What is Impact Force?
Impact force is the force felt by the climber or rescuer and equipment at the termination of a fall. It is also the number that is used to show a rope’s ability to absorb the energy created during that fall. A fall on static rope with little elongation and a fixed anchor point will generate much higher impact forces than a fall on dynamic rope using a running belay. There are two measures of impact force. Theoretical impact force is the impact force without any extraneous variables. Actual impact force is the force created when you take into account a dynamic belay and friction developed over both the carabiners and rock. The UIAA mandates that the impact force generated on the first fall must be less than 12kN for a single rope. This test uses a static belay with a fall factor of 1.7 or a 4.6meter (15′) fall on 2.5meters (8′) of rope. This test demonstrates a very severe fall and generally is not applicable for real world climbing situation but does give a good basis for comparing the relative elongation characteristics of different ropes. Real world experience has shown that rarely are impact forces higher than 10kN generated during a climbing fall. Again, in order to limit the impact force is it important to place protection whenever possible and to utilize a dynamic belay.