As a result of the recent fires in alpine road tunnels, the authorities in many countries are reviewing both the fire life safety provisions in all their existing tunnels and also the design requirements for new tunnels. But why did these two incidents happen? Is there any reason they occurred within two months of each other and what can be learnt from them? Apart from the fact that they were both large fires in single-tube road tunnels, there are few similarities between the two incidents.
The Tauern Tunnel fire was the result of an accident at traffic lights in the tunnel involving a vehicle carrying dangerous goods.The accident and the ensuing fire could equally well have occurred outside the tunnel and there would probably have been a similar number of fatalities. Initial press reports indicated that there were no problems with the operation of the equipment and systems and the emergency procedures were carried out as planned.
The Mont Blanc Tunnel fire was completely different. There was no accident; the margarine and flour carried on the vehicle which started the fire are not considered to be dangerous goods and, if the initial fire had occurred outside the tunnel, there may not have been any casualties. The deaths in the Mont Blanc Tunnel were totally attributable to the fire itself, its severity and its duration.
The joint French/Italian report on the incident stated that there were known shortcomings in the ventilation and other emergency systems in this old tunnel and that they had not been addressed by the tunnel management. The report includes 41 strong recommendations, of which over two thirds are directly concerned with tunnel management and operating practices. Only a quarter of the recommendations directly concern the equipment and facilities themselves.
The other aspect common to both incidents was bad driver behaviour – almost certainly causing the initial accident in the Tauern Tunnel and certainly increasing the severity of the Mont Blanc fire. Drivers do not appreciate the risks of getting too close to the vehicle in front on the open road, let alone in tunnels. The French authorities responsible for the Fréjus Tunnel now insist on a minimum spacing between vehicles using the tunnel even if the traffic comes to a standstill. This simple measure, had it been in force in the Mont Blanc Tunnel, would certainly have reduced the rate at which the fire spread and probably the number of fatalities.
Most major road tunnels have several fires a year but they are usually small and quickly go out; there are no casualties and there is little damage to the tunnel. Occasionally, there are larger fires which result in fatalities but these are rare. Interestingly, the number of fatalities in a tunnel fire does not appear to be related to the length of the tunnel, so the trend to require longer tunnels to have relatively more safety provisions may not be the correct approach.
Improving tunnel safety
It is over 30 years since the first major alpine road tunnels were opened and many lessons have been learnt about improving the security of tunnels. First, it has been appreciated that safety in the event of a fire or any other emergency is not something that can be bought and included in the tunnel like, say, an emergency telephone system. Safety is provided by a combination of: the tunnel’s design and layout; the equipment and systems installed in the tunnel; and the performance and behaviour of the tunnel operators, emergency services personnel and others involved in the incident , including those trapped in the tunnel. Only when all three aspects work together successfully can the required levels of safety be achieved.
What are the basic concepts underlying the provision of safety in tunnels? In the best hypothesis, fire and rescue personnel might be able to reach a fire in an urban tunnel some minutes after the fire alarm has been raised. But many tunnels are remote and it is unlikely that emergency personnel would reach the site before either the fire has finished or lives have been lost. As a result, it is essential that the tunnel itself is designed to minimise the size of the fire and that equipment and facilities are provided to enable those trapped in the tunnel to rescue themselves.
The main objectives of the tunnel’s design and of the ventilation and other safety facilities which are installed are: to provide a place of safety for those trapped by the fire and a clear and safe escape route to that place of safety. The secondary objectives are: to provide access to the fire site for emergency personnel, equipment and vehicles, and to minimise damage to the tunnel and its facilities.
Ideally, all the fire life safety issues for a new tunnel should be resolved before the tunnel alignment is finalised and the first tunnel cross section is drawn. This process needs to involve various members of the design team including civil and M&E engineers, together with experienced tunnel operators and representatives of the emergency services. There may be many options to be investigated and changes to be made but the compromise design must be safe in the eyes of all concerned including, most importantly, those whose responsibility it is to operate the tunnel.
This integrated approach very early in a project is becoming more usual in some countries but still has to be adopted in many others. As well as providing a safer tunnel, it usually reduces the total project costs simply because no late changes are required to satisfy safety requirements. In the past, this was not often the case. Tunnel designers had often sorted out how they would build their hole in the ground long before considering how it would become a usable tunnel, with the inevitable costs associated with late changes to a project.
