Category Archives: Ropework

Near Miss – April 2022

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Potentially dangerous interaction between Petzl RIG & Micro Traxion

It should be noted that this issue may also be possible with other similar equipment from a range of different brands.

It is important to state from the outset that the equipment used in the described incident below was not at fault and was in a good state of repair. Although it was ‘human error’, I don’t believe this type of event has been recorded before and the purpose of this report is to raise awareness of an unlikely, but possible, potentially dangerous interaction between 2 common devices used in the LCMLA Vertical Award scheme.

On the afternoon of the second day of a Vertical Leader training course in April 2022, we were covering the use of Traxion and pulley/jammer systems for hoisting. I had already demonstrated to the two candidates how to use and release the Traxion devices. They both competently demonstrated their ability to do so safely at ground level (but still with a full body weight on it) with both a Pro Traxion and Micro Traxion device. One candidate went up a 5m training pitch to a ledge with a Y hang and installed a Petzl Micro Traxion as part of a haul system. They then proceeded to haul another T/A about 1.5m up the wall. At this point of the exercise, they were to reverse the haul and lower the person on the rope. The candidate used a Petzl RIG (version 2 D021AA00) on the ‘dead’ side of the rope to lift the T/A enough to release the toothed cam on the Micro Traxion. This was successfully achieved but a moment later the T/A on the rope went into freefall, dropping around 1.5m onto the ground. This all occurred under direct supervision of the T/A and at no point had anything been done by the candidate that was not expected or safe.

The exact details of the few minutes after the fall are irrelevant here, but the T/A was thankfully uninjured, although a little bruised. The candidate was asked to leave the equipment exactly as used and make their way down safely.

The 2 devices were being used on Petzl Parallel 10.5mm rope (good condition) and using Petzl OK oval triple action or screw action locking karabiners. All equipment was compatible and being used as per manufacturers instructions and LCMLA scheme best practice.

When the situation was calm again and everyone was known to be okay, I ascended to the look at the setup. I had already formulated a hypothesis about how this had occurred. Seeing the equipment and speaking to the candidate and T/A had confirmed that both the Micro Traxion and Petzl RIG were being used correctly and the RIG handle was in the locked position when the fall occurred. Once I was able to see the exact position of the equipment, I was confident that I had identified the reason for the fall and was able to replicate it in situ (on camera) and again on the ground later.

Probable Cause

The candidate and T/A were similarly matched in terms of bodyweight, but perhaps the T/A was slightly heavier. As the candidate released the teeth of the Micro Traxion from the rope, they were raised up in their harness by the weight of the T/A below. The candidate’s hands were on the Micro Traxion and bracing against the wall. The rope in the RIG was not being held. The RIG had its handle in the locked position. As the participant was lifted, the top of the RIG came into contact with the base of the Micro Traxion. The Micro Traxion moved between the RIG side plates and it pressed the top of the RIG’s cam down, at the point where the ribs are, opening the cam and releasing the lock on the rope. Without a hand on the rope, and with pressure on the cam top, there was no locking or breaking action on the RIG. This resulted in the release and drop of the T/A.

The candidate would not have been expected to have a control hand on the rope at this point. The RIG was in the locked position and is a hands-free device in that mode.

I filmed the interaction in the exact location and have uploaded it to a private link on YouTube:

https://youtube.com/shorts/oEE4bQcBFbc

Comments

  • This interaction was not a fault of the equipment, nor was it something that is isolated to these two items of equipment. I anticipate it would be possible to recreate the issue with a range of cammed belay devices and pulley/jammer setups.
  • The participant was not at fault and operated the devices according to the manufacturers instructions and the training given.
  • The supervising T/A (on the rope) was not at fault and was observing the operation throughout.
  • A heavier casualty on a rope being counterbalanced by a lighter rescuer likely increased the chances of the 2 devices coming together.
  • The position of the Traxion in relation to the RIG was unfortunately in the ‘sweet spot’ to cause this issue. It is something that might take many attempts to recreate, but clearly will, and has, always been possible.
  • This incident would fall under the user-error category, but as it was something that had not been witnessed or reported before, I don’t believe it was reasonably foreseeable by anyone involved. That said, it is now a known issue and should be accounted for in training and safeguarding trainees.

Follow up actions

  • This confirms to me the importance of a close-to-ground practice session in a controlled environment when first teaching these skills.
  • I shall now specifically demonstrate this interaction as part of my teaching when using RIGs or similar devices.
  • I shall introduce a requirement when training to either:
    • Maintain a hold of the dead rope during the counterbalance manoeuvre, even on a locked belay device, or,
    • Tie a backup knot a short way down the dead side of the rope to act a blocker in the event of uncontrolled release.
  • I shall highlight the issue when I do Vertical Core Skills assessments if the candidate is unaware.

It should be noted that this issue may also be possible with other similar equipment from a range of different brands.

Tutor XG rope test – Thanks to Spanset

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I have spent some time at Spanset in Middlewich over the last couple of months, doing my IRATA L1 and a few other bits. Some of you will perhaps know that Spanset have been particularly friendly to cavers, donating large amounts of new rope to expedition groups and competition winners on places like UKCaving forum. On my last visit to Middlewich last week, I was offered some rope to play with and provide feedback on. Although this is not a new type of rope, it is something that is only recently been taken on by Spanset and as far as I’m aware, there are no cavers out there using this stuff just yet. I’ve been kindly given 100m of this rope to test and report back on. If anyone wants to borrow a bit for a day or 2, just ask.

