NEW ORLEANS – A deepwater oil platform that burned for more than a day after a massive explosion sank into the Gulf of Mexico on Thursday, creating the potential for a major spill as it underscored the slim chances that the 11 workers still missing survived.

The sinking of the Deepwater Horizon, which burned violently until the gulf itself extinguished the fire, could unleash more than 300,000 gallons of crude a day into the water. The environmental hazards would be greatest if the spill were to reach the Louisiana coast, about 50 miles away.

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Supply vessels attempt to douse the flames engulfing the Deepwater Horizon oil rig Wednesday in the Gulf of Mexico. The platform sank Thursday, and a Coast Guard spokeswoman said the uncapped well could be spilling up to 336,000 gallons of crude oil a day. The Associated Press

Crews searched by air and water for the missing workers, hoping they had managed to reach a lifeboat, but one relative said family members have been told it’s unlikely any of the missing survived Tuesday night’s blast. The Coast Guard found two lifeboats but no one was inside. More than 100 workers escaped the explosion and fire; four were critically injured.

Carolyn Kemp of Monterey, La., said her grandson, Roy Wyatt Kemp, 27, was among the missing. She said he would have been on the drilling platform when it exploded.

“They’re assuming all those men who were on the platform are dead,” Kemp said. “That’s the last we’ve heard.”

Jed Kersey of Leesville, La., said his 33-year-old son, John, was a roughneck aboard the rig and was sleeping when the explosion occurred. He said his son told him that all 11 missing workers were on the rig floor at the time of the explosion.

“He said it was like a war zone,” said Jed Kersey, a former offshore oil worker.

An alarm sounded and the electricity went out, sending John Kersey and other workers scurrying to a lifeboat that took them to a nearby service boat, his father said.

“They waited for as many people as they could,” Jed Kersey said. He added that his son wasn’t ready to talk publicly about his experience.

ENVIRONMENTAL THREAT GROWS

As the rig burned, supply vessels shot water into it to try to keep it afloat and avoid an oil spill, but there were additional explosions Thursday.

Officials previously said the environmental damage appeared minimal, but new challenges have arisen now that the platform has sunk.

The well could be spilling up to 336,000 gallons of crude oil a day, Coast Guard Petty Officer Katherine McNamara said, but she didn’t know whether that was occurring. The rig also carried 700,000 gallons of diesel fuel, but that would likely evaporate if the fire didn’t consume it.

Coast Guard Rear Adm. Mary Landry said crews saw a 1-by-5-mile rainbow sheen with a dark center of what appeared to be a crude oil mix on the surface of the water. She said there wasn’t any evidence crude oil was coming out after the rig sank, but officials also aren’t sure what’s going on underwater. They have dispatched a vessel to check.

The oil will do much less damage at sea than it would if it hits the shore, said Cynthia Sarthou, executive director of the Gulf Restoration Network.

“If it gets landward, it could be a disaster in the making,” she said.

Doug Helton, incident operations coordinator for the National Oceanic and Atmospheric Administration’s office of response and restoration, said the spill is not expected to come onshore in next three to four days. “But if the winds were to change, it could come ashore more rapidly,” he said.

At the worst-case figure of 336,000 gallons a day, it would take more than a month for the amount of crude oil spilled to equal the 11 million gallons spilled from the Exxon Valdez in Alaska’s Prince William Sound.

The well will need to be capped underwater. Coast Guard Petty Officer Ashley Butler said crews were prepared for the platform to sink and had the equipment at the site to limit the environmental damage.

Oil giant BP, which contracted the rig, said it has mobilized four aircraft that can spread chemicals to break up the oil, along with 32 vessels that can suck more than 171,000 barrels of oil a day from the surface.

‘HOPING FOR GOOD NEWS’

Crews searching for the missing workers have covered the 1,940-square-mile search area by air 12 times and by boat five times. The boats searched all night Wednesday.

The family of Dewey Revette, a 48-year-old from southeast Mississippi, said he was also among the missing. He worked as a driller on the rig and had been with the company for 29 years.

“We’re all just sitting around waiting for the phone to ring and hoping for good news. And praying about it,” said Revette’s 23-year-old daughter, Andrea Cochran.

Adrian Rose, vice president of rig owner Transocean Ltd., said Thursday that some surviving workers told company officials that their missing colleagues may not have been able to evacuate in time. He said he was unable to confirm whether that was the case.

Those who escaped did so mainly by getting on lifeboats that were lowered into the gulf, Rose said. Weekly emergency drills seemed to help, he said, adding that workers apparently stuck together as they fled the devastating blast.

“There are a number of uncorroborated stories, a lot of them really quite heroic stories of how people looked after each other. There was very little panic,” Rose said.

The U.S. Minerals Management Service, which regulates oil rigs, conducted three routine inspections of the Deepwater Horizon this year — in February, March and on April 1 — and found no violations, MMS spokeswoman Eileen Angelico said.

The rig was doing exploratory drilling when the explosion and fire occurred, sending a column of boiling black smoke hundreds of feet over the gulf.

Rose has said the explosion appeared to be a blowout, in which natural gas or oil forces its way up a well pipe and smashes the equipment. But precisely what went wrong was under investigation.

Transocean Ltd. spokesman Guy Cantwell said 111 workers who made it off the Deepwater Horizon safely were ashore Thursday, and four others were still on a boat that operates an underwater robot. A robot will eventually be used to stop the flow of oil or gas to the rig, cutting off the fire. He said officials have not decided when that will happen.

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