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Do nuts >4kn fail in real world use?

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 timparkin 25 Jul 2020

A recent post about the new DMM halfnuts had me thinking about whether 4kn or 5kn nuts fail in real world use? The BMC have said in their microwire article that a reasonable fall (0.5FF) can create 6-7kn. 

If this was the case and people must be using the Wild Country Superlight Rocks (first two at 4kn and remaining at 6kn)  then we should be seeing lots of nuts breaking (presumably the wire). 

I've had a good search around and can only find mention of micro walnuts and microwires breaking - nothing above 2kn that I can find. 

I'm not looking to use much smaller protection but has anybody heard of any nuts breaking that are rated at 4kn (or 5kn?). i.e. I'm wondering whether a three sigma 5kn rating is pretty safe for most purposes.

[The only real world fall tests I've seen - i.e. with floppy bodies -  are on the Petzl website and How not to Highline which  both show normal falls rarely hitting 4kn and 0.7 FF falls just hitting 5kn]

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 Sean_J 25 Jul 2020
In reply to timparkin:

Short answer, yes. Imagine a scenario where you're climbing on a single rope, with a nest of gear. You fall, and the top piece nearly holds but then blows. You now have a rope that's already fairly stretched, and you're still falling at a fair speed. You then come onto the lower pieces, which are thankfully very good pieces and they hold despite the rope not having fully recovered its elastic properties. Forces on the gear are relatively high, probably a lot more than 4-5kN. And yes, it did hurt a fair bit. Result was having to retire a few bits of kit, including a cam with a flat-spot and a slightly bent krab :o

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 duchessofmalfi 25 Jul 2020
In reply to timparkin:

Yes - they fail by the wire snapping (never happened to me but seen on videos) and they can fail because they are very small and even with good placements the rock can fail or that flake can flex and they can pull through (I've seen this happen more than once and I've seen brassies cut through rock leaving a tiny nut shaped groove). Despite this I'd still place them and I've seen them hold falls but you shouldn't kid yourself that they are bomber. 

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 Rick Graham 25 Jul 2020
In reply to timparkin:

Yes, but not very often.

Seen and heard stories of broken wires, size 7 so not micro, karabiners, cams, rope slings, ropes. Usually some additional factors involved, such as rock abrasion, but generally gear is pretty bombproof but never infallable. Seen lots of good looking gear pull through and some " how did that manage to hold a fall" incidents. Expect surprises.

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 timparkin 25 Jul 2020
In reply to Sean_J:

> Short answer, yes. Imagine a scenario where you're climbing on a single rope, with a nest of gear. You fall, and the top piece nearly holds but then blows. You now have a rope that's already fairly stretched, and you're still falling at a fair speed. You then come onto the lower pieces, which are thankfully very good pieces and they hold despite the rope not having fully recovered its elastic properties. Forces on the gear are relatively high, probably a lot more than 4-5kN. And yes, it did hurt a fair bit. Result was having to retire a few bits of kit, including a cam with a flat-spot and a slightly bent krab :o

But no broken wire on a relatively clean but of gear? I know there are outliers such as ropes getting caught behind flakes and causing FF>2 etc but I'm just looking for a real world case of a wire breaking.

p.s. It would be interesting to test that suggestion of shockloading gear in a cluster! Not sure a 'common sense' thought experiment works in these types of dynamic situations.

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 timparkin 25 Jul 2020
In reply to duchessofmalfi:

Yep I've seen videos of a wire snapping but only on things like a microwire or a black diamond 1 or 2 stopper. The main reason things fail seems to be rock which can happen regardless of rating.

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 danm 25 Jul 2020
In reply to timparkin:

Most falls will generate a force in the range of 3-5kN, which explains why a 4kN rated microwire may or may not break in a typical fall. A particularly hard fall may generate up to 6-7kN, which makes things a bit more certain, but falls like that are pretty rare. If you go back a few years, the gate open requirement for karabiners was pushed upwards to 7kN as it was discovered that newer lightweight snapgates would very occasionally fail at less than this, which gives a good empirical measure of the maximum magnitude of forces on the top anchor.

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 timparkin 25 Jul 2020
In reply to Rick Graham:

> Yes, but not very often.

