Oil spill clean-up should focus on shoreline rather than sunken tanker

Oil sitting in a tanker that sank off the coast of Spain may be better left untouched, despite attempts by an international operation to retrieve the 70,000 tonnes of crude oil trapped in the Prestige’s hull at the bottom the sea.

Rescue operations to pump the oil from the partially ruptured single-hull tanker have been hampered by stormy conditions. Clean-up operations along the shoreline are making better progress in scooping up some of the 6,000 tonnes of oil that escaped when the vessel first encountered stormy weather.

At temperatures close to zero at a depth of 3,500 metres, the viscous oil is likely to solidify into a gel, which will make it harder to pump up to the surface. “Oil has been successfully recovered from sunken ships before,” Douglas Cormack, chairman of the British Oil Spill Control Association told edie. “But pumping the oil becomes more difficult with depth and viscosity.” In this case, the ship is the deepest ever to be recovered, and the oil is heavy, crude oil.

Various methods have been proposed to melt the oil to make it more easy to pump, including heating the oil with microwaves or mixing it with dissolving chemicals to ‘thin’ it. “The most successful method of reducing the viscosity of the oil in these situations has been to heat it using hot liquid pumped through heat-exchange pipes around the ship,” says Cormack. “It’s more difficult to mix a light chemical with a semi-solid material, because it wouldn’t diffuse easily through the oil. You would need some method of mixing them to speed up the thinning process.”

In sunken tanker situations, it is sometimes better to concentrate efforts on the oil that has been spilled, and wait for the first signs of release – which may not occur for decades – from the sunken vessel before starting a deep sea recovery operation, continues Cormack.

Depending on sea and shore conditions, natural processes can remove the oil from the sea, so efforts should be focused on the more vulnerable shores. Those that have high winds and strong waves, where the surf is hitting the rocks, will have enough energy to break up even the stiffest oil, says Cormack, while in winter conditions, the sea is often agitated enough to break up the oil into small droplets that are more easily degraded. Clean-up operations should therefore be focused on sheltered, sandy shores, where the oil can be shovelled up and steam-cleaned off the rocks.

Arguments continue over whether Prestige should have been brought closer to shore into a sheltered spot, rather than towed further out to sea, so that the bulk oil could be more easily transferred to another ship. Countries differ in their strategies for tackling distressed oil tankers. While the UK government works with salvage teams to decide the best overall course of action, regardless of objections from protest groups, some governments are less willing to front the clean-up operation and inevitable publicity that ensues. It may be easier not to take action, to tow the tanker away from the shore and let the owners deal with the consequences, rather than deciding on a course of action and mounting a full-scale operation that could incur liabilities.

Edie recently reported on research that reveals that many species have still not recovered from the 1989 Exxon Valdez spill in Prince William sound in Alaska (see related story). The Woods Hole Oceanographic Institute has also found that the effect of oil spills could be permanent (see related story).

Loyola de Palacio, EU Vice-President of transport, told the European Parliament that the Prestige accident could have been avoided if proposals made by the European Commission to ban single-hull tankers by 2002 had been fully adopted.

Palacio has written to Member states urging them to accelerate legislation to improve port inspections of high-risk tankers and replace single hull ships with double-hull designs. Single-hull vessels are due to be phased out in 2015. All new oil tankers built since 1996 are required to have double hulls.

The EU is also setting up ship traffic monitoring system that will be in place from 2004, while Member States are developing strategies to accommodate ships in distress in dedicated places of refuge. But the EU has yet to establish a compensation fund. The COPE Fund proposed by the Commission would ensure that €1 billion would be available to pay compensation for any oil spill in EU waters. A separate international fund, FIPOL, is being set up by Member States, but will only receive final approval next May.

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