Testing the strength of heavy duty caving belts

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!

Worn Connectors – Pull Testing 11-6-2017

Over the last few months I’ve been collecting a few bits of retired equipment from stores checks and ‘isolation’ bins with a view to looking at loss of strength due to wear. Nothing here constitutes a scientific test and this is purely for my own satisfaction, but I’m writing it up anyway. I used my home made breaking rig with the Hilti HAT-28 anchor tester to provide the pull force. Each item was pulled up to the maximum possible load of the Hilti, 20kN, and the results were recorded.

Petzl Omni SL

Rated to 20kN main axis. Worn inside arc in 2 places after use with large steel pulley for 12 months. Failed PPE inspection due to wear depth being felt by fingernail and visually obvious.

Pulled to 20kN – No breakage, gate / lock working correctly.

I suspect that the wear on this item had not yet reached a sufficient depth to form a significant weak point. The connector was certainly retired at an appropriate time, i.e. with visible wear but before strength loss occurred.

Petzl M33 OK Oval SL

Rated to 24kN main axis. Wear visible at both ends of the connector. Large radius wear from twin cheeks of a steel pulley and small / deep radius wear from a long term connection to a steel 7mm Maillon Rapide.

Pulled to 20kN – No breakage, deformed beyond elastic recovery. Gate no longer closes and shape is visibly distorted. This item deformed at 15% below its rated strength. This shows that wear had already reduced the strength of this connector and it should really have been retired before reaching this level of wear.

Petzl Vertigo Twist Lock

Rated to 25kN on main axis. Worn on inner surface due to repeated contact with steel cable zip wires whist in use as a cowstail. Retired during routine PPE inspection.

Pulled to 20kN – No breakage, deformed heavily under test but recovered almost completely after. Connector permanently deformed and the gate locking mechanism does not function correctly. This item deformed 20% below its rated strength. This shows that wear had already reduced the strength of this connector and it should really have been retired before reaching this level of wear.

Do not take this test as advice to use kit beyond it’s manufacturer stated working life. Get a qualified person to advise you if unsure or go and do a PPE/FPE inspector course. If you have any retired gear you want to send to me to test in this manner then please get in touch.

Coiling Caving Ladders

Caving ladders are an integral part of the LCMLA Level 2 award. Being practiced with a ladder not only saves time but lots of faff. It can be hard to pack loosely coiled ladders into tackle bags, meaning they get dragged and thrown about the cave, something that no kit really deserves. Practice coiling your ladders and look well polished on your assessment and in front of your clients.

Struggling with ladder coiling? Collar me for a face to face demo or contact me.

Can you cut rope with a household jet washer?

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. Also check out these guys to find the proper clothing to use at sea.

Studies have perfectly proved that Husky tile saws possess a high reputation or reliability for their strength or longevity. They are also very easy to use. This is largely because they are manufactured for the everyday user and not the consummate professionals. One great advantage about them is that they’re really easy to work with and install as well as being light weight enough for a person to easily move around a large project if needed. In addition, it is reassuring to know that the company takes the time in making sure that their products are well-equipped with all the necessary tools and safety accessories that will help make sure you’re satisfied with your purchase.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

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!