Published: Apr 28, 2010 5:24 PM EDT

NEW ORLEANS, Louisiana - Racing against a threat to environmentally sensitive marshlands, authorities planned to begin Wednesday burning some of the thickest oil from a rig explosion off the coast of Louisiana.

A Coast Guard spokesman says the burn was expected to begin in the morning.

Petty Officer 2nd Class Prentice Danner says fire-resistant containment booms will be used to corral some of the thickest oil on the water's surface, which will then be ignited. It was unclear how large an area would be set on fire or how far from shore the first fire would be set. The slick is the result of oil leaking from the site of last week's huge explosion of the rig Deepwater Horizon that left 11 people missing and presumed dead. Oil continues to spill undersea at an estimated rate of 42,000 gallons a day.

Robot submarines have been unable to cap the well. Operator BP Plc. says work will begin as early as Thursday to drill a relief well to take pressure off the flow from the blowout site. That could take months. Winds and currents in the Gulf have helped crews in recent days as they try to contain the leak, but it has moved steadily toward the mouth of the Mississippi River, an area home to hundreds of species of wildlife and near some of the Gulf's richest oyster grounds.

Meanwhile, the cost of the disaster continues to rise. The Deepwater Horizon exploded on April 20. The rig was owned by Transocean Ltd. and operated by BP. Industry officials say replacing the Deepwater Horizon would cost up to $700 million. BP has said its costs associated with containing the spill are running at $6 million a day.

The company said it will spend $100 million to drill the relief well, which it does not expect to be operating for up to 3 months. The Coast Guard has not yet reported its expenses.

Gulf spill gives Gov. Crist pause over drilling

Florida Gov. Charlie Crist touched ground after about 90 minutes above the Gulf of Mexico on Thursday and had no doubts about where he stood on oil drilling off his state's shore: Not now, no way. Crist was awed - and not in a good way - at the huge oil spill spreading from a damaged rig off the Louisiana coast and had nightmare visions of the same situation in Florida.

"Clearly it could be devastating to Florida if something like that were to occur. It's the last thing in the world I would want to see happen in our beautiful state," Crist said. "Until you actually see it, I don't know how you can comprehend and appreciate the shear magnitude of that thing. It's frightening."

Crist, who opposed drilling off Florida's coast until softening his stance over the past two years, said there is no question now that lawmakers should give up on the idea this year and in coming years. He has said previously he would support drilling if it was far enough from shore, safe enough and clean enough. He said the spill is proof that's not possible.

Coast Guard Capt. Steve Poulin, the sector commander for coastal Mississippi, Alabama and the Florida Panhandle, briefed Crist on the situation before he, the governor and Florida environmental secretary Michael Sole boarded a C-144 aircraft for a 90 minute flight above the gulf. With Crist strapped in a backward-facing chair, the Coast Guard opened up the entire back of the plane to give him a wide view of the dark oil slick spreading in a 80- by 42-mile blob in the gulf.

"It's enormous. It's everywhere. It's absolutely unbelievable in it's magnitude," Crist said. On his flight back to Tallahassee, Crist said the spill is evidence that drilling technology can't meet his criteria for drilling off Florida. "Clearly that one isn't far enough and that's about 50 to 60 miles out, it's clearly not clean enough after we saw what we saw today - that's horrific - and it certainly isn't safe enough. It's the opposite of safe," Crist said.

Poulin told Crist that at best, the spill can be contained in two weeks by placing a dome over the pipe that broke during an April 20 explosion. But Poulin said a dome has never been used at such an extreme depth - 5,000 feet. If it doesn't work, Poulin told Crist and Sole that another option is to drill a new line next to the broken one to relieve pressure. That could take 90 days. "Wow, 90! Ouch," Sole said.

Meanwhile, 1,000 barrels of oil a day are gushing into the gulf. Poulin said it's hard to tell how much is making it to the surface and how much is being suspended in the depths. A shift in winds over the next few days may push the water toward the gulf coast, but Poulin said he don't know when, or if, the coastline could be hit by the oil slick. As soon as he arrived back home, Crist called Florida National Guard Maj.

Gen. Douglas Burnett and emergency management director David Halstead and asked them to work with Sole and the Coast Guard to make a plan to protect Florida's beaches should the oil be pushed by wind and waves toward the Panhandle. "It's gianormous," Crist told Halstead.

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