DMM sling testing

dmmclimbing.com/knowledge/h…
This video offers some solid data as far as the difference between how an overhand knot affects fall forces in nylon vs how it affects dyneema during a factor 1 and factor 2 fall. Really worth ten minutes of your time if you aren't fully aware of the differences!

There are 2 key points that this video does not address that are indirectly related; 1 breaking point for a harness which I believe is around 15K and the point at which a human body starts to experience deadly internal injuries which again is 15K. This is why a harness breaks at 15K because it serves no purpose to hold if you are dead anyway. Several of the falls where the sling held generated forces over or at around 15K which would still be catastrophic. Please do not quote me the strength of the belay loop which is not the point at where a harness will break apart, the belay loop is attached to the harness which breaks at a lower impact.

DavidLG wrote:There are 2 key points that this video does not address that are indirectly related; 1 breaking point for a harness which I believe is around 15K and the point at which a human body starts to experience deadly internal injuries which again is 15K. This is why a harness breaks at 15K because it serves no purpose to hold if you are dead anyway. Several of the falls where the sling held generated forces over or at around 15K which would still be catastrophic. Please do not quote me the strength of the belay loop which is not the point at where a harness will break apart, the belay loop is attached to the harness which breaks at a lower impact.

But the biggest thing that is neglected in the video is the fact that a human body isn't a rigid steel weight. In a fall, the human body bends and deforms which significantly lowers the force on the gear. The amount that the force is lowered is going to depend on many different factors which is why a rigid steel weight is used, to help eliminate variables, but it is just something to keep in mind.

kennoyce wrote: But the biggest thing that is neglected in the video is the fact that a human body isn't a rigid steel weight. In a fall, the human body bends and deforms which significantly lowers the force on the gear. The amount that the force is lowered is going to depend on many different factors which is why a rigid steel weight is used, to help eliminate variables, but it is just something to keep in mind.

I do not think that your point is as relevant when it is in a thread trying to heighten a sense of caution not to minimize it. That is not to say that your statement is wrong just that in the context of this thread it may not be as important/relevant unless in every case it would lower forces to an acceptable level which I do not think it does.

DavidLG wrote: I do not think that your point is as relevant when it is in a thread trying to heighten a sense of caution not to minimize it. That is not to say that your statement is wrong just that in the context of this thread it may not be as important/relevant unless in every case it would lower forces to an acceptable level which I do not think it does.

Okay, I'll just come out and say it. You'll never break a sling whether it be dyneema or nylon by factor 2ing onto it. It just wont happen. Will it hurt? yes, but it won't break the sling. Ripping gear however is a totally different story, so yes, caution is warranted.

you might break a dyneema sling, but likely not a nylon

its not simply a matter of the stretch of nylon, though that is a factor ..

but also because dyneema slings loses its strength quite rapidly with abrasion and use ... they should all be retired within 2-5 years of decent use, or when it gets somewhat fuzzy ... mixed slings last a bit loner but still arent as wear resistant as nylon

for folks who use a permanently attached "PAS" style tether, it see quite a bit of abrasion as its always rubbing against the rock and yr harness points

there was an accident where a dyneema sling snapped ... this lead to the development of the beal dynaconnect dynamic tether

;)

kennoyce wrote: Okay, I'll just come out and say it. You'll never break a sling whether it be dyneema or nylon by factor 2ing onto it. It just wont happen. Will it hurt? yes, but it won't break the sling. Ripping gear however is a totally different story, so yes, caution is warranted.

Thanks for the input. I am sincerely interested in your statement as I have not seen any studies on the impact force of a real person. Do you have any back-up that you can provide? If you are accurate it does change the need to warrant extreme caution.
Again, thanks and looking forward to your response.

A few years ago a climber took a FF2 onto two draws chained together and clipped to a bolt. One karabiner broke and the guy decked but survived with no injuries. Edelrid recreated the accident and measured 27kN. The harness didn´t break, the bolt didn´t break and the climber sustained no injuries requiring hospitalisation.

Jim Titt wrote: A few years ago a climber took a FF2 onto two draws chained together and clipped to a bolt. One karabiner broke and the guy decked but survived with no injuries. Edelrid recreated the accident and measured 27kN. The harness didn´t break, the bolt didn´t break and the climber sustained no injuries requiring hospitalisation.

did they recreate the accident with steel weights ... or with soft squishay masses?

if you are talking about this one ... it was petzl who recreated the incident with steel weights, not good squishiness and a harness

the analysis also shows that the climber broke the climber likely with the gate open ... a ~6-9 KN scenario at the time of the break

hell the breaking OG biner might have saved his back =P

uiaa

uiaa

uiaa

theuiaa.org/upload_area/fil…

ive stupidely taken the same fall on a knotted nylon 120cm sling ... i got a sore back and whipash for a week or two

sling and carabiner were fine ... as the offset i placed held

probably because the biner and nut were good ole made in wales DMM

;)

DavidLG wrote: Thanks for the input. I am sincerely interested in your statement as I have not seen any studies on the impact force of a real person. Do you have any back-up that you can provide? If you are accurate it does change the need to warrant extreme caution. Again, thanks and looking forward to your response.

http://caves.org/section/vertical/nh/pdfs/nh54.pdf

Another high force test consisted of fall factor 1 drops onto Spectra daisy chains... The peak forces generated by the steel plates are anywhere between 5% and 37% greater than the peak forces generated by the Rescue Randy.

