Avalanche airbags, training and risk homeostasis

You are standing at the top of a north facing bowl with your buddies. You pull your collar up to keep out the cold. The wind is blowing against your back, you can hear tiny snow crystals as they impact on your helmet. Below an untouched stash of powder on a 35 degree slope running out into woods. Perfect ski conditions. You don’t want to hang around. You agree with your friends to ski one at a time and wait at the tree line, a great spot to grab some video. Helmetcam… check, shovel, probe… check, beacon, uh oh.

avalanche airbag
Avalanche airbag survivor, photo D.Givois

In your hurry to get the first lift this morning you left it on the table. You tell your buddies you are going to bail, you’ll ski back down the ski runs and meet them in resort, maybe film a bit from the top as they go down first though.

You and your friends have just become victims of risk homeostasis. This is the theory that everyone has their own personal risk level. Reduce the risk in one area and they will compensate to bring the overall level back in equilibrium. Would you ski the slope without your avalanche airbag (referred to as ABS in this article) and beacon? Not likely!

Of course risk homestasis depends on being able to accurately assess what the extra risk is. In the above example what are the chances that the slope will slide? Alain Duclos, avalanche expert with the Chambery court in the French Savoie comments “there is a belief that we can predict avalanches. It is not true! We can simply predict the conditions that favour their release. There is a big difference.” Our bowl is the right angle and aspect and it is being wind loaded but what is the snow-pack like? Is there a dangerous weak layer in the first meter of snow that can collapse and trigger an avalanche as the skier heads down slope?

The second point, once caught and buried what are the chances of being rescued alive? Most backcountry travellers have the famous Brugger avalanche survival curve in their heads. That shows that 93% of skiers are still alive after 15 minutes burial. Sounds like pretty good odds. Our team have put some factors on their side. They intend to ski one by one and will wait out of the fall line. They also have the right search and rescue gear. However the reality is that only 50% of buried skiers equipped with a beacon are found alive. American avalanche expert Bruce Tremper argues that “avalanche beacons have probably killed more people than they have saved.”

Snowpulse user

What about ABS? It is known that the biggest factor in surviving an avalanche is not getting buried. This is the principal difference between a beacon - a search and rescue and frequently body recovery device and the airbag which is a survival aid like a life jacket. Statistics compiled by the SLF in Davos between 1991 and 2010 record 262 cases where ABS were used, in 255 (97.3%) the victims survived[1]. None of the victims suffered head injuries and 94% of injuries were to legs or arms or were minor. The 7 deaths concerned secondary avalanches, cliffs or large avalanches. Last season in France out of 38 uses of ABS 36 victims survived with no serious injuries.

Invented in 1985 uptake of the system has been comparatively slow until recently. This is partially explained by cost, weight and problems with carrying the gas cartridges on aircraft. However two recent court cases may practically mandate its use for snow professionals and possibly for guided groups.

There are now four different systems on the market aimed at ski tourers, the original Austrian ABS system, Snowpulse which we have covered extensively and offers more protection to neck and head. Backcountry Access who also sell the AvaLung introduced their own system last year and finally Mystery Ranch, based in Montana. There are also backpacks compatible with the ABS Vario system developed by French piste rescue services.

Lets look at professional use first. Introduced to France in 1995 the system has seen widespread use amongst piste services since 2003, particularly for avalanche control work. A key event occurred on the 19th of January 2004 when patroller Eric Peymirat was killed securing slopes close to the Col de l’Aiguille in the resort of Ste Foy Tarentaise in the Savoie. In October, 2008 the Limoges appeal court awarded damages of 40,000 euros to Eric’s parents. The court decided that Mr Peymirat had ample time to use an ABS, if he had been supplied one by his employer, before being buried and were impressed by the survival figures complied by the SLF. In Canada, the British Columbia Coroner’s Service has officially recommended that guiding operations use ABS. The recommendation is based on the case of a guide in Northern BC who survived an avalanche on the surface and was able to rescue his client who did not have an ABS.

Jean-Louis Tuaillon, piste director at Chatel and an evangelist for ABS use as well as a developer of the Vario system has analyzed accidents by piste patrollers in France. Over the last 6 years there have been 41 avalanches where piste patrollers were equipped with ABS systems. Given what we know about survival rates that is a significant number of lives saved along with a reduction in the severity of injuries. Compare that with 29 deaths between 1971 and 2006, Mr Tuaillon estimates 20 lives could have been saved by ABS during that period. The high mountain terrain where much avalanche control work takes place is an ideal environment for the ABS system. It seems clear that for piste patrollers, rigorously following an avalanche control plan, the ABS is a life saver and risk homeostatis plays no real role.

What about recreational skiers including guided groups? Unlike patrollers this class of user has a wide choice about routes or whether they ski or not.

On the 19th January, 2006 a guided group skied the Combe des Lanchettes. The avalanche risk was ⅘. The group were equipped with ABS but two young skiers were apparently unable to activate their systems given the scale of the slide and perhaps lack of sufficient training.

On the 1st January 2010 three skiers, including a local high mountain guide were killed by a massive avalanche, again in the Combe des Lanchettes. They had actuated their ABS but were buried under 6 - 10 meters of snow. The avalanche risk was ⅗.

