HOUSTON — Cutoff valves like the one that failed to stop the Gulf of Mexico oil disaster have repeatedly broken down at other wells in the years since federal regulators weakened testing requirements, according to an Associated Press investigation.
These steel monsters known as blowout preventers or BOPs — sometimes as big as a double-decker bus and weighing up to 640,000 pounds — guard the mouth of wells. They act as the last defense to choke off unintended releases, slamming a gushing pipe with up to 1 million pounds of force.
While the precise causes of the April 20 explosion and spill remain unknown, investigators are focusing on the blowout preventer on the Deepwater Horizon rig operated by BP PLC as one likely contributor.
To hear some industry officials talk, these devices are virtually foolproof.
But a detailed AP review shows that reliability questions have long shadowed blowout preventers: