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redpoint73


Dec 21, 2006, 7:14 AM
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Re: [s2w] Clipping in with static material when cleaning [In reply to]
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s2w wrote:
But so far, no one has posted about taking a bad fall on static material, which is a good thing. This is sport climbing, after all; we're not supposed to be getting seriously hurt. But the bad part is that there don't seem to be a lot of real world experiences we can learn from.

In reply to:
It should be noted that people have died in this situation. A climber died at the Red last year due to falling while being clipped directly to the chains w. a draw. The draw failed, he decked and died. Of course, there is no way of knowing how far he dropped in order to make the draw fail.

That is spooky. Do you know if it was just a single pitch sport climb? Or how the draw failed? I've heard of a couple of cases where the biner has broken from sitting in the hanger incorrectly and having its nose loaded. Just another reason to stay redundant, I guess.

Yes, it was a single pitch sport climb. I did a search on Google and can't find a web article for it (I think I read it in a climbing mag). But I am pretty sure the nylon dogbone failed, not the carabiner. I remember thinking to myself it was a textbook example of why you should not fall on static material, and to stay redundant even if you feel comfortable with what you are doing.


redpoint73


Dec 21, 2006, 7:20 AM
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Re: [jimdavis] Clipping in with static material when cleaning [In reply to]
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jimdavis wrote:
Um, why is it your cleaning the anchor and not setup to rap/ lower?

So you've got your 2 draws or whatever your anchor is made of...you top out, sling into your anchor, untie, thread the rope, setup to rappel, backup your rap or tie a BHK below your device, weight the rope, and take apart the anchor.

Where is the problem with this that requires loading the bolts w/o the rope, and w/o the anchor in place?

Cheers,
Jim

Thats exactly what he is talking about. His point is: that where he climbs, he is not always able to weight the sling while he is slinged to the anchor while he is rethreading the rope. His question is: if you fall for some reason at this point, what kind of force will your body be subject to due to the static material of the sling (b/c the sling will catch you before the rope is weighted).


s2w


Dec 21, 2006, 9:22 AM
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Re: [redpoint73] Clipping in with static material when cleaning [In reply to]
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Thanks for understanding me and clarifying, redpoint73.

I think we all agree that taking a fall on static material should be avoided, whether it be slings, quickdraws, (especially) daisy chains, etc. My questions remain what is the magnitude of force generated in a short (not factor 2) fall, and what is the magnitude where you start to risk injury.

I think I have a partial answer to the second question, from the March 15, 2006 entry on BD's website:

http://www.bdel.com/...p_archive.php#102706

You have to scroll down a ways to get to it, so I'll quote it here: "Also remember that typical falls in the field are in the 2kN (sporto soft catch) to 5kN (harsh, kidney-wrenching) range."

So it sounds like the force above which you may get seriously hurt is about 5 kN. Knowing that the sling would break at 15-20 kN is good to know, but the more critical number is at what point you start to get hurt. In fact, your back would already be broken or worse if you were ever exposed to the amount of force necessary to break the sling.

So that brings me back to the first question, how much of a fall on static material would generate 5 kN? This is more for my own morbid curiosity than anything else, as I don't plan to fall on static material anytime soon.

I also am not too keen on doing my own human test, and keep taking longer and longer falls until my back breaks. But it seems like there should be some kind of drop tests or calculations out there that could take mass, sling material, length of sling, and length of fall, and come up with a force generated.


redpoint73


Dec 21, 2006, 9:46 AM
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It would not be too hard to determine by testing. All that would be needed is a drop tower, load cell, and some weight. You should e-mail KP at Black Diamond and ask him to do it. He seems up for testing crazy shit in his lab.


jt512


Dec 21, 2006, 10:00 AM
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s2w wrote:
Thanks for understanding me and clarifying, redpoint73.

I think we all agree that taking a fall on static material should be avoided, whether it be slings, quickdraws, (especially) daisy chains, etc. My questions remain what is the magnitude of force generated in a short (not factor 2) fall...

