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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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tomtom
Social climber
Seattle, Wa
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Oct 30, 2006 - 07:06pm 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.
I have, on a number of occasions, taken a double length 8 mm runnner, used carabiners to clip to a two bolt anchor, and then tied a figure 8 into the doubled strands (a la a cordelette). Then clipped the bight with a biner and used it as a power point for a top rope anchor or for fixing ropes for jugging. I haven't noticed any issues with knotting the runners in this fashion.
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TGT
Social climber
So Cal
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Oct 30, 2006 - 08:02pm PT
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I've cliped into plenty of anchors built the same way by partners. That's what got me thinking, especially if any testing has been done with that configuration with a loosely tied knot and shock loaded where the knot cinches down in an instant creating friction on the strands. Or, the cyclical loading that can happen on belay anchors in a semi hanging or hauling situation in particular.
I'll bet the girth hitch looked perfect till the instant it snaped also.
I like the shoe string runners and will continue to use them as such. But, I think I'll stick to the thicker ones for building anchors other than caribiner to caribiner applications.
I've used nylon string to saw thru PVC pipe and HDPE tanks on many occasions. It works faster than a saw.
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MZiebell
Social climber
Prescott, AZ
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Oct 30, 2006 - 09:17pm PT
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"At times the sling may have been stored in the same pack as a Bosch battery."
vs.
"Sport Climbing Is Neither"
Hmmm...
Evolution happens?
: )
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bspisak
climber
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Nov 10, 2006 - 02:24am PT
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Any further info on this?
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Brian in SLC
Social climber
Salt Lake City, UT
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Nov 10, 2006 - 10:08am PT
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Excellant, K13!
Whew...makes me feel better...(I girth hitch and knot dyneema slings all the time...).
-Brian in SLC
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couchmaster
climber
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Nov 10, 2006 - 11:34am PT
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Brian: before you breath too easy: the track which Joseph H. was sniffing down, was trying to answer the question:"What is the effect on aging on strenght of super thin Dyneema material?"
That is a different question than BD was asking which was: "What is the effect of girth hitching NEW Dyneema vs nylon sling material (and various combos thereof?"
I thought that the BD summation that Shermans slings may have been nicked ignores Josephs supposition, suspicions and suggestions concerning older Dyneema material and aging. I suspect JH is on the right track, and that we may have seen the first incident of this effect just take place with John Shermans slings.
A better test would be for some of you guys who climb a lot, like Werner or Ron O, to send in some well used, desert bleached, dyneema slings to BD and see what happens in those tests. Critical to the test would be knowledge of how old and how many climbing days/days out which the slings were subjected to.
To better view real world conditions girth hitch a skinny supersling that is 3 years old or older and been out a lot (Probably like Shermans was) and lets see what those numbers looks like. Maybe even run it over a rough surface when it gets pull tested to simulate real world conditions. Shermans slings may have had a rough surface against to rub against which may have excaberated the effect of aging and helped cause that clean break which the BD engineers are discussing.
Don't breath too easy until the age issue is looked at.
Joseph was talking about doing this test himself, but maybe BD can follow up and pull some old ones since they have the testing facility all set and gaged for it.
regards:
Bill
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Brian in SLC
Social climber
Salt Lake City, UT
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Nov 10, 2006 - 02:10pm PT
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Just scroll down to the testing KP and folks have done earlier this year. UV light aging type data, comparing nylon to dyneema. The dyneema stuff seems to lose less percentage strength. Some great stuff in there. The old draws info is pretty interesting. Anyhoo, worth reading through the older testing info. I think he gets a ton of info on older spectra/dyneema, albiet quickdraws and wider material.
Yeah, didn't maybe exactly simulate John's debacle, but, gave me what I was really looking for.
There's no doubt that these thinner slings will have a shorter life. Just like a smaller diameter rope (ie a Twin v a Double v a single). It is going to be hard to retire them, though, as older nylon slings are hard to judge the age of, if they've been kept out of the elements.
I'll have to say, some of the first thin dyneema sling I've been using for over a year now is looking pretty dirty and a bit ratty. Maybe their while color will help highlight that issue more. Are gettin' fuzzy a bit too.
Can be hard to extrapolate some of this data, but, I did wig a bit when I saw that original busted thin dyneema sling. What I wanted to see was testing that I hadn't seen done before. Dyneema girthed to dyneema and nylon. What was neat was the drop test v the tensile (and somewhat unexpected). Pretty cool.
