BY THE end of the year, trains shuttling trucks through the Channel Tunnel will carry a novel water misting system that can automatically extinguish any fires that break out.
The system, the first in Europe, is designed to prevent a catastrophic fire like the one that broke out in November 1996 on a train carrying trucks through the tunnel. Putting out the fire took nearly seven hours, endangering the lives of dozens of firefighters and truck drivers and severely damaging the tunnel. It was six months before the tunnel got back to normal operations.
The report of the official inquiry into the fire was published in 1997. It made dozens of recommendations, largely aimed at improving the fire drill of Eurotunnel, the company that operates the tunnel and runs the shuttle trains that carry trucks and cars. However, a new analysis of the fire by consultant engineer Colin Kirkland, who was in charge of building the Channel Tunnel between 1986 and 1993, discloses details about the fire that were largely overlooked by the official report. His analysis appears in the journal Tunnelling and Underground Space Technology (vol 17, p 129).
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鈥淭here were lots of problems,鈥� says Kirkland. He says that one of key lessons to be learned from the incident was that there should be some way of controlling fires on trains carrying trucks, as there is for car shuttle trains. On these trains halon gas floods carriages once passengers have been evacuated. The official report made no such recommendation for truck shuttles.
At the time, the strategy for dealing with a fire in a tunnel was for the train not to stop but to leave the tunnel, so that the fire could be fought in special sidings at either end. But Kirkland points out that an unrelated safety system gave a false alarm and forced the burning train to stop in the tunnel.
The shuttle trains that carry trucks have jacks to stabilise the wagons while the 40-plus tonne lorries are being loaded. Sensors detect if a jack has not been raised, otherwise a train could be derailed if a hanging jack struck a rail.
But these sensors, says Kirkland, 鈥減roved unreliable, frequently giving warning signals [that were] later found to be incorrect鈥�. Eight minutes after the first smoke alarm had gone off, a jack sensor gave a false alarm and the burning train was stopped.
Eurotunnel鈥檚 firefighting strategy then hit further problems. The tunnel has a supplementary ventilation system for removing smoke, but there was a delay of 20 minutes in switching it on. 鈥淪omebody turned it on maximum,鈥� says Kirkland. This ran the risk of fanning the flames. It then took several more minutes before someone arrived who knew how to control the vanes of the fan so that it extracted as much smoke as possible while minimising the danger of accelerating the blaze.
But once the train had stopped it couldn鈥檛 be restarted, because heat and smoke had cut the electricity supply from the overhead power line. The supply in the tunnel is divided into 1200-metre sections. but, the train, which is 780 metres long, had ended up smack in the middle of the dead section. If it had straddled two sections, it might still have been able to move. 鈥淚t was Murphy鈥檚 Law,鈥� says Kirkland.
Many of the defects identified in the official report have been corrected. The ventilation system is now switched on as soon as a smoke alarm goes off. And the faulty jack sensors have been replaced.
The fire drill has changed too. If a fire breaks out, or a fire is suspected, the train is stopped and the truck drivers are evacuated from their carriages. Any fire will then be fought in the tunnel. The new water mist system will suppress the fire for long enough for the British and French firefighters to arrive.
Eurotunnel carried out tests of a water mist system last year in a mock-up of the Channel Tunnel near Stockton-on-Tees. The tests showed that a spray of droplets 90-micrometres across could cut the temperature of a fire raging at more than 800 掳C to around 50 掳C in five minutes, leaving only minor smouldering. And the mist鈥檚 performance wasn鈥檛 affected even when the fire whipped up gale force winds.