> Seen and heard stories of broken wires, size 7 so not micro

12kn breaking is pretty extreme - I would hope this was something wrong with the gear as that would be nearly 8kn  on the climber (I don't think they'd walk away from that!).

> karabiners, cams, rope slings, ropes. Usually some additional factors involved, such as rock abrasion, but generally gear is pretty bombproof but never infallable.

Yep - seen a few one in a million examples of gate opening on carabiners etc. and gear over edges etc. I'm interested in the smallest gear breaking in normal falls.

> Seen lots of good looking gear pull through and some " how did that manage to hold a fall" incidents. Expect surprises.

Try asking a geologist 'what rock is that' and you'll find out how little you can tell from just  looking at something. I looked up how granite decomposes recently (google "granite  gru") taught me a few things about how solid looking rock can be like a biscuit.

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 timparkin 25 Jul 2020
In reply to danm:

That gate open info is interesting... thanks Dan!

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 Rick Graham 25 Jul 2020
In reply to timparkin:

> 12kn breaking is pretty extreme - I would hope this was something wrong with the gear as that would be nearly 8kn  on the climber (I don't think they'd walk away from that!).

> > karabiners, cams, rope slings, ropes. Usually some additional factors involved, such as rock abrasion, but generally gear is pretty bombproof but never infallable.

> Yep - seen a few one in a million examples of gate opening on carabiners etc. and gear over edges etc. I'm interested in the smallest gear breaking in normal falls.

> Try asking a geologist 'what rock is that' and you'll find out how little you can tell from just  looking at something. I looked up how granite decomposes recently (google "granite  gru") taught me a few things about how solid looking rock can be like a biscuit.

My son , who can be a bit dismissive of my passed down wisdom on climbing matters, was  once asked in a climbing interview what he had learn from his dad.

The answer was " get plenty of gear in".

At least he admitted to accepting some advice 

Safety in numbers.

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 Michael Gordon 25 Jul 2020
In reply to Sean_J:

> Imagine a scenario where you're climbing on a single rope, with a nest of gear. You fall, and the top piece nearly holds but then blows. You now have a rope that's already fairly stretched, and you're still falling at a fair speed. You then come onto the lower pieces, which are thankfully very good pieces and they hold despite the rope not having fully recovered its elastic properties. Forces on the gear are relatively high, probably a lot more than 4-5kN. 

I don't think I've previously ever heard someone suggest that a higher bit of gear failing would actually result in an increase in the force put on the bits below. The scenario doesn't make sense to me. The rope stretching is it absorbing the force of the fall, and the more it needs to absorb the more it will stretch under that weight. As soon as your weight is off the rope (due to the gear ripping) it will de-stretch. Your speed of descent will also have reduced inversely to the amount of stretch the rope has undergone. 

If the top bit of gear is good enough to take a lot of the stretch out of the rope, it will also have been good enough to reduce the force by way of reducing acceleration. If on the other hand the top bit is shit, then it won't slow you down but neither will it take much stretch out of the rope. I don't see how you could have one but not the other.

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 Rick Graham 25 Jul 2020
In reply to Michael Gordon:

Its often a complicated equation but I am always wary of clipping high a poor piece rather than relying on.a good piece lower down below my waist.

The poor piece rips and you have taken up some of the ropes shock absorbancy, but may have more rope out than if you did not use the upper piece, hence more chance of decking. Two ropes help giving more options.

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 Franco Cookson 25 Jul 2020
In reply to timparkin:

Unless you're really heavy or planning on taking abnormally large lobs, I wouldn't worry about gear breaking. I've taken hundreds of falls and have often had placements break/gear pull, but never the stuff break. A lot of these falls have been on the smallest sliders, RPs, skyhooks, micro tricams etc. In the unlikely event that the placement was more solid than the runner, it would likely take so much out of the fall that you'd effectively be 'restarting' your descent (decelerating loads) and as long as the ground was close, or you had another runner to stop you, you'd probably be fine. 

Of far more importance is thinking of ways to reduce peak impact - use revolver crabs on low KN runners, place loads of gear, use stretchy/ thin ropes, have a light belayer, get them to run in with the fall, have a couple of bomber cams low down so that all of their movement is in slack paid out (rather than their weight also coming onto the top piece). 

