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clmbnski
Feb 16, 2002, 1:58 AM
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Registered: Feb 11, 2002
Posts: 85
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I dont know where this topic should go but I just thought of it. The other day I was discussing with my friend what type of carabiner to buy. The only difference between the two was that one was rated at 21KN and the other at 24KN. I then realized that there is probably no situation that would put that much force on a carabiner. I told my friend that your had would probably let rope slide through the device before the force ever got up to 21KN. He then told me that you can only hold 4KN with a belay device and cams fail around 12KN. I dont really know if these numbers are right but if they are then their isnt any reason to buy something with that much strength if your protection would fail first. Is there any reason to buy a very high strength carabiner? Any comments?
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elcapbuzz
Feb 16, 2002, 2:07 AM
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Registered: Aug 24, 2001
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I'm not sure about the rating on the belay device. It doesn't sound right.
Ok, every piece of pro could blow on the whole pitch. Unless your standing on the ground the carabiners that are clipped to the belay anchors are whats going to save your life.
So, yes. They need to be rated that high.
Cheers, Ammon
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jt512
Feb 16, 2002, 3:39 AM
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Registered: Apr 12, 2001
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First, a side point: I doubt that any cam would hold 12 kN of force. Cam strength ratings are BS because in the field (as opposed to the lab) the cam will pull out of the rock or break the rock before the cam itself will fail. Don't count on a cam to hold much more than 2000 lbf.
Okay, now to the main point: How much force does a carabiner need to hold. Assume you are falling on a single biner, as you would be by falling on an intermediate piece of protection (ie, not the belay anchor). The force on the biner is the sum of two forces: the force on the falling climber and the force on the belayer.
The force on the falling climber is a function of the belayer's weight, the fall factor, and the dynamic properties of the rope.
The force on the belayer is a little more complicated. It is the lesser of (1) the maximum force the belay device can hold (about 4 kN for an ATC, much more for a gri-gri) and (2) 66% of the force of the on the falling climber.
Thankfully, most falls are less than factor-1 falls; such a fall is not likely to put more than about 5 kN on the falling climber. The belay device will feel 66% of this, or 3.33 kN. Adding those together, the carabiner will feel 8.33 kN. So you are correct that any closed carabiner will hold this amount force.
The problem, though, is that the gate of the carabiner is likely to be open at the moment of impact, either due to vibration caused by the rope (gate flutter) or by inertia caused by the gate being banged into the rock when the climber falls. Open-gate strengths of carabiners range from 7 kN to 10 kN -- right in the range of force which they are likely to hold. This is why the only important rating of a carabiner is its open-gate strength.
-Jay
[ This Message was edited by: jt512 on 2002-02-18 15:40 ]
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