Avalanche Primary Search Techniques

All the books and references I have found seem to indicate that a primary search is carried out as a "ladder" search down the avalanche slide, starting above where the victim was last seen. What is not covered in much detail is numbers of skiers required for this search - is it just one??. Is there a case for using a "line abreast search" with a number of skiers spaced at 15m - 20m intervals, and 10m from avalanche edge, conducting a search side slipping down the avalanche slide path. In maritime search and underwater diver search scenarios, a line abreast search plan is the most efficient in terms of area covered and time taken. Ladder searches are used when there is a shortage of searchers, but it is very much second best.
So my question is how many skiers would make up a group that is small enough to get around reasonably quickly but large enough to provide sufficient search and management resources. It seems that it is desirable to have the group leader taking charge and then post 1 skier as a sentry/guard. To the guard I would also add comms - give him the mobiles to raise the external alarm, a PMR radio to remain in contact with the leader - he may have to climb to get a mobile signal, and mini flares (if available) to fire off at intervals. I would also have a prepared card in the country language that the comms number can read out if he is not too hot with the language - or if the telephone operator is not - much long the lines of the marine VHF Mayday card - what, where, when and details. And then the search team, how many? A search team of 4 could cover a search front of 65 - 80m wide. If the search front is wider, then perhaps a combination of line abreast and ladder. If 1 or 2 skiers were unfortunately carried away, then starting with a group of leader plus 6 or 7 would seem to offer a good capability in the worst case scenario. Any comments??

colinstone wrote:Is there a case for using a "line abreast search"

Yes, there is, but...

colinstone wrote:Ladder searches are used when there is a shortage of searchers

You've answered your own question there; the life expectancy of someone buried is measured in minutes so a search can't wait and has to go with whoever is on the slope.

Large groups going off-piste are a big no-no (obvious problems keeping separation across suspect slopes, etc.) so search plans have to assume there are limited numbers of people available.

If you're "lucky" and an avalanche occurs on or near lift-served terrain (or within a few minutes flying time of a helipad!) then help may arrive more quickly and then you're into having a properly led search, etc.

I'm in no way an expert, but good sources of everything off-piste and avalanche-safety related are PisteHors and Henry's Avalanche Talks.

Thanks - and I had been reading around various backcountry and ski touring books, PH and HAT and the 2008/9 FR avalanche review. The latter seems to indicate that having more not fewer in a group would be advantage - the average deaths per incident is 1.46. The reference books only seem to have the ladder search - hence my posting.

Howeever, my basic Q remains - how many in a group?

From the marine and diving perspectives, there are several search techniques that are employed to cope with the differing conditions - number of search units, visibility, search equipment etc etc. In many ways the diving enviroment is most similar to the alpine one - lack of air, lack of visibility, search numbers etc but I would not want to go all the way down the diving route with laying jackstays etc!!

Anyway, it all appears to be food for thought!!

There are different search techniques depending on how many people are spare to do the search, the size of the debris and the devices being used.

Modern transceivers have a search radius of up to 60m so if the Debris is 80m wide then theoretically one person could walk straight down the middle of the debris and still have a 20m overlap on his search range on each side. If the Debris is 120m wide then two people walking straight down the debris 40m from the edges, and 40m apart would have the same effect.

Unfortunately in the mountains we probably never have an ideal situation if something goes wrong. The debris can be two wide and you might only have one person searching. Then they would need to do a zig zag search down the debris where each zig or zag would be close enough to each other to have an overlap and ensure no part of the debris is left unsearched. As things get more complicated with multiple burials, larger search areas etc then you need to adapt the the techniques to make the search as quick as possible without leaving any dead spots in the search pattern.

Many beacons have information on searching techniques on the back or in the instruction manual, but you can not beat doing an avalanche course

ir12daveor wrote:
Modern transceivers have a search radius of up to 60m so if the Debris is 80m wide

That's not correct, old analogue transceivers may have a reception range up-to 60m. Modern devices manage nothing like that. In practical application you would assume a range of no more than 30m.

ir12daveor wrote:....then theoretically one person could walk straight down the middle of the debris and still have a 20m overlap on his search range on each side. If the Debris is 120m wide then two people walking straight down the debris 40m from the edges, and 40m apart would have the same effect.

