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World’s fourth longest rail tunnel gets gas protection

24 December 2008

Protection from gas hazards in one of the world's longest rail tunnels is being provided by monitoring systems from Crowcon Detection Instruments. The Crowcon systems are designed to detect potentially flammable and toxic gases before they reach hazardous levels.

Two Crowcon Xgard detectors on tunnel wall
Two Crowcon Xgard detectors on tunnel wall

The 28km long Guadarrama Tunnel in Spain, the fourth longest rail tunnel in the world, and the 8.5km San Pedro Tunnel – Spain’s longest – together form part of the recently-opened Madrid-Valladolid high speed rail link. The Guadarrama Tunnel comprises two parallel tunnels connected by cross-passages every 250 metres, as well as a 500 metre-long emergency room, located equidistant from both tunnel entrances. The San Pedro Tunnel, which also comprises parallel tunnels, is connected by cross passages every 400 metres.

Crowcon was chosen by Telefonica Ingenieria de Seguridad from a number of competitors as part of the detailed engineering project. Telefonica Ingenieria de Seguridad was responsible for the entire development of the project, including the design, implementation, integration and maintenance of all the control, safety and security projects for the tunnels.

Over 500 Crowcon detectors are installed throughout the tunnels. Carbon monoxide (CO), nitrous dioxide (NO2) and oxygen (O2) levels are measured by intrinsically safe Xgard detectors (validated to IEC61508 SIL2/3), while methane (CH4) levels are detected using Crowcon's flameproof (Exd) infra-red Nimbus units. Signals from all these detectors are processed by over 70 Vortex rack-mounted controllers, which are connected to PLCs via RS485 and provide operators with all gas readings and alarm/fault information.
If any of the detectors register dangerous levels of any of the gases, ventilation and exhaust systems are automatically triggered by the Vortex control panels, which also pinpoint which detector is in alarm mode and immediately transmit this information via PLC to a Scada system which transmits the information to control rooms in Madrid and Segovia.

Internal combustion engines emit exhaust fumes that contain significant quantities of CO and NO2 (both highly toxic). If a tunnel is inadequately ventilated, these gases can accumulate to concentrations that can become hazardous to human health. Oxygen depletion is also a risk in tunnels and confined spaces where a fresh-air supply may be limited. In the absence of adequate ventilation the level of oxygen can be reduced surprisingly quickly by breathing or combustion processes. Oxygen levels may also be depleted due to dilution by other gases such as carbon dioxide, nitrogen, argon or helium, and chemical absorption by corrosion processes and similar reactions.

Under EU regulations fire and gas safety systems are obligatory in tunnels over 500m in length. The legislation has been driven by a number of high profile disasters, such as the Mont Blanc car tunnel fire in 1999 in which 30 people died.

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