December 2005
Tyroleans and zip wires do break. AALS have heard accounts of several rope tyrolean traverses and one cable zip wire which broke whilst in use. Fortunately no one was seriously hurt.
There is fairly good guidance available on setting up rope tyroleans. Using two ropes is very common practice with one tensioned more than the other. The idea is that if the tighter one breaks the load will drop onto the looser one which should have enough 'sag' to prevent it breaking. Be careful however that the person can not hit the ground on rope stretch. Be careful not to tighten the tight one too much.
The cable is more interesting - it broke at mid-point, i.e. the bottom of the sag. It seems water accumulated there and corroded the inside of the cable, leaving no indication on the outside. Replacing cables periodically seems prudent, as does sending down a heavy test weight every now and again. Two or three times body weight at least.
