How much friction for your device?
We were interested to know how much a lowering device can hold for rescue in particular and personal use.
The testing is for practical use when out on a rescue, training or instructing a group about how much it can hold in relation to:
- the particular device
- the friction range minimum and maximum
- for the friction setting mode
The keyword to think about here is ‘guide.’ We can’t give a definitive number and say that’s what your device will hold. Influences on friction include:
- the actual load
- grip strength of the person
- environmental conditions (wet, cold, dirt)
- new/old rope, size/type of rope, and
- contact with the terrain, such as edge protection and pulleys.
It’s a place to start and then adjust as necessary.
Context
We are looking at non-mechanical devices used for backcountry applications, including canyoning, caving, alpine, and rock climbing. For comparison, we have tested a lightweight rope rescue lowering device and the Munter/Italian Hitch.
We have successfully used a 9.5-10mm rope for several years in rescue. We can use standard equipment and operate with two tensioned ropes or a single rope, which is suitable based on testing.
What do we want to know?
Friction testing the device (or hitch) involves:
- Testing multiple friction settings from low to high, including standard and redirected in a carabiner.
- Testing the minimum and maximum for each friction setting:
- The minimum is the thumb and finger holding the rope.
- The maximum is one gloved hand gripping onto the rope.
Materials used
Lowering devices
- Conterra Scarab (rescue lowering device)
- Aspiring Brakebar Rack (caving descent device)
- Petzl Huit (figure-8 style device used in canyoning/sport mode)
- Petzl Reverso (belay device)
- Single and Double Munter/Italian Hitch
Rope
Korda’s Dana 10
- Manufacturer: sacidkordas.com, Type: Canyoning rope semi-static A, Diameter: 10 mm
- Weight: 68 g/m, Breaking strength: 27.80 kN, Static elongation: 2.7% (150kgs)
- Materials: Core/Sheath – Nylon/ Nylon, Standards: EN 1891:1998, type A
PMI Classic Sport
- Manufacturer: pmirope.com, Type: Static, Diameter: 10 mm
- Weight: 66 g/m, Breaking strength: 27.00 kN, Static elongation: 1.9% (136kgs)
- Materials: Core/Sheath – Nylon/ Nylon, Standards: Cordage Institute CI 1801 static rope
Sterling Canyon Tech
- Manufacturer: sterlingrope.com, Type: Static, Diameter: 9.5 mm,
- Weight: 63 g/m, Breaking strength: 30 kN, Static elongation: 3.9% (136kgs)
- Materials: Core/Sheath – Technora/ Nylon, Standards: Cordage Institute CI 1801 static rope
Testing procedure
A repeatable test procedure was set up.
Slow Pull
- A 50kN vertical testbed was used at Aspiring Safety, Christchurch, New Zealand.
- A new rope was used for the start of testing. The same section of rope was reused between tests.
- All tests were completed between 12mm pins and 12mm carabiners.
- One test was undertaken on each variation by the same person with their dominant hand.
- Testing was undertaken over several different days at least a week apart.
- Testing speed was set at 100mm/minute. The sample rate of the testbed is 60Hz
How much friction do you need?
With friction on your lowering device, the critical thing is getting the amount just right. A smooth lower allows any attendant(s) to walk at a reasonable speed for the terrain and the rescuers (undertaking the lowering) to remain in control.
A balance between movement and control.
Too much friction
Too much friction is a real pain as the attendant(s)/stretcher moves too slow with less control over their balance. When on a slope, the attendants have to pull against the lowering system, putting more load onto the anchor than is needed. There is often associated loss of cognitive control as frustration sets in for all parties.
Other considerations:
- For a top-down style rescue, you often lower a stretcher (litter) and attendant (bearer) without a patient, thus only 100kg.
- You need to know how to rig, change/adapt your system to get less friction. For example, if your ropes run over any edge protection, this will reduce the friction you need.
- With two evenly tensioned ropes and 2kN overall on the system, the load is only going to be around 1kN on each device most of the time.
