Education and equipment reduce Swiss avalanche deaths

There has been a significant drop in the number of avalanche deaths in Switzerland over the last 30 years despite a marked rise in the number of winter sports enthusiasts going outside of marked and secured ski runs. That is according to an article by theSwiss Federal Institute for the Study of Snow and Avalanches and published in the December edition of the Swiss Alpine Club’s house magazine.

Using their database of mountain and winter sports accidents the Davos based institute has analyzed the 30 year period from 1977 to 2006. Over that time 3434 winter sports enthusiasts were buried in 1619 avalanche incidents resulting in 703 deaths. The number of burials runs at around 35 to 40 per year, this figure hasn’t changed. However the number of deaths has dropped from 27 during the first part of the period to 20 over the last 15 years. There has been an increase in the number of skier triggered avalanches, this can be partially explained by better reporting of minor incidents.

The media talks a great deal about the dangers taken by off-piste skiers. Currently 60% of incidents involve ski tourers and 40% off piste skiers. There is a very slight trend towards off-piste, however ski touring incidents are more serious (more victims per incident).

There has been a significant decrease in serious accidents involving guided groups (UIAGM, ski instructors and qualified club ski leaders). Guided groups also appear less frequently in statistics dropping from 40% of incidents in 1977 to 20% today. It should be remembered that such accidents often have legal ramifications for the group leader. Better education and appreciation of avalanche risks by leaders accounts for part of this improvement.

The number of live rescues has increased. At the end of the 1970s 60% of buried victims died compared to 40% today. Where a victim is rescued by companions the mortality has dropped from 34% to 20% compared to 88% to 70% for organized external rescue. The biggest factor is burial time which has decreased from 150 minutes in 1977 to 80 minutes at the start of the 1990s to 30 minutes today. For beacon wearers, the overall mortality rate has dropped from 49% to 29%. The widespread adoption of avalanche beacons and the improvement in technology as well as better training accounts for much of this improvement. The average burial depth for fatalities has remained constant at 120cm and 70cm for survivors.

The debate over multiple burials looks set to continue. The study showed that the number of multiple burial incidents has decreased to just 16% of accidents since 2000. Only 5% of incidents had more than two victims. However no distinction is made in these figures for “true” multiple burials, where special techniques must be used to isolate signals from beacons. This drop can be partially explained by the size of groups involved in avalanche incidents which has decreased from 3.6 to 2.8 but also by better education about group management and route choices. The report suggests that back-country enthusiasts focus their search and rescue training on efficient single victim searching, shovelling techniques and first aid.

The study also looked at the number of incidents at individual risk levels on the 5 point scale. Although there has been a significant increase in incidents at Considerable risk (3/5) when this is normalized against the number of days at this risk level there is no discernible trend. Moderate and Considerable risks concern the majority of Swiss incidents however it would appear that back-country enthusiasts are not taking more risks than previously.

Further Information

The article was first published at the ISSW in 2008

Posted by davidof on Tuesday, 13 January, 2009 at 05:12 PM

I really enjoyed reading your post. Glad that I stumbled across your blog!

Posted by Snowboarding Expert on  Wednesday, 14 January, 2009  at 09:04 AM

David, thanks for another of your careful insightful summaries of helpful information about skiing. You are amazingly good at it.

I can’t say I would have predicted those results. The opposing argument is that as safety equipment and information improves, humans use it to go closer to the edge in raising the level of risk. But here I think that more people are getting out more often, but the overall burial rate is not rising.

I have imagined that the increased reliance on avalanche beacons leads to more people taking stupid risks with the justification that “it will be OK because I’m wearing a beacon”. But perhaps it’s more like that even if beacons were not sold as magical safety talismans, people who are open to taking stupid risks would just find a different justification.

The more detailed inferences are tricky to assess because we’ve got much more accurate and complete info about the negative outcomes than we do about the exposure base. Like here’s two “bias” trend factors which I’d _guess_ are in the exposure base through the period of the study: party sizes are generally getting smaller, and more parties are not “guided”.

But I’m not criticizing, because I don’t see how we’re likely to get much better data about the exposure base in the future—so might as well make inferences from what we’ve got.

It’ll be interesting to see what will happen to these trends in the next 10 years, with a whole new kind of information from user-supplied trip reports (and videos).


Posted by  on  Thursday, 15 January, 2009  at 04:03 PM

Reading the original paper was easier than I expected—good thing you posted the link.

Slight clarification:
The number of _complete_ burials per year does not show any trend over the period of the study.

I think the number of partial burials _reported_ does show an increasing trend (Figure 1 in the paper), but the authors interpret that as a changing trend in how incidents are reported and/or recorded (and I assume they are correct).

The authors are well aware of the problems with lack of accurate knowledge about the exposure base.

Their analysis of low versus moderate versus considerable risk levels was an interesting attempt, but I think it’s a very tricky question and I didn’t find it convincing. I think a more careful statement would be, “No definite evidence was found of some trend from 1988 to 2006 that recreationists are taking on more or less avalanche risk—but the exposure base and definitions are so sketchy that who knows.”


Posted by  on  Thursday, 15 January, 2009  at 04:46 PM

Actually I think the _overall_ data of the paper supports the idea that recreationists are taking on _less_ avalanche risk on a trend over the longer period from 1977 to 2006.  Simply . . .

More people per year are getting out there, but only the same number per year are getting completely buried.

This is independent of people getting better at using avalanche beacons, and independent of tricky questions of low versus moderate versus considerable.

It rests on three assumptions:
(1) number of complete burials is reported fairly accurately.
(2) true number overall serious avalanche accidents correlates with number of complete burials - (though there are several other ways than burial to die or get seriously injured from an avalanche)
(3) “true avalanche risk probability” correlates with true number of serious avalanche accidents - (the other possibility is that there’s a trend of recreationists taking on more “true avalanche risk probability”, but just getting very lucky in not suffering the consequences).
Actually the “true probability” for a specific ski tour on a given day is unknowable, but surely depends substantially on several factors other than the official risk level 1-5 number for the day.

I think those assumptions are reasonable for the data used in the paper.


Posted by  on  Thursday, 15 January, 2009  at 05:33 PM

Thanks for those thoughtful comments Ken.

> I can’t say I would have predicted those results. The opposing argument is that as safety equipment and information improves, humans use it to go closer to the edge in raising the level of risk.

I would have assumed the same. For example some studies show that helmet wearing, seatbelts, airbags all lead to people taking more risks. I’m not sure the Swiss data can necessarily be extrapolated to other areas though. My experience of Swiss skiers is that they are more risk averse/conservative than the French - there is less focus on extreme descents etc. It would be interesting to see the French / US figures to see if there is any trend.

It is interesting that the overall burial trend has not increased in line with the increase in skier numbers. This must be down to less risk taking as you say, but why? Again researchers like McCammon claim that as skiers gain knowledge they tend to take on more risk so you would expect burials to increase at the same rate as the increase in skier/days.

Posted by davidof on  Saturday, 17 January, 2009  at 07:09 PM
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