Note that even with the steel weights, the highest force recorded in a FF1 fall onto Spectra was ~12 kN, and none of the daisys fully failed.

It's a bad idea to whip directly onto a static tether, but I also think that the hysterics about it are overblown. Don't do it, but if you do you probably won't die.

I'm wondering if fall factors or length of fall are a more appropriate factor when dealing with things that are less dynamic in nature i.e. rope vs nylon sling vs dynmeema. My thoughts are things fall at a rate of roughly 32 feet per second squared times mass would equal a higher kn impact(the longer the fall) where the material we are attached to have less ability to absorb the impact. Anybody out there to help give a layman's answer to this question. Jim Titt or R Gold please jump in on this. Yes, I know that my free fall rate does not include air resistance.

DavidLG wrote:There are 2 key points that this video does not address that are indirectly related; 1 breaking point for a harness which I believe is around 15K and the point at which a human body starts to experience deadly internal injuries which again is 15K. This is why a harness breaks at 15K because it serves no purpose to hold if you are dead anyway. Several of the falls where the sling held generated forces over or at around 15K which would still be catastrophic. Please do not quote me the strength of the belay loop which is not the point at where a harness will break apart, the belay loop is attached to the harness which breaks at a lower impact.

Harnesses dont "break at" 15kN. That is the UIAA minimum standard, but every harness I have ever owned far exceeds that standard. Even most sport climbing G strings will exceed that standard. Most harnesses hold around 25kN. Wild Country harnesses are rated for 25kN 3-Sigma (or at least the ones I owned were). I have never seen a climbing harness that was officially rated for only 15kN and legitimately only held around 15kN when new.

Also, exceeding the UIAA maximum impact force of 12kN is not going to result in some bloody explosion with your spine snapping into several pieces and instant, gruesome death. The UIAA standard of 12kN came from an old study on paratroopers, which found the maximum impact force of a parachute opening could not exceed 12G if the paratrooper were to survive without injury*. IF you were to exceed 12G, it would possibly result in injury (but it's not a guarantee), but it would not necessarily result in death. It would take a much higher impact force to result in death. How high? That depends entirely on the duration. There have been recorded instances of people surviving (with serious injury) in excess of 200G for an extremely short period during a race car crash. Likewise, exposure to just 3.5G for a period of 24 hours would probably be lethal I would suspect.

• The math works out likes this:

The UIAA standard weight is 80kg, but it is a rigid weight. An 80kg rigid weight is roughly equivalent to around a 102kg flexible mass. To calculate kN from G force we go:

102kg * 12 (Max G force our climber friend can withstand without injury) * 9.8 (M/s^2, the acceleration of gravity on Earth) = 11,995N or 11.995kN, thus the UIAA maximum impact force standard of 12kN.

If we extrapolate this to the 60/100/160 ratio the UIAA and Petzl uses to determine the force exposed to the top piece (60% to the belayer, 100% to the climber, 160% to the anchor), we get 19.2kN (round up to 20kN), which happens to be the strength requirement for most carabiners, and bolts/ hangers in tension and it's also where my name comes from.

You can read more here: theuiaa.org/upload_area/fil…

DavidLG wrote:I'm wondering if fall factors or length of fall are a more appropriate factor when dealing with things that are less dynamic in nature i.e. rope vs nylon sling vs dynmeema. My thoughts are things fall at a rate of roughly 32 feet per second squared times mass would equal a higher kn impact(the longer the fall) where the material we are attached to have less ability to absorb the impact. Anybody out there to help give a layman's answer to this question. Jim Titt or R Gold please jump in on this. Yes, I know that my free fall rate does not include air resistance.

It's impossible to say one is more important than the other as it's entirely scenario driven. However, we do know that flexible human masses, nylon harnesses, imperfect falling angles (you rarely fall perfectly straight down), ect, remove energy from the system, and we know that longer falls involve larger amounts of energy, which will tax the limit of how much energy the above-mentioned objects can dissipate.

Consider an example. Say I took a steel locking biner, clipped it to a hanger and my belay loop, climbed as high as possible, then let go. I would in essence be taking an FF2 right onto a steel biner, which on paper would have an impact force so high it would rip a 1/2" bolt clean from the wall. In reality, the amount of energy involved in such a short fall is so low that the items mentioned above can easily dissipate it, thus the theoretical 50kN fall is reduced to more like 4kN, if that. On the other hand, if I chained 10 steel biners together and repeated the scenario, that would produce sky-high impact forces as my body, harness, ect. cannot dissipate enough energy to keep the impact forces low.

