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crunch
Social climber
CO
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Topic Author's Original Post - Oct 20, 2006 - 01:31pm PT
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John Sherman just yesterday had a dyneema sling break, under bodyweight.
The Verm has been packing on a few pounds lately, but he never suspected he was at the rated breaking strain of dyneema.
He was on rappel, cleaning a new line, and, up above, one of his two rappel anchors failed, causing him to fall a couple feet before the other held. When he scrambled back to the top, it turned out that what broke was a dyneema sling girth hitched to another skinny Spectra-style sling. It looked like one skinny sling cut right through the other, right at the girth hitch knot.
The slings in question were not rubbing on anything. The dyneema appeared to break right at the girth hitch knot, with the break having a fairly sharp edge, indicating cutting rather than tearing/shearing. Verm was rappelling and cleaning using a static rope, which presumably was putting small ("chunky" bodyweight) but repeated shock loads on the webbing until, fiber by fiber, it broke/cut.
He will send the webbing for testing.
Consider using carabiners to connect Spectra/Dyneema slings to each other, especially for any fixing/rappelling/toproping purposes.
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Mungeclimber
Trad climber
one pass away from the big ditch
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Oct 20, 2006 - 02:05pm PT
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ack!
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Maysho
climber
Truckee, CA
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Oct 20, 2006 - 02:25pm PT
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John Sherman, rappelling and cleaning?
Now wait a darn minute, the man who made the "sport climbing is neither" stickers?
Maybe mistaken identity. If not and he is now deranged or something, I would love to find him. I met him by rescuing him from a stuck prussick on rappel when we were both kids, and subsequently enjoyed many a fine after school (high school!) sessions with him at Indian Rock.
Peter
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feelio Babar
Trad climber
Sneaking up behind you...
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Oct 20, 2006 - 04:04pm PT
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New thin Dyneemas are like Razors....BD test lab assured me that girth hitching them to any other runner was a recipe for disaster. Heads up out there!
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GOclimb
Trad climber
Boston, MA
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Oct 20, 2006 - 04:56pm PT
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Holy sh#t. Thanks for the heads up!
GO
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Kevster
Trad climber
Evergreen, CO
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Oct 20, 2006 - 07:44pm PT
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What's the concensus on Dynema to Dynema girthing?
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Chaz
Trad climber
So. Cal.
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Oct 20, 2006 - 08:03pm PT
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On my very first day climbing, the guy running our Intro To Climbing Day stood on a sling, and passed a piece of webbing through the loop. He then proceeded to saw back and forth with the webbing. In just a few seconds the sling was cut through. He told us to never set up any part of our system to have nylon on nylon.
These were nylon slings. There was no such thing as Dyneema or Spectra then.
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Jaybro
Social climber
The West
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Oct 20, 2006 - 09:49pm PT
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not unlike the logic that precludes girth hitching wires with sling.
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healyje
Trad climber
Portland, Oregon
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Oct 21, 2006 - 06:02am PT
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Thanks Bill, yes I tested some two year old Mammut dyneema slings and received the results Bill listed. Those breaking strengths, while about 2/3's of their rated strength is still better than most stoppers. Mammut was explicit in saying these skinny dyneema slings are an exercise in weight reduction and the trade off with them is they should be treated as a consumable with a 2-3 year lifespan.
In no way are the material characteristics of dyneema slings remotely the same as nylon ones. Dyneema fibers break over time and the sharper the bends the more fibers that break hence the caveat about girth hitching them together or to things like wires or bolt hangers. Sharp and self-abrasive bends are simply a disaster waiting to happen. I'll keep using and testing a few of mine each year and see how they fare, but I'm replacing the majority of them at the end of this season. Again, they simply don't have the longevity of nylon webbing or supertape.
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crunch
Social climber
CO
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Topic Author's Reply - Oct 21, 2006 - 02:17pm PT
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crunch
Social climber
CO
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Topic Author's Reply - Oct 21, 2006 - 02:24pm PT
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The deal is that the testing done shows that the webbing is weakened, but still way strong for bodyweight use. The age is also pretty irrelevant, John's webbing was just a few months old.
John emailed me this from darkest Arizona:
Dyneema sling failure under very low load when girth hitched 10-19-06
On Oct 19th I experienced a partial rappel anchor failure when a Dyneema sling used as part of the anchor broke at the point where it was girth hitched to a wider Spectra sling. The anchor was set on Oct 15th, 30 feet back from the top of the cliff and used only for rappels and was never subject to any sudden impacts. The anchor was equalized for the direction of pull with the girth hitched point of failure on one side. In theory this part of the anchor should have only been subject to half the loads, however because the equalization point was a clove hitch it is possible that one side could have taken the full load (body weight only) if the angle of the rope changed. The rappel line was a static rope and I was using a Grigri as my rappel device. Where the rope ran over the lip of the cliff it was padded with a piece of carpet. Every morning the anchor was inspected for soundness (especially any chewing by rodents) and seemed sound. When loaded, the Dyneema sling was suspended in mid-air with absolutely no contact with the rock to cause abrasion. The anchor was rappelled on a total of seven times (sling failed on 7th rap). As we were cleaning routes, the time of rappels varied from about 10 minutes to one hour. There was a small amount of rain on the 17th and possibly some showers on the 18th, however the rappel line felt dry on the 19th. The failed sling was in use less than one year and showed no signs of damage prior to this incident. The girth hitch feels quite tight after the break. When the sling finally failed I was partway down a slab with multiple points of contact between the rope and the rock to reduce the force on the anchor. I was stationary at the time and suddenly dropped a foot when the sling broke. The point where the Dyneema failed was Dyneema pinching Dyneema and not in contact with the Spectra (see photos). The Dyneema sling that broke was an 8mm Mammut runner. The sling it was girth hitched to was a 5/8-inch Misty Mountain Spectra runner. The broken ends of the Dyneema feel soft, not fused.
