BP engineers started late Thursday lowering a giant concrete cap over a blown-out wellhead on the bottom of the Gulf of Mexico — a desperate move to contain the leak spewing an estimated 200,000 gallons of crude oil a day into the surrounding waters.
The barge Joe Griffin arrived at the source of the leak carrying the 100-ton concrete-and-steel contraption known as a "cofferdam" Thursday morning. But the lowering of the box was delayed because of dangerous fumes rising from the oily water in the windless night, the captain of the supply boat hauling the box told The Associated Press. A spark caused by the scrape of metal on metal could cause a fire, Capt. Demi Shaffer said.
If it works, the system could collect as much as 85 percent of the oil that's been leaking nearly a mile down, and direct it to the surface so it can be contained and removed.
The mission took on added urgency as oil started washing up on delicate barrier islands.
A sheen of thick, tar-like oil surrounded the vessel at the site 50 miles off the Louisiana coast. Engineers say the cap is the best short-term solution for controlling the gusher since the Deepwater Horizon offshore drilling rig exploded and sank two weeks ago, killing 11 people.
The Joe Griffin was expected to meet up with a Norwegian vessel, the Boa Sub C, equipped with a crane that will be used to lower the cap to the wellhead.
BP spokesman Bill Salvin said the drop is expected at about noon local time Thursday.
Such an operation has never been tried at such extreme depth, said Doug Suttles, the British oil giant's chief operating officer.
"You can imagine we're landing a very, very large metal building on the sea floor to capture the flow," he said. "This has to be done at a depth of 5,000 feet, so it's a complex task."
Once the cap nears the seabed, remotely operated underwater vehicles will be used to guide it into place. A steel pipe will be attached to a tanker at the surface and connected to the top of the cap to move the oil.
"It's very dark down there ... and we will have lights on the [submersibles], and we know exactly where to put this and guide it into place," said David Clarkson, BP's vice president for project execution.
But even if crews are able to successfully lower the structure in place over the leaking pipeline, there are other potential problems. At 5,000 feet, the water is just 10 degrees above freezing. That, combined with crushing pressure at that depth, could cause the siphon pipe to clog up and prevent the oil from being channeled to the surface. To combat that problem, crews plan to continuously pump warm water and methanol down the pipe to dissolve any clogging.
Engineers also worried about the volatile cocktail of oil, gas and water when it arrives on the ship above, but they believe the liquids can be safely separated without an explosion.
Meanwhile, Interior Secretary Ken Salazar halted all new offshore drilling permits nationwide until at least the end of the
month while the government investigates the Gulf spill.
On Wednesday, BP announced the first small success in containing the spill. Using robotic submarines, the company's engineers managed to install a valve on the leaking pipes — sealing off one of three holes. It won't reduce the amount of oil being discharged but does set the stage for further attempts to stem the flow, company officials said.
Meanwhile, a rapid response team planned to head to the Chandeleur Islands off Louisiana on Thursday to look into unconfirmed reports that oil from the spill had made landfall there, Coast Guard Petty Officer Erik Swanson said.
Dozens of boats have been working around the clock in recent days, laying and repositioning inflatable booms designed to halt the surface flow of the oil slick, which threatens beaches, fragile marshes and wildlife along the U.S. Gulf Coast.
Globules of oil are already falling to the bottom of the sea, endangering virtually every link in the ocean food chain.
Scientists say bacteria, plankton and other tiny, bottom-feeding creatures that might consume the oil will be eaten by small fish, crabs and shrimp. They, in turn, will be eaten by bigger fish, such as red snapper, and marine mammals like dolphins.
There was also concern that the slick could get into the powerful north-flowing Gulfstream current and move up the East Coast.
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