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JeffreyR

Carabiner Failure...?

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broken%252520carabener.jpg

 

One of my friends was slack-lining and had a carabiner snap. It was a fairly short line (no more than 30') and shouldn't have been under a huge load. Any thoughts...?

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Interesting... I was climbing with a guy who was demo-ing gear for BD over 15 years ago, and we were demo-ing the new (at the time) Fin biner. I failed one in a fall from several feet above the bolt. Only time I've ever seen that, until your pic.

 

Carlos sent the broken Fin back to BD, and it wasn't long before the design was changed, then discontinued altogether. Curious, was your biner ever dropped onto a solid surface from height? Mebbe a micro-fracture? From the failure location, it's possible that it was over-torqued. I hesitate to say stress corrosion cracking given where it failed, but it's also a possibility...

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Slack lines put anchors under gigantic loads via the following equation:

 

Load = 1/2 * (Wt of person + slackline)/COS(1/2 * Catenary Angle),

 

where

 

Catenary Angle = 180 degrees for a perfectly flat slackline under load

 

As Catenary Angle approaches 180 degrees (taughter slackline), COS (1/2 * 180) = 0, so Load on the anchor goes to infinity.

 

 

If your Weight is 1 kn (224 lbs), and

Load at Failure for a 1 biner anchor = 22 kn, then your Catenary Angle is

 

Angle = 2 * ACOS(1/2 * 1 /22) = 177 degrees

 

If the gate was somehow kinked open, your biner breaking strength drops to 8 kn

 

Angle = 2 * ACOS (1/2 * 1/8) = 172 degrees

 

If you want a 3x factor of safety for a single biner anchor at this weight, then you need a Catenary Angle that is no larger than:

 

Angle = 2 * ACOS (1/2 * 1*3/22) = 172 degrees

 

BTW, the shorter the line, the less spring deflection you've got, the closer the Catenary Angle gets to 180 degrees, and the larger the loads. Longer slack lines, despite adding the extra weight of the rope, generally have lower anchor loads.

 

You might consider using big stainless locking biners for slacklining rather than those light weight jobbies. Don't use clove hitches for attachments either. They can get so tight you've got to chop the tat/rope to get them off. Rewoven figure 8 is good.

Edited by tvashtarkatena

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This is also why, when climbing, you...

 

a) should never use the American Death Triangle for anchors and

 

b) should set up your equalized anchors such that the angle of the dangle (angle between the two equalized stands) is 60 degrees or less.

Edited by tvashtarkatena

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Stop this microfracture business. That's not how aluminum fails.

 

Aluminum is a ductile material that deform much more readily than it cracks. The cracks that do develop are not hidden.

 

Material failure is a pretty complicated business. A lot more info is needed to even speculate what went wrong. Right now, the only assumption that can be made is that the carabiner broke.

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Wow tvashtarkatena! Very nice response - and it totally makes sense. I don't slackline, but I really enjoyed reading about how the loads get calculated. Amazing how much load is there and even worse because of the length of the slackline.

 

Edited by CaleHoopes

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Ziplines, slacklines, tyroleans...all basically face the same anchor load problems.

 

When in doubt, let it sag.

Edited by tvashtarkatena

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Pat,

We go thru that same thought process in mountain rescue when setting up a Kootenay Highline for river/canyon crossings. Although we don't carry calculators, we've carry it all "up here" and paint the numbers with a very wide brush, and target a 10:1 static system safety factor. So yeah, we let it sag if we can (deep canyon), or double up on the number of lines in the span if we can't (not enough clearance to keep subject dry/safe).

 

And NO KNOTS in the mainline - friction wraps only, cuz you already know the answer to that one...

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Right now, the only assumption that can be made is that the carabiner broke.
I'd say that's far more than an assumption right now... :whistle:

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Any thoughts...?

take it back to rei - i'd be less than 100% satisfied :)

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I've witnessed two BD hotwires snap, as well as climbed with a friend who had just seen a Mammut moses snap. These were all in climbing applications. I think it happens much more frequently than many climbers would guess.

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Ziplines, slacklines, tyroleans...all basically face the same anchor load problems.

 

When in doubt, let it sag.

'Let it sag' generally isn't an option for slacklining and tightrope - you want it tight or it isn't worth doing at all. So rather than 'let it sag', I'd say when in doubt - beef it up - go steel as suggested and beef up every element of the system you can if doing longer lines.

