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Petzl: Real world fall factors, effective rope length, and rope drag implications for impact forces

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bearbreeder · · Unknown Hometown · Joined Mar 2009 · Points: 3,065
FrankPS · · Atascadero, CA · Joined Nov 2009 · Points: 276
Petzl: Real world fall factors, effective rope length, and rope drag implications for impact forces

bearbreeder wrote:http://www.petzl.com/files/all/product-experience/SPORT/R32-PE-CORDES-EN.pdf enjoy ;)
"Enjoy"? I don't even enjoy the title of your thread. Sounds like a complicated science project! :)
mark felber · · Wheat Ridge, CO · Joined Jul 2005 · Points: 41

Well worth reading, and it wasn't that complicated.

Jason Halladay · · Los Alamos, NM · Joined Oct 2005 · Points: 15,153

And not all reading...some links to some good illustrative videos in there too. Thanks for sharing the link bearbreeder.

Keith Boone · · Henderson, NV · Joined Jul 2013 · Points: 492

Thanks

David Gibbs · · Ottawa, ON · Joined Aug 2010 · Points: 2
Theoretical fall factor
The fall factor is often used to quantify the severity of a climbing fall.
It can have a value between 0 and 2 in climbing.


I've been thinking about that -- the limit of fall factor to a maximum of 2. Specifically, after reading a bunch of the stories about really big whippers where the belayers talk about "yarding in slack".

If somebody takes a fall directly off the belay in a multi-pitch climb, and the belayer pulls in some slack, couldn't that, theoretically, result in a fall factor greater than 2?
David Coley · · UK · Joined Oct 2013 · Points: 70
David Gibbs wrote:Theoretical fall factor The fall factor is often used to quantify the severity of a climbing fall. It can have a value between 0 and 2 in climbing. I've been thinking about that -- the limit of fall factor to a maximum of 2. Specifically, after reading a bunch of the stories about really big whippers where the belayers talk about "yarding in slack". If somebody takes a fall directly off the belay in a multi-pitch climb, and the belayer pulls in some slack, couldn't that, theoretically, result in a fall factor greater than 2?
Yes.
However, this means pulling in the rope very fast indeed and reacting that fast will be hard. E.g. 2m of rope out no jesus piece, falls 4m FF =2. If 1m of slack taken in, fall 3m on 1m of rope FF=3.

For normal falls onto a piece, the FF will reduce however: 12m rope, 2m above last piece, falls 4m, FF=4/12=1/3.
If 1m slack taken in she falls 3m on 11m of rope, FF=3/11 which is <1/3.

If you play with the math for a bit you will see the condition required for the switch from a positive to a negative.

This also points to the theoretical situation where a FF2 onto the belay would be REDUCED if more rope was let out. e.g. 2m above belay not jesus, FF=4/2=2. Let 2m of slack out and FF=6/4=1.5
bearbreeder · · Unknown Hometown · Joined Mar 2009 · Points: 3,065

david gave the math above

in reality i wouldnt overly worry about it

the reason you are pulling in slack is to prevent them from decking or hitting something ... in that case thats your primary consideration

i will say however that if your belayer does sit down or keep running into a catch you better have a bomber piece ... as that would put more force on the top piece ... think the reverse of a dynamic catch

and you better watch your heels for that swing ... youre getting a V HARD catch

;)

David Gibbs · · Ottawa, ON · Joined Aug 2010 · Points: 2
bearbreeder wrote:david gave the math above in reality i wouldnt overly worry about it the reason you are pulling in slack is to prevent them from decking or hitting something ... in that case thats your primary consideration i will say however that if your belayer does sit down or keep running into a catch you better have a bomber piece ... as that would put more force on the top piece ... think the reverse of a dynamic catch and you better watch your heels for that swing ... youre getting a V HARD catch ;)
I'm aware of the reasons why -- the trade-off between a harder catch vs the person falling too far and hitting something.

It is just that I keep seeing people saying the theoretical maximum fall factor is 2, and from all the logic I could work out, this is not the theoretical maximum.

Yeah, in practice, you won't likely see higher than 2 (and only rarely approach 2), but if one is talking theoretical, one must account for even highly unlikely circumstances.
David Coley · · UK · Joined Oct 2013 · Points: 70
David Gibbs wrote: I'm aware of the reasons why -- the trade-off between a harder catch vs the person falling too far and hitting something. It is just that I keep seeing people saying the theoretical maximum fall factor is 2, and from all the logic I could work out, this is not the theoretical maximum. Yeah, in practice, you won't likely see higher than 2 (and only rarely approach 2), but if one is talking theoretical, one must account for even highly unlikely circumstances.
One climbing situation when it can happen is if the rope between a falling leader and the top piece catches on the way down behind a flake. This could well give a FF>2, but then the rope might well be cut by the flake anyhow.
David Gibbs · · Ottawa, ON · Joined Aug 2010 · Points: 2
David Coley wrote: One climbing situation when it can happen is if the rope between a falling leader and the top piece catches on the way down behind a flake. This could well give a FF>2, but then the rope might well be cut by the flake anyhow.
Urgh, yuck. Yeah, you could get an arbitrarily high fall factor out of that (if you don't cut the rope, of course).

