Avalanche airbags do not float the wearer to the surface. Many pack manufacturers have begun to feature integrated that quickly inflate with the pull of a handle near the chest and help float the pack’s wearer to the surface of moving avalanche debris.
Snow airbags inflate using a cylinder of either compressed nitrogen or compressed air or a battery-powered electric fan. Think of these airbags as the avalanche equivalent of a personal flotation device (PFD, a.k.a. life jacket).
But there are some important differences:
1. Unlike with most PFDs, the wearer needs to pull a handle on the pack shoulder strap, which inflates the bags on the outside of the pack. According to the latest peer reviewed study about 20 percent of airbag users either did not or were unable to deploy the airbag. Thus, it’s important to regularly practice deploying the airbag.
2. Do not float the wearer to the surface like a PFD does. Instead, they work through inverse segregation in granular flow, meaning that when particles of snow are bouncing around in a moving, larger objects rise to the top. Assignment: go shake a bag of potato chips to watch the large chips rise to the surface and the crumbs sink to the bottom. It sounds sketchy, I know, but this airbags actually work quite well and float quickly in moving debris.
3. Do not work if the avalanche debris is not moving fast enough or far enough for the particles of snow to bounce around, jostling each other (granular flow).
4. They are generally ineffective in terrain traps where avalanche debris piles up quickly and deeply, nor do they work when a secondary avalanche, or a secondary wave of the same avalanche, piles additional debris on top of victims after they come to a stop, leaving them completely buried, often very deeply.
5. Similar to a PFD, avalanche airbags generally do not protect against the trauma of hitting trees and rocks on the way down. About a quarter of avalanche victims die from trauma. In runouts with lots of obstacles to hit on the way down, a much higher percentage die from trauma than other causes.
A pack fitted with an avalanche airbag will quickly inflate when the wearer pulls the handle on the chest strap. The airbag makes you into a larger, more buoyant object, which floats to the top of debris.
In the early days, marketing by some this airbag manufacturers on their effectiveness was overly optimistic—advertisements like “97% effective” or something similar. The big problem with this number comes from the earliest studies of effectiveness, which included everyone who was caught in an avalanche and was wearing an airbag pack, including many people who were unlikely to ever have been buried anyway due to the type of (small and unlikely to bury someone) or people who were able to escape off a moving slab.
A tagline like “97% effective” does not account for the fact that approximately 90 percent of people who get caught in avalanches will survive irrespective of whether they are wearing airbags. Luckily, are surprisingly benevolent in that regard.
To get more-realistic numbers a group comprising many of the world’s top experts on avalanche rescue and the medical aspects of avalanche accidents conducted a landmark study. They looked at a total of 424 documented victims from around the world who were seriously involved in an accident, filtering out smaller and ones that people were able to escape to the side of and looking only at avalanches where an airbag “had a chance to make a difference.”
They further narrowed the data pool by only considering incidents with multiple involvements, including people both with and without airbags in the same, so they could make statistically valid apples-to-apples comparisons. Because of these filters, as they admit, the data set is skewed toward a more pessimistic effectiveness assessment of airbags.
According to this study, a deployed airbag will reduce mortality by 50 percent (22 percent mortality for the control group versus 11 percent for people with a deployed airbag). But because 20 percent of the people in the data set were unable to deploy their airbags, including the nondeployments reduces the survival rate for avalanche-airbag users to 41 percent. So, the use of an avalanche-airbag pack will save less than half of those who otherwise would have died.
The downsides to avalanche-airbag packs are cost. They are two to three pounds heavier than the nonairbag packs people already wear.
There are pluses and minuses to different airbags’ inflation methods. For those inflated by a cylinder of either nitrogen or air, in the United States as of this writing, commercial airlines do not allow transport of pressurized cylinders. For the compressed air, simply depressurize them and travel with them unsealed in your carry on. Carry the pack and cylinder together, so the agents screening luggage can see the purpose of the system.
You will then need to refill the cylinders at your destination at a scuba shop, an airbag dealer, or with a personal foot pump you can purchase from the manufacturer. Many cylinder-inflated systems also utilize a small explosive charge to puncture the cylinder valve, which of course is not allowed on commercial flights either. Compressed nitrogen cylinders have to be sent ahead via freight.
In contrast, airbag packs inflated with a battery-powered fan are allowed on commercial airlines, but you need to carry any spare batteries in a carry-on. The other big advantage of fan-powered airbags is they can be inflated as many as five times per day on a fully charged battery. One brand also deflates three minutes after inflating, which can create a large airspace behind the head of a completely buried victim.