Black tide threatens disaster on US south coast

After a rig explosion in the Gulf of Mexico, thousands of gallons of oil are polluting the sea and threatening beaches and fisheries.

The US president, Barack Obama, last night sent in military engineers to help to deal with a giant oil slick in the Gulf of Mexico that is threatening an environmental disaster. Gulf fisheries and oyster beds on the coast of Louisiana, sandy beaches in coastal Alabama and Mississippi, and the livelihoods of many ordinary Americans are among the economically significant resources threatened by the oil leaking from the Deepwater Horizon rig, which exploded on April 20 in a well blowout, killing 11 people, and sank two days later.

The oil, now leaking at an estimated rate of 5,000 barrels a day, represents a daily loss of more than US$400,000 (Dh1.5 million) to BP, the company licensed to produce it. But that is a drop in the ocean compared with the $1bn that some experts say Britain's biggest oil company may have to pay to clean up the mess and settle legal claims from people affected by the disaster. BP said it welcomed help from the military. "We'll take help from anyone," said Doug Suttles, the company's chief operations officer. But time may be running out - oil from the spill is within 12 miles of the coast, and it could reach shore as soon as today.

If the well cannot be closed, almost 100,000 barrels of oil - 4.2 million gallons - could spill into the Gulf before crews can drill a relief well to alleviate the pressure. The Exxon Valdez, the worst oil spill in US history, leaked 11 million gallons into Alaska's Prince William Sound in 1989. Since the Macondo well lacked a remote-control shut-off switch, which some countries require for offshore oil production, BP has tried for the past few days to use robotic submarines, operating 1,500 metres below the surface, to activate a giant plug with valves attached, called a blowout preventer, to stop the oil flow.

That has not worked, and new leaks have been discovered from at least two other parts of the platform. BP has moved on to Plan B, which involves constructing a giant steel dome to place over the sunken platform and contain the oil. There is no guarantee that this would work at such a depth, and fabricating the dome will take two to three weeks. At the same time, the company has hired blowout specialists to drill two slanting "relief wells" to intersect the one causing all the trouble. Cement and special mud will be pumped down one of the relief wells to plug up the damaged well and divert a controlled flow of oil into the second relief well. But the delicate operation, involving state-of-the-art precision drilling and pressure control technology, could take months.

On the surface, BP, the US Coastguard and others deployed a 150-metre boom to corral thousands of litres of the thickest oil for towing to a remote area where it could be set on fire. A test burn on Wednesday was successful, leading to a decision to try the approach on a larger scale. Greg Pollock, the head of the oil spill division of the Texas General Land Office, which is providing equipment for the clean-up crews in the Gulf, said: "When you can get oil ignited, it is an absolutely effective way of getting rid of a huge percentage of it." When the flames go out, the material that was left resembled hardened balls of tar that could be removed from the water with nets or skimmers, he said.

However, the controlled burn technique has never been tried off the US coast, Mr Pollock said. For BP, the accident in the Gulf of Mexico is the latest in a string of disasters. In 2005, an explosion at the company's Texas City refinery killed 15 workers. The following year, oil leaking from a damaged pipeline on the North Slope of Alaska that was transporting the company's oil contaminated the tundra on which Arctic species, including caribou, depend for food.