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rgold
Feb 15, 2013, 5:48 AM
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Almost all my slings are dental-floss spectra. I carry one or two of the thick nylon Mammut slings for slinging flakes and other features with edges I think might cut the thin spectra stuff. I prefer a nylon PAS, since it is functionally identical to the spectra ones, cheaper than the spectra ones, and stronger than the spectra ones. But for ultra-lightness and/or wet winter/alpine applications, many climbers would find spectra to be preferable. As for what other people, including my partners, do, I don't care one way or another.
As for the "yer gonna die" stuff, it centers around taking high fall-factor falls directly onto slings, something everyone admits is a very bad idea whether or not it actually breaks the sling. The one incident of this sort I know of was a factor-2 fall by a climber on a nylon quickdraw that the nylon withstood but which broke one of the carabiners. This was more like a factor 3 fall but does suggest that extremely high loads can result from short falls by human bodies on sling material when the climbing rope is not involved and the siings are short.
There is absolutely no question that spectra is worse than nylon if it is called on to absorb fall energy, which is not a job slings are supposed to do, and that the problem is compounded when there are knots in the slings. What climbers do with this information if (a) they understand it and (b) they consider it significant to practical climbing situations is, always has been, and always will remain a personal decision.
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BillyCrook
Feb 15, 2013, 6:57 PM
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rgold wrote: The one incident of this sort I know of was a factor-2 fall by a climber on a nylon quickdraw that the nylon withstood but which broke one of the carabiners. This was more like a factor 3 fall
How can you exceed 2? Was he solo-ing and just happened to clip into something while he was falling? Was he clipped into a vertical rope way above an a bolt?
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rgold
Feb 15, 2013, 7:11 PM
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BillyCrook wrote: rgold wrote: The one incident of this sort I know of was a factor-2 fall by a climber on a nylon quickdraw that the nylon withstood but which broke one of the carabiners. This was more like a factor 3 fall How can you exceed 2? Was he solo-ing and just happened to clip into something while he was falling? Was he clipped into a vertical rope way above an a bolt?
It was a factor-2 fall on a short quickdraw. If the quickdraw was altogether 4 biners long with a 2-biner length sling, then the fall height was 8 biners with energy absorbed by a two-biner length of nylon, which gives a fall factor of 4. Since the biners flex a little and so might absorb some fall energy, I rounded down to fall factor 3.
The one test I've heard about establishing a UIAA-style impact force rating for nylon slings came out to 18 kN. It doesn't seem possible to find a value for spectra because it breaks in a factor-2 drop test.
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marc801
Feb 15, 2013, 7:44 PM
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Gmburns2000 wrote: Also, I rarely clip directly to the cam. I prefer to extend it, for various reasons depending on the circumstances that are mostly dictated by where and the type of routes I climb. So even if they had dyneema slings, I wouldn't use them much except to clip to my harness.
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wivanoff
Feb 15, 2013, 7:59 PM
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marc801 wrote: Gmburns2000 wrote: Also, I rarely clip directly to the cam. I prefer to extend it, for various reasons depending on the circumstances that are mostly dictated by where and the type of routes I climb. So even if they had dyneema slings, I wouldn't use them much except to clip to my harness. Then how are you accomplishing extending if you're not clipping into the cam sling?
"Alpine Quickboys"? 
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Gmburns2000
Feb 15, 2013, 8:09 PM
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marc801 wrote: Gmburns2000 wrote: Also, I rarely clip directly to the cam. I prefer to extend it, for various reasons depending on the circumstances that are mostly dictated by where and the type of routes I climb. So even if they had dyneema slings, I wouldn't use them much except to clip to my harness. Then how are you accomplishing extending if you're not clipping into the cam sling?
that was an oversight on my part.
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JimTitt
Feb 16, 2013, 5:38 PM
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BillyCrook wrote: rgold wrote: The one incident of this sort I know of was a factor-2 fall by a climber on a nylon quickdraw that the nylon withstood but which broke one of the carabiners. This was more like a factor 3 fall How can you exceed 2? Was he solo-ing and just happened to clip into something while he was falling? Was he clipped into a vertical rope way above an a bolt?
The incident rgold is probably referring to was a climber replacing bolts and was using 3 (if I remember right) quickdraws to reach up to the placement, he fell and broke one of the karabiners. He survived the resulting groundfall. One of the rope companies recreated the incident and the force was something like 27kN.
Thereīs a write-up somewhere which i can probably find later but the lessons are clear enough anyway!
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USnavy
Feb 16, 2013, 10:51 PM
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JimTitt wrote: BillyCrook wrote: rgold wrote: The one incident of this sort I know of was a factor-2 fall by a climber on a nylon quickdraw that the nylon withstood but which broke one of the carabiners. This was more like a factor 3 fall How can you exceed 2? Was he solo-ing and just happened to clip into something while he was falling? Was he clipped into a vertical rope way above an a bolt? One of the rope companies recreated the incident and the force was something like 27kN.