Anytime I knot a sling or a rope, I kinda mentally make a 50% reduction in strength.
Retire the thin stuff sooner: check.
-Brian in SLC
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couchmaster
climber
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Nov 10, 2006 - 04:24pm PT
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OK I see that now: thank you. Guess I should have looked at the older data. It is still hard to tell what the superthin Dyneema/Spectra would look like in a few years: but this gives ya pause:
"March 15 , 2006 — Spectra vs. Nylon–Real World Wear
So I've been wondering how Spectra wears vs nylon slings. I'm currently working on an experiment, but until I get the results, check this out.
A guy here at work had two quickdraws sitting in the back of his open pickup truck for over 6 years. They have seen sun, snow, rain, heat, cold, etc, etc.. Fortunately for me, one was spectra, one was nylon. Ah ha....
Remember, when new, the rating for a sling is 22kN. Also remember that typical falls in the field are in the 2kN (sporto soft catch) to 5kN (harsh, kidney-wrenching) range.
The nylon sling (top) broke at 11.6kN
The Spectra sling broke at 5.3kN
Based on this as well as earlier findings (in emails below), it's looking to me like Spectra deteriorates moreso than nylon...and to the point that it's SCARY.
Bottom line—retire old beat-up gear.
Later,
Kolin"
They don't give out diameters of slings tested in that one or the draws tested in the other one. Given that the thin stuff (like Sherman had break) is generally pretty new, I suspect that it would not be unreasonable to get half that strength when it's that age, which means easy potential to break with bodyweight only when it's aged and well used. It looks like they plan on more testing of aged Spectra. I like and agree with the bottom line too: "Bottom line—retire old beat-up gear."
Nice job getting on this BD ! Thanks from us all.
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healyje
Trad climber
Portland, Oregon
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Nov 10, 2006 - 04:34pm PT
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Bill,
Yeah, just replaced all my Mammut dyneema slings and am sending the old ones out to be tested and will post the results when I get them. I think we can all do a lot of girth hitch testing and find it hard to reproduce John's result under test conditions. My opinion is that our possible inability to reproduce John's result is completely secondary to the reality of what occured in this incident. I'd say take a second hard look at that close up photo - the sling didn't "break", it was clearly and cleanly "cut" on itself.
My take away is that these skinny slings are quite capable of doing that when girth hitched irrespective of the fact we have difficulty reproducing it. I suspect the diameter / size of what is being hitched is more than a little relavant as is how the hitch is "dressed" relative to 'how on edge' the sling is to itself. Bottom line - I wont be girth hitching skinny dyneema slings unless I feel so under the gun for some reason and never in a situation where it would be subject to a continuos load such that "sawing" could occur.
I've been climbing on the Mammut dyneema slings exclusively for three seasons now and will continue to do so, but I also have some of their 12mm versions and that's what I use at key clips. After two or three seasons I can feel enough irregularities in some of the slings to get the idea their at the end of their useful life. Also, these babies "fuzz up" hard with use as a result of fibers breaking and that alone is probably a fair indicator or remaining utility. I'm going to rate the "fuzz" factor of each sling and see how that correlates to tested strength so it will be interesting to see the results.
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Brian in SLC
Social climber
Salt Lake City, UT
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Nov 10, 2006 - 04:35pm PT
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Those dyneema slings from Mammut haven't been on the market that long. Less than two years?
I could see if you left them outside in the sun for a while, but, most of us just expose gear to sunlight and weather when in use (ie, not fixed like some of the draws in KP's tests, or that old webbing from the back of a truck). Not that I don't run into crunchy old webbing at rap stations from time to time...
Good stuff, though.
-Brian in SLC
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healyje
Trad climber
Portland, Oregon
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Nov 10, 2006 - 04:40pm PT
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I didn't get mine out of channel and this was my third season on them...
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Brian in SLC
Social climber
Salt Lake City, UT
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Nov 10, 2006 - 04:56pm PT
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Anyone know how old the Sherman dyneema sling is?
It has a yellowish threader in it, which I don't recall as being in the first generation available (which was gray?).
-Brian in SLC
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healyje
Trad climber
Portland, Oregon
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Nov 10, 2006 - 05:09pm PT
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I believe he said it was less than a year old and in good shape...