It depends on the material you are falling onto. F = ma. Force = Mass * Acceleration. The acceleration in a climbing fall is the deceleration you experience when you hit whatever material you are falling on. Acceleration (or deceleration, if you prefer) is relatively low for dynamic ropes, so your impact force is relatively low; but extremely high for static materials, so your impact force is high. Simply stated, the faster you come to a stop, the greater the impact force.

In reply to:
...and what is the magnitude where you start to risk injury.

It's thought to be somewhat greater than 12 kN, which is why the max. impact force for a dynamic rope allowed by the UIAA is 12 kN.

In reply to:
So it sounds like the force above which you may get seriously hurt is about 5 kN. Knowing that the sling would break at 15-20 kN is good to know...

Your reasoning is incorrect. When you are falling onto a material whose tensile strength exceeds the force that will produce injury, you will be injured. If your impact force is, say, 18 kN, and the static sling you are falling onto doesn't break, then, if the injury threshold is 12 kN, you will be injured.

In reply to:
In fact, your back would already be broken or worse if you were ever exposed to the amount of force necessary to break the sling.

Exactly.

In reply to:
So that brings me back to the first question, how much of a fall on static material would generate 5 kN?

You'd have to be able to estimate the deceleration to determine that. Tough to do. Maybe a materials engineer will read this and be able to help out.

Jay


s2w


Dec 21, 2006, 5:40 PM
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Re: [jt512] Clipping in with static material when cleaning [In reply to]
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jt512 wrote:
s2w wrote:
...and what is the magnitude where you start to risk injury.

It's thought to be somewhat greater than 12 kN, which is why the max. impact force for a dynamic rope allowed by the UIAA is 12 kN.

Good info. It is interesting how much larger this is than the "harsh, kidney-wrenching" force of 5 kN mentioned by BD. Makes me wonder if the 12 kN UIAA value is a force that wouldn't kill you, but could still leave you injured.

In reply to:
In reply to:
So it sounds like the force above which you may get seriously hurt is about 5 kN. Knowing that the sling would break at 15-20 kN is good to know, but the more critical number is at what point you start to get hurt.

Your reasoning is incorrect. When you are falling onto a material whose tensile strength exceeds the force that will produce injury, you will be injured. If your impact force is, say, 18 kN, and the static sling you are falling onto doesn't break, then, if the injury threshold is 12 kN, you will be injured.

Not sure what your disagreement is; this is exactly the point I've been trying to make. You can still get hurt at a force below the breaking point of the sling.

The 5 kN number for injury threshold may be wrong, though. For obvious reasons, it would be hard to determine exactly what that number is.

In reply to:
In reply to:
So that brings me back to the first question, how much of a fall on static material would generate 5 kN?

You'd have to be able to estimate the deceleration to determine that. Tough to do. Maybe a materials engineer will read this and be able to help out.

Hopefully. I'm surprised no one has more detailed info on this; it doesn't seem like that unusual of a question.


coastal_climber


Dec 21, 2006, 7:45 PM
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Re: [jt512] Clipping in with static material when cleaning [In reply to]
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jt512 wrote:
coastal_climber wrote:
In reply to:
Yeah, a 2-foot fall onto a static tie-in would be quite serious. I suspect that you could break your back.

Laugh

I had a feeling someone might interpret my remark as facetious. It wasn't. I suspect that such a fall, or more accurately, such a sudden stop, would be quite serious. Try this experiment: Take off your shoes (to eliminate any cushioning they might provide). Climb onto a 2-foot-high chair, and jump down onto a hard surface, paying close attention to how you land. How did you land? Flat-footed with your knees locked? No way. You landed on the balls of your feet and bent your knees. This decelerated you over about a 6-inch "crumple zone," if you will. Now, climb back up on the chair, and just imagine what would happen if you jumped again, but landed flat-footed with your knees locked. (If you actually try to land this way, you won't be able to. Your reflexes will take over and you will land safely.) Now, imagine taking the same jarring fall onto static material tie-in at your waist. I really think that such a fall could be life threatening.

You have to understand that the impact force is proportional to your rate of deceleration; rapid deceleration (ie, stopping quickly) means high impact force. In theory, if you stopped instantly, the impact force would be infinitely high, no matter how short a distance you fell; a one-inch fall would kill you! In reality, of course, you can't stop with absolute instantaneity. A fall onto a "static" sling would still have some slight deceleration, but it would be so minimal that your injuries would likely be severe. So, even short falls onto static materials must be categorically avoided.

