Let’s “get real” about multiple burials.

Posted on February 10th, 2014 by | 2 Comments

 

“Five killed in Loveland Pass avalanche.”

 

“Three die in out-of-bounds snowslide near Stevens Pass.”

 

Attention-grabbing headlines like these are unfortunate and tragic. Are multiple fatalities in avalanche accidents becoming more common? Should this influence your decision when buying snow safety equipment? The answers are no and no, respectively.

 

Here are the realities: Statistics indicate that multiple burials have actually decreased over the past decade. And they also indicate that you’re much better off using your brain–and your shovel!–than relying exclusively on the multiple-burial features on your avalanche beacon. Get educated, learn proven “backup” search techniques, learn strategic shoveling, and practice all of this several times every season.

 

11th Annual Beacon Bowl and Avalanche Awareness Day

 

“Marking” is Born

 

Multiple-burial talk has its genesis in the guiding world where, for economic reasons, large groups often ski together—and occasionally get buried together. If an accident occurs, the rescue expert in the group (usually the guide) is expected to find all the victims while guests act as assistants or bystanders. To become a certified guide, a candidate is usually required to find at least three victims (one more than two meters deep and two in close proximity) in a short period of time, with minimal assistance. In more realistic guiding exams, the candidate is required to find only some of the victims, but must dig them out within the time limit, usually well under ten minutes. From this world, “marking” functions on avalanche beacons were born. Marking enables the searcher to suppress the signal of the found victim, then move on to the next victim while others begin shoveling.

 

Multiple Burial Stats

 

How does this apply to recreational backcountry riders and how well does it all work?

 

Statistics show that as recreational backcountry use has increased relative to guided backcountry use—and equipment and avalanche education have become more widespread–the proportion of multiple burials has decreased over time. Currently in the US, Canada and Europe, about 15 percent of accidents involve multiple burials.  A recent study by the Swiss Avalanche Institute concluded that burials involving more than two people have gone from 10 percent before 2000 to less than 5 percent since 2000. And only about 1 percent of accidents involve close-proximity burials, in which the victims are buried within 10 meters of each other (see http://www.backcountryaccess.com/research ). Only in close-proximity situations are most multiple burials solved any differently than a single burial.

 

In most cases involving two or more avalanche burials, the victims are located the same way as single burials, either “in series” or “in parallel.” In the former, a single rescuer locates the first victim, digs enough to provide that victim an airway, then moves on to the next victim (“in series”), preferably turning off that victim’s beacon before moving on. In the latter, two or more searchers fan out across the avalanche debris pile (“in parallel”) and isolate signals as they go.

 

The only exception is when the victims are close together, within about ten meters of each other. In this case, it’s possible to skip right over one victim’s signal by charging off in the wrong direction. Or in the “parallel” multiple-searcher scenario above, one searcher might end up isolating two signals, but the other searchers might not isolate any. In rare “close proximity” burials like this, special search techniques or technologies can come in handy.

 

Special Techniques

Proven techniques used to solve these situations include “micro search strips”–popular in Canada–and the European-inspired “three circle method.” We won’t get into details (for more info, see our Tracker2 and Tracker3 Advanced Owner’s Manuals), but they’re based on using signal strength to isolate each victim. Generally, the searcher begins at the victim’s last seen point and systematically travels through the debris, making sure he or she doesn’t miss any areas. All modern avalanche transceivers are programmed to bring you to the strongest signal, although some do this a lot better than others. As long as you keep moving—and stick to a disciplined search pattern–you’ll find all of them. Keep in mind that if you can’t turn off the found victim’s beacon, you’ll have to ignore that signal as you move away from it. (The Tracker3 performs exceptionally well in these scenarios due to its robust signal strength filtering, instantaneous “real-time” display, and very useful close-proximity indicator, which appears when more than two victims are within five meters of the searcher.)

 

Micro strip search avalanche beacon techniques

Schematic representation of a debris area and micro search strip lines with their associated dimensions (not to scale).

