Where there's smoke…

时间:2019-03-08 08:14:04166网络整理admin

By Rob Edwards IMAGINE the horror. Driving with your family through a long tunnel, you suddenly hit a thick wall of smoke and slow to a stop in a line of traffic. Somewhere up ahead, a truck is burning. What do you do? Get out of the car and try to blindly fight your way through the scorching smoke to an exit? Or sit tight, in the hope that the smoke will clear before it kills you? In the past three months, hundreds of motorists have faced this appalling dilemma in Europe’s Alpine tunnels. Of the 42 people who died after fire swept through the Mont Blanc tunnel on 24 March, all but 7 had stayed in their cars. They were poisoned by fumes from the fire, which started on a Belgian truck carrying margarine and flour near the middle of the 12-kilometre tunnel between France and Italy. In the Tauern tunnel under the Austrian Alps, 12 people are believed to have died on 29 May when a truck carrying paint caught fire after a multiple vehicle pile-up near one end of the 6.4-kilometre tunnel. But dozens more managed to escape the smoke by walking the 600 metres to the near end of the tunnel—and a few even survived by making their way on foot to the far end of the tunnel over 5 kilometres away. Thankfully, in the context of the millions of journeys through the tunnels each year, the risk of death or injury is very small. Nonetheless, many transport experts fear the dangers are increasing. Until the disasters at Mont Blanc and Tauern this year, deaths in a tunnel fire had never reached double figures (see Table). One exacerbating factor, experts agree, is the huge increase in traffic using Alpine tunnels. The Mont Blanc tunnel was designed to carry 450 000 vehicles a year—yet in 1997 it was used by 1.1 million vehicles. The number of vehicles driving through the 16-kilometre St Gotthard tunnel in Switzerland, one of the world’s busiest, has more than doubled to 6.5 million a year since 1981, with the number of heavy goods vehicles (HGVs) tripling to a million a year. “We have to ensure that the safety of tunnels is improved,” says Dougal Drysdale, a fire safety engineer from the University of Edinburgh. “The fact that we’ve had two fires in such a short time is really quite alarming. It gives me the impression that standards are not being maintained.” The two disasters certainly have similar characteristics. Both tunnels are simple, long holes more than 25 years old, with two lanes of traffic moving in different directions. The fires both involved HGVs and reached metal-melting temperatures of over 1000 °C that made the identification of bodies almost impossible. The incinerated remains of the forty-second victim of the Mont Blanc fire were only found by police sifting through the wreckage six weeks later. As well as generating fierce temperatures and being hard to escape, tunnel fires are more dangerous because limited oxygen means they produce more carbon monoxide. A higher proportion of HGVs in tunnel traffic increases the risk of fires. An analysis published last year by the Permanent International Association of Road Congresses Technical Committee (PIARC), the world advisory body on roads, showed that the rate of truck fires in tunnels was much higher than that of car fires. In the Mont Blanc tunnel—before this year’s fire—there were 12.9 truck fires per 100 million vehicle kilometres compared with 1.5 car fires. Problems in HGVs’ electrical equipment and overheating in their braking and gearing systems often start the fires. These can ignite loads that burn much more fiercely than car fires. According to PIARC, a fire in a single HGV can release 30 megawatts of heat, compared with five megawatts from a large burning car. After the Mont Blanc disaster, Michel Charlet, the mayor of Chamonix on the French side of the tunnel, called for HGVs to be banned from it. The road industry defends the safety record of HGVs and disputes the need to transfer freight to rail. Hans Müller of the International Road Transport Union in Geneva points out that over 10 million trucks used the major tunnels in France, Switzerland and Austria without any fatalities in 1997 and 1998. This year’s disasters were “an unfortunate coincidence”, he says. “Tunnels are worth billions of pounds to the European economy.” However, Paul Scott of consulting engineers Ove Arup in London argues that freight should be transferred to rail because rail tunnels are “three or four orders of magnitude safer”. There is less risk of a collision, the drivers are more experienced and the traffic is easier to manage, he says. Three years ago, there was a serious fire in the Channel Tunnel, which started on an HGV aboard a train. It caused £200 million damage—but no lives were lost. Stuart Jagger of Britain’s Health and Safety Executive’s fire laboratory in Buxton near Manchester thinks this was because the Channel service tunnel provided people with a smoke-free escape route. Like other experts, however, Jagger does not believe that service tunnels are the answer in every case. A solution for single tunnels might be to bore a second tunnel to separate traffic going in opposite directions—and reduce the risk of collisions. It has the added advantage that if a fire breaks out in one tunnel, people can escape via cross passages to the other. But, like a service tunnel, it is very expensive. There may other, cheaper ways of reducing the fire risk. In 1991 the operator of the Mont Blanc tunnel, Autoroute et Tunnel du Mont Blanc, cut fire-proof shelters into the side of the tunnel every 300 metres. Unfortunately, two of those who died in this year’s fire were poisoned by fumes after they had sought refuge in the shelters. Another suggestion is to fit sprinklers at regular intervals along tunnels. But European road tunnel operators, concerned about the cost of such a move—and unconvinced of its effectiveness—have yet to show any great interest in the idea. Eurotunnel, on the other hand, is considering the installation of a “water mist” system on board its HGV shuttle trains. Some experts argue that a well-designed and well-operated ventilation system is the key to controlling the smoke from tunnel fires. “History shows that when such a system is not present or not used, the outcome is frequently disastrous,” says George Grant, an Edinburgh-based fire consultant. Others, however, point out that ventilation systems can fan fires by supplying them with oxygen. If ventilation is used to control fires, it has to be done in a coordinated way—which was not the case during the Mont Blanc fire. A preliminary report into the disaster by French government investigators in April said that, while French operators reversed the ventilation to suck the smoke out of the tunnel, Italian fans blew air in. Many experts believe the Italian authorities’ action made the situation worse at the French end: instead they should have sucked smoke out from their own side. There had not been any joint fire drills for 10 years, the report observed, partly because of “local personal conflicts”. While the experts debate the best methods of minimising the risks, cars and trucks continue to pile into the old tunnels that criss-cross the Alps. In fact, because Mont Blanc and Tauern are likely to remain closed for months, there will be much heavier traffic in the alternatives—the 12.9-kilometre Fréjus tunnel between France and Italy, and the 5.1-kilometre Felbertauern tunnel in Austria. Like Mont Blanc and Tauern, both Fréjus and Felbertauern are simple single-bore tunnels carrying two-way traffic. In a survey of 20 central European tunnels this month, the German automobile association, ADAC, rated Felbertauern as the most dangerous because it lacked emergency escape routes and had an outdated ventilation system. “I’m certainly keeping out of these tunnels in my car this year,