Explosion-damaged oil rig sinks

NEW ORLEANS, April 22 (UPI) -- An oil rig weakened by an explosion that left 11 workers missing sank in the Gulf of Mexico off the Louisiana coast Thursday, authorities said.

U.S. Coast Guard Petty Officer Tom Atkeson said the rig, which had been taking on water from two days of firefighting efforts, went down "sometime this morning," The New York Times reported.

Atkeson said response vessels at the scene would work to "mitigate the effects of the pollution." It wasn't clear how much oil spilled into the ocean, he said.

The collapse of the Deepwater Horizon rig came as rescuers continued their search for the crew members missing since the explosion late Tuesday.

The mobile drilling platform in mile-deep water about 50 miles from Louisiana is owned by Swiss corporation Transocean Ltd. and leased by British Petroleum.

"We have no idea where the 11 unaccounted-for personnel are at this time," Adm. Mary Landry, U.S. Coast Guard District 8 commander, said before the collapse. "The 11 people are unaccounted for and we will continue the search-and-rescue case until it's reasonable that we might not find anybody out there."

Federal officials said the rig was inspected three times in 2010, including once earlier in April, and received no violation citations, WWL-TV, New Orleans, reported.

A Transocean official described the explosion as a well blowout.

"There's undoubtedly some abnormal pressure built up in the marine riser which comes from the sea bed, from the blowout preventer stack, to the rig," said Adrian Rose of Transocean. "Obviously hydrocarbons under pressure -- gas or oil -- got into the riser, and as it came up the riser, it expanded rapidly and ignited."

The rig had 126 crew members on board at the time of the explosion, Transocean officials said.

BP officials said they didn't believe the $350 million rig was leaking oil into the gulf, but as many as seven oil spill response vessels were on standby, if needed.