New study suggests that North American Avalanche survival time is half what was previously thoughtPosted: March 7, 2012
Ten minute survival in western wet snow is shown by the study.
Dr. Pascal Haegeli, a researcher from Vancouver BC has recently published a study in the Canadian Medical Association Journal titled “Comparison of avalanche survival patterns in Canada and Switzerland.” There are several notable things to take away from this study.
1. The survival time for a victim in an avalanche has been 18 minutes based on a study done in Switzerland in 1998. (Falk M, Brugger H, Adler-Kastner L. Avalanche survival chances. Nature 1994;368:21.) This 1998 study is not being dismissed. Differences between the types of snow, terrain, etc. are the cause for the discrepancies between the two studies.
This study says that avalanche survival time is probably only Ten (10) minutes.
The Swiss study developed the avalanche survival curve based on the amount of time a person was buried.
The probability of survival remains above 91% during the first 18 minutes of burial (“survival phase”). This phase is followed by a precipitous drop to 34% between 19 and 35 minutes be – cause of asphyxiation of most people (“asphyxia phase”). Between 35 and 90 minutes, the survival curve levels out (“latent phase”) because of the survival of people with patent airways. Thereafter, survival drops again as those buried eventually succumb to lethal hypothermia complicated by progressive hypoxia and hypercapnia.
2. There was no statistical difference between the overall survival rate of the Canadian study (Haegeli) and the Swiss study (Brugger).
…the Canadian survival curve showed lower chances of survival at all burial durations compared with the Swiss survival model, with a quicker drop in survival in the first 35 minutes and poorer survival associated with prolonged burials.
3. Most Swiss avalanches occur above tree line. Most North American avalanches occur below the tree line. Trauma fatalities are significantly greater in North America.
In the Canadian sample, trauma accounted for more than half of the deaths among people extricated in the first 10 minutes (Figure 1), which highlights the strong influence of trauma on the early phases of the survival curve. The probability of survival at the end of the first 10 minutes was 77% in the overall survival curve for Canada, as compared with 86% in the asphyxia-only survival curve.
4. There were statistically different survival chances between different climates in North America. Western (maritime) snow climates had shorter overall survival times. Western snow climates are characterized by wetter, heavier snow.
The survival curves for the transitional and maritime snow climates were characterized by a considerably earlier drop in survival compared with the curve for the continental snow climate.
The study also offered speculation that heavier denser snow prevented chest movement preventing the victim from breathing if buried.
Snow density is defined as the overall mass of snow per unit volume (kilograms per meter cubed). Typical densities of seasonal snow vary from 30 kg/m in dry, newly fallen snow to 600 kg/m in wet spring snow.
These results highlight the importance of prompt extrication by companions, especially in areas with a more maritime snow climate. 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.
5. The study recommended that Airbags and Transceivers be used as they offered the best options to speed up rescue.
The use of avalanche airbags to prevent burial and avalanche transceivers to speed up the locations of buried avalanche victims are recommended. Both of these safety devices have been shown to reduce mortality significantly.
The study had numerous interesting facts about avalanche burials.
The two longest burials among survivors in the Canadian sample (120 and 300 minutes) both occurred in urban settings, whereas the maximum burial time among survivors in a remote setting was 55 minutes.
For other articles on Avalanches see:
See this article by Earn Your Turns: Canadian Study reduces Avalanche Survival Time, http://www.earnyourturns.com/9079/avalanche-survival-time-reduced/
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