NTSB concludes Shell failed to implement a towing plan for the Kulluk drilling rig sufficient to address the risks of towing the rig from Alaska to Seattle.
The likely cause of the grounding of the Kulluk drilling rig in late 2012 was an inadequate assessment by Royal Dutch Shell plc of the risks of towing the rig, meaning that a tow plan insufficient to address that risk was implemented, the National Transportation and Safety Board (NTSB) reported Thursday.
The Kulluk departed from near Unalaska, Alaska Dec. 21, 2012 and was underway to Seattle for maintenance repairs. The rig, which was under tow by the ice-class, anchor handling tow supply vessel Aiviq, grounded in heavy weather near Ocean Bay on the eastern coast of Sitkalidak Island.
Given the risks associated with this transmit, including the likelihood of the tow encountering severe weather, Shell and its contractors, particularly Offshore Service Vessels, the operator of the Aiviq, who reviewed and approved the plan should have mitigated those risks or departed at a time when severe weather is less likely. Shell and its contractors could have included additional tow vessels to the entire transit to reduce the likelihood of a catastrophic result.
NTSB said the accident did not result from one error or mechanical failure. The agency attributed the accident to shortcomings in the plan’s design, including the fact that the tow plan and towing equipment had only one external review, the lack of requirement for the U.S. Coast Guard to oversee the tow.
“Although multiple parties were involved in the review and approval of the tow plan, the ultimate decision to approve and implement the tow was Shell’s,” NTSB said in the report. “The dynamics of a single entity approving a go/no-go decision in the face of risks, with multiple parties involved, have been addressed in studies of previous catastrophic events. This research demonstrates that, even with formal review processes involving multiple entities, the ability of parties involved in a decision to articulate and draw attention to risks is limited when a single entity bears ultimate decision-making responsibility and at the same time favors a particular outcome of the decision.”
NTSB was unable to determine as to why the ice-class, anchor handling tow supply vessel Aiviq, which was towing the rig, lost engine power at a critical point in the journey. Coast Guard investigators believe that the design of the fuel oil storage tanks’ common vent and overflow system were flawed, and led to the seawater contamination of the fuel tanks during the vessels voyage in rough sea conditions. But Offshore Service Vessels said that fuel contaminants were present in fuel taken on by the Aiviq in Dutch Harbor, and that this contamination, rather than the seawater that entered the system later, led to the engine power loss.
NTSB said the source of the fuel contamination was outside of its investigation scope, and therefore was not determined.
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