Crevasse rescue: "drop loop C" tips
There are many approaches to crevasse rescue. The traditional method of a 3:1 mechanical advantage “Z drag” was the standard, and it’s still worth learning.
(There's actually a more modern approach to the Z drag where you drop one end of the rescue rope to the victim and set up a 3:1. Here's a complete article about the drop end 3:1 method.
A popular (and modern) method is to use a 2:1 “drop loop / drop C” system.
Advantages of the 2:1 drop loop over the traditional 3:1 Z drag:
Can avoid the often significant problem and friction of the loaded rope cutting into the lip of the crevasse.
Puts the lowest possible load on the anchor. The lower the mechanical advantage, the less force goes onto the anchor. This could be a good thing in crevasse rescue.
Victim can assist by pulling on one strand of the dropped loop, more below.
If you have brake knots in the rope, you can bypass them.
It can be easier to set up.
Downsides:
Can require more rope (but with some crafty rope tricks, not always, see below.)
Notes . . .
With a 2:1 system like this, two reasonably strong team members on top should be able to pull out one person who's in the hole, especially if the victim can assist in the process by pulling down on the load strand of the rope. Doing this creates a little slack, and reduces friction on the lip.
In reasonable conditions, ONE fairly strong person on top may be able lift the person in the crevasse. The technique for this is rather than simply pulling with your hands, drape the rope over your neck, bend your knees, and do squats. If you can deadlift 100 pounds or so, you ought to be able to lift your partner. Remember, you have a (theoretical) 2:1 MA. Here's a short Instagram video clip demonstrating this.
Alternatively, you can lower a carabiner or pulley to your victim and have the progress capture on the top. There are pros and cons to both of these methods, we’ll cover those below.
Progress capture on top, or on the victim?
With the drop loop C, you have two options where to put the progress capture pulley: 1) You can lower it down on the rope to your unfortunate partner, or 2) you can have it up on top. There are a few advantages to having it on the top.
If you set it up backwards, you can easily fix it. A progress capture pulley like the Traxion has to be set up correctly, otherwise you will not be able to pull. This might seem simple when you're training on a nice sunny day, but in the pressure of a rescue it can be easy to set it up incorrectly. If you do that on top, it's simple to flip it around and correct your mistake.
It’s easy to reverse the direction of pull. If for any reason you decide you need to lower your victim, you can easily do this on top by disengaging the cam. It’s much more complicated to do this if the Traxion is on your victim. Important: when your victim gets close to the top, have someone monitoring them carefully to be sure they don't get pulled into the lip of the crevasse.
Less chance of snow/ice getting jammed in the cam mechanism. As the Traxion gets pulled up near the lip of the crevasse, there's a chance that snow could get jammed into the cam mechanism, and potentially cause it not to engage properly. Pro tip: If the Traxion is on top, you can dig out a little hole underneath with your hands so the pulley is pretty much hanging in the air, and is not in contact at all with the snow.
The victim can help out
With the drop loop system, half of the rope is being pulled up and half is not moving. If the victim is functional, they can help the process a lot by pulling down on the side that’s not moving. This greatly reduces the pulling force required by the hauling team on top. If you do this, be careful not to get your hand or glove sucked into the pulley.
Another option is that the victim can pull down or even start ascending on the original rope strand they fell in on. Doing this can pretty much completely remove their weight from of the drop loop C, which again makes hauling online easier for the people on top.
A 2:1 drop C creates the lowest forces on the anchor
In crevasse rescue, your anchor might be an ice ax buried in a quickly excavated T-slot. Depending on snow conditions, how deep you’re digging, and whether you stomped down the area in front of the ax, the strength of this anchor can vary a lot.
So, given that you're anchor might be less than ideal, it might be a good idea to have rigging that puts the least possible force on the anchor. That's what you get with a 2:1 - about 1x of your pulling force gets applied to the anchor.
To explain this, I’m going to take a quote directly from the outstanding book, “The Mountain Guide Manual”, by Rob Coppolillo and Marc Chauvin (pg. 216).
“When not moving, the climber is suspended on two strands and the friction on the lip removes forces on the anchor. What's the haul begins, only one side of the loop moves, meaning that only half of the friction needs to be overcome while the other half of the friction continues to aid the anchor.”
A redirect makes a 3X force on the anchor
You might be tempted to put a progress capture pulley on to the anchor, run the pulling strand through that, and then pull toward the victim. This can work. But, this redirect puts a load on the anchor that's about three times your pulling force. Minimizing load on the anchor in a crevasse rescue is usually a good thing, so be mindful of this.
Alternative way to rig it is with the progress capture on the anchor, but then you pull in line with the rope rather than a redirect. This minimizes friction, and put a load on the anchor only (about) one times your pulling force.
Friction hitches work for a progress capture
Check out this nice diagram from Ortovox. A prusik hitch goes on each side of the drop loop. As you pull up, the blue helmet rescuer advances the prusik, capturing the load. (See the video at bottom for a demo of this.)