You simply would not do that. A standard group primary search protocol would search not more than 10m from the edge of the debris field with not more than 20m between searchers. This would apply to analogue or digital devices. I'd also submit that were the range reliably 60m, which it is not, then you would search 50 metres from the edges and 100m between searchers to achieve maximum coverage, those proportions are incorrect and fail to factor for adverse antenna alignment, deep burial or weak batteries.

In practice you would adjust these distances based on the number of searchers. With enough people I would organize a group primary search at around 10m range, ie 5m from edge of debris with 10m between searchers. However, in practice I would consider using a single person to make a primary search if they entered the debris from above and it was not more than around 50m wide, I would strongly favor this protocol in the event of multiple burials.

For a single searcher you would travel at 90' to the falline across the debris with the widest search not more than 10m from the edge of the debris field, moving up or down to give not more than 20m between traversals.

Also, a debris field 120m wide would be an avalanche of devastating proportions, I would suggest a group on the mountain would be overwhelmed by such an incident and would be simply unable to mount an effective recovery

http://www.pieps.com/en/lvs/pieps-dsp.html

Sorry, it appears mine is 50m not 60m. Either way nearly all transceivers that are worth their salt these days have three antennas and have a similar range.

ir12daveor wrote:http://www.pieps.com/en/lvs/pieps-dsp.html

Sorry, it appears mine is 50m not 60m. Either way nearly all transceivers that are worth their salt these days have three antennas and have a similar range.

You need to check that or better understand the practical implications as there is a difference between perpendicular range and inline range. The pieps has a good range, in optimum conditions a perpendicular range of around 40m IIRC, but it doesn't alter what we think of as standard search protocols as a guide, leader or avalanche trainer would teach on a course as you rightly recommend.

Pieps and the Pulse manuals suggest fairly aggressive parallel search distances of around 50m IIRC ie a working range of a 25m search distance which is rather less than 50 or 60m.

Which is a distraction and the sort of distraction which I find rather dangerous. Practically, a group would not expect to find a debris cone of the sort of size where this becomes an issue where the group itself is of a size to make a difference. Real world group sizes, and skills, along with real debris sizes mean you're nearly always better using a single searcher for the primary search and deploying your additional people to triage and fine search.

I don't have any intention at all of trying to recall in an incident what the effective perpendicular ranges of half a dozen sorts of transceivers are and adjust a grid accordingly and neither should you. This is why we have standard protocols, teach them and use them, it's easier and it's safer.

If you want to improve your ability to move safely in winter environments I'd suggest concentrating on this type of decision making and not get caught in the sort of datasheet comparisons of transceivers another ski forum seem to find so fascinating :-)

If you are in a group with mixed gear, and you're dealing with someone that's memorized the data-sheet and not really understand the problem at hand, then I suggest you bury a device and get the group to walk towards it in a straight line each stopping as they get first signal. Try it again with the transmitter aligned differently and/or swap batteries around if they're not getting it. if that's not working out then I'd reserve their skills for digging in the event of a slide :-)

You don't need jackstays as your footprints show even in avalanched snow, which in my experience is a very different animal to pisted OR any other snow that has not been moved around much.
I went on a course in The States at Estes park organised by the Colorado Mountain School. I don't want to sound patronising but these courses are a great way to stay OUT of trouble.. The search and rescue bit really is the last resort. P art of your question is left out.. where did your virtual avalanche start? where were you? If you see someone carried off and you see an arm or foot sticking out of the rubble go there first... organising a pretty pattern of people on the slope is great in theory but it takes no time at all for someone to die once in the snow. Many people think of an avalanche as a bit of a sluff that looks pretty spectacular. The reality is EXTREME VIOLENCE. Think of it as being attacked by a 120 mph bulldozer thats having a bad hair day and is half the size of your average town. If an avalanche can rip out trees [in milliseconds] whats it gonna do to your new jacket? Once the obvious sites have been checked then go into secondary search mode. Breckenridge put out a taped off area where you could practice using transponders. Maybe it was 50 x 50 yds, with ten transmitters. Two of us took half an hour to find them all and it was hard work... going uphill at that altitude without a lift wasn't exactly making me look like an olympic athlete on a mission for gold, more like a clapped out old fart looking for the last oxygen molecule on the hill.
Doing the course in America I thought was good value, but I did have the time which a lot of people couldn't wangle. A course anywhere is a good idea as it dissolves a lot of the angst about what is and isn't good practice.