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Chockstone Forum - Gear Lust / Lost & Found

Rave About Your Rack Please do not post retail SPAM.

Author
Slings at Anchors
kieranl
29-Sep-2014
11:18:43 AM

Slings at Anchors from DMM Climbing on Vimeo.



Some lessons in breaking gear and bodies.

Looking at the numbers, consider that 12kN is generally accepted as the maximum force that an uninjured human can tolerate. So pretty much all of the tests with slings produce potential fatal forces. Of course, as he says in the video, the situations are not real-world but if you're in the habit of clipping in directly with a sling, PAS or daisy and then moving around you probably want to think about it.
mikllaw
29-Sep-2014
1:55:23 PM
Perhaps you'd survive 12kN in a full body harness (based on the old WW2 parachute tests), but in a climbing harness you'd be a very bit damaged.

One aspect of the testing is that, as the top load spreader bar can swing in space, all the tests where the slings were knotted allowed the rig to equalise. The loads would be higher, and the slings 'more broken' if they were tested on 2 fixed anchor points.
martym
29-Sep-2014
4:52:51 PM
On 29/09/2014 mikllaw wrote:
>Perhaps you'd survive 12kN in a full body harness (based on the old WW2
>parachute tests), but in a climbing harness you'd be a very bit damaged.
>
>One aspect of the testing is that, as the top load spreader bar can swing
>in space, all the tests where the slings were knotted allowed the rig to
>equalise. The loads would be higher, and the slings 'more broken' if they
>were tested on 2 fixed anchor points.

Mikl - a humble question - is the un-fixed load spreader bar the way they measure the force? How would they measure it on a fixed point... is that doable?
patto
29-Sep-2014
5:47:07 PM
I wouldn't worry about breaking slings. A soft body would at least double the energy absorbing capacity of the system. Also the centre of mass would rotate a little further increasing the time of energy absorption and thus reducing the overall force.

In short the values obtained in such tests are not at all representative. In real life failure of the sling is very unlikely. Death is very unlikely, but injury is quite likely. Either way. Don't fall on static slings.

Here is some tests that a few daring climbers did:

Geir Hundal
Jeff Fassett and I conducted a simple test using a dynamometer attached to a bolted anchor. In the first part of the test, I attached to the anchor using a daisy chain so that i hung freely two feet below it. With a backup rope in place, I pulled myself up a few inches and let go so that I fell statically on to the anchor. The force on the anchor was shocking - the dynamometer measured a peak force of 900 pounds on the first drop. I subsequently took slightly further falls, and found that the force on the anchor was over 2,000 pounds when falling just one foot. I stopped at this point simply for comfort.

So according to their measurements he got up to 8.9kN until he stopped for comfort reasons.
Dr Nick
29-Sep-2014
6:15:35 PM
I wonder how much difference knotted slings would make, rather than sewn. I know from experience that slings I've fallen on are much harder to untie (if it's possible at all) than ones I've simply body weight tightened. This suggests there's a bit of slip, which would do something to reduce the impact, at least on the first fall.

Mikl (or anyone else), do you have test equipment that can play nicely with shock loads so we could do some testing?
kieranl
29-Sep-2014
7:34:45 PM
I think the video showed that knots in the slings could reduce the impact force. But mucking around with those is tinkering at the margins when it's clear that the easiest way to reduce the impact force is to attach yourself with the rope.
Dr Nick
29-Sep-2014
8:16:40 PM
Absolutely - but I'm curious as to what a difference my tight-arse slings make over shop bought stuff. I've got a couple of sewn slings, but I mostly just buy a bunch of tape and tie water knots.

(In other words, I want to be able to claim my tight-arse tendencies are a safety feature!)

sliamese
30-Sep-2014
2:54:59 PM
>Looking at the numbers, consider that 12kN is generally accepted as the
>maximum force that an uninjured human can tolerate.

no thats when things start getting damaged inside, hence the limit of 6kN to any persons!
kieranl
30-Sep-2014
4:08:32 PM
On 30/09/2014 sliamese wrote:
>>Looking at the numbers, consider that 12kN is generally accepted as the
>>maximum force that an uninjured human can tolerate.
>
>no thats when things start getting damaged inside, hence the limit of
>6kN to any persons!

Not sure why you're saying "no", we're both saying the same thing with different words.
patto
30-Sep-2014
4:56:27 PM
The "force" somebody can withstand depends on where, how and how long it is applied for.

The guy I linked about experienced a painful 9kN. (We really aren't talking about organ damage here though, more pelvis bruising and whiplash to back/neck.)

John Stapp was subjected to forces of over 34kN! (46.2G!) (Though that did temporarily blind him and give him a host of other non life threatening injuries.)
(http://en.wikipedia.org/wiki/John_Stapp)
(https://www.youtube.com/watch?v=s4tuvOer_GI)

-In a top rope "fall" the peak forces are around 1.6kN.
-A decent lead fall is probably around 4.5kN.
-A factor 1 fall is around 6kN. (So people rope jumping would experience around 6kN)
-A factor 2 fall is around 8kN.
(http://bealplanet.com/sport/anglais/forcedechoc.php)

(A factor 1.77 fall has to be less that 12kN for an 80kg person according to UIAA.)

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