Forces at work in a real fall
The values of the forces at work in a climbing fall that one finds in the literature or on the Internet are mostly derived from tests and numerical models based on the standard model (rigid masses, falls on a fixed point…). So reported values are high, as they are the product of harsh tests. In order to determine the forces actually encountered in the field, we performed a series of fall tests with the climbers in three configurations, corresponding to higher and higher fall factors.
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.
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The results shown are valid only on the tested configurations and cannot be generalized to all situations. However they help us evaluate falls involving real people. To ensure repeatability of our protocol, each test was repeated at least three times.
Notes
Despite our desire for a rigorous protocol, measurement uncertainty related to these results is significant. We can estimate at + or - 0.3 kN. The forces presented are thus the result of the average of the tests, rounded to 0.5 kN.
We made the choice to focus on the forces on the climber, the belayer, and the redirect point. However, the force value alone does not characterize a fall. Other factors come into play to quantify the severity of a fall, notably the force rise time and the direction of pull. These different factors are not studied here and will be the subject of a future publication.
Fall factor 0.3
This first series represents a common climbing situation.
Test conditions
- Climber: 80 kg
- Belayer: 80 kg
- Rope length: : 6.9 m
- Fall length: 2 m
- Rope: VOLTA 9.2 mm
- Belay device: GRIGRI 2
To ensure a certain repeatability, the climber always falls from the same position and the belayer is neutral (non-dynamic belay).
For this test, we chose not to clip the first quickdraw, in order to avoid blocking belayer displacement.
Results
Climber
Impact force ≈ 2.5 kN
The climber experiences the fall as a soft catch.
Note the significant climber displacement, despite the short fall distance.
Belayer
Impact force ≈ 1.5 kN
For the belayer, the fall is easy to stop.
Anchor
Impact force ≈ 4 kN
Note:
Despite the short fall distance, the climber ends up not far from the ground. This significant displacement is explained by two points:
- the line was straight, with little friction in the quickdraws.
- the first quickdraw was not clipped, so belayer displacement was not limited.
This situation is common in the gym, where the main hazard is a ground fall.
Advice
Systematically clipping the first quickdraw reduces the chance of a ground fall, by limiting belayer displacement.
Fall factor 0.7
This second configuration represents a fall on a multi-pitch climb, at the start of a pitch.
Test conditions
- Climber: 80 kg
- Belayer: 80 kg
- Rope length: : 3 m
- Fall length: 2 m
- Rope: VOLTA 9.2 mm
- Belay device: GRIGRI 2
The belayer is tethered to the belay with an 80 cm lanyard. This length was chosen according to the location of the belay station: the belayer is below an arete, the 80 cm lanyard helps limit belayer displacement.
The belay station has no freedom of movement - it is equivalent to a fixed point. We made this choice to increase the repeatability of the test. A more common belay station gives the belayer more freedom of movement and thus yields lower forces. By contrast, the redirect point has significant freedom of movement; with a shorter anchor, the forces would be higher.
Results
Climber
Impact force ≈ 3 kN
The fall is impressive for the climber, but not painful.
Belayer
Impact force ≈ 2 kN
The force is not significant, but the belayer is stopped harshly at the belay station. Stopping the fall can be difficult if the belayer is surprised.
Anchor
Impact force ≈ 5 kN
Note:
An initial series of tests was conducted without a redirect point on the belay. As the first anchor point was offset to the right of the belay, the belayer was pulled sideways in the fall, then stopped harshly by his lanyard. Sustaining such a load is hard on the human body.
Advice
A redirect point in-line with the belay (or otherwise on the belay) helps ensure a good direction of pull on the belayer, which makes stopping the fall less painful, and thus easier.
Fall factor 1
This configuration represents a fall on a multi-pitch climb when leaving the belay.
Test conditions
- Climber: 80 kg
- Belayer: 80 kg
- Rope length: : 3.6 m
- Fall length: 3.6 m
- Rope: VOLTA 9.2 mm (Impact force: 8.6 kN)
- Belay device: GRIGRI 2
The belayer is tethered to the belay with an 80 cm lanyard.
The belay station has no freedom of movement - it is equivalent to a fixed point.
Results
Climber
Impact force ≈ 4 kN
Such a fall is impressive for the climber and is rare in the field. However, the force is quite bearable.
Belayer
Impact force ≈ 2 kN
As with the factor 0.7, the belayer is stopped harshly at the belay station: arresting the fall can be painful and difficult.
Anchor
Impact force ≈ 6 kN
Note:
The force on the anchor is significant.
Such a pull is no problem for a solid fixed anchor.
However, it would be critical on a dubious point such as a small wire or bad piton.
Advice
Belayer movement helps dissipate the fall energy and thus limits the force. Thus the belayer is advised to have a long tether to allow displacement. Obviously, the length must be suitable for the situation.
The first point after the belay must be solid.
Conclusion
These tests have enabled us to put values on falls involving real people. These values will serve as a basis to study some particular points of the fall.