The first thing that some of you will notice is that this looks exactly the same as the Mammut Pro Static that has been available for some time. You might be tempted to click away now as that rope was truly terrible once it had stiffened up, but this is not the same stuff. From my understanding, Teufelberger took over the production of Mammut ropes some time back and now produce similar looking, but different spec ropes. Only time will tell if this doppelganger remains supple.

So, the details are as follows.

Teufelberger Tutor XG 10.0mm
Semi-static EN1891 Type A

Polyamide construction divided into 41% sheath and 59% core.
Stretch in normal use <5%
Shrinkage <6%
61g per meter

Apparently this is designed with teaching in mind (hence Tutor) and as a general rope access rope. Off the reel it feels supple and as you’d expect a new rope. The instructions provided did not give specific advice on whether it needed a pre-soak before its first use, so I did so anyway. Soaking for 24 hours, with 2 changes of water, before air drying and cutting. The 100m drum was reduced to a 44m, 33m and 19m rope, showing some shrinkage straight off the reel (as expected). In use, the ropes are marked up as a 40m, 30m and 18m. This is my most frequently used range and should permit me to get lots of use out of this stuff.

The rope was prepared and logged onto my system on the 1st of September. I’ll be keeping a track of how much use it has and reporting back when I have something interesting to say. I’ll probably start with an initial use post as soon as I can and follow it up with something longer term.

New Petzl Stop

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Rumers have been circulating for a while now about a redesigned Petzl Stop being in development and test. The first pictures have now emerged following an expo in China. Thanks to Qi Woo for posting these on the Rope Test Lab Facebook Group. I have made a few limited observations based on these few images.

From this pre-sale version, we can see the device remains an assisted braking descender but is now marked as certified to EN 15151-2 (2012), which is the “Breaking Device” standard and indicates this can be used as an assisted belay device, which the previous version was not certified to. This would be a major draw for instructed caving where there is a shift away from ‘historical’ use of the current Stop and towards devices with full certification for each job we ask them to do while at work. It’ll be interesting to see this new Stop go head to head with the RIG2 device which is being picked up by more and more cave leaders.
The new Stop is compatible with 8.5mm to 11mm ropes, which just about covers the full range of diameters cavers are likely to need, although not quite down to the 8mm stuff which is becoming more popular with sport cavers. Interestingly, the new Croll S is compatible with 8-11mm rope.
The assisted braking / control handle has changed from a push-in to a pull-down style operation, much like the Petzl RIG or Kong Indy Evo, something that will be welcomed by some, but disliked by others. I am happy about this, as I’m someone who has started to develop hand pain from the current squeeze operated handle after longer trips or many lowered clients.
The device no longer seems to have user replaceable bobbins, as evidenced by the lack of hex head nuts and bolts on the frame. It does seem that both bobbins are made from the same metal, making me think this is a full stainless steel bobbin device, which should give much longer lifespan over the alloy bobbin version. We should also see an end to grey ropes in the kit store now there is no alloy to wear and coat the rope.
We’ll need to wait and see what that little hole is for in the handle. Remote braking release perhaps or just a pre-production moulding feature?

I have not seen a release date for the UK market yet and I look forward to getting my hands on the user instructions when they are issued. What will be very interesting to see is specifically how Petzl supports the use of this device for lifelining (and rescue hauling) as it might be used in instructed caving. Could this be the Stop we’ve always wanted, or will the professional caving market continue to migrate to the excellent RIG2 device, with its multi-function EN standard compliance?

In addition to the Stop pictures, we can see a completely redesigned Freino krab, with its braking spur repositioned to the opposite end of the karabiner when compared to the previous version. Eagle eyed readers will spot that this krab is attached to a red device in the photo below. We are also looking at a new version of the Petzl Simple. This does still have hex head bolts so may retain its user-replicable bobbins. They bobbins even seem to be symmetrical, making them reversible too.
I’m sure we’ll see more in the coming weeks.

I’ll get my hands on one of these new Stops as soon as they become available. Until then, if you need to talk about lifelining or abseil devices appropriate to your underground operation, feel free to get in touch. For technical advice to the outdoor industry or LCMLA courses, see www.undergroundspecialist.co.uk

Testing the strength of heavy duty caving belts

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A Method of Testing the Strength of Heavy Duty Caving Belts

The aim of this was to establish a method to test the strength of heavy duty caving belts that did not rely on having access to a load cell. I hoped to produce a simple system that needed very little equipment and that would deliver a test load to a belt that exceeded the minimum strength requirement for its use.

Why? Well I felt that I needed to have some kind of empirical justification to use an item of non-PPE equipment in the role of a height security device. I didn’t feel that “because we have always used them in this way” was a sufficient argument for their use. As far as I’m aware there has never been a failure of a caving belt that led to an accident, but that is not really a reason for never questioning their use in this role. These are my personal thoughts and it does not constitute ‘advice’ or the position of the BCA Training schemes.

A quick note on use of belts – The user should never be in a position where they can become suspended on a belt alone. Additionally, they must never be subjected to falls or dynamic loads. They are for restraining movement to keep someone away from a fall hazard or preventing a slip becoming a fall on easy angled ground. They are no substitute for a harness where suspension is possible.

