What is the worst underwater tunnel accident

PRO BAHN Newspaper 79

The construction of new single-tube tunnels is not responsible

by Dieter Walter (from PRO BAHN newspaper 3/99: Danger in the tunnel)

A fire in the tunnel is a nightmare. Statistically, the risk of being involved in a tunnel fire is very low, but the thought of it affects the human psyche much more than, for example, the fear of an accident on the open road, be it road or rail. In the last few months, reports of catastrophes in tunnels with numerous dead and injured have increased and fueled public discussion.

Tunnels - the dangerous bottlenecks

The news has been rolling lately. There were several fire disasters in tunnels with numerous casualties to report. A selection of the terrible news:
  • April 10, 1995 in the Pfänder tunnel near Bregenz (Austria) four cars go up in flames in a mass collision. A family of three burns to death.
  • 18.3.1996: In a tunnel near Palermo a tanker truck drives onto a minibus and explodes. 5 dead, 26 injured.
  • 11/18/96: In the Eurotunnel under the English Channel, a truck on a freight train catches fire. Fortunately, there are no human casualties to be mourned.
  • 2.3.1999: On the ICE route Hanover-Würzburg, a wagon with cellulose and paper catches fire in a 1.7 km long tunnel near Göttingen.
  • 24.3.1999: A truck goes up in flames in the Montblanc tunnel between France and Italy. The fire spreads to other vehicles. 42 people die and many are injured.
  • May 29, 1999: A rear-end collision occurs in the Tauern tunnel on the Salzburg-Villach motorway, which in turn leads to a devastating fire. 6 people die, over 50 are injured.
  • 1.6.1999: In the railway tunnel at the Brenner Pass, a lorry loaded with phosphorus catches fire on a rail freight car. People are not harmed.

These and other accidents have meanwhile led to an extensive safety discussion in which politicians, safety and traffic experts and citizens' groups take part. The requirements include checking the safety of all rail and road tunnels, building at least one second tunnel tube and installing technical safety systems.

What happens in a tunnel fire?

Suppose there is a rear-end collision in a road tunnel with only one tube. Most of the time, the traffic is too dense to bring the following cars to a standstill, so several vehicles are usually involved. If a fire breaks out, it usually has devastating consequences. There are often no escape routes (especially in the predominantly older Alpine tunnels) and safety requirements for fighting a source of flames. Heavy smoke makes it difficult for those involved to escape and for rescuers to gain access. Ventilation systems are often not adequately set up for such disasters. A great deal of heat develops, and the tunnel becomes a blast furnace within a short time. The tunnel ceiling collapses because the temperature difference between the poorly heat-conducting, i.e. relatively cool rock and the great heat inside the tunnel creates tension in the concrete that causes it to burst. After the fire has been extinguished or suffocated, the heat lasts for many hours. Rescue missions are therefore often only completed after days, and the identification of the dead is not always possible.

Time bomb one-tube tunnel

The danger is greatest in a tunnel with only one tube, in both road and rail tunnels. The number of dead and injured can more than double, not only because both directions of travel are affected, but because the second directional tube also lacks an escape and rescue option. The subsequent construction of second tunnels is therefore demanded more and more loudly and sustainably by politicians and citizens' initiatives, but is not possible in all cases for technical and cost reasons. As recent accidents have shown, the rail tunnel appears to be safer. Signal control makes it easier to regulate access to rail tunnels. In addition, rail-bound vehicles often come to the tunnel exits in the event of a fire, where rescue measures are much easier to carry out. But this appearance of greater security is deceptive. When there is a high volume of traffic, especially when traveling long tunnels, it is not always possible to allow only one train to enter a tunnel at a time. The following horror scenario would be conceivable: An ICE derails at high speed shortly after entering a tunnel (conceivable cause: material faults, technical and human failure, terrorist attack). The wagons are instantly wedged between the tunnel walls. Since the tunnels on high-speed lines were usually built as single-tube tunnels and, despite all experience, are still being built, it is quite possible that an oncoming train has already entered the tunnel, can no longer be braked and into the The scene of the accident is racing. At high speeds, such as those driven on ICE routes, none of the occupants should survive, since contact with the tunnel walls is tantamount to a frontal impact. Should someone survive anyway and get out of the armored wagons despite severe injuries, it should hardly be possible to reach one of the built-in escape shafts and to get outside via long flights of stairs due to the strong heat and smoke development.

Scare tactics?

Perhaps this scenario is an exaggeration, but sometimes disasters cannot be imagined even if they actually happened. They are always conceivable: As has been shown, accidents in tunnels are not uncommon, and rail accidents are also not uncommon. The accident in Eschede is so far an exception only in terms of its extent. Trains also derailed in Hanover and Immenstadt, and in the second case there were again fatalities and injuries. Attacks on trains by loosening the screws or hooked claws are unfortunately not uncommon. So you only have to combine the accident in Eschede with the fire in the Montblanc tunnel and you have it, the "greatest accident to be expected" (GAU). Certainly the statistical probability of such a super-accident is very small. But just as a chain is only as strong as its weakest link, people's safety should, as far as possible, be based on the worst possible accident possibility. Unfortunately, this is not always feasible, but the accident in the Eurotunnel between France and Great Britain on November 18, 1996 shows that safety is not just wishful thinking.

