Major road tunnel fires are thankfully rare incidents. Rail tunnel fires rarer still. Yet, when they do occur, the cost can be devastating in terms of the high numbers of casualties, substantial repair costs and significant, often nationally felt economic disruption.
The Gotthard Tunnel fire marked an especially low point in tunnel safety. Considered one of the safest in Europe, the Swiss road tunnel, some 17 kilometres in length had many safety features such as a parallel evacuation tunnel and safety cells every 250 metres. The fire that occurred in October 2001 involved the collision of two trucks just one-and-a-half kilometres from the south entrance.
The crash resulted in an inferno that reached 1,200°C, fusing some 40 vehicles into a molten mass. Thick smoke reduced visibility, hampered breathing and made escape difficult – all but one of the fatalities was a result of the smoke, not the flames. 11 people lost their lives and the economic disruption between northern Europe and Italy was severe. The tunnel had carried 1.2 million lorries and millions of motorists a year. It was the third Alpine road tunnel, in less than three years, to be closed after a major fire.
In May 1999 the Tauern Tunnel fire in Austria claimed 12 lives and closed for three months of repairs. The fire in the Mont Blanc Tunnel, which links France and Italy, burned for 53 hours and was more devastating: 39 people died, the tunnel was closed for repairs for three years while 380 million Euros were invested in repairs and improved safety measures. Repercussions also included €13.5 million (US $17.5 million) in compensation paid by the Italian tunnel operator and a custodial sentence for its head of tunnel security.
There was also the Kaprun rail tunnel fire in Austria in 2000 that claimed the lives of 155 people in a matter of a few minutes – there were only 12 survivors.
While tunnel fire safety has undoubtedly improved, often as a direct result of such catastrophes, many countries have neglected to improve safety. Moreover, the danger posed from tunnel fires can never be eliminated. Continual review and improvement, shed of complacency, is essential.
Specific Dangers of Tunnel Fires
Fires in tunnels present particular dangers, more so than many open air environments.
Firstly, there are the high heat release (HHR) rates. Vehicles release heat far more vigorously in confined spaces than open areas. The HHR is four times as powerful in tunnels as open areas. Tunnel tests show that a car fire can produce 2.5 MW to 5 MW, heavy goods vehicles 20 MW to 30 MW and tankers from 50 MW to as much as 200 MW (as illustrated by the Runehamar Tunnel tests) at the top end of the spectrum. Fortunately steps have been taken to make rail stock less combustible. The compartmentalisation of wagons, the control of combustible material and fixed fire suppression and the implementation of regular fire drill test procedures has improved fire safety levels for both goods and passenger trains.
There is also the dense smoke, which can be highly poisonous. Mont Blanc’s fumes contained cyanide and carbon monoxide. The speed of the smoke outpaced those who decided to run; those that attempted to escape using their vehicles found that the smoke choked off the oxygen to their engines, which ground to a halt.
Fighting the Fires: The Challenge
When a fire takes hold in a tunnel it presents a number of specific challenges and dangers to fire fighters:
- Incredible heat – in the case of Mont Blanc, it took five days for the tunnel to cool.
- Thick toxic fumes.
- Poor or no visibility.
- Confined operating space for emergency services.
- Airflow that generates aerodynamic disturbance affecting smoke behaviour
We can also add the problems of communication and with international tunnels, different authorities from different jurisdictions and countries, perhaps languages, working together under pressure.
The Need for Fire Detection Measures & the Response
Tunnel designers have often looked at causes of accidents, which although naturally important are perhaps a distraction from concentrating on fire detection and prevention that can help avoid lethal situations altogether. It is essential that fire detection and prevention systems reduce the risk and enable fires to be contained and extinguished before developing into unstoppable infernos.
Indeed, a new EU directive (2004/54/EC) that came into force at the end of April 2014 is a very positive step. In terms of incident and fire detection monitoring, systems need to be implemented for tunnels over 500 metres long. For those over 3000 metres, video systems are mandatory.
Yet, it must be stated that many countries and regions outside the EU have very poor standards of fire detection and prevention. As road and rail tunnel fires are rare occurrences, only the terrible experience and pressure resulting from a major catastrophe is likely to be a catalyst for change.
Safety Legislation & Regulation
There are no globally-binding guidelines for road or rail tunnel safety.
The integration of the EU has enabled it to implement binding safety regulations for an area encompassing 500 million people for road tunnels. However, most regions do not have the level of integration and co-operation to bring about better fire safety measures. Rail tunnels are not covered in the same way, even in the EU. The EU’s technical standard “Safety in Railway Tunnels” is a framework standard rather than a specification. The NFPA 130 does not cover the issues of fire safety in rail tunnels.
Research and the identification of suitable regulations continue to be pursued by The International Tunnelling Association’s Committee on Operational Safety of Underground Facilities. Both the International Tunnelling Association (ITA) and the World Road Association (PIARC) have published guidelines and best practices for the safe construction and operation of tunnels, but these are non-prescriptive.
It is not an encouraging picture for solid forward thinking change that will save lives and property.
Fire Detection & Suppression in Practice
Many fires start with a smouldering phase. At this stage fires can be dealt with, even by non-emergency staff, contained and extinguished before disaster unfolds.
Fire detection systems need to recognise danger early. Suggested solutions that rely on heat activation alerts generally take too long. For example heat sensing cable that short circuits when the thermoplastic melts and raises the alarm. Moreover, such systems provide no visual information to help tackle the blaze. There are other systems that can be considered such as infra-red, air sampling and other linear detection systems in addition to the above that include optic sensors.
Visual Smoke Detection (VSD) solutions are possibilities that can be considered to provide early warnings. VSD uses changes in its wide field of view to alert operators, remotely or on site to potential fire danger. Visual verification aids operators gage the level of danger and guide the response. Potential interference to fire detection such as car fumes and the movement of vehicles do not affect its effectiveness.
Our controlled tests at the Sydney Harbour Tunnel in Australia, using a vehicle fire generating temperatures in excess of 500°C generated an alert after just 14 seconds with a further 30 alerts during the test using a VSD solution.
Let us not forget about fire suppression solutions, which can be used effectively in conjunction with fire detection solutions:
- Sprinklers, standpipes and hydrants.
- Deluge, possibly with foam.
- Water curtains – efficient at blocking flames spreading and good for compartmentalising fires, protecting tunnel structures and facilities and cooling temperatures.
- Water mist.
Other steps such as those introduced by the Mont Blanc authorities, for instance checking trucks before they enter the tunnel are to be commended. Educating tunnel users on how to deal with fire situations is highly valuable in minimising risks and consequences. Some operators regulate the number of goods vehicle that can use a tunnel at any one time.
With all systems there needs to be co-operation towards finding the best solution for each tunnel from fire engineers, emergency services, government agencies, tunnel workforces, owners and other parties.
Conclusion
Fire detection and prevention are not extras but essential tools to protect tunnels and their users from catastrophe. The possible cost in lives, property loss and disruption caused means that investing fully in fire protection measures is a sound use of funds.
Tunnel fires can be tragic, terrifying and costly but above all predictable. The technology has matured, is proven and available to provide very early warning of fire which ultimately saves lives.
For further information, go to www.firevu.co.uk
About the Author
Ali Aleali is Business Development Manager for FireVu
