With rail tunnel development booming worldwide, fire protection and safety measures have come to the fore once again. With key technologies such as reaction-to-fire properties of rolling stock, fixed fire suppression systems, improved fire detection systems including video-based automatic incident detection systems and the automatic deployment of pre-set emergency plans, the industry tries to minimise the danger of tunnel fires.
The importance of understanding all aspects of tunnel fire safety from structural design to acceptable risk, national and regional safety standards and key technologies, will be discussed at Arena International’s third annual Fire Protection and Safety in Tunnels event, taking place in Salzburg, Austria, on 11 and 12 October 2011.
Ahead of the event, railway-technology.com speaks to UK-based fire safety engineering company Mosen managing director Fathi Tarada about the best approaches to tunnel fire safety, including fire suppression and heat release, the need for a set of global standards and the importance of control and management measures on rolling stock and its payloads.
Elisabeth Fischer: Why are fires inside train tunnels so dangerous?
Fathi Tarada: Rail tunnels generally have a smaller cross-section compared to road tunnels, so there is less chance that the smoke from a train fire can stratify above escaping passengers. This means tenability conditions for evacuees can be quite poor.
The smaller cross-section can also lead to a more rapid spread of fire, through radiative feedback and stronger convective heating. There is simply less time for people to escape to safety.
Rail tunnels do not generally have many escape routes, with exits generally being designed at about 1km centres. Many older rail tunnels do not have any exits at all, apart from the portals. Such legacy tunnels may also not be furnished with a walkway, so passengers may have to walk along the track, which could be ballasted or even electrified.
All these factors can make fires within rail tunnels very dangerous indeed. On the other hand, passenger trains are now built to high standards of fire protection, with very limited combustibility. The 7/7 bombings in London highlighted the fact that the underground trains did not burn after detonation of an explosive device, but merely smouldered. The real danger is with freight trains and trains carrying dangerous goods, where the combustible load can be very high.
EF: How important is fire prevention within the overall safety mix?
FT: The prevention of fire is probably the single most important safety measure for tunnels, hence it is of utmost importance in the overall safety mix. Regular fire risk assessments are required, and may have saved for instance the 155 people who perished in the Kaprun funicular rail fire in 2000.
It is a sad fact there are many unknown risk factors such as arson or terrorism, which can lead to significant damage and loss of life. The Daegu subway fire in Korea, which killed 198 people, was started by an arsonist, but the spread of fire was facilitated by the combustible materials in the two affected Metro trains.
The railway safety management systems must be robust enough to account for reasonably foreseeable risks. In particular, they should reduce the likelihood of any fires occurring in the first place, to mitigate the consequences should a fire break out, and ensure rapid recovery of rail services after any incident.
EF: What is the best way to prevent fires in tunnels?
FT: The best way to prevent fires is to control the type of combustible material permitted into a tunnel in the first place. A lot of very good work has been undertaken in improving the fire resistance specifications in rolling stock.
However, this does not address the real danger of fires on goods trains or heavy goods vehicle shuttles, where the amount of permitted combustible material is uncontrolled. We only have to recall the Channel Tunnel fires of 1996, 2006 and 2008 to highlight this danger.
Clearly, there are many mitigation measures that can be employed to reduce the risk of a fire spreading within a train, including fire compartmentation and fire suppression. However, in order to prevent fires occurring in the first place, greater emphasis has to be put on effective control and management measures on the rolling stock and its payloads.
This means that rail and haulage operators must also play their part in ensuring their equipment is well maintained, regularly inspected and fully operational.
EF: How important is fire safety awareness within the workforce to decrease risk levels within a tunnel?
FT: Regular training of railway operators in fire safety is essential, and should not be considered in a perfunctory manner. This should include routine training on the use of fire extinguishers for example, and also more complex matters, like when and how to evacuate passengers in a rail tunnel. Fire drills and exercises can be very useful ways to check the outcome of the training, and also to test fire procedures and communication channels with the fire brigade.
EF: What is the best approach towards ensuring viability and reliability of tunnel protection systems to guarantee optimal safety?
FT: Ideally, all three components of fire safety in tunnels, the infrastructure, rolling stock and railway operations would be designed, managed and operated together in a way to ensure the viability and reliability of the tunnel protection systems.
In reality, these components are usually the responsibility of different parties. In some cases this diffusion of responsibilities can cause lacunae to appear in the management of fire risks. It is thus the ultimate responsibility of the railway authorities to ensure all stakeholders in the railway industries take their duties seriously, and make the necessary long-term investments in safety.
EF: Heat release is often said to be the key of keeping fires under control. What is the correct rate for rail tunnels?
FT: There have been a number of research projects to determine heat release rates of fires in rail tunnels, and such research efforts are still underway, for example, through METRO, a three-year Swedish research project relating to infrastructure protection.
Thankfully, fire heat release rates from passenger trains have reduced significantly over the years, due to improved rolling stock specifications. It is difficult to give precise values, but in my experience, typical design values for metro car fires have dropped from 15MW a decade ago to about 7MW today. It is arguable that further reductions could be reasonably justified – based on the deployment of fire suppression systems, for example.
EF: How do fire suppression systems fit into other fire protection systems?
FT: Fire suppression systems are only one part of the answer, never the whole solution to the mitigation of fire risk. Where they are specified, based on a risk assessment and a cost and benefit analysis, it is important that they are backed up by a robust fire detection system, and as part of an emergency plan are clearly understood and implemented by the railway operator.
Ventilation systems may have to be matched to the fire suppression system, based on a holistic strategy for smoke control, fire-fighting and evacuation. Having said all that, I do believe fire suppression systems can have a very useful part to play in reducing the risk that small fires can grow into dangerous and uncontrolled conflagrations.
EF: How important is it to set global standards of fire safety in tunnels?
FT: Sadly, there are currently no global standards for fire safety in tunnels, but there are a number of national and regional standards. NFPA 130 is highly influential in English-speaking countries, but does not deal with all the issues relevant to fire safety in tunnels.
The EU’s technical standard for interoperability on ‘Safety in Railway Tunnels’ has a much broader remit, but is best understood as a framework standard, rather than a specification.
Efforts are underway to identify suitable regulations and best practices through the International Tunnelling Association’s Committee on Operational Safety of Underground Facilities, and research efforts are on-going on specific issues related to rail tunnel fire safety.
It would certainly be of benefit to the industry and to the safety of worldwide travelling public to harmonised global standards for fire safety in tunnels, since the costs of compliance could thus be driven down, while ensuring a high level of protection. We will have to wait and see whether this actually happens in the future.
The Fire Protection and Safety in Tunnels event will take place in Salzburg, Austria, on 11-12 October 2011.