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

I just posted about this recent incident on the Canyoning Australia forum (https://canyoning.org.au/forum/viewtopic.php?f=14&t=284), but figured it was also relevant to US canyoneers.

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.



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).

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.

I've outlined the lessons I took from it here: https://canyoning.org.au/forum/viewtopic.php?f=14&t=284

I'd really appreciate any additional thoughts / lessons regarding this incident.

Question: was the first step in the failure that the sleeve -- under load -- "unscrewed" itself?

I don't believe anyone saw the failure occurring. It was only noticed once it was in that open position with the rope caught on the edge of the sleeve. My assumption is that the screw thread was corroded to such a point that the sleeve simply pulled open, rather than unscrewing.

Thanks for the wake-up call and thank goodness nobody was hurt.

What size quicklink do others recommend? I have a bunch of 6mm oval mallions but am always hesitant to use them. They are rated for 400kg but they just look like a skinny bit of bent wire and don't inspire confidence.

Thanks for the clarification. Of course, all quick links are not created equal. I think your explanation of a corroded screw thread makes sense. If the problem was corrosion, at least that is something that is open to inspection.

Most of my quick links come from Home Depot. I know what people are thinking. I think the "standard" WLL on these is 1540 lbs (or in that neighborhood).

Can you tell us how wide the inside of the delta is?
If the wide part of the triangle were facing down the rope could shift to the sleeve side and un-spin the sleeve
if the rope shifted.
Generally the wide part of deltas are for use with sling of the same width, not rope.
I have not seen deltas used in Southwest canyons.
We all use ovals
Best, Todd

8mm and/or 5/16" in the least for me. I've bought them in bulk in stainless.

I think I posted this before, but, here's some test results from a few years ago from hardware store rapides. The second set tested as "cut through" were cut with bolt cutters at the position that a rope would nest into. In other words, worst case if you were using them as a rappel anchor.

Ultimate Strength of New Rapides on Pins
Rapide Sample Test Config Peak Load (lbf) Failure Mode/Notes
9.1 mm X-section 12 mm pins 7442 Thread shear
8 mm X-section 12 mm pins 7061.7 Thread shear
7 mm X-section

12 mm pins 6754.4 Thread shear
Ultimate Strength of Damaged Rapides or Alternate Configurations
Rapide Sample
Test Config Load (lbf) Failure Mode/Notes
9.1 mm x-section Rapide cut through-12mm pins 1205 Pin pull through cut
9.1 mm x-section Rapide cut through- on rope 740.2 Rope pull through cut
8 mm X-section Rapide cut through-12mm pins 743.7 Pin pull through cut
7 mm X-section Rapide cut through-12mm pins 544.3 Pin pull through cut
7 mm X-section 2nd Test on same piece-Rapide cut through-12mm pins 88.5 Pin pull through cut
8 mm X-section Snap Link Biner on Rope 1950 Key hook pulled thru Nose Key slot
6 mm X-section Tested on Rope 5908 main body failure (not at threads)

I don't really know what a "working load limit" is, but....

People rap off something rated to only 250 kgs? Aren't most biners like 22 kN? That's like 4500 lbs. 250 kg is like 550 lbs.

These Petzl quicklinks are rated to 5500 lbs

https://www.rei.com/product/471288/...MIs-r5tsmC4QIVmYzICh0gQAlpEAQYASABEgLc0PD_BwE

I'm barely willing to rappel off a sandtrap that will only hold 250 kg. No way I'd use hardware rated that low.

Your limit for a sandtrap is about your body weight? I wouldn't call that a "safe working load"...ha ha...

Working Load Limit is the same (or similar) to safe working load or normal working load. What it means is that hardware has a safety factor, typically 5 or 10 to one, applied. So, at a safety factor of 10 to one, you have a more realistic and comparable rating of 10 X 250kg. Or, around 24.5kN. So, nearly the same or more than your carabiner example.

Edit to add, from my data above, a 6mm rapide failed at 5908 lbf. That equates to 26.28kN. Probably some margin in the design of the one that failed...still...troubling info.

That sounds more reasonable.

I've rappeled off many sandtraps that held less than body weight, for better or worse. But the mechanism of failure is never the rapide coming open! The whole thing just goes over the edge. That's what the four testers in front of me are for.

It would be helpful to know what SIZE this triangular Maillon was, but...

A TRIANGULAR Maillon is the not the best tool for this job. We generally use the oval ones, called "Normal" or "N" by Maillon Rapide.

Tom

It was a 6mm delta, galvanized.

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.

6mm == 1/4" which is the smallest size rapid link even bold people would use.

I sell a lot of 7mm galvanized steel, which seems like a good normal-use size.

I suspect someone had a 6mm Delta for some other use, and just used on that rappel.

I also suspect that the test loading of the Delta is probably a point vs. a wide strap; while loading for the rappel was perhaps concentrated across the gate leg.

Tom

Yes to 7mm. No to 6mm. When weight savings is THAT important, you're either exploring or doing non-trade-route canyons, in which a proper aluminum rap ring gets the job done.

Manuals on troubleshooting suggest the highest probability for identification/resolution and then cascade probabilities/resolutions. Applying that model here I would need some convincing that the highest probability and cause for failure - the screw gate was not closed completely - was not the real beginning of this failure scenario. That's at the high end of the probability spectrum with "it unscrewed itself" at the other end.

From the article, "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."

I use a delta maillon on one of my rope climbing systems. I have more than once thought that it was closed when in fact it was only slightly closed, maybe one or two threads worth. It was hand-tight and stopped turning so it seemed like it was closed; that didn't mean it had all-thread-coverage. A spec of grit, worn screw mechanism that starts a cross thread, mud caked inside the screw-gate, being a few reasons one might think its closed when in fact it's not.

And once you bend one of those deltas the probabilities of not securing it properly go up quickly....MO.

Accidents/near misses tend to have an immediate cause and a systemic cause. A Micro and a Macro. This is a good example of that.

Cause A: the maillon opened up while someone was rappelling.
Cause B: the maillon was not fully closed even though someone checked it.
Cause C: the anchor was inspected, but the inspection was not successful in noticing the maillon was not effectively closed.
Cause D: the anchor was inspected, but the inspector did not identify that this maillon was not an appropriate piece of gear for this function.
Cause E: canyoners in this country do not generally use maillons, and thus are not well-versed in the subtleties of maillon use.
Cause F: canyoners in this country do not generally carry maillons to replace inappropriate maillons when they come across it.
Cause G: a poorly-trained canyoner used an inappropriate maillon in this canyon.

I hold that these are all causes of the near miss, and that focusing on one specific cause is misleading.

Tom

in european caving - we have a saying :

" screw down - to avoid screw-ups "

basically - the screw closure on a rigging connector - should be orrientated " down " when loaded

this helps to eliminate a lot of vibration // cyclic induced unscrewing