The death of a 43-year-old man who was crushed when an 800 kilogram concrete soakwell lid fell on him during work on an apartment complex in WA’s Pilbara region was “the final and fatal link in a chain of errors”, an inquest has heard.
Robert Stephan Hamiora Serjeant had more than 25 years' experience as a qualified rigger and had been working on a fly in fly out basis at the Pelago West development in Karratha in July 2011 when the accident occurred.
As the soakwell lid was lifted by a crane onto a flatbed truck, the connecting clutch on one of two cables snapped, causing it to flip and fall onto Mr Serjeant, who was some five metres away holding a tagline to stop the lid swinging into other objects.
The WA Coroner's Court heard on Monday the clutches and anchors fabricated into the soakwell lid were mismatched as they were designed to bear differently weighted loads.
Expert witness Rod Mackay Sim, an engineer who has worked with prefabricated concrete components for 34 years, said the large, flat panel only had two lifting points, which made for an inherently unstable design.
Normally, there would have been three or four lifting points.
"It should have been stable enough so it can be lifted without anyone being anywhere near it," Mr Mackay Sim said.
He said it was inconceivable Mr Serjeant, with his long experience as a rigger, wouldn't understand how the ubiquitous clutch and anchor systems fitted together, but he may not have appreciated how unstable two lifting points were.
Connecting the mismatched equipment was the final and fatal error, he said.
"I think, unfortunately, Mr Serjeant was the final and fatal link in a chain of errors," Mr MacKay Sim said.
"It's an unfortunate tragedy of circumstance."
It's possible the cable would not have disconnected had the soakwell lid been lifted with the correct type of clutch, he said.
The design, manufacture and supervision of lifting precast concrete components for use in civil works is not currently covered by any Australian Standard.