The containment vessel is lowered into the Gulf of Mexico at the site of the Deepwater Horizon rig collapse, Thursday, May 6, 2010. (AP Photo / Gerald Herbert)

By HARRY R. WEBER and TAMARA LUSH – Associated Press Writers ON THE GULF OF MEXICO (AP) — Workers late Thursday started lowering a giant concrete-and-steel box over the blown-out oil well at the bottom of the sea in a risky and untested bid to capture most of the gushing crude and avert a wider environmental disaster. A crane lifted the box from the boat named The Joe Griffin and crews from a second boat started the box on its slow journey a mile underwater. It would take hours to reach the seafloor. “We haven’t done this before. It’s very complex and we can’t guarantee it,” BP spokesman David Nicholas warned earlier.

Video Exclusive raw video: Oil containment box lowered. AP Exclusive raw video shows workers easing a giant concrete-and-steel box into the Gulf of Mexico late Thursday, starting the long process of lowering the contraption over the blown-out oil well. (May 6)

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. 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. Deckhands wore respirators while workers on surrounding vessels took air-quality readings. Crews later were able to start the work. Black oil coated the white shell of the box as it was being lowered. 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. …

AP: Giant box lowered in Gulf to battle oil spill