Failure of a maillon (quick link) in Blue Mountains canyon

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T2
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Failure of a maillon (quick link) in Blue Mountains canyon

Post by T2 » 14 Mar 2019, 10:52

A couple things to highlight up front. I am writing this based on information from a party member on the relevant trip. I wasn’t there, didn’t see the maillon fail, and haven’t examined it.

The information I have is that the maillon that failed was a Maillon Rapide brand, zinc plated steel Delta (triangular) maillon. The stamped rating confirmed it was 6mm diametre and had a Working Load Limit (WLL) of 250kgs. This is a good brand, rather than a hardware store knock-off, and is a reasonable diametre (I've certainly found much smaller maillons in canyons).

(For anyone unsure of what I'm talking about, there are the little metal screw links often called quicklinks, rapid links, maillons, etc. They are commonly used in canyons to make the pulldown easier, reduce rope wear on the slings, and to allow ‘biner blocks / knot blocks for single rope abseils.)

What happened:

The incident occurred in a sandstone slot canyon in the Blue Mountains that is reasonably well known, but not particularly popular due to its remoteness. There are probably only a few dozen groups that visit it each year. It is popular enough to have fixed anchors (natural anchors with slings and maillons). The group that had this near miss were all experienced canyoners.

The first person in the group checked the anchor and rigged the rope. They said the screw gate was lose but was then tightly closed by hand. The triangular maillon didn’t appear to be misshaped. They descended without incident.

The next member of the party then descended. They also noticed nothing wrong with the maillon before setting off. They were not heavy and did not do anything unusual or shock load the anchor while descending.

As shown in the photo below, the maillon failed catastrophically during this descent. Thankfully the rope caught on the bent arm until the abseiler reached the ground. Had the rope not caught, the person would have suffered a serious fall.
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Lessons:

Given that the maillon that failed was a recognised brand, a reasonable diametre, and being used well within its safe working load, this incident is particularly concerning. It highlights how easily a core component of an abseiling anchor can fail, with potentially catastrophic consequences. Some of the lessons I have taken from this incident include:

1) Always check each anchor. Examine the full length of any tape / webbing to ensure it is satisfactory. Check maillons or other components to ensure they are in reasonable condition, are of an adequate diametre, and are appropriately rated. You are trusting your life to the anchor. Based on appropriate safety margins, I recommend only using 5mm or larger maillons.
2) Maillons, like carabiners, lose the majority of their strength if the gate is open. In the case of a maillon, ensure the gate is screwed firmly shut. Check the screw thread is undamaged (if the thread is worn, the gate will no longer work, resulting in a dramatic loss of strength). If there is any possibility that the maillon is damaged, remove it. Position the maillon in such a way that it screws downwards to close (so can’t work loose).
3) Not all maillons are made equal. Walk into any hardware store and you can find a range of quick links for sale. These are superficially indistinguishable. Most of these are not tested and rated to a level that makes them safe for use as an anchor. If the maillon does not include stamped ratings that indicate an appropriate strength, remove it. Also note that maillons can come in both stainless steel, and zinc-coated versions. Only use stainless steel maillons in moist canyon environments as corrosion can seriously reduce strength. The stainless steel versions are also much stronger than zinc coated maillons. For instance, the 6mm Delta Maillon Rapide in stainless steel has a WLL of 450kgs. The identical zinc coated steel version has a WLL of just 250kgs.
4) Consider using alternatives for fixed anchors, such as rappel rings. These rings are not only stronger than maillons because they don’t have a screw thread / gate that can corrode or be damaged, but they are also made of aluminium alloys, so don’t corrode. Additionally, unlike quick links there are not cheap hardware store knock-offs available, so they are easier to visually check.



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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by hankmoon » 14 Mar 2019, 12:21

Thanks for posting and glad to hear no-one was hurt! A few thoughts/questions:

The first person in the group checked the anchor and rigged the rope. They said the screw gate was lose but was then tightly closed by hand.
Any chance of learning more about the "screw gate was loose" part? Specifically, was "loose" meant to convey "unscrewed," or something else, such as a wobbly nut?
Maillons, like carabiners, lose the majority of their strength if the gate is open.
Carabiners are designed with significant gate-open strength and are so marked and rated. Maillons have no such rating and should be considered to have a gate-open strength of zero.

"You can't beat luck" Whew.

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by T2 » 14 Mar 2019, 12:31

Hank, in relation to the "screw gate was loose" comment, I've confirmed that it was not unscrewed when they came to it (it may have been a half turn unscrewed). Rather, they were conveying that it was not screwed tight or rusted shut. The nut part did not seem wobbly. So it appeared to be properly functioning.

And really good point about the fact that a maillon with an open gate should be considered as having zero strength. Given all this strength then relies on the screw thread keeping the nut closed, any maillon where the thread is damaged, corroded, or unable to be inspected should be considered unsafe and be removed immediately.

And you're spot on about how lucky they were. Could easily have been a much worse outcome!

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by LachlanB » 15 Mar 2019, 09:58

Ack, I think that incident is basically everyone's worst nightmare on rope!

So I'm still scratching my head as to why the maillon failed... It was from a reputable brand and rated, had just been tightened, and had been assessed by two experienced individuals to be functional. At least in the photo, the thread looks to be ok. Something has gone wrong with the gate, but why the catastrophic failure?

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by dyl_jo » 15 Mar 2019, 19:51

In addition to the great suggestions above, I think it's also worth adding that it is highly desirable to back up anchors to test them. For example, for the first person down, they rig up on a single rope attached directly to the anchor in question (sling/maillion/tree/etc), then the other half of the rope (or a separate rope) is used to belay the first abseiler of a totally separate anchor (eg your own sling on the same tree, or an artificial removable anchor like a few cams equalised together, or even a meat anchor!). That way if the "questionable anchor fails, then the first abseiler is protected. And if the questionable anchor passes the test, you can then remove the back up and have the rest of your group descend with more confidence. (and ideally, the back up remains until the "LAPAR": last person at risk. Bonus if the LAPAR is the smallest person in the party! [but ideally they also need to be very competent at self rescue as there is no-one else left at the top]). In this case, it could easily have saved a life.

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by hankmoon » 16 Mar 2019, 13:19

Maillon Rapide info from http://peguet.fr

Galvanized maillons: WWL / BL (kg) / weight (g)

6mm std oval: 400 / 2000 / 35
7mm std oval: 550 / 2750 / 51
6mm delta: 250 / 1250 / 39
7mm delta: 400 / 2000 / 58

A 6mm std. oval provides 60% greater strength than a 6mm delta, at a lower weight. Why choose a delta? Maybe to handle fatter ropes? Personally I'm a fan of the strength : weight ratio on the 7mm std. ovals. I see no advantage to the 6mm size; when weight is that important, e.g. explorations or remote canyons, I like T2's suggestion to use aluminum rap rings. I carry a few of the SMC rings (11g) in my bag on most trips.

Questions: Was the maillon saved? If so can a better photo be posted of the threads, including the nut threads? I'm wondering whether the threads show damage or defect. If not, how did it fail?

Anyone know the length of the drop where this happened?

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by T2 » 18 Mar 2019, 13:18

I've been sent some further photos of the maillon in question.

The first shows the maillon immediately after it failed. You can see that the rope has been caught on the nut, while the sling has caught on the bent end near the thread.

The following three photos are close-ups of the nut and screw threads at either end. While there is a mild amount of corrosion on the outside, the nut and thread appear to be in good condition. This seems to confirm that the failure was not due to the nut coming undone. As others have stated, a maillon has no rated strength in the open position. This confirms how violently a maillon can fail if the nut is not firmly shut.
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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by Kosta » 18 Mar 2019, 13:51

What is the part that actually failed? I mean, there must be some damage for it to come undone. If the threads on both ends and in the nut are still in working order it looks more like the maillon wasn't closed or the nut was tuned to open open for whatever reason... - or am I missing something?

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by T2 » 18 Mar 2019, 14:33

Kosta, those photos make clear that the screw thread / nut appear to be in good working order, so the failure was not caused there.

The description I was originally given was that when rigging the abseil, the first person found the nut was loosely closed (i.e. it could be screwed and unscrewed by hand). The first person finger tightened it.

There are a couple factors here that may have contributed to the failure. Firstly, it is almost impossible to tighten a maillon appropriately by hand. Given this, it is fair to assume that the nut was not tightened to manufacturer specifications at the time it failed. Secondly, the nut was opening in a downward direction. Given it was only tightened by hand, it is possible the rope rubbing against the nut or just vibration caused by the abseil shook the nut loose. Once the nut came undone, the maillon failed, which demonstrates why maillons have no rated strength in the open position.

Below are the recommendations from the website of Peguet, the manufacturer of Maillon Rapide. You'll probably have a better idea of the force that can be applied, but it seems a small shifter / wrench would be needed to apply the appropriate tightening torque.
Recommendation
  • Consider breaking load limit in kN engraved to the rod.
  • Visual check of complete nut screwing compulsory; no thread must be showing.
  • Maillon Rapide quick links are only to be loaded along the major axis.
  • Maillon Rapide quick links should be carefully checked at regular intervals. If you are in any doubt about the safety of a quick link after checking, replace it with a new one.
  • When fastened with a wrench up to the proper tightening torque, Maillon Rapide quick links are considered a permanent connector.
Tightening torque (Newton metres)
The tightening torque required for a maillon of the following diameters is:
6mm -- 1.20 Nm
7mm -- 2.5 Nm
8mm -- 3 Nm

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by Vertical_Wookiee » 19 Mar 2019, 06:20

If it was closed at all, and bent this much when it was open, the tension at the thread would have kept it closed even if it was only finger tight.

I'm absolutely sure this falls in to user error.

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by Flynny » 19 Mar 2019, 15:37

For what it is worth myself and 2 friends used that maillon the week before. We each checked it and noticed nothing wrong. We replaced several anchors that trip but none of us felt the need to replace that one..... Kinda scary

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by Flynny » 19 Mar 2019, 15:49

T2 wrote:
18 Mar 2019, 14:33
Firstly, it is almost impossible to tighten a maillon appropriately by hand. Given this, it is fair to assume that the nut was not tightened to manufacturer specifications at the time it failed.
Torquing it to spec does not add strength, it just prevents the nut undoing.

I'd be speculating but most likely possibilities

It's possible that movement/vibration/jolting on the rope may have caused it to undo. This can happen even if the nut opens upwards, though that is less likely get the right frequency of vibration and up she goes

or

The last person to check opened it instead of closed it? Easy to do when you are excited/nervous/fatigued/distracted

Or

The rope was payed out during or between abseils and rubbed on the nut pulling it around as it went

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by Skinner » 19 Mar 2019, 18:01

Thanks T2 for sharing this. A bit scary and it will make me be even more careful when checking quick links. I don’t always have a shifter, but will make sure I do.
Can’t see that it did this if was done up well.
Maybe someone needs to do some testing to try to replicate what could have happened. It would be good to find out how much it being done up contributes to strength. Perhaps the manufacturers have some data on this, but it would be good to test ones that have been in the field.

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by tom_brennan » 20 Mar 2019, 08:24

Prior to 2005, in canyons around Sydney we almost exclusively abseiled directly off the tape or rope anchor. This had been the case for some 40-50 years.

It was only around 2005 that maillons ("quick links") started appearing in the Blue Mountains. There may have been a few odd ones here and there prior to that. It probably took another 2-3 years for them to become prevalent in all of the common canyons.

Initially I avoided using them, mainly because I thought they were unnecessary. They were an additional point of failure. It was also quicker to pass a handful of coils through the sling for short drops.

It was some years before I eventually succumbed and started using the maillons regularly. But it is a sobering reminder that just because they're solid metal, doesn't mean they can't fail.

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by DaveJones » 20 Mar 2019, 18:22

WOAH!
I'm probably largely responsible for the 2005ish increase in quicklinks (Maillons) because I started the "Great Quicklink Experiment" on the old OzCanyons forum, not only placing some myself, but also encouraging others to place them which they did. The idea was to see if:
a) People would use them
and
b) The die hards would steal them (some did)

Surely the triangular ones aren't going to be as strong as the straight ones?
The 6mm maillion is rated for 400kg with 2000kg breaking.

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Re: Failure of a maillon (quick link) in Blue Mountains canyon

Post by T2 » 10 Oct 2019, 18:09

This incident really made me stop and think about the use of maillons / quicklinks, and whether there were better alternatives available.

There are a number of concerns, including the vastly different strength and construction of items that look superficially similar. I don't think most canyoners could tell the difference between an appropriately rated maillon used in industrial and climbing settings, and some cheap quicklink with no rated strength from Bunnings. Even when the quality item can be identified, I think many groups would fail to inspect the thread and ensure the nut was fully tightened.

I think rigging rings provide a superior outcome for a number of reasons. Firstly, being a solid ring, there is no gate or nut that can pose a potential point of failure. Appropriate rings are also clearly marked with their rated strength, making it easy for future canyoners to inspect the anchor and assess its safety. Quality ones are also incredibly strong (stronger than a carabiner). The ability to safely load them in three directions -- if it's a central component between two equalised anchors -- is another plus. But best of all, the safety inspection simply requires looking at the ring and confirming there isn't excessive wear (like you would a 'biner), so no special skills, knowledge, or equipment required. As a component that is designed for rigging uses, it's also well suited to being used as part of a releasable anchor system, as part of a haul or lowering system, and in a myriad of other ways.

Given all that, I looked around for an optimal product that would be strong, hard wearing, yet light and compact enough that people would actually carry them and replace anchors as needed. The strongest aluminium ring on the market is made in the USA by SMC (https://www.canyongear.com.au/product/smc-rigging-ring/). By bringing them over in bulk, they actually work out cheaper that maillons, but with a range of advantages.

In the coming months, I'm going to donate a bunch of them and ask for volunteers to update anchors in a number of Blue Mountains canyons, particularly those that are lesser visited and contain lots of rusty old maillons of unknown origins or strength. Get in touch if you're interested and I'll let you know once I'm ready to go with it.
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