Or, a similarly ugly situation... as you fall past a draw, it catches and clips part of your harness (e.g. belay loop).
Fiona Dunne · · Lynchburg, VA · Joined Aug 2008 · Points: 56

Anyone happen to have a saved copy of this or know where to find it? The link seems to be dead. Thanks.

Greg D · · Here · Joined Apr 2006 · Points: 883
David Gibbs wrote: I, but if one is talking theoretical, one must account for even highly unlikely circumstances.
Well the scenario you are talking about is not just extremely unlikely, it is next to impossible. Keep in mind a freefalling body will fall 16 feet in one second. In your example of 4 m this is less than 16 feet so what you are proposing is someone can pull this off in less than three quarters of a second. For example instantly take brake off, yard in an entire meter, put brake on, lock off, catch person. i'd love to see that. Just not when you were belaying me because you probably just drop me. And if you do manage to pull this off with impeccable timing and lightning reflexes you just increased the fall factor so you should not have done it in the first place.
Scot Hastings · · Salt Lake City, UT · Joined Apr 2013 · Points: 35

The same discussion with lots of pretty pictures is in the latest Petzl catalog, "2014 Verticality - Lighting", starting on page 12. Movement has some you can take home.

I honestly hadn't thought much about the effect of rope drag on fall factor, but it makes a lot of sense. The effect definitely makes it a lot easier to get close to FF1, too. All the more reason to manage rope drag.

David Gibbs · · Ottawa, ON · Joined Aug 2010 · Points: 2
Greg D wrote: Well the scenario you are talking about is not just extremely unlikely, it is next to impossible. Keep in mind a freefalling body will fall 16 feet in one second. In your example of 4 m this is less than 16 feet so what you are proposing is someone can pull this off in less than three quarters of a second. For example instantly take brake off, yard in an entire meter, put brake on, lock off, catch person. i'd love to see that. Just not when you were belaying me because you probably just drop me. And if you do manage to pull this off with impeccable timing and lightning reflexes you just increased the fall factor so you should not have done it in the first place.
I agree in practice -- you're unlikely to attain even a "true" factor-2 fall. I said that.

When one talks about theoretical possible values, you have to include the next-to-impossible cases, too.

Let's say I am (for some strange reason) lead-belaying with a gri-gri attached to the anchor, and my leader is 20m out, run-out the whole way. I then slip and fall off the belay stance holding the slack end of the rope, which pulls my leader off, and pulls rope through the gri-gri, taking slack as I fall. I forgot to clip-in, too, so I keep falling until my end of the rope comes taut. That should get a noticeably higher than 2 fall-factor for the leader. Unlikely? Yes. Possible? Yes. Therefor, it must be included in a discussion of "theoretical maximum fall factor". But does not need to be included in discussions of practical situations.
Scot Hastings · · Salt Lake City, UT · Joined Apr 2013 · Points: 35
David Gibbs wrote:Let's say I am (for some strange reason) lead-belaying with a gri-gri attached to the anchor, and my leader is 20m out, run-out the whole way. I then slip and fall off the belay stance holding the slack end of the rope, which pulls my leader off, and pulls rope through the gri-gri, taking slack as I fall. I forgot to clip-in, too, so I keep falling until my end of the rope comes taut.
Yeah, don't do that.

Seriously, though, what's the point of all this? FF2 should be avoided at all costs. How will acknowledging the extremely remote possibly of FF>2 change this discussion?
Greg D · · Here · Joined Apr 2006 · Points: 883
David Gibbs wrote: Yes. Therefor, it must be included in a discussion of "theoretical maximum fall factor". But does not need to be included in discussions of practical situations.
No. Those are Darwin discussions.
bearbreeder · · Unknown Hometown · Joined Mar 2009 · Points: 3,065
Fiona Dunne wrote:Anyone happen to have a saved copy of this or know where to find it? The link seems to be dead. Thanks.
go heres for petzls online version

petzl.com/en/Sport/Fall-fac…

petzl.com/en/Sport/Forces-a…

and more at the links on the right hand side ...

;)
Guideline #1: Don't be a jerk.

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