Guide ATC / Rope slippage on a fall.

Hi, I'm fairly new to trad and right now I'm reading up on fall forces and fall factors... Trying out the online Petzl fall simulator.

Being a BD product I can't enter my Guide ATC as my belay device on the Petzl simulator, so I'm using a Reverso as the closest option. In entering simulated falls I was really surprised how much rope slippage can occur through the Reverso during a leader fall. Is rope slippage on a Guide ATC about the same or does the friction side cut it down a bit?

In a real life fall situation it seems that the belayer will stand a very good chance of sustaining serious rope burns in arresting the fall. It is a matter of belay technique to avoid this possibility?

Thanks,
Glenn

Hey freerangequark. slippage is not a problem. it is a benefit mostly. all belay devices have some slippage. autolocking devices like a grigri have less. this is an important source of energy absorbtion. the amount of slippage will vary depending on the device, the rope diameter, the rope slickness (new ropes, dry treated ropes) etc. in terms of slippage we are talking about inches not feet provided you are using a device that is rated for your rope thickness. I weigh in @ over 2 bills. I fall all the time. My partners often use bd atc guides or whatever. No problem catching my fat ass without rope burn.

the biggest risk is the human element. be sure you and your partner go out and buy a "pay attention". then, buy a "really pay attention". and be sure you get a "really friggin seriously...pay attention". happy climbing!

Yes, I noticed that when a Gri-gri is used as the belay device, the max impact forces sustained by the climber and the belayer increase due to a lack of rope slippage. What I think is confusing me is that that the rope slippage on the Reverso simulation was listed at "3m" which seems rather excessive and hence my question about the rope burn.

Here's the simulation...
en.petzl.com/petzl/SportCon…

Thanks for any clarification you can provide.

Glenn

The way I heard it was that a grigri is a static belay device that disipates no force when catching a fall. So this would cause more stress on the parts in the stystem and the anchor. like stated above a reverso or a guide would be a dynamic device that helps disipate force and is a positive thing. not shock loading the anchor is a good thing.

FRQ -
One thing you have to remember about the Petzl Simulator is that it assumes that the belayer doesn't move during a fall. Typically, most falls will pull the belayer up off their stance, reducing the forces and the belay device slippage. Of course, this is only if there is a protection piece above the belay and is therefore less than a factor 2 fall.

It is crucial to remember the importance of placing a piece soon after the belay, otherwise the possible fall and rope slippage (rope burn = loss of control) could be disastrous.

A belay glove is certainly a good idea as long as it is dexterous enough to fiddle with the ropes & gear. Otherwise, the only belay technique that can help is having a DILIGENT READY BELAY since falls happen so fast and reaction time is typically too slow.

To echo Casey's post, there are lead falls and then there are LEAD FALLS. A fall where the leader is far up the pitch and there's a lot of rope out isn't going to generate nearly as much force (or rope slippage) on the belay device as a fall onto a placement that's just off the ground/belay anchor. And as Casey noted, in a multi-pitch situation where the leader falls directly onto the belayer/anchor, the force will be so high that rope burns due to slippage would be the least of your worries.

I use the ATC Guide and have never experienced significant rope slippage in catching leader falls, though I have been pulled up and/or jumped to soften the catch. As for belay gloves, I don't typically use these for belaying, but since veteran climbers that I greatly respect, like Richard Goldstone, advocate gloves, I think it deserves serious consideration.

JL

This is an area where rope diameter also matters in relation to the device. The smaller rope diameter in relation to the device & you can have difficulty in controlling the brake if a leader takes a long runout fall -- even if you are locked off.

Though, a certain degree of rope slippage is a good thing in absorbing energy.

freerangequark wrote:What I think is confusing me is that that the rope slippage on the Reverso simulation was listed at "3m" which seems rather excessive

I played with the fall simulator in a few different scenarios and am skeptical about the way they apparently calculate rope slippage. It certainly doesn't match my real-world experiences with leader falls.

