Oslo-based Det Norske Veritas (DNV) confirmed Greenpeace's own estimate of the oil content of Shell's redundantstorage buoy was grossly exaggerated because it was based on ''obvious misinterpretations''. The environmental group admitted the error last month.
The oil company had to abandon sea dumping after Greenpeace's protests inspired a European petrol boycott. The 14,500-tonne Spar is now anchored in a Norwegian fjord while Shell works on new disposal plans. DNV was paid pounds 200,000 for its investigation.
Shell hired DNV because Greenpeace complained there had been no independent checks before Shell got government approval to dump the massive structure in deep water.
It found Shell may have seriously underestimated the quantity of polychlorinated biphenyls, PCBs. These are used in electrical equipment and are among the most persistent, toxic non-pesