In 2004, another study was commissioned by the Minerals Management Service. It found that the company making the blowout preventers had used a faulty formula to determine how much force would be needed for the device to slam down on a pipe and clamp it shut. "It provided shear forces lower than required or desired in many cases; in other words, there was little safety factor built in," the study said. The research also noted that the failure of a blowout preventer helped lead to the second largest oil spill on record - a 1979 disaster off the Yucatan Peninsula that emptied an estimated 140 million gallons into the ocean.
If the devices were not strengthened, the report warned, the dangers of another large spill would escalate, the report said.
"As smaller operators with limited appreciation of the risks venture into ever deeper water, the industry's risk increases. It appears that at least some of the rigs currently in operation have not considered critical issues necessary to ensure that their shear rams will shear the drill pipe and seal the wellbore."
BP did not respond to emailed questions about blowout preventers, and could not be reached by phone. Transocean spokesman Guy Cantwell (no relation to the senator) declined to speculate about why the blowout preventer did not work last week. But he told ABC News Wednesday that the company had had no reason to believe it would not.
"Everyone wants to know about the cause," Cantwell said. "We're going to wait for the facts before we reach any conclusions. But I can tell you, this rig had a very good safety and environmental record."
Elmer Danenberger, a former chief of Offshore Regulatory Programs for the Minerals Management Service, told ABC News that regulators require the rigs to test the blowout preventers every two weeks, and there had been a test on the Deepwater Horizon within hours of the explosion.
Danenberger said it was possible that "some kind of violent flow after the BOP test might have done some damage," and rendered it inoperable. But that "is just speculation," he said.
"To be honest, I can't remember an offshore blowout where the BOP totally mis-functioned like this," he said. "There are going to be a lot of people waiting to hear what happened here -- wanting to know why didn't this safeguard work?"