What strength does a belt need to be?

Well, this one is a potential can of worms…. Let’s be clear, the manufacturers do not condone the use of their heavy duty belts for taking any load at all beyond hanging your battery or lunch box from it. There is a historical use in cave and mine exploration that involves using the belt for the purpose of slip prevention and security on steep ground when combined with a rope belay or cowstails. If you were intending to use it for this purpose, especially as a leader of others, you’d need to be 100% sure that the belt was strong enough for that role. The manufacturers do not state this type of use is approved or list any strength rating on the product or the literature accompanying it. You must conduct your own test and risk assessment if you are to use them in this way.

If you want an item that has a certified standard for this type of use, you could choose to use a climbing harness, caving harness or potentially an EN358 work positioning/restraint belt.

For anticipating loads that could be applied to a belt in use, I have used a mass that is comparable to the maximum user weight ratings on some of the common PPE equipment at the time of writing: 120kg (Mass)
The caver has a short dynamic rope lanyard of 50cm length, fixed from their belt to an anchor. As discussed above, the user should never be subjected to a fall or suspension, but I am using the forces that it is possible to generate in ‘foreseeable misuse’ as a starting point for considering how strong a belt needs to be.
If they climb above the anchor, until the lanyard is tight, then ignoring all stretch or slack in a system, a possible FF2 fall of 1 metre can occur.
This FF2 fall will likely result in injury and, as a rule, cavers avoid putting themselves in a position where this kind of drop can be taken. By not climbing above the attachment point of there lanyard, the resulting fall cannot exceed FF1, or 50cm in this case.
When using dynamic rope cowstails, the UIAA standard permits stretch up to 40% of original length. For a 50cm cowstail, this is 20cm, or 0.2m (Impact Distance).

For a Fall Factor 2 (1m drop on to 0.5m cowstails)

velocity = √ (distance x acceleration due to gravity x 2)

v = √ (1 x 9.81 x 2)
v = 4.43 m/s

Kinetic energy = 0.5(mass x velocity²) 

Ke =  0.5 (120 x 4.43²)   
Ke = 1177.5 Joules

Impact force = Kinetic energy / Impact distance

IF = 1177.5 / 0.2
IF = 5887.5 N

Impact Force = 5.89 kN

This is clearly a very serious amount of force and is only a hair under the threshold that the work at height industry uses as a maximum safe force the human body should be subjected to. An impact of around 6kN on the body will cause injury in a lot of cases and should certainly never be taken on a heavy duty caving belt. It is beyond anything we should ever do when wearing belts and is included only to demonstrate the risk of improper use. A FF1 drop is still something to be avoided, but is more realistic of a potential real world scenario.

For a Fall Factor 1 (0.5m drop on to 0.5m cowstails)

velocity = √ (distance x acceleration due to gravity x 2)

v = √ (0.5 x 9.81 x 2)
v =  3.13 m/s

Kinetic energy = 0.5(mass x velocity²) 

Ke =  0.5 (120 x 3.13²)   
Ke =  587.8 Joules

Impact force = Kinetic energy / Impact distance

IF = 587.8 / 0.2
IF = 2939 N

Impact Force = 2.94 kN

So a 0.5m drop on to a 0.5m dynamic lanyard may produce a force of around 3kN for a 120kg caver. This does not take into account any stretch or bounce. This figure seems pretty reasonable, but we should seek more evidence to reinforce this for our follow up testing.

When considering the use of caving belts, can we can compare it to something done in another industry? Well yes, work restraint systems often make use of padded restraint belts instead of harnesses. One of the critical requirements for this system is that a user may not be permitted to go into suspension on this system. That seems very close to how we should be using heavy duty caving belts. When consulting BS8437 – Code of practice for the selection use and maintenance of personal fall protections systems and equipment for use in the workplace, we can identify that restraint belts need to conform to EN 358. Accessing this standard is expensive and no doubt the items conforming to this standard will have a very high safety factor. What we can get from BS8437 is the recommended strength of anchor points for use in a work restraint system. This is 3 x the mass of the user. A correctly installed and utilised work restraint system is only required to have an anchor of 3 x users mass. For our 120kg caver, this would be 360kg, or 3.6kN in force.

For our 120kg fictitious caver, we can mathematically predict a theoretical force of just under 3kN for a FF1 drop. We can also see that and anchor of 360kg (3.6kN) would be required if using similar techniques in work restraint. The figures are not exactly a match, but are comparable. Taking the worse case figure is probably the safest option going forward, so our belts must be capable of taking a force greater than 3.6kN for a scenario that does not involve wildly inappropriate use.

Safety Factor?

Apply to this any safety factor you wish. The 3kN figure from the maths is indicative of the maximum possible force generated in a FF1 drop on 50cm cowstails, the real world figure will be far lower due to stretch and slippage of the belt on the body and the sagging of the rope the caver is connected to. The BS8437 figure is a 3 x safety factor over the user’s mass anyway. You could argue that belts tested to 3.6kN would be sufficient as an indicator of appropriate strength if you never operated with cavers heavier than 120kg.

Belt Strength

Accepting all this, we are left with the figure of 3.6kN as our chosen minimum requirement for the strength of the heavy duty caving belt for any user we might encounter regularly (3 x 120kg based on BS8437).

