Why is the fall factor important in climbing?
During a fall a climber gains great speed towards the ground, generating kinetic force that at the end of the fall is transmitted in part to the series of equipment used for the climb (harness, rope, quickdraws) and in part to the climber.
The most dangerous part of a fall in an ideal situation, ignoring case-specific dangers such as rock ledges, is the final part: when the rope extends and the climber has to withstand the force caused by sudden deceleration.
Studies carried out by the Air Force proved that the maximum impact force a person can withstand is about 15 times his or her weight. If falling head-down the maximum force a person can withstand is reduced to 4 times his or her weight.
If a person weights 80kg, the maximum impact force he or she can withstand is 80 x 15 = 1200 kg. (1200 kg correspond to more or less 1200 daN, or 1.2 kN)
How do you calculate the Fall Factor?
The Fall Factor is a relationship between the height of the fall, the length of the rope between the climber and the last anchoring point. It is expressed in decimal values, which in sport and alpine climbing go from a minimum of 0 to a maximum of 2. In certain cases, like in via ferrata, the value can be higher than 2, but in this article we will concentrate on the basic understanding of sport climbing fall factor. These are two typical situations:
First case: a climber reaches 12 meters of height and falls. The last quickdraw is 3 meters below his or her harness. The belayer blocks the rope and becomes the last fixed point. The Climber will fall a total of 6 meters (3+3) with 12 meters of rope to absorb and dissipate the force. Fall Factor is measured dividing the meters of fall by the meters of available rope. FF=6/12= 0.5
Second case: this case can happen when climbing on multi-pitches. The lead climber starts climbing the second pitch but after 2 meters he or she falls before being able to place the first quickdraw. The belayer blocks the rope and the climber falls a total of 4 meters (2+2). The falling factor will be calculated again by dividing the height of the fall by the length of available rope.FC=4/2= 2
In the first case the falling factor could increase if, for example, the rope gets stuck on the last quickdraw or on a rock formation.
In order to be certified by European Standards and by the UIAA, the impact force a climbing rope transmits to the climber must be lower than 1200 daN. Climbing ropes absorb the impact force by elongation, usually transmitting an impact force between 800 and 900 daN, depending on manufacturer and model. With use and wear a rope becomes less elastic, increasing thus the impact force transmitted at the end of a fall.
When buying a new climbing rope it is important to check all the measures stated on the label. You can see below a table of values for three half-ropes by Beal. You can notice that the fifth column states the impact force values Beal guarantees, followed by guaranteed number of falls and elongations.