Another Accident due to mis-use of the Gri-gri

Agreed, but common sense doesn't always prevail and isn't always right. In this case, what is "obvious" to you obviously isn't obvious to some other people. And rightly so; in the math world the first place we look for errors in an argument is in claims said to be "obvious."

I might have added that since there is no back and forth motion as there is with an ATC and its anchor carabiner, that the Grigri had to be engineered to minimize the friction from the capstan effect, otherwise it would be too hard to pump slack to the leader even with the cam held down.

But please, it is not all these details, but the observation in my last paragraph that, I hope, is of importance.

Gri

Atc

Just for fun and totally unscientific:

Results

The load is 1 gallon of water plus the metal clamp. The Gri required 42 ounces (710 grams) on the brake strand to stop the load. The ATC required 2 ounces (59 grams) to stop the load.

Edit: static friction vs kinetic friction was taken into account.

Greg, thanks for the additional evidence. The light weights might be a problem, but the trend is already clear.

BillS wrote:Please first solve for the friction variable in those equations, then get back to us about how useful they are.

First understand the point of the post, then get back to me with snide questions.

BillS wrote:On that note, static friction is greater than kinetic friction. Kinetic friction is reduced by heat and velocity. This is the heart of the matter, as I see it.

All covered in the linked article. I didn't think it necessary to mention. Your comment that "kinetic frictions is reduced by heat and velocity" makes no sense, by the way.

BillS wrote:I'll let the presumption and pompus windbaggery continue.

How very good of you---especially after adding to it.

BillS wrote:FWIW, I'm in agreement with Mort.

Me too.

Yes static friction is greater than kinetic friction. I did take this into account by accelerating the load to go into kinetic friction mode. If the load did not come to rest I added a bit of weight to the brake strand. Repeat until there was enough weight on the brake to arrest the load.

Again, very crude experiment.

BillS wrote: A rope will glaze at the belay device and at the top biner in a hard fall. The speed of the rope also appears to do a nice job polishing gloves and skin. This changes the friction. A rope will also "vibrate" at high velocity, reducing the contact - also opening biner gates and what-not. Carry on, nothing like listening to an academic.

come on - rgold's posts are consistently interesting and he summarizes his main points in a way that make sense to someone without a background in physics. Nobody claims to have a perfect theoretical understanding, but I'd far rather read a post from someone who tries to understand the key physics, and makes well-reasoned practical arguments, than from someone who provides a list a bunch of irrelevant sounding secondary concerns and rude comments.

BillS wrote:Carry on, nothing like listening to an academic.

Oh good, then let me explain my remark:

As regards kinetic friction and velocity:

From hal.archives-ouvertes.fr/fi…:

Almost three centuries ago Charles Coulomb (1736-1806) discovered that kinetic friction does not depend on the sliding velocity [1]. Later, more careful experiments showed that this law is only approximately valid [2–7]. Friction does depend on the sliding velocity, but this dependence is far from universal: some measurements find an increase when velocity increases, while others find a
decay [8–10] or even a more complex non-monotonous behavior [2].

From stle.org/resources/lubelear…

Friction is not always independent of velocity. If we exclude very low speeds and very high speeds, the friction coefficient is constant and independent of sliding velocity. But at very high speeds, the friction coefficient generally has a slightly negative slope; that is, the friction coefficient decreases gradually as the speed increases.

As regards kinetic friction and heat:

From scitation.aip.org/content/a…

In this paper we describe a relatively simple experiment that can be done to test the effect surface temperature has on kinetic friction, and that depending on the materials being used, the coefficient of kinetic friction does indeed increase as the surface temperature of one of the materials increases.

From journalamme.org/papers_vol2…

Up, down, up, down...
Dependence of kinetic friction on heat

But all this is a nerdy distraction from a much more important point. So allow me to repeat myself:

Let’s suppose that I’m wrong (hardly an unusual circumstance) and there is no such thing as situation that would physically overwhelm a belayer even though the belayer does everything correctly. Then we can still say that the problem brought to our attention by John at the beginning of this thread is one that will, at the very least, greatly increase the demands on the belayer, way past anything that they are used to dealing with when using a Grigri. Forgetting all the arguments about unconditional belayer responsibility, isn’t the prospect of a sudden huge increase in the performance demands on the belayer enough, all by itself, to merit serious consideration of John’s warning? And isn't it right, in terms of the actual tragedies that have happened, to let it go at that?

Kedron Silsbee wrote: come on - rgold's posts are consistently interesting and he summarizes his main points in a way that make sense to someone without a background in physics. Nobody claims to have a perfect theoretical understanding, but I'd far rather read a post from someone who tries to understand the key physics, and makes well-reasoned practical arguments, than from someone who provides a list a bunch of irrelevant sounding secondary concerns and rude comments.

I'm sure Bill S is just one of many who find it irritating to be confronted with facts and logic.

For my part, I'd love to have seen this message thread given a more useful title: 'Another Accident due to mis-use of the belay device.' In 10 years of climbing, I've been dropped/near-dropped three times, and none of these involved a gri-gri.

JL

Perhaps someone would like to start a thread entitled "20 ways to drop the leader" (or some other number...), wherein we could categorize, by device, how to mess up. Might be helpful to have around.

rgold wrote:Perhaps someone would like to start a thread entitled "20 ways to drop the leader" (or some other number...), wherein we could categorize, by device, how to mess up. Might be helpful to have around.

- not pay attention

- have too much slack out

- not have a solid brake hand (which isnt too close to the device)

- not double checking the setup (also fault of climber)

- not recognizing weight and strength differences (also fault of climber)

- poor understanding of gear placements, zippering and forces (also fault of climber)

- defeat the cam through poor/unapproved belaying techniques (in the case of assisted braking devices)

other than hard to control things like rock/icefall, heart attack, getting mauled by a bear, etc ...

thats about it

its pretty damn simple, yet folks screw it up over and over again

belaying is something that almost everyone thinks they are good at, yet in reality many arent, nor can many accept that their technique is poor

psmag.com/navigation/health…

theres a reason why even "experienced" folks drop others, even with grigris ...

a belayer who thinks they have nothing to learn is the one you should be walking away from ...

everytime a good belayer belays they should ask themselves what they could have done a bit better ... just like a climber who asks how they could have climbed better

belaying is the most important thing in climbing ... folks who dont take it seriously are knowingly playing russian roulette with someone elses life

here is perhaps the best article ive seen on the subject ...

I have some bad news for you: you’re probably not a great belayer. In fact, you might not even be a good one. How do I know? It’s a matter of odds. Everyone thinks they’re better than average. That’s normal, but, of course, it’s wrong. Most of us are just average, as per the definition of average. And in belaying, as in working at Chachkies, doing the bare minimum just isn’t good enough. Basically, we should all be angling towards better pretty much all the time.

The Good, the Bad, and the Oblivious

Just consider: how many times have you visited a crag and seen bad belaying, and lots of it? Giant loops of slack, untended brake-ends, unlocked biners, chronic short-roping, belayers chattering obliviously on the ground while their climbers crux out high above sketchy pro? Visit the Internet and search the forums for tales of such belaying incompetence—they are numerous. Climbing Magazine has been running a weekly series on bad belaying practices and Rock and Ice has some interesting examples of bad belaying in their Weekend Whipper series. Petzl (my employer) created a video called “The World’s Worst Belayer” (see below) which exaggerates for comedic effect some of the many very real epic belaying fails occurring all across the globe at any given moment.

If you’re like me, you like to think you never do stuff like this. But if you’re like me when I’m feeling honest, you can probably recall moments when you’ve perpetrated the same sketchy acts of belaying yourself. Maybe it was only for a moment, and maybe it doesn’t happen often (or so you like to tell yourself), but that’s the thing about belaying: most days out we’ll be fine, but when those fateful moments arise and bad habits intersect with bad luck, bad things are gonna happen. Sure, we feel competent, but the hard truth is, as a species, humans are pretty poor at evaluating our own ability level at most tasks.

Consider a study conducted by the insurance agency Allstate: two-thirds of respondents ID’ed themselves as excellent or very good drivers… and then went on to admit to doing things bad drivers do, like texting, excessive speeding, and even drinking and driving or falling asleep at the wheel. Another example would be the 68% of University of Nebraska faculty who rated themselves in the top 25% for teaching ability. Something just doesn’t add up… .

At the crags, I’ve seen folks lying down to belay. I once watched a girl clip herself with a daisy chain to a pack full of softball-sized rocks in an effort to add ballast against her much-heavier partner (when he fell, he pulled her and the pack up, sending the whole unfortunate situation sailing over the edge of a small drop-off). At a gym I saw a woman’s rope slide from her harness loop and swing away when she was 20 feet up the wall—she’d failed to finish her knot and her belayer had failed to do a simple check before telling her she could “climb on.” I bet every one of these folks would, given a survey on the topic, rate themselves “good” belayers.

The Problem with N00bs

Cornell University psychology professors David Dunning and Justin Kruger conducted a study to explore how people perceive their own ability level in a given activity. Throughout the study, they observed that incompetent people have some common traits; they:

1. tend to overestimate their own level of skill;
2. fail to recognize genuine skill in others;
3. fail to recognize the extremity of their inadequacy…

As Dunning put it, “If you’re incompetent, you can’t know you’re incompetent. … the skills you need to produce a right answer are exactly the skills you need to recognize what a right answer is.”

Consider this in light of the fact that, according to an Outdoor Industry Association survey, more than a quarter of the three-million-plus people climbing in 2012 were first timers. (One can only guess how many more than a quarter could safety be classified as n00bs.) And most of these have learned to belay via quick lessons from their friends (who are probably only slightly more experienced themselves) or from gym instructors, who vary widely in teaching ability and even in belaying ability. Many new belayers, by dint of their newness, lack the skills to properly evaluate their own skill level. They don’t even know what they don’t know.

Have You Ever Been Experienced?

But surely you’ve noticed plenty of long-time climbers who give blood-curdling belays, too? Their inability to follow proper protocol can’t be attributed to lack of experience. Such cases most likely stem from a combination of hubris and lack of feedback.

Dunning has suggested that one of the culprits behind people’s poor ability to self-assess is that most folks shy away from giving negative feedback. That’s understandable—critical interaction is uncomfortable, especially with a stranger. But if accurate feedback is critical for improvement, it might be worth braving the awkward social moment when you feel the urge to step up to a guy or gal who’s totally blowing it on the belay and say:

“Hey, friend, I’m super psyched to see you’re having a great time at the crag with your buddies, but I’d just like to point out the fact that the way you’re belaying is wildly unsafe and, even if you and your unsuspecting partner walk away from this whole affair unharmed, which is unlikely, I still might die of a heart attack from having to watch you. Allow me to offer some pointers…”

It might not always go over well. Heck, you might get yelled at. But at least Droppy McBelaypants won’t be able to say no one ever warned him or her. In my experience, though, most folks of all ability levels are pretty open to a friendly pointer, when delivered in a non-confrontational manner.

Of course, if an experienced climber with entrenched bad habits refuses to accept feedback, unless they’re at a gym and you’re an instructor, there’s probably not much you can do about. As one mountainproject.com commenter put it, “I’ve left a few crags before just because I’ve seen terrible belays and I wasn’t in the mood to see somebody deck.” In the end, each climber/belayer must be responsible for him or herself.

The Good News

Let’s face it: belaying, like a lot of climbing safety know-how, is fairly complicated, with an array of non-obvious cause-and-effect calculations that can only be learned through training, practice, and real-world experience. Even with modern assisted-braking devices, there is narrow margin for error, and a moment’s inattention or a seemingly small misstep can lead to injuries ranging in severity from rope burn and twisted ankles to compound fractures and graphic brainspills.
The good news is, we can all be better. No matter how long you’ve been climbing and belaying, and no matter how we’ll you think you belay, there’s room to improve. Step one is admitting you might have a problem… or at least that you’re not perfect. Once you do that, you can work towards higher levels of competence and even someday mastery.

Dunning and Kruger identified a fourth trait among those who grossly overestimate their own abilities, which is that they: “recognize and acknowledge their own previous lack of skill, if they are exposed to training for that skill.”

Simply put, most of us should probably take the time to bone up on our belay technique, learn, discuss, and observe. Check out online resources, sign up for more in-depth courses at the gym or with a guiding service, pick the brain of experienced and trusted sources, etc. Basically, ruthlessly hunt down and exterminate bad habits that could get your climber hurt. (Heck, if everyone just did the hard work of paying better attention to his system and his climber, all manner of lousy things could be avoided!)

Be open and work to improve, just like you work to improve your technique or endurance whenever you climb, and soon you can say with a much greater level of statistical accuracy that you are, indeed, a great belayer.

thestonemind.com/2014/07/15…

Dana Bartlett wrote:I always belay seconds with a plaquette device in guide mode. This lets me do other things while I'm belaying.

That's nice. But can you tell us the failure modes in this scenario and how people have been dropped. What you need to do to avoid them??

I use baby wipes after a wet fart. But I don't go announcing that on the Internet.

Uh, Greg: you just announced it.

My training made me worried about my abilities from the very beginning. We tried holding weights dropped with fall factors in the UIAA test range (before the UIAA had promulgated such numbers). Everyone, old or young, noob or experienced, failed to catch the leader at least once. We learned that you had to be totally ready and on top of the situation, otherwise the weight would plummet to the ground with a sickening thud.

But there is no such thing as resting on your laurels. A number of us caught the weight a few times and then dropped it later. Just because you have been successful doesn't mean you will continue to be.

