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Infrastructural Fires

Mont Blanc Tunnel, Italy

Overview

Location: Between Courmayeur, Italy and Chamonix, France
Fire Event: 24 March 1999
A truck fire at Kilometre 6.7 into the Italian part spread to 35 other vehicles, creating intense heat and toxic fumes that killed 39 people.
Fire duration = 53 hours
Fire Damage: Extensive tunnel roof and road pavement damage
Construction Type: Reinforced concrete
Fire Resistance: No fire protection. No sprinklers.
Function: Road tunnel
Dimensions: Width = 8.6m; length = 11.6 km

The Tunnel

The Mont Blanc tunnel is a road tunnel in the Alps connecting Chamonix of France and Courmayeur of Italy, beneath the Mont Blanc massif. At 11.6 km, the tunnel was the longest road tunnel in the world at the time of its completion in 1965.

The Mont Blanc Tunnel is a single-bore, two-lane tunnel. The horse shoe shaped tunnel has a 7 m wide roadway with two 0.8 walkways on each side. Every 300 m, there are vehicle rest areas, 3.15 m wide by 30 m long, situated on alternating sides of the roadway and numbered from 1 to 36 in the France-Italy direction. Opposite to each rest area, there is a designated U-turn for trucks.

The roadway slab and the ducts beneath are reinforced concrete structures. However, the 0.5 m thick tunnel lining was pure concrete without reinforcement.

Fire Protection System

The fire protection systems before and after the 1999 fire are compared as follows:

At Time of Fire (1999)
After Refurbishment at 2002
  • Safety niches at every 100m containing a fire pullbox and two fire extinguishers
  • Fire niches at every 150 m with water supply for fire fighting
  • Alarm and fire detection system
  • Pressurised safe refuge or emergency shelter at every 600 m with two-hour fire rating (18 in total) without a safety
  • Outdated ventilation system with ducts underneath the roadway and limited smoke extraction capacity
  • Two command and control centres at both ends with a firefighter team at the French entrance
  • Traffic signals every 1.2 km
  • Fire-resistant stainless steel cladding fitted to walls
  • Concrete-lined pressurised emergency shelters at every 300 m (37 in total), fitted with fire doors and connected to a safety corridor parallel to the tunnel
  • A total of 116 smoke extractors at every 100 m
  • Heat sensors at both ends of the tunnel to detect overheated trucks before they enter the tunnel
  • Three command and control centres; the newly added central centre has a round the clock firefighting team
  • More traffic lights and flashing warning signs

The Fire

On 24 March 1999, a Belgian truck with a refrigerated trailer carrying margarine and flour caught fire and stopped at Kilometre 6.7 in the France-Italy direction. The fire quickly spread to the vehicles behind the truck. The intense heat and smoke filled the entire tunnel section preventing emergency rescue and fire fighting operations.

It was believed that the fast growth of the fire was due to the large fuel load of the truck including:

  • 550 litres of diesel in the truck's fuel tank
  • 9 tons of margarine and 12 tons of flour carried by the truck
  • The shell of the refrigerated trailer made of a combustible isothermal foam

At the time of the fire, there was a weak air flow (1 to 1.5m/s) in the Italy-France direction, forcing the smoke and flame spread mainly in the direction of the French entrance. As a result, many vehicles stopped behind the truck were trapped and caught in the fire.

The fire burned for two days and reached temperatures of 1000°C, killing 39 people, mainly the drivers trapped in the tunnel during the fire. Most of the drivers stayed in or near their vehicles and those who tried to escape could manage to make only 100 ~ 500 m before collapsing due to smoke. This indicated that the smoke was very toxic. The CO content was reported to raise quickly over 150 ppm within minutes.

In addition to the huge human loss, over 30 vehicles were also destroyed. All these vehicles were between the rest areas 19 and 23, over a distance of 1.2 km.

A brief account of the fire development is given as follows:

Time
Fire Development
10:46
A Belgian truck entered the tunnel and started to emit smoke very quickly
10:52
White smoke was seen coming out of the cab by oncoming trucks between Kilometre 2 or 3.
Obscuration detector in rest area 18 was activated. The operator at the French control station saw the smoke in the tunnel through the cameras at rest areas 16 to 19, and the smoke on the almost stopped truck.

10:53

The truck slowed down and stopped at rest area 21. According to the driver, within 30 seconds, everything was ablaze.
The nearest sensor of the fire detection system, operated by the Italian side, was placed out of service the night before
10:55
Several alarms observed including a phone call at rest area 22 and a fire pullbox alarm from rest area 21. The tunnel was closed at 10:55.
The smoke spread very quickly and filled the tunnel up to area 18 within 10 minutes after ignition.
11:00
Firefighting from the tunnel operators of both sides failed to control the fire.
Investigation discovered that most of the victims died within 15 minutes of the fire first being detected.
11:11
Firefrighters from Chamonix and Courmayeur had arrived at both entrances of the tunnel respectively.
11:15
First Chamonix firefighters' vehicle stopped at 2.7 km from the truck on the French side due to smoke and heat
11:20~11:30
Courmayeur firefighters came within about 300 m of the truck, then were forced to go back to refuge area 24, which was 0.9 km from the truck. The second French firefighters' vehicle was stopped at 4.8 km
11:54
Rescue mission was carried out using the fresh air channels located under the road, saving the lives of some people
18:35
6 people in the refuge room 17 were saved
2 days later
Completely extinguishing of the fire took 50 hours

The damage

The major fire damage to the tunnel structure included:

  • tunnel roof of over 900 m long was seriously damaged (spalling)
  • ceramic tiles fell of on nearly 1 km
  • safe refuges near the fire were severely damaged
  • asphalt road pavement of over 1.2 km long was damaged

The vehicles destroyed in the fire included:

  • 2 emergency vehicles,
  • 23 trucks,
  • 10 passenger vehicles
  • 1 motorcycle

In addition, tunnel equipment over a considerable distance was destroyed or severely damaged by the high temperatures and fire by-products.

Analysis

The fire highlighted the dangers of smoke in an enclosured area without an adequate smoke extraction system, including:

  • obscurity which may prevent people from fleeing due to lack of visibility
  • toxicity which incapacitates the mobility of people and may be fatal
  • temperature which also incapacitates and may be fatal

The spalling of the tunnel roof concrete lining was due to the dehydration of concrete. When concrete is exposed to high temperatures for long periods of time, its strength and stiffness reduce accordingly. In addition, the chemical bonds between the water molecules in the concrete break down, destroying molecular links that bind together the various materials that make up concrete. Subsequently, the concrete loses its cohesion and weakens, pushing pieces of the concrete off the tunnel linings layer by layer. In the Mont Blanc Tunnel fire at 1999, a certain part of the tunnel roof lining completely collapsed and exposed the rock layer.

It was also noticed that the combustion of the asphalt pavement over a length of 1.2 km might release an estimated calorific energy equivalent of the burning of 85 cars or 12 trucks. To improve the fire resistance of tunnels, reinforced concrete pavement may be a good option.

Sources of Information

  • BBC News Online / World / Europe - UK Edition
  • Minister of the Interior, and Ministry of Equipment, Transportation and Housing, (1999). "Task Force for Technical Investigation of The 24 March 1999 Fire in The Mont Blanc Vehicular Tunnel - Report of 30 June 1999" (English translation).
 
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