Statistics on types and survivability of anchor failures?
The most recent (2013) edition of Climbing Anchors, by Long and Gaines, makes some interesting statements in the preface about catastrophic failures of anchors. Long first says that: when belay anchors fail, it's usually in cases where the gear was placed in a horizontal crack, and the anchor was subjected to a shock load sideways to the intended direction of pull. He attributes this to anecdotal reports. He also says the following, which I find very surprising.
Because statistically, the majority of climbing accidents occur from leader falls, we'd expect catastrophic anchor failure to result from a leader taking the dreaded Factor 2 ripper right onto the anchor. Not so. Most of these failures involved a leader belaying a second up on a toprope.
So from this information, it sounds like these failures often happen the first time the anchor is ever loaded, i.e., it was such a poor anchor that it wouldn't hold even a top-rope fall.
Is it possible to find systematic statistics anywhere on the types of anchor failures (top-roping, leading, ...) and how survivable they were? In the case of the leader belaying the follower, it seems like the failure might actually be survivable in many cases, since there might still be a lot of gear down below that hadn't yet been cleaned. (But the belayer had better maintain a serious death-grip on the rope!) Even if, as Long says, few failures are from factor-2 falls, those are probably the ones that would not be survivable at all, since there is no other gear present.
I'm also having a hard time reconciling the statements that:
- "anchor failures are usually from a load "sideways to the intended direction of pull,"
- they usually happen while the leader is belaying the follower.
When the leader is building the anchor, his rope is trailing right back toward his last piece of pro, so it should be dead obvious what the direction of pull is going to be when he catches a fall by the follower. The exception would be, I guess, when there is a traverse from the last piece to the belay station, and the follower takes a fall after cleaning that final piece (and in this case, the anchor failure is probably not going to be survivable).
I would also be interested in statistics about how many accidents are caused by anchor failures while climbing, as opposed to rappelling. The latter seems more common, which probably isn't so surprising, since people usually try to make their belay anchors really bombproof.
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Personally, I can easily see how this unintended loading can happen.
Second gets to a tricky part, asks leader for beta, leader moves over to get a better view of second.
This question is an example of one of the really hard problems in climbing. It's almost impossible to get feedback about how well you are building your anchors. You just don't get many chances to be wrong.
99% of the time any protection you place simply won't be tested in any way. Most of the time it simply doesn't matter if you build a crap anchor or a bomber one. If nobody falls or the belayer has a good enough position to hold the fall with body weight, the anchor never gets stressed. It's next to impossible to know if you are good or just lucky.
You can develop or follow really bad practices for a very long time and not suffer any consquences. The America Death Triangle is a classic example. In the 70's when I was learning to climb, that was standard practice in the USA. Everybody I climbed with used it, so I used it too.
Ideally, you'd like to spend time building anchors and throwing dummies off cliffs, but that's expensive in ropes and time.
One way you can get better at building anchors is aid climbing, but that pretty old school these days.
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There are no statistics because no-one really keeps statistics about anchor types in accidents. Possibly also because anchor failures are extremely rare.
However, individual case studies on specific anchor failures do exist. For example, http://publications.americanalpineclub.org/articles/13201215224/Rappel-Anchor-Failure-inadequate-Anchor-and-Backup
It is also largely impossible to examine, objectively, the "bombproofness" of an anchor which is highly subjective. The best we can do (objectively)
- Examine placements
- Sanity Check rigging (no force multipliers)
- Check for objective hazards (loose rock, avalanche, etc)
The rest is a matter of personal preference/belief and to a large degree - luck. We limit our exposure and rarely do we maximally load our anchors.
We have good objective knowledge on which anchors do not work, but there is much less clear information on how generally applicable anchors can survive extremes, and much debate can be had about the best anchor to use and which specific corner case allows it to shine, but in the end the only answer is
It Depends, but KISS
Rarely do we build "universal anchors" and as an example most climbers will rappel off of something much less "bombproof" than they would belay from (application specific subjectivitiy). If you anticipate side-loads then you must build to withstand side-loads, but agonizing over side-loads in every situation is somewhat counterproductive.
However, Statistics do dictate that minimizing exposure increases your odds of survival the most and simplicity reduces chance of error so most effective use of your time is to develop reliable systems that you can build fast and in the most situations and can do fatigued and on 72 hours with no sleep
The best we can get are accident publications. In the US and Canada this is "Accidents in North American Mountaineering/Climbing" published by the American Alpine Club.
The best conclusion to draw from the published statistics here is that the vast majority of accidents involve a leader fall with inadequate protection and generally as often as not involve no belay at all. Rappel errors account for some amount of accidents, but this category includes rappel errors of all kinds.
What we can say is that pulled gear, or gear failure (the rarest of events) is only a contributory cause in approximately 400 out of 8000 accidents in North America between 1951 and 2017
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