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rgold
Feb 17, 2013, 1:08 AM
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Why ludicrous? No one said the climber in question was subjected to 27 kN. For whatever reason, the biner presumably broke at some unknown lower number. The main point is that the load potential in such situations is enough to break something critical, and a secondary point is that this has actually happened; it isn't hypothetical.
Of course, this has nothing to do with dyneema vs. nylon, in fact I think the sling in question was nylon. I mentioned the example to point out that very short falls on slings are potentially very dangerous.
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USnavy
Feb 17, 2013, 3:24 AM
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rgold wrote: Why ludicrous? No one said the climber in question was subjected to 27 kN. .
Actually Jim did make that claim, although possibly not knowingly and not directly. He said that a manufacturer recreated the incident. Clearly the manufacturer did not correctly mirror the scenario if they got 27kN. They may have partly replicated the scenario. But they did not replicate the results. Both parameters would be required to claim they properly replicated the scenario. What they probably did was use a steel weight in a scenario that did not result in the carabiners failing in the open gate position. That may be similar to the scenario at hand. But similar and exact are two very different parameters in this conversation.
You are correct that short falls on static materials can produce high loads. Everyone knows that. But everyone also knows that a steel weight is not analogous of a fleshy human in static falls.
(This post was edited by USnavy on Feb 17, 2013, 3:25 AM)
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JimTitt
Feb 17, 2013, 7:53 AM
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USnavy wrote: JimTitt wrote: BillyCrook wrote: rgold wrote: The one incident of this sort I know of was a factor-2 fall by a climber on a nylon quickdraw that the nylon withstood but which broke one of the carabiners. This was more like a factor 3 fall How can you exceed 2? Was he solo-ing and just happened to clip into something while he was falling? Was he clipped into a vertical rope way above an a bolt? One of the rope companies recreated the incident and the force was something like 27kN. Which is a ludicrous notion. Harnesses are only required to hold 15kN, and the human body cannot withstand more than 12kN (some sources say 10kN). If he was subjected to 27kN, I strongly doubt his back would be in one piece. What very likely happened is the gate on one of the carabiners opened, possibly due to flutter, and the actual force was limited to the failure strength of the failed biner in the open gate position.
While the minimum requirements for harnesses is 15kN all manufacturers make them stronger. I have one somewhere rated to 25kN and can well believe my work harness is stronger than that.
Your knowledge of survivable g-forces is woeful, the 12kN standard is for long-period accelerations without injury, John Stapp survived 46.2g for over a second. For shorter periods which falling on quickdraws would certainly be we can look at:-
Kenny Brack (Indy Car) recorded 214g
David Purley (F1) calculated 180g
Robert Kubica (FI) recorded 75g
While all of these are in the more advantageous body position they show that your contention "the human body cannot withstand more than 12kN (some sources say 10kN)" is clearly rubbish and your proposal that the testers knew nothing clearly also worthless.
(This post was edited by JimTitt on Feb 17, 2013, 7:54 AM)
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USnavy
Feb 17, 2013, 9:10 AM
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JimTitt wrote: USnavy wrote: JimTitt wrote: BillyCrook wrote: rgold wrote: The one incident of this sort I know of was a factor-2 fall by a climber on a nylon quickdraw that the nylon withstood but which broke one of the carabiners. This was more like a factor 3 fall How can you exceed 2? Was he solo-ing and just happened to clip into something while he was falling? Was he clipped into a vertical rope way above an a bolt? One of the rope companies recreated the incident and the force was something like 27kN. Which is a ludicrous notion. Harnesses are only required to hold 15kN, and the human body cannot withstand more than 12kN (some sources say 10kN). If he was subjected to 27kN, I strongly doubt his back would be in one piece. What very likely happened is the gate on one of the carabiners opened, possibly due to flutter, and the actual force was limited to the failure strength of the failed biner in the open gate position. While the minimum requirements for harnesses is 15kN all manufacturers make them stronger. I have one somewhere rated to 25kN and can well believe my work harness is stronger than that. Your knowledge of survivable g-forces is woeful, the 12kN standard is for long-period accelerations without injury, John Stapp survived 46.2g for over a second. For shorter periods which falling on quickdraws would certainly be we can look at:- Kenny Brack (Indy Car) recorded 214g David Purley (F1) calculated 180g Robert Kubica (FI) recorded 75g While all of these are in the more advantageous body position they show that your contention "the human body cannot withstand more than 12kN (some sources say 10kN)" is clearly rubbish and your proposal that the testers knew nothing clearly also worthless.
(This post was edited by USnavy on Feb 17, 2013, 9:37 AM)
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JimTitt
Feb 17, 2013, 11:51 AM
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Given that the data logger would have been fixed to the car, not him then possibly he didnīt have to survive the full 214g since a small amount of give is inherent in the harness.