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knudeNoggin
climber
Falls Church, VA
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Dec 30, 2006 - 01:00pm PT
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BUMP , 2006'last (nearly)
healyje wrote:
Yeah, just replaced all my Mammut dyneema slings and am sending the old ones out to be tested and will post the results when I get them. I think we can all do a lot of girth hitch testing and find it hard to reproduce John's result under test conditions. My opinion is that our possible inability to reproduce John's result is completely secondary to the reality of what occured in this incident. I'd say take a second hard look at that close up photo - the sling didn't "break", it was clearly and cleanly "cut" on itself.
Any results for the testing?
Btw, it's been 2 months since Mammut promised to investigate this--any results?
Frankly, I find all the scarmongering willingness to believe the most incredible
things about the slings to be way out of line. HMPE is notoriously hard to cut,
yet this sling showed a near razor-sharp cut line, and OUTSIDE OF THE KNOT
(which, by report testimony, was still tight post-break). At least one of those
who regularly tests cordage opined that such sharpness is UNcharacteristic of
breakage from loading alone. Looks to me as though someone with a knife
sabotaged the sling quite carefully. It sat up there from the 15th to break on
the 19th, recall.
Check the climerware site for various test results of HMPE slings with nylon;
there is no alarming result there. Shrinking the sling diameter if anything
ought to make knotting more dependable--the relatively wide aspect of
traditional tape is more awkward for knotting.
But try this: just interlock two slings a FEW times (vs. the ONE time of a "Girth"
Hitch)--and the structure should look like an extended Square knot (Surgeon's
Knot plus, actually), each sling equally twisting around the other. This is something
a bit beyond what Climerware's site shows; it is very simple to do, and very easy
to undo; it should be stronger, too.
*knudeNoggin*
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Curt
Boulder climber
Gilbert, AZ
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Dec 30, 2006 - 01:20pm PT
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"...Frankly, I find all the scarmongering willingness to believe the most incredible things about the slings to be way out of line. HMPE is notoriously hard to cut, yet this sling showed a near razor-sharp cut line, and OUTSIDE OF THE KNOT (which, by report testimony, was still tight post-break). At least one of those who regularly tests cordage opined that such sharpness is UNcharacteristic of breakage from loading alone..."
When I got Sherman's original e-mail regarding this situation, I replied to him that I also thought the sling was cut--the edge where the failure occurred is simply too clean and straight for me to think othewise. Of course, it's quite a stretch from that conclusion to "sabotage" so I hardly think that is very likely. I do think it is possible that the sling was either partially cut before being girth-hitched, or that some piece of glass, sharp rock, etc. somehow became stuck inside the girth-hitch.
As for the OP observation that Verm is gaining weight--it's probably just the two new carbon-steel hip joints.
Curt
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GOclimb
Trad climber
Boston, MA
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Jan 22, 2007 - 06:40pm PT
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Don't breath too easy until...
Frankly, I think a lot of us won't be breathing too easy for as long as there's no definitive explanation for what happened, because frankly, aside from the possibility that they were sabotaged or unusually cut by glass or something, none of the causes of breakage make a lot of sense. That is to say - there *is* a cause of breakage/cuttage that makes sense, but it's out there, unknown.
Reminds me of the case of the canadian climbers who's rope got sliced by something, likely inside the gri-gri, that was never quite understood or discovered.
GO
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ricardo
Gym climber
San Francisco, CA
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Jan 22, 2007 - 08:03pm PT
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you guys do know that girth hitching 2 slings together lowers strength .. (quite a bit -- dont remember the stated ammount) ..
.. you'd have to be a little gutsy to girth hitch those skinny slings together for an anchor ..
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couchmaster
climber
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Jan 23, 2007 - 01:01am PT
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It looks like girth hitching 2 together diminishes the stength at least 50%. Depending on who you look at.
Here is the Mammut observations about Shermans break:
http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?do=post_attachment;postatt_id=469;
It should be up on the Mammut site soon.
Here is Jim at Sterling Ropes observations who came in better: (Wootles on ST?) http://neclimbs.com/forum.php
"OK, so curiosity got the best of me...
I decided I would sacrifice one of my own 8mm Dyneema slings. I rigged up the drop tower with the skinny Dyneema sling girth hitched to a thicker 5/8" one which was Spectra/Nylon mix. Both slings were used.