JL

A number of points:

1. The Petzl simulator (and most theoretical models) use a relatively simple equation that either ignores or only partially accounts for friction through the carabiners and against the rock. The result is that more fall energy has to be absorbed by the rope running and so the predictions of rope running are probably on the high side.

2. The great majority of climbing falls have low fall factors and do not produce very large loads at the belay device anyway.

3. Even when the fall factors are larger, there are usually enough sources of friction in the system dissipating fall energy so that it is rare for most belayers to experience the rope running.

The net effect is that many climbers can climb for years---or even an entire career---and catch many leader falls without ever having the rope run.

On the other hand,

4. Both sophisticated mathematical modeling and extensive practical testing by the Italian Alpine Club (CAI), as well as an extensive historical record of belay testing in the US in the 50's and 60's make it clear that if the belayer is exposed to a high fall-factor situation with few sources of friction, there can be significant amounts of rope running.

5. How much rope runs depends on the friction in the system, the amount of friction supplied by the belay device, and the strength of the belayer's hand. The CAI tests also indicate that there is enormous variation in the performance of experienced individual belayers, so much so that it was hard to get useful data from repeated trials.

I have slightly oversimplified the discussion of rope slippage here, because there are, in reality, two phases of rope slippage, one of which does not produce burns. In the first, or what the CAI calls the inertial phase, the brake hand is pulled up to the belay device. Depending on the position of the brake hand at the moment of impact, this could involve as much as two feet of rope running through the belay device under resistance with no slippage through the brake hand, producing perhaps the energy absorbtion of a Screamer. If the additional energy absorbtion of the inertial phase is not enough to stop the fall, then in the next phase the rope is pulled through the belayer's hand under whatever tension the belayer is able to maintain.

6. As for the friction supplied by the device, the original Reverso was at the bottom of the heap---in my opinion, it was dangerously inadequate for severe falls. Although I have seen no comparative figures for the BD Guide ATC, I am sure that it has a significantly higher braking factor than the original Reverso had.

7. The CAI tests showed that the lifting of the belayer has a relatively minor effect in reducing the peak load to gear, and that only a fraction of the lifting occurs up to the moment of peak load, the majority occuring after the gear has already been maximally stressed. These results are for a non-locking belay device for which other force dissipation factors are involved and these apparently mitigate the contribution from belayer lifting.

8. Another set of tests has shown that, with a Gri-Gri, a properly timed belayer jump can result in a decent load reduction to the top pro. (Note: a Gri-Gri will not slip in any climbing fall caught by pro. There is a chance, depending on the rope and other frictional factors, that a Gri-Gri might slip in a factor 2 fall.) Of course, "properly timed" is critical, and given the very large variation in belayer performance in the CAI tests, one has to wonder whether even an experience jumper can regularly reduce peak loads with a Gri-Gri.

In summary, as with a number of issues in climbing (equalizing belay anchors, backing up rappels, wearing helmets, etc.), there are practices that are effective a large majority of the time but which may not work well or at all in a very small number of exceptional cases. Since the rope doesn't slip in most climbing falls, there is usually no difference in imposed peak load for a Gri-Gri and ATC-type devices. However, in high fall-factor low-friction circumstances, the rope slippage is a potential safety valve that may keep peak loads within the limits sustainable by trad gear, where as the same gear will blow with a Gri-Gri. I say "potential safety valve" because without gloves, it isn't clear that rope slippage will be controllable. If the belayer cannot maintain full strength grip or even loses control, rope slippage becomes not a safety valve but a liability. Moreover, even if the belayer hangs on, the burns sustained can range from annoying to exceptionally severe---as in down to the bone.

Using an ATC-type device rather than a Gri-Gri means (if you were to think logically about it) that you want the potential safety-valve effect that might come into play in exceptional circumstances. Not wearing gloves turns that potential effect into a liability and so contradicts choosing the ATC-type device---at least that's the way it appears to me.

Hi,

Thank you to everyone for the replies on this thread, it has certainly given me a lot better understanding of fall dynamics and a lot more to consider when climbing trad. I appreciate the help.

