Zip Wire Failure
Fatal accident in Australia
In October 2019, an 86-metre zip line termination failed and two patrons dropped to the ground, causing fatal injuries to one and serious injuries to the other. The two patrons were travelling along the zip line, one behind the other, with a rope link between them.
Rope terminations on zip lines generally use either of two basic types of rope termination:
- pressed ferrule or swage type rope terminations (refer Photograph 1)
- wire rope grips (e.g. bulldog grips) (refer Photograph 2).
Both pressed ferrule terminations and wire rope grips rely on the application of pressure between two parallel sections of wire rope, the rope tail and the loaded section. The applied pressure creates frictional resistance to avoid failure of the termination by preventing relative movement.
Over time the wire rope characteristics may change (e.g. the rope diameter may reduce) so that a termination which previously withstood applied loads may suddenly slip and cause failure of the zip line.
Visual inspection of rope terminations may not be adequate on its own as a means for verifying the ongoing adequacy of terminations.
The rope tension in zip lines can be extremely high and includes:
- pre-tension applied to the rope during set up (to reduce sag, i.e. ‘catenary’)
- tree movement
- the additional loads applied by patrons using the zip line.
It is important to note that loads applied by patrons to the zip line and its end anchorages will be many times their self-weight due to the triangulation effect of the load. For example if a 100 kg patron uses a zip line, the additional tension applied to the zip line and its anchorages could be more than five times greater (i.e. potentially in excess of 500 kg force).
The full report