I hung 100kg on it and then proceeded to bounce the crap out of it to simulate multiple (way over 150) small loads. The bounces were between 2 and 4 inches. I did this by hand by pulling the sling off axis and letting go. Not a lot of force but these were very static little drops; you wouldn't want 100kg to fall on your toe from 4". I stopped periodically to check the hitch and to give my arms a break. The hitch was warm but wasn't showing any signs of damage. It was starting to look obvious that the slings were not going to break, at least not any time soon, so I lifted the 100kg up about 8" and let it drop. The skinny sling broke but does not look quite the same as the one in Verm's pix. I did not measure the force but I have to believe Verm was not generating anywhere near the amount of force I was. Keep in mind he had a rope in his system and while it was static it would still have absorbed some force."
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Mimi
climber
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Jan 23, 2007 - 01:22am PT
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Since no one has posted this yet today. Here's the latest from Mammut on the Verm sling-break incident. Sorry the pics don't copy over.
Hello all,
As you were all cc’d on this original email, I thought you might be interested in the results of our testing of this sling. I apologize in advance if any of you get this more than once, etc. The full report will be available within a few days on the Mammut website, hopefully by the end of the week. If anyone has any questions please feel free to let me know, and I’ll try to help.
Take care,
Dave
Dave Furman
Hardgoods Category Manager
Mammut Sports Group, USA
135 Northside Dr
Shelburne, VT 05482
(800) 451-5127
http://www.Mammut.com
Report on the Breaking of a Girth-Hitched Sling, prepared by Mammut Sports Group.
1/10/2007
Recently a girth-hitched Mammut 8mm Contact sling was broken in what was described as a relatively static, low-load application. The climber sent an email to many of his friends warning them of the possible danger of girth hitching the newer skinny slings, which quickly made its way around the inboxes and internet forums in the US.
After conducting a series of tests using static, dynamic and cyclic load testing to attempt to reproduce the conditions of the accident the broken sling was compared to the broken test samples using a microscope to examine the break characteristics, which are indicative of the mechanism of breakage. The broken sling did not exhibit any sign of chemical contamination, there was no melting of the fiber ends as is always the case in slings broken under load, the break was located outside the girth hitch rather than inside as would be expected if the knot were the source of the weakness, and the linear break very closely matched those achieved by cutting in the test samples.
Based on this and previous testing, climbers should be aware that the strength of any slings that are connected with a knot can decrease over 50%, regardless of size.
However, based on the fact that a UIAA certified sling holds at least 22kn (roughly 5000lbs), when girth hitched 880DaN or 2000lbs strength should remain in the worst case. With normal human weight and under the described circumstances of the accident, this force could only have been reached with a multi-meter drop. Because of the lack of melting and the lack of similarity to any of the tested breaks, we do not believe the sling broke due to any force applied to it, even taking into consideration the weakening effect of the girth-hitch. The most plausible scenario, borne out by the linear characteristics of the break and location of the break outside the knot, is that the sling was cut with a very sharp object. The only difference is the pulled thread—it seems plausible that this thread could have been the only one not cut through and therefore it held the anchor in place so it appeared to be intact, and finally it broke under a relatively low load.
Climbers should be aware that all slings, whether skinny or fat, Dyneema/Spectra or Nylon, are susceptible to significant strength loss due to a girth hitch, and should use any connecting knots with extreme caution. The safest way to obtain a longer sling is to carry and use a longer sling in the first place, rather than connecting them at all. If two slings must be joined, the strongest way to do so is with a carabiner.
Further information on this test report can be accessed on the Mammut website under Technology>Harnesses>Sling Report.
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healyje
Trad climber
Portland, Oregon
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Jan 23, 2007 - 01:25am PT
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No results yet. The slings are in a box in a corner at the tester's office and it happens at their leisure so it may be a bit longer yet. The slings to be tested are variously two and three years old, well-frayed, and have all shrunk about an inch from the length of new ones. Last year's testing put them at 14k so it will be interesting to see what another year did to them.
But, with regard to the knotting issue, to some extent I think it's common sense to a degree - I mean just look at the damn things - if they don't look to you like they're really pushing the limits of plausibility then you must be pretty damn young or too used to all the new light gear. I have no problem accepting the idea that girth hitching them is a bad idea.
