Author Topic: Pulley jammer warning  (Read 2777 times)

Offline mikem

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Pulley jammer warning
« on: June 14, 2019, 10:57:38 am »

Offline Speleotron

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Re: Pulley jammer warning
« Reply #1 on: June 15, 2019, 09:18:30 am »
I always thought that anything which might involve falling onto a jammer is dodgy; why you wouldn't just use an italian hitch?
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Offline JoshW

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Re: Pulley jammer warning
« Reply #2 on: June 15, 2019, 09:45:18 am »
I always thought that anything which might involve falling onto a jammer is dodgy; why you wouldn't just use an italian hitch?

hauling on a loaded italian hitch is near on impossible.

but agreed on the life lining on a jammer being dodgy for me.

Offline Speleotron

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Re: Pulley jammer warning
« Reply #3 on: June 15, 2019, 09:58:08 am »
Yes I meant for belaying/lifelining not z-rigging or hauling etc. And you can make the italian hitch auto-locking as well https://andy-kirkpatrick.com/cragmanship/view/locking_munter
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Offline JoshW

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Re: Pulley jammer warning
« Reply #4 on: June 15, 2019, 10:15:55 am »
Yes I meant for belaying/lifelining not z-rigging or hauling etc. And you can make the italian hitch auto-locking as well https://andy-kirkpatrick.com/cragmanship/view/locking_munter

I guessed you meant for belaying/lifelining, but sometimes they can turn to needing to haul somebody

Offline Speleotron

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Re: Pulley jammer warning
« Reply #5 on: June 15, 2019, 10:21:18 am »
OK fair one
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Offline Bob Mehew

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Re: Pulley jammer warning
« Reply #6 on: June 15, 2019, 11:04:59 am »
The report of the work on which the notice was based can be downloaded from https://drive.google.com/file/d/1XLZyRdMzNjlnUar5LA0r_rVk-nqfLu2F/view?usp=sharing .  No doubt, BCA's E&T, QMC and Training committees will issue minutes in due course covering their deliberations.

Two asides: I would observe that the terms belaying / lifelining / progress capture / hauling etc seem to me to be splitting hairs and fundamentally are covering the same task with the same potential fault scenarios; and that a person falling even short distances on low stretch (SRT / semi static) rope can be seriously hurt.

Offline JoshW

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Re: Pulley jammer warning
« Reply #7 on: June 15, 2019, 11:17:42 am »
The report of the work on which the notice was based can be downloaded from https://drive.google.com/file/d/1XLZyRdMzNjlnUar5LA0r_rVk-nqfLu2F/view?usp=sharing .  No doubt, BCA's E&T, QMC and Training committees will issue minutes in due course covering their deliberations.

Two asides: I would observe that the terms belaying / lifelining / progress capture / hauling etc seem to me to be splitting hairs and fundamentally are covering the same task with the same potential fault scenarios; and that a person falling even short distances on low stretch (SRT / semi static) rope can be seriously hurt.

from my perspective the difference between hauling and the other three is that hauling has 0 potential (outside of gear failure) for a distance to fall. the other three introduce the chance of a shock loading.

Offline Badlad

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Re: Pulley jammer warning
« Reply #8 on: June 15, 2019, 12:22:06 pm »
This is a very old technique which hopefully is finally being committed to history.  There are many other methods and devices which can achieve the same thing in a much safer way - and are recommended by the manufacturer for that purpose.

Regardless of the deformed equipment, the force on the body or the potential damage to the rope the greatest danger with this method is not being able to release it under load.  Any lifelining, capture or whatever you wish to call it should be releasable under load with the ability to lower back to safety in a controlled manner.  The fatality on Giants pitch a few years ago springs to mind where those lifelining with a cammed device were unable to release the exhausted climber and he died stuck on the pitch under a waterfall.

I am very surprised this fact alone wasn't good reason enough to stamp out the practice.

Offline droid

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Re: Pulley jammer warning
« Reply #9 on: June 15, 2019, 12:35:13 pm »
Was that Garlands? 15 foot pitch, usually taken far too lightly. Gets VERY wet.
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Offline Speleotron

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Re: Pulley jammer warning
« Reply #10 on: June 15, 2019, 02:05:59 pm »
Was that Garlands? 15 foot pitch, usually taken far too lightly. Gets VERY wet.

Agreed. I couldnt remember all the reasons why I dont like this method but you've just reminded me. I find setups which are hard or impossible to realease to be a bit scarey when you think about what might happen.
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Offline mikem

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Re: Pulley jammer warning
« Reply #11 on: June 17, 2019, 08:52:50 am »
The only question I have is where was the load cell located? As force on climber will not be the same as force on pulley (the easiest place to locate the cell).

Offline Bob Mehew

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Re: Pulley jammer warning
« Reply #12 on: June 17, 2019, 09:42:16 am »
The only question I have is where was the load cell located? As force on climber will not be the same as force on pulley (the easiest place to locate the cell).
The location of the load cell does not influence the force seen by it, see page 6 in http://www.roperesearch.co.uk/pdfs/the%20rig%20v2.PDF . It only affects the timing of when the force is seen.  (http://www.roperesearch.co.uk/index.html provides more detailed information on the rig.)

The report of the work shows the location of the pulley or jammer for all bar two of the drops is at the top of the rig.  The load cell is immediately above that point.  (The set up was device / crab / shackle / load cell whose black end protrudes through the horizontal beam.)  The only cases where it was not, were drops 34 & 35 BPC 40 where the set up is shown in diagram 8 in the report.

Offline Antwan

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Re: Pulley jammer warning
« Reply #13 on: June 18, 2019, 06:13:39 am »
If you do have to haul with that specific equipment the jammer should be on the other side  :spank:

If it rises when you haul hang some krabs on it.

Offline mikem

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Re: Pulley jammer warning
« Reply #14 on: June 18, 2019, 06:50:16 am »
But even if you assume that there is zero extension in the low stretch rope, the 6.7kN recorded by the load cell has also been dissipated into bending the pulley and stripping the rope, so won't be equal to that experienced by the climber...

Climbing walls are now using semi-static ropes for top roping, but they will always have at least the full length of the climb between the belayer & climber (so still a reasonable amount of rope to minimise the fall factor), whilst a caver slipping at the top of the pitch will have hardly any rope between them - should we still be advocating dynamic rope, or is the effective distance so short that it will make hardly any difference?

If you do have to haul with that specific equipment the jammer should be on the other side  :spank:
In which case the full load will go onto the jammer, so the effective force on the climber will be higher (you're probably better off damaging the pulley!)

Presumably the climber or rope in Giants got caught somewhere, so couldn't be pulled up that little bit to release the jammer, which would be the same whichever side of the pulley it was.
« Last Edit: June 18, 2019, 07:21:24 am by mikem »

Offline Bob Mehew

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Re: Pulley jammer warning
« Reply #15 on: June 18, 2019, 09:06:22 am »
But even if you assume that there is zero extension in the low stretch rope, the 6.7kN recorded by the load cell has also been dissipated into bending the pulley and stripping the rope, so won't be equal to that experienced by the climber...
What is your evidence for this statement?  It is not force that is dissipated, it is energy. 
Climbing walls are now using semi-static ropes for top roping, but they will always have at least the full length of the climb between the belayer & climber (so still a reasonable amount of rope to minimise the fall factor), whilst a caver slipping at the top of the pitch will have hardly any rope between them - should we still be advocating dynamic rope, or is the effective distance so short that it will make hardly any difference?
The point you miss is that the belayer will have a bigger effect in reducing the peak forces seen by the system since their body is not as resilient as the steel.  (The report touches on this point.)  The feature of the system we are discussing (pulley and toothed jammer) is that there is no equivalent human body, just steel.  If you look at the detail you will see that the peak force in the simpler set up of just a toothed jammer is higher (10 BPC 40) than for pulley and toothed jammer (12 or 20 BPC 40). 