I find it almost impossible to be as alert and ready as I was for those tests, knowing (after the first one anyway) exactly what was going to happen and when. So thank god when I've had to catch a high fall-factor fall (one factor 2 and one around 1.7 so far) in the real world, I was up to the task, and I've never yet dropped anyone, although on a few occasions some leaders have complained that they fell a lot further than they were expecting to, and that was probably my fault for allowing too much slack to accumulate.

Now I'm old. I'm not as strong, not as fast, and not as smart. Plus I'm doing easier climbs than I used to, and by and large none of us fall much, so outside of the gym I don't catch real leader falls much any more. It all adds up to a decline, any way you look at it, in both ability and practice, and honestly I worry that the role of experience in this context is to induce complacency.

One thing I've done is to embrace technology when I think it will make me safer. Since all the issues mentioned are compounded when climbing with half ropes, I've put aside my ATC's for outdoor climbing and use an assisted locking device in the hope that it will provide a little cushion against age and experience-induced incompetence. But indoors I use an ATC, because I think it helps to keep good habits sharper, and besides there's only one rope to manage indoors.

Having adopted an assisted locker, I want to know as much as possible about its ins and outs and any possible anomalous behaviors it may have. The thing is supposed to help me not to mess up; I sure as hell don't want to mess up because of it. That's an ongoing process, and unlike the apparent attitude of some of the posters to this thread, I'm more than grateful to hear about anything that could go wrong.

rgold wrote: Oh good, then let me explain my remark: As regards kinetic friction and velocity: From hal.archives-ouvertes.fr/fi…: Almost three centuries ago Charles Coulomb (1736-1806) discovered that kinetic friction does not depend on the sliding velocity [1]. Later, more careful experiments showed that this law is only approximately valid [2–7]. Friction does depend on the sliding velocity, but this dependence is far from universal: some measurements find an increase when velocity increases, while others find a decay [8–10] or even a more complex non-monotonous behavior [2]. From stle.org/resources/lubelear… Friction is not always independent of velocity. If we exclude very low speeds and very high speeds, the friction coefficient is constant and independent of sliding velocity. But at very high speeds, the friction coefficient generally has a slightly negative slope; that is, the friction coefficient decreases gradually as the speed increases. As regards kinetic friction and heat: From scitation.aip.org/content/a… In this paper we describe a relatively simple experiment that can be done to test the effect surface temperature has on kinetic friction, and that depending on the materials being used, the coefficient of kinetic friction does indeed increase as the surface temperature of one of the materials increases. From journalamme.org/papers_vol2… Up, down, up, down... But all this is a nerdy distraction from a much more important point. So allow me to repeat myself: Let’s suppose that I’m wrong (hardly an unusual circumstance) and there is no such thing as situation that would physically overwhelm a belayer even though the belayer does everything correctly. Then we can still say that the problem brought to our attention by John at the beginning of this thread is one that will, at the very least, greatly increase the demands on the belayer, way past anything that they are used to dealing with when using a Grigri. Forgetting all the arguments about unconditional belayer responsibility, isn’t the prospect of a sudden huge increase in the performance demands on the belayer enough, all by itself, to merit serious consideration of John’s warning? And isn't it right, in terms of the actual tragedies that have happened, to let it go at that?

It´s sort of interesting really, the dynamic coefficient of friction has been shown experimentally and theoretically to vary between 0 and 2. At the pressures (the important variable for us) we work with it is in the range of 0.3 to 0.16, 0.2 is a useful number to work with for most belay devices.

Apropos capstan theory;- our daily climbing experience shows us this can´t be the complete answer to how belay devices work, a 3mm cord would give the same braking effect as an 11mm rope if the theory is correct in our application. Similarly when we are rapping one strand or two would give the same resistance, clearly they don´t. I still can´t really understand how Attaway overlooked this but we had another guy at Cambridge University who took best part of a year to work it out as well.

The way to get drop the leader AND get rope burns on both hands with a correctly loaded GriGri is to hold the climber-side strand with your hand too low, the Grigri comes upwards and your hand prevents the cam opening. This is a known failure mode and clearly described here:- petzl.com/en/Sport/Belaying…

A variety of variables can effect belay applications of the "capstan theory." When using a flat, two-dimensional belay device, such as the Sticht plate, the rope will lock up more easily when using one carabiner if the slot on the device is about twice as long, plus the thickness of the carabiner, as the rope is thick. In fact, the rope will lock up too easily and this often prevents quick feeding of slack. Using two carabiners will prevent premature lock-up, yet makes catching a fall more difficult. That said, I and my usual partner, Mike Endicott, have never had difficulty catching each-other's leader falls when using two carabiners.