Since the current combined strength requirements for an FIA 6 point harness is 110kN and for a 5 point about 100kN clearly the FIA think that 100g or thereabouts is a reasonable mark to aim for. As these are the minimum strengths and one would imagine a certain amount of margin is built in by the manufacturers Iīd hesitate to say a racing harness would certainly break.
The current F1 safety cell requirements are:-
The peak deceleration over the first 150mm of deformation does not exceed 10g ;
- the peak deceleration over the first 60kJ energy absorption does not exceed 20g ;
- the average deceleration of the trolley does not exceed 40g ;
- the peak deceleration in the chest of the dummy does not exceed 60g for more than a cumulative 3ms, this being the resultant of data from three axes.
These are being modified due to the coming rule changes and most current safety cells are tested to 60g, a fair indication of what the survivable forces are though to be.
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david_g48
Feb 17, 2013, 1:08 PM
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Jim
Are you comparing apples to apples when you use race car drivers and climbers? There are a lot of different dynamics when you introduce a car seat and a harness that spread forces out over a larger area of the body etc. I am not doubting your expertise just trying to understand. Like US Navy I have read that forces around 15K in a climbing harness produces some dire results on the human body. Not necessarily death but close. With a climbing harness a lot of the force will be applied to the back of the spine which will probably not happen in a car. Please expand on your sources and thoughts using simple terms for those of us who are not as educated in the physics of impact.
Thanks, I always enjoy your posts.
David
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JimTitt
Feb 17, 2013, 2:57 PM
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david_g48 wrote: Jim Are you comparing apples to apples when you use race car drivers and climbers? There are a lot of different dynamics when you introduce a car seat and a harness that spread forces out over a larger area of the body etc. I am not doubting your expertise just trying to understand. Like US Navy I have read that forces around 15K in a climbing harness produces some dire results on the human body. Not necessarily death but close. With a climbing harness a lot of the force will be applied to the back of the spine which will probably not happen in a car. Please expand on your sources and thoughts using simple terms for those of us who are not as educated in the physics of impact. Thanks, I always enjoy your posts. David
"Well I did write "While all of these are in the more advantageous body position" for that very reason!
USNavyīs contention was that the human body canīt withstand 12kN or so and there are also other posters on the climbing forums that seem to have the impression that around this level humans spontaneously turn to a mush of bones and organs dripping out of their harness. Clearly this isnīt the case. From the little Iīve read the major danger in high g-force impacts is rupture of the aorta which may or may not occur around 70g.
Other peripheral damage is what concerns us and why the impact level is set much lower since it is not merely survival which is required but surviving without severe injury or in an industrial fall-arrest context no injury. How and why the levels in the various standards are derived are mostly explained here http://www.hse.gov.uk/research/crr_pdf/2002/crr02411.pdf which gives a good insight into where the difficulties lie.
Itīs worth noting that aircraft seating for example is designed to withstand 16g and allow the occupant to be able to exit under their own power so clearly the FAA feel one can easily survive this level of impact without debilitating injury (this is part of the test). The central seat belt anchorage point in your car has to hold 40kN which also implies that even with the poor restraint offered by this design impacts of this level are survivable and worth protecting against.
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rocknice2
Feb 20, 2013, 1:08 PM
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There was a test done in the late 40's by the USAF on ejection seats. This report is not the 1947 study but another study done later in 1967.
http://www.dtic.mil/...GetTRDoc?AD=AD664553
on page 25 - JOHN H. HENZEL, CAPTAIN, USAF, MC wrote: U. S. ejection catapult specifications necessary to optimize chances of safe escape from aircraft were accurately defined between 1945 and 1947. Ames (1947-1948), aware of the increased dynamic overshooting that occurs with high onset rates, cautioned during that period that such overshoot would be negligible with onset rates below 200 G/sec. In 1947, ejection seat equipment developed by the Army Air Forces and the Ordnance Department provided a terminal velocity of 60 ft/sec with a maximum of 14-16 G on the subject at a rate of 175 to 200 G/sec.
This 15G limit should equal 12kn for an 80kg mass if my math is right. Which it's not in many cases.
The human body can withstand incredibly high G forces up to 300G but for very very short periods of time.
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qtrollip
Feb 21, 2013, 4:25 AM
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So where does Petzl's new Spirit dogbones - made from Polyester - fit into all of this?
http://www.mec.ca/AST/ShopMEC/Climbing/Carabiners/Quickdraws/PRD~5031-654/petzl-spirit-express-quickdraw.jsp
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USnavy
Feb 21, 2013, 5:25 AM
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qtrollip wrote: So where does Petzl's new Spirit dogbones - made from Polyester - fit into all of this? http://www.mec.ca/AST/ShopMEC/Climbing/Carabiners/Quickdraws/PRD~5031-654/petzl-spirit-express-quickdraw.jsp
(This post was edited by USnavy on Feb 21, 2013, 5:27 AM)
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