The effectiveness of avalanche airbags.

As a mountain and ski guide in St. Anton we  have the goal to provide the highest safety standards possible for our clients.

Of course the main thing is the right guiding style in combination with the avalanche risk level – groups size – weather- skiing level and many other facts. In the other hand we can help people to pick the right equipment like skis, helmet, avalanche transceiver and other safety gear.

The avalanche airbag was a revolution in how to avoid and avalanche burial and is the only rescue kit which is working on the burial aspect.

The following article is very specific and my English is not very scientific but anyway I tried to do the best to translate this article which was in the magazine “Berg und Steigen”.

 

Conclusion first :-)

The statistic risk of a critical burial is

 

• 47% for victims without airbag
• and 20.1% for victims with inflated airbag.

 

The effectiveness of avalanche airbags.

 

Which benefit has an avalanche airbag?

In addition, there are several studies: some by manufacturers, others are not quite up to date, most are not comparable because different numbers where used in the studies. Haegeli Pascal and his team of authors have analysed, evaluated and

presented it in an international study, the effectiveness of avalanche airbags with the latest data.

 

From Pascal Haegeli, Markus Falk, Benjamin doubt,

Emily Procter, Frédéric Jarry, Spencer Logan, Kalle

Kronholm, Marek Biskupic, Hermann Brugger

 

In the last five years, avalanche airbags spread rapidly under recreational athletes as ski tourer, freeriders or mountain guides. A few years ago only a few different airbag models where available on the market.

In these day’s skiers can choose now between different models from several manufacturers.

The avalanche airbag has the potential to save an enormous number of human life.

The avalanche airbag is unique as an avalanche emergency equipment, because only the airbag can avoid full body burial – the main reason for the death of most avalanche victims.

Some avalanche organisations recommend the avalanche airbag therefore also as a useful adjunct to standard avalanche emergency equipment with beacon, shovel and probe.

 

While the underlying mechanisms for the effectiveness of avalanche airbags with mathematical study’s and field tests convinced, is the precise impact on the death rate (or mortality) still much debated. Manufacturer provide avalanche airbags happy as the ultimate avalanche emergency equipment represents (eg “97% chance of survival”, “8 times safer!” 2), while prominent avalanche instructors see this marketing as contradict. They say: the airbag prevents out of 100 avalanche deaths probably less than 10. Because both sides claim that their analyses are on solid based data and confirmed with statistics, it is for the laymen difficult to fathom what is right now.

 

A clear and represented presentation of the real influence of airbags is extremely important because survival statistics are the most important criteria when buying a avalanche airbags.

(see study by Christie, 2012).

There are a numbers of independent statistical comparisons to clarify the effectiveness of the airbag. The most famous is the analysis Brugger et al. (2007). Because of their elderly age and the rather limited number of analysed accidents with avalanche airbag is the validity of this study limited, and therefore must be interpreted cautiously.

The aim of this article is the effectiveness of avalanche airbags to illuminate up to date. We refer in this article of the published results of a recently

Study in the journal Resuscitation (Haegeli et al., 2014). We don’t want to simply reflect only the results of the study, but take the opportunity, the problem of statistical evaluation of avalanche emergency equipment to describe in more detail.

 

Mortality, mortality difference and mortality ratio

In principle, it is important in the interpretation of statistical information on the effectiveness of emergency equipment to consider always the following aspects:

 

• Which question we try to answer?
• On what data the analysis relies?
• What assumptions were made during the analysis?

 

Without a clear understanding of these aspects have statistics – although perhaps technically correct – only a small influence. This additional information is crucial for a meaningful interpretation of statistics and a realistic picture of the effectiveness of the emergency tool (avalanche airbag).

 

So first decide specific question.

We think that the following questions are the most interesting:

 

• How does the use of an avalanche airbag influence the death probability

in a serious avalanche detection?

 

• What proportion of avalanche deaths could be prevent by have a wide spread usage form avalanche airbags.

 

The statistical metrics answer these questions, the mortality difference for the first and the mortality ratio for the second question. These two measures are closely related, but offer different perspectives. It is therefore important to understand their differences exactly.

We now use the results of Brugger et al. (2007) to

to explain these two statistical metrics in detail. The record this study contained is information over 1504 avalanche victims, the outdoor terrain in Switzerland and Austria were recorded between 1990 and 2005 by avalanches. There were 35 victims equipped with avalanche airbag.

If we normalize these acts they show that out of 100 involved people survived 81 persons without airbag (control group) because they either were not buried or rescued in time and in addition were not injured fatally. This corresponds to a death probability or mortality of 19%. Of 100 people involved with airbag (treatment group) survived 97 which corresponds to a mortality rate of 3%.

Brugger et al. (2007) shows that the use of a avalanche airbag mortality significantly decreased by 16 percentage points from 19% reduced to 3%.

This is called mortality difference.

The mortality ratio in the study by Brugger et al.

(2007) is 15%, which means that out of 100 avalanche deaths without

Airbag 15 victims would have died anyway even if all had been equipped with an avalanche airbag. In other words, the use of avalanche airbags of 100 deaths can prevent 85.

 

Only relevant cases

The currently available studies are mainly based on a European record, the airbag manufacturer of ABS and the WSL Institute for Snow and Avalanche Research SLF were combined together. This data set includes a wide range accidents of large avalanches with several burials up to small accidents with individual victims or concerned that the person could escape avalanche burial.

A detailed description of the specific selection criteria is therefore extremely important for the interpretation of the results.

