Scientific American

Every winter the allure of skiing on deep, untracked mountain snow attracts skiers to backcountry areas. Yet the thrill of skiing in an off-the-beaten-path bowl with waist-deep powder comes with a risk of being caught in a dangerous, potentially life-threatening avalanche.

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Most experienced skiers pay close attention to avalanche safety and carry specialized equipment such as avalanche beacons, shovels and probes that can help in location and rescue. This season a new device has been added to the tool kit: an “avalanche air bag” equipped with inflatable bladders that fill instantly in the event of a snowpack slide. When an avalanche strikes, skiers can be carried along in a thunderous mass of snow moving up to 100 kilometers per hour down the mountainside. Death is usually caused by suffocation.

At the first sign of danger, a skier pulls a ripcord that activates a cartridge of compressed air or nitrogen, which inflates bladders within two or three seconds. Some brands use single U-shaped bladders that protect the back of the skier’s head and shoulders. Other manufacturers use dual bladders in case one is damaged or fails to fully inflate. The North Face ABS (air bag system) uses compressed nitrogen to inflate two integrated, high-volume air bags that keep the user on the surface of the avalanche by equalizing the volume and density of the victim relative to the surrounding snow. In general the bladders hold between 85 and 150 liters of air—enough to keep an adult skier near the surface of an avalanche slide. The bladders are designed to stay inflated for several minutes.

Keeping the skier near the rushing snowpack’s surface lessens the chance he or she will be be suffocated. The principle is the same as what keeps brazil nuts near at the top of a bowl of mixed nuts—bigger and less dense objects tend to rise to the surface. “Avalanche air bags are not flotation devices,” says Pascal Haegeli, an avalanche safety researcher atAvisualanche Consulting and an adjunct professor at Simon Fraser University’s School of Resource and Environmental Management in British Columbia. “They don’t work like a life vest that you use when boating. It’s not a buoyancy effect, it’s a sorting effect. The bladders make the skier a larger particle within the avalanche debris.” (This YouTube video provides an example of a skier deploying an avalanche air bag during a snow slide in the Snake River backcountry near Montezuma, Colo.)

Few air bag models are designed to deploy automatically, although some feature a wireless activation remote. This makes it possible for a skier in an emergency to inflate not only his air bag but also the air bags of other members of his group. Models vary sharply in price, anywhere from about $500 to more than $1,200, depending on the materials used and the features offered—the lightest backpacks are typically the most expensive.

The air bags have received credit for saving lives. Nearly a year ago, anavalanche on Stevens Pass in Washington State swept professional skier Elyse Saugstad more than 600 meters in 30 seconds. Saugstad credits her air bag with keeping her head above the snow slide, which killed three other skiers in her group.

Other ski experts confirm that they do help. “Although air bags don’t do anything to prevent trauma, they do prevent a lot of avalanche victims from death or injury from asphyxiation,” says Jonathan Shefftz, aNational Ski Patrol avalanche instructor who trained at the American Institute for Avalanche Research and Education. “If you can see part of the victim, that reduces or avoids the need to use a beacon search to find a buried victim. Avalanche air bags are not foolproof, but they definitely offer a very big measure of additional protection.”

Air bag–equipped backpacks are beginning to improve safety, Haegeli says, but they don’t eliminate the risk. “They were able to save some lives, but there were still fatalities even with fully deployed air bags,” he says.

The best way to avoid getting caught in one of these snow slides is to follow local avalanche forecasts, carry safety equipment and understand how to use them if caught in a slide.