If you look carefully at the close up diagram in the circle, you can see that this progress capture friction hitch is attached to the same friction hitch that is securing the blue helmet rescuer.
Here's a video that shows this in action. This particular technique starts at about 4:10.
image: https://www.ortovox.com/uk/safety-academy-lab-ice/chapter-3/rescuing-a-companion
Easily convert a 2:1 to a 6:1
If you need additional pulling power, it's easy to convert this drop loop 2:1 into a 6:1 mechanical advantage system. Here's an article about how to do that.
Clip an additional carabiner to the anchor to serve as a redirect. As mentioned above, this does increase force on the anchor, compared to your original 2:1.
Add a friction hitch, carabiner and pulley (if you have one) to the previous pull strand.
Clip the tail to the pulley. You created a 3:1 on top of a 2:1. Multiply these values together to get a 6:1 compound system. (If you have only one pulley, it should go on the part of the system that's closest to your hand that's doing the pulling. This creates the greatest efficiency in your haul system. This system also works if you only have carabiners and no pulleys, but it's less efficient.)
Here's a pro tip for rigging a drop C more easily, from IFMGA Guide Ben Markhart.
Add a locking carabiner to the pulley, clip a sling to this, and then clip another locker to the end of the sling. Instruct your crevasse rescue victim to clip the bottom locker onto their harness. This can be helpful in a couple of ways:
Provides a nice hand hold for the victim, which can help keep them more upright.
Can help “extend” the dropped loop rope if the rope is too short. (More on that below.)
(The downside to doing this is that the victim is not able to pull down on the half of the loop that’s fixed, which can make hauling for your buddies on top quite a bit easier. Like most things in climbing, there's a trade off.)
Check out Ben’s short Instagram video here.
Ben explains:
“Your instinct is to want to hold onto something, and it makes it lot more comfortable on your core muscles. So this makes people want to grab about 8-12 inches above the pulley if there is no extension, now the rope has to slide though your hand to haul and is easy to get sucked into the pulley if your not careful. This way you hold onto the sling, much more comfortable.”
screen grab from Ben markhart, https://www.instagram.com/p/Cd_OOQJJeHh/?hl=en
What if you don't have enough rope to reach the victim with a drop loop?
Solution #1: Extend the pulley
This is one of the most common concerns and potential downsides of using a drop loop system. Here are several solutions.
In the last photo above, I extended the drop loop with a 60 cm sling and a locker. How about extending it with something longer? Like maybe a cordelette, either in a tied loop or a single strand with a bight knot at both ends? Doing this extends the clipping point so it reaches your victim. Nothing in the rulebook says that the lowered pulley has to be clipped directly to the harness of your victim. Lower the pulley as far as you can, and extend it with whatever slings/cordelette you have the rest of the way if needed.
A possible downside to doing this is that the pulley might get wedged into the snow at the lip of the crevasse. If you knock down a lot of the loose snow and prepare the lip properly, this hopefully is not an issue.
Also, the anchor needs to be back from the edge at least the distance of your cordelette. If you don't do this, you will run out of rope to pull while your victim is still below the lip.
Solution #2: Your progress capture doesn’t need to be on the actual anchor
When you drop a loop of rope to your partner, one side of the “C” is fixed to the anchor, and the other side is what you pull on. If you don't have twice the length of rope between you and your victim, you can tie a bight knot anywhere on the fixed side of the “C” and clip your progress capture to this knot. This might let you stand in more convenient position, to maybe more easily monitor your victim. This can also mean that you don’t need twice the length of rope between you and your victim. Maybe only 1.5 times, as shown in the photo below.
What if the victim is unconscious, and can’t attach the pulley to themselves?
First off, if your partner is in really bad shape, your first step in rescue might be to rappel into the crevasse and try to do some first aid, at least be sure they’re breathing. If you do this, you might be able to attach a hauling system to their harness.
If you have a Petzl Tibloc, and can lean over the edge of the crevasse to reach free hanging rope, here’s an option. (If these two things are not possible, you might be better off doing a traditional 3:1 Z drag from the top, or maybe having a rescuer rappel down to the victim and attach the pulley.)
Put the drop loop through a Traxion (or a pulley) and engage the cam.
Clip the Traxion with a locker to a Tibloc installed upside down on the rope strand going down to your victim.
The Tibloc will (hopefully) slide down the rope toward the victim and stop when you run out of rope, or it rests on their tie in knot . Then you can 2:1 haul with a progress capture, without the pulley actually being attached to the victim. See photo below.
screen grab from: https://youtu.be/lsTihq92IlQ
Here's a nice video from some expert German guides showing how to do this, along with some other great techniques. This particular “lower the Tibloc trick starts about 5:30.
Tip for loading the rope correctly into the Traxion: “teeth to tail”
It's very easy to load the rope into the progress capture pulley the wrong way, especially if it's in a strange angle or you're stressed from a rescue.
A good mnemonic to remember the right way: “teeth to tail”. That means the toothed part of the spring-loaded cam goes to the tail of the rope, or the part that you need to pull. Here's a photo.