In twin-tube tunnels, regularly spaced cross connections for vehicles and/or pedestrians allow those trapped to escape easily to the safety of the opposite tube. These cross-connections, combined with effective emergency ventilation to control the smoke spreading, ensure a relatively high level of security in the event of a fire in a twin-tube tunnel.
Single-tube tunnels pose a far greater challenge to fire life safety. The principal problems are providing escape facilities for those trapped in the tunnel and smoke free access routes for them and for the emergency and rescue personnel to reach the fire site. In the past, in tunnels with transverse or reversible semi-transverse ventilation systems, this was assumed to be provided by exhausting the smoke from the traffic room into the exhaust duct. However, as was clearly demonstrated in the Mont Blanc, Tauern and other incidents, this cannot be relied upon.
The options for escape facilities are either: a smaller service tunnel parallel to the main tunnel, like that in the Gotthard Tunnel; escape tunnels from the tunnel to the open; or smoke and fire proof rescue rooms in which those trapped could wait in safety until the rescue services arrived.
A parallel service tunnel is expensive but provides a level of safety approaching that of a twin-tube tunnel. In the early stages of a project it may be possible easily to incorporate escape tunnels by modifying the horizontal alignment of the tunnel. Rescue rooms may seem the cheapest option but a secure fresh air supply and communications must be guaranteed and there is no access for the emergency personnel apart from the tunnel portals. The potential psychological problems of people being ‘trapped’ in the room must not be underestimated, particularly after the Mont Blanc incident.
Once the basic design has been settled, the effectiveness of any of the systems falls into the hands of a detail designer who needs to specify a system which can be shown to have proven reliability with, ideally, built-in redundancy and fail-safe operation. The equipment itself, and its control and monitoring systems, obviously needs to be manufactured, installed and commissioned correctly and there the job of the design engineer is usually complete and the tunnel is handed over to its new owner. Once it is opened, the responsibility for safety in a tunnel rests entirely with its owners. It is their duty to ensure that the security provided by the designers is fully realised. However, it is the designer’s responsibility to ensure that owners fully understand the basis for and reasoning behind the tunnel design and the equipment installed in it.
To maintain the tunnel’s security, its equipment and systems need to be regularly tested, maintained and, when necessary, upgraded. However, by far the greatest impact on its safety are the people associated with the tunnel, and a culture of safety must be encouraged. Regular training must be carried out to ensure that everybody is familiar with the relevant procedures and that the procedures themselves continue to be tested, reviewed and possibly revised.
What about older tunnels?
The decisions about safety facilities to be made by the owners of older tunnels are much more difficult than the ones to taken by the designers of a new tunnel. Should a new safety measure or an upgrade to an existing system be introduced or not? Should the safety facilities in the tunnel always reflect the latest design guidelines or be updated only when the tunnel is completely refurbished? Should a tunnel be closed or the traffic restricted until its security is brought up to currently acceptable levels? If a tunnel were to be closed for upgrading, would the personal and/or societal risks on alternative routes be higher or lower than continuing to use the ‘less safe’ tunnel? Should the basis for any decision be ‘safety at any cost’ or should it be ‘cost-effective’?
Nobody can dispute that road tunnels have improved transport infrastructures and saved many lives because, for example, high volumes of traffic have been removed from congested urban areas. The table on page 29 shows that there have been 97 fatalities in road tunnel fires world wide. Although no fatalities are acceptable, it should be recognised that the same number of fatalities occurs every few days on the roads in the UK alone. The worrying trend is the increased number of fatal fires in recent years. Is this due to the increased number of tunnels, the increased traffic, worse driver behaviour or is it a lack of investment in either equipment and people?
It can only be hoped that, as a result of the Mont Blanc and Tauern tragedies (which accounted for over half of all the fatalities), the lessons have started to be learnt and a stronger safety culture will prevail amongst all involved in the design and operation of road tunnels.
Tunnel designers have to appreciate fully that the design and layout of a tunnel is inseparable from its security in the event of a fire or any other emergency. Ventilation and all other aspects of fire life safety are not straightforward and cannot be ‘bolted on’ later. Owners and operators have to realise that, no matter how good the safety systems and facilities are in their tunnel, they will only function satisfactorily with the correct motivation and training of the staff responsible. The fact that most tunnel fires are minor is no reason for anybody to be complacent.
Unfortunately, tunnel designers and owners alike have little control over what is probably the greatest threat to safety in a tunnel: the behaviour of the tunnel users themselves.
Related Files
Fire Safety Diagram
