11/16" nylon, impact force 18.4kN, held
1" nylon, impact force 21.11kN, held
1/2" Spectra, impact force, 20.02kN, failed
5/8" Spectra, impact force, 19.2kN, failed
10mm Dyneema, impact force, 18.9kN, failed

Sorry to start yet another thread about slings, daisies, PASes, etc., for anchoring, but I don't think this issue has been addressed yet. I feel the situation I'm about to describe is common enough to do so in its own thread. First a reference point... Jim Ewing's static anchor drop test results. The are the results of high-factor falls onto static materials, instead of dynamic climbing rope.

I don't know the details of this test, but I assume he is dropping a chunk of metal that is attached to the anchor. This does give really high shock values.

However, the human body inside of a harness has a lot more give. The harness will change shape and the body has a bit of give to it, unlike a piece of metal. So a person won't generate this high of static loads.

Dropping onto an anchor is going to be a shorter distance than some of the falls on a daisy while aid climbing. The metolious spectra adjustable daisy has broken in this situation, but I think part of it is due to the ajustment mechanism.

It is certainly good to be careful in this situation and using a nylon sling instead of or in addition to a spectra is a good idea also. However, I can't remember hearing of fatalities from this.

How was the test set up? Was there any knots in the material?

I question whether 3 ft. of dynamic rope vs. 3 ft. of sling material will make that much difference in reducing the impact force of the type of fall described here. Will it make the difference and will you avoid injury. It's going to be a hard fall anyway.

Disclaimer: this is totally non scientific as it is a very small sample and should not be considered conclusive in any way shape or form. Personal results may vary and may cause serious injury or death. Listen to your mother and quit climbing.

Here's a snap shot:
approximately 4 foot drop, factor 2, 80kg, all forces in kN, all specimens are new, 2nd drops carried out 5 minutes after the 1st.

10.4mm (single) 1st drop = 7.24, 2nd drop = 9.82, held both
8.8mm (half) 1st drop= 8.95, 2nd drop = 12.15, broke at knot on 2nd
7.7mm (twin) 1st drop= 7.32, 2nd drop = 9.83, broke at knot on 2nd
8mm acc cord (for laughs) 1st drop = 13.59, broke at knot on 1st

Again, this is a SERIOUSLY HARD drop and is impossible to duplicate in real life.

As to the shock absorbtion of a short piece of climbing rope; the impact force is entirely a function of the ratio between the length of the fall and the length of the rope catching it. A 3 foot fall on 3 feet of rope creates the same impact force as a 30 foot fall on 30 feet of rope. A short piece of rope will soften a short fall as well as a long piece of rope will soften a long fall, in other words.

I question whether 3 ft. of dynamic rope vs. 3 ft. of sling material will make that much difference in reducing the impact force of the type of fall described here. Will it make the difference and will you avoid injury. It's going to be a hard fall anyway.

After all, the impact absorbtion of a dynamic rope comes from having a lot of rope out. The more rope between you and the belay, the lower the fall factor (well that's part of the equation anyway). Which is precisely why the most dangerous falls are the ones that happen when you fall directly onto the belay before putting the first piece in, with very little rope out-the factor two falls.

I like the screamer idea BTW.

Anyone know what the impact force of a fall onto 3 ft of rope would be vs. sling.

I agree with Jay, but allow me to put on my devil's advocate blouse and panties. Those force figures are for perfectly static weights being dropped on the various materials. Has anyone ever seen any data illustrating how "elastic" the human body is? Obviously a 150lb bag of guts is going to absorb some of the force from a high fall-factor fall...but how much?

Many years ago aid climbing (back when I aided with a fifi hook), I had a piece pop and I fell about 5 feet, and while falling my fifi hook happened to snag onto a biner of a stopper and I came to a very static stop (and people use to warn about fifi hooks breaking, I wish). I came out of it ok. Although a month later i could still see the ugly yellow marks on my hips and legs from where the harness caught me.

one of the employees there had fallen about three feet onto a sling clipped to a bolt a couple of months before, and his back had still not recovered. It had mucked him up worse than one would ever have thought.

4.2 EFFECT OF JOLT
Jolt is defined as the rate of onset of acceleration. For the range of acceleration or deceleration
considered in this study it is probably best explained as

Initial peak acceleration
________________

Rise time

which can be expressed in m/s(cubed) or, as in most of the papers reviewed, G/s.



The human body can tolerate very high jolt levels over very short periods of time, usually because the amplitude, or distance travelled, is small. Jolt becomes a serious problem when the duration or amplitude increases. For subjects exposed to positive G the means of constraint of the body is
important.

If the torso is positively secured, as for example in a modern ejection seat, the basic vertebral strength can be enhanced because the bulk of muscle and general body tissue provides support for very short periods of time.



It appears that most of the workers in the area of +Gz research have concentrated on tolerance of the spinal column. Where the subject individual is less securely constrained (as in an industrial
harness) the risk of spinal damage increases with high G forces and with high jolt levels! There is greater risk of flexion of the spine, and consequent injury. There is also a risk of internal injury due to inertia of the major organs. Figure 4 illustrates how
the heart and lungs are separated from the lower organs (liver, kidneys, intestines etc) by the diaphragm. In a fall-arrest event a reasonably erect spine is, to an extent, supported by the bulk of the musculo-skeletal system, but the inner organs are more ‘loosely’ suspended and thus more affected by jolt. Swearingen [47] tells of crashes where helicopter pilots died of ruptured aortas, and argues that 10G measured at shoulder level is a survivable maximum for helicopter pilots.
Wallace and Swearingen [51] also describe a tragic case where 6 young men died in a light aircraft that hooked a power line and came to earth “in a flat attitude”. None of the victims showed any external sign of injury. All had died from “severe impact trauma to internal organs (brain, heart, liver, spleen etc)”. In both reports the levels of positive G and jolt were unknown, but the nature of the injuries alerts the reader to the vulnerability of the inner organs in conditions of high
positive G and jolt.


*Emphasis mine*