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.
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But the lowering of the box was delayed late Thursday 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.
Deckhands wore respirators while workers on surrounding vessels took air-quality readings. It was unclear when they would be able to proceed, though crew members were hopeful it would still be on Thursday night.
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 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 isn't concerned about that. Underwater robots have been clearing debris near where the box will be placed to avoid complications.
The well blew open on 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.
On Thursday, oil reached several barrier islands off the Louisiana coast, many of them fragile animal habitats. Several birds were spotted diving into the oily, pinkish-brown water, and dead jellyfish washed up on the uninhabited islands.