Feb 27 2012

Canadian Study reduces Avalanche Survival Time

An updated study of avalanche survivability statistics, spearheaded by Pascal Haegeli, PhD and published in relative obscurity in the Canadian Medical Association Journal last year indicate that survivability chances are significantly lower than previously thought, at least in Canada compared to Switzerland.

Comparing Swiss VS Canadian avalanche survival rates over time.

For years avalanche educators have reasoned that the commonly accepted statistics derived by Brugger and Falk’s study of Swiss avalanche incident data did not accurately reflect probabilities for North America. The rationale was simple; nearly all the Swiss data was based on incidents above treeline while in the US and Canada skiing among trees is more common than not. As noted in the CMAJ report, “the universal validity of the [Swiss] survival curve and recommendations derived from it [were] unknown.”

Finally Dr. Haegeli decided to put the speculation to rest and the results are sobering. The commonly accepted survival phase for burial in an avalanche is about 18 minutes long based on Brugger and Falks analysis of 946 Swiss avalanche fatalities from 1980 to 2005. This more recent study of 301 fatalities in Canada suggests 10 minutes would be a more appropriate guideline, almost half the reigning mindset.

Breakout of Canadian survival curves by snow climate.

According to this study, if you’re buried in an avalanche your chances of survival drop precipitously – with survivability dropping below 80% after only 10 minutes. By the 15 minute mark you’re in the 50/50 range, and dropping fast. And if you happen to get buried in a moist, maritime snowpack, by 20 minutes you’re as good as dead.

Overall survivability is about the same for either country; 46.2% in Canada versus 46.9% in Switzerland. However, survivability over time drops faster in Canada than Switzerland. The equality in overall survival is attributed to faster extrication times in Canada due to companion rescue efforts. The 10 minute guideline means avoiding getting caught, or buried, through the use of airbag packs or other survival strategies. In the event people are caught and buried, efficient shoveling techniques are essential for survival.

In a related study 33% of non-survivors had major trauma, and two-thirds of these trauma related deaths involved collisions with trees. Within the dataset analyzed for this study, 18.9% of Canadian avalanche deaths were due to trauma, the rest to asphyxia.

Zooming in on the first hour of burial - Canadian survival curves by climate.

This study did more than just tabulate overall survival rates for avalanche victims, it also broke out the differences in survival rates for maritime, transitional, and continental snowpacks. Not surprisingly the survival rate was the lowest in a maritime snowpack (41.7%) versus continental (43.6%) or transitional (50.8%). Surprisingly the trauma rate in maritime was only 5% and the average burial depth one meter. The same average depth was noticed for a transitional snowpack, but the incidence of trauma increased to 30%. In a continental snowpack trauma accounted for 9.6% of deaths, but the average burial depth was deeper, 1.5 meters. There was also a higher incidence of snowmobile deaths (27.7%) in a continental snowpack compared to a transitional (19.7%) or maritime (11.1%) snowpack.

If that all seems like a lot to digest in such a short space, it is. The bottom line, you simply don’t want to get caught. Take an avalanche course to learn as much as you can to 1) avoid getting caught, 2) know how to avoid getting buried if caught (use an airbag pack), and 3) know how to search and dig so you can unbury a friend fast enough to save them if they are caught, and if you’re the one buried, how to survive long enough until they dig down to you (use an AvaLung).

Ski hard, play fair, and come back home.

Link to full article in CMAJ, March 2011 here.

© 2012