Too little friction
Too little friction is not good. If we have to over-grip the rope, we can suffer from fatigue in the forearm (being pumped). You can lose control if you are not on it and stop and adjust things before this happens.
To avoid this situation:
- Initially, start conservatively with more friction than we need and then subtract to the point where there is a balance between movement and control.
- Once you have experience with the combination of the device and the friction setting for the terrain and load, you develop a go-to friction setting.
Types of friction
When researching the information for this post, we found this graph and definitions (1) that made sense when you think about how friction works. The test results record limiting friction – the maximum value.
Definitions
Static friction:
Friction between two or more solid objects that are not moving relative to each other is called static friction.
Limiting friction:
When the body overcomes the force of static friction, it reaches a maximum value which is called limiting friction.
Kinetic friction:
After the body starts moving and friction decreases, the value is called kinetic friction.
Test data
Conterra Scarab
- Tested with 9.5mm Sterling Canyon Tech
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 1 | Scarab 1 horn | 0.4 | 0.5 |
| 2 | Scarab 2 horns | 0.7 | 1.4 |
| 3 | Scarab 3 horns | 1.1 | 1.8 |
| 4 | Scarab 4 horns | 2.6 | 3.7 |
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 5 | Scarab 1 horn +carabiner | 1.0 | 1.2 |
| 6 | Scarab 1 horn +carabiner+ 1 horn | 1.1 | 1.8 |
| 7 | Scarab 3 horns +carabiner | 1.8 | 2.8 |
Aspiring Brakebar Rack
- Tested with 10mm PMI Classic Sport
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 8 | Brakebar rack low friction | 0.4 | 0.6 |
| 9 | Brakebar rack low friction + thumbed bar | 0.8 | 1.0 |
| 10 | Brakebar rack 4 bars | 0.6 | 1.4 |
| 11 | Brakebar rack 5 bars | 1.3 | 2.2 |
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 12 | Brakebar rack 2 bars + carabiner | 0.2 | 0.5 |
| 13 | Brakebar rack low friction + carabiner | 0.7 | 1.2 |
| 14 | Brakebar rack 5 bars + carabiner | 1.3 | 3.6 |
Figure-8 device
- Tested with 10mm Kordas Dana
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 15 | Figure-8 device canyon style low friction | 0.3 | 0.6 |
| 16 | Figure-8 device canyon style high friction | 0.8 | 1.3 |
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 17 | Figure-8 device canyon style low friction + carabiner | 0.4 | 1.2 |
| 18 | Figure-8 device canyon style high friction + carabiner | 1.0 | 2.3 |
Petzl Reverso
- Tested with 9.5mm Sterling Canyon Tech
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 19 | Reverso low friction | 0.4 | 0.7 |
| 20 | Reverso high friction | 0.7 | 1.3 |
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 21 | Reverso low friction + carabiner | 0.8 | 1.3 |
| 22 | Reverso high friction + carabiner | 1.1 | 2.4 |
| 23 | Reverso high friction + carabiner + carabiner | 2.0 | 3.6 |
Munter/Italian Hitch
- Tested with 10mm PMI Classic Sport
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 24 | Munter / Italian | 0.5 | 1.4 |
| 25 | Double Munter / Italian | 1.4 | 3.9 |
| # | Lowering Device | Thumb and Finger (kN) | Hand (kN) |
| 26 | Munter / Italian + carabiner | 0.7 | 1.3 |
| 27 | Double Munter / Italian + carabiner | 1.6 | 4.1 |
Conclusions
- We found out, as a guide, the range of friction we could hold for the particular lowering device in various settings for rescue and personal use.
- Think about the influencers of friction in your particular situation and then (if you have no prior experience) choose a conservative setting to start.
- Reduce friction to get a balance between movement and control of the load.
Download the one page ‘Lowering Device Friction Summary’ below.
From the team at Over the Edge Rescue
Grant
