One thing that all infrastructure owners fear is fire in a tunnel.
Restricted access, the distance from emergency services, and the problems caused by trapped smoke and fumes are all the stuff of nightmares for the tunnel owner. As a result, they plan for it, practice dealing with it, and have all sorts of detection, fire-suppressant equipment and procedures in place to handle it.
The channel tunnel is no exception. At 31.4 miles long, it has the longest undersea portion of any tunnel in the world.
It also has plans in place to handle fire. It has a full-tunnel simulator in which its staff practice dealing with fires and, once a year, the tunnel itself is closed entirely overnight so that a full-scale practice can take place, complete with actors playing the part of hysterical or injured passengers.
While the last thing that tunnel operators like Eurotunnel want is a real fire, they are well-prepared for one.
Which is just as well, as they have just had their third. On 17 January, a smouldering load on a lorry aboard one of the heavy goods vehicle shuttles filled the tunnel with smoke and brought operations to a standstill. No-one was hurt and Eurotunnel’s safety precautions worked perfectly.
Exit via the service tunnel
The first indication that something was wrong came as a CO2 sensor triggered an alarm. While that is serious, a major incident is only confirmed if a second CO2 sensor also activates, which it did.
Once the alarm is raised, what follows is largely automatic.
If the train is close to the end of a tunnel it either continues onwards to the outside world or, if it has only just entered the tunnel, it stops and reverses out. However, in this case the train was too far from a portal to do that, so it was brought to a halt inside the tunnel.
The freight shuttles are 773 metres long (840 including locomotives). However, all drivers and crew are forbidden to ride in their vehicles and instead travel in a club car immediately behind the leading locomotive. So they are all in one place.
It is necessary, at this stage, to understand the layout of the tunnel. The two bores of the railway tunnel are 25 feet (7.6 metres) in diameter and approximately 98 feet (30 metres) apart. Between them runs the 16 feet (4.8 metre) diameter service tunnel. Cross-passages (11 feet / 3.3 metres in diameter) run between the service tunnel and the running tunnels every 375 meters with sealed doors on their outer ends.
The service tunnel contains a roadway which is used by rubber- tyred service vehicles. These have interchangeable payload ‘pods’ and are used for maintenance, people transport, communications and fire fighting/rescue. The larger type of vehicle can even utilise a buried wire guidance system at which time it is limited to 50mph.
So once a fire is detected on board a freight shuttle, the train is brought to a halt with the door of its club car in line with one of the access doors to the service tunnel. Each access door is appropriately marked by a signal board and the train driver parks alongside this marker, automatically placing the club car door in the correct place.
All passengers are issued with smoke hoods to protect them from the effects of smoke inhalation and from getting particles in their eyes. They are then guided off the train onto the walkway that runs the full length of the tunnel, and then through the door into a cross- tunnel and thence into the service tunnel.
The service tunnel is maintained at a higher air pressure than the running tunnels. Hence, once a connecting door is opened, the air blows out of the service tunnel creating a smoke-free ‘bubble’ around the door.
The locomotive has a connecting gangway through to the club car, so the drivers can also exit the train that way. In the recent incident, 38 passengers and four Eurotunnel staff were safely evacuated from the train.
First and Second Lines of Response
Once the train is stationary, more sensors detect how far down the train the fire is. A high-pressure water ‘mist’ is spayed from the tunnel’s fire mains to both damp down the fire and also prevent oxygen being sucked into the fire down the tunnel (pictured above).
If the fire happens to be adjacent to the club car, the hoods will also protect the disembarking passengers from the high- pressure spray. However, in this recent incident, the site of the fire was part-way along the train, well away from the club car.
Fire officers from the First Line of Response teams constantly patrol the service tunnel, checking equipment and monitoring operations. They can therefore quickly be on the scene of an incident – they don’t have to come into the tunnel from one end. These first responders are backed up by a Second Line of Response team.
The tunnel is divided into English and French sections halfway across. There is even a line painted on the wall to show the notional border. As the latest fire occurred south of that line, the incident was handled by French fire service personnel and paramedics.
The response teams extinguish any remaining fire using hoses plugged into the fire main using hydrants located at the cross- tunnel access doors. The ‘fire engine’ pods on the service vehicles include the equipment and chemicals for producing foam if it is required, and they also carry dry- powder fire extinguishers, so most types of fire can be handled.
While the fire is being extinguished, the response teams also check the entire train for other problems. If any further people are encountered, for example illegal stowaways, they are gathered up and moved safely into the service tunnel. None were discovered during any of the incidents that have happened so far.
Inspection and rectification
Once the fire is out, and the rescued passengers and crew have been taken to the terminal for medical checks, the train and tunnel is inspected by the accident investigation team. Again, in this case it was a French team.
As access is limited, and it is difficult to get a good look at the tunnel lining with the train in the way, it won’t be long before the train is removed. Eurotunnel has several diesel-powered shunters fitted with exhaust filters which it uses for train recoveries.
With the train out of the way, engineers can inspect the tunnel lining properly. On this occasion, a few pieces of equipment, including elements of the catenary, had to be replaced due to smoke damage and then the whole tunnel needed a good wash down using high pressure hoses. Twenty-four hours later the tunnel reopened.
Compare this with the situation in September 2008. Once again no-one was injured (although
a few people were treated for smoke inhalation) but that fire caused €60 million of damage and closed the north tunnel bore for four months. Almost everything in the tunnel – communications, signalling, sensors, track, overhead wiring, water mains, drainage, access doors and even the concrete lining – had to be replaced.
So, even though Eurotunnel is well prepared for another fire if one should break out, it won’t stop management praying that it will never happen again.