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QC Lab: How Sketchy Is a Sharp-Edged Carabiner?

Wednesday, September 7, 2016
I've yanked a lot of worn, sharp-edged biners off of routes, and I've tested a lot of them. It's not the ultimate strength that makes me the most nervous; it's the risk of cutting a rope.

I've had several friends whip onto sharp biners with the end result being the sheathing (i.e., the sheath gets cut and exposes the core) of the rope and possibly soiling of their shorts.

I haven't personally ever heard of a rope getting cut all the way through as the result of falling onto a sharp-edged biner, though possibly it has happened? [Note: see end of article for addendum] Regardless, we decided we'd see what it would take and set up a test in the QC lab.

We grabbed some old, sharp, worn biners that I had removed from a local sport climbing cliff, a few ropes (some new ones, some totally beat-up ones, some end sections, some middle sections (all about 10.5 mm) and went down to our trusty drop tower.

QC with KP biner trench

QC with KP biner trench

Test Method

We didn't perform every single permutation and combination of possibilities, just enough to get a general idea of what would happen in certain situations. We started off using a fall factor of 0.6, 80 kg of mass and a slightly dynamic belay. If the rope didn't cut clean through on the first drop, we would continue dropping the mass on the same location of the rope until it broke. Obviously, this isn't super realistic as I'm sure if you were to take a gnarly fall and sheath your rope, hopefully you have the sense to NOT go up and fall again on the EXACT same spot on your rope.

We then upped the ante a bit by increasing the fall factor to 1, increased the mass to 100 kg and used a static belay.


The Results


QC with KP chart 2

Observations, Comments & Conclusions



So what does all of this mean? We haven't performed nearly enough experiments to create any form of concrete conclusion, but we can make some general observations and comments, as well as decide if/what we would like to test next:

  • You can't really compare all of this data apples-to-apples since the amount of sharpness from one style of biner to another is a bit different. This can have a drastic influence on the outcome of the test.

o It appears that a typical climber (~ 80 kg) in a typical fall (fall factor of 0.6 or less, using a slightly dynamic belay) onto a sharp-edged biner is unlikely to cut the rope clean through in one single fall.
o However, depending on the sharpness of the biner, and type of belay, it IS possible that the rope will cut clean through on the second drop.
o As expected, a higher mass with higher fall factor and static belay does result in the rope cutting earlier, in one case, with a BRAND new rope, on the FIRST DROP! (i.e., heavy climber + new rope + sharp biner + gnarly fall = CUT ROPE)

  • New biners are much more gentle on ropes than a sharp-edged biner.
  • A dynamic belay is much more gentle on ropes than a static belay.
  • Even a brand new large-radius biner (like the RockLock) can cause damage to the rope if all of the other parameters are not in your favor (e.g., old rope, static belay, gnarly fall, heavy climber).

If we were to continue along this line of experimentation, we could perform a more complete matrix of testing, changing only one variable at a time, which could possibly shed more light on which factors have the largest effect on the likelihood of the rope being damaged during a fall.

Moral of the Story



Though it is unlikely a fall onto a sharp-edged biner would cut your rope, most likely the sheath would get cut, exposing the core. However, it's always better to be more safe than sorry and swapping out old beat-up gear is a good habit to get into.

Climb safe out there,
KP

Sharp-Edged Carabiner Testing Addendum


During the testing of the rope-grooved carabiners we focused on whipping, or falling, onto the biner. I recently got an email asking about the likelihood of the rope being damaged by the sharp edge of a carabiner if it was the first biner of a route. I'm sure we've all seen fixed draws at the crags, or even at the local gym, where the first biner has been rope-grooved, resulting in a sharp edge. This is because most people belay standing back from the wall and when lowering the leader, your rope, which has picked up dirt and grit, slowly saws away at the biner. This is most prevalent on fixed first quickdraws and is a good thing to watch out for!

I hadn't heard of any accidents caused by this, but a reader from Germany just notified me that in early 2008 there was one in Prague where this exact scenario caused a new 11 mm rope to break clean through sending the climber, who was not hurt, to the ground. The report is in German, but the photo and diagram make the story clear.

So what is the moral of the story (part 2)? A sharp-edged or worn carabiner isn't only dangerous when you fall onto the biner, but can severely damage the rope anywhere in the system under the correct circumstances. As always, it's best to swap out gear that you feel is unsafe.

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Kolin Powick (KP) is a Mechanical Engineer hailing from Calgary, Canada. He has nearly 20 years of experience in the engineering field and has been Black Diamond's Director of Global Quality since 2002. Kolin oversees the testing of all of Black Diamond's gear from the prototype phase through continual final production random sample testing. If you have a technical question for KP, please email him at askkp@bdel.com and he will TRY to respond.


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