It can also be safer

Take the Eurotunnel, for example: In the accident in the Euro Tunnel under the English Channel, a striking truck driver on the French side hurled incendiary device onto a truck that was driving into the tunnel on a transport wagon. Shortly after 9 p.m. the engine driver reported a fire in the rear of the train. It is mandatory to continue to the tunnel opening on the other side in the event of a fire. Halfway through, however, the emergency braking was triggered by a warning signal in the driver's cab. Now the train driver would have had to uncouple the locomotive and the club car in which the truck drivers were at the push of a button in order to save himself and the passengers to the tunnel exit, but the emergency system did not work because the power supply was interrupted. The steward of the club car prevented panic among the passengers and led them through an emergency exit into the service and rescue tunnel between the two tunnel tubes. At the time of the accident, five trains were in the tunnel at the same time. They were evacuated smoothly. The first fire engines from France arrived after twenty minutes, and the British rescuers were deployed an hour later. The fire developed a heat of over 1000 ° C: rails bent up, wagon wheels merged with the tracks, the concrete wall of the tunnel tube burst. It was deleted by Tuesday morning. 800 m of tunnel as well as several kilometers of overhead lines and signal systems were destroyed. The request of the operating company to resume operations on the same day in the undamaged opposite tube was rejected by the "Channel Tunnel Safety Authority" and the plant was shut down. For the time being, only freight trains were allowed to pass (source: "Zeit" archive). Only two weeks later did the first passenger traffic roll through the Eurotunnel again. This example shows the following: The courageous intervention of the specially trained staff as well as the construction of the tunnel itself (two main tubes, additional service and rescue tubes, technical safety devices) and additional safety regulations saved lives and prevented the worst.

Take the belt tunnel as an example

The railway tunnel under the Great Belt between the Danish island of Funen and Zealand is also considered to be similarly safe. Here, too, there are two independent tubes as well as a rescue and supply tunnel. In the main tunnels there are "platforms" on both sides of the tracks, which make it easier to reach the escape doors. The entire course of the tunnel is monitored by video; the simultaneous entry of several trains into one tube is not intended. Freight and passenger traffic are also kept strictly separate. The speed is limited and the train crew has been specially trained. In the passenger trains there are detailed instructions on what to do in the event of an accident, which are explained to the passengers over loudspeakers before they enter the tunnel. So security is not a utopia, but unfortunately it does not guarantee ultimate protection either. Complete security and protection against all conceivable and unthinkable possibilities are not feasible. If only because there are imponderables that cannot be foreseen, even with the best will in the world. For this very reason, however, all available and conceivable options should be exhausted in order to increase safety in road and rail tunnels. As with all accidents, the emergency can and must be evaluated to improve safety.

Minimum requirements for safety in tunnels

In all tunnels, whether rail or road, the tracks or lanes should run in two separate tubes. A third tube should guarantee escape routes and quick access for security forces. The tunnel tubes must be monitored electronically and by video. From a certain length of the tunnel, security forces should be present at all times. Strict distance controls in car tunnels, drastic penalties for violations. A suitable counting system for vehicles must be introduced in road tunnels so that, on the one hand, the number of vehicles in the tunnel can be limited by a traffic light system and, on the other hand, in the event of an accident, the rescue workers know immediately how many vehicles are involved. The transport of dangerous goods may no longer be conducted through road tunnels. The transport of goods and passenger cars by rail must be offered in a more attractive and cost-effective manner. In rail tunnels, passenger and freight traffic, especially those with dangerous goods, must be kept separate. In the case of rail tunnels in single-tube operation, it must be ensured that there is only one train in the tunnel at a time. Limitation of the driving speed in all tunnels. The construction of new tunnels should be avoided as far as possible (road tunnels by increasing the piggyback offer of the railways, rail tunnels by tilting technology and consequently easier above-ground routing possible).

Perspective for the railway

In general, there is a requirement that rail traffic should be preferred to passenger and especially road transport, even more so for tunnels. Rail transport services are currently being strengthened in both Switzerland and Austria in order to compensate for the bottlenecks caused by the closure of the road tunnels. This is the chance for Deutsche Bahn to turn such an offer into something permanent. To do this, however, safety in rail tunnels in particular must be guaranteed. Single-tube tunnels, as Deutsche Bahn is currently still building and planning against its better judgment on high-speed lines, are not suitable for guaranteeing the safety of passengers. The principle of safety always has to be about speed on the one hand and cost savings on the other.

Single-tube tunnels on German railway lines: two-way traffic, no escape routes.

Prototype of the Eurotunnel: two separate tubes, an escape tunnel in between.

PRO BAHN Newspaper No. 79 (3/1999)