Probing Probes - Length and Materials Explored
**Updated with responses from G3 and BCA**
Next up in Phil’s Winter Gear Discussion Series is Probes and this one is a lot less cut and dried.
(Previous discussions/rants include skis, bindings and poles).
Probes – it’s a collapsible stick, how can Phil possibly complicate this or have a poorly edited 2008-word one-sided discussion about it?
Pull up a chair you young whippersnappers and let me show you how.
Probes seem to come in two lengths 240cm and 300/320cm and two materials – aluminum and carbon fiber. It used to be 240cm and 320cm, but then companies started coming out with carbon fiber ones and I think that people didn’t understand why they were more expensive and didn’t weigh any less than the aluminum ones so I think the 300cm length popped up as a way to make the carbon ones look lighter. Seriously, the G3 Speedtech Probe 320 (aluminum) weighs 0.92g/cm while the G3 Speedtech Carbon Probe 300 weighs 0.95g/cm so at an equal length they would weigh pretty much the same. Fun. Anyway the weights between the two materials are roughly the same, so what’s the difference?
Personally the difference I’ve noticed the most is that the CFRP (carbon fibre reinforced polymer) probes are stiffer – they don’t flex as much. When you’re building a pit for an extended column test (ECT), you use two probes and a cornice saw to cut out the back of the column. Carbon probes are nice for this since they don’t flex as much and are easier to work with. That said, aluminum probes are quite a bit cheaper, so that’s what I use, the difference isn’t big enough for me to justify the added cost – but that’s very much a personal thing.
Well what do the companies say?
“The big difference between carbon and aluminum will be weight. Aside from that generally speaking the aluminum probes will be more robust, though the carbon probes are still very strong.”
“Regarding materials, carbon is lighter but not quite as durable. Fine for companion rescues, but aluminum (or steel) are better for organized rescue. ”
So when it comes to material, Phil’s advice is ‘if you like carbon, buy carbon, if you’re cheap, buy aluminum’.
The real discussion, and why I’ve gathered you all here today, is length.
Now, first you should know my biases. I tend to be a weight weenie. I like light gear. That said, I’ve always carried a 320cm probe on the basis that people are recovered alive from depths up to over 2m. A 240cm probe would meet my internal math if I drove it all the way down to the top of the snow – but a) I might not remember to when I’m in a borderline panic and b) dropping to my knees with every probe attempt would take longer and slow me down.
I’m 178cm tall so If I drive the probe down as far as my hands go without bending down, then there’s probably 80cm of probe above the snow. With a 320cm probe that puts my tip 240cm down. With a 240, I’m only probing to a depth of 160cm which just seems too shallow to me.
But is that actually accurate?
After years of passionately arguing something without any supporting evidence whatsoever, I decided to see what the research actually says.
Most research looks at survival rates versus time and the shocking conclusion is that the longer you’re buried, the worse your chances (especially in coastal snowpacks). So, we want to minimize the length of time spent probing. Well, that reinforces my argument that a 320cm probe pushed 240cm down is probably better than a 240cm probe pushed 240cm down since you eliminate dropping to your knees in the avalanche debris with every step. A couple of seconds each time could add up.
But Bruce Jamieson, UofC avalanche researcher extraordinaire and one of Phil’s top 10 nerd crushes, wrote a paper with Tim Auger of Banff National Park that looked at the grim idea of triage by probe depth – probe less deeply so that you’re faster on the basis that anyone deeper than a given depth is probably dead anyway.
Basically, they found that survival drops off a cliff as burial depth exceeds 1.5m – so are you better off to only probe 1.5m down, but covering correspondingly more ground in the same time since each probe attempt should be faster? Eeeeee…
They started by compiling statistics from Switzerland and US on burial depth vs. outcome. Getting deeply buried sure isn’t good. For the Swiss statistics for example, 95% of people recovered alive were buried to a depth of 1.5m or less. The US numbers were pretty similar with very few people recovered from a depth greater than two meters.
The reasons are myriad (deeper burials generally come from bigger, more violent slides, there’s more compaction, less air, etc), but time is clearly an important factor. With this in mind, they ran some real-world tests out in Rogers pass where they compared two probe techniques – a classic coarse search with rescuers closely spaced, probing directly in front of them and then step forward and the Three-Hole-Per-Step probing where rescuers are more widely spaced, but probe left, right and centre with each step. They also tested two probe depths (3.2 and 2.4m probes plunged to 2.1 and 1.5m respectively) to measure any increase in search speed.
What they found is interesting.
When looking at the 1 hole per step technique, rescuers averaged 7.42 holes/person/minute when doing a “full depth” probe to 2.1m. When the probe depth was shortened to 1.5m, that rate increased to 8.03 holes/person/minute – an 8% increase in speed.
The 3 holes per step technique to a depth of 1.5m resulted in a probe rate of 13.21 holes/person/minute – an increase in speed of 65%.
Now, in each of the preceding cases, there was a ‘Probe Master’ – one person was calling out direction ‘step forward, probe right, probe left, probe middle’. The result is that everyone waits for the slowest person to finish their probe attempt. In a final test, the researchers directed the ‘rescuers’ to probe at their own speed doing the 3 holes per step technique. The result was a probe rate of 12.06 holes/person/minute which indicates that just having someone set a rhythm can save you 10%.
Okay, so what does this all mean?
