A tower crane load has been dropped to the ground in Queensland, following a hoist rope failure in October 2018.
According to a Workplace Health and Safety Queensland incident alert, the hoist rope on a tower crane at a construction site broke while lowering a load.
While no-one was injured, it was a dangerous incident that could have had very serious consequences. Investigations are continuing.
The incident alert said that selection of an appropriate rope for a crane is a complex issue due to:
- rope loading, frequency of use (ie, operational cycles) and rope speed;
- rope sheave dimensions including diameters and sheave profiles — a rope sheave needs to match the rope profile as much as practicable. If the sheave is too tight or too loose the rope will be damaged;
- the material that the sheave is constructed from can impact on the wear rates of the sheave — a worn rope sheave will accelerate rope wear and damage;
- tensile grade of the rope wires — higher tensile strength wires may appear to provide longer life, but in reality this may not always be the case. The individual wires may be less flexible and prematurely fail depending on factors such as the numbers of operational cycles, working loads applied and potential shock loading;
- a rope of higher strength wires may have a life significantly less than a rope of lesser strength and greater flexibility;
- environmental factors (such as the tower crane being used in a coastal environment);
- rope lubrication and maintenance.
The alert said that crane owners are encouraged to only use steel wire ropes of a specification (make, construction, strength) that is both approved and supplied by the tower crane manufacturer for the particular make and model of crane. Where rope of an alternative specification is used:
- written verification from the crane manufacturer that this rope may be used with the tower crane should be obtained;
- an inspection of the rope should be carried out by a third-party competent person with expertise in the inspection of steel wire rope (National Association of Testing Authorities accreditation of the company carrying out the inspection is one way of helping to demonstrate the quality of this inspection).
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