Figure-8 Device Blocks for Canyoning 2021
Catching up with another canyoner recently they showed me a failure method for a particular Releasable Figure-8 Device Block (Releasable-8 Block) used as a setup for abseiling in a canyon.
This block is called Releasable-8 Block V1 (for reference purposes) – above left and middle. It’s worth noting that rigged correctly and threaded through a small ring, rapide or chain, the V1 block works well and does its intended job.
As a backup, you can use a carabiner on the small hole (minimum) – above the left. Alternatively, a quickdraw is attached to protect against accidentally abseiling on the wrong rope until the final canyoner – above middle.
The problem is if you accidentally or incorrectly clipped the Releasable-8 Block V1 by the small ring of the figure-8 device, with body weight, it would fail, and you would head downwards quickly – above right.
This issue is a lack of understanding of the purpose of a Releasable-8 Block. Once loaded, you need to be able to release it. So the incorrect rigging loads the figure-8; you cannot drop a loop and lower the load.
‘But this would never happen’ I hear you saying.
The reason for this article and testing is there was a near miss. Someone rigged the Releasable-8 Block V1, incorrectly clipped the small hole directly into the anchor, and luckily had a short free fall into a deep pool.
Goals of the testing
This near-miss prompted me to test various versions (and failure methods) of the Releasable-8 Block compared to other baseline methods.
- Releasable-8 block – normal loading
- Releasable-8 block forwards load small eye clipped – if you accidentally clipped the small eye into the anchor, load the block during the abseil.
- Releasable-8 Block backwards load small eye clipped, e.g. when there is a quickdraw backup – if you accidentally abseiled on the wrong rope, the one coming out of the bag.
- Figure-8 knot on a bight – as a baseline
- Munter Mule overhand – as a baseline for an alternative releasable system
- Biner block – as a baseline for a non-releasable block
(Reference material for this section: Canyoning Technical Manual)
Releasable systems (contingency anchors)
It is essential to have a pre-rigged lowering set up to release the abseil line in many canyoning situations.
Make sure you have enough rope left at the anchor to lower the person to the bottom, i.e. at least the length of the pitch.
When the pitch is longer than half the rope, you need to join another and set up for a big pitch. To have a releasable system, you need to either rig on the topside of the bend or be prepared to pass a bend.
A releasable system is an active risk management tool used for:
- When the abseiler has jammed their descender, clothing or hair, the system needs to be lowered – however, in other circumstances, such as a foot entrapment or being stuck behind a waterfall, lowering the abseiler could worsen the situation.
- While a canyoner is abseiling, managing sharp edges by lowering the rope very slowly, ‘bleeding the rope’. This lowering spreads any wear over a larger surface area. Re-setting the rope length between each canyoner is needed.
- While the first canyoner is abseiling, set the length by lowering the rope.
The method uses a tied off figure-8 abseil device as a releasable block. It is ideal for lower anchors as the block is directly on the anchor ring. Very little re-rigging is needed for the last canyoner down. You need a spare (second) figure-8 device on your harness.
Munter mule overhand (Italian hitch tied off)
The Munter is a releasable abseil method tied off with a Mule and finished with a carabiner or overhand knot. Ideally, the Munter mule needs to be used on a higher anchor as the method takes more space than the releasable-8 block.
Non-releasable systems are fast and efficient methods to rig either smaller dry pitches or for the last person down.
As these systems cannot be released, rescue is much more difficult. For example, to lower someone from a biner block, you need to: apply a small raising system or counterbalance, remove the block and transfer the load to a lowering system.
Before using a non-releasable system, consider the pitch hazards and the experience of the canyoners. Sharp edges are more difficult to manage as the rope is fixed during an abseil. The two strands or stone knot abseil is a suitable solution as it shares any wear over two ropes.
A biner block is a fast and efficient method of rigging smaller dry pitches. This method is standard for the last canyoner (pitch leader) with the Munter Mule. The biner block cannot be released, meaning rescue is more complicated. Only deploy the rope you need out of the pack. Use with caution on sharp edges due to the single fixed strand.
Slow pull tests
- As each test destroyed the rope, it was new for every test.
- Carabiners and rapides, where they were undamaged, were reused for multiple tests.
- All knots and hitches had hand tension with all strands pulled tight.
- Each testing series records the slow pull tests set up (see Appendix 1-2).
The slow pull testing was in one location.
- Aspiring Safety, 1/6 Burdale Street, Riccarton, Christchurch, New Zealand.