Also, over two years of replacing anchors I rapped with loads in a setup that included a Petzl Shunt and a figure-8 rigged with two girth-hitched, short Mammut dyneema slings that were then tightly taped in place with sport tape. These two slings are part of the batch being tested, and after removing the tape (see photo) they still looked brand new after two years - except, the inner one against the figure-8 was glazed to the point of the appearance of melted plastic about halfway through the sling (unfortunately no photo of the glazing). This inner sling was the one my haul bag was always on so between that and the Shunt it wasn't a safety problem beyond losing the bag; but it does point out again that they're not particularly burly.
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WBraun
climber
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Jan 23, 2007 - 01:32am PT
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"If two slings must be joined, the strongest way to do so is with a carabiner."
Well that's the been de facto standard for a long long time now. I can't believe people girth hitch slings on high potential loads. I couldn't even believe Sherman did that. You girth hitch slings together at anchors you're asking for trouble.
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craig mo
Trad climber
L.A. Ca.
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Jan 23, 2007 - 06:49pm PT
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I cant believe there is enough stretch action at the knot to cut it.It looks like it was cut with a knife.I dont want to believe that.Is that A posibility? Is this place visible from afar? Do people still hate rap bolting?
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knudeNoggin
climber
Falls Church, VA
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Jan 24, 2007 - 07:15pm PT
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The Mammut report confirms assessments of some of us of the cut sling
--i.e., that it was cut, not broken by any sort of loading or fatigure
from use or chemical degradation.
Now, we really should wonder how/why:
(1) Is the OP playing a hoax on us?
(2) Could this cut be made while loaded?
(3) ... or if not, then it was perhaps quite carefully cut only 98%
so as to hide that fact, with the part maybe pushed just behind
the collar of the Girth Hitch--pulled out a bit on loading.
(4) BUT the OP states he was on rappel, ... --i.e., weighting
the line! Could the 2% of HMPE uncut hold that weight for
the duration (i.e., could it have been pre-cut instead of cut WHILE
he was loading it)?
(5) OTOH, would a cut under his rapping loading be so straight?
--I guess a quick slice w/sharp knife would do so, but note how
un-frayed that end is (I'm wondering at whether one should
expect some evidence of it flying apart if cut loaded)!?
In short, though we should feel relieved about the scares advanced
re knotting HMPE dental floss etc., the fact is that this report was
made to the forums and to the vendor, at no insignificant concern
to us all; and if not an unfunny hoax, the guy on the sharp end
of this cordage must be wondering how unfunny the prank
of sling-cutting was, or ... ?!?!
But it seems that this sling couldn't be cut where it was in situ
w/o notice that there was a 2nd anchor point, which gives some
further things to wonder about.
*knudeNoggin*
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healyje
Trad climber
Portland, Oregon
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Apr 18, 2007 - 11:49am PT
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Got the results of the testing of a sampling of my now retired three year old Mammut 8mm Dyneema slings. These numbers are down from the two year old test average of about 14kn. These are normally rated 22kn new:
# 1) 8 mm Mammut girth hitched to 3/4" Nylon = 11.55 kN.
# 2) 3/4" Nylon girth hitched to 8 mm Mammut = 11.76 kN.
# 3) 8 mm Mammut girt hitched to 13 mm Dyneema = 8.32 kN.
# 4) 8 mm Mammut girth hitched to biner = 12.28 kN.
# 5) Ultimate tensile strength = 11.24 kN.
# 6) Ultimate tensile strength = 11.9 kN.
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scuffy b
climber
The town that Nature forgot to hate
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Apr 18, 2007 - 03:14pm PT
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Wow, Joe. I mean Wow.
3 years brings them down to slightly more than 50% of their
rated strength?
I guess I'm going to be sporting a bunch of new slings this year.
Thanks for the heads-up.
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Chiloe
Trad climber
Lee, NH
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Apr 18, 2007 - 03:19pm PT
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Joe, as I read your data they suggest that most of the strength reduction could be due to age, with relatively minor additional reduction due to the girth hitching itself. In fact, only the 8mm-to-Dyneema hitch looks weaker than the "ultimate tensile strength" alone. Is that your interpretation too?
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Jonny2vests
Trad climber
Nottingham, UK
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Dec 18, 2007 - 04:50am PT
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I know this post is past its sell by date, but I thought I'd offer a Brits perspective.