Jay


Sorry, but at the moment it seems quite funny considering the previous posts. I've taken some short hard falls, and they aren't anything to laugh at.


Partner rgold


Dec 21, 2006, 9:14 PM
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Here's some theoretical calculations that give a sense of how bad things might get. Suppose you clip in with a short draw, step up a bit and then slip so that you take a "factor-2" fall on the draw. (The quotation marks are there because the actual fall factor is much worse.)

A while ago Petzl tested one of their nylon runners and found it had a UIAA impact rating of 18 kN. If the draw is 6 inches, add a carabiner on each end and the thing you're taking the "factor-2" fall on is about 1 foot long, meaning a fall of 2 feet. But there is only 6 inches of nylon present to absorb the fall energy, so the fall factor is 24"/6" = 4. That's right, a fall-factor of 4 on material with an 18 kN UIAA impact rating. The result, using the standard equation for impact load and an 80 kg leader, is a peak load of nearly 27 kN, which will bust a lot of gear, and apparently has in the two cases I've heard about.

The results would be higher with spectra.

Another poster asked how much of a fall (I assume on a two-foot runner) it would take to produce a 5 kN impact. Using the 18 kN figure from Petzl again, the result is a fall factor of 0.1, or a bit less than two and a half inches.

Caveats: These calculations assume the sling tension is a linear function of elongation, i.e. Hooke's Law, and this is only an approximation, although in many cases a reasonably accurate one, of the real situation.

It is also true that carabiners deform under load and so can absorb some fall energy. I assumed above that the energy absorbed by carabiner deformation is negligible.

Bodies on the end of the rope seem to be able to absorb a substantial amount of the fall energy.

The 12 kN injury threshold came, I think, from Army tests using parachute harnesses. A climbing harness might concentrate the impact somewhat more. The worst case is if the falling climber tilts backwards and is roughly parallel to the ground and facing up when the impact occurs. In this case the impact will be delivered to the spine and it is probable that a broken back will result. I have read of a sport-climbing fall, involving a much lower impact than we are speaking of here, that broke the leader's back in this way.

Caveat on the caveats: I think the results are sobering even if it were to turn out that the ideal numbers are off by, say, 25% in these cases.


s2w


Dec 21, 2006, 9:55 PM
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redpoint73 wrote:
It would not be too hard to determine by testing. All that would be needed is a drop tower, load cell, and some weight. You should e-mail KP at Black Diamond and ask him to do it. He seems up for testing crazy shit in his lab.

Done. I'll post up if he gets back to me.


oetkb


Dec 21, 2006, 10:06 PM
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There is some quite interesting information in the following:

http://www.hse.gov.uk/...df/2003/hsl03-09.pdf

The paper is a UK study on aspects of industrial fall safety, but has an interesting history of "impact testing" and quite a bit of relevance to climbing, and in particular to the subject of this thread.

Highlights:

pg3: 12G recommended maximum deceleration with parachute harness (note: not 12kN, although that value appears to be derived from the 12G value).

pg4: Only full-body harnesses are now considered suitable, and the standard for "arrest force" is 6kN (EU) and 8kN (US/Canada).

pg5: Discussion of 12kN maximum for parachute harnesses, difference between parachute harnesses and industrial harnesses, and that 12kN assumes fit young men.

Of particular interest to climbers is the bit about parachute harnesses having "greater torso constraint than industrial harnesses" considering our climbing harnesses have no torso constraint at all.

pg15: Table 1 shows the differences in deceleration levels (G) for different body weights at 4kN, 6kN, and 8kN "arrest force".

Some of what I took from the paper is:

1. Fall forces on climbers' bodies are generally considerably less than we tend to think (otherwise we'd end up injured a lot more often).

2. Because of our (climbers') waist-level arresting point, we are very lucky that force levels are typically as low as they are.

3. Don't fall on static materials.


jt512


Dec 21, 2006, 10:08 PM
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rgold wrote:
The 12 kN injury threshold came, I think, from Army tests using parachute harnesses.

