Tri-Axial Loading a Carabiner: Is it safe for slacklining?

First Things First…What Is Tri-Axial Loading?

I recently posted an instructional video on how to set up a Yogaslackers E-line kit. In this tutorial I tri-axial loaded a carabiner at one anchor point. Let’s talk a bit more about that, including what it means and the safety implications involved with this rigging technique.

What does Tri-axial loading a carabiner mean? The quick answer is, you have 3 points of connection on a loaded carabiner (under tension) instead of two, hence the “Tri”.

For example, you take an anchor sling or span set and wrap it around a tree. You connect the span set together with a carabiner. Then rotate the carabiner so the top of the gate opening is facing away from the tree. (This forces the span set or anchor ends to be on one side of the carabiner.) Next, you connect your slackline to the other side of the carabiner. This creates 3 points (the two anchor end points and the slackline point) that when tensioned, results in a tri-axial loaded carabiner. See photo below.

example of tri-axial loading

The Carabiner Basics…

Let’s start by saying there are many styles and shapes of carabiners out there. Many get used for a variety of hobbies and work-related reasons. Each one, according to its size, shape, and type of metal, has ratings for load strength. The back portion of the carabiner or the spine (opposite of the gate side) is the strongest part of the carabiner. The spines designed to support the majority of the load, when loaded from two points. Particularly when the two points are connected to the top and bottom curved edges of the carabiner (the elbows) closest to the spine edge. This is the ideal configuration to use on a carabiner.

There are 3 ways manufactures typically measure carabiner strength. Major axis strength, gate open strength, and minor axis strength. Major axis is along the spine, like I described above. Gate open means loaded from two points (the elbows) while the gate is literally open. Minor axis is when the carabiner’s load is pulling on the long sides of the carabiner. This means the gate is under force, making it the weakest configuration to use on a carabiner.

Diagram of carabiner strengths Source- https://www.blackdiamondequipment.com

 

 

Is Tri-axial Loading Safe For Short, Low Tension Slacklines?

I want to be clear, I support carabiners being used in accordance with manufactures specifications. And as far as I can find, no manufactures say try-axial loading is okay! I am curious about tri-axial loading and slacklining. Specifically with short, low tension lines (such as the E-line) and with oval carabiners. Over time I have experienced and researched the use of tri-axial loading within the forest service industry, slacklining, towing cars, climbing, circus, and even in the construction and heavy equipment moving industries. It doesn’t mean any of this is okay or correct.

However, there are some clear examples of break tests that have been done on tri-axial loaded carabiners and they performed pretty good. I have a couple resources for you to look over. Both these links have great information in them, some of which show results from tri-axial loading. Check them out…

Once you’ve explored them, let me know what you think about it. Leave a comment below!

The break test with tri-axial loading on D shaped carabiners, did not perform as well as the oval carabiners did. When tri-axial loaded, they could lose up to 50% of their rated load strength. Oval carabiners hardly lost any breaking strength. Hence, my curiosity about the oval carabiner!

Some tri-axial load break strength test results. Source https://www.blackdiamondequipment.com

I Want To See More Data!

The fact is, improper use of carabiners can be risky and cause serious injury, damage or death. Here is one example from a very scary circus incident. The primary cause seemed to be improper use of a carabiner. Check out the link for more information.

Failed carabiner from the circus incident. Source: www.osha.gov

What I really want to know is…

Can a slackliner create enough force playing on a tri-axial loaded carabiner, on a 40 foot low tension garden line (not tricklining), to actually break the carabiner?

I know many slackers who have tri-axial loaded for years, myself included. I’ve only heard about a carabiner failing a couple times. One time, the gate wasn’t locked which mis-shaped the carabiner. The second time, the carabiner was under high tension on a longline setup. The non-locked carabiner was me. (Whoops, live and learn.)  But seriously, I’ve never heard of an oval carabiner failing during use, while tri-axial loaded on a short, low tension line. Have you?  If so, I want to hear about it. Do you have any data to share? Send me a message or an email if you do.

I want more data before I can make a definitive conclusion whether it’s safe to tri-axial load steel or aluminum oval carabiners. Data that specifically relates to short, low tension slacklines.

 

Let’s Learn Together

I had a friend reach out to me about the video I mentioned in the beginning of this blog, shedding light on the recent discussion surrounding the use of tri-axial loaded anchors. I am grateful for it, because it inspired me to scour the internet for info and data on this subject. (You can browse a bunch of links I found below.) It’s helping me stay up-to-date on current safety protocol, as well further explore how these standards apply to the world of slacklining.

I scrolled through one online feed that cited movement studies in which the slackline did damage to carabiners. Another feed discussed the average force generated from a slackliner on a short line, which apparently was less than 4Kn. (The average carabiner is rated around 20Kn, when used along the major axis.) That’s way below the break point of most standard carabiners, even when tri-axial loaded.

Let’s be real, there is always room to learn new things. Learning about carabiner safety and questioning how it applies to specific activities is a good way to find clarity. If you have conducted any test that can be applied to this conversation, please share. Or if you have any fancy rigging tricks and techniques you want to share, we would like to hear about it. Everyone’s experience is valid. I’m particularly curious about tri-axial loaded aluminum oval carabiners break strength tests.

Who has the equipment and wants to play?

 

The Study Continues

Here’s a fun picture I came across in my research, that said this is an example of how to tie your anchor sling to prevent tri-axial loading…any thoughts?

This is presented as an option to eliminate tri-axial loading. http://blog.alpineinstitute.com/2016/07/triaxial-loading-on-trees.html

My question for this picture: Does the twist and the knot compromise the strength of the sling?

As far as my previously published tutorial video is concerned, I am going to leave it up for now…BUT…I recommend that tri-axial loading ONLY be used on short, low tension lines. As soon as I can complete more tests, or locate data from other experiments, I will release an update on this subject matter. Please join me in this discussion, because every bit of data could be useful. The study continues…

 

Peace,

Buddy Thomas

 

In addition to those listed above, here are some additional resources I used for this blog:

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