-Glenn

rgold wrote: As for the friction supplied by the device, the original Reverso was at the bottom of the heap---in my opinion, it was dangerously inadequate for severe falls. Although I have seen no comparative figures for the BD Guide ATC, I am sure that it has a significantly higher braking factor than the original Reverso had.

In Manin et al., Rock climbing belay device analysis, experiments and modelling, Engineering of Sport 6, pp. 69-74, 2006, there's a table comparing the force multiplication factors of six devices, including the old Reverso and the ATC XP. The rope was a 9.7 mm Beal.

The Reverso was indeed near the bottom of the heap with a factor of 5.5, very close to those of the figure eights. The ATC XP, on the other hand, had the highest factor (11). My impression is that the ATC Guide and the Reverso 3 should be closer to the XP than to the old Reverso.

saxfiend wrote: I played with the fall simulator in a few different scenarios and am skeptical about the way they apparently calculate rope slippage. It certainly doesn't match my real-world experiences with leader falls. JL

We've gone round and round on this topic several times on various forums. And for all the engineering and science around the topic, the fact remains that in thirty four years of belaying on more or less every kind of device including various forms of body belaying, I've never had a locked off rope slip through my hand in any perceptible way or amount when holding all manner of falls.

Healyje wrote: I've never had a locked off rope slip through my hand in any perceptible way or amount when holding all manner of falls.

And yet, reputable sources report rope slippage in actual falls.

If you just pull your brake hand back properly when the leader falls, you'll catch the fall with no problem - every time.

The rope provides all the dynamic effect you need to safely arrest a fall.

I'm not sure how many of you are familiar with the "belay mitten", but if you're extremely concerned about rope runs, I say that wrapping a loop or two around your brake hand will help eliminate slippage. You have to watch out for pinching your hand in the belay device, but your leader isn't going to deck unless you have protection ripping out. If you need to reduce the load on pro, hopping definately helps in that circumstance.

Not So Famous Old Dude wrote:If you just pull your brake hand back properly when the leader falls, you'll catch the fall with no problem - every time. The rope provides all the dynamic effect you need to safely arrest a fall.

I'm not sure it's so black-and-white. A new rope guarantees the force on the falling climber is less than, say, 7.5 kN. Friction at the top anchor means that the brake strand sees less than 5 kN. The combination of a strong hand with a good brake and proper technique (opening up the angle of the two strands in and out of the belay device to about 180 degrees, as you point out) is likely to match those 5 kN and no rope will slip through the device. Of course, if the fall is not so extreme and the rope goes through multiple anchors, the likelihood of slippage further decreases.

Take an old Reverso, an old, thin, slippery, stiff rope, and a feebler hand, and you may see rope slip. In the paper I cited above, they used a "mechanical belayer hand" to guarantee uniformity. They set it up to produce some 160 N of gripping force max. In a 1994 study, Mauthner and Mauthner concluded that the average gripping force was a bit above 200 N (I don't know what population they considered, though I believe that their study was addressed to the SAR crowd.) If you take 200 N and multiply them by 5 you get a lot less than the 7 kN that may come from that old, stiff rope.

Then there's a fall directly on the belay device. We should never let it happen, but...

It's also important to realize that once the rope starts slipping, the amount of slip is related to the height of the fall rather than the fall factor. Said otherwise, it's related to energy rather than force.

brenta wrote: I'm not sure it's so black-and-white.

The physics are not so black-and-white for sure. I don't presume to argue physics.

I suppose my post was just intended to underscore the idea that perhaps we tend to overanalyze things sometimes, when real safety is derived more from paying attention, anticipating problems, and practicing simple, reliable techniques.

For new climbers: You don't need to jump up, you don't need to give slack, you don't need to do anything to catch a lead fall safely and without injury other than to simply pull your brake hand back and wait for the climber to come onto the rope.

Not So Famous Old Dude wrote:perhaps we tend to overanalyze things sometimes, when real safety is derived more from paying attention, anticipating problems, and practicing simple, reliable techniques. For new climbers: You don't need to jump up, you don't need to give slack, you don't need to do anything to catch a lead fall safely and without injury other than to simply pull your brake hand back and wait for the climber to come onto the rope.