Well, I have a few take-aways from this paper:
In the event that you have to do a probe line, technique matters. The 3 holes/person technique lets you cover way more ground with a given number of rescuers than the old coarse search technique.
Having someone set a rhythm also has an appreciable effect on speed. A coordinated rescue is important.
The speed advantage of probing to only 1.5m had the least effect of the measured variables – but the effect was still there. If faced with having to do a probe line over a large area, it could be advantageous to limit probe depth to 1.5m.
But, Tim and Bruce’s paper looks at probe lines not at a rescue where there’s a single person buried with a full functioning beacon where you’ve homed in on them and are doing your final probe locate. In that case speed is still of the essence, but I don’t care how deep the person is, I was to do everything I can to get them out and I think that the time savings per hole becomes less relevant.
Think of it this way: doing a probe line, between all the rescuers you could do several hundred probe attempts. A one second speed increase on each probe, times a couple of hundred probe attempts, could be minutes saved.
On the flip side, if I’ve homed in on my ski buddy using a beacon and I know he’s within a small area, the time lost by not probing deeply enough and missing him on the first pass is probably way greater than just driving my probe all the way in the first place and the time cost of probing to full depth a dozen times is something in the neighbourhood of a dozen seconds. Not huge, though I admit that every second counts.
There’s a recent paper by E. Procter et al. (sorry, couldn’t find a non-paywalled source, but I can show my copy to anyone who’s interested), which looks at the effect of burial duration, burial depth and the presence of air pockets and their effect on the survivability of avalanches in Switzerland and Austria.
The results are grim. Time it appears, isn’t everything, but it’s a lot. The mortality rate of victims buried 16-35 minutes was found to be 8.7 times that of people rescued within 15 minutes. This reinforces the adage that you have 15 minutes (10 minutes in Canada!) to rescue someone and have a good chance of their surviving. The effect of burial depth was extracted through a regression analysis and it was found that compared with a someone buried less than 40cm deep, mortality rates increased sharply as depth increased, reaching a mortality rate of 4.92 times that of a shallow burial when the victim is more than 120cm deep.
Like I said, the results are grim, speed is of the essence and depth of burial decreases your odds of survival rapidly due to increased rescue time and just the mechanics involved. Making a great case for airbags, not making a great case for carrying a super long probe.
Ultimately though, I keep coming back to Figure 1 in Tim and Bruce’s paper. In it, it shows the number of victims recovered alive and dead at different burial depths. Looking at the US data which likely most closely parallels the Canadian data given the similar snow packs, you can see that there are an appreciable number of people recovered alive from burial depths of 6-7 feet (183-213cm). There are no recorded live recoveries below that (though their dataset covers the years 1951-1991 and my guess is that numbers are improving).
I can see the argument for limiting probe depth to 150cm when dealing with a large search area. But you can sort of do that with either a 240 or 320cm probe. When doing a single recovery, once I’ve started my probe spiral, I feel like I’d rather have a 320cm probe so I can quickly probe the very limits of recoverable depth – which (old) data indicates is at least 210cm – without having to drop to my knees with each probe attempt, but it’s seems clear to me that it’s no longer a cut and dried thing and I don’t think I can conclusively say that a longer probe is inherently better.
Alright, so now I’m casting about for stuff to support my long probe = better bias. Let’s look at some of the other usage models for probes then.
Probing the snowpack - nice to know how deep the snow is and if there are distinct layers down there. You can only go as deep as your probe, so long probes are nice for fat snowpacks.
Profile Pits – The ECT requires two probes to isolate the column. Assuming a 2m deep pit, with a 240cm probe you’ve only got 40cm of actual penetration providing support. The extra length of a 320cm probe is an advantage here.
Figure 1: Christine demonstrating why you don't get the shortest person to stabilize the probes when isolating a column in an ECT. Not the cleanest pit we’ve ever done.
Crevasse Probing – I really like a 320cm probe for crevasse work, but again I think you can probably make a credible argument for a 240cm probe being adequate.
Ridgeline/Cornice Probing – Same deal as crevasses. I like knowing if I’m standing on a ridge or a cornice and a cornice can easily be more than 2m thick, but once again I think a credible argument can be made for a 240cm probe being adequate.
Figure 2: Charlie Plays another fun round of 'ridge or cornice'.
Okay, so I’ve blathered on for a while about why I do things and why it maybe doesn’t matter as much as I thought, but what do the companies that make these things actually say?
“I would say that probe length also is related to snowpack. Probes are often used not just for rescue, but to feel for layers and to probe for obstacles before digging a snowpit. If you live in an area with a deeper snowpack you’re going to need a longer probe to get a better “feel” for what’s below you.”
“For length longer probes will be good for areas with deep snow packs, the shorter ones for shallower snow-packs as well as they will save some weight and bulk.”
Extra bonus tidbit I got from BCA when I asked where the 240cm and 320cm lengths came from in the first place:
“As basic as it sounds, the 240 and 320 lengths are common mainly because they’re multiples of 80 cm and this is the most common—and therefore most economic—stock section length available from the factories.”
Conclusions:
Use whatever makes sense to you and I have nothing of use to tell you.
I’ve always used a 300+cm probe and quietly judged people who used shorter ones. After actually reading and considering things, I’m going to keep on using 300+cm probes, but I won’t look down my nose at people who don’t.
Unsurprisingly, it looks like technique and practice matters a lot more than what gear you use.
Grumpy, cantankerous, wildly opinionated and so much more! Getting really tired on skis is what makes me happy.