Unfortunately we don't have three load cells to do the experiment to show that the force is the same along the whole length of a multi component system. 

Offline andrewmc

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Re: Pulley jammer warning
« Reply #16 on: June 18, 2019, 09:34:08 am »
The rule is simple.

Don't belay with your teeth, or anyone or anything else's.

Use one of the thousands of safe belaying systems used by climbers for generations, ranging from body belaying (properly done), chucking the rope around a (suitably smooth) rock, Italian hitches, Fig 8s, belay plates, guide mode belay plates, Stops, grigris, Rigs, ID's, all the way up to hanging an autobelay at the top of the pitch if you feel the need. Just don't use anything with teeth...

PS some of the above systems are a lot better than others!

Offline Roger W

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Re: Pulley jammer warning
« Reply #17 on: June 18, 2019, 10:04:12 am »
The rule is simple.

Don't belay with your teeth, or anyone or anything else's.



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Offline mikem

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Re: Pulley jammer warning
« Reply #18 on: June 18, 2019, 05:31:09 pm »
I'm not suggesting using a pulley jammer, but trying to get my head around whether the force on the climber will be the same as the force on the pulley (which is what was recorded).

Energy = Force x distance, so if energy is lost in the deformation of the pulley, but distance remains the same, the force must surely also reduce...

& I'm not missing the effect of the belayer, just hadn't mentioned it as my question was whether belaying at the top required a dynamic rope (as many cavers are switching to semi-static without realising the difference from top roping, where it is now common practice).

Also the document referred to by Bob suggests a Stop is not suitable for belaying when only threaded around one bobbin.

Offline andrewmc

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Re: Pulley jammer warning
« Reply #19 on: June 18, 2019, 05:37:44 pm »
Energy = Force x distance, so if energy is lost in the deformation of the pulley, but distance remains the same, the force must surely also reduce...

As an (ex) physicist, it's complicated, because people fail to properly include the effect of time dependence in that (simplified) equation.

Offline Bob Mehew

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Re: Pulley jammer warning
« Reply #20 on: June 18, 2019, 09:41:55 pm »
Like andrewmc says, it is complicated and frankly I can't explain it even in simple terms.  Whilst it is not quite a replica of the drop test, has a number of similarities.  The slinky shows you can get variable forces along the length of the slinky since from Newtons 2nd law (F = m * a), some parts of the slinky are accelerating and other parts are not.  I suggest our drop test is similar to a speeded up version of the slinky.  My expectation is the peak force seen by any part of the set up is the same, it just occurs at slightly different times.  (Though the time frame will be different in rope & steel since the speed of sound is different.)

mikem - Would you like to come to the Bradford to witness an experiment where we locate a second load cell within the system?

The use of low stretch (semi static / SRT) ropes in place of dynamic ropes risks giving the climber a bigger peak force.  But as I indicated, if the climber is being belayed by another person using the classic belay stance, then that will reduce the peak force seen by the climber.  That will be less true if one uses one of the other belay systems.

The report states "Discussions with representatives of Petzl have clarified that the manufacturer does not consider the Petzl STOP to be a belay device of any form.  Furthermore, Petzl have never advocated the use of the STOP part threaded. So use of the STOP in this manner would be out with manufacturer’s guidance."  BCA have urged "cavers to only use devices ... in line with current manufacturer’s instructions."

Offline mikem

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Re: Pulley jammer warning
« Reply #21 on: June 19, 2019, 08:15:04 am »
I think these tests are applicable in theory to the pulley jammer scenario (the anchor impact forces are very similar), the climber creates the force on the top anchor, but experiences a much smaller force themself. The force on the jammer is what deforms the pulley (obviously the jammer is not as forgiving as a belayer on a long length of rope, so climber will experience a greater percentage of the total than shown here, & until the pulley deforms will experience almost all the force): https://www.petzl.com/US/en/Sport/Forces-at-work-in-a-real-fall

On Mendip laddering is still the norm, so belaying from fixed anchors at the top is commonplace, therefore it would be useful to know if a short length of dynamic will make a significant difference to using semi-static when someone comes off the top of the pitch with some slack in the belay...

