Fathi tarada, managing director of tunnel and fire safety consultant Mosen, says the provision of combustion-resistant rolling stock, and that can be easily evacuated, is crucial in metros. He highlights the recently published EU standard EN 45545 to specify engines and carriages.

Tarada notes, though, that it will take time to shift all rolling stock over to higher standard fleets, which therefore presents some ongoing risk – despite underground railway tunnels and stations being, he says – "without any doubt, generally safe."

Karl Fridolf, a fire safety researcher with SP Technical Research Institute of Sweden, says the self-rescue principle "is essential" when discussing evacuation of underground transportation systems.

The key to the metro design would then be to enable passengers, in an emergency, to "evacuate to a safe place" with the technical installations of the subway system providing them sufficient help to do so. No waiting for the arrival of emergency services personnel; instead, the design – the designer – must show how successful evacuation can be achieved under different scenarios.

Fridolf says there are many different technical installations related to life safety, and their choice and use differs between projects. Systems can include emergency exits (including those in tunnels), exit signage, fire alarms, smoke extraction systems, and sprinklers.

WATER

Armin Feltmann, sales engineer on tunnel systems with water-based fire safety systems manufacturer Fogtec, says fire loads have changed in recent years which consequently demands improved fire safety measures in metro stations.

Feltmann says there are, basically, two protection concepts in approaching fire safety in metros and these focus on the rolling stock and the infrastructure, respectively.

With respect to infrastructure, fixed fire safety system (FFFS) can protect station structures. The FFFS is based on high pressure watermist technology, with nozzles and pipework installed above the railtracks. The watermist is designed to minimise the effects of the fire, suppressing it through fast activation (by using clean water, rapid release is possible without danger or delay), reducing heat radiation, and cooling the gases and smoke which reduces their volume, thereby also cutting down the load on the ventilation system.

The combination of benefits of the suppression system, which chokes off the fire and helps contain the area being affected, helps passengers evacuate and fire fighters gain critical access – nearer to the source of the incident, and sooner. The containment also minimises the damage to the station infrastructure, and therefore downtime for repairs – "even in the case of severe fires," says Feltmann.

Fogtec"s technology is also a key component of the FFFS system that helps to manage fire safety in one of the world"s longest underground rail links – the Channel Tunnel. Like on that giant transport scheme, watermist systems can be retro-fitted in urban transit networks like underground metros – "especially when there is only little space available," says Feltmann.

Although retro-fitting in any engineering context may present its own challenges, the possibility to introduce the watermist system, for example, could offer potential cost savings compared to other approaches, he suggests. Key factors in the possibility to do so come from infrastructure protection and less ventilation capacity being needed, says Feltmann. Recent implementation of the watermist system in Budapest saw metro operator BKV retro-fit the system into nine stations of its M2 line. BKV introduce the system from the outset in the design of 10 stations on the M4 line. In addition the to main platform areas in stations, key sections to be protected by watermist systems include escalators, cable tunnels, and the control and inspection room.

SYSTEMS

Draeger takes a broad, integrated systems-based approach to safety management in tunnelling projects, including provision for dangers of toxic gases and fire safety – during both construction and operational phases of an infrastructure scheme, such as a metro.

During the construction phase, a variety of equipment can be in place to help safety, such as refuge chambers, medical equipment, fire trucks and ambulance trains. For this phase, and operations, there can be monitors (including access to tunnels) and various detectors (gas, smoke, infrared). Refuge chambers are being adapted from the mining sector to play an increasing role in many types of tunneling projects, and would help in a variety of risk scenarios. Manufacturer MineARC Systems has seen its refuge chambers used as part of safety solutions on metro projects in Kuala Lumpur and Doha. Other manufacturers include Strata Worldwide. MineARC notes it is possible to incorporate refuge chambers into transportable standby safety systems during the operational life of tunnel projects.

Testing, Testing

Use of the assets needs to be coordinated with effective operational rules – eg a trains on fire should not stop but continue, at a pre-determined control speed, to the closest station to evacuate its passengers.

But when testing people in a smokefilled space, as could be experienced by passengers in a tunnel or possibly having been delivered to a station platform, the emergency criteria must take-in further aspects, including, and not least: safety is in the eye of the beholder.

If people are thrown into a situation, what might they think they see? The mind tries to make sense of the world through patterns, and in split seconds what might be constructed in the mind, and believed, may well be acted upon.

Fridolf tells of a test where some people moved sharply away from an exit fitted out, from the design concept, to have green and white halogen spotlights. Why? In debriefings, the people – only aware they were in a smoke-filled tunnel – said they thought the lights were on the front of a train. Not a door leading to safety