Sorry, since the discussion was on rope slippage, I took your earlier comment to be about that. I agree with all of the above. If I'm allowed an analogy, a beginner driver attempting a heel-and-toe downshift is more likely to do damage than good.

brenta wrote: "I'm not sure it's so black-and-white. A new rope guarantees the force on the falling climber is less than, say, 7.5 kN. "

Sounds like a bit of a misunderstanding of Impact Force ratings on ropes. New ropes don't guarantee anything about the force on a falling climbing. The number the guarantee is in reference to is a test result on a specific fall factor (i believe 1.78) with a specific weight (i believe 80kg=176lbs). This will give one imformation regarding the ropes' ability to absorb energy. These numbers change with age and usage among other factors.

Greg D wrote: Sounds like a bit of a misunderstanding of Impact Force ratings on ropes. New ropes don't guarantee anything about the force on a falling climbing. The number the guarantee is in reference to is a test result on a specific fall factor (i believe 1.78) with a specific weight (i believe 80kg=176lbs). This will give one imformation regarding the ropes' ability to absorb energy. These numbers change with age and usage among other factors.

Greg, I'm familiar with the way impact force is measured and with its meaning. I'm also familiar with the literature on modeling a climber's fall. There is no misunderstanding on my part, though if I had anticipated your objection, I would have stated a few assumptions more clearly. Let me elaborate.

The conditions of the so-called UIAA fall are such that in normal climbing falls the force on the climber will not exceed the declared impact force. If you know the principles behind the design of the safety chain, you are aware that a primary intent of the designers of the standards was to be able to put an upper bound on the force on the climber and the top anchor. Of course, you can have fall factors higher than 1.78 and even higher than 2, not just on a via ferrata, but even in standard roped climbing. That's one issue I was not explicitly addressing in my analysis, because it was only tangential to it, but see below.

I was trying to show that it is reasonable to assume that under favorable circumstances a belayer may arrest even a serious fall without rope slipping through the belay device. To prove that claim, one needs to start with a bound on the force. In this context, I stand by my statement that in a normal, albeit possibly serious, fall, in which all the rope paid out participates to some degree in stopping the falling climber, a new rope (not only first fall, but no appreciable degradation from belaying and rappelling as discussed, for instance, here) will exert a force that can be bounded. I chose 7.5 kN as a representative figure because (a) that would make my back-of-the-envelope computation easier; (b) it's at the lower end of the spectrum of what is available today for single ropes. That leads to quite reasonable assumptions about the gripping force required to keep the rope from slipping.

On the other hand, I was also trying to show that under unfavorable circumstances some rope would slip. Note how, in that second part of the discussion, I refer to an "old, thin, slippery, stiff rope." Note, specifically, the contraposition of new to old. Also, thin, slippery ropes typically lead to lower force multiplication factors in the belay device, and the rope may have a high impact force to begin with.

Note also that I mentioned a direct fall on the belay device as one not accounted for in the favorable case. If, on the other hand, the fall factor is greater than 2 because only part of the live rope is involved in catching the fall--say, the live rope got stuck behind a flake or managed to wrap itself around a horn--then the belayer has no part in stopping the fall and the case is irrelevant to this discussion.

In sum, my assumption that the fall was at worst a UIAA fall was both conscious and justified. So was the guarantee you didn't like. I hope you'll like it better now.

brenta, thanks for your explanation. I would like hear more on fall factor exceeding 2. In your example "a rope getting stuck or wrapping around a horn" I would like some clarification how this can exceed 2. Yes, potentially virtually eliminating any slippage in say a perfect lassoo of a horn. A rope lodged behind a flake may still have some "slippage" as the rope cinches tight.

But, factor 2 is only theoretical, not achievable in real life because of slippage among other factors. Even with a gri gri there is a minor amount of slippage as the device begins to lock albeit small. Graphing fall factors would look like a parabolic, approaching 2 towards infinity, but never reaching 2.

Again, I would like hear more on fall factors exceeding 2. I always like to broaden my scope of knowledge. Thanks for the discussion.