ON THE GULF OF MEXICO -- Workers gathered to begin lowering a giant concrete-and-steel box over the blown-out oil well at the bottom of the sea Thursday in a risky and untested bid to capture most of the gushing crude and avert a wider environmental disaster.
"We haven't done this before. It's very complex, and we can't guarantee it," BP spokesman David Nicholas warned.
The 100-ton containment vessel is designed to collect as much as 85 percent of the oil spewing into the Gulf and funnel it up to a tanker. It could take several hours to lower it into place by crane, after which a steel pipe will be installed between the top of the box and the tanker. The whole structure could be operating by Sunday.
The mission took on added urgency as oil started washing up on delicate barrier islands.
The technology has been used a few times in shallow waters, but never at such extreme depths -- 5,000 feet down, where the water pressure is enough to crush a submarine.
The box -- which looks a lot like a peaked, 40-foot-high outhouse, especially on the inside, with its rough timber framing -- must be accurately positioned over the well, or it could damage the leaking pipe and make the problem worse.
BP spokesman Doug Suttles said he is not concerned about that happening. Underwater robots have been clearing pieces of pipe and other debris near where the box will be placed to avoid complications.
"We do not believe it could make things worse," he said.
Other risks include ice clogs in the pipes -- a problem that crews will try to prevent by continuously pumping in warm water and methanol -- and the danger of explosion when separating the mix of oil, gas and water that is brought to the surface.
"I'm worried about every part, as you can imagine," said David Clarkson, BP vice president of engineering projects.
If the dome works, a second one now being built may be used to deal with a second, smaller leak from the sea floor.
"Hopefully, it will work better than they expect," first mate Douglas Peake said from aboard the ship that brought the box to the site.
The well blew open April 20 when the Deepwater Horizon drilling platform exploded 50 miles out in the Gulf of Mexico, killing 11 workers. It has been spewing an estimated 200,000 gallons a day in the nation's biggest oil spill since the Exxon Valdez disaster in Alaska in 1989.
Interior Secretary Ken Salazar on Thursday halted all new offshore drilling permits nationwide until at least the end of the month while the government investigates the Gulf spill.
Oil slicks stretched for miles off the Louisiana coast, where desperate efforts were under way to skim, corral and set the petroleum ablaze. People in Mississippi, Alabama and Florida watched in despair.
The dropping of the box is just one of many strategies being pursued to stave off a widespread environmental disaster. BP is drilling sideways into the blown-out well in hopes of plugging it from the bottom. Also, oil company engineers are examining whether the leak could be shut off by sealing it from the top in