HOUSTON (Reuters) - The U.S. Coast Guard on Wednesday set a "controlled burn" to battle a giant oil slick from last week's deadly offshore drilling rig explosion, as the spill threatened wide-scale coastal damage for four U.S. Gulf Coast states.
The leaking well, 5,000 feet (1,525 metres) under the sea off Louisiana's coast, has created an oil sheen and emulsified crude slick slightly bigger than the U.S. state of West Virginia, the Coast Guard said.
Eleven workers are missing and presumed dead after the worst oil rig disaster in almost a decade. Swiss-based Transocean Ltd's Deepwater Horizon rig sank on April 22, two days after it exploded and caught fire while finishing a well for BP Plc about 40 miles (64 km) southeast of the mouth of the Mississippi River.
The burn began at 5 p.m. CDT (11:00 p.m. British time), an agency spokesman said. Workboats were to pool segments of the spill inside a fire-resistant "boom," essentially a floating corral, to be towed to a remote area for burning, the Coast Guard said.
The agency said it planned "small, controlled burns" of several hundred gallons each lasting about an hour and invisible from shore.
BP, which owns the well, is spending millions of dollars a day on what it has called the largest oil spill containment operation in history, involving dozens of ships and aircraft.
"We will not rest until we have done everything to bring this under control," said Andrew Gowers, head of group media for London-based BP, likening the spill's consistency to "iced tea" with the thickness of a human hair.
At midday Wednesday, the edge of the spill was 23 miles (37 km) off the Louisiana coast, near fragile estuaries and swamps teeming with birds and other wildlife. A shift in winds could push the spill inland to the Louisiana coast by this weekend, according to forecasters at AccuWeather.
Tarballs and emulsified oil streamers could reach the Mississippi Delta region late on Friday, said Charlie Henry, an expert with the National Oceanic and Atmospheric Administration.
Along with a large seafood industry, the area contains key wildlife habitats in the Pass-A-Loutre Wildlife Management Area and Breton National Wildlife Refuge on the Louisiana coast, which are teeming with nesting birds.
"It's premature to say this is catastrophic," said Coast Guard Rear Admiral Mary Landry, who is heading the federal cleanup effort. "I will say this is very serious."
The spill could be devastating for fishermen and oystermen that rely on estuaries and swamps along the Mississippi River for their livelihood. For a factbox of potential environmental impacts, follow the link [nN28185887].
"We're sitting here half praying and half with our fingers, toes and everything else crossed," said Byron Encalade, president of the Louisiana Oysterman Association in Pointe A La Hache, who lost five boats when Hurricane Katrina hit in 2005.
As the oil spill grows, so does the chance that it will affect efforts by the U.S. Congress and President Barack Obama to open more offshore areas to limited oil and gas drilling.
"This brings home the issue that drilling despite all the advancements in technology is still a risky business," said Athan Manuel of the Sierra Club, an environmental group.
Preparations were underway to deploy thousands of feet of floating booms in Louisiana, Mississippi, Florida and Alabama in an attempt to contain the oil slick, the Coast Guard said.
The Louisiana accident is the worst oil rig disaster since 2001, when a rig operated by Petrobras off the Brazilian coast exploded and killed 11 workers.
The spill is not nearly as big as the Exxon Valdez disaster, which spilt about 11 million gallons (50 million litres) of oil into the Prince William Sound in Alaska in 1989. BP's well is spewing about 42,000 gallons (190,900 litres) of oil a day into the ocean, the Coast Guard estimates.
Additional reporting by Kristen Hays in Houston and Pascal Fletcher in Miami; Editing by Mary Milliken and David Gregorio