The likelihood of surviving an avalanche depends on where you are when it happens. Canadian avalanches kill much quicker than their Swiss counterparts, possibly because of denser snow conditions, a new study finds.
During a complete burial (in which the head and neck are covered in snow and breathing is impaired) survival decreases over time. In the traditional avalanche curve, survival is more than 91 percent for up to 18 minutes of burial, though it drops steeply to 34 percent after 35 minutes have elapsed. These deaths are due to the lack of oxygen under the snow.
Some avalanche victims, the 34 percent who last longer than 35 minutes, don't suffocate, but instead die from hypothermia. These statistics, based on rescues made in Switzerland, are the basis of the international recommendations for rescue and resuscitation after avalanches, as well as the safety and rescue devices used by search crews.
To figure out if the Swiss data applied to other areas, Pascal Haegeli of Simon Fraser University in Burnaby, British Columbia, and his team looked at statistics from Canada. They analyzed data from 301 Canadian and 946 Swiss records of avalanches from 1980 to 2005.
They found that Canadian victims died much quicker than Swiss victims, though the survival rate is the same (46.2 percent of victims in Canada survived, while 46.9 percent of those in Swiss avalanches survived) because the Canadian avalanche response teams were quicker to find and extricate the victim. They responded in an average of 18 minutes post-burial compared with a 35-minute average for the Swiss.
For Canadian avalanches, only about 35 percent of people buried for 10 to 20 minutes survived, in comparison with about 70 percent in Swiss avalanches for that same period. This effect was especially abundant in the "maritime" climates, which are characterized by abundant snowfall and mild temperatures, resulting in denser (heavier) snow. The denser snow limits the oxygen available to the buried victim, while also putting more pressure on them, preventing chest movement, the researchers said. [What Causes Avalanches?]
"Although the 'survival phase' has commonly been described to be about 18 minutes long, our analysis shows that the first 10 minutes might be a more appropriate general guideline for Canada and other areas with a maritime snow climate," the authors write in the March 21 issue of the Canadian Medical Association Journal . So far this year, avalanches have killed 11 people in Canada and 7 in Switzerland.
The authors' suggestions include shortening the "survival window" and increased use of "avalanche airbags" (inflatable pillows that help the person stay above an avalanche) for backcountry skiers and snowmobilers and GPS sensors to help locate burial victims, though education and avoidance are most important.
"Given the quick drop in survival associated with complete avalanche burials, emphasis on education and avoidance of avalanches remains paramount for promoting safety during winter outdoor travel in mountainous terrain," the authors write.
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