Things have really gone wrong when multiple members of your group have been caught in an avalanche. Please keep in mind that it's already a challenge to search, locate and dig out one victim within 18 minutes. Just imagine what a challenge it is to save more victims within that timeframe.
The number of multi burials has decreased to only 5 percent of all the avalanche victims since 2000. This is a relatively low number, but such accidents tend to get more exposure in the media, giving us the impression that we, as skiers or snowboarders, need to be able to perform such a rescue. Let's be clear: It's definitely important to know how to perform a multiple burial rescue, but it's even more important that you know how to perform a single burial flawlessly. If you’re spending most of your time learning multiple-burial techniques then you might be missing the bigger picture. Especially if you consider that most of these multiple burials are solved no differently than single burials. Only in close-proximity situations are most multiple burials solved any differently than a single burial. But research shows that only about one percent of accidents involve close-proximity burials, in which the victims are buried within 10 meters of each other. The techniques below are therefore applicable to only one percent of all the avalanche incidents.
Keep in mind
Digging is the biggest challenge in avalanche rescues. Digging takes the most time (far more time than the search process). If you ride in a small group (let's say four or five people) and two of your friends are missing, what are you going to do when you have found one of them? Not dig him up? Or do you immediately start digging? Exactly. In small groups you need to start digging with the entire group and you don't have the 'luxury' of sending someone to search for the second victim.
Most of the avalanche transceivers have a 'mark' function. When your transceiver gets two signals, it leads you to the strongest (closest) one. After you've localized the victim with the fine search, you can 'block' his signal using the 'mark' function on your transceiver. The avalanche transceiver will now lead you to the second victim. Please note that most mountain guides do not use the mark function on their transceiver. They use techniques where they trust the signal-strength search techniques such as micro search strips.
What to do?
Again, you should be very happy if you can rescue one victim within 18 minutes. Remember that multiple burials only are 5 percent of the total amount of avalanche victims. But this is what you have to do when you're in a situation where two or more people in your group are caught in an avalanche AND your group is large enough to perform the multiple burial search.
When the signals do not overlap you basically perform a 'normal' (which you perform when there's only one victim) search proces, but twice. When the signals do overlap, then there are two options. The three circle method or micro search strips.
Three circle method
When teaching “special case” multiple burial searching, a standardized approach should be used that is reliable across all beacon types. The most reliable and intuitive approach is the Three Circle Method. This method relies on signal strength analysis rather than signal timing analysis (“marking”) to isolate signals. Therefore it is not vulnerable to inadvertent and confusing signal losses when victims’ signals overlap.
- The first circle should be performed with the searching beacon as close as possible to the snow surface. This offers better resolution when the victims are in very close proximity to each other.
- The method is not complete until the searcher has walked all three circles and pinpointed all signals within or near the 18-meter diameter.
- Once the second victim is located and/or recovered, and others remain unfound, the searcher should complete the original series of circles around the first victim, rather than starting a new set after locating each one.
More about the three circle method is to be found here.
Micro search strips
With multiple burials within less than 10 meters (where the signals of the transceivers overlap), you can use micro search strips.
- Start searching for the first victim using the 'normal' search pattern.
- If your group is large enough than some members of your group start digging for the first victims after locating him or her.
- You should move about three meters in the direction that you initially approached the first victim. The transceiver should indicate a distance of three meters to the first victim.
- You can start a 'normal' signal search, with the difference that you have to keep around three meters between each search strip. It's quite similar to the Three Circle Method, where you are also looking for an unexpected change in the distance to the first victim.
- When your transceiver picks up the new signal (you can see the number changing), stay on that narrow search strip until your display shows a distance less than approximately four meters.
- When that happens, use the fine search technique to locate the second victim. If your transceiver leads you back to the first victim, return to the previous micro-strip location and continue searching.
Please note that it's more important to wait for a significant and unexpected change in the distance shown by your transceiver, than take the actual distances on the display too literally. By making three-meter search strips, you'll be closer to the second victim than to the first victim. That is the essence of this searching technique. Read more about multiple burials here and here.