Metro rail: A passage to safety

C Shivakumar

Chennai:

As the work on underground passage for metro rail is gaining pace, Chennai Metro Rail is ensuring that the safety of passengers are given a priority as it is constructing cross passage between the two tunnels to help the commuters escape in case of any eventuality.

Chennai Metro Rail General Manager (construction) V Somasundaram told Express that the tunneling works are being done while keeping the safety of commuters in the underground stretch.

Interestingly the world has witnessed several tunnel fires such as the Mont Blanc tunnel in 1999 and the Swiss St Gotthard tunnel in 2001. These have raised concerns about fire safety in tunnels globally resulting in many countries adopting codes for exit routes in tunnels, including a minimum distance between points of escape to the ground surface. If a project includes two parallel tunnels, cross passages linking both tunnels can be provided. In case of any eventuality, the commuters can escape through the cross passage and walk to the next station.

International experts feel these cross passages must be guaranteed free of smoke in order to provide a visual indication of safe evacuation paths to escaping passengers, to protect passengers while they are traversing the cross-passages, and to ensure that the non-incident tunnel is kept clear of smoke.

Somasundaram said metro rail is building a cross passage every 250 metres. He also says the distance between both the stations are 1.5 km and in case of eventuality, a commuter has to walk not more than 700 metres.

In the United States, the main standard that gives guidance on

the requirements for spacing of cross passages in railway tunnels is around 750 metres. For twin bore tunnels, cross passages may be used in lieu of emergency exit stairways to the surface and shall not be farther than 244 metres apart. The cross passages should be protected with fire door assemblies having a fire protection rating of 1-1/2 hours with a self-closing fire door.

In the United Kingdom, the distance between cross passages should not exceed 100 m while in Germany, the corresponding distance between emergency exits must not be greater than 300 meters on an average. In France the maximum distance between two stations or fire brigade access points is 400 metre.