The tube (ATC)-style device is designed to prevent premature lock-up, but it also makes it harder to catch a fall, especially when using thin ropes. When using a single rope with a tube, I like to use the pointed end of the Petal Attache for the rope-bearing surface, because this configuration will allow the "capstan" to get pulled up inside the tube and help brake the rope more easily.

When using thin ropes, the most important consideration is to use a device that is made for thin ropes. The V cross-section, which first appeared on the Trango Jaws, helps with thinner ropes, although I find that the shallower, flaring Vs on the ATC Guides DON'T provide sufficient friction for lead belaying with thin ropes.

When using the Gri, my belayers will use thicker ropes, rather than thinner.

Jim Titt wrote: The way to get drop the leader AND get rope burns on both hands with a correctly loaded GriGri is to hold the climber-side strand with your hand too low, the Grigri comes upwards and your hand prevents the cam opening. This is a known failure mode and clearly described here:- petzl.com/en/Sport/Belaying…

I think this could put the final piece in the puzzle in some cases:

• Overgripping with the feeding hand can initially keep the cam from engaging and cause the rope to run.
• If the feeding hand is also too close to the device, it can press on the cam then the cam stays disengaged. [Edited to remove incorrect wording. I said "pulled onto the cam" but that can't be right---the rope is pulling away from the cam, not towards it.]
• Once that happens, you are belaying with a disengaged Grigri, which is not equivalent to an ATC.

The fact that two (known) conditions have to be met helps to explain the rarity of the phenomenon, especially in view of likelihood that many belayers do grab hard with the feeding hand, especially when lifted and nothing bad happens. If a fall happens just after the belayer is pulling in some slack, i.e. for a take, it is quite possible that the feeding hand could be right on top of the device at the moment of loading.

It is too bad that Petzl chose to illustrate the second condition with a picture that also shows the climber not using the brake hand, because that suggests there is a potential danger only if the brake hand is not on the rope.

Added in edit: Now that I've had to correct the second bulleted item, it has again become less clear how the rope keeps running through the system after the cam has been initially disengaged by the feeding hand pressure.

Mort wrote: You may be wrong in some cases, simple as that. Glad you and Slim won't be belaying me.

Sure I may be, but if you seriously held the brake end and the Grigri doesn't lock, we'd have seen a lot more of these accidents. You contend somehow holding the climber's end was the problem. Well, what if you (as the belayer) didn't but somebody else did? What if it wasn't a person but friction thru the rope system (from the rope running over a small roof or what not). Can you explain to me, how besides voodoo magic, the Grigri would behave differently in these situations?

There have simply been too many cases of people blaming the machine rather than the operator (how about the good ol' accelerator controversy?) And in the heat of moment, what you think you are doing may be very different from you are actually doing. There is a good reason we are taught not to use both of our feet driving an automatic (or heel/toe with one foot), even though it would reduce reaction time with an expert driver.

reboot wrote: Sure I may be, but if you seriously held the brake end and the Grigri doesn't lock, we'd have seen a lot more of these accidents. You contend somehow holding the climber's end was the problem. Well, what if you (as the belayer) didn't but somebody else did? What if it wasn't a person but friction thru the rope system (from the rope running over a small roof or what not). Can you explain to me, how besides voodoo magic, the Grigri would behave differently in these situations? There have simply been too many cases of people blaming the machine rather than the operator (how about the good ol' accelerator controversy?) And in the heat of moment, what you think you are doing may be very different from you are actually doing. There is a good reason we are taught not to use both of our feet driving an automatic (or heel/toe with one foot), even though it would reduce reaction time with an expert driver.

Clearly you are missing the point, it is voodoo magic, and this voodoo magic only effects tradladytes from the 60's or those just starting out. The Grigri is the Devil. All those who use it are from the dark side, and should expect burned hands and broken feet. As for engineering, pssst! Devils work I say.

BillS wrote:My take is simple - an oscillating rope traveling at high speed over a cam will have less contact with the cam than a slow moving one, certainly less than a fixed one - less kinetic friction.

The obvious flaw with this concept is that if the rope is oscillating it will vary between having more less normal force and more normal force on the cam so at some point in the wave it is more likely to lock. Since the rope is running through the belayers (burning) hand one would normally assume any oscillation is damped out by the burning flesh and the entry to the GriGri anyway. Don´t you think it is more likely the melted sub-cutaneous fat is lubricating the rope and preventing it locking?

Gri Gri's are like computers in that they're only as smart as the person using them...