Tunnel fires – why they are vulnerable and the possible solution

Major tunnel fires can be catastrophic with the scale of lives lost and property damaged. The particular nature of fires in such confined spaces presents special challenges for fire engineers, health and safety professionals and emergency services.

In March this year, more than 30 people died after an explosion and fire engulfed dozens of vehicles in the Yanhou Tunnel in China. A coal truck rear-ended one of a four-tanker convoy loaded with highly flammable methanol. The collision resulted in a fire and explosion, which engulfed more than 40 cars and commercial vehicles. While we do not know the full economic consequences this particular tunnel fire, to give an idea of the costs of tunnel fires we can go back to Europe for a moment.

The Channel Tunnel fire in the UK in 2008 lasted 16 hours and cannot be described as a particularly major fire. Yet, repairs cost Ä60 million and the loss of business through disruption to rail services was Ä200 million. The horrific Mont Blanc Tunnel fire on the France / Italian border that claimed 39 lives resulted in multi-million Euro fines for the companies involved and custodial sentences for senior executives responsible for safety.

The potential consequences of railway tunnel fires, both materially and in in terms of loss of lives often exceed such road tunnels disasters.

Thankfully road and rail tunnel fires that lead to major catastrophes like these examples are relatively rare, particularly when thinking about the considerable levels of traffic they accommodate. Yet, when disaster happens it can be particularly costly in terms of life and property, as well as causing substantial disruption lasting months and even years.

Surge in road and rail tunnel construction in Asia Pacific

The Asia Pacific region has experienced an impressive boom in tunnel building for rail and road transport in the past 20 years. The transportation tunnels – metro, rail and road – that have been built are incredible endeavours as shown by the following examples.

The Guangzhou Line 3 at 60 kilometres is the longest metro in the world. It is followed by the Beijing Subway at 57 kilometres. There are plenty of Chinese and Korean underground metro tunnels that closely follow in scope. Seikan Tunnel, 23.3-kilometre with a long portion under the seabed, is both the longest and the deepest operational rail tunnel in the world. Japanese tunnels, such as Seikan, can be older constructions as Japan experienced economic prosperity from the 1960s onwards.

In 2006, Taiwan opened the longest underground road tunnel in Asia, it was the 5th longest in the world. The Hsuehshan Tunnel is nearly 13 kilometres long and took nearly 14 years to complete. The next year, the Zhongnanshan tunnel bettered that by becoming the second longest road tunnel in the world, some 18 kilometres long.

While such constructions can be state of the art, the level of fire detection and suppression measures, as well as fire resistant design, can vary significantly across the region. Some countries match or exceed the standards in the west; others fall terribly short or are just starting to implement measures. Yet, whatever measures have been implemented, the risk of a major conflagration can never be fully eradicated.

The specific danger 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 generate heat far more vigorously in confined spaces than open areas. The HHR can be four times as powerful in tunnels compared with 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.

Then there is the dense smoke, which can be highly poisonous and more deadly than flames.

The speed of smoke in tunnel fires can outpace those who decide to escape on foot; those that attempt to escape using their vehicles can find that smoke chokes off the oxygen to their engine, which grinds to a halt.

Roads in China are known to be among the most dangerous in the world with more than 70,000 fatalities and 300,000 injuries every year, according to the country’s Public Security Ministry. With such terrible statistics, addressing fire tunnel risk is essential.

Fighting the fires: the challenge

When a fire takes hold in a tunnel it can present a number of specific challenges and dangers to fire fighters:

• Incredible heat that can take days to cool.
• Thick toxic fumes.
• Airflow that generates aerodynamic disturbance affecting smoke behaviour.
• Poor or no visibility.
• Confined operating space for emergency services.

We can also add the problems of communication with international tunnels: different authorities from different jurisdictions, perhaps languages, working together under pressure.

The need for fire detection measures and the response

Tunnel designers often concentrate on the causes of accidents, which although naturally important are perhaps a distraction from concentrating on the 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.

Major incidents can generate unavoidable political pressure for a high level of tunnel safety, which can then be reflected in improved engineering standards for structural fire protection, evacuation, detection and suppression systems. As incidents are rare, the push in developing Asian Pacific countries to greater fire safety might be a slow process, until a catastrophe strikes. Even more developed countries, such as Japan, must review fire detection and prevention regularly.

Fire detection and prevention regulations and measures though are likely to evolve as an improved understanding of risks and technology improves.

Tunnel fire legislation in the Asia Pacific region

April this year was the deadline for implementing the EU’s 2004/54/EC directive. It mandated that road tunnels for all 28 EU member states must have fire detection monitoring for tunnels over 500 metres long, with video detection systems being mandatory for tunnels longer than 3,000 metres.

There are no global guidelines, and the Asia Pacific region does not have the political and legal integration of the EU to implement binding safety regulations. 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. Research and the identification of suitable regulations continue to be pursued by The International Tunnelling Association’s Committee on Operational Safety of Underground Facilities.

Countries in the Asia Pacific region vary, as do other regions, in the pursuit and implementation of regulations. Yet, whatever the legislation, neglecting adequate fire safety measures leaves the operator, local authorities and politicians open to serious disaster situations.

Fire detection and 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 warning. VSD uses changes in its wide field of view to alert operators, remotely or on site to potential fire danger. Possible interferences to fire detection, such as car fumes and the movement of vehicles, do not affect its effectiveness. FireVu’s controlled tests at Sydney Harbour Tunnel, using a vehicle fire generating temperatures in excess of 500 degrees C generated an alert after just 14 seconds with a further 30 alerts during the test using FireVu’s 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.

Passive fire prevention can minimise fire damage to infrastructure, with options ranging across micro mono-filament polypropylene fibres added to the concrete mix of wall linings, fire resistant panels and cementitious coatings. Other steps can include checking trucks before they enter the tunnel and educating tunnel users on how to deal with fire situations.

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.

The Asia Pacific region’s fire tunnel safety reflects the area’s major period of change. Safety measures and regulations vary, but as an appreciation of the danger of tunnel fires become stronger, then the appropriate steps will be taken. Hopefully it will not take more disasters such as Yanhou Tunnel to bring fire tunnel safety to the fore.

For more information, go to www.firevu.co.uk