Appendix 5: Analysis of solutions observed in the field - Use of a single ascender with knots in the rope.
Warnings
- Carefully read the Instructions for Use used in this technical advice before consulting the advice itself. You must have already read and understood the information in the Instructions for Use to be able to understand this supplementary information.
- Mastering these techniques requires specific training. Work with a professional to confirm your ability to perform these techniques safely and independently before attempting them unsupervised.
- We provide examples of techniques related to your activity. There may be others that we do not describe here.
Primary system: one ascender on the rope.
Secondary system: knots tied in the rope while climbing, below the ascender.
The knots are left in the rope below the climber.
Advantages:
- Simplicity of the system and its installation
- Low equipment cost
Disadvantages:
- The redundancy principle is not followed with respect to the belay rope WARNING, repeated rubbing against the rock can quickly cut your only rope.
- Need to regularly have both hands free to make knots: impossible if the climb is overhung, so there is a risk of climbing rather far above the last knot in certain sections
- In case topping out is necessary to exit the route, retrieving a rope with many knots in it could be complicated or even dangerous
Risks in case of primary ascender malfunction:
- Significant potential fall length
- The user will fall to the first knot in the rope The ascender is not designed to sustain the impact on the knot.
Results of a series of tests carried out by Petzl:
Test scenario: simulation of primary device malfunction. Cam intentionally deactivated for the test Fall onto the knot with an 80 kg dummy attached to the ascender.
The start of the fall is fixed 2 m from the anchor, at an average position: closer to the anchor, the fall factor will be higher and the impact more severe.
Two fall heights were envisioned:
- Standard fall height = 2 m fall above the knot (factor 0.5)
- Fall height of a climber required to climb through a sustained section = 5 m fall above the knot (factor 0.71)
The same falls were repeated on 11 mm diameter dynamic, low stretch kernmantel, and static ropes.
During these tests, the knot stopped the fall each time. However, stopping the fall is not a sufficient result to validate these tests, because the climber is then faced with other problems.
- The impact force is high: always greater than 4 kN, and up to more than 8 kN for falls on static and low stretch kernmantel ropes
- The rope is sometimes damaged (sheath torn, several core strands broken): when the cam re-engages during the fall, or when impacting the knot
- The device is damaged by the impact in most cases:
> MINI TRAXION: bent side plates and axle. The device is no longer usable; the climber must use another ascender, or descender, to escape.
> MICRO TRAXION: bent moving side plate and axle. The device might be usable for escape, but must be retired immediately afterward.
> ASCENSION: bent frame in the most severe cases. The device might be usable for escape, but must be retired immediately afterward. The knot jams between the carabiner and the body of the device. In case of a poor attachment, the rope will come free.
Petzl does not recommend this solution as its effectiveness is uncertain.
