TRACKSIDE FIRE SAFETY

Trackside fire safety is outside the remit of this paper. However some basic fundamentals will be discussed here, to outline the key assumptions. Station planners need to know these requirements to reflect them in the design of their mass transit systems

Trackside fire and life safety is to enable a tenable condition in the trackside, to enable the passengers to then either evacuate via the walkway to a safe place, or the train will take the passengers to the station, where they can then detrain to safety. The discussion below relates to underground station, whilst at grade or elevated systems have a simpler needs.

Fig. Latest NFPA 130 2023 version. Only hardcopy available

The trackside life safety and security will have its own strategy, one that needs to be a line wide document, if not a system wide document. Mostly trackside fire safety will be based on the NFPA 130:

Section 6 for the trainways requirements, such as materials, fire ratings, etc.
Section 7 will discuss the smoke extraction / vent requirements.
Sketch on right shows dimension for the evacuation walkway

Fig. Trackside egress passage requirement

Sketch showing potential train sets between stations spaced apart 1 KM

The above shows trackside between two stations, that is 1km apart. As you can see, the track can easily house three car sets that is nominally 200m long (Say 8 - 9 cars). However, no system will be so rich that they may have that many trainsets in the tracks between these theoretical two stations, or even is possible, the logistic of the life safety and smoke management + the best 2minute headway, will not allow this to happen. Which brings us to the next sketches below.

Further NFPA 130, Section 6.3.1.4 does not allow the trackside to be more than 762m between egress points. Which implies that many sites will require cross passages between stations, or if in longer tunnels, both cross passages and ancillary buildings, which will house ventilation plants, intervention shafts for the first responders, evacuation point for passengers, etc.

TUNNEL SMOKE ZONES

Normal Operational Scenario

The tunnels can be considered as an underground trapped space, where train moves at suitably great speed and mass. Hence when these trains drive within the tunnel, the engine compartment will push the air in front, and the volume of air will compress and have no place to go, making the progress of the train more energy inefficient. This is mitigated by allowing tunnel vent ducts between the ends of the station to the ambient, now the piston effect of the trains pushes and pulls the air out of the tunnel to the ambient, creating a tenable condition mechanically for the trains.

Emergency, train on fire scenario.

If the train should catch fire, the rolling stock will drive to the station to disembark the train. However, if the train is also crippled, then a tenable condition needs to be created, a suppression and smoke extraction system is deployed. The suppression system is using the trackside water hydrant system. The smoke management will be as per the sketch above right.

Depending on the exact location of the crippled train, the furthest Tunnel Vents Fans (TVF) will be activated. This station TVF will suck the smoke away from the passengers, who will now escape to the nearest station platform. Hence this TVF system will allow a safe evacuation of the smoke in the tunnel.

SMOKE MANAGEMENT SYSTEMS

Image left. Tunnel Vent Fans

Which can be anywhere from 12m to 18 meters long and usually in pairs or more

Photo shows fan in the center (Centrifugal fan), with silencer/dampers to the two side, connected with metal transitional housing, sized to ensure no velocity loss.

These ducts will require huge ventilation louvers on the ground, the size will be governed by the size of the tunnel and other parameters. However, they may be closed to 4 times the duct size

Some of the key aspects that is important for station planners, resulting from the trackside requirements in stations are as follows:

Trackside ventilation plants. They will either be housed in stations, or plant buildings need to be designed for this.
Ducts & ventilations towers at ground level needs to be provided
Integration of walkway, services from the trackside needs to be integrated into the station box, etc.

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