So as long as we can apply a test force of 3.6kN or more to the belt, we can be assured that the item can hold the greatest possible force we can apply to it in proper use. The only remaining factor of concern is that would applying this force in test render the belt unsafe to use again, in essence, are these tests destructive? Only 1 way find out…..

Testing

Using 1 very large Corsican Pine and a good sized Birch tree, we set up a pull testing rig with a simple 3:1 theoretical configuration. I used a Rock Exotica load cell to get live feedback on the testing here but if you copy the method, you would not need to use one.

For the estimation of test force we regarded each person capable of pulling 50kg (see Gethin Thomas’ work on tyroleans). Through a theoretical 3:1 MA system that would be 150kg per person. With 5 undertaking the pull reaching 750kg and 6 equalling 900kg or approximately 7.5kn and 9kN respectively.

Kit used (minus load cell): Petzl rescue pulley, Petzl Basic jammer, Petzl Partner pulley, Lyon wire sling for tree, assorted karabiners, 20m rope.

Due to the force expected to be placed on the rope, I did not anticipate that I would be able to untie the end knot (fig 8 loop). This was accurate and the knot had to be cut from the rope end. Bare this in mind with your own rope!

We also used a Petzl Rollclip to redirect the angle of pull to make it easier to stand on the tarmac of the road alongside the trees.

Initially we had 5 people pulling the first test on a Lyon roller-buckle belt (brand new).
This produced a force of 5.9kN with no damage or slippage. This is lower than expected but there was a lot of tightening in the knot and stretch in the rope coupled with a general timidness of the pulling team.

The remaining tests used 6 people to pull. This one was conducted on my 10 year old Caving Supplies square buckle belt (already retired). This belt has nicks, fluff and rust and comfortably took a force of 7.74kN showing no damage or slippage. Next came my current AV belt, with it’s central maillon removed and directly attached to the pull line. This belt held 7.7kN without failure or slippage. Finally, the pulling team seemed at their most confident that nothing was going to break and send shards of metal and wood at them so they really gave the last belt some pain. This Warmbac square buckle belt was subjected to 8.64kN with no damage or slippage noted at the time.

It is not surprising that the force exerted by the pulling team was less than the theoretical 3:1 system implied. In practice with the loss of friction due to bearings and turns in the rope a 2.5:1 is a more real world figure and so our 5 x 50kg pulling average adults could be expected to make 625kg/6.25kN using this system.

On this test we pulled the belts to a far higher force than would be needed in a periodical strength test to simply demonstrate that this lower level of testing would not damage the belts. Using 4 people to pull on a 3:1 MA (2.5:1 actual) system in a reasonable way with un-gloved hands, would produce a force exceeding 3.6kN. This would not require a load cell to demonstrate if the method was followed correctly. Using 3 strong people on the same 3:1 (2.5 actual) system would probably be reasonable too.

50kg x 4 people = 200kg x 2.5 mechanical advantage = 500kg or 5kN
50kg x 3 people = 150kg x 2.5 mechanical advantage = 375kg or 3.75kN

Conclusions

Using a system like the one shown here, with 4 people pulling at average strengths, you can apply a force greater than 3.6kN to your test belt.

Once the test is complete you should thoroughly examine the belt like any other item of textile PPE to see if any damage or slippage has occurred. Any that do show signs of damage should be retired. Any slippage may be down to the buckle, but if the belt comes off or strap slides through the buckle under load, it should be deemed as having failed. If a belt has taken the test load and shows no damage or deformity then you can be comfortably sure that the belt will be fit for its intended use whilst still in that condition.

Final inspection of belts:
Lyon roller buckle                                5.9kN            No damage
Caving Supplies square buckle           7.74kN          No damage
AV maillon closed harness buckle       7.7kN            No damage
Warmbac square buckle                      8.64kN          No damage, slight curvature to webbing now when hung vertically which indicates over stretching or broken fibres down one side.

Again, this level of force was beyond what you would test to, but demonstrates that the 4 person 3:1 pull will not damage a belt that is not already fit for the bin.

A Note on Load Testing PPE

We don’t load test PPE. PPE is supplied with declarations of conformities and CE/EN markings. So long as you purchase via a reputable retailer or from the maker, this is the evidence that the product meets the minimum criteria set out in its approval standard.
Caving belts are not PPE and have no categorisation under the PPE Regulations. It therefore falls to the user to ensure they are fit for purpose, and that may involve a test of strength as outlined in this blog post. Ultimately, you must conduct your own risk assessment and define a way to show they are fit for use, copying a blog post won’t cut it with HSE!

Inspections

Lastly – all of this testing and use is predicated on you treating your belts as an item of PPE. They should be purchased new, inspected prior to use and have a recorded inspection every 6 months like any other PPE item. They should be in the same good condition as any textile item of PPE and retired from service if damaged, worn, contaminated or subjected to any load exceeding their safe limit. It is recommended that anyone in charge of inspecting PPE be trained and certified to do so.

As a side note, I maintain that the Caving Supplies belts are the tanks of the heavy duty caving belt world and, if kept very clean, will ultimately outperform every other type or brand available. I think this test shows that well as the CS belt had at least 5 more years of abuse over the other belts. I will dispose of the Warmbac belt just in case but don’t tend to use these anyway, but that’s another blog post!

More force testing on 5:1 systems

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This post follows up on some initial testing done on 5:1 mechanical advantage systems used to tension tyrolean crossings done a few months ago. I suggest anyone who has not read that report catch up with it here before reading on as I don’t explain everything again here.

