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OTO 2001/054

Report on the investigation into the snagging of hooks and their indiscriminate shedding of slings/penants: phase 1

Addresses the potential for hooks, that are typically associated with offshore crane activities, to snag and /or to indiscriminately shed their slings or pennants. The Hook snagging study involved a series of practical tests conducted by HSL (Sheffield) using various steel sections as snagging elements which were swung into, at various approach angles, by both single point (with spring action safety catch) and load closing type hooks. Tests repeatedly showed that both hook types would snag readily, particularly so on scaffold tubing, flat plate and lipped materials such as equal/unequal angle sections etc. The sling study also involved a programme of practical testing, initially conducted on HSL Buxton's mobile site crane, where it was found that one of the primary causes of sling shedding, under no load conditions was due to a phenomenon known as "Interrupted Simple Harmonic Motion" (ISHM). The dangers arising from both the snagging of hooks and the shedding of slings/pennants from hooks when operating in an offshore environment can be potentially lethal. Makes several recommendations for design improvements to equipment and its operation as to reduce risks and enhance safety in the workplace. Also recommends that further tests to quantify the magnitude of the forces involved in ISHM mode should be carried out under a phase 2 report.

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Updated 2010-03-19