There have been four ski related avalanche incidents involving fatalities so far in France this season, two of them with airbag users. On the 5th of December a small avalanche killed three ski tourers below the Col des Ayes in the Chartreuse mountains. Two of the skiers had airbags and at least one had been triggered. The skiers were carried into trees below the col and it appears that trauma was the principal cause of death. There was no avalanche bulletin issued for the day but rescue services and Meteo France had warned of a considerable risk after three major snowfalls in a week. On the morning of the slide strong, southerly winds were transporting a lot of snow onto north faces and the temperature had risen considerably over 12 hours.

On the 26th December a group accompanied by a ski instructor was hit by a slide in the Combe de Signal in Val d’Isere. The avalanche risk was ⅗ and the bulletin warned of slabs on most slope aspects especially above 2000m (the accident occurred at 2600m). Two of the group were taken, one was able to inflate her airbag and was buried but visible on the surface following a secondary avalanche. a second victim was unable to deploy his ABS and was buried under 75-100cm of snow. Despite a fast rescue by his group he died later in hospital.

AMGA certified ski mountaineering guide guide Don Sharaf is worried about the move to ABS systems becoming an industry standard without some consideration of their use. While the ABS keeps the victim on the surface it will also carry him with the debris flow (see Snowpulse video). A 1996 study by the SLF using dummies showed that the ABS equipped dummies ended up lower down the slope. A non-ABS victim who manages to release his skis will find it easier to get out of the moving snow (skiers and boarders really need to use releasable bindings in avalanche terrain).

If you are skiing in terrain where there are trees, cliffs then, Sharaf says “you want to get out of that debris as soon as possible”. The Col des Ayes incident may be such a case although it should be noted that a non-ABS equipped skier was also killed. Sharaf points out that “it requires split-second decision making and exceptional clarity to decide whether you should deploy an airbag while caught in the moving snow” but that ultimately it is the skier himself “who is the on-off switch”. Well that is apart from remotely triggered ABS.

Dale Atkins has raised an important point regarding AvaLung systems which appears to relate to the two incidents above where victims were unable to actuate their ABS. Dale says that AvaLung users must train with their system, say by rolling fast down a snow covered slope. Could similar advice apply to ABS? Would it make sense for ABS to design a training system, with the same trigger mechanism but no airbags, specifically for this use?

The French and Swiss figures speak for themselves. The ABS is a real lifesaver. However as the system moves into more widespread use (ABS have sold 50,000 systems over 25 years) the four incidents outlined above, with 6 deaths in 2010 in France, show that route choice can be decisive. ABS themselves highlight that “an avalanche airbag does not replace care and knowledge, it is a good compliment to the safety of back-country travellers.“

[1] Note that some of these skiers would not have been buried even if they had not been equipped with an ABS system. If we take the ANENA 2004-10 figures of 38% of avalanched skiers being completely buried then you probably have closer to a 1 in 10 chance of being killed using an airbag in a slide where you would otherwise have been buried.


The Avalanche Review, Vol 29. No 1. October 2010.
Neige et Avalanches. October 2010 no 131.

Posted by davidof on Tuesday, 28 December, 2010 at 06:19 PM

Excellent article. Quite a number of the 7 points mentioned in Ian MacCammons ISSW article on Heuristics come into play. In the end it’s always worth asking yourself if your decision would be different without probe, shovel,beacon,ABS.  It shouldn’t be but it often is.

Posted by Davy Gunn on  Tuesday, 28 December, 2010  at 06:56 PM

So many good points made so well, David. Very good overview of the “latest thing”. Let me try a different angle ...

Avalung. Most of the comparisons are between ABS versus Beacon. I’d rather see it compared ABS versus Beacon alone versus Avalung plus Beacon.

For me using the Avalung for several years, I think the advantages are: (a) less hassle in airline travel; (b) no danger of accidental deployment while say riding up a ski lift; (c) lighter weight and I can easily use it and backpack I prefer; (d) less subject to ...

“risk homeostasis”: I don’t think wearing the Avalung makes me more willing to ski more dangerous slopes, because it only helps if I first get buried. And getting buried seems like a pretty scary experience. The possibility that my buddies won’t be able to find me under the snow so it might take me two hours to suffocate to death instead of just twenty minutes is not comforting. Nor is the idea of survival with oxygen-deprivation brain damage.

ABS used by non-professionals I would suspect is going to increase the willingness to ride riskier slopes on riskier days, with the wishful thinking that “Not only am I not going to die; I’m not even going to get buried.”
Good that this article pointed out the negative possibilities.

Actually I don’t think most skiers are seeking for an “equilibrium” of risk. Most skiers most of the time just want steep untracked powder snow. If they could obtain that risk-free, that would be just fine with them. It just happens that the slope angles for best powder skiing are the same as for max probability of avalanche, and that (nowadays) the timing before most slopes get massively tracked up is before the snow has been able to go thru some cycles to stabilize.

Evidence of _lack_ of “risk homeostasis” among experienced skiers: (a) In areas with knowledgeable backcountry skiers (as opposed to off-piste skiers), the safer slopes tend to get skied earlier and more often. (b) As avalanche understanding and education has improved over several decades in Switzerland, the amount of backcountry touring has greatly increased _without_ a proportional increase in avalanche burials + deaths.

Let’s hope that ABS continues that trend.


Posted by  on  Tuesday, 28 December, 2010  at 09:32 PM
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