Safe set up of mobile concrete placing booms
A hefty fine recently imposed on a subcontractor working on the Toowoomba Second Range Crossing has highlighted safety issues with concrete placing boom operation.
Concrete placing booms can fall because the ground is too soft, inadequate timber is under the feet, short-legging, and operating in zones that the manufacturer doesn’t allow. As well, mobile concrete placing booms are getting bigger and stability is an increasing problem.
The recent Toowoomba case saw the contractor fined $50,000 over a safety incident in which a mobile concrete placing boom became unstable and tipped, putting workers at risk.
In the mobile crane industry, many of the stability lessons have already been learnt. For example, if you order a large slewing mobile crane, the owner will generally supply large bog mats with the crane, reducing the possibility of outrigger pads digging into the ground.
In the Second Range Crossing incident, the mobile concrete placing boom was a large 60m unit with high outrigger loadings up to 43 tonnes per outrigger. The pad size under each outrigger foot was too small and the unit was set up on sloping ground exceeding the maximum angle specified by the manufacturer.
In another incident south of Brisbane in August, a mobile 37m mobile concrete placing boom stood up on its rear outriggers when the operator was unfolding the boom towards the rear of the unit. In this case, the manufacturer did not allow the unit to be folded within the 30-degree zone either side of the hopper. The operator was fortunate as the unit sat back down on its front outriggers when the boom was folded in.
Information on operating rules for setting up mobile plant on outriggers isn’t always obvious and might only be provided in the manual. While some modern mobile concrete placing booms, cranes and elevating work platforms have computers that help prevent the boom going into unstable zones, others do not. In addition, some computers require accurate information to be entered by the plant operator.
There is no substitute for detailed training for the operator and that includes familiarisation training for the specific make and model of plant being operated. This is on top of the training an operator receives for a high risk work licence to operate the plant.
Plant owners need to provide adequate timbers, pads or bog mats so the plant can be set up safely. The principal contractor must also provide information on the ground conditions and where underground services are located. Written instructions from a geotechnical engineer may also be needed, particularly for heavy lifts, large plant, or where the ground bearing capacity is suspect.
More information on these two recent prosecutions and others can be found at Office of the Work Health and Safety Prosecutor Court Reports 2020.