- During safety testing, BOP components and control systems had 62 failures across 238 subsea wells drilled over three years (2004-06) in the Gulf of Mexico.
- Four of the 62 BOP breakdowns were "safety critical failures," i.e., failures that would "prevent the BOP or a component of the system from closing and sealing on demand and allowing an uncontrolled release of fluid from the well bore," the study found. One safety-critical failure was so severe that, if a blowout had occurred at the time of the test, "they would not have been able to contain it." That amounts to one "safety critical" failure for every 59.5 wells drilled in the test period, and one per 9.5 rigs.
One of the components subject to failure was the blind-shear ram—the last-line-of-defense emergency hydraulic piston that is supposed to slice through the drill pipe and seal the well. If that fails, as it did on the BP Deep Horizon then….well, you know what happens.