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Catastrophic failure extensively damages truck

Collapsed boom damages truck
Collapsed boom damages truck

An aerial lift machinery accident severely damaged a heavy vehicle in North Queensland.

Authorities recently investigated how a mobile concrete placing boom suddenly collapsed onto a truck cabin, crushing the roof and cracking the windscreen. It also damaged a formwork deck being poured at the work site.

WorkCover Queensland discovered the equipment was more than 32 years-old and had a crack through the top of the king post (slew turret). This is believed to have caused the 32 metre machinery’s catastrophic failure on 8 March 2022.

“The king post had a pre-existing crack through approximately 40 per cent of the original material area, and the crack had been present for some time. The pre-existing crack was discoloured with rust and grease,” it said in a safety alert.

Investigators found no accurate way to check for cracks without lifting the king post out with a crane for a full inspection.

“When the king post was mounted on the pedestal, the pre-existing crack would have been hidden behind the king post slew bearing and a cover obscuring the bearing. An external inspection of the king post and a function test of the unit would not have identified the presence of the pre-existing crack,” the safety alert said.

Concrete placing booms are prone to metal fatigue and cracking due to a high degree of cyclic loading from the concrete pump’s “pulsating action”.

“As the units age, cracking and wear will become more common as they approach or exceed their design life [and] the need for comprehensive inspection becomes extremely important as the units age. An external inspection of the unit alone, without dismantling, will not be adequate to see all high-stress areas,” the alert said.

“All concrete placing booms need to be maintained and inspected in accordance with the manufacturer’s instructions and the criteria specified in the concrete pumping code of practice.”

Investigators cautioned against skipping the lengthy dismantling process to save time.

“The decision not to dismantle should not be based solely on the placing boom owner stating that the unit has had minimal use. The owner should be aware that obtaining a report from the certifying engineer, that does not comply with the criteria in the code, does not demonstrate compliance with all the duties for owners of plant under the Work Health and Safety Act,” they said.

“Fortunately, the boom did not strike the boom line hand or other workers on the slab being poured.”

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AMSJ April 2022