Multiple burials revisited

There is quite a battle raging in the normally sedate world of avalanche research. On the one hand Team Backcountry Access says that true multiple burials are so rare that backcountry travellers should focus on shovelling and probing techniques, on the other side Manuel Genswein, avalanche educator and expert in multiple burial search techniques, accuses the other side of “statistical tricks” and says Backcountry Access are ignoring the “inconvenient truth” that the Tracker beacon is technologically“out of date”.

Although wary of the increasing complexity (and cost) of today’s avalanche beacons we shared Genswein’s worries about the statistical basis of the research. Fred Jarry of the ANENA (http://anena.org), the French Association for the Study of Snow and Avalanches has crunched their own extensive database with some interesting conclusions[1]. The ANENA receives some funding from ski resorts but can be considered independent.

Jarry analyzed 440 accidents between October 1999 and September 2007. It is impossible to separate true multiple burials, those where the victims are close enough together to require special search techniques, from their data. In 41% of the incidents there was no or only partial burial, in 47% of cases a single burial. 12% were multiple burials. Ignoring incidents where no-one is completely buried, and for which the statistical data is far from complete then multiple burials rise to 20% overall with 7% involving more than 2 victims.

There is a marked difference between ski touring and off piste skiing. Of the 112 recorded ski touring accidents 21% involved multiple burials. However if we separate incidents where the group is climbing the figure rises to 26% compared to 17% for descending. Genswein and Harvey[2] suggest that real multi burial scenarios are much more common for ski touring groups when climbing. This seems logical, it is much harder for a climber to escape a slide and for logistical reasons group members are frequently climbing above each other at the same time.

There were 135 off piste incidents and just 13% were multiple burials. Part of the difference is accounted by the fact that off piste skiers are nearly twice as likely to be alone but the risk of a multiple burial is almost twice as frequent for climbing groups.

So can we say that multiple burials are much more common than would appear from the BCA sponsored research and that any group not carrying the latest 3 antenna avalanche beacon with marking features is playing Russian roulette? Things are not quite so straight forward. Jarry went on to analyze how many of the groups were actually capable of mounting a search and rescue in a multiple burial situation. For the incidents analyzed the average burial depth was 120cm. That requires a tonne of snow to be moved to free the victim. To effectuate a rescue in the critical 15 minutes after burial at least two diggers are required[2]. For each victim there must be two people on the surface.

If we take ski touring groups 16% of skiers travel alone. In 54% of cases there were sufficient diggers for a single burial, in 22% cases enough resources for a double burial, in 6% of cases enough for 3 burials. Of course multiple burials are more likely in bigger groups but that still means that in just 6% of cases were ski touring groups able to mount an effective multiple burial rescue. 27% of accidents involved lone off-piste skiers. In 52% of cases there were enough resources for a single burial, 13% for two burials, 4% for 3 burials. That means that in around 3% of cases there were sufficient resources for a multi-victim rescue.

Without rejecting the advances in beacon technology there are some clear lessons. Ski touring groups should take particular care in route choice when climbing giving priority to low slope angles and ridges. Group size is important. Standard texts on backcountry travel suggest between 3 and 6 group members and this is confirmed by the data. Any bigger increases the change of multiple burials and becomes unmanageable. Less than 3 and there are insufficient resources to mount a self rescue. While ski touring groups may benefit from more sophisticated beacons - especially as outside S&R often take time to arrive on the scene of an incident, off piste skiers should travel in groups, observe and carry at least basic beacon technology. The Pieps freeride, BCA Tracker or Ortovox F1. The ANENA study supports BCA’s claim that freeriders in particular should focus on strategic shovelling techniques and safe travel procedures and worry less about the technology.

Further Information

[1] Jarry F. When do we dig? Snow and Avalanches, no 121, April 2008 http://www.anena.org
[2] Genswein, M. and Harvey, S., “Statistical Analyses on Multiple Burial Situations and Search Strategies for Multiple Burials.” ISSW 2002.
[3] Strategic Shovelling, the Next Frontier in Companion Rescue. Bruce Edgerly and Dale Atkins http://www.backcountryaccess.com/english/research/documents/EdgerlyAtkinsISSW06.pdf
[4] Multiple Avalanche Burials, rarer than you think http://pistehors.com/news/ski/comments/0817-multiple-avalanche-burials-rarer-than-you-think/

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