Karabiner gates and foreseeable error

Sorry if that last post didn’t make much sense – and no, don’t worry, I’m not turning into a grouchy old man, just my thoughts – and they don’t always have to make sense… 😉

I was thinking about karabiner locking mechanisms before, prompted by a video posted on Facebook that shows an Locksafe Ultra O rolling out as it the locking mechanism is pushed against and past a limb. This failure mechanism is not specific to one brand, but rather inherent to the lift, turn and push type triple-action gate.

Essentially the limb in the video is doing exactly what you would have to do to unlock and open the gate. This phenomenon is known as roll-out. Statham and Roebuck wrote a report, Karabiner Safety In The Arboriculture Industry, for the UK Health and Safety Executive a couple of years ago, in which – amongst other things – they describe some roll out testing they performed on a range of connectors  commonly used in tree care and how they all struggled with the test set-up shown below.


The locking mechanisms that did best out of the lot was the Petzl Ball Lock, then still the plastic version with the thumb print on it. In my eyes though, it would be a bit hasty to start crying foul and accusing manufacturers of making bad quality gates. Essentially, this is not a design flaw, but rather it is operator error: In a cluttered environment it is up to the operator to ensure that the locking mechanism shall not come into contact with the structure and inadvertently be pushed open. Look at any user instructions and somewhere in there you will find a pictogram or text warning against this exact case, as in screen shot of the Petzl Carabiner Experience PDF shown below…

This is actually talking about something different, which is the danger of cross loads and lever action across the gate, but the fact remains: It is a clear warning against loads on the gate and once again emphasizes the importance for visual inspection, especially in an environment, like in tree climbing, where the connector is frequently being loaded and unloaded, making a cross load on the gate more likely.

What is clear though is that there is not one type of locking mechanism that addresses all issues. The Ball Lock type mechanism mentioned above may solve roll-out type problems, but especially the old plastic version had a low tolerance to outside loading of the gate. So, it is really up to the operator to consider what type of environment he or she intends to use the connector in, obviously the requirements you make of a karabiner is not the same when climbing large, open-canopy trees or when cone picking in the forest – and to choose an appropriate type karabiner. Depending on the situation, this may have a triple-action or a screw gate – or yet another type.

For more info, here is a link to the Go Configure article that Chris wrote a couple of years ago for ISA’s Arborist News.

The video below illustrates a different case:

Here a light tap on the outside of the gate is sufficient to push it open. This is a different matter alltogether: From a design point of view this sort of load is a foreseeable error. Whilst superficially the Skylotec Pinchlock karabiner has similarities with the Magnetron by Black Diamond, the failure mechanism in question is specific to this karabiner as the rods that locate into the slot on the nose have a round profile, rather than the square ones on the Mangetrons, that on top of it don’t only rely on springs to locate the rods, but also use a magnet to ensure correct closure. In an outside-loading situation the round rods on the Pinchlock are simply pushed up and out of the slot, a tap against the side of the hand being sufficient to do so.

Again, this is not a value judgement, it is merely an observation, as for all I know there may be an application where this type gate is spot on, but certainly a busy, cluttered environment such as a tree canopy is probably not one of them.

V-Rig rocks!

Working on a mixed species alley along a road here in Basel on the way out to Alschwil consisting of Sopphora japonica, Cladastris lutea and  Robinia pseudoaccacia. 

Especially the Sopphoras are really quite big trees – well, not exactly monsters, height-wise, maybe 22m, but just ridiculously wide with limbs taking off in the direction of the horizon. Looking at some of the structures you can’t help but think that trees have a sense of humor (ok, dreadful piece of anthropomorphizing there, I realise!) or are daring each other to grow further and further out.

Be that as it may…

Frankly, on jobs like this I am just so grateful for having the V-Rig technique in my mental tool box. In my opinion this is the most functional way of working with two anchor points for a number of reasons:

  • low friction
  • load is equalized between the two anchor points
  • mechanical advantage when returning up the limb
  • low lateral forces on the anchor points (unless you are level with and suspended between them)

This technique is known by a number of names, like the M-Rig, as some credit it to Mark Chisholm or the V-Rig, makes more sense to me, as that describes the line of the rope between the two anchor points. The first time I saw this technique demonstrated was by John Hartil in 2002 or thereabouts. Sometimes it’s hard to put a specific name to a technique, the truth being that it’s shown by one person and someone else adopts it, takes it and evolves it further. I am, however a great believer in crediting ideas, as it puts them in a context, it’s not just something that popped up out of the ether, all nicely configured, but rather something that evolved over time with names and stories attached to it.

There came a moment on the job this morning, where I found myself almost horizontal to the two anchor points, waaaaay out in the canopy– over the road – using my lanyard as an extra tie in point. Using one point this would have been a nigh impossible point to reach. Apart from spreading the load to two anchor points, I also find it helpful to be able to balance between two anchor points, as this is inherently more stable than just the one and returning off a long flat limb like this is just so much easier with the mechanical advantage integrated into the system.

V-Rig permitting easy movement back and forth, here to install a bracing system

Key to using this technique (or any technique, come to that), is to have the gear handy. If it’s a major hassle to organise it all, you won’t do it, and believe me, that’s me speaking from experience. On trees like this I will have a compact, adjustable thimble saver stowed on my harness, then all I have to do is to lanyard in, release the swivel on the rope bridge that I have secured to one side with a short sling with a Revolver karabiner on it, install the saver, sling through top hole of the Hitch Climber pulley, catch the high line with the Revolver, attach the whole combo onto the swivel and I’m all set to go. I’m not saying, do it like this, but suggesting that you develop a sequence in which you install gear and rig techniques and they will automatically get easier to use and therefor the decision to employ them so also becomes easier.

For trees like this, I would be stuck without having been introduced to the V-Rig all those years ago, so thanks to John, Mark and whoever else thought this one up. And spread the word, it certainly beats the old karabiner in a sling redirect technique hands down, that much is for sure!

Rigging Hubs

Rigging Hubs resulted out of discussions I described in the Tripple Whammy post the other day.

The aim was to come up with a device that could act an easy interface between metal connectors and textile elements, such as slings or rigging lines. It should provide the possibility of direct attachment with connectors, as well as directly knotting onto it – also it should be possible for the device to accommodate running ropes. As such it needed to have rope friendly radii and surfaces, be tolerant of funky loading and intuitive in use. The result was the two sizes of Rigging Hubs…

The uses we foresaw were initially 2D uses, i.e. in an up/ down and left/ right orientation, whether this is in a rigging application, drifting masses between two anchor points, as a base anchor or as a floating climbing anchor point.

On the way we also came up with some off-beat applications, sure there’s plenty more you can come up with 😉

Increasingly though we had questions regarding 3D use, i.e. horizontal orientation and loading of the Rigging Hubs. Initially we were not able to answer this question, as it had not been tested in that orientation. However, we requested DMM to do the additional tests which demonstrated that the Hubs have an ample breaking strain in that orientation and consequently ended up with even more uses.

This process resulted in a super-strong, super-versatile piece of kit that has many uses and, looking back, I wish I had had for a number of technical rigging jobs, as it makes your life so much easier when inter-connecting hardware and textiles.

Tripple Whammy

I was thinking yesterday about how your mental focus evolves over time and about how you collect mental cornerstones on the way that you construct a foundation around, that you then base your thoughts and assumptions on. Sometimes these aspects of focus may be expressed in key words or terms.

It’s one of the things that always strikes me when watching an Arbormaster presentation, is how this is something that they are really good at, clearly identifying key words and then hammering them home. As a spectator this makes it easy for me to follow the red thread of a presentation and it also gives me a nugget of information that I may choose to take home with me.

For us, when we were launching into what was to become treemagineers, configuration was such a key word. A lot of the issues that Chris and I would discuss during work revolved around how we use PPE (Personal Protective Equipment) components and how we assemble them into systems. Our impression was that if we could ensure correct configuration, the rest would follow. Configuration became a key word that we would use to communicate our point, to identify issues, i.e. misconfigurations, but also the solution, i.e. correct configuration. The friction hitch based work positioning system built around the Hitch Climber pulley was the result out of this process.

Hitch Climber pulley
Hitch Climber pulley

It incorporated a number of novel concepts, such as:

  • system split into two karabiners, one on top of the Hitch Climber to attach the splice into, the other on the bottom to attach the eye to eye sling onto. This set up reduces the amount of sit-back when ascending and also eliminates three-way loading when work positioning on large stems, …
  • correct alignment of connectors: All connectors are loaded along the major axis, as they were designed to be. Also the points of loading are close to the 12mm pins used in the certification process. This ensures performance in line with the MBS indicated by the manufacturer, and finally…
  • rope friendly interfaces: the chosen manufacturing process, hot forging, allowed the Hitch Climber to be designed with flowing, rounded surfaces that are inherently rope-friendly.

These points, in our opinion, encourage and aid the end user to consider correct configuration of his or her equipment.

In time though we came to realise there was another, important point to be taken into consideration, compatibility. It is important not just to ensure that components are well configured, but also that neighboring elements are mutually compatible with each other. These discussions  led to a series of tests a couple of years ago examining the compatibility between ascenders, ropes and lanyards. Compatibility issues can be very complex and challenging to resolve if no guidance is provided by the manufacturers. One output out of these discussions was the presentation Good Choices, Poor Choices – Discrete performance loss, accumulated performance loss and assembling fall protection systems with confidence.

Ascender configuration comparison
Ascender configuration comparison

The third term that forms this tripple whammy is resilience. Here is what the Oxford Dictionary of English has to say on the topic:

Pronunciation: /rɪˈzɪlɪəns /

The ability of a substance or object to spring back into shape; elasticity

This is obviously the missing element when considering system design: You want your system to have the ability to return to its original form after having been loaded, regardless of whether it is a karabiner, a harness, a rigging or a climbing system. In a past blog post I described the high cycle testing we did some years back. Essentially that was assessing the resilience of the material used to manufacture the eye to eye slings under low load and high cycles. Or the testing we did last week in Dunkeld, which was – amongst other things – to take a closer look at the resilience of rigging systems used in tree care.

Resilience can be the result of design, materials or the manufacturing process – or a combination of the above, however it is not something superficial or something that can be added on as an afterthought: Resilience ought to be a key consideration and objective that runs through and permeates the whole design and manufacturing process – pretty styling of a fragile assembly or system is not an acceptable substitute for resilience.

So if you asked me today what I feel key requirements are that we should be making of our PPE assemblies and systems, I would answer you that they shall be well configured, mutually compatible and resilient. If these three points are taken into account I believe that we are on a viable path towards ensuring good system design.

In case you had ever wondered…

Remembered this, made me smile at the time… It was a response to a query on Treebuzz, where someone was asking where he could get hold of some of the material the treeMOTION is made of, seemingly to make his own DIY version of it – ask a question and you will get an answer.

The manufacturers of the harness have finally allowed me to disclose for the first time in public here on Tree Buzz what the base material of the treeMOTION is made of:

It is in fact made of the hide of the exceedingly rare and rather vicious hippogriff.


Today these can only be found in a remote part of eastern Rumania in the foothills of the Carpathians, where for many centuries the Comaneci-Georghiou family have bred them for their hides, as well as for substances made from their apocrine sweat glands used in the preparation of traditional Ayurvedic medicines. In the middle ages hippogriff hides were used when manufacturing suits of armor for the under armor garment, being amazingly tough in relation to their weight, on a par with modern high-tech fibres such as Kevlar etc.

For many years this traditional material was forgotten, but has in recent years experienced a resurgence in a range of uses, for example for the airbags in the Rumanian-built Renault-owned Dacia cars, bullet proof vests for the Rumanian SWAT teams etc.
For us this material seemed an obvious choice, but be warned, it is fiendishly hard to get hold of.

There, now you know, but keep it to yourselves!



Article on testing of damage to synthetic fibres

At the Climbers’ Forum in Augsburg Angela Sipos from Teufelberger presented some preliminary results of on-going testing that they are doing regarding various types of damage to synthetic fibres, such as abrasion, heat, exposure to various chemicals, UV exposure etc.

Rope failure due to overload
Rope failure due to overload

Here is a summary of the findings that she and her colleague presented.

Obviously, it’s in German, but Angela will be attending the NZ arb conference in Rotorua in October and will be presenting these results there.

As I understand it, these tests were intended to establish a baseline in quite general terms, the plan is to continue these tests and taylor the types of damage to be more specific to what might be encountered in tree care.

Final day of testing

Today concludes a week of rigging testing in the Highlands – and what a week it was!

As I wrote earlier this week, it’s much to early to even consider communicating any conclusions or wisdom in regards to what we were testing, however these days have certainly given us much to think about and discuss – not to mention 120GB of video and photo footage.

I would like to use this opportunity to mention how thoroughly annoying GoPros can be. Not just because of the weeks worth of wobbly, uncut helmet cam footage (that always makes me feel rather nauseous and bores me  to tears after about fifteen seconds) we are bombarded with via Youtube  and the likes, but mainly because they are soooo temperamental, which is not ideal if you have four cams dotted around the site fifteen meters up trees. Still, minimum one was working all the time.

We feel strongly that it is essential to continue building on the insights gained through research such as the HSE and Forestry Commission Rigging Research, or work done by people such as Andreas Detter or Peter Donzelli to increase our understanding  in regards to the ways in which we work and techniques that we employ, and where possible to identify ways in which we can make them safer, more ergonomic and/ or more efficient. Hopefully in the future weeks and days such as this past one will contribute something towards these goals.

We had the privilege of having a fantastic team working with us, as that is always the thing that makes or breaks this kind of enterprise. So big thanks to Jon Turnbull, Henk Morgans and Georg Schwenteck for helping to work through a really very demanding schedule – and of course to Chris for making this all happen in the first place.

Day three of testing

Day three, what can I say?

Fantastic weather and big forces sums it up. Best explained with some pictures…

Things get heavy

Wow! That was an interesting day yesterday. And it was only day two of the week, wonder what more is going to come to light.

Don’t expect any quick statements regarding the testing. The temptation of course is to rush out to share snippets of information, but the truth is when it comes to rigging, caution may be advisable when attempting to express generic guide lines. Rigging is complex. Many factors come into play, that will influence the way the machine you have built into the tree behaves – and that is one of the things we are trying to improve our understanding on.

So the next steps will be mulling over the data, evaluating all of the video and photographic footage and trying to formulate coherent conclusions that are of use in the field. The problem is not lack of data, but the sheer volume of it, and this will only increase by the end of the week.

Bit of rain over night, cleared now, so it looks like we’re good for today, which is fantastic as it means we can press on…