One aim of our study was the compilation of a larger, geographically broader and more focused on the effectiveness record. We investigated for all existing avalanche accident reports with at least one person involved with airbagfrom sources in Canada (Canadian Avalanche Association), France (Association Nationale pour l’Etude de la Neige et des

Avalanches), Slovakia (avalanche prevention center), Norway

(Geotechnical Institute Norway, Red Cross Norway),

Switzerland (WSL Institute for Snow and Avalanche Research SLF) and the USA (Colorado Avalanche Information Centre).

To ensure that the results of our analysis

represent truthfully the effect of airbags, we only took relevant

avalanche observations with the potential for a complete burial

in our data set. We have achieved that

by only taking accidents with avalanches of size class 2 and higher

and only avalanche victims who were seriously in the avalanche

involved (were involved in the avalanche flow properly or

hit by the avalanche from above and partially or completely buried). Avalanche victims, only close to the avalanche or stopped in the avalanche or even were able to ski out of the avalanche, were from the data set excluded as an airbag in these cases, would not has the opportunity to influence the outcome of the accident. The resulting data set contained 245 accidents with 424 seriously people involved. 264 (58%) of the victims were involved with an inflated airbag, 61 (14%) had an airbag which was not inflated and 117 (28%) were not using an avalanche airbag.

 

What have we found out?

The statistic risk of a critical burial is

 

• 47% for victims without airbag
• and 20.1% for victims with inflated airbag.

 

The mortality is determined by the burial grade and also the avalanche size and significant mechanical injury. The statistic mortality is 43.8% for critical trapped victims and 2.9% for non-critical buried avalanche victims.

The calculated mortality without an airbag is 22.2%, while with inflated airbag 11.1%. The resulting mortality difference is 11 percentage points (95% confidence interval is

-4 to -18 percentage points) and the adjusted mortality ratio is 0.5 (95% confidence interval 0.3 to 0.7).

 

That means that of 100 victims without an airbag, which were seriously involved in an avalanche accident, 22 were killed and 78 survived because they had no serious injury, not been buried or were rescued in time. Out of 100

Victims with the inflated airbag 11 people would die, because they are buried with inflated airbags or be fatally injured.

This means that 11 additional people – equivalent to the half of the avalanche deaths – would have survived because of to the avalanche airbags. This effect is indeed significant, but not as big as before believed (-11 percentage points compared to -16 percentage points in Brugger et al., 2007). In addition, the mortality of airbag users

significantly higher than previously reported (11% vs.

3% in Brugger et al., 2007). Although this difference is partly generated by the fact that our analysis of large avalanches is focused with several people involved, it is clear that avalanche airbags not guarantee your survival.

Even if all the victims in the existing record had used an inflated airbag, would be one of nine Victims died.

 

How is it with non-inflated avalanche airbags?

Until now we considered only the benefit of inflated airbags. The 11-percent point reduction in mortality is the best case effect when the airbag is inflated. Past studies have shown, that not inflated airbags are a serious problem.

These concerns are confirmed by our study. According to our entire data set of avalanche airbag users is the rate of the deflated airbags around 20%

(61 of 307) – as in the study by Brugger et al.

(2007). Therefore not inflated airbags lead to a reduction the mortality reduction from 11 to 9 percentage points (that is, 80% of 11 percentage points).

 

What are the reasons for not inflated airbags? Of the considered cases was information from 52 accidents available:

 

• 60% of the airbags were not initiated by the user (of the 52 cases which were not inflated)
• 12% maintenance error (eg cartridge is not installed correctly)
• 17% device error (eg problems when revisions design or in production led)
• 12% destruction of the airbag during the avalanche

 

In relation to the total number of airbag users, the destruction rate was

2% (6 of 307) and the error rate in devices

3% (9 of 307).

 

However, we found a significantly lower non-trigger rate for professional avalanche professionals (eg guides or patrollers) compared to recreational athletes (5% versus 14%). This indicates that training and more familiarity with the airbag and the trigger mechanism can bring substantial improvements in use.

 

What about risk compensation?

• Do I know my rescue kid? Do I know in general, that it is there?
• Applies me the rescue equipment negatively, physically and / or mentally?
• Is the effect of the rescue equipment directly to the motivation or the goal of my activity connected?
• How much control do I have over my actions?

Can I change my actions at all, if I want?

 

Avalanche airbags seem to score in all four characteristics:

• It is difficult to hide the fact that we carry an air bag,

: every time you take the backpack off or redress,

you will be remembered. In addition, the airbag needs regular attention during a tour.

• airbags are expensive and heavy. The handling on a tour can be a challenge.
• If the main motivation of a tour is skiing downhill difficult and steep slopes, then the Benefit of the airbag comes just right
• While recreational athletes have freedom and control of action, professional avalanche patroller and mountain guides are more bounded.

 

From this list of characteristics we can conclude that the potential for risk compensation under airbag users clearly exists, especially among recreational athletes who are primarily interested in the athletic aspect of the sport.

This means that the personal safety income which is made by an airbag is rapidly destroyed when the users therefore betakes in trickier terrain where larger avalanches are likely.

 

Conclusion

What are the main conclusions from the study?

• Airbags are a valuable avalanche emergency equipment, but the impact on mortality is less than assumed and survival is not guaranteed.
• Avalanche victims, which are seriously caught by an avalanche of Size 2 or bigger, the risk of death with an inflated Airbag decreases from 22% to 11% . This means, that inflated airbags can prevent from about half of all deaths.
• Not inflated airbags remain the main limiting factor of the airbag. The observed non-trigger rate over all cases is 20%.

 

• 60% of cases of non-inflated airbags go on a lack of activation back by the user. Familiarity with the release procedure and proper maintenance are important