Cordelette - fixed loop? Or no?

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Ed Hartouni

Trad climber
Livermore, CA
Jul 10, 2014 - 07:38pm PT
total belay anchor failure is rare because there are few falls that actually load the anchors much beyond body weight. When was the last time you held a factor 2 fall?

the forces of falls are largely damped by the other parts of the system, the ropes and the anchors along the lead... which do blow occasionally.

But we don't know about any anchor failure unless it is reported, and that is usually only for a serious injury accident.

most belay anchors never hold much more than body weight (aid anchors might hold static loads up to 500 lbs)
ruppell

climber
Jul 10, 2014 - 07:44pm PT
Sure. How about the pieces that make up the anchor? I've fallen on a lot of gear. Well over 100 placements. I've only had two pieces ever fail. One broke the rock it was placed in and one was just a crappy piece. So my first hand observation is a 2% failure rate with normal forces. Assuming a factor two fall onto the anchor what is the probability that all three pieces fail?

We don't have that data but you'd have to agree the chances would most likely be pretty small.
jstan

climber
Jul 10, 2014 - 08:12pm PT
Forces on the anchor are surprising. Everyone really should go out and measure this a few times.

As has been stated things like the length of rope in the system are critically important. Tie your swami into an anchor and drop six inches. Don't try dropping a foot.

Using a piece of perlon I made a device for measuring peak force, and then dropped a US army duffle bag filled with 165# of shale about 40 feet. Free fall. When a belay was given I got about 500# on the anchor. When I tied the belay to a big tree I measured about 1000#. There was about 100 feet of rope in the system.

I also set up to watch the failure of a nut from close by in the same kind of fall. I thought I might be able to see how it failed. I used a rusty old 1/2" angle as the backup. About all I saw was a big cloud of rust. The duffle bag was cool with the whole affair.

PS
Don't take anyone's word on this. Go measure.
rgold

Trad climber
Poughkeepsie, NY
Jul 10, 2014 - 08:20pm PT
Ruppell, we're speaking about forces that might be triple the ones your "normal" falls engendered, so any attempt at extrapolation from that personal experience is going to be seriously flawed.

But that may not be the point. Suppose we stipulate that the probability of failure of your belay anchor under a severe fall (and factor 2 isn't the worst, the worst is factor 1.8 with the belay redirected through the belay anchor) "would most likely be pretty small." Of course we have absolutely no practical clue what "most likely pretty small" actually means. In a lot of statistical work, "most likely pretty small" means 1 in 20. That doesn't sound good to me for a belay anchor, although the owner of Metolius has stated that's about what you can expect from a cam placement. In high-precision manufacturing, "most likely pretty small" means "six sigma," or very roughly 1 in 300,000. BD rates its gear to "only" 3 sigma standards, meaning the probability of failure at a load below the given rating is about 1 in 770. So how does 1 in 1000 sound for a probability of catastrophic belay failure? Is that "pretty small?"

Part of this is to suggest that it doesn't matter that the probability of total failure is "pretty small." The smallness is certainly is of little consolation if you find yourself and your partner(s) plummeting to the ground. The question some folks find worth discussing is, "are there simple rational ways to make failure less likely?" The mindset is that we don't know what the odds are, and even though we believe them to be massively in our favor, we are not against trying simple things to make them a little better, and avoiding obvious things that will make them a little worse.
ruppell

climber
Jul 10, 2014 - 08:46pm PT
You guys are the math wizards here. If you say a standard probability of a single cam failing is 1/770 I believe you. My carpenter brain says even with two cams that ratio goes way up. With three even higher. Also how is BD testing their cams? The point is anchors don't fail often. Hence the "small" chance. I'm all about climbing as safe as possible. I just don't worry about my belay failing.

In situations where a fall onto the anchor can occur I always have my belayer tie off at least ten feet down from the anchor. Then I clip a piece of the anchor and climb. Luckily, I can climb pretty well and have never actual taking that fall. If I ever do though it's at least reducing the fall factor significantly. It also provides an adding benefit of the belayer being able to get out of the way.
Ed Hartouni

Trad climber
Livermore, CA
Jul 10, 2014 - 09:45pm PT
an anchor failed high on DNB, three pieces, leader on easy ground took a force 2 fall on it not too far out,
it is speculated that the three pieces were all behind the same flake, and the flake blew...

don't do that...

the party of two experienced climbers went all the way to the ground.
rgold

Trad climber
Poughkeepsie, NY
Jul 10, 2014 - 10:05pm PT
Actually Ed, that was four pieces. The party was using 9mm half ropes and the anchor was constructed using both ropes. One rope has a blue Alien and a #4 BD stopper clove-hitched in series, the other rope had a purple and a green camalot clove-hitched in series. The leader had about 25 feet of rope out and no protection or carabiners were found on the rope, so possibly a 50 foot factor-2 fall. I don't think anyone knows for sure exactly where the fall happened or whether the leader was, in fact, on easy ground; the DNB is rather run out in some places. All we know for sure is that the four anchor pieces blew. These were very experienced climbers, by the way, and they had recently done a bunch of other hard Yosemite routes.

The AAC Accidents in North American Mountaineering 2002 has these details. The report mentions that "at least 5 other cases of complete anchor failure (protection pulling out---not breaking) have occurred in the last 30 years in the Park."

This means I have to substantially revise my "one failure every ten years" remark.
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