||Between Pas de Calais, France and Kent, U.K.
||18 November 1996
A truck fire on a freight train towards England developed
into an intense tunnel fire at 19 km into the tunnel from
the French end, severely damaging the concrete lining and
tunnel facilities. Nobody died.
Fire duration = over 7 hours
||Extensive tunnel lining spalling and damage
to tunnel facilities over a length of 480 m.
||High strength reinforced concrete or cast
||No fire protection. No sprinklers.
||Length = 50 km
Internal diameter of Running Tunnels = 7.6 m
Internal diameter of Service Tunnel = 4.8 m
The Channel tunnel, also known as Chunnel tunnel or Eurotunnel,
is a railroad tunnel beneath the English Channel connecting Coquelles,
Pas de Calais region in France and Cheriton, Kent in England.
The tunnel has a length of approximately 50 km, of which 37 km
are under the English Channel.
The tunnels were mainly constructed in a Chalk Marl layer about
40 m under the sea bed. Chalk Marl has high clay content and
is relatively impermeable to water, which provides the ideal
condition for a underwater tunnel.
The Channel Tunnel comprises 3 separate tunnels. The outer North
and South Running Tunnels of 7.6 m diameter are 30 m apart, with
each containing a single lane railroad line. The middle Service
Tunnel of 4.8 m diameter is for maintenance and emergency. The
Running Tunnels are connected to the Service Tunnel by cross
passages at every 375 m. The two Running Tunnels are also connected
by Piston Relief Ducts of 2 m diameter at every 250 m to balance
the air pressure due to the "piston effect" caused by the passage
Most part of the tunnels is lined with precast high strength
reinforced concrete lining rings of 1.5 m wide, with a thickness
varying from 400 to 800 mm depending on the loading conditions.
Where concrete lining was inappropriate, cast iron lining rings
It is interesting to note that due to a poorer impermeable soil
condition, the French undersea tunnels were lined with a water-tight
bolted and gasketed segmental concrete lining. The English tunnel
lining was a concrete expanded segmental lining with grouted
voids to control water ingress.
Fire Protection System
The fire protection systems of the Channel Tunnel at the time
of the 1996 fire are listed as follows:
At the Time of Fire in 1996
protection to concrete lining
- Airlocks at the entrances
to the Service Tunnel
- Exit of each cross-passage into the Running Tunnel has
a fire-resistant door which is normally closed
- Piston Relief Ducts have dampers which are kept open during
- The undersea crossovers have fire-resistant doors which
separate the tracks in the two Running Tunnels
||The system comprises 33
detection stations in each Running Tunnel. Each detection
- Ultraviolet and Infrared flame detectors
- Optical and ionization smoke detectors
- Carbon monoxide (CO) detectors
- Aspiration tubes around the circumference of the tunnels
directing gases to the analysis units
- An unconfirmed alarm is triggered by the activation of
a single ionisation or optical detector
- A confirmed alarm results from the activation of either
a flame detector or from both an ionic and an optical detector
- Such two alarm levels is used to reduce false alarms
- 250 mm diameter wet main
along the Service Tunnel
- 100 mm diameter wet main along both Running Tunnels
- Wet mains inter-connected at cross passages, supplying
hydrants at every 125 m in the Running Tunnels
- Total capacity of 4000 m3/hr
- The air pressure in the
Service Tunnel is maintained at a higher level than that
of the Running Tunnels to prevent smoke from entering the
Service Tunnel and allow a "bubble effect" to be created
at the opening of a cross-passage door
- The Supplementary Ventilation System functions to clear
smoke away from any area in the tunnel to enable any emergency
- First Line of Response
(FLOR) teams are stationed at the Emergency Centres near
to the Service Tunnel portals
- Second Line of Response (SLOR) teams are the Kent Fire
Brigade and the Fire and Medical teams in the Pas de Calais
On 18 November 1996, a truck fire on Heavy Goods Vehicles (HGV)
shuttle No 7539, travelling from France to England, forced the
train to stop in the South Running Tunnel at about 19 km from
the French entrance. The fire emitted intense smoke which rapidly
engulfed the Amenity Coach and the front locomotive, preventing
immediate evacuation of the 31 passengers, 2 crew members and
the driver onboard. The evacuation could only commence about
23 minutes later.
The original drive-through strategy allowed the fire developed
substantially while the train was still moving in the tunnel.
After the train had stopped, fire development rapidly accelerated,
first towards the front of the train due to the "piston effect".
The fire spread towards the rear after the Supplementary Ventilation
System had been activated.
A brief account of the fire development is given as follows:
- The train entered the
South Running Tunnel.
- A 1~2 m fire flame was seen beneath a lorry abroad the
train by some security guards and reported to the Terminal
Control Centre in the French terminal.
- The Terminal Control Centre
informed the Rail Control Centre.
- Tunnel fire detection system gave first "unconfirmed"
- Four further "unconfirmed"
- The Rail Control Centre informed the train driver of the
possible onboard fire and the train would be diverted to
the emergency siding in the UK terminal.
- The onboard fire alarm system warned the driver of a fire
in the rear locomotive.
- A fire on the rear locomotive
was confirmed by both onboard and tunnel fire detection systems.