1. Larks footing (or as you call it Girth Hitching) slings together has always verged on the taboo in the UK. Firstly, the sawing action apparent here is well understood (yes, I know, I need a reference here), though admittedly, I would expect there to be some fusing or melting. I've noticed from several trips stateside that larks footing is commonplace which surprised me.
2. Any knot weakens rope or tape and this is proportional to the sharpness of the bend in the knot involved. Girth Hitches have very sharp bends.
3. Personally, I wouldn't have used a sling anyway, why not equalise using the rope and have less links in the belay chain to fail?
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Tom Hanson
Trad climber
Castle Rock, CO
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Dec 18, 2007 - 11:26am PT
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Personally, I hate these new 9.8 - 10.2 "single" ropes.
What ever happened to those good old 11mm's?
Spectra-sling? Forget that dental floss crap and use time tested 1" tubular.
Ultra-light biners? I'd use them for a keychain, but for actual climbing (even projecting sporty lines at my limit) I'd prefer to use a Stubai steel biner.
I weigh in at 200 lbs and don't mind hiking in an additional ten pounds of gear if it means that I can have total trust in my gear.
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knudeNoggin
climber
Falls Church, VA
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Jan 15, 2008 - 01:43pm PT
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Thanks to Healyje for this report:
> Got the results of the testing of a sampling of my now retired three year old Mammut 8mm Dyneema slings.
> These numbers are down from the two year old test average of about 14kn.
> These are normally rated 22kn new:
>
> # 1) 8 mm Mammut girth hitched to 3/4" Nylon = 11.55 kN.
> # 2) 3/4" Nylon girth hitched to 8 mm Mammut = 11.76 kN.
> # 3) 8 mm Mammut girt hitched to 13 mm Dyneema = 8.32 kN.
> # 4) 8 mm Mammut girth hitched to biner = 12.28 kN.
> # 5) Ultimate tensile strength = 11.24 kN.
> # 6) Ultimate tensile strength = 11.9 kN.
But this is incomplete in a few ways. Firstly, we don't know (except for #4-6) WHICH sling broke.
(Though the lowest value is for two made of HMPE.) Secondly, in the case of tape-to-tape, we
don't know the dressing of the knot--was it like the OP's (nearest to what obtains around a rigid
object, such as the 'biner), or like that shown in climerware's site, or the other form shown by
Kolin Powick ("strop bend")?
Chiloe smartly observes:
> Joe, as I read your data they suggest that most of the strength reduction could be due to age,
> with relatively minor additional reduction due to the girth hitching itself. In fact, only the
> 8mm-to-Dyneema hitch looks weaker than the "ultimate tensile strength" alone.
> Is that your interpretation too?
Ostensibly, one should conclude from this data exactly the OPPOSITE of the continued
ranting against "girth hitch"--i.e., that GHing has NO reduction in "ultimate strength",
both showing as 11kN above. But except for Chiloe's unanswered question, I don't see this,
but do see the continued nonsense.
--to wit, from a Brit:
Jonny2vests
> ... I thought I'd offer a Brits perspective.
>
> 1. Larks footing (or as you call it Girth Hitching) slings together has always verged on the taboo
> in the UK. Firstly, the sawing action apparent here is well understood ...
Firstly, but for Bill March's mistake, the historical name is "lark's HEAD"; the Brits seem
to have a lower estimate of this. (-;
As for this alleged "sawing action apparent" in J.Sherman's broken sling (the only rupture shown
in this thread), apparently J2v didn't bother much reading or comprehending Mammut's report on
the sling, and commonsense understanding of what a sawing action would do, in terms of the
resulting edge of the ruptured pieces (also testified to by those who've broken such material).
*kN*
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steelmnkey
climber
Vision man...ya gotta have vision...
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Jan 15, 2008 - 02:28pm PT
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Over on mountainproject, it was stated by those in the know that someone had intentionally cut the sling to cause an accident.
This was the statement:
"The conclusion of the manufacturer was that it had been intentionally cut. The testing was also unable to replicate the failure results. There was a thread about it on Rockclimbing.com I think. Unless somebody claims responsibility we will never know for sure."
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crunch
Social climber
CO
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Topic Author's Reply - Jan 15, 2008 - 03:32pm PT
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knudeNoggin, thanks for your analysis. And to Healyje. And the others who have wondered and posted about this.
knudeNoggin, you pondered about whether this was a hoax. As the OP, I can confirm that as far as I know, this is not a hoax.
