Snow business

 作者:祁叉壶     |      日期:2019-03-08 05:18:01
By Nancy Watzman in Denver SKIERS and walkers who get caught by an avalanche could be saved by a simple contraption that extracts air from the snow itself. Called the AvaLung, the device could help them survive being buried in the snow for up to an hour, by which time help may have arrived. Normally, the chances of surviving burial in an avalanche are slim. Approximately one-third of people caught in an avalanche are killed by injuries from rocks, trees, debris or the force of the snow itself. For the remaining two-thirds who are alive when the snow settles, survival is possible only if they are found and dug out quickly. After 15 minutes, there is a 90 per cent chance of survival. But after 35 minutes, suffocation will have killed 70 per cent of people who have been buried alive. In the tightly packed debris of an avalanche, victims typically have only a small pocket of air to breathe. The oxygen is rapidly used up, and replaced with carbon dioxide. Exhaled air also contains moisture, which condenses into water, then freezes in a suffocating “ice mask” on the victim’s face. But even avalanche debris contains 40 to 60 per cent air, and for light, powdered snow the figure can be as high as 90 per cent. But the mouth and nose simply don’t provide a large enough surface area to extract the air from the snow. What is needed is a broader surface. In a classic middle-of-the-night eureka moment, a possible solution struck Thomas Crowley, an occasional back-country skier and a medical professor at the University of Colorado in Denver. He conceived a device in which a broad, hollow chamber, covered by a filter, is sewn into the front of a jacket and attached to a breathing tube. To keep carbon dioxide levels down, one-way valves direct exhaled air to a chamber on the victim’s back, where it is vented. Crowley cobbled together his prototype from plastic tubing and a pair of nylon tights. Encouraged by the results, he built a workable device and licensed the technology to Black Diamond Equipment, a company in Salt Lake City, Utah, that makes mountaineering equipment. In August 1998, Crowley and Black Diamond tested the device on three male volunteers whom they buried in snow on Mount Hood in Oregon. Oxygen levels for two of the three remained above 90 per cent of saturation after they had been buried for an hour. For the third subject, the level fell to 81 per cent after 45 minutes, a result that testers blamed on a faulty valve. Other tests by the company have shown that volunteers maintain oxygen and carbon dioxide concentrations, blood pressure and heart rhythms at “acceptable levels” for up to an hour when using the AvaLung in conditions designed to simulate an avalanche. Rescue experts caution that the AvaLung is no substitute for shovels, probes, beacons and—most important of all—training. “I’m afraid that people think that the more they can festoon themselves with safety devices, the safer they will be,” says Don Bachman, executive director of the American Association of Avalanche Professionals. Says Crowley: