Using figure 8 descenders on anchors

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Skinner
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Using figure 8 descenders on anchors

Post by Skinner » 30 Jan 2019, 20:18

On the long weekend I went through Serendipity as I wanted a shorter canyon after a big day through Bell Creek the day before. I haven't done that canyon for a very long time. I was surprised to see figure 8 descenders being used to run the rope through at two of the anchors. I haven't seen this before, but I don't often do the more popular routes.
They were set up in a way that they couldn't hit rock and I assume that they were set up by some of the guide companies. The rope certainly ran very smoothly on the pull down, but I was not that comfortable about the use of an alloy device in the anchor that I had no idea of the history (but not enough to change it).
The modern use of steel mallions was a good improvement over rope on sling that used to be used, or rope around trees which was bad for the tree, but I am not sure about the figure 8 descender.
Is this being used in other canyons? Is there a reason for it over a steel mallion which is stronger and cheaper? Does anyone else see any issue?



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T2
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Re: Using figure 8 descenders on anchors

Post by T2 » 31 Jan 2019, 09:12

Mark, you didn't take a photo you can share did you? It'd be good to visualise exactly what you're talking about.

From the sounds of things, they are probably just using old Figure 8s as an alternative to placing a maillon. Although I was wondering if they were installed in such a way that the Figure 8 could actually be used to rig for contingency, allowing people to be lowered if required. Alternatively, if it was a setup to have a fixed top belay in place. Hard to comment too much on the specifics without being able to see exactly what was installed.

Your main question seems to be whether leaving fixed alloy items as part of anchors is a safe practice. Overall, I'd say yes. The lifespan of an alloy item in a canyon will be longer than a traditional steel maillon, due to its better resistance to corrosion. As long as the item is properly rated, you should be confident that it can more than handle the relatively small forces placed on an abseil anchor. There are actually items specifically designed for this purpose (generally referred to as "rap rings") that are little alloy loops that can be used as part of the anchor. One example here: https://www.climbinganchors.com.au/omeg ... c-rap-ring. The benefits are the same as for maillons: reduced wear on the sling, often lower friction that running rope through sling, and they allow for 'biner blocks etc. In countries where single rope techniques are standard (pretty much the rest of the world) they are a common sight. Most rap rings are rated to at least 20kN, which is five times the force put into the system even in a rescue situation where you're picking off an injured abseiler.

Appropriately rated Figure 8 descenders are usually even stronger, so as long as these ones didn't have a ridiculous amount of wear that had cut through the metal (more than a third of the body) I'd be absolutely confident that they were suitable for the task. That said, if you're trying to reduce visual impact, a smaller maillon or rap ring will be a much better option than leaving old descenders at the top of every drop!

Skinner
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Re: Using figure 8 descenders on anchors

Post by Skinner » 01 Feb 2019, 19:13

Thanks Tim.

They were set up like a mallion as far as I could see with the tape passed through the small ring.

My question was not regarding the strength as an anchor, more about the possibility of fracture in alloy, especially figure 8 descenders. Is that still an issue with them? How do I know they weren't dropped onto a rock before being used on the anchor? The advantage of steel is their robustness, disadvantage weight and potential to rust. They are usually pretty cheap as well.

I did notice in an older photo online that figure 8s have been there for a while in a hors in serendipity. I just hadn't come across it before and was wondering if they were used elsewhere and was it something commercial groups like to use. You used to only find slings that you threaded the rope through in canyons. Now you often find a mallion on a sling. In more popular routes a ring bolt or anchor station. I was wondering if other canyons have figure 8s as I hadn't seen that before. I wouldn't like to use them if they had potential to hit rock.

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Re: Using figure 8 descenders on anchors

Post by Kosta » 01 Feb 2019, 20:05

The whole thing about carabiners getting micro-fractures when being dropped is an urban myth. The effect happens with other materials (I think ceramics, or so), but not with alloy. Bjorn researched the topic a while ago: https://fatcanyoners.org/2012/05/05/dropped-carabiners/

His bottom line is, that unless there is clear visual damage, the device can be considered safe.

Skinner
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Re: Using figure 8 descenders on anchors

Post by Skinner » 02 Feb 2019, 09:22

Thanks Kosta. This is why I posted the question, to get some information back.

I have read the article before. Did they test any figure 8s in the test or was it just biners? I remember years ago when working with abseil groups that they would collect all the figure 8s that had been dropped and send them away to X-ray in a batch to see if they had internal cracking.
Something to do with the design of a figure 8 that made them more susceptible to cracking when dropped than a carabiner.
Was this urban myth too? I imagine it could be. Has there been any testing done specifically with figure 8s?
Do we still need to be concerned when a figure 8 is dropped? What are the the commercial groups procedure in this case?

Great to have this forum to ask these questions.

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Re: Using figure 8 descenders on anchors

Post by Flynny » 04 Feb 2019, 18:09

Skinner wrote:
02 Feb 2019, 09:22
T
Something to do with the design of a figure 8 that made them more susceptible to cracking when dropped than a carabiner.
I always thought it was the heating and cooling that descenders went through that added to the issue.

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