Offline MarkS

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Re: Pulley jammer warning
« Reply #22 on: June 19, 2019, 08:54:27 am »
On Mendip laddering is still the norm, so belaying from fixed anchors at the top is commonplace, therefore it would be useful to know if a short length of dynamic will make a significant difference to using semi-static when someone comes off the top of the pitch with some slack in the belay...

I suspect whether a difference is significant depends on all manner of things, such as your definition of significant, the type of knot(s) in the system, whether they have been pre-tightened, how much slack is in the belay, whether the belay is directly above the climber, how high the belay is above the climber, what the belay device is, what sort of harness (or belt?) the climber is wearing...

Ultimately, all belaying should be done with kit and methods falling within manufacturers' guidelines, e.g. a grigri + dynamic rope. There are so many variables that I suspect advice on what else may be OK is going to be subject to so many caveats as to make it worthless.

Offline andrewmc

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Re: Pulley jammer warning
« Reply #23 on: June 19, 2019, 09:16:10 am »
On Mendip laddering is still the norm, so belaying from fixed anchors at the top is commonplace, therefore it would be useful to know if a short length of dynamic will make a significant difference to using semi-static when someone comes off the top of the pitch with some slack in the belay...

a) don't do this (the bit in bold) - obviously it can still happen, but if it's a risk, put in a traverse line and use your cowstails; if you can't be bothered, then don't fall off!
b) an appropriate belay device will limit the load e.g. from memory of something Jim Titt said years ago on UKClimbing I think a standard climbing belay plate will slip at 2 kN or so and an Italian hitch at about 3 kN, a Rescuecender (not supposed to be used for belaying) is designed to slip at 4 kN (I think), and something like an I'D or Rig (probably similar for a GriGri) will slip at 6-8 kN I think (depending on the rope - skinny rope, more slippage which can be up to a metre or more...). And Lyon Equipment found a Stop cut/damaged the rope on large dynamic falls (due to the edges on the plates I think).

I'm fairly confident that the small amount of dynamic will make bugger all difference. See the difference in forces between static and dynamic cowstails - about 1-2 kN I think. You are better off with cowstails with knots in static rope than sewn cowstails in dynamic rope, for example.

Swildons has a thread and a P-bolt for a safe approach traverse line. GB ladder dig has a thoroughly bizarre and not entirely safe method of access, but anchors well back from the pitch once you are up there. Can't remember about Sludge Pit. Eastwater 35ft pitch has dodgy old anchors but plenty of backups and you can run a traverse/anchor backup line from the chamber before. If you can't get on/off a ladder pitch safely, then I would suggest it is not well bolted/conceived...

'Bottom-roping' is obviously safe with a semi-static rope (possibly safer as there is less stretch making it harder to deck out on falls near the ground) but so is 'top' top-roping, done 'correctly' i.e. the climber does not climb above the anchor, or if they do they don't fall off, or if they do they fall off slowly (e.g. sliding off a ledge and THEN falling)!.

Offline Ed W

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Re: Pulley jammer warning
« Reply #24 on: June 19, 2019, 09:33:25 am »
I am probably being a bit thick, but is the high peak force more a factor of the high Fall Factors (1.4 to 1.7) rather than being due to the jammer?  It should be no surprise that a semi-static rope will generate high peak forces in such conditions.  Isn't it also a little unrealistic for caving lifeline situations, where the worst result of a FF1 is the impact with the floor of the pitch.

I'm not advocating the use of jammers in a lifeline system, more a defence of semi-static rope for lifelining as long as slack is minimised to keep FF as low as possible.
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