Tyrone Benton, who operates underwater robots that do the actual work on the complex, giant machinery a mile underwater, says one of the robot's cameras spotted a leak on a control pod of the blowout preventer (BOP).
The BOP is essentially the emergency shutoff valve fixed permanently to a wellhead on the seafloor. The Deepwater Horizon's BOP is as tall as a house and the control pods, of which this rig had at least two, are the brains of the machinery - a combination of mechanics and electronics.
"We saw a leak on the pod, so by seeing the leak we informed the company men," Benton told the BBC in an interview for its investigative program "Panorama," which airs Monday night.
He said his supervisors told BP and the company in charge of the BOP, Transocean, and their management teams made the decision to shut down the leaking control pod and rely solely on another, meant as backup.
"They have a control room where they could turn off that pod and turn on the other one, so that they don't have to stop production," Benton told the BBC's Hillary Anderson.
One expert on ocean oil drilling from the University of Texas called the decision to keep the BOP operating after the discovery of the leak "unacceptable."
"If you see any evidence of the blowout preventer not functioning properly, you should fix it by whatever means possible," professor Tad Patzek told the BBC for its report.
The decision appears to have been made to save money. Shutting down the entire BOP would have meant a complete halt to Deepwater Horizon's work - at a time when the BBC says BP was spending $500,000 every day to keep it running.
U.S. lawmakers have repeatedly accused BP of putting profits over safety in their operation of the rig.
In an interview with CBS News chief investigative correspondent Armen Keteyian just as BP attempted to plug the hemorrhaging BOP with a powerful blast of debris, company boss Tony Hayward said his "focus throughout my tenure as CEO, which is now just over three years, (has been) on safe and reliable operations… It's been our number one priority."
Meanwhile, dozens of BP workers tasked with boring through thousands of feet of seafloor to bisect the gushing well and relieve pressure on the Deepwater Horizon well are getting on with their work, "."
CBS News correspondent Mark Strassmann reports that the relief wells need to reach a depth of 18,000 feet - and a target only about 7 inches wide - to allow BP to cap the leaking well. Currently, the drilling crews are at about 16,000 feet, but due to the unpredictable nature of the task at hand, it's still unclear whether BP will meet its mid-August goal to put a cap on this still-unfolding disaster.
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A detailed AP review has shown that reliability questions have long shadowed blowout preventers:
• Accident reports from the U.S. Minerals Management Service, a branch of the Interior Department, show that the devices have failed or otherwise played a role in at least 14 accidents, mostly since 2005.
• Government and industry reports have raised questions about the reliability of blowout preventers for more than a decade. A 2003 report by Transocean, the owner of the destroyed rig, said: "Floating drilling rig downtime due to poor BOP reliability is a common and very costly issue confronting all offshore drilling contractors."
• Lawsuits have pointed to these valves as a factor in previous blowouts.
It is unclear why the blowout valves on the Deepwater Horizon didn't stop the April 20 blast that killed 11 workers and has sent millions of gallons of oil spewing into Gulf. Interviews with rig workers conducted as part of BP's internal investigation into the explosion indicate that a methane gas bubble escaped from the well and expanded quickly as it shot up the drill column, a series of events that included the failure of the blowout preventer and explosion of the rig.
Transocean claims to have checked the Deepwater Horizon BOP just three days before the blast and found it in good working order.