Forums: Climbing Information: Gear Heads: Re: [JimTitt] Spectra vs. Nylon: Edit Log


Feb 17, 2013, 1:10 AM

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Re: [JimTitt] Spectra vs. Nylon
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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.
Okay, you called it, I got it wrong. From the studies I read, my understanding was that 12kN was an upper limit. But, if Brack pulled 214gs and weighed 175 lbs, he was subjected to 166kN. By comparison, 5/8" or 16mm 6x19 steel cable fails at 143kN. Even if a human could withstand that much force, a standard 5-point racing harness certainly would not. So I question their claim that he was able to survive forces in excess of the weight of two semi-trucks.

(This post was edited by USnavy on Feb 17, 2013, 1:37 AM)

Edit Log:
Post edited by USnavy () on Feb 17, 2013, 1:11 AM
Post edited by USnavy () on Feb 17, 2013, 1:14 AM
Post edited by USnavy () on Feb 17, 2013, 1:17 AM
Post edited by USnavy () on Feb 17, 2013, 1:37 AM

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