A massive operation is under way in and around the Gulf of Mexico to halt a leak from a blown-out oil well and prevent the spread of the slick. The graphic above shows the scene 1,524m (5,000 feet) beneath the waves where oil is leaking out of the damaged remnants of the oil well apparatus.



Below we explain the various attempts to stem the leak from the damaged oil lines on the sea bed. Underwater efforts to cap oil leak Initially, BP tried to lower a 125-tonne, 18-metre (59 feet) high container dome over the main leak on the sea floor. However, this failed when gas leaking from the pipe mixed with water to form hydrates, ice-like crystals, that blocked up the steel canopy. Instead, engineers have lowered a smaller device onto the site. Dubbed the Top hat, it will sit over the tear in the pipe and partially stop the leak. To prevent the build up of hydrates, methanol is pumped into the top hat to disperse the water and gas. The top hat is 1.5m (5 feet) high and 1.2m in diameter. Two special side lines are used to pump methanol into the top hat to displace water and gas leaking from the broken oil pipe. This should prevent the build-up of hydrates. Once in place, oil can be pumped up to the surface. BP plan to lower the original subsea containment dome over the top hat to provide a better seal over the leaking site and pump oil up to the surface. This time, it will be attached to a pipe that can pump warm water into the dome to prevent the build-up of hydrates. BACK {current} of {total} NEXT Meanwhile, four robotic submersibles have been trying to activate the blow-out preventer, a set of huge valves designed to seal the well. Experts believe the blow-out preventer (BOP) must have partially triggered otherwise the flow of oil to the surface would be more extreme than it is. In an unusual move, BP, the British oil giant which contracted another company to drill the well, has also started using dispersant chemicals down at the leak site as well as on the surface. A long-term solution is also in progress - drilling a relief well which can tap into the leaking well and take the pressure off the broken well. However, it could be three months before this is operational. Up to five thousand barrels a day are thought to be leaking from the site of the Deepwater Horizon rig which sank on 22 April after an explosion in which 11 workers lost their lives.

The delicate eco-system of the gulf coastline is rich in wildlife including the brown pelican, many species of duck, turtles, and whales. There are fears that the disaster could reach the scale of the 11m gallon Exxon Valdez spill off Alaska in 1989. How the oil has spread

Approximate oil locations 22 April - 15 May TACKLING THE OIL SLICK Emergency teams are using several methods in attempts to deal with the oil at the surface, which has created a slick covering about 2,000 sq miles (5,200 sq km). More than 275 vessels, including skimmers, tugs, barges and recovery vessels, are being used. Skimmers, which skate over the water, brushing up the oil are also being employed and more than 90,000 barrels of oil-water mix have been removed. Around 190 miles of floating boom are being used as part of the efforts to stop oil reaching the coast. A US charity is even making booms out of nylon tights, animal fur and human hair. Hair donations have been sent from around the world to help make the special booms, which will be laid on beaches to soak up any oil that washes ashore. Dispersant chemicals, rather like soap, are being sprayed from ships and aircraft in an effort to help break down the oil - which is also degraded by wind and waves. Burning is another method used to tackle oil spills - although it can be tricky to carry out and has associated environmental risks such as toxic smoke. So far emergency crews have had little success in containing the spill using those methods. New underwater technology aimed at stopping crude oil rising to the surface at the site of the leak has had some success.







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