Why? Because the items I listed earlier only remove a fairly fixed amount of energy from a fall. Sure, as the impact force increases, your body can elongate a bit more, and so can your harness, but only to a point. Eventually that stuff just cant elongate anymore and it wont remove any more energy from the system.

This is exactly why screamers can actually be harmful in some conditions and simply ineffective in others. If you fall with a screamer at your foot, the amount of energy in the system is low, thus the screamer can dissipate a larger proportion. But if you take a massive whip on the screamer, the proportion of energy it can dissipate is much lower and therefore the screamer is less effective. If you place a screamer right out of the belay and whip on it big, it can increase the impact force because the increase in energy created from increasing the impact force of the fall through extension can exceed the fixed amount of energy removed from the system by the screamer.

I don't buy your last point re. a Screamer potentially making things worse. As long as the device requires a greater force to rip (i.e. absorb more energy over the elongation distance) than gravity puts in, there will be a net reduction in fall energy to be dealt with by the rest of the system. Screamers rip at about 450lb; gravity will exert less than half that on a falling climber, so there is less energy overall.

Whether you buy Yates' claims or not, independent testing has shown that Screamers reduce peak force: blackdiamondequipment.com/e…

Some independent test shows some reduction, other independent testing shows little, none or even an increased anchor load.

In theory, a screamer with a low enough activation force could increase the anchor load in a lead fall. This is because the leader drops twice the screamer elongation but the work done against stitch resistance is only for the screamer elongation. So in order to have any effect at all, the screamer activation force has to be more than double the climber's weight, otherwise there will be a net loss of energy and so an increase in anchor load.

Ordinary screamers do activate at more than double most people's weight, so some fairly small amount of energy will be absorbed. One problem with screamers is that they can only remove a fixed amount of energy from the system, so that as the fall gets longer, the amount of energy removed is a smaller and smaller proportion of the total amount of energy to be absorbed, and the screamer fairly quickly becomes irrelevant, except for dropping the leader further. There is some hope that the screamer might reduce loads on a short high fall-factor fall, but the evidence is not conclusive. Nobody with any practical or theoretical experience believes Yates' numbers.

One theory for how the anchor loads might actually be increased is that the screamer reduces the load to the belay device and prevents any slippage there. This might be a good thing, but on the other hand it is possible that slippage through the belay device might absorb more fall energy than the screamer would have.

rgold wrote:In theory, a screamer with a low enough activation force could increase the anchor load in a lead fall. This is because the leader drops twice the screamer elongation but the work done against stitch resistance is only for the screamer elongation.

Ah, that's what I was missing. Thanks.

rgold wrote:Some independent test shows some reduction, other independent testing shows little, none or even an increased anchor load. In theory, a screamer with a low enough activation force could increase the anchor load in a lead fall. This is because the leader drops twice the screamer elongation but the work done against stitch resistance is only for the screamer elongation. So in order to have any effect at all, the screamer activation force has to be more than double the climber's weight, otherwise there will be a net loss of energy and so an increase in anchor load. Ordinary screamers do activate at more than double most people's weight, so some fairly small amount of energy will be absorbed. One problem with screamers is that they can only remove a fixed amount of energy from the system, so that as the fall gets longer, the amount of energy removed is a smaller and smaller proportion of the total amount of energy to be absorbed, and the screamer fairly quickly becomes irrelevant, except for dropping the leader further. There is some hope that the screamer might reduce loads on a short high fall-factor fall, but the evidence is not conclusive. Nobody with any practical or theoretical experience believes Yates' numbers. One theory for how the anchor loads might actually be increased is that the screamer reduces the load to the belay device and prevents any slippage there. This might be a good thing, but on the other hand it is possible that slippage through the belay device might absorb more fall energy than the screamer would have.

The problem with stitched-type screamers is the peak load to failure varies considerably with the speed the load is applied. To break the stitches first you need to tension them which means the threads have to slide through the parent material and frictional hysterises means this becomes harder and harder to do the faster you load them. The failure scan of a screamer is a jagged line with peaks as the stitches fail and valleys as the next stitches tension and the mean gives the rated failure load. Tested at higher speeds the peaks can be nearly twice the nominal rating.
It is also the case that delaying the onset of the maximum force imposed on the rope/belay device may well (depending on how long the screamer takes to activate) cause the maximum force on the top piece to be increased, this can be seen by looking at the load curves from belay devices and time shifting the maximum belayer force to coincide with the maximum rope tension.
The CAI tests show undoubtedly that screamers become less effective with larger falls and in the end counter-productive, whatever Black Diamond say based on a minimal amount of poor testing.