For this batch of testing I used the same site but rigged things using metal strops instead of rope loops. This would act more like the solid bolt anchors used underground and would nearly eliminate false readings from knots tightening.

I used 2 types of readily available Type A rope

  • 11mm Mammut Performance semi-static
  • 10mm Beal Antipodes / Industrie

The tests were repeated with 3 different progress capture devices

  • Brand new Petzl Stop (rigged both fully and half threaded)
  • 10 year old worn Petzl Stop fully rigged
  • Brand new Petzl RIG

I created a 5:1 system on 10m section of rope using a Petzl Ascension jammer, Petzl Tandem pulley and a Petzl Partner pulley. These are all items that would likely be used by leaders underground or of similar type. No big rescue pulleys or prussics.
I pulled all of the tests on my own with un-gloved hands. I weight approx. 90kg and pulled as hard as I could using just hand grip.
The final tension in the line was estimated by hanging off it and the force on the jammer ascertained using a Rock Exotica Enforcer load cell measuring in kN.

11mm rope

New Petzl Stop – fully rigged
2.06kN
2.10kN
New Petzl Stop – half rigged
1.96kN
2.04kN
Old Petzl Stop – fully rigged
2.04kN
2.04kN
Petzl RIG – belay mode
1.94kN
2.08kN

10mm Rope

New Petzl Stop – fully rigged
1.88kN
1.88kN
New Petzl Stop – half rigged
1.70kN
1.82kN
Old Petzl Stop – fully rigged
1.98kN
1.92kN
Petzl RIG – belay mode
1.78kN
1.80kN

There clearly was a drop off in force required to tension a 10mm system over the 11mm system, although only small. The fully rigged Petzl Stops required the highest force to tension although the old Stop in the 10mm test oddly required more than the new one (*see foot note).

I took the highest force generating configuration and added some more people to the pulling end.

11mm rope with a fully threaded brand new Petzl Stop

2 smaller adults pulling
2.00kN
2.22kN
2.34kN

2 small adults & myself pulling
3.56kN
3.24kN
3.54kN

I think it is entirely possible to exceed the 4kN figure if 3 large and/or strong adults were to be pulling on a 5:1 tensioning system. Both ropes used were clean and supple, with a dusty rope friction would again increase and coupled with some less efficient pulleys might tip the force higher still. I think that it is still appropriate to give out the advice that no more than 2 people are used to tension 5:1 systems, perhaps 3 if using youths or very small adults but certainly no more. The force required to damage a rope at the teeth of the jammer is rather large, especially on 11mm rope, but repeated tensioning on the same spot in the rope may, over time, lead to degredation of the rope.

The best advice I can give is to echo what is already taught at LCMLA and CIC:

  • Keep your pulling ratios at 5:1 or lower and don’t exceed 10 men equivalent pulling power. i.e. 3:1 with 3 pulling or 5:1 with 2 pulling.
  • Keep ropes clean and supple.
  • Use only Type A ropes compatible with your choice of progress capture device.
  • Thick ropes are stronger and stretch less but require more force to initially tension.
  • Thinner ropes are strong enough but stretch a little more and require less force to initially tension.
  • Where very high tension systems are required consider doubling up on ropes and using a non-toothed rope clamp like a prussic or Petzl Shunt / Rescuecender.
A final thought. It is only a short period that the tension is applied to the rope via the teeth of a jammer in these set ups. It is the resultant tension and forces in use that are just as, if not more important to keep an eye on. Tensions in tyroleans can easily exceed 2.00kN, the maximum load Petzl advise for a Stop descender. Consider all components carefully and practice safely before using for real.
* Having given this some thought I believe that I can explain the added friction for this configuration. Over its life, the older Stop has been used for many miles of 10mm rope, wearing the alloy bobbin into a matching profile. Now there is a larger contact area between the alloy and the rope when compared to the brand new Stop. The larger contact area requires more friction to overcome and hence the greater force required to pull the rope through.
2 Stops

Loads on a 5:1 Tensioning System

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Tyroleans have been a bit of hot topic with me recently. I’ve developed some sites to use in my woodland near Whaley Bridge and been involved in some testing with BCA Trainer Assessors for the LCMLA scheme. We’ve measured the actual forces held by the anchors in a number of tyroleans but a really interesting questions was yet to be answered definitively:

In using a high mechanical advantage tensioning system, how much force is being applied to the rope via the teeth of the jammer and could we be at risk of damaging the rope?

To explain, when using a 3:1 or 5:1 system as is common with tyrolean set-ups, a toothed jammer is most commonly used to create the attachment point on the rope to build the mechanical advantage system. The force applied by whomever is hauling in is multiplied in a mechanical advantage system, which is kind of the point, and all this force is transmitted to the rope via the toothed jammer. The picture below shows a 5:1 set up with a Rock Exotica Enforcer load cell.

5to1 load test (1)

If you omit the load cell from this set up you have a standard 5:1. As you can see it is the toothed cam on the Petzl Ascension device that is the contact point with the rope. This device, like many of the Petzl rope clamps, is approved for use with 8 to 13mm ropes but comes with the warning that the toothed cam can damage or cut the rope at forces around 4kN for smaller diameters and 6.5kN for the largest. As it is hard to compare one rope to another, even of the same diameter, most rope professionals simply take the 4kN figure as that which must never be achieved in use.

