INTRO: Sprinklers inside freight shuttle wagons are the favoured option for protecting the Channel Tunnel from the costly damage caused by the November 1996 fire. Richard Hope watched a full-scale test in a specially constructed wind tunnel
PERCHED INCONGRUOUSLY on a concrete apron behind Darchem Engineering’s works in Stillington, County Durham, is half a tunnel made of corrugated steel. One side is curved to match half the internal profile of a running tunnel under the English Channel down to the level of the walkway; the other is flat, representing the vertical centre-line of the bore.
One end of this unique structure is open. The other splays out to accommodate a formidable array of fans powered by diesel-alternator sets delivering 1·5MW. For this is a wind tunnel, and its sole purpose is to test the effectiveness of measures designed to avoid the structural damage which resulted in six months of single-track working through the middle third of the Channel Tunnel after the disastrous fire of November 18 1996.
Fire suppression needed
That fire started in a lorry trailer aboard a freight shuttle, and was well alight as the train entered the Tunnel. The French authorities decided it was arson, but no arrest followed.
Numerous technical and procedural changes have been made by Eurotunnel to reduce the risk of fire breaking out on a lorry, and to ensure the safety of lorry drivers who ride in a conventional passenger coach behind the leading locomotive. In particular, optical smoke opacity detectors on the loading wagons at the front, middle and rear of each freight shuttle - which had been slow to react to the 1996 fire - have been recalibrated and tested to the satisfaction of the Channel Tunnel Safety Authority. This involved test runs through the Tunnel using simulated smoke.
The most important procedural change is that, following a confirmed fire alarm, freight shuttles no longer attempt to reach the emergency siding at the destination terminal. Instead, the freight shuttle driver makes a controlled stop so that his passengers can be evacuated into the service tunnel - as eventually happened without serious injury in 1996. For Eurostar, passenger shuttles and through freight trains, drive-out-if-you-can remains the first option.
But this policy change leaves a burning train stationary in the Tunnel. One important lesson of 1996 was that by the time fire-fighters arrive on the scene, and evacuation of passengers from the service tunnel has been completed, the fire is likely to have spread to several lorries and be out of control.
Last time, the total cost to Eurotunnel’s insurers in physical damage and lost revenues exceeded £60m. To prevent a repetition, the company decided that some way of suppressing a fire on a lorry must be devised.
Do it on the train
Consultants Kennedy Donkin studied two basic ways of doing this. The first, which gained favour early in 1997, was the installation of fire suppression stations at about 5 km intervals. The shuttle driver would try to reach one of these, and passengers would be evacuated as water sprays fed from the fire main deluged the burning wagons.
This policy was adopted in the Seikan Tunnel, where emergency evacuation stations with water sprays were built at the two coastal shafts. They have since become tourist destinations in their own right, with timetable stops and guided tours (RG 12.90 p959).
Closer analysis revealed serious weaknesses in this option: