance to the exit can be monitored. This requires systems that can deliver reliable information about the situation in the tunnel and in front of the tunnel portal that goes above and beyond video monitoring. For this purpose, video monitoring technology was combined with radar technology. The best systems of this type use algorithms that can independently identify potential sources of disruption. This reduces the burden on the surveillance staff and automates the identification of incidents.
Experience has shown that people can make mistakes when monitoring surveillance systems. In contrast, Automated Incident Detection (AID), which is used by video and radar systems, is capable of automatically detecting a wide variety of incidents that could lead to serious consequences in a tunnel – such as the development of smoke. Using intelligent zoning and virtual barriers, an alarm can be automatically triggered if the camera or radar detects one or more incidents. Immediate intervention prevents any escalation of the incident.
Part of this safety infrastructure in the Gotthard Base Tunnel is the heat detection system FibroLaser from Siemens (see figure 1). It enables control of the fire alarms and ventilators, the localisation of hotspots for activating the extinguishing system, an adequate response time for critical situations (prealarm) and a quick alert with corresponding control in the event of fire (alarm). The precise localisation of the source of the fire is possible down to a resolution of half a metre.

Redundant protection and safety systems

FeuerTRUTZ International: Well Protected Under the Mountain
Fig. 3: A smoke detector protected by a cage (Photo: Siemens)

International railway guidelines only prescribe the installation of an automatic incident detection or fire detection system for stations and emergency stations in railway tunnels. Trains need to have an independent fire detection system. However, studies have shown that a holistic protection and safety approach along the whole length of the tunnel delivers better results.
In the Gotthard Base Tunnel, both tunnel tubes are connected every 300 m by cross passages so that the train passengers can flee into the other tunnel tube in the event of a fire. If a serious incident occurs, the evacuation of up to 1,000 people is possible at the two 600 m long emergency stations in each tunnel tube. In order to ensure this doesn’t need to happen in the first place, the entire tunnel system is fitted with very many sensors, monitoring equipment and control devices that are connected to the two control centres at the north and south portals via thousands of kilometres of fibreglass cables. The monitoring data is checked by the control centre within a few milliseconds.
At the four emergency stations, the fire can be localised using three different detection systems. The tunnel tubes have also been fitted with redundant fire detection systems: A FibroLaser cable is not only fitted to the ceiling but also to the floor because a locked wheel on the train or leaking liquids could, for example, also catch fire. Specially reinforced cable was required for laying on the floor to protect it against water spray and mechanical stresses (see figure 2). The cable for the ceiling could not contain metal to ensure there was no electromagnetic interference between it and the 15 kV overhead power lines.
The heat detection system was supplemented by thermal imaging cameras and smoke detectors, which constantly check the temperature and air for smoke particles. In order to protect this equipment against the harsh conditions in the tunnel, it was packaged in cages (see figure 3) – these were also specially produced for the Gotthard Base Tunnel, where the safety systems have to fulfil the highest requirements for fail-safe operation. Everything is designed for trains that can travel at 270 km/h; although the stipulated top speed is 250 km/h. The engineers have thus planned with some room to spare.

FeuerTRUTZ International: Well Protected Under the Mountain
Fig. 4: Despite the latest safety technology: A little assistance from above cannot hurt even deep under the mountain. Saint Barbara is the patron saint of miners. Her statue has a prominent position in an alcove of the Gotthard Base Tunnel. (Photo: Siemens)

Data as a safety resource

Data mining has taken on ever greater significance in recent times and it can also be employed to further increase the safety in tunnels. The digital collection, linking and evaluation of data helps to check the appropriateness of safety measures and systems and supports the reliable and optimal flow of traffic. The safety of tunnels and ensuring they are continuously available can be further improved through data mining.

Summary

One of the priorities in the operation of tunnels is preventing fires. Maintaining a high level of safety is thus at the forefront of operational procedures. Using an integrated approach in which all potential incidents are monitored and alarms automatically raised, it is possible to intervene as early as possible and prevent the fire and smoke from spreading. In addition, it ensures an effective and coordinated response in the event of a major incident.

Other tunnel projects

The protection and safety systems in ­tunnels are now highly developed thanks to the pooling of a diverse range of the ­latest technical solutions. It is thus no ­coincidence that planners are tackling ­increasingly ambitious projects. Other ­tunnels setting new world records are on the way:

  • The Brenner Base Tunnel that is currently under construction is set to be the longest railway tunnel in the world at 64 km when complete.
  • The planned Fehmarnbelt Tunnel between the German Baltic island of Fehmarn and the Danish island of Lolland at a length of almost 18 km will be the longest immersed tunnel in the world for combined rail and road traffic.

Author

Jürgen Poslovski: State Certified Technician specialising in electrical engineering, with a focus on data electronics; employed by Siemens as a Senior Sales Consultant for Solution Safety & Security and responsible for tunnel fire detection systems at the Siemens Competence Centre for Tunnels in the Germany South Team

The article was published in FeuerTRUTZ International, issue 1.2017 (January 2017).
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