The notion of a train carriage that is packed to capacity catching fire is the subject of any commuter's worst nightmares. The idea of such a disaster happening deep underground is beyond terrifying.
To protect passengers, rolling stock and rail infrastructure against the threat of fire, rail engineers face a difficult task. Fire within an enclosed space can quickly become out of control and the damage caused by smoke can be as devastating as the heat itself. Preparing against this involves extreme scenario planning and the delicate balancing of a fully integrated solution.
The construction of an entirely new rail network, however, gives engineers the opportunity for innovation and careful planning. The long-awaited London Crossrail project set for 2017 provides just such an opportunity and also a plethora of unique challenges. To discuss the intricacies the new UK mega project presents, rail experts from around the globe met in March 2009 at the ViB Fire Protection of Rolling Stock conference held in London.
Government approval for the £16bn London Crossrail project – Europe's biggest civil engineering project – was announced in December 2008 as a bold move to reduce congestion in the capital, boost economic growth and revitalise deprived areas.
The line is scheduled to begin running in 2017 and will stretch from Maidenhead and Heathrow in the west out to Shenfield and Abbey Wood in the east. Trains will run over 90km of existing rail and 21km of new sub-surface twin-bore rail tunnels.
The project also involves the construction of eight new sub-surface stations and the upgrading of 28 existing surface stations.
The challenge of fire safety on Crossrail
The threat to human life in the event of a fire outbreak is evident when you consider the sheer number of passengers travelling on the rail network. Crossrail is expected to see an estimated 200 million commuters traversing London each year. When complete, 24 brand new trains will carry around 1,500 passengers in either direction through the city centre during peak times each day.
Speaking at the ViB Fire Protection of Rolling Stock Conference, Crossrail systems and rolling stock manager Michael Kilby said that it was necessary to think of fire safety in terms of life safety. "The major challenge in protecting lives on Crossrail is to achieve an integrated solution catered to this high-density metro, which also has the challenge of meeting with up with miles of existing rail infrastructure," he said.
Life-threatening train fires due to purely technical problems are rare, especially on electric trains. The biggest risk to human life when this does occur is caused by panic and secondary incidents. A fuel tank breakaway on a 1995 train in Maidenhead caused major panic and the death of one man who jumped from the train.
What some might consider to be a bigger threat, especially after the series of coordinated attacks on London's transport network on and after July 2005, is terrorism. In addition, anti-social behaviour and negligence keep fire engineers awake at night.
The design philosophy behind protecting passengers on Crossrail is to avoid an incident train being stranded in the tunnels. As well as being engineered to be fire resistant, trains must be kept moving so that the incident can be managed in the nearest station. The maximum travel time between all stations is three minutes.
Trains will be built using the latest fire-resistant materials, but the design of the project is based on avoiding immobilisation should a fire break out. This involves ensuring running capability by preventing signal point failure, allowing for manual driver override and protection of train bus cabling.
Any outbreak will primarily be managed by the heating, ventilation and air conditioning (HVAC) systems, which can control and restrict the flow of air through the train. London Underground principal fire engineer Martin Weller says managing the spread of smoke is the best way to reduce panic.
"To increase survivability in a small enclosed space we need a HVAC system that can handle smoke flow and maintain ventilation," he says. "Right now we are using modelling to understand flow of smoke."
Train interiors will also be designed to limit the concentration of fire, using no luggage stacks or litter traps. Crossrail is also considering the use of open wide gangways in train carriages as a method of fire-resistant construction and to allow for fast passenger access at stations. Smoke detection systems as well as new optical detection techniques will be used throughout all train carriages.
Fire detection and management: an integrated approach
Weller says that to adequately protect the public an integrated approach must be adopted. "At the end of the day a railway is a machine from getting people from one place to another and this machine includes the rolling stock, stations and tunnels," he explains. "When thinking about fire safety you have to think about it as an integration of systems."
Fire detection and management onboard rolling stock is the first line of defence for fire outbreak management – stations are the next. All Crossrail stations, below and above the surface will be built to stringent fire safety standards, including dedicated escape routes and fire-fighting lifts. High platform doors will allow for quick passenger exits and fire suppression equipment will be in easy reach.
Smoke control in stations will be handled by HVAC systems specifically designed for ventilation and extraction, and will be controlled automatically from a route control centre. Making sure all these elements work together will be key to fighting fire on London's new commuter routes.