Let's say you're skiing in the backcountry, looking for some powder but instead, you trigger an avalanche.
If you have an avalanche air bag pack strapped to your back, you just yank the cord. That deploys the air bag, which keeps you close to the surface and easier to dig out, says Andy Wenberg with Backcountry Access, one of several companies making the devices. When deployed, his company's version of the air bag comes out like wings.
"The whole idea when you deploy that thing in an avalanche is you're avoiding burial death," he says.
They look something like car air bags, but they work on an entirely different principle. Car air bags lessen injury by stopping you from crashing into the dashboard. Avalanche air bags don't stop you from crashing at all. They keep you safe simply by turning you into a larger object.
"And larger objects rise to the top of avalanche debris," says Bruce Tremper of the Utah Avalanche Center. He says it's about the physics of granular flow.
"Take a bag of tortilla chips and, of course, you want the big pieces, not the little crumbs and so you shake the bag up and down, and the big pieces come to the surface," he says.
Geologists noticed that big trees and big rocks rose to the surface in avalanches. So why not make people bigger?
One reason avalanche air bags have been slow to catch on in the U.S. they've been popular in Europe for more than a decade is because the TSA doesn't allow passengers to fly with the canisters used to inflate the air bags. Ski resorts and backcountry guides are beginning to keep canisters on hand so people don't have to fly with them.
Amie Engerbretson, a professional skier, says she wears an air bag backpack whenever she skis into the backcountry. She needed it a couple of months ago near Alta, Utah.
"I made my turn, I felt the snow shift under my feet, and then I saw cracks visibly shoot everywhere. And that moment I immediately reached up and released my air bag," Engerbretson says.
The next thing she knew, she was being carried along. She came to rest at the bottom of a gully under 2 feet of heavy snow.
"Obviously it's scary, but without an air bag I probably would've been buried 5 to 7 feet deep, which is a very dangerous burial depth," she says.
Instead, rescuers used beacons and probes to find her and dig her out in less than five minutes.
Tremper says that if every backcountry skier, snowboarder or snowmobiler wore them, "they would probably save about half the people who would otherwise have died in avalanches; so they work pretty well." Since Christmas, avalanches have buried 15 people in the U.S.; eight have died.