Skiing off piste comes with risk, not least being caught in an avalanche. But wearing a backpack that incorporates an avalanche airbag has been shown to save lives by preventing burial, so more and more people are wearing them, even though, buying one is a major investment.

Costing upwards of £400, they are certainly one of the most expensive items a skier or snowboarder will buy and hope never to use. Here we answer FAQs and round up latest models.

Why do I need an airbag?

In an avalanche, larger objects rise to the surface, while smaller objects sink to the bottom. An airbag system incorporated into a backpack, with a large balloon or balloons that inflates at the pull of a cord, is designed to make the person wearing it larger so that they naturally rise to the surface of the snow.

The Arc'teryx Voltair avalanche airbag is inflated by an electronic blower Credit: © 2015 Angela Percival ALL RIGHTS RESERVED/Angela Percival

How effective are they?

Avalanche airbags are designed to prevent the wearer from being buried, which is key to survival in the event of an avalanche – suffocation is the main cause of death. And they have been shown to work effectively. The latest research is a 2014 study that looked retrospectively at avalanche data from around the world between 1994 and 2012, in which at least one person was wearing an airbag. It found that those wearing an inflated airbag had an 89 per cent chance of survival, compared to 78 per cent for those who were not.

This means that wearing an inflated airbag improved the chance of survival by 50 per cent. This is an impressive figure –however, the study also found that 20 per cent of people wearing airbags hadn't deployed them, for reasons including simply not pulling the trigger or having an incorrectly set up system.

The study, which was conducted by experts from avalanche research organisations in Switzerland, France, Italy, America, Austria and Canada among others, also found that the effectiveness of wearing an airbag is reduced by outside factors – such as the size of an avalanche, and whereabouts in its path the victim is caught.

Can I practise using my airbag?

Most airbags' balloons can only be deloyed once before the gas cylinder or cylinders that power them need replacing, however it may be possible to practice pulling the trigger without inflating the balloon, so a new gas cylinder isn't needed. A couple of newer systems are powered by battery-powered electronic blower, which makes realistic practice easier. Practice is essential so that pulling the trigger will be instinctive in an emergency – reactions are often affected by distress. It's also important to become familiar with the inflation process and the workings of the backpack – including set up and packing down – before hitting the slopes. The airbag system should also be tested regularly – at least once a year – to ensure it’s working correctly.

Does an airbag make an avalanche transceiver less necessary?

Anyone going off piste should wear an avalanche transceiver, and also carry a shovel and probe. In some ways this essential kit is more important than an airbag, because rescue teams can use the signal from the transceiver to find people if they are buried. It also means those in a group who aren't buried can assist in finding others. As with the airbag, it's important to practise using a transceiver so that it will be second nature in an emergency.

How do I replace my cylinders?

Most airbag systems use gas cylinders/canisters to inflate the balloons. These may not automatically be included in purchase of the system but come separately, with the option to buy steel or lighter carbon cylinders. These cost from around £90 each for steel, £100 for carbon. In general, once empty they need to be exchanged or refilled by an approved dealer (for around £20), although some can be filled at home or at other outlets.

Can I take it on a plane?

Probably is the short answer. The International Air Transport Association says that carrying an avalanche airbag backpack is allowed as long as it meets its guidelines and is packed in such a way that it won’t be accidentally triggered. To be sure, look at how the particular airbag can be made fly safe – they vary – and check with the airline at least two weeks before flying.

Here's our pick of the latest models

All prices include backpack and airbag system, and gas cylinder if needed.

Best for ultra lightness

Ortovox Avabag Ascent 30L (£570)

The tiny Ortovox removable system is extremely light at 690g (1kg including carbon cylinder) // Can be pulled without cylinder for training // Balloon’s welded seams keep it compact // Avabag unit works with other Ortovox backpacks // Total weight including backpack 2,170g.

ortovox.com

Best for relaxed flying

Scott Backcountry Guide Alpride 30L (£620)

Scott’s removable system uses two disposable, affordable cylinders (£35 a set) // These are similar to those in life jackets and allowed in hand baggage // System weighs 690g; 1,130g including cylinders // Works with other Alpride ready backpacks // Total weight including backpack 2,690g.

scott-sports.com

Best for travelling light

Mammut Ultralight 3.0 20L (£500)

The 3.0 removable system is Mammut’s smallest, lightest yet // Weighs 1,010g with carbon cylinder // Square balloon inflates behind head // Includes test trigger for training without inflating // Works with other Mammut backpacks // Total weight including backpack 1,510g.

mammut.ch

Best for game-changing tech

Arc’teryx Voltair 30L (£1,315)

Six years in the making and launched in 2015, Arc'teryx's system uses an electronic blower powered by a cold-resistant rechargeable battery to inflate the balloon // Can be used more than once in an outing // With no cylinders to refill, it’s easy to do realistic practice // Balloon shape allows good peripheral vision when inflated // Rather than tucking away, trigger handle twists 90 degrees to lock/unlock and feels different each way round // Battery easily disconnected for flying // Total weight including battery 4,290g.

arcteryx.com

Best for dual bag reassurance

Arva Reactor 32L (£565)

The balloon on Arva’s removable system inflates behind the head and around the pack // Its wide shape is designed to encourage upward movement // Balloon has two chambers to improve reliability in case of a puncture // This construction also improves shock absorbency // At 790g for the system - 1,100g including carbon cylinder - it weighs less than more traditional two-balloon systems // Can be transferred to different-sized Arva Reactor backpacks // Total weight 3,140g.

arva-equipment.com