- Vertical testbed 1.6m Electronic Universal Testing Machine, Model WDW-50
- Maximum Test Force 50kN, sample rate 60 per second
- Jinan Chuanbai Instrument Equipment Co Ltd
Practical use testing
- Practical use testing (lowering) occurred at Over the Edge Rescue, 55 Mckenzie Street, Geraldine, New Zealand. https://overtheedgerescue.com
- 80kg test mass contained in a 70 litre PVC bag (Aspiring Safety) filled with four bags of 20kgs of gravel. The test mass is secured into each bag so it can’t shift during testing.
Petzl Huit – Figure-8 device
- Material(s): aluminum
- Weight: 100 g
- Rope compatibility: 8 to 13 mm (single and half ropes)
- Working load limit: 100 kg
Korda’s Dana 10 – Rope
- Manufactured by: Korda’s (https://www.sacidkordas.com/en/producte/dana-10/)
- Type: Canyons rope semi-static A
- Diameter: 10 mm
- Weight: 68 g/m
- Breaking strength: 27.80 kN
- Static elongation: 2.7% (150kgs)
- Core proportion: 61%
- Sheath proportion: 39%
- Materials: Core/Sheath – Nylon/ Nylon
- Standards: EN 1891:1998, type A
Korda’s Dana 9 – Rope
- Manufactured by: Korda’s (https://www.sacidkordas.com/en/producte/dana-9/)
- Type: Canyons rope semi-static B
- Diameter: 9 mm
- Weight: 54 g/m
- Breaking strength: 22.20 kN
- Static elongation: 3.8% (150kgs)
- Core proportion: 58%
- Sheath proportion: 42%
- Materials: Core/Sheath – Nylon/Nylon
- Standards: EN 1891:1998, type B
Figure-8 on a bight knot (control)
- Figure 8 on a bight – 9 and 10mm rope.
Munter Mule Overhand
- Munter Mule Overhand – 9 and 10mm rope.
- Clove hitch – 9 and 10mm rope.
Figure-8 Block V1
- Figure-8 Block V1 – 10mm rope.
- Figure-8 Block V1 load forward small eye clipped – 10mm rope
Figure-8 Block V2
- Figure-8 Block V2 through an 8mm rapide -10mm rope
Figure-8 Block V3
- Figure-8 Block V3 through an 8mm rapide – 9 and 10mm rope
- Figure-8 Block V3 load forward small eye clipped – 9 and 10mm rope
- Figure-8 Block V3 load backward small eye clipped – 9 and 10mm rope
Figure-8 Block Mule Overhand (MO)
- Figure-8 Block MO through an 8mm rapide – 9 and 10mm
- Figure-8 Block MO load forward small eye clipped – 9 and 10mm rope
- Figure-8 Block MO load backward small eye clipped – 9 and 10mm rope
Note: for information about how to tie the variations see the testing report at the end of the post and the video below.
Slow Pull Test Results
Kordas Dana 10mm Semi-static rope
Slow pull tests (100mm/minute)
|Items tested||Avg. kN||%||# Tests||Comment|
|Figure-8 on a bight knot||19.53||70||5||Broke at the knot|
|Munter mule overhand||15.35||55||3||Broke at the 12mm carabiner|
|Biner block||16.31||59||3||Broke at the 8mm rapide|
|Figure-8 device block V1||16.17||58||3||Broke at the 8mm rapide|
|Figure-8 device block V1 forward load small eye clipped||1.29||5||3||First Slip 0.88kN, kept on slipping|
|Figure-8 device block V2||3.56||13||3||First slip 3.08kN, kept on slipping|
|Figure-8 device block V3||16.12||58||3||Broke at the 8mm rapide|
|Figure-8 device block V3 forward load small eye clipped||3.95||14||3||First slip 2.43kN, kept on slipping|
|Figure-8 device block V3 backwards load small eye clipped||22.64||81||3||Broke at the Figure-8 device|
|Figure-8 device block mule overhand (MO)||16.58||60||3||First slip 10.13kN, MO unwound from the Fig-8 360 degrees. Broke at the 8mm rapide|
|Figure-8 device MO forward load small eye clipped||19.07||69||3||First slip 4.59kN, MO unwound from the Fig-8 720 degrees. Broke at one side of the fig-8 device|
|Figure-8 device block MO backwards load small eye clipped||7.70||28||3||First slip 7.44kN, kept on slipping, the overhand bight started to get pulled through and get smaller|
Kordas Dana 9mm Semi-static rope
Slow pull tests (100mm/minute)
|Items tested||Avg. kN||%||# Tests||Comment|
|Figure-8 on a bight knot||15.95||72||5||Broke at the knot|
|Munter mule overhand||12.98||58||3||Broke at the 12mm carabiner|
|Biner block||13.82||59||3||Broke at the 8mm rapide|
|Figure-8 device block V3||7.59||35||3||Kept on slipping|
|Figure-8 device block V3 forward load small eye clipped||2.98||13||3||Kept on slipping|
|Figure-8 device block V3 backwards load small eye clipped||19.08||86||3||Broke at the rope clamp (1), and figure-8 device (2)|
|Figure-8 device block MO||13.2||59||3||First slip 5.14kN, MO unwound from the Fig-8 360 degrees. Broke at the 8mm rapide|
|Figure-8 device MO forward load small eye clipped||16.87||76||3||First slip 2.06kN, MO unwound from the Fig-8 720 degrees. Broke at one side of the fig-8 device|
|Figure-8 device block MO backwards load small eye clipped||7.12||32||3||First slip 5.92kN, kept on slipping, the overhand bight started to get pulled through and get smaller|
Note: for analysis of the slow pull testing see the report at the end.