5to1 load test (3)

Using 2 people to tension the 5:1 system, the Enforcer gave a max force of 2.88kN through the jammer. Had we been on more solid ground (and my partner not been a positively tiny 5’2″ & 50kg) I think we could have gone higher.

Inspecting the rope (Gleistein 9mm Type A) after moving the jammer showed a flat spot and gaps in the sheath where the teeth had opened up the weave. There was some furring but it was impossible to say if this is new or was already present on this rope.

5to1 load test (5) 5to1 load test (6) 5to1 load test (7)

A repeat test on a different section of rope produced a force of 2.66kN and a similar flat spot and sheath opening.

We then set up a standard 3:1 ‘z-rig’ and repeated the test.

3to1 load test (1)3to1 load test (3)3to1 load test (2)

This test gave us a force of only 1.84kN using the same 2 person team with a less pronounced, but still visible, opening of the rope sheath bundles and overall flattening.

I think these observations uphold the understanding that the tensioning in tyrolean systems must be done with great care and by using the least amount of tensioning required for the crossing. I will conduct a further observational test at a real underground site with 10mm or above diametre rope for a comparison but the force figures will not be too dissimilar. It would be interesting to find the 2 heaviest/strongest volunteers I can and use them on a 5:1 system to see if it is possible to creep further toward the 4kN limit.

In conclusion, you can get close to, or potentially exceed, the 4kN safe load on a toothed-cam jammer when using tensioning systems in tyroleans. Tyroleans really are an element of verticality that you need to understand well and get training for to know how to be safe. Go and do a CIC/MIA/UKMR or other course or get in touch with me for a chat.

I’ll be investigating this further at some point but it might be worth looking at employing the use of a non-toothed rope grab like the Petzl Shunt or even an appropriate prussic knot as a way of limiting damage to ropes in high mechanical advantage systems.

NB – The current Petzl literature for the current Croll and Basic do not show a load at which the ascenders may damage the rope. These devices are sold as personal ascenders and are only labelled to take up to 140kg of user weight.

Woodland Tyrolean Development

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Recently I headed out to our private woodland site to have a play with my new Rock Exotica Enforcer. We have recently developed a tyrolean crossing here along with calculations of anticipated loads and safety factors. Using the Enforcer on this tyrolean would give a real world check of my calculated figures as well as giving me a relatively safe and controlled location to experiment.

The tyrolean spans a 20m gully and is rigged using large trees slung with Lyon steel strops and the tensioning is done on the lower end using a 3:1 system through a Petzl RIG clutch. In this testing I purposely tried to over tighten things to see how much tension, and hence force at the anchors, it was possible for 1 person to produce.
I used a 5:1 pulley system and installed the Enforcer between the anchor and the RIG so it gave a reading on the total tension force being held by the lower anchor strop.

The calculations I had done previously were based on an average weight of participant of 100Kg. The span was measured and the sag was estimated at 10% as in practice we’ve found it impossible to achieve less than that with semi-static rope (usually more like 15-20%). The load on each anchor (so x2 for the rope itself) was calculated using a number of methods, some involving scary trigonometry, but the simplest equation was:

Tension = (Load × Span) / (4 × Sag)
Tension = (100kg × 20m) / (4 × 2m)
Tension = 250kg (roughly translated to 2.5kN)

The WLL (working load limit, or safe working load) of each component was calculated at a fairly standard ratio of 5:1, that is a fifth of its MBS (minimum breaking strength). Using this ratio the lowest figure was 4.8kN for a Petzl OK Oval karabiner. Technically the Petzl RIG is weaker but as it will slip before it’s WLL is reached then it can be discounted*.

*providing the RIG is not locked off and the rope is dogged back into the rigging so a running slip could not result in a complete slackening of the system.

So the maths with a 10% sag gave me 2.5kN tension force on each end of the tyrolean.

The tension force graph is downloaded off the Enforcer to iPhone and then edited in Microsoft Excel looks like this, with Time on the x and Force in kN on the y axis. Click to expand:

Little T 5to1 Graph

The graph starts with me applying tension to the system and having a few test bounces. The main force peak near 2m20s is me hanging suspended and pulling myself to the centre of the crossing and bouncing. I then pull up to the higher end, take a breather, and run back off, giving the last spike.

Little T 5to1 Graph top end

The second graph was me installing the Enforcer at the high end of the tyrolean crossing and tensioning it back up again with the 5:1 system. The tension at the top anchor was a little less than before on the lower anchor but the peak tension (me doing a running jump crossing) was similar to the previous graph.

Some interesting observations from the day:

  • At no point was it possible to install more than 1.5kN of pre tension in the rope prior to crossing. This was tested up to 9:1 and on 2 different tyroleans.
  • Tension in the line always dropped after the first crossing and remained at or below 1kN. Probably after the knots tightened up.
  • Tension could then be raised back up with additional hauling but the force remained below 1.5kN. Do not keep re-tensioning in real use as the increase in tension for each loading may cumulate to break a rope. See BMC technical reports.
  • The peak force was close to our 2.5kN calculation. This is predicated on having at least 10% sag in the system. A set of specifications for mechanical advantage systems and number of people pulling should be set by a company to limit over tensioning.
  • Whatever the tensioning method, we could not achieve less than 10% sag on a tyrolean in use with a correctly installed clutch.
  • Even on a 9:1 tensioning system the peak force created was only 2.8kN, probably because the Petzl RIG slipped at that point.