Verm told me about this incident. Now, I've known Verm for maybe twenty five years; he seemed genuinely shocked about what had happened. He is well aware that a mechanical failure of climbing gear like this would be a very serious issue. He asked myself and a number of other folks to spread the word about this, because he was worried about someone else repeating this more or less body-weight break, but without the anchor redundancy that saved him. Hence my posting.
The sabotage theory is unlikely:
1. The location is extremely obscure. I've climbed there. Someone would have had to follow him, without alerting his dog, and then spend some time carefully cutting right inside the knot, to do this.
2. To deliberately stage this "accidental" and yet enigmatic breakage would be somewhat pointless. A disgruntled anti-Tamo/anti-Verm saboteur would surely make the damage obviously human-caused, to make some kind of warning. Or just cut the rope itself to, ahem, get the point across more strongly.
There might be a complex combination of factors, old worn webbing, bouncing repeatedly many many times, perhaps the same knot left tied for several rappel/cleaning sessions. Perhaps there was some kind of accidental cut already, and the new knot slid into place right there on the existing damage.....
The usage was not exactly regular climbing usage, almost industrial usage, and for this kind of usage, as I recall from the times I cleaned windows on rappel, it's customary to use really heavyweight versions of everything, because everything gets more beat up. Using ultra-skinny lightweight webbing would not seem a very good idea.
Evidently this failure is not easily reproduced. That is puzzling and frustrating. But on the bright side, if this failure is so difficult to reproduce, it's unlikely to be repeated.
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healyje
Trad climber
Portland, Oregon
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Jan 15, 2008 - 05:41pm PT
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I was having my Mammuts tested annually and the progression was basically:
22kn > 14kn > 11kn > 8kn > ?
My take on this informal but competetnt testing is that the stiff dyneema fibers break over time using them as alpine draws. Mammut's response to me was that these slings are designed as a consumable, ultra-lightweight sling for ascents which demand such optimizations. 'Consumable' being the key word. Today's material science isn't at a place yet to provide us with dramatic weight savings without something giving either in size, strength, or longevity. Trading away size (length) and strength isn't an option in slings so what has to 'give' is longevity.
The upshot? I wouldn't climb on skinny dyneema slings more than three moderate or two hard years at the outside max.
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Mimi
climber
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Jan 15, 2008 - 05:44pm PT
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I spoke with Verm when this thread started and he didn't believe anyone had cut the webbing when I asked if that was a possibility.
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knudeNoggin
climber
Falls Church, VA
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Jan 16, 2008 - 02:31pm PT
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> he did not believe ...
> The sabotage theory is unlikely:
Beliefs & likelihood are less durable grounds for a conclusion than the scientific
testing & analysis (microscopic, even) done by Mammut. Quite simply, the break
was a cut, and by a sharp enough object running perpendicular to the axis of
loading (so much for the supposed "sawing action" that might come from cyclic
loading). You can't just dismiss this because someone thinks it unlikely.
As for the ability for someone to find the sling etc., that maybe narrows the
suspects; re the dog, well, it wasn't there all the time, or it might have known
the sabateur and reacted quietly. What I think wasn't answered by Mammut is
how much force the few bits of uncut fibre could've supported, such that the
break didn't come on initial but only later-along loading.
I simply cannot understand how everyone is so quick to dismiss the absence of
ANY resemblance to breakage--no irregularity, no melted fibres, no adequate
force--resulting from normal circumstances, and the attested match to being cut
by a sharp object. And for the breakage to occur from knot action and yet the
cut lie just outside of the knot, which remained intact ... ?! Even some embedded
bit of sharp rock/sand/glass would have to work miracles to cross the strand and
cut it so evenly, and outside of the knot.
Now, re Healyje's tested slings, there is yet the oddity that, if Chiloe & I are reading
the results correctly, it made NO difference really whether the slings were GH'd or
not ("ultimate strength")? I don't believe this, but the test data has about 11kn for
both cases. Perhaps Healyje can reply something like "what I chose for Ultimate
testing were the worst, most ragged-looking slings, since I wanted to see how
badly ...", and we then have some reason to understand how they got the same
strength as some better-condition slings GH'd (which other testing & Mammut's
report suggest might be 50% of ultimate strength). ??!
*kN*
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Short one broke @ 12.93 kN (2902 lbf)
Let us know!