Disregard Sean J's post. It's absolute nonsense.

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 jimtitt 25 Jul 2020
In reply to timparkin:

> p.s. It would be interesting to test that suggestion of shockloading gear in a cluster! Not sure a 'common sense' thought experiment works in these types of dynamic situations.

It's been tested decades ago, Marc Beverly et al in a paper something like "Sequential Failure of Rock Climbing Protection".

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 Michael Gordon 25 Jul 2020
In reply to Rick Graham:

I'm wary of that too, but just because of increased slack in the system should it fail and the resultant bigger fall than because of 'pre-stretched' rope concerns. Really two ropes is nearly always best for trad.

Post edited at 13:46
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 Rick Graham 25 Jul 2020
In reply to Franco Cookson:

Two comments Franco .

1. Most of  your post is quite correct and plausible, but you are blessed with a lightweight frame and legendary bounceability.

2. Harsh on SeanJ, his post was not bollocks. However ,as these scenarios are not replicable, we will never know the outcome of choosing different piece clipping options.

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 mrjonathanr 25 Jul 2020
In reply to Michael Gordon:

Edit: it seems complicated. Here’s the paper referenced above

https://mra.org/wp-content/uploads/2016/05/Beverly_Sequential_Falls2.pdf

Post edited at 14:22
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 PaulJepson 25 Jul 2020
In reply to timparkin:

https://m.youtube.com/watch?v=m8z6adEqaOs

That's a good video about where the forces are. 

I think Dave M snapped a brass offset on a whip off Rhapsody, if I remember correctly? 

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 Sean_J 25 Jul 2020
In reply to Franco Cookson:

No need to be an arse about it Franco.

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 Sean_J 25 Jul 2020
In reply to Michael Gordon:

Yes, I know the theory. Explain why I ended up with 2 f*cked bits of kit though....

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 timparkin 25 Jul 2020
In reply to Franco Cookson:

> Unless you're really heavy or planning on taking abnormally large lobs, I wouldn't worry about gear breaking. I've taken hundreds of falls and have often had placements break/gear pull, but never the stuff break. A lot of these falls have been on the smallest sliders, RPs, skyhooks, micro tricams etc. In the unlikely event that the placement was more solid than the runner, it would likely take so much out of the fall that you'd effectively be 'restarting' your descent (decelerating loads) and as long as the ground was close, or you had another runner to stop you, you'd probably be fine. 

Many thanks for that Franco! 

> Of far more importance is thinking of ways to reduce peak impact - use revolver crabs on low KN runners, place loads of gear, use stretchy/ thin ropes, have a light belayer, get them to run in with the fall, have a couple of bomber cams low down so that all of their movement is in slack paid out (rather than their weight also coming onto the top piece). 

Should there be a "lightweight belayers" brokering website where they compete to be rented out for sketchy headpoints? ;-)

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 timparkin 25 Jul 2020
In reply to jimtitt:

> It's been tested decades ago, Marc Beverly et al in a paper something like "Sequential Failure of Rock Climbing Protection".

Cool paper! I ♥ science... 

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 Sean_J 25 Jul 2020
In reply to timparkin:

Apologies for the lack of clarity - my point was that a fall that damages a cam and a krab in such as way as I experienced is quite possibly above the breaking strain of a small nut. I have heard of and seen photos of small wires that have broken (RPs etc) in what would be considered a "normal" fall with no weird conditions, but I have no helpful insights on how common this actually is.

Not sure why I had so many dislikes for my initial post - maybe the armchair physicists disagreed with my real-world experience. Maybe some posts explaining why my reasoning may not be sound would be more helpful than a snide thumbs down.

Post edited at 15:28
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In reply to Sean_J:

I seem to recall, a year or two ago, someone posted a video, in which their top runner, a full strengh (12kn) wire broke resulting in a partial groundfall (caught on the next one down). It was reckoned to be to do with how the wire was loaded on the rock.

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In reply to timparkin:

How many times do people fall on these though. I tend to place as a last resort, in multiples and definitely try and avoid falling on small wires. Not sure if I've ever fallen on less than Rock/Wallnut 1 size.

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 WillRhodes 25 Jul 2020
In reply to timparkin:

I snapped a 4kn wc super light one yesterday; it was quite low down (ie. my only runner) and a hard catch. It snapped at the swaging rather than at the wire, which surprised me. That said, it did take almost all the force out of the fall, but not quite... Suspect it would have been fine with a soft catch and higher up a pitch (fall factor roughly models the forces generated, right?)

I shouldn’t have been up there really, had a bit of migraine so wasn’t climbing well nor concentrating on gear etc. Fortunately landed on my feet and was largely unscathed. A good reminder to put plenty of gear in when close to the ground.

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 timparkin 25 Jul 2020
In reply to DubyaJamesDubya:

> How many times do people fall on these though. I tend to place as a last resort, in multiples and definitely try and avoid falling on small wires. Not sure if I've ever fallen on less than Rock/Wallnut 1 size.

Probably a lot less than other nuts but with the new DMM Halfnuts and the Wild Country Superlight rocks both having a 4kn rating for the smallest two peices and with the Superlight Rocks being comparatively popular already, I imagine they've been fallen on quite a bit?

Remember those 4kn bottom two peices from the Halfnuts and Superlight Rocks are weaker than 8 out of the 11 available DMM brass microwires and there is only one DMM microwire actually weaker than them (the 0 brass offset at 2kn). 



 

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 timparkin 25 Jul 2020
In reply to WillRhodes:

> I snapped a 4kn wc super light one yesterday; it was quite low down (ie. my only runner) and a hard catch. It snapped at the swaging rather than at the wire, which surprised me. That said, it did take almost all the force out of the fall, but not quite... Suspect it would have been fine with a soft catch and higher up a pitch (fall factor roughly models the forces generated, right?)

Thanks for the comment Will! It shows that these need to be wary of (but useful as long as you are)

Have you got a photo we could see? 

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 Franco Cookson 25 Jul 2020
In reply to Sean_J:

My dislike of the post was that it seemed to be suggesting that placing a runner above a cluster was a bad idea, which it definitely isn't! 

Reading it back, maybe you weren't suggesting that, so sorry for the branding as nonsense. It does however seemed like such a specific scenario that considering the nature of the OP, it's not really worth much consideration.

I wouldn't normally post on threads of this nature, but I've seen a few pretty bad falls over the last few weeks and I really think we could do with some more thought being put into how we plan for lobs. Low early runners, half ropes and belayers in the right place can make the difference between soft catches and big injuries. It's really that simple. 

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In reply to Rick Graham:

He’s just jealous that he’s not done as many E5s as you, Rick! 

😂

He needs to pull his finger out and get himself up you’re ‘F&F’ routes at Dove. Having said that, so do I! They look fantastic 

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 Rick Graham 25 Jul 2020
In reply to Duncan Campbell:

> He’s just jealous that he’s not done as many E5s as you, Rick! 

Only E4 when I did them, not on sight either.

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In reply to timparkin:

> Probably a lot less than other nuts but with the new DMM Halfnuts and the Wild Country Superlight rocks both having a 4kn rating for the smallest two peices and with the Superlight Rocks being comparatively popular already, I imagine they've been fallen on quite a bit?

> Remember those 4kn bottom two peices from the Halfnuts and Superlight Rocks are weaker than 8 out of the 11 available DMM brass microwires and there is only one DMM microwire actually weaker than them (the 0 brass offset at 2kn). 


I was an early adopter of Superlight Rocks but when I had a think about the strength of them I decided I wasn't comfortable the sacrifice v benefits so stopped using them.

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 Rick Graham 25 Jul 2020
In reply to DubyaJamesDubya:

> I was an early adopter of Superlight Rocks but when I had a think about the strength of them I decided I wasn't comfortable the sacrifice v benefits so stopped using them.

They may not be as strong as other options but often fit well where nothing else does at all.

I would not try any hard route without them nowadays.

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 GPN 25 Jul 2020
In reply to timparkin:

https://www.ukhillwalking.com/forums/rock_talk/40_ft_ground_fall_video-658643?v=1#x8502149

Here’s a video of a 6kN wire breaking in a fall. There’s a fair amount of ill-informed speculation in the thread, but it goes to show that even large wires can break. Obviously the single rope/Grigri set-up is fairly unusual in the UK.

Post edited at 20:39
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 David Coley 25 Jul 2020
In reply to Sean_J:

> Short answer, yes. Imagine a scenario where you're climbing on a single rope, with a nest of gear. You fall, and the top piece nearly holds but then blows. You now have a rope that's already fairly stretched, and you're still falling at a fair speed. You then come onto the lower pieces, which are thankfully very good pieces and they hold despite the rope not having fully recovered its elastic properties. Forces on the gear are relatively high, probably a lot more than 4-5kN. And yes, it did hurt a fair bit. Result was having to retire a few bits of kit, including a cam with a flat-spot and a slightly bent krab :o

Looking at the paper Jim point to, this would seem not to be the case: "Except for knot tightening, we did not observe rope hardening in the two impact drop. The rapid unloading after an anchor fails appears to reset the rope to its initial state. Testing on two impact drops showed that failing a piece of climbing protection absorbs energy and reduces the total fall factor."

So ropes do seem to recover very fast.

I think the last bit of the quote means that although because the climber is moving, the effective FF on the second piece is higher than on the first (assuming the gear is evenly spaced), the effective FF on the second piece is lower than if the first piece had not been there. So if your lower piece would not snap if the top piece had not been placed, it will not if the top piece is placed

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 timparkin 25 Jul 2020
In reply to GPN:

> Here’s a video of a 6kN wire breaking in a fall. There’s a fair amount of ill-informed speculation in the thread, but it goes to show that even large wires can break. Obviously the single rope/Grigri set-up is fairly unusual in the UK.

Yes I'd seen that one before.  It certainly looks odd when you look at the damage on the nut etc. It's a shame Black Diamond hadn't got more involved in the answer. Did he confirm that it was a BD Stopper no 4 (hard to tell from the picture)?

It does look like it's possible that the swage stuck and a single strand was loaded. The rope wasn't running straight, gri gri  used, etc. However, like you say, it shows that multiple things can add up to problems quite quickly!

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 mrjonathanr 25 Jul 2020
In reply to DubyaJamesDubya:

The longest fall I have taken was over 40’ onto an RP2 which held. I retired it, but they are quite strong. 40’ from about 55’ up so FF around 0.75

> How many times do people fall on these though. I tend to place as a last resort, in multiples and definitely try and avoid falling on small wires. Not sure if I've ever fallen on less than Rock/Wallnut 1 size.

Post edited at 22:47
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In reply to Rick Graham:

> They may not be as strong as other options but often fit well where nothing else does at all.

> I would not try any hard route without them nowadays.


Actually I think there are other options (DMM offsets and others) it's just they are lighter but achieve it by too great a sacrifice of strength.

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 jezb1 25 Jul 2020
In reply to DubyaJamesDubya:

> Actually I think there are other options (DMM offsets and others) it's just they are lighter but achieve it by too great a sacrifice of strength.

It might be too great a sacrifice for you, but plenty of people are happy with them.

They are a different shape to standard DMM offsets, as well as being lighter, so may make the most of a potential placement when other bits of kit don’t.

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In reply to mrjonathanr:

> The longest fall I have taken was over 40’ onto an RP2 which held. I retired it, but they are quite strong. 40’ from about 55’ up so FF around 0.75

It's well established that people fall on small wires. I was just trying to give another reason why people aren't breaking them as often as the OP expected

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In reply to jezb1:

> It might be too great a sacrifice for you, but plenty of people are happy with them.

> They are a different shape to standard DMM offsets, as well as being lighter, so may make the most of a potential placement when other bits of kit don’t.


I agree. It's personal choice. I've not missed them.

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 rachelpearce01 26 Jul 2020
In reply to Franco Cookson:

I'm interested inn the low early runners idea? cams, so you can move slightly back from the base of the crag and step forward to absorb a fall? I'm light so I always go up anyway but id like to know what you mean exactly.

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 cpowell 26 Jul 2020
In reply to rachelpearce01:

Normally the belayer is a couple of feet back from the base of wall, either due to topology or so they can get a better view of the climber, so even if the belayer doesn't step back it can result in less slack.