Now that we have established the figure-8 block V3 and figure-8 block mule overhand is suitable, we compared and contrasted how easy they are to use in reality. I have compared this to tying Munter Mule Overhand and biner block to make this relevant.
Initially tie – covert to lower – reinstate to tied off – convert to retrieve
- The gear taken from the harness is in time when initially tying
- Fig-8 blocks completed with a quick draw backup with carabiners closed
- The tying method is correctly DRESSED when finished
- Lowering setup rope charged with 5kg
- Time is the average of 3 attempts in seconds
- Each attempt is made smoothly at NORMAL speed
(Note: I didn’t set out to undertake the method as quickly as possible. I undertook a smooth speed that was not rushed (NORMAL) with a high-quality result (DRESSED), so I could consistently compare methods.)
- Done on flat ground with an anchor at head height with 9mm rope
|Type tested||Time to tie initially (sec)||Time to convert to lower (sec)||Time to reinstate to tied off (sec)||Time to convert to retrieve (sec)|
|Figure-8 device block V3||19||10||14||5 (quickdraw)|
|Figure-8 device block MO||33||9||26||6 (quickdraw)|
|Munter mule overhand||23||9||12||25 (biner block)|
|16 (biner block preloaded)|
|13 (to double rope)|
Note: for analysis of the efficiency tests see the report at the end.
Convert to lower – lower the load – reinstate to tied off
- Figure-8 block versions (V3 and MO) and Munter Mule Overhand (MMO) were tied in both 9mm and 10mm rope.
- An 80kg load was lowered onto the Figure-8 blocks and MMO.
- The anchor was a free hanging 8mm oval rapide.
- The Figure-8 blocks and MMO untied and lowered then retied a minimum of 2 times over a 10m lower.
Figure-8 device block V3
Figure-8 device block MO
Munter mule overhand
Note: for analysis of the practical use see the report at the end.
Figure-8 device blocks
- From a slow pull testing point of view, only two figure-8 blocks performed to a satisfactory level: Figure-8 block V3 and Figure-8 mule overhand (MO).
- When you consider time to tie initially, convert to lower, reinstate to tied off and convert to retrieve, there was very little in it. Not enough to argue one way or the other.
- When you convert to lower, lower the load and retie when loaded; both blocks performed well in 10mm rope. However, the mule overhand version in 9mm was more challenging to reinstate to tied off while this was easy in the V3. Also, there was noticeable twisting observed when lowering.
- Considering all the things we have learned, we recommend both the V3 and MO figure-8 device blocks for 9mm and 10mm ropes.
Munter mule overhand and biner block
- From a slow pull testing point of view, the Munter Mule Overhand (MMO) and biner block performed to a satisfactory level.
- When you consider time to tie initially, convert to lower, reinstate to tied off and convert to retrieve, there was very little in it compared to the figure-8 blocks. Not enough to argue one way or the other.
- When you convert to lower, lower the load and retie when loaded, the MMO performed well in both 9 and 10mm ropes. Also, there was no noticeable twisting observed when lowering.
- Considering all the things we have learned, we recommend the MMO and biner block for 9mm and 10mm ropes.
- We set out to test various versions (and failure methods) of the figure-8 block compared to other baseline methods. We went quite a long way down the rabbit hole, but out the end came an understanding of the tools we use and how they perform.
- There are many canyoners using the Figure-8 device block as they find it easier to tie, and it’s quick to transition from abseil to retrieval modes.
- The Munter Mule Overhand (MMO) is ideal for situations where you need to lower and then reset the rope. For aquatic canyons, especially with sharp edges, this is our go-to method. The MMO easily converts to a biner block. Also, from time to time, for the last person down, we use double rope for sharp edge management or tricky retrievals where we want a clean rope. Converting the MMO to a double rope is straightforward.
- In the end, both the figure-8 device block and MMO/biner block are tools in the toolkit to manage risk in the canyon environment. Using both methods and applying them in appropriate places is the recommended approach.