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'Taught' is assumed, but a few degrees of sag (when weighted) goes a long way. Reducing force on the anchor to an acceptable level given your setup is your first consideration. Beefing that anchor up is your second. You can have a nice, tight line and an catenary angle less than 170 degrees, no problem. Been there, done that.

 

If you've got a cell phone with a calculator, you can use a lighter test weight to calculate what your catenary angle would be under full load by measuring the line deflection under that test load, the distance between the anchors, and then applying a little trig 101. If your angle exceeds what it should under your max allowable Load (given the equation above), then you need to back off on the tension until it doesn't.

 

Better to know than to guess and just 'beef things up'. An anchor failure in these applications can be kinda bad.

 

 

Edited by tvashtarkatena

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I once blew out an old oval on a short sport climb fall. The biner did not break but was bent backwards leaving the gate wide open. It still held the rope in the hanger though. I think I still have it laying around somewhere.

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'Taught' is assumed, but a few degrees of sag (when weighted) goes a long way. Reducing force on the anchor to an acceptable level given your setup is your first consideration. Beefing that anchor up is your second. You can have a nice, tight line and an catenary angle less than 170 degrees, no problem. Been there, done that.

 

If you've got a cell phone with a calculator, you can use a lighter test weight to calculate what your catenary angle would be under full load by measuring the line deflection under that test load, the distance between the anchors, and then applying a little trig 101. If your angle exceeds what it should under your max allowable Load (given the equation above), then you need to back off on the tension until it doesn't.

 

Better to know than to guess and just 'beef things up'. An anchor failure in these applications can be kinda bad.

I've been walking for a long time and never met anyone who ever took this analytic approach to anchors in either climbing or tightrope. Not really of any interest to me either - I take an 'Edisonian' approach to such affairs and if I have the slightest doubt around the setup relative to the tension I want to walk at then I go bigger on the components. Also, the tension I walk at isn't really a negotiable / optional attribute of the rig - it's either tensioned 'right' or it's not worth doing.

 

That's particularly so in my case in that I don't walk webbing, but rather heavily-tensioned 10.5mm rope. The forces involved are substantially higher than your typical slackline and I also walk at 9 feet up so it's not a situation where failure is an option.

 

To each his own I suppose...

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6709645295_c789807b2f_z.jpg

 

Assuming a weight of 1 kn (224 lbs), if 22 kn is used as a breaking load, then a 3 x safety factors means keeping the slackline angle below 172 degrees. A 10 x safety factor means keeping below 154 degrees.

 

Not real hard to engineer a safe system with a known safety factor. Seems like a bit of a freebie, to me, at least. 'Never had a failure' can be had with a safety factor of 1.0001...yeah...not comforting. Seems like a few minutes boning up on some simple math would be worth it to anyone setting this stuff up on a regular basis. If you're just slacklining 2 feet over the lawn, however....

 

Regarding regular climbing anchors...0 degrees splits the load evenly between anchors. At greater than 60%, the anchor load starts slowly creeping up beyond that half and half relationship, hence that guideline.

 

 

 

Edited by tvashtarkatena

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You can do a quick visual check of your slackline angle by simply carrying something like this in your kit. If you're above 172 degrees with your lightest person, I'd be worried.

 

6709861171_cebbaa6f3d_z.jpg

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broken%252520carabener.jpg

 

One of my friends was slack-lining and had a carabiner snap. It was a fairly short line (no more than 30') and shouldn't have been under a huge load. Any thoughts...?

 

One more observation: It's better not to tie 1" webbing knots directly to any biner (as shown in the pic). The knot itself can cause the loaded webbing to be slightly off center, thus cocking the biner and potentially greatly reducing its breaking strength. Make sure that webbing, or whatever you use, is seated in the biner properly. Best just to run it through and tie your knots elsewhere.

 

I guess that most biners fail because the biner gets similarly cocked somehow, the gate is nudged open, or some combination of the two, even if momentarily, during a fall or other high stress situ.

Edited by tvashtarkatena

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Looking at where the biner broke, it appears that it was an open gate failure.

If the gate was closed, there would likely be some stretching before it broke.

 

The gate may have rubbed against something or experienced the infamous solid gate "gate flutter" while being loaded.

 

 

Edited by Mugsy

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I'm seeing a little backwards 's' shaped deformation just left of the break, which would happen with an open gate, but that could be my imagination.

Edited by tvashtarkatena

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