Evaluating blocks as rap anchors

[AOC]

Last week while rapping off Mt. Sill in the Sierras I had a close call when a refrigerator-sized block shifted in mid-rappel. My alert partner shouted a warning and I was able to quickly get my weight off the rope and escape the system. I had bounce-tested the new anchor and called it good. I'm thinking now I may not have tested it at the proper angle given the orientation of the descent gully.

 

In light of my lucky break, and the heartbreaking events on Sharkfin Tower, I'm wondering if there is any technique, other than (proper) bounce-testing, to evaluate blocks that appear solid as the Parthenon?

[glassgowkiss]

99% of accidents follows this pattern: a couple of bad decissions mixed with pure bad luck. most of the time we can get away with a slap on the wrist, but sometimes shit hits the fan.

imo having a hammer and some pins would be a good idea for going alpine. it's a norm for the canadian rockies, but for the cascades very few people take it.

hammer will allow you to test integrity of the blocks better then anything. pins are resonably cheap way to get your ass down. and for crying out don't rap of a single point. have a back up- second can pull it, but back up your rap. and put a new sling on old anchor.

[jmace]

I dont think I would bounce test any block, maybe try and lever it off but if you bounce test it what happens if it fails? Those knid of raps are very delicate and your partner should not be tied in to the block, at least I wouldnt.

[AOC]

Good points. The main anchor was backed up with gear, but the back-up would have been useless if the block fell. Either I would have been crushed or the backup would surely have failed. I bounced tested it while tied into the back-up gear only.

[klenke]

Ultimately, whether you test (bounce, lever, or otherwise) any block anchor candidate would have to do with if anyone was below you (other parties), whether that was your only choice no matter what, and so on. Dynamic yet iffy decisions often have to be made if you're going to get down versus staying there all night waiting for other forms of rescue.

 

You can set a back up anchor (if available) in case a primary block fails but pray that the failing block doesn't flog you on acceleration past you.

[glassgowkiss]

one thing for sure- you are not going to learn this stuff on internet. only hours spent climbing count. you might get an idea or two, but only hours roped up count at the end, so we can pretty much close this topic. everything else is just pointless speculation

like i said- majority of accident is a simple accumulation of bad decission mixed with bad luck.

[specialed]

Look at where and how the block is attached, kick it, try and move it, whatever. Try and back the first rappeller up with cams and shit. Rapping off some blocks is just going to be a gamble whatever you do.

[sobo]

This is a really difficult concept, because stability of blocks in this size range is so hard to judge. These blocks are typically huge, and as Cobra Commander mentioned in the NCNP accident thread, we often assess them with a "looks bomber to me" comment and carry on.

 

It's really hard to tell by kicking the thing, because it prolly outweighs you by 60 to 75 times your own weight (a cubic yard of "solid generic rock" weighs about 4,000 lbs. - extrapolate this to a "refrigerator-sized" rock, which is about 3 cubic yards, or about 12,000 lbs.). If it's going to go, you're not gonna know it by kicking it unless it's going right now.

 

There was a car-sized block outside the entrance of this cave near VA Tech several (15?) years ago. It was the standard rap anchor to rig up a free rappel into the cave (Pighole, I think, was the name, for any Hokies who may be reading this and are familiar with the area). Peeps had been rapping off this thing for decades and decades, myself included. One day, a guy from the Cave Club rigs up, goes over the edge into the pit, and the block follows him down. It's my understanding he's still under it. Who'd a thunk it would have ever pulled off?

 

Point is, that size of block, you just can't tell until it's actually going down. Similar thing happened to me at Vantage about the same time as the incident above, but that chosspile is a different story!

 

edited to change the name of the cave after verifying Smokehole was incorrect

Edited July 18, 2005 by sobo

[Rad]

Don't forget to apply your knowledge of physics in setting anchors and rappels.

 

When possible, sling the base of blocks and avoid anchors that may torque or lever the block out of its resting position.

 

A back-up anchor is a good idea, but it can be time consuming and impractical to set them at every rap station on long descents.

 

If you use a back-up anchor make sure it is completely independent (e.g. separate crack system). Stoppers in cracks on opposide sides of a large block are NOT independent.

 

Rappel separately and avoid bouncing to minimize forces applied to the block.

 

Don't be cheap! Place a fresh sling, leave an extra stopper and carabiner, or even two, if necessary. Your life is worth more than the $20 you may spend replacing those few pieces.

[sobo]

Amen to all of that! Nice summary, Rad.

[forrest_m]

i agree, a hammer is a good tool for testing, but if you don't have one, a thorough kicking is better than nothing. (while still on rappel from the previous anchor if possible). LOOK for any movement, any shifting dirt around it. If the block is big enough to rap on and you can get any visible motion from it, it's not solid. LISTEN for any hollow sounds, thuds, rock-on-rock grating. the block is big enough to rap on and you hear anything but solid rock, it's not solid.

 

all that said, sometimes you have to use something that is questionable. in that case, it is probably better to use something wedged into the side (stopper, chockstone, knot) rather than slinging the whole block, because the force from your rap would lock the big block into place rather than pull it out/off. (this often uses a lot less sling, too).

 

on a tangential note, if you ever find yourself in a rescue situation, remember that climbing gear is really "optimized" for light weight and dynamic loads. in a rescue situation, with multiple people weighting an anchor and an "inert" subject, it is very easy to develop forces large enough to break standard climbing gear or cause failure in ordinarily solid anchors. obviously, in an emergency, you do what you need to do, but if there's any way to get redundancy into your system you should try to do it.

[klenke]

Re: Forrest's last paragraph:

In Kelly Bush's Sharkfin accident report, this appears to be a possible explanation for the anchor failure: too much static loading on the block.

[knotzen]

This is a good discussion. Can't tell you how many times I've looked at a block used for a belay or rappel anchor and wondered how secure it really was (i.e, what it would take to move it). Even in L'worth. It's just really hard to tell, and often they appear to be the only anchors available. And people are so relucant to leave gear behind; the Sharkfin Tower accident has given me new respect for really making sure your anchor is just about nuclear-bomb proof, to the greatest extent possible. And no, $20 is not too much to ensure a safe return.

[Dr_Crash]

The really bad thing is when you really cannot know until the thing goes, like in sobo's example, or like that flake on Midway that everybody had climbed on but decided to fall on my head and my belayer's leg when our friend went on it. Absolutely no warning, and our friend had climbed it 2 minutes before downclimbing and restarting.

 

Speaking of flakes instead of blocks, if that's all you have, it's relatively easy to figure whether they're hollow or not by tapping them. And I've been given the advice to use nuts rather than cams behind them if possible, as the cams would lever off in the case of a fall (for rapping, nobody would leave a cam unless it's the only option). Seems to make sense to me, what do people with more experience say?

 

drC