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BP report on cause of Gulf oil spill spreads the blame

Human and mechanical failures led to the Deepwater Horizon blast and the subsequent Gulf oil spill, finds a BP report released Wednesday. Transocean and Halliburton are also cited.

By Staff writer / September 8, 2010

A boat motors near oil sheen in the Gulf of Mexico, between the Deepwater Horizon oil spill site and the Louisiana coast on Aug. 3.

Gerald Herbert/AP/File


The Deepwater Horizon oil well blowout that killed 11 men and resulted in the largest oil spill in US history was the result of a series of human and mechanical failures by "multiple companies and work teams," including the companies' own representatives, according to a report by BP released Wednesday.

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The failures contributed to an accident in the Gulf of Mexico that, BP says, was caused by "a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces," the report said.

IN PICTURES: Louisiana oil spill

The 193-page report, not counting hundreds of pages of appendices, was based on BP's own internal investigation. It cites a sequence of critical failures by its own staff, as well as rig operator Transocean and the cementing company Halliburton. They include the following:

  • Faulty cement and other barriers "at the bottom of the Macondo well that failed to contain hydrocarbons within the reservoir, as they were designed to do, and allowed gas and liquids to flow up the production casing."
  • Incorrect evaluation of negative pressure test results by BP and Transocean representatives, though "well integrity" had not been fully established at that point.
  • A critical 40-minute period during which the Transocean rig crew – the operator of the Deepwater Horizon rig – "failed to recognize and act on the influx of hydrocarbons into the well until the hydrocarbons were in the riser and rapidly flowing to the surface."
  • After the gushing oil and gas mixture reached the rig, a routing of that flow to a mud-gas separator, "causing gas to be vented directly on to the rig rather than being diverted overboard."
  • A flow of natural gas into the engine rooms through the ventilation system. This created a cloud ripe for ignition that the rig’s fire and gas system did not prevent.
  • Failure of the rig’s massive blowout preventer on the sea floor to automatically seal the well, "probably because critical components were not working." 

The four-month investigation that undergirded the report was conducted by Mark Bly, BP's head of safety and operations, who headed a team of specialists.

The report – which also offered 25 recommendations for improving deepwater oil drilling practices – was nevertheless hampered in arriving at any definitive conclusions in some areas because key evidence was not available to BP itself. The blowout preventer, for instance, was only raised from the ocean bottom over the weekend.

But BP's outgoing chief Tony Hayward said the investigation clearly showed BP was not solely responsible and that "multiple parties, including BP, Halliburton, and Transocean, were involved."

"The investigation report provides critical new information on the causes of this terrible accident," Mr. Hayward said in a statement. "It is evident that a series of complex events, rather than a single mistake or failure, led to the tragedy."