Cold comfort

时间:2019-03-08 08:05:09166网络整理admin

By Debora MacKenzie EVERY winter, thousands of skiers seek the thrills of untouched snow away from the beaten trails. But off-piste skiers risk being buried by an avalanche, and many have taken to carrying electronic transmitters that are supposed to summon help should the worst occur. However, recent studies suggest that their faith in the effectiveness of these beacons may be misplaced. Catastrophic avalanches that engulfed villages have hit the headlines in recent weeks. But most avalanches are triggered by their victims and most of those injured are skiers. In Switzerland, for example, 95 per cent of all deaths in avalanches were people skiing off-piste at the time. According to Georges Krüsi, of the Swiss Federal Institute for Snow and Avalanche Research (SLF) in Davos, off-piste skiers normally wear beacons to help locate them in the case of an accident. Each skier in a group sets their own beacon to transmit a signal at 457 kilohertz. If an avalanche buries some members, the others switch their units to receive mode, and then listen for the beeps emitted by buried transmitters. The signals become stronger as the rescuers get closer, and users are trained to search systematically in a grid pattern. But an analysis of rescue attempts using this method in the US since 1977 suggests that this is not very effective. The Colorado Avalanche Information Centre has found that professional skiers such as ski guides took 18 minutes on average to reach their buried companions, but only 59 per cent of victims were still alive when found. Ordinary recreational skiers—the vast majority of would-be rescuers—took an average of 32 minutes to reach the victims, and found only 32 per cent of them alive. “There is no doubt that a beacon is better than no beacon,” says Blyth Wright of the Scottish Avalanche Information Service. But the Americans concluded that “further technical developments of the transceiver are mandatory”. This year several manufacturers have put new beacons on the market, with small screens that display the direction and distance of the signal they are receiving. The SLF has evaluated the new devices, and Krüsi says they are “a step in the right direction”. But they are difficult even for professionals to use, he says, and so do not yet offer clear advantages over the old beacons. Currently the signals do not carry more than 50 metres. Longer-range beacons are being proposed to track skiers and hikers. Some parks in Canada are experimenting with giving hikers radio transmitters of the type normally used to track caribou,