Using knotted parachute cord to arrest a crevasse fall

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Claim: Using a knotted parachute cord to arrest a crevasse fall is bad advice.

Bear advocates the use of knotted parachute cord to arrest a crevasse fall. This is questionably the most dangerous bit of advice so far in the show.

1. Parachute cord has a low breaking strength. See Using parachute cord to abseil down a cliff for a discussion of the strength of parachute cord.
2. Knots, no matter how many or what kind will not arrest a crevasse fall. A knot has a very small cross-sectional area to grip with.
3. When Bear pulls himself out of the crevasse, he pulls out the very knot that was supposed to have arrested his fall without backsliding back into the crevasse. I strongly suspect he was anchored using real climbing gear for this scene.

Update: The edited version of this episode confirms that this scene is staged.

[edit] Analysis

Oppose: Minor, but while there's certainly no sound logic to the "knots" (as though a few square inches of cross section plowing through a compactable powder will do anything), there could be a logic to the bag of snow.

Support: Except that it doesn't work that way. Entire rope teams of climbers have been dragged into a crevasse, and they're actively trying to avoid it - what chance does a bag of snow have of arresting a fall? The answer? Absolutely none. This is another STUNT with no basis in reality. If you try it - you WILL die. Simple as that. Don't believe me? Try it - let's see what happens.

Oppose: I've tried it, and i'm still alive. Using knots at intervals in a rope is a tried and tested technique used extensively, especially by Europeans in the Alps. A single knot can indeed arrest your fall when it digs into the snowy lip of a crevasse. This technique is especially useful in two-man rope teams, since the blocked knot can remove most of your partner's weight from your self-arrest. If you're alone, the bag of snow on the other end provides the friction necessary to help the rope dig in on the lip of the crevasse, and not fly over it. I have personally thrown myself into crevasses during rescue training, and can attest that this technique works. It is also mentioned in basic mountaineering references, such as "Mountaineering: The Freedom of the Hills" (7th edition)[1]. As Bear mentioned, "This is a technique that Alpine guides have been using recently as a way of self-arresting you". He didn't make it up personally. Note: this technique doesn't work on late-season uncovered icy glaciers, nor is it always a good idea when on a 3- or 4-man rope team, since it makes pulling the fallen climber out more difficult.

Support:I'm very familiar with your referenced book - yet I can find no reference to this technique. One of the standard approaches to roped glacier travel is to keep slack out of the rope, not knotting it and dragging it with slack. Since you provided the reference, can you also provide a specific page? Otherwise, I stand by my initial assertion.

Oppose:The trick of knots is true and widely used here on Alps (I am from italy). Knots are called "Ball knots" and are indeed realized on the main rope every 10 mt to prevent falls in crevasses. Here you can find the official CAI (Club Alpino Italiano, Italian Alpine Club) manual in pdf: [2]. You can read about it at page 100, "Nodo a Palla"

Support:This doesn't address the issue of parachute cord strength, however. If it's 550 cord, that could support a little over twice an adult male with limited gear's weight. Any jolt at the end from a sudden stop would easily snap it. Parachute cord weak.

Oppose: Parachute cord is definitely not the best option, but weaving several lines together (looks like bear uses 5-10 cords) should suffice to hold your weight in a survival situation

Oppose: "Any jolt at the end from a sudden stop would easily snap it." Parachute cords receive 'jolts' like this when a parachute opens during skydiving. If he was only using one of the many parachute cords the 'jolt' could easily exceed 550 lbs or force and break, however he is using multiple lines (as stated above).

Support: Knots also reduce the strength of a rope or cord[3] by 20% to 50%.

Support: The re-edited version confirms that he used a safety line and the whole scene was staged. I will again assert that the use of knotted cord to arrest a crevasse fall is NOT accepted practice and is extremely dangerous.

Support: Strength of the rope and probability of this even working aside, I would think that the energy lost by dragging a bag of snow behind me would make my survival less likely before even taking into account falling into a crevasse.