Fall Factors Explained

The following article is based on text from the book Trad CLIMBING + published by Rockfax. This article version was written by Adrian Berry and Alan James, and the illustrations are by Ray Eckermann.


When you fall off a route the piece of equipment that contributes the most to absorbing the energy of the fall is the rope. In general, the more rope freely available to stretch during the fall, the safer the fall will be and this can be measured by using a ratio known as the fall factor.

The fall factor is simply the distance fallen, divided by the amount of rope available to absorb that fall. The principle is that, the lower the fall factor, the safer the fall. The distance fallen isn't important on its own and in some situations longer falls are safer than shorter ones, which is contrary to what most people might expect. The important thing is how much force is transmitted to the top piece of protection and this is where the fall factor comes into play - a large fall factor (which can be a very short fall if low on a pitch) transmits a large force, and a small fall factor (which can be a huge 'winger' if high on a pitch) transmits a smaller force.

The illustrations below show several different situations and the fall factors you might experience.

Fall factors - a soft fall

Here, a climber has taken a 2m fall with 10m of rope out giving a fall factor of 0.2 (2/10) - a very soft fall.

Fall factors - a fall from high on a route

If the climber had been twice as high on the route (20m), and taken a longer fall of 3m, the fall factor would be only 0.15 - significantly less - and safer - even though it might have been a bit more scary!

Fall factors - a fall from low on a route

In this example, the climber has once again fallen 3m, but had only just moved above the belay, and so only had 3m of rope out - giving a high fall factor of 1.0.

Fall factors - a fall past a belay

Here, our friend has fallen 6m, with only 3m of rope to absorb the fall, producing a very large fall factor of 2.0. If the belayer had quickly reacted and taken in some slack (an intuitive reaction) while his friend was whistling past (an armful is about 0.5m), the fall factor would have increased to a very worrying 2.4.

Fall factors - friction in the system

Real world fall factors

The fall factor is a very useful way of understanding just how the forces of a fall are dissipated and the role of the rope in not just stopping a fallen climber but stopping them gradually.

The examples above are highly simplified and in each example the rope is running perfectly free. In practice, each time the rope runs against either a karabiner or the rock, it reduces its ability to absorb force through its full length.

In the example on the right, the presence of only four twenty degree bends in the rope caused by runners is enough to more than double the fall factor from 0.3 to 0.6 due to the added friction in the system.

A more severe point of friction, such as a ledge where protection has been placed at the back, or the lip of an overhang, where protection has not been sufficiently extended, can as much as double the force on the top piece of protection - taking it into the realm of failure.

So are long falls safe?

Far from it, since there are many other crucial factors you need to consider. The further you fall, the more likely you are to hit something - this could be the ground, of course, but it could also be a ledge, or a protruding section of rock. In addition, the effects of a swing are increased if you fall further.

The main point to learn from fall factors is that a fall from low on a pitch often transmits more force to a runner than one from high on a pitch, even if you only fall a short distance. When you fall past a belay, the fall factor can become critical. The way to counter this is make sure your early runners are good ones, and place a few when leaving stances on multi-pitch routes.

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This is the second thread about this article, that is because we had an earlier one in which I had made a huge and very significant mistake, and kept trying to reinforce my mistake. The mistake was all my own addition both in the article, and then more dramatically on the thread itself. It was only by going back to Adrian's (now-printed) text that I was able to see my mistake. We got quite a few replies to that thread and many of them made good points. An especially useful mathematical point was made by jkarran:If you have a runner at R meters, climb X meters past it, and there's an additional Y meters of slack: Based on the "distance fallen/available rope" equation FF = (2X + Y)/(R + X + Y) plug some numbers in and it becomes apparent that you need to be falling past your belayer before increasing Y reduces FF, up to that point increasing Y marginally increasess FF. Not a common scenario in my limited experience. Since this article is tied to an FAQ, it is important that it contains good information, therefore I had to remove the thread with all my nonsense in it. Apologies for all who took the trouble to reply (and especially those I made condescending replies to) and rest assurred, the information in the book is correct, is it only this numpty who doesn't know what he is talking about. Alan
I think you are looking at the old version since that line has been removed. Try refreshing your browser to see the later version. Current article views number at the bottom is 417. If you see a number less than this then you may well be looking at an older version. Cheers Alan
Try holding down shift at the same time. Seems to be a problem with Firefox in particular where by you really have to insist that it gets a new page. Alan
20 Nov, 2007
Funny thing is that fall factors are rarely crucial but really important when they are. People seem to get away with terrible treatment of their ropes in the lower fall factor region (eg repeated biggish indoor falls around 0.5 with no rope rests in between) where if you logged it cummulatively (as manufacturers say), ropes could be retired in a single session! Also in this area of rope lifetimes, many people worry too much about ropes snapping and too little about losing elasticity.
20 Nov, 2007
There is also a problem refreshing it using Internet Explorer (I'm using version 7) Yes I could delete my entire cache, but I don't want to do that - it means I have to log on to sites like this
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