Offshore platform decommissioning near miss

The Department of Energy, Mines, Industry Regulation and Safety of Western Australia (DEMIRS) has published Significant Incident Summary No. 6 relating to the unexpected movement of the Sinbad topsides during its removal in 2021. The summary can be found here.

What happened

In 2021, there was a near miss incident for two workers beneath a swinging suspended load while decommissioning part of a monopod offshore platform in the northern waters of Western Australia. The workers were cutting through the monopod’s main leg (caisson) when the topside, which was rigged to a crane on a vessel, unexpectedly moved and detached from the supporting monopod and swung over the workers. The crane operator quickly manoeuvred the topside away from the workers, lowering it into the water to control its motion. The workers disembarked from the main leg to the designated crew safety vessel without incurring any injuries. The topside platform was safely retrieved onto the crane vessel.

Contributory factors

Factors assessed as having contributed to the incident included:

• Dynamic forces that could be applied to a rigged load while a crane was in auto-tensioning mode were inadequately understood or considered when developing the lift plan;
• The requirement for pre-load tension was not subject to adequate technical assessment;
• The platform rotated on separation; the engineering assessment did not identify the turning motion induced by pre-load tension;
• An over-reliance of previously successful methodologies rather than the analysis of their suitability to the specific tasks of this activity.

Actions

DEMIRS outlined the following measures to minimise the risk of a similar incident while conducting decommissioning activities:

• A technical assessment of lift plans to identify and consider all forces acting on a load, including forces which may be unintentionally applied due to automatic settings and crane modes;
• Use of castellated cut designs where a possibility of rotation (turning moment) of the load exists;
• Consider and assess the whole of life design, including commissioning and decommissioning procedures;
• Ensure workers are not under suspended loads.

Members may wish to refer to:

• Serious incident: topsides started swinging during lifting