If it works, the rectangular structure with a pyramid-shaped dome on top will capture as much as 85 percent of the leaking crude, Doug Suttles, London-based BP’s chief operating officer for exploration and production, said yesterday…

May 8 (Bloomberg) — BP Plc is lowering and placing on the seafloor a 40-foot-tall steel chamber that represents its best hope of stopping its Macondo well from spewing oil into the Gulf of Mexico until the flow can be fully stanched.

BP expects the containment system to begin funneling leaking oil to an overhead drillship by May 10, Tom Keilman, director of government and public affairs, told reporters today on a conference call. The edges of the chamber will sink into mud 5,000 feet (1,524 meters) under the surface of the Gulf.

If it works, the rectangular structure with a pyramid- shaped dome on top will capture as much as 85 percent of the leaking crude, Doug Suttles, London-based BP’s chief operating officer for exploration and production, said yesterday at a press conference in Robert, Louisiana. The well began spilling oil after an April 20 explosion on Transocean Ltd.’s Deepwater Horizon rig, which sank in the Gulf two days later.

“They have to lower it quite precisely,” Suttles said. “The tolerances are very tight.” Operators of a ship-mounted crane about a mile above the leak lowered the containment box toward the well yesterday.

To stop the rest of the leaking, BP has 20 experts studying the possibility of injecting pieces of rubber into the well, Suttles said. The containment box is a stopgap measure until BP can complete a well started May 2 aimed at relieving pressure so the leak can be plugged with cement.

Hoping for Success

“We hope it is going to work, but you can’t just risk everything and hope it works,” BP spokesman Mark Salt said in a telephone interview. “You have to explore other options.”

The April 20 explosion and fire aboard the Deepwater Horizon, which BP leased from Geneva-based Transocean, killed 11 workers and led to a spill estimated at 5,000 barrels a day.

A bubble of methane gas that shot up the drill column and burst through several seals and barriers caused the blast, the Associated Press reported late yesterday, citing interviews with rig workers obtained by a California engineering professor.

BP’s Salt declined to comment on the AP report. The U.S. Coast Guard and the U.S. Minerals Management Service will begin an investigation May 11 to identify the factors leading to the incident, according to a government statement issued today.

The U.S. Fish and Wildlife Service yesterday stopped public access to Louisiana’s Chandeleur and Freemason islands, where BP and federal officials Thursday said oil from the spill first reached shore.

Wildlife Refuge Closed

The islands comprise the Breton National Wildlife Refuge. Barring the public will protect nesting birds and speed cleanup work, the Fish and Wildlife Service said yesterday.

The National Oceanic and Atmospheric Administrationyesterday widened a fisheries closure in the Gulf of Mexico, calling it necessary to reassure consumers that fish and shrimp caught in the region are safe to eat.

Calm seas have enabled BP to burn as much as 9,000 barrels of oil from the surface, Suttles said. The Coast Guard and BP have been skimming oil from the Gulf. Oil accounts for about 10 percent of the 45,000 barrels of oil and water skimming boats have recovered so far, Suttles said.

Controlled burns won’t be done today because of high winds, Coast Guard Petty Officer Connie Terrell said in a telephone interview. BP plans to do more skimming today and to drop additional dispersant on the oil slick, company spokesman Mark Proegler said.

Containment Efforts

The Minerals Management Service, overseer of offshore drilling, completed inspections of all deepwater drilling rigs operating in the Gulf without identifying hazards, regional director Lars Herbstsaid at the press conference in Robert.

Inspectors checked test records of blowout preventers, an assembly of valves atop wells on the seafloor. The blowout preventer on the BP well failed to stop a mixture of oil and gas from ejecting unexpectedly and igniting the rig, according to Suttles. Houston-based Cameron International Corp. supplied the blowout preventer for the Deepwater Horizon.

Besides possibly injecting rubber cuttings into the well, engineers are considering installing a second blowout preventer atop the first, Suttles said.

Some of the methods being studied to stop the leak could instead increase it if they don’t work, Suttles said. Before the containment box can be installed, robots must make sure the area is clear, Suttles said.

Robot Clearing

Water temperatures of about 42 degrees Fahrenheit (6 Celsius) and pressures of 2,300 pounds per square inch may cause natural gas in the oil, estimated at 3,000 cubic feet per barrel, to freeze as it rises.

BP plans to circulate warm surface water and antifreeze around the pipe to prevent clogging, Dave Clarkson, the company’s project manager for the underwater containment plan, said on a May 5 conference call.

Similar containment boxes have been used to funnel crude from leaking wells in shallow water. This is the deepest deployment of the system, according to a fact sheet provided by BP.

BP fell 13.1 pence, or 2.3 percent, to 553.9 pence yesterday in London. The shares have dropped 15 percent since the rig exploded.

To contact the reporters on this story: Jessica Resnick-Ault in New York at •••@••.•••; Jim Polson in New York at •••@••.•••.

Last Updated: May 8, 2010 12:47 EDT