UKC

I have read many times that Dyneema slings have no dynamic properties therefore they should never be shock loaded. Being relatively inexperienced, I follow this advise religiously when using slings at anchor points but I have often wandered how come that hexes and cams all have slings to clip on to. Does that mean that any eventual impact of a fall will be absorbed by the rope and it doesn't shock load at all the sling attached to the protection? 

exactly this..... The rope is the dynamic element so mainly  problwms  when a climber clips into a sling at a belay, there then isnt dynamic rope in the system

Indeed - if there's rope in the system it's not really a problem (though I suspect falling onto a sling at the end of a short amount of rope at a belay would still be unpleasant).

Yes, that's it. Ropes, knots and soft meaty masses like climbers and belayers deform reducing peak force, belay devices slip doing much the same.

With a simpler set-up, just a sling arresting a slip at a belay for example there is much less available deformation resulting in a much higher force for a given amount of fall energy dissipated than would be the case if the rope were in the set-up.

jk

Good, thanks for clarifying this!

In a first aid course I was shown a rather disturbing x ray of a spine, this person had clipped into a wire sling strait from bolt to harnes stood up in some etriers and slipped. The spine was very clearly broken and a life in a wheel chair was the result. The caver had stood up 750mm from the bolt resulting in a 1500mm fall, not very far at all.

The same goes for nylon slings as well.  (I believe that nylon has rather more inherent elasticity than dyneema, but the point is that slings of either type are made from flat woven tape whereas climbing ropes have a complex structure involving a spiral-woven tube - analogous to the Chinese Finger Trap https://en.wikipedia.org/wiki/Chinese_finger_trap - enclosing bundles of specially-treated fibres, all carefully designed to work together so as to give the rope the desired dynamic properties.)

You should think of all 'gear' you place as non-dynamic. The rope is the dynamic part of the system.

This isn't a reason not to use them at anchor points, simply make sure there's no slack in the system.

Yeah, so why call it Dyneema?

Because "ultra high molecular weight polyethylene" is a bit of a mouthful?

A reasonably understandable analogy is that falling from height X onto a non-dynamic setup in a harness is basically equivalent to that self same fall being directly onto your backside onto a slab of concrete or rock.  (In some ways it may be worse, because if you fall on your backside it's generally a bit bouncy due to the muscles and potentially lard there).

Of course there's also the risk of the sling failing and thus it turning into a much larger fall onto your backside.

Older sling or cordette's were more dynamic and I know some people who make their own slings from dynamic rope, but I don't personally think that the dynamic properties will be noticed over such a short length. As you say hexes/cams etc are on dyneema or wires, neither are dynamic, same with quickdraws so it must be the rope that is the dynamic part of the system.

That is a similar analogy to the one I use for rope techs. Imagine falling 2 metres onto a scaffold pole with your lower back taking the full force.

There is a good video on the DMM website of them testing both Dynema and nylon slings.