The security features of the Mont Blanc Tunnel | Science| In-depth reporting on science and technology | DW | 17.07.2015
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The security features of the Mont Blanc Tunnel

Fifty years ago the alpine tunnel between France and Italy opened for traffic. Thousands of cars passed through it - until 1999 when there was a devastating fire. What lessons have engineers learned from the disaster?

The Mont Blanc Tunnel is not like any other road tunnel: at 11.6 kilometers long, it was the world's longest road tunnel when it opened for traffic on July 19, 1965. It held that title until 1978, when the Arlberg Road Tunnel opened in Austria, breaking the record by two kilometers. Today, the Mont Blanc Tunnel still ranks as the eighth-longest road tunnel in the world.

Everything went alright for more than 30 years, but then disaster struck: on March 24, 1999, the motor of a truck carrying margarine and flour went up in flames, probably after the air filter caught a cigarette butt.

The truck driver stopped his vehicle in the tunnel and escaped. He survived, but 39 people in following cars were unable to get out in time and died in smoke and fire. It took firefighters more than two days to extinguish the blaze.

Three years later - after substantial repairs and redesigns, including a whole new security concept - the tunnel reopened.

Rubble is being removed after the 1999 tunnel blaze at Mont Blanc (Photo: AP P. Gardin)

39 people died in the blaze of 1999

Better communication among the emergency crews

The first flaw in the 1999 emergency response was sluggish communication between Italian and French emergency crews. When the alarm was triggered inside the tunnel on Italian territory, the information did not get through to the French side immediately, even though the French teams were located geographically closer to the burning truck. Four minutes were lost - valuable time for firefighters trying to extinguish a fire that is just starting to spread.

Today, there is one central control facility that coordinates the activities of two response units on the Italian and French sides. Alarm systems, such as emergency phones, are located at 100-meter intervals throughout the tunnel. All of them are connected to the central facility, which is also where the 120 security cameras are being monitored.

Shelters for escape and firefighting

A second flaw lay in the tunnel's architecture: The existing shelters were not heat-resistant enough to withstand fires longer than two hours. Today, the 37 shelters, which are also linked by an escape-tunnel, are able to cope with temperatures of up to 1,000 degrees Celsius for a long time.

Each shelter is equipped with phone lines to the central control facility and with firefighting equipment. In addition, there are 78 smaller firefighting booths where firefighters can extinguish blazes from a more protected environment.

Four water tanks, each of them holding 120 cubic meters of water, ensure that there are always enough reserves at hand.

The new architecture is completed by three evacuation tunnels, which also double as air vents. One of them connects all the shelters. There is also a channel holding the water-pipe for firefighting and one exhaust channel to remove smoke from the tunnel. 76 steel fans, so called "overhead air accelerators," pump smoke out of the tunnel into the exhaust channel.

In the middle of the tunnel, there is a small firestation - a garage with a firetruck and an emergeny medical aid vehicle. The longest possible distance that fire crews need to travel to the location of an accident has thus shrunk from almost six kilometers to just over two-and-a-half kilometers.

Using sensors to prenvent emerging dangers

Recognizing emerging dangers, such as smoking cables, is at least as important as fighting full-fledged fires. Many fires would have never started, had someone recognized the cause of them early on. That's why sensors are constantly delivering data to the central control facility.

At the beginning of the sensor network stands an infrared-camera - scanning all vehicles that enter the tunnel. This helps to identify cars and trucks with motors that may be overheating or with payloads that may have heated up - like coolers for refrigerated goods.

Those vehicles will not be allowed into the tunnel until their engines have cooled down. The entire tunnel is also plastered with 3,860 smoke- and fire detectors: one every three meters.

Trucks entering the Mont Blanc tunnel (Photo: AFP, Getty Images/ Clatot)

Trucks entering the tunnel are being scanned for overheating motors

Driving slow and keeping distance

Another way of preventing accidents early on is by ensuring that people are neither speeding nor tailgating. The maximum speed in the tunnel is 70 kilometers per hour. But that is not enough: drivers have to keep a distance of at least 150 meters from the car ahead. 20 radar units ensure that everybody abides by the rules. To prevent traffic jams, traffic going into the tunnel is regulated - having people wait before going in is preferable to congestion inside the tunnel.

If a problem still occurs, 20 traffic lights in each direction can signal drivers to stop immediately. In a worst case scenario, half barriers will go down. If warning signals at the shelters light up, all car drivers have to leave their cars and the tunnel pipe and enter the safety rooms.

12 FM channels ensure that every driver can get immediate information about the situation in the tunnel. If you turn on your radio, you can practically not miss it.

The transport of dangerous goods through the tunnel is strictly limited. Highly dangerous chemicals mustn't be transported at all.

It has now been almost fourteen years since the reopening of the Mont Blanc Tunnel - and so far, the security measures have prevented mayor accidents.

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