Nice of the UIAA to set the max impact force standard for ropes right at the injury threshold, huh?

Jay


(This post was edited by jt512 on Dec 21, 2006, 10:25 PM)


s2w


Dec 21, 2006, 10:19 PM
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Great info, rgold, thanks.

rgold wrote:
The result, using the standard equation for impact load and an 80 kg leader, is a peak load of nearly 27 kN, which will bust a lot of gear, and apparently has in the two cases I've heard about.

The results would be higher with spectra.

Another poster asked how much of a fall (I assume on a two-foot runner) it would take to produce a 5 kN impact. Using the 18 kN figure from Petzl again, the result is a fall factor of 0.1, or a bit less than two and a half inches.

Any chance you could post the standard equation you are speaking of? Or if not, could you do a calc to see how much of a fall would produce a 12 kN impact, on the same two-foot nylon runner? I would like to get an idea of how the force varies with fall distance in that situation.

In reply to:
I think the results are sobering even if it were to turn out that the ideal numbers are off by, say, 25% in these cases.

Agreed. It's definitely something that it's good to be aware of if you are in this type of situation, clipped in with static slings with any significant amount of slack.

Really appreciate your sharing of your findings with us.


Partner rgold


Dec 22, 2006, 12:38 PM
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s2w wrote:
Any chance you could post the standard equation you are speaking of?

Attached here as a .pdf file is the equation (and its derivation for those who might be interested).

Edit: Expanded version including differential equation derivation has replaced original attachment.


(This post was edited by rgold on Dec 27, 2006, 2:49 PM)
Attachments: StandardEqn.pdf (93.2 KB)


jt512


Dec 22, 2006, 10:25 PM
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rgold wrote:
s2w wrote:
Any chance you could post the standard equation you are speaking of?

Attached here as a .pdf file is the equation (and its derivation for those who might be interested).

Thanks for writing that up. I'd seen the conclusion before, but never knew whence it was derived [I just wanted to throw a "whence" in there].

Something I never realized is that the model implies that the max. impact force is not proportional to the fall factor. For instance, for an 80 kg climber (obviously a trad), doubling the fall factor from 0.5 to 1, increases the max. impact force by only about 35%.

Jay


Partner rgold


Dec 23, 2006, 9:31 AM
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jt512 wrote:
I'd seen the conclusion before, but never knew whence it was derived

Warning: math rant follows.

I gave the derivation that is mathematically the simplest. The simplicity of the math is obtained by using a principle of physics that is not really so simple; conservation of energy. It is also possible to obtain the same result without reference to conservation of energy by using the differential equation for simple harmonic motion, thereby trading sophistication in one realm for sophistication in another.

The differential equation approach has significant advantages if one wants a more accurate model. The equation for simple harmonic motion can be modified to include a damping term. Experimental results suggest that damped harmonic motion provides a more accurate model of the elongation phase of rope deployment (although I don't know of any arguments that explain why, in principle, this should be the case, other than the observation that the rope behavior looks like that of a critically damped spring).

It is also possible, using differential equations, to model the sections of rope between pieces of pro separately and thereby take into account the fact that, because of friction in the system, different sections of rope are loaded differently and therefore make different contributions to the absorbtion of fall energy. Of course, once one sets up such a system of equations, the idea of a closed-form formula for peak impact load goes out the window and numerical methods are used to find and/or plot approximate solutions.

Edit: The .pdf attachment posted above has been updated to include the differential equation approach.


(This post was edited by rgold on Dec 27, 2006, 2:51 PM)


macblaze


Dec 26, 2006, 10:13 AM
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zip_ty wrote:
I picked up a Metolius Personal Anchor System instead of slings or a daisy chain.
...
It stays out of the way very well on my harness but I'm wondering if anyone else has experience actually using one. Are they strong/safe?

"Nobody really addressed this within the context of the thread. I'm going to assume that all the arguments against slings/daisys apply to the PAS as well ...right?