What factors might have increased the load beyond body weight?
* Pendulums across the face, about 10 foot lateral swing at most, 30 feet below the point the rope ran over the top of face.
* Extra force applied when prying loose blocks of with a prybar. In theory this force could not exceed the amount I could deadlift. In this situation I don’t beleive I ever exerted more than 100 pounds of additional downward force on the rope.
* Sudden drops onto rappel line after it was unweighted when standing on ledges. At times the rap line was partially unweighted, but because I am nervous/careful when it comes to ropework I always sucked up the rope through the Grigri before reweighting it.
* Extra weight of bolting gear, prybar, etc, about 40 pounds at most.
I don’t believe any of the above factors is significant, especially since all of these take place below the lip where the friction of the rope on the lip would reduce the load on the anchor.
At times the sling may have been stored in the same pack as a Bosch battery. Is there any evidence that NiCad cells emit anything that can damage Dyneema?
At present my best guess as to why the sling failed is that when girth hitched tightly such a small diameter sling can cut through itself (the sling suffered a very clean break). In this incident I can imagine that the girth hitch received numerous small tugs under low load (body weight and less) and this might have caused a repeated microscopic nipping or sawing action that eventually cut through the whole sling (the wider Spectra sling it was girth hitched to also had some fibers cut at the point of contact with the Dyneema). I am trying to contact the equipment manager from Mammut to have this sling failure expertly analyzed. Until then I suggest that Dyneema slings should never be girth hitched or otherwise knotted.
John Sherman
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susan peplow
climber
Desperately Seeking Climbing Related Topic!!
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Oct 21, 2006 - 11:21pm PT
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He doesn't look too frightened to me. However, does look like he's looking for a date. Holy Crap Johnboy!
Maybe it's bad Camo juju? Nahh
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healyje
Trad climber
Portland, Oregon
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Oct 22, 2006 - 06:17pm PT
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The photos are pretty informative.
The Dyneema sling was cleanly "cut" through the majority of the thickness of the sling and it looks as though the few long, loose threads were the result of the actual failure event once enough thickness was cut to cause failure. The knot bend clearly acted as a transverse knife edge in this case and it would be interesting to know how the two strands of dyneema were dressed under that bend / knife edge - were they in a perpendicular-side-by-side, flat-side-by-side, or one-on-top-of-the-other configuration. Not sure if it would have made any difference and the whole event just speaks to not girth hitching high tech fiber slings. I use a rack of these same Mammut slings and have always made it a point to never girth hitch or otherwise allow a dyneema-on-dyneema condition to exist.
If you can get that sling back to Mammut it would also be interesting to see a failure test on the sling about two inches down from the break. I'd bet it would be close to the rated strength of the sling.
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Brian in SLC
Social climber
Salt Lake City, UT
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Oct 23, 2006 - 11:09am PT
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Scary. Please post any follow up information on this. I use these slings all the time, girth hitched, slip knotted, knotted, etc.
Yikes!!
-Brian in SLC
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TGT
Social climber
So Cal
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Oct 23, 2006 - 11:55am PT
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From the look of the photo and where the failure occured I'd suspect that ANY knot in that thin a Dynemea sling could produce a similar failure. I fully expected to see the failure in the sling that was girth hitched to, not in the one that had the girth hitch tied in it. I'll bet an overhand, figure 8 or anything else could do the same thing. Aybody done any testing?
Keep in mind that that stuff is just UHMW Polyethylene and has about the same melting point as a plastic sack.
I use them, but would never tie a knot in one except under dire circumstances. It also could be critical to not use them in the belay in a position where the rope or anything else could come in frictional contact with them.
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TradIsGood
Fun-loving climber
the Gunks end of the country
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Oct 23, 2006 - 12:08pm PT
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Looking forward to seeing results of lab work on this.
That "cut" is so even and so perpendicular, except at the edge!
No real evidence of stretching during whatever caused the cut.
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Mimi
climber
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Oct 25, 2006 - 10:34pm PT
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Verm received this email from Mammut about the sling failure. The Mammut rep emailed everyone on Verm's mailing list so I'm sure he won't mind me posting it here.
John,
First, please know that I am very concerned by the incident you reported in your email below and that I would greatly appreciate the opportunity to discuss this with you as soon as possible. Mammut strives to engineer the finest equipment available with the consumers' safety as a guiding principal and paramount concern. Further, as you state, we need to provide the sling in question to the designers at Mammut in Switzerland for a thorough analysis. We as a company will stand behind our products and work to provide the analysis results to the entire climbing community.
Sincerely,
Jeff Cunningham
Jeff Cunningham
National Sales Manager
Mammut Sports Group, Inc.
135 Northside Dr.
Shelburne VT, 05482
800-451-5127 Ext.110
F) 802-985-9141
http://www.mammutusa.com
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doug redosh
Trad climber
golden, CO
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Oct 28, 2006 - 11:06pm PT
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Whatever happened to using 3 pieces of protection for an anchor, especially if one will be rapelling off of it?
If one goes, there is no longer redundancy.
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SuperTopo on the Web
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Short one broke @ 12.93 kN (2902 lbf)
Let us know!