"It ws the mystery that wouldn’t go away after the oil stopped gushing: Why did the blowout preventer of the drilling rig Deepwater Horizon fail to prevent the blowout of April 20, which killed 11 people and led to the historic BP oil spill?
The official answer came Wednesday, and it was both strikingly mundane and, at least for critics of the petroleum industry, alarming.
The forensic analysis of the blowout preventer, or BOP, conducted under contract to federal investigators by the Norwegian company Det Norske Veritas showed that the initial loss of well control — and the violent surge of oil and gas up the well — caused the drillpipe to buckle and move slightly off center. That fouled the operation of the blind shear rams, the blades designed to close on the drillpipe and shut in the well.
This final line of defense was overmatched by the blowout once it began. When the blades closed on the pipe, the misalignment prevented the shearing surfaces of the rams from achieving a clean cut. Moreover, the rubber “packers” around the blades were unable to make a tight seal. The drillpipe snagged the rams in a partially open position."