It does seem kinda a wierd that given the math in this thread that Metolious still says things like:

The PAS is yet another example of Metoliusí commitment to products that are safer by design. It is designed to give the climber a high-strength anchor connection while threading for the lower, setting up a rappel or belaying. "

Just wondering...


dan2see


Dec 26, 2006, 11:44 AM
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rgold wrote:
A while ago Petzl tested one of their nylon runners and found it had a UIAA impact rating of 18 kN. If the draw is 6 inches, add a carabiner on each end and the thing you're taking the "factor-2" fall on is about 1 foot long, meaning a fall of 2 feet. But there is only 6 inches of nylon present to absorb the fall energy, so the fall factor is 24"/6" = 4 ...

Don't panic!

When I fall in my sit harness, with my own weight, the material pulls out about 6 inches (I think). It's a bit of dynamic slack.

Actually the first 3 inches of the fall is easy slack in the swammi belt, before the harness starts to tighten up. But then the whole rig tightens up, and a certain amount of elastic force pulls the knot further away from my body.

My harness is close to my center of gravity, and it has a good grip on my pelvis. But my legs and upper body will take a little time to start moving.

I don't mean to minimize the problem of falling on you sling, I just think your gear will survive. But your fall factor of "4" on that static anchor might be a lot softer than that.

On the other hand, this slight slack means that, if you do slip off your foothold, then by the time you react to the motion, you're already on your way down. You won't have time to catch your fall by grabbing on a nice handy flake. Your whole fall would be over and done with, before you even realize you've just tested that solid bomber static set-up.


dan2see


Dec 26, 2006, 11:51 AM
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Recently somebody posted a link to a Petzl page (I think) that showed the correct sequence to re-thread the TR anchor for cleaning.

Their procedure suggested:
- When you clip yourself to the anchor, sit on your sling.

At the time I didn't think that was too important. Now this thread makes it plain.

I searched but failed to find it. Can anybody find the Petzl link and post it here?


Partner bdplayer


Dec 26, 2006, 7:12 PM
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zip_ty wrote:
I picked up a Metolius Personal Anchor System instead of slings or a daisy chain.
...
It stays out of the way very well on my harness but I'm wondering if anyone else has experience actually using one. Are they strong/safe?

I've been using one for a little while now, about a half year of pretty frequent climbing and love the thing for what it is. Yes, it is a static link in the system, but as long as there is virtually no extention, then you mitigate the issue (for the most part, I know, I know) of shock loading.

How it is superior to a daisy chain, is that it is made of a series of loops, individually stitched out the wazzoo, as opposed to a daisy chain, which has a history of "zippering." After the daisy zippers, it hits the end, and loads the system pretty darn good. Provided it doesn't break, but that's pretty rare from what I hear (no personal experience with one breaking). The PAS has about as much chance of breaking as a carbiner or dyneema sling, which is good and bad. It won't break on you, but it may rip some pieces out of the wall if it shockloads the system.

Just gotta make sure that don't happen..... Don't be a dumbass and you'll be happy(er).


Partner rgold


Dec 27, 2006, 2:56 PM
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A few comments...

Dan2see suggest that the various amounts of "give" in the system will mitigate the extremely high impact numbers I gave for a factor 2 fall on a draw. True enough, but those ideal limits are so high that there is potential for serious problems nonetheless. And since their have been at least two instances in which a draw has failed with a human rather than a test weight clipped to it, these concerns are not unrealistic.

As for the comments about the Metolius PAS, it is safe in the sense that I don't think it will break in a factor 2 fall onto the anchor (Edit: This supposition is wrong. Jim Ewing of Sterling Ropes has broken two PAS's with factor-2 falls), something that cannot be guaranteed for daisies and spectra runners. And it is also safe in the sense that the pockets are full-strength and cannot be clipped so that a fall releases the carabiner completely at a few hundred pound load. But, as Bdplayer says, it does not avoid the potentially serious problem of high anchor and body loads if it is called on to stop a fall directly.

Edit: The results I've seen so far seem to indicate that spectra/dyneema runners and daisies cannot reliably withstand a factor 2 fall. Act accordingly.

Finally, my math rant generated some questions about the differential equations approach to maximum impact load. So I expanded (and slightly revised) my write-up posted back here so that now both the conservation of energy approach and the differential equations approach are included.


(This post was edited by rgold on Dec 30, 2006, 4:50 PM)

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