The 2.8kN high figure was achieved on a 50m tyrolean set up later that day. Here I was using a 10mm Beal rope today with a MBS of 24kN and 5:1 WLL of 4.8kN. The 5:1 safety factor is acheived with this rope. The rope I have on order for this when it is done with the public is a Mammut 11mm, the same as we use on the 20m line. It has a MBS of 35kN and hence a 5:1 WLL of 7kN, far above the expected loads in use.

Why all this effort? I like to know that the real world forces are actually near to how we calculate things, especially in tyrolean systems. Vector forces are scary and you just need to watch YouTube clips of slackliners breaking rated kit to see that. I can sleep well knowing all our research and calculations are backed up by real world testing and I can be confident that we are delivering as safe a service as we can.

Thanks for reading and remember, I can be hired to come to your site and test your rigging with the Enforcer too. Contact me direct for a quote and a chat.

Can you cut rope with a household jet washer?

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After the last blog post where I tried to compare washing a caving rope in a washing machine to jet washing I thought I’d try to see how much damage I could do to a rope with a jet washer.

This photo was from the previous test where I exposed the rope to a full power, fine jet for approximately 30 seconds.OLYMPUS DIGITAL CAMERAI could not see any evidence to say that the rope had been damaged by the jet wash exclusively. The longer fibres shown here could have been the result of the already cut fibres in the sheath (short cut sections showing) being forced out from under another braid. Of course, the damage may be down to the jet wash alone. I think the only real way to progress with this test is to take a piece of brand new rope and jet wash it. I don’t have any laying about right now so I did some more testing with the leftover Beal Antipodes 9mm from the previous testing. Anatomy of a ropeI hypothesis that the worst case scenario is a rope being jet washed up against a solid surface whilst under moderate tension. The tension would keep the rope in the jet longer and the solid backing would provide a surface for the fibres to be crushed against or even abraded. It had occurred to me the damage could come from the power of the jet rubbing the rope against a course material.
The backing for this test was a piece of porcelain tile, almost completely smooth to the touch. The tile sat between the rope fibre and the wood in the test device I knocked up.Test assembly v1I tested each size of bundle on both full power and the normal setting that I use for washing. Both jet setting were fired at point blank range into the fibres for 60 seconds. This test was repeated at least twice for each sample after it was checked close up.
This sample had been washed on high power/very tight jet for 120 seconds. The jet was directed at the same area of the sample for all the test time. For scale, the fibre here is about size of that very tough cotton used for stitching canvas and kit bags together.One strand

The fibre bundles became so small that I could easily break them in my hands. This one was no bigger than a piece of cotton.Cotton thinkI figured that if my jet wash could not cut through a piece of sample that was thin enough to break easily with my hands then I did not need to progress onto smaller samples.

Conclusion?

As before, I need to state that this back garden test does not give a statistically sound result and as such only serves to show what occurred in this one instance of testing.

I could not get my jet washer to cut any size of sample on this test. In both high power/confined and low power/wide spread modes, I saw no damage to the rope fibres. No doubt individual filaments of the fibres may well cut very easily but they break with the slightest of effort in the hands anyway so I doubt the value of that observation. The cotton size sample was the smallest test size and even that could be broken by hand with little effort. It is also worth noting that this experiment was done on a 7 year old rope that had seen high use in very abrasive environments over its life.

Challenge

I’d really like for other cavers to go out and try this experiment for themselves. Take a small piece of old or new semi-static caving rope and split it down to various sample sizes. Use a domestic jet washer / pressure washer on it’s highest setting and see if you can cut or damage the sample. For consistency, do it in 60 second, point blank range bursts.
Let me know via the contact address on my website or via the thread on UKCaving what happens. Failures to cut are just as important as actual cuts, so let me know either way.

Thoughts on jet washing caving ropes

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I thought I’d ponder a little bit about the ‘myth’ of jet washers and caving ropes. I say myth because it appears that there is no real test data out there in the caving community. Recent caving forum discussions about jet washing happened to coincide with an associate company requesting we don’t use jet washers on their kit earlier this week and the two events spurred me to type something up.

Disclaimer – This is not a scientific, empirical experiment and you should always follow the care instructions of the equipment manufacturer.

I have used all sorts of methods for washing ropes over the years and most of my older ropes have been subjected to each at one time or another. Some times a rope may simply get dunked in the stream by the cave, other times I see fit to pull it through my home made rope washer but, more often than not, I get the jet wash on them.
The jet wash is always set to its lowest power and widest spray pattern. I’ve caused real damage to wood and clothing before by using the jet wash on full power so I am cautious. Some site this as the reason you should never use a jet wash on ropes. I agree. If you don’t know how to wash with a jet wash don’t do it. That, and if you don’t know how to operate your washing machine and it ends up on a boil wash, you probably shouldn’t put your ropes in there either.
This Beal 9mm got a super fine jet of water for about 30 seconds at point blank range in a test today. Damaged Rope

Apart from being incredibly clean for a 7 year old rope, you can clearly see the elongated sheath fibres. I’m not convinced the jet wash cut any fibres, more that it simply forced the already cut and abraded fibres out from under the other braids. The core was not exposed. I’d not want to do this to my ropes ever but I would call it far from ‘cut’ or ‘shredded’ as some anecdotal tales from the web recall.

