Understanding fall factors is a very important to understand what climbers experience when they fall. At a very surface-level of understanding, know that while rock climbing, Fall factors range from 0 to 2, and the closer to fall factor is to 2, the more force the climber – and the whole system – feels. Anyone who experiences a factor-2 fall will at the very least be feeling sore for a while afterwards, and may go as far as breaking bones and even have gear break on them leading to possible death. As a climber and belayer, your goal should be to create systems and put yourself in situations with the smallest possible fall factor.
More specifically, the fall factor is the ratio between the length a climber falls before the rope starts to stretch and the amount of rope available to stretch. In terms of how the fall factor relates to impact force, there’s some pretty intense formulas that take into account elasticity of the rope, the cross-section of the rope, and a slew of other factors. You’re welcome to calculate it for yourself, or you can go with the idea that closer to 2 is bad, closer to 0 is good.
So how do we calculate fall factors? It’s pretty simple: It’s the length of the fall divided by the amount of rope available to stretch.
The best way to make sense of this is to look at a few examples and calculate the fall factor.
Meet O and B. They’ve been climbing together for years. They are trained professionals, so this goes without saying, but don’t try the following at home.
As O starts climbing, B feeds out some rope. The amount of rope between O and B is theoretically the Length of Rope available to stretch (we’ll explain the “theoretically part soon). If the rock O is holding onto right now breaks under the tremendous strength of O’s grip, the climber will fall at least double the distance to its last piece of protection. That distance is what you use for Length of Fall. I say “at least double the distance” because there’s a number of factors involved, such as amount of slack in the system and whether or not the belayer jumps up. For the sake of this article, let’s assume that the rope that B has given O is exactly what O needs and not an inch more, and let’s assume that when O falls, B is able to plant themselves and not move an inch.
Now, let’s start adding some numbers. Let’s put the equation back up so it’s easy to reference
Ex 1: O has climbed 10 feet, and is 5 feet above the last draw. What’s the fall factor if O were to fall now?
Answer: Answer: If O is 5 feet above the last draw, the length of fall will be 10 feet (2x five feet), the length of rope available to stretch is 10 feet. The fall factor is 10/10 = 1
Ex 2: O has climbed 20 feet, and is 5 feet above the last draw. If O were to fall now, what the fall factor be?
Answer: If O is 5 feet above the last draw, the length of fall will be 10 feet (2x five feet), the length of rope available to stretch is 20 feet. The fall factor is 10/20 = 0.5
Ex 3: O has climbed 50 feet, and is 10 feet above the last draw. What’s the fall factor if O were to fall now?
Answer: O will fall 20 feet with 50 feet of rope available to stretch. The fall factor is 20/50 = 2/5 = 0.4
Between Ex. 1 and 2, O fell the same distance, but the fall factor was doubled in example 1 than in example 2. This translate to a much high impact force on O at the end of the fall. Although O fell twice as far in Ex 3 than in Ex 1 or 2, the fall factor was lower. This means that Ex 3 was actually the softest and most comfortable fall with a lower impact force on the climber. This happens because there is more rope in the system to stretch and absorb the energy of the fall. Moral of the fall factor story is that as long as there are no ledges or other things to hit on the way down, bigger falls tend to be much softer and more comfortable. Consider that next time you’re a few feet above your last bolt and screaming at your belayer to TAKE. As long as the fall is safe, it’ll probably feel much nicer if you took the slightly longer fall than if you got tugged into the wall forcefully by your belayer taking as per your instructions. In fact, once you start getting into fall factors at 1 or above, you can have really painful falls.
Last thing to discuss is factor what I meant when I said “The amount of rope between O and B is theoretically the Length of Rope available to stretch”. There are occasions when not all the rope in the system is available to stretch. This typically happens when the rope take sharp turns at different biners or obstacles, causing a great deal of rope drag. When you have a lot of rope drag, the friction between the rope and the carabiners makes it such that only a portion of the rope is available for stretch, which can dramatically increase the fall factor (and lead to a higher impact force, and a less pleasant fall).