SMOKE MANAGEMENT

In case of fire, the station system needs to ventilate the smoke from the incident area. One common method to enable evacuation during fire is to keep the smoke above a certain height. The zone above the agreed nominal smoke clear height, will be the smoke zone, where the collected smoke will be ventilated by dedicated fans. The passengers can escape in safety. Ref Sketch above.

Signages are a very important during emergency evacuation. Particularly during fire and smoke, the agreed smoke clear height needs to ensure that this height allows for the installation of the vital exit and directional signages.

The other method is to purge the whole area of smoke. Similar in concept to ventilating smell from toilet. Where fans will change the whole volume of air in certain zones, to the required numbers of times. The Singapore MRT requires 9 air changes per hour to enable such large volume as below to be safe for evacuation during fire.

This system would work well in large double height areas, etc.

In the most complex underground system, such as the Hong Kong MTR, the following systems will be required  (Other system will have less, or different systems).

1. Tunnel Ventilation Fans: These Tunnel Ventilation Fans (TVF) will be housed in the station box, or in Plant Buildings, between tunnels. This plant room suits will require control rooms, vent shafts. high power, etc. ultimately adding complexity to station design, requiring considerable versatility for station planners to optimise this requirements and enabling an efficient station box design. 

2. Trackside Ventilation Fans. The trackside that is enclosed within the station box will need to be smoke vented. These fans work in push and pull mode, called Trackside Supply Vent Fans (TSVS) or Trackside Exhaust Vent Fans (TEVS). Some systems may only have exhaust fans and the supply air is vented from the tunnels. The complexity of these plant rooms are akin to the TVF system, designing these together will be beneficial to the station planning. cost and maintenance.

3. Station Smoke Vent System: Smoke in the station public areas will need to be vented. These are managed either via using dedicated smoke vent fans or perhaps even the station AHU system.

For Station Planners, it is highly recommended to understand the schematics of the all these system, then design the associated spaces.  

Spaces and volumes in station are large, it would be impractical for the MEP ventilation fans and systems to vent all areas. Hence spaces need to be divided into smaller chunk of spaces/volume, which are then made tenable for evacuation in case of fire by smoke extractions fans.