Zip Line Anchorage Failure

Purpose

This safety alert highlights the recent failure of a zip line anchor (termination). The information applies to a specific type of zip line anchorage system.

This is the second failure of a zip line in Queensland. In 2019, a zip line termination, consisting of four wire rope grips (bull-dog grips), failed because the grips had not been tightened enough and the wire rope was able to slip when two patrons were on the zip line. This previous incident resulted in a fatality and serious injuries to the other patron.

Background

The high ropes course (the course) involved in the second incident had been installed at the workplace in 2021. The course used a system of wire rope and anchors that allowed patrons to travel throughout the length of the course without having to unclip and reclip to separate wire ropes. To achieve this, it utilised a unique system to anchor the wire rope along the course.

The anchor that failed consisted of a 12 mm diameter galvanised steel wire rope fixed inside a stainless-steel tube using epoxy resin. The tube was welded to a bracket that was bolted to a mounting plate. The mounting plate allowed the entire assembly to be attached to a timber post or tree. This complete anchor assembly, as originally designed and installed, was rigid without the ability to move or rotate.

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Action required

Zip lines of a similar design

All high ropes courses with a similar design to the one associated with this incident (i.e., with rigid anchors consisting of a wire rope passing inside a tube) should be removed from service and thoroughly inspected by a competent person.

Considerations by zip line designers

When new designs for anchoring systems are developed, designers need to thoroughly consider the effects of all loading conditions on the components. The choice of connection used can significantly impact the loading experienced by the components. In addition, changes in geometry can significantly impact localised stress concentrations and reduce fatigue strength.

Fixed connections involving changes in geometry combined with various materials can make it difficult to determine the maximum localised stresses that are likely to be experienced throughout the component. This in turn can make it difficult to determine whether these stresses are likely to induce a failure of the component.

As such, new designs need to undergo thorough analysis for all potential failure modes to ensure that the design is safe. This should consider operational and environmental factors (wind, temperature, atmospheric corrosion, cyclic loading, etc.), all operational and environmental loads, and any damage that is likely to occur during operation.

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Further information

Further information is provided in:

• Alert: Zip line terminations published by the Office of Industrial Relations on 9/12/2019
• Australian Adventure Activity Good Practice Guides
• AS 2316.2.1:2016 Artificial climbing structures and challenge courses Part 2.1: Flying foxes and challenge ropes courses – Construction and safety requirements (EN 15567-1:2007, MOD)
• AS 2759-2004 Steel wire rope – Use, operation and maintenance