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.