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'The Exxon Valdez is Going to Pale in Comparison'
US Military Joins Gulf of Mexico Oil Spill Effort
The US military has joined efforts to stop an oil leak in the Gulf of Mexico as fears rise about its scale.
Five times as much oil as previously thought could be leaking from the well beneath where a rig exploded and sank last week, US officials said earlier.
The slick is 45 miles (72km) by 105 miles (169km) - almost the size of Jamaica - and heading for the US coast.
A third leak has been discovered, and a fire-fighting expert said the disaster may become the biggest oil spill ever.
"Probably the only thing comparable to this is the Kuwait fires [following the Gulf War in 1991]," Mike Miller, head of Canadian oil well fire-fighting company Safety Boss, told the BBC World Service.
"The Exxon Valdez [tanker disaster off Alaska in 1989] is going to pale [into insignificance] in comparison to this as it goes on."
Scientists say only a quarter of local marine wildlife survived the Exxon Valdez disaster.
Some 5,000 barrels (210,000 gallons) a day were now thought to be gushing into the sea 50 miles off Louisiana's coast, said the US Coastguard's Rear Admiral Mary Landry.
If those estimates are correct, the spill could match the 11m gallons spilt from the Exxon Valdez within two months.
The scale of the operation to contain the oil spill and protect both the US coastline and wildlife is unprecendented, with the military and other government agencies collaborating with BP - which had hired the sunken rig - and industry leaders.
Welcoming the US military's offer of help, BP's Chief Operating Officer Doug Suttles said the company would take help from anyone to combat the spill, but gave no specifics of what form that help might take.
Efforts to stem the flow are being complicated by the depth of the leak at the underwater well, which is about 5,000ft (1,525m) beneath the surface.
Weather forecasters have meanwhile warned that changing winds could drive the oil slick ashore by Friday night. Its leading edge is now only 20 miles (32km) east of the mouth of the Mississippi.
A coast guard crew has set fire to part of the oil slick in an attempt to save environmentally-fragile wetlands.
The "controlled burn" of surface oil took place in an area about 30 miles (50km) east of the Mississippi river delta.
But Mr Miller warned that burning off leaking oil was not a long-term solution.
"The object of this game is to shut off the flow," he said.
Engineers are working on a dome-like device to cover oil rising to the surface and pump it to container vessels, but it may be weeks before this is in place.
It is feared that work on sealing the leaking well using robotic submersibles might take months.
BP is also working on a "relief well" to intersect the original well, but this is experimental and could take two to three months to stop the flow.
President Barack Obama had been briefed on the new developments, and BP has welcomed the offer of assistance from the defence department to help contain the spill.
Seventy vessels - oil skimmers, tugboats barges and special recovery boats that separate oil from water - as well as five aeroplanes were working to spray dispersants and round up oil, BP said.
Eleven workers are missing and presumed dead after the worst oil rig disaster in almost a decade.
Louisiana Governor Bobby Jindal said the top priority was "to protect our citizens and the environment".
With the spill moving towards Louisiana's coast, which contains some 40% of the nation's wetlands and spawning grounds for countless fish and birds, it was hoped a "controlled burn" of oil contained by special booms would limit the impact.
Environmental experts say animals nearby might be affected by toxic fumes, but perhaps not as much as if they were coated in oil.
On Wednesday afternoon, BP and coastguard boats swept the thickest concentrations of oil into a fire-resistant boom.
This was then towed to a five-mile "burn zone" set up inside the slick, where it was set alight shortly before nightfall.