What are climbing forces in the real world?
When measuring forces on climbing gear, most tests are done without human bodies, using very harsh falls onto a fixed point. Well, fortunately the clever gear testers at Petzl got some real-world results more relevant for actual climbers.
image: screengrab from: https://www.petzl.com/US/en/Sport/Forces-at-work-in-a-real-fall
First, a video from Petzl.
They put force measuring devices on the belayer, the climber and the top piece of gear, had them take some increasingly severe falls, measured everything, and took video.
The belay device was a Grigri 2.
They summed everything up with clear diagrams, short videos showing some big falls, and some conclusions - yet another reminder why the Petzl website is great!
Disclaimer: there are many variables involved in testing forces like this. This is not a comprehensive study with definitive results, but more of a way to get people thinking about general technique and assumptions.
Click the button below to see this great article and videos for yourself.
Here are some personal takeaways. What are yours?
Even in a relatively low factor fall, due to rope stretch and belayer displacement, the falling climber can go a VERY long way.
The relatively low numbers help explain why a knotted Dyneema sling rated to 22 kN may break in a harsh drop tower test, but is extremely unlikely to break in the real world.
The upward movement of the belayer when catching a fall can do a lot to lower the forces on the climber and the gear.
Using an assisted braking belay device such as a Petzl Grigri is an excellent choice if you think you're going to be catching some major whippers. (But you already knew that, right? =^)
Even in a high force, factor 1 fall, there’s relatively little force on the belay anchor. Only a tiny bit more than a factor 0.3. Low forces on the anchor, that's good!
You can’t really do you “live body” testing like this with much more than a factor 1 fall, because somebody's gonna get hurt.
I know, you're wondering what about that dreaded, mythical factor 2 fall, the one that pretty much never happens in the real world, but still the one everybody's worried about? To protect against that, you can do a few things. The best one is for the leader to place so in gear as soon as possible after leaving the anchor. If that can’t be done, you can consider a fixed point belay. This doesn’t change the fall factor, but it gives a higher likelihood of a successful catch in the event it happens, without slamming the belayer into the wall. Another option, for more extreme situations, if the terrain allows it, is for the belayer to lower themselves down below the actual anchor, to put more rope in between them and the leader, and then have the leader clip the anchor is the first piece.
Gray dot = force on the top piece of gear
Blue dot = force on the climber
Black dot, force on the belayer
Fall forces in CLIMBING. image: https://www.petzl.com/US/en/Sport/Forces-at-work-in-a-real-fall
Second, a video from How Not to Highline.
Ryan Jenks, the creative force behind the popular YouTube channel How Not to Highline, measured a bunch of gym falls in a similar way. Below are some of his numbers. While perhaps not a rigorous scientific study because some variables changed from test to test, it does provide interesting numbers.
Fall factors were not measured, so it's a little hard to compare directly to the Petzl study. Note that the measured force never exceeded 5 kN in any part of the system . The only time it came close were static fall and a Z drag fall, where it got close to 5 kN on the top piece of gear.
There are many, many variables to consider when trying to determine these numbers, but these two studies can give you a rough idea of real world forces on the belayer, on the climber, and on the top piece of gear.
image: Screen grab from https://www.youtube.com/watch?v=m8z6adEqaOs
Want to learn more? See these articles that cover similar studies by Petzl.