One of the UK’s busiest train stations was evacuated recently causing disruption to rail services but fortunately with no injury to the public. In light of this incident we take a brief look at some of the ways the evacuation process can impact on the fire strategy of a busy train station:
- Means of escape – to enhance life safety in transit buildings where there are high occupancy loads and the occupants are unlikely to be familiar with the evacuation procedure, it is essential that there are an adequate number of exits so that should one be impeded by fire, occupants are able to evacuate via the remaining exits. These routes should also be wide enough to allow a high rate of escape (persons per minute). In some cases the route of escape is extended or the final exits are not wide enough, therefore it is necessary to establish how long it would take for the occupants to evacuate the building and review this against the time it would take for the space to become untenable – known as an ASET/RSET Assessment. One of the benefits of transitbuildings is that they generally contain substantial floor to ceiling heights, which allow longer evacuation periods due to the time it takes for the smoke layer to build up.
- Fire alarm and detection system – this needs to be carefully considered when designing the fire strategy as the detection period is the first stage in determining how long the evacuation of occupants will take. To ensure business continuity, imperative for a transport hub such as this, limiting the risk of a false alarm via implementing an investigationperiod is essential. It is also possible to design the system so that if a certain zone is affected, only the occupants within that area need to be evacuated.
- Fire management strategy – as transit buildings are large occupancy environments filled with people who are unlikely to be aware of the building layout, it is essential that station staff are trained to a level to ensure the evacuation process is orderly and efficient. Part of this training may also include the communication between staff to ensure that if evacuation is carried out to one area of the building, occupants within the station will not walk into the affected area.
- Compartmentation – separating the station into a number of zones will limit the area affected by the fire and mean that only the affected compartment would need to be evacuated, thus improving the business continuity of the station and putting less onus on staff as fewer occupants need to be evacuated. The size of the compartment is critical in determining the fire strategy of the building. Simply following the guidance in codes is to look at the provision of sprinklers and / or high levels of compartment walls or expensive fire curtains/ shutters. The alternative is to fire engineer an approach, to look at the different building features and operational needs to minimise high cost systems or look to utilise what is known in the trade as ‘virtual compartments’. In the case of very large transit buildings, the ASET/RSET assessment may demonstrate that the occupants will be able to evacuate the extended compartment safely, however there are other occasions where additional features are required to mitigate the extended compartment sizes, such as smoke venting.
- Smoke venting – depending on the assessment for the means of escape from the building, it may be necessary to provide smoke venting to maintain the smoke layer at a high enough level to allow the occupants to evacuate the building without being affected by the smoke. As transit buildings generally carry out a simultaneous evacuation philosophy of the whole building or the affected compartment, smoke venting is not always necessary but can be a very efficient additional feature to mitigate extended travel distances or extended compartment sizes, the amount required should be determined by looking at the fire size, fire growth and the rate in which it will fill the space.
