Who, what, why: How do airbags protect against avalanches?

Media playback is unsupported on your device
Media captionAn airbag in action

A party of about a dozen skiers in the Italian Alps deployed airbags after being caught in an avalanche. Some of them may have survived as a result - but how do they work, asks Tom de Castella.

The group of friends were off piste near the resort of Argentera when the avalanche struck. They were all wearing backpacks with an avalanche airbag. Two local guides were among the group.

One of them, Graeme Porteous, from Wimbledon, was hurled into a tree and died soon after alpine rescue workers arrived. But the others survived.

All the skiers managed to deploy their airbags, says Arnaldo Giavelli, the mayor of Argentera and also a ski instructor, who was quickly at the scene. None of them were buried by the avalanche, which might have been as a result of the airbags.

However, it was not a big avalanche, Giavelli says - Porteous was unlucky to be thrown into a tree. So it is hard to say for sure whether the airbags saved the survivors.

Research by avalanche expert Pascal Haegeli suggests they do save lives. The risk of burial under the snow was 47% with no or non-inflated airbag and 20% with an inflated airbag. A deployed airbag cut the risk of mortality from 22% to 11% in such cases.

The risk of avalanches is far greater off piste than on groomed slopes. Nigel Shepherd, chief mountain adviser for the Ski Club of Great Britain, says it's a "no-brainer" for off-piste skiers to use an airbag. The biggest problem is having time to deploy it. "Very often it's the last thing you think of when it hits you. And then it's too late - you can't get your hand up to pull the handle."

The airbag does not make the user float. It works according to particle physics, says Michael Vollmer, a product manager at Mammut, one of the manufacturers. It's like the Cornflakes packet where the big pieces rise up to the top. "It increases the wearer's volume. You become a bigger particle in this moving mass of particles."

It might stop you being buried under the snow - asphyxiation is the biggest cause of death in avalanches, according to Haegeli. But an airbag does not help with collisions against trees or if someone is thrown into a crevasse.

There are a number of different types and makes of the airbags. ABS systems have two bags - one packed into either side of the backpack. BCA Float systems have one large bag in the top of the backpack. Unlike car airbags which are triggered automatically, avalanche bags are typically triggered manually with a cord pull.

Former British alpine ski racer Konrad Bartelski is sceptical. "All these new bits of equipment that appear to make things safer reduce the fear factor. And being scared and respecting the mountain is the best way to be safe." If going off piste he recommends taking a guide and using a transceiver - a beacon which allows rescuers to find the wearer if they are buried. He fears airbags may lead to complacency and more risk taking.

Subscribe to the BBC News Magazine's email newsletter to get articles sent to your inbox.