A member has reported that, during the work on a floating production storage and offloading unit (FPSO), a diver’s umbilical became fouled on a flexible riser.
The riser had been disconnected from the underside of the FPSO by an air diver working at 40fsw. The diver had rigged up a tirfor for a lateral pull to aid separation of the riser which was secured to the support vessel crane and winch with 10T webbing slings.
When the lateral pull was applied, the flexible riser dropped, parting the slings resulting in an uncontrolled descent to the seabed at -100msw.
At this point, the diver’s umbilical was fouled on the crane wire resulting in the diver being dragged down to -70fsw before he could clear himself and return to the dive basket for recovery to the surface.
The company found the root causes to be the following:
- The riser was substantially heavier than expected and detailed by the client;
- Webbing slings were used as opposed to wire rope slings.
The company has introduced the following measures from lessons learnt:
- Umbilical management is critical for all diving operations. Excess and unwanted umbilical slack should be taken up at all times by the diver tender. The diving supervisor, diver and tenders should be alert and proactive in this respect;
- Webbing slings should not be used underwater particularly when contact with sharp edges is possible;
- Attention to detail when calculating weights underwater to include marine growth and dynamic loading should identify the need for proper and suitable rigging;
- The diver is to remain well clear and if possible return to surface when such activities are planned.
Members are reminded of the need for a robust risk assessment system and diving project plan to be in place before diving operations should commence.
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