Moving on. The rope I chose to retire was a Beal Antipodes 9mm semi-static that I purchased in 2007. The rope was one of my main users for 3 years as a 40m before being cut into 2 shorter lengths for cave leading handlines and general Italian Hitch duties. For the last 2 years it has languished unloved in the shed and has been the subject of much abuse in non life-critical applications. It’s probably not been washed for a year but before that it saw regular jet washing and stream dunking.

I cut the length in half and removed a control sample from either piece. The two 1m control sections came from the very end of the rope, where it was marked, and roughly half way along the 20m length respectively. I single daisy-chained one 10m length and double daisy-chained the other.

Test rope setup

The 2 longer lengths were soaked in cold water for 10 minutes as a pre-treatment.

As this was happening I cut open the 2 control lengths for a comparison.

End of rope section:Mid rope inner sheathEnd reel control Mid rope section: OLYMPUS DIGITAL CAMERAMid rope inner

The 2 samples looked very similar and I’m happy to say, despite years of being jet washed, were relatively clean and un-abraded inside. The fluffing you see was caused by the cut into the rope.

I dropped one of the test lengths in the washing machine. I set it to ‘delicate’ on a cold wash with no spin after first running a rinse cycle to clear any detergent. It had a 62 minute wash time.
While this was going on I jet washed the other test length in the same manner I do all my ropes. The process took approximately 5 minutes and once complete the rope was allowed to drip dry until the washing machine had completed it’s cycle.

After washing After washing

In both photos the washing machine cleaned rope is at the top and the jet washed one at the bottom.
I think it’s clear to see from the photos, and certainly was in real life, that the jet washed rope was far cleaner than the machine washed rope. It also had a much suppler feel and was more knotable over all. Remember the ropes have been identically treated until this very last wash in this test.ComparissonThe rope on the left is the machine washed and the one on the right has been jet washed.

It is hard to draw conclusions from the comparison here as this is only one wash cycle. The jet wash seemed to get the better results in terms of appearance and suppleness but the internals of the ropes looked very similar.
The one thing that I do take from this test is that despite the differences in the test washing, all the samples from this rope did not show any appreciable abrading of internal fibres from grit ingress. The anti jet wash argument is that the force of the water pushes grit into the core, causing damage. What I observe here is that this is an incorrect assumption as the 4 sections of visible inner on this very old, well used and heavily jet washed rope show no signs of damage by internal abrasion.

My theory is that the jet washing forces the grit and mud through the core and out the other side of the rope, as opposed to moving it into the core and it magically stopping there. I always clean my ropes after each trip. Perhaps they simply do not stay dirty long enough for the grit that does enter the core to be damaging. The outer sheath shows far more wear and damage than any of the internal structures of the rope.

I continue to believe that regular low-power jet washing does no harm to my ropes. I do know that some manufactures do not suggest using a jet wash on ropes and you should make your own choice with reference to the manufacturer’s guidelines. I will continue to cut open ropes as they are retired and will update this blog should my opinions or observations change. Meanwhile, if there is anyone out there prepared to take this subject up for a dissertation or just for interest then get in touch!

Gleistein GeoStatic NE 9mm rope – 18 months use

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It’s now March 2014, about a year and a half after I bought my first length of the Gleistein Geostatic 9mm rope.
The 31m length I bought was soaked at home and measured to 32m, no doubt down to Shaun at Hitch N Hike’s generous measuring style!
I labelled it up as a 30m and went about using it.
I re-measured it today and it came in just over 29m, a shrink of 3m since initial cutting, approx. 9%. So it seems, just like any other rope, once it’s cut you still need to factor in about 10% for shrinkage over the life of the rope. I’m still happy because there was no noticeable shrinkage after cutting and soaking when first purchased in Sept 2012.

I have a 21m length bought about a year ago that has just re-measured to 19m. This length has had a hard life already, it is my traveling rope on cave leading work and has been dragged through numerous Italian hitches whist being covered in grit and the particularly abrasive mud in Peak Cavern’s trade routes. It has done a good job at sawing through my alloy krabs but the rope itself is still in excellent condition. There is some light fluffing on the sheath comparable with some of my far less used ropes and the colour, like the 29m length, has faded into a more pastel orange. It still handles extremely well, clearly not as supple as when new but a massive improvement over the 2-3 yr old Mammut 9mm I have, which is more akin to wire cable now.

My cleaning regime for all my semi-static ropes is simple and it gets done after every trip. For clean trips it is just a spray with the hose or a dunk in clean water to remove particles from the surface. More often than not it gets a low power jet wash (controversial I know!). Never force dried, only hung in a spare room or over the bath.

I’ve got 3 lengths now, each bought about 6 months apart and will continue to purchase this rope as my current ones approach retirement.
In another year and a half, when this rope is no longer in service I’ll do a final post mortem report. I’d also like to send a few samples to be tested by the BCA and Bob Mehew to see what toll the hard life has taken on it.

Gleistein is still available at Hitch N Hike as cut lengths or entire reels: http://www.hitchnhike.co.uk/acatalog/gleistein-9mm-geostatic-ne.html

The initial blog post is here: http://www.peakinstruction.com/blog/first-look-at-gleistein-geostatic-ne-9mm-semi-static-rope/