- The train had travelled 10 km into the tunnel.
| The French First Line
of Response (FLOR) team comprising 8 firefighters left the
French Emergency Centre.
|The train stopped adjacent
to the cross-passage at PK 4131.
| The train driver was trapped in his
cab and the passengers could not be evacuated due to dense
| The French FLOR team entered the
Service Tunnel. One minute later, the UK FLOR team also entered
the Service Tunnel.
- Supplementary Ventilation
System had been reconfigured to move smoke along the South
Running Tunnel towards France.
- The train passengers were evacuated.
- The French FLOR team arrived at cross-passage
4131 and saw the evacuated passengers.
- The train driver was later rescued from his cab.
- The UK FLOR team entered the South
Running Tunnel to inspect the exact location and extent of
- It was found that the fixed tunnel equipment had been damaged
and five wagons were involved in the fire at the rear rake
of the train.
- Fire was confirmed between
cross-passage doors 4163 and 4201.
- In the following 5 hours, the fire was attacked by the
combined force of the French and UK firefighters.
- The centre of the fire was
extinguished. Minor fires were extinguished during the
- Smouldering debris continued to be dealt with until 03:00
on 20 Nov.
The fire caused considerable damage over 480 m long of the tunnel
Extend of Damage to Concrete Lining
Extreme damaged zone
50 m between
PK 4186 and PK 4191
- In many places, the lining thickness was reduced to an
average of 17 cm
- In a few places, as much as 40 cm thick concrete spalled,
leaving only 51 mm of concrete remaining and exploding all
- No damage to concrete grouting and rock
- The whole section was reinforced and rebuilt
Severely damaged zone
290 m between
PK 4180 and PK 4209
- In many places, the depth of concrete spalling was between
5 and 20 cm, exploding the first layer of steel reinforcement
- The lining was repaired without replacing the steel reinforcements
Substantially damaged zone
480 m between
PK 4172 and PK 4220
- Superficial damage to concrete in some places, but the
steel reinforcement was not exposed
- The lining was repaired without replacing the steel reinforcements
Besides the concrete lining, the cross-passages and Piston Relief
Ducts near to the fire, the walkways and the concrete track-bed
were largely undamaged.
In addition, the tunnel equipment over a considerable distance
was seriously damage by the high temperatures and smoke, including:
- Over 500 m of railway track and supporting track blocks
- Over 800 m of traction power catenary
- Several kilometres long of electrical supply and fibre optic
communications cables, together with some lighting systems, fire
detection stations, signalling systems, and electromechanical
equipment for cross-passages and Piston Relief Ducts
The fire had little effect on the front rake of the freight
train but the rear rake was very severely damaged. Ten HGV wagons
and their contents and the rear loading wagon were completely
destroyed. Three wagons and the rear locomotive were seriously
The 1996 fire highlighted the potential disaster of explosive
spalling behaviour of high strength concrete (HSC) in high temperatures.
During the fire, large quantities of concrete exposed to the
fire had spalled off from the tunnel lining. This resulted in
very fine concrete rubble collecting on the access walkway and
the roof of the HGV wagons. The consistently falling off of the
hot concrete debris endangered the life safety of the emergency
personnel who were carrying out the rescue and fire fighting
The extend of the concrete spalling was shown by the ultimate
collapse of the roof of some HGV wagons in a "V" shape
due to the weight of the collecting concrete debris. Thankfully,
the extensive spalling of the concrete lining did not endanger
the stability of the tunnel.
The experimental studies in history have shown that moisture
content, strength and stress levels are the main factors governing
spalling of concrete at elevated temperatures. Compared to normal-strength
concrete, HSC subjected to high temperature heating has a higher
susceptibility to explosive spalling. This may be due to the
- low permeability of HSC retains the moisture inside the concrete,
resulting in a high moisture content
- dense cement paste prevents heated moisture from escaping at
elevated temperatures, resulting in a high pore pressure
- HSC is normally subjected to higher compressive stresses than
lower strength concrete
Generally, a combination of pore pressure, compression in the
exposed surface region of concrete as well as internal cracking
are all required to cause explosive spalling.
Two possible ways of minimising the risk of extensive spalling
of concrete lining for tunnels are (for more information, please
see the Section on Concrete Materials):
- Providing fire-proof coatings to the exposed surface of concrete
which is unable to resist fire
- Adding polypropylene fibres into concrete which melt during
a fire thus creating paths in the matrix for water vapour to
It is important to take into consideration the actual or realistic
material behaviour in the design of the fire protection systems
of a tunnel to protect the integrity of the tunnel in a fire,
particularly for tunnels built through poor ground condition.
Sources of Information
- BBC News Online / World / Europe - UK Edition
- Department of Transport - Channel Tunnel Safety Authority (1997).
Inquiry into the Fire on Heavy Goods Vehicle Shuttle 7539 on
18 November 1996, The Stationery Office, London.
- Comeau, E. and Wolf, A. (1997). "Fire in the Chunnel!"
NFPA Journal March/April 1997, pp58-64.
- Kirkland, C.J. (2002). "The fire in the Channel Tunnel."
Tunnelling and Underground Space Technology, 17, pp 129-132.