The belayer needs to be briefed to expect an indwards rather than upwards pull however!

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 Franco Cookson 26 Jul 2020
In reply to rachelpearce01:

Definitely need to be a camming device. Maybe not the best idea on a long pitch, as it will increase drag (unless you can lob some revolvers on) . Being light as a belayer is great, but even then, if you're pulled up you will be arresting the fall more quickly than a heavier person being pulled inwards. 

The basic principle is that you have more rope out and the rope from your belay plate goes less vertically up to a runner. Both of these things should reduce peak impact force. The video linked above is a perfect example of what happens if your first runners are up high on a short route and there is no give in the belayer's position (single rope, gri gri, heavyish chap belaying) - not that I'm criticising the guys in the video, it was just an unfortunate set of circumstances. 

It is however also worth mentioning that being pulled laterally as a belayer is an easy way to get injured. It's quite surprising how easily you get pulled inwards (involuntarily), even if you're heavier than the climber.

Post edited at 10:43
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 cpowell 26 Jul 2020
In reply to Sean_J:

> Not sure why I had so many dislikes for my initial post - maybe the armchair physicists disagreed with my real-world experience. Maybe some posts explaining why my reasoning may not be sound would be more helpful than a snide thumbs down.

Hi Sean_J

I think the issue is that if the rope is being stretched the top piece has taken a reasonable amount of force on it - a rubber band needs both ends held to stretch it.  If this is the case the falling climber will be decelerated by that force slowing them down.

If the piece then fails or rips the climber will start accelerating downwards again until the next piece catches them, but they will be moving at a slower speed than if there was no top piece.

The very fact there is a second piece means the original fall is not a factor 2, so the rope will still have some stretch in it.

So we have the situation where the falling climber has been partially slowed by the failing top piece and the rope still able to stretch, both of these means the peak force on the second piece will be lower than if there was no top piece.

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 David Coley 27 Jul 2020

Franco or Jim:

re revolver-like carabiners on the top piece. I know these work well to reduce drag, but do they work to reduce peak force in a fall? I thought (possibly in error) that they were rubbish as pulleys once loaded as they don't have proper bearings and no better than a normal carabiner when hauling for example.

Thanks

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In reply to DubyaJamesDubya:

> It's well established that people fall on small wires. I was just trying to give another reason why people aren't breaking them as often as the OP expected

Top runner here was an HB2, which snapped.


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 Franco Cookson 27 Jul 2020
In reply to David Coley:

Jim will be a lot more use than me on anything scientific when it comes to revolvers. Anecdotally, they definitely seem to work - potentially because during a fall they spin prior to the rope being fully weighted, so 'flatten the curve' of the fall being arrested (to use a trendy phrase).? 

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In reply to danm:

>  If you go back a few years, the gate open requirement for karabiners was pushed upwards to 7kN as it was discovered that newer lightweight snapgates would very occasionally fail at less than this,

A few decades more like! I remember it was mid 90s when 7 KNs became the norm for krabs gate open, then the BD Hotwire came along and showed wiregates could easily have 9 kn gate open strength whilst weighing less or no more because of the mass taken out of the gate. Although i think already hot forging had led to 9 kn gate open strengths - my absolute favourite krabs when I started were HB Hi-lites (if I remember the name correctly), I still have a couple. And then DMM Mambas and Cobras came along with very good gate open strengths too, the result of clever molding also.

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 timparkin 27 Jul 2020
In reply to Dave Garnett:

> Top runner here was an HB2, which snapped.

Thanks for replying Dave!

Would that be an original HB2 or the new DMM and if the original, do you think they were the same strength  (if DMM then the fall must have been around 6kn given the  5kn plus three sigma rating). 

[ HB2 is the third smallest, very slightly smaller than a number one walnuts (2mm vs 2.5mm  wire) ]

Was the fall a big one with much rope out?

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In reply to timparkin:

It would have been an original HB.  There wasn't a lot of rope out (he barely missed the floor as it was), so a fairly high fall factor and no scope for any attempt at a soft catch (not that they had been invented in 1987).  In any case, I think it likely that the wire ran over the edge of the crack.  If that happens, I think any kN rating is pretty irrelevant. 

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