 

Special Technologies

 

The above might seem like a lot of excess running around, especially when lives are at stake and the clock is ticking. Enter “marking,” also known as “flagging” or “signal suppression.” Most digital avalanche transceivers, including Tracker3, now offer a feature that enables the rescuer to press a button that suppresses the signal of a victim that has been found, then immediately see the signal of the next-closest victim and move directly to that location.

 

This technology can work great, especially with only two victims. But once there are more than two, it gets increasingly unreliable. A 2011 report in the professional journal, The Avalanche Review concluded that marking functions fail up to 70 percent of the time in scenarios involving three and four victims. And once it fails, you’re worse off than if you simply used one of the proven signal-strength techniques above. That’s because when using marking, the user abandons the disciplined search pattern that’s required to ensure that all victims are found. Once you get off that pattern, all bets are off on a thorough search. (For this reason, the Tracker3 avalanche transceiver only suppresses one signal at a time—and it defaults back to search mode after one minute of suppression.)

 

What causes this failure? A phenomenon called “signal overlap.” This is when the “beep” from one victim’s avalanche beacon occurs at the same time as another victim’s “beep.” When this happens, the searcher’s avalanche transceiver no longer knows how many signals are present. If the rescuer “marks” a victim, then both signals could be eliminated—whether or not both victims have been located. Also, when signals overlap like this, a signal that has been marked can all of a sudden become unmarked. The only way to salvage your search at this point is to “reboot” your transceiver (turn it off and on again), go to analog mode with some models (Barryvox Pulse), or go to the “scan” function on others (Pieps Pro). But if you don’t know you should do this—or aren’t very good at it—then your search can quickly turn into a train wreck.

Avalanche Beacon Signal Overlap and Signal Separation  

Realities

 

As you can see, avalanche transceivers are not foolproof in multiple burials–even the most expensive and sophisticated ones. So keep it real and remember the following:

 

• The biggest challenge in most avalanche rescues is digging. This takes far more time than the beacon search. In most recreational avalanche incidents there are barely enough shovelers to excavate a single victim, let alone two or more. Are you really going to NOT dig somebody up? For these reasons, in almost all multiple burial scenarios, “marking” is a luxury. People will die if you don’t start shoveling–immediately.

 

• Don’t be misled by “marking.” It has major limitations. In most guiding exams involving three or more victims, guides generally do not use marking: they use proven signal-strength search techniques such as micro search strips. This is because there’s a good chance marking will fail.

 

• It’s more important to master 1- and 2-victim scenarios and “strategic shoveling” than it is to focus on complex, special-case multiple burials. When practicing multiple burials, try marking or signal suppression first. If that doesn’t work, use micro search strips. To learn more about these proven techniques, go to http://www.backcountryaccess.com/research  or our T2 and T3 Advanced Owner’s Manuals.

 

• Better yet, prevent multiple burials from happening. You can do this through smart route planning, safe travel techniques (one at a time), and effective group communication: lots of discussion, open sharing of ideas, and the efficient use of two-way radios.

 

The good news is that even though they attract lots of attention, complex special-case multiple burials are about as likely to strike as a millennial avalanche path. Get educated, practice the basics, stick to good travel protocols–and you’ll stay out of the headlines.

  • paul

    I see in that picture above, the ski patroller is using a Tracker 1 beacon, that version has a much shorter range of detection and is not as good as a tracker 3 for multiple burials, I have to wonder why would the people most likely to need to use a beacon, not have the latest beacons available, or is that just a very old photo.

  • Bruce_Edgerly

    Good eye, Paul. Just a stock photo. But be careful about what you say regarding how various beacons work for multiple burials. The Tracker DTS is an awesome beacon for doing micro search strips, due to its fast processing speed–better than most beacons with full-on “marking” functions. But it doesn’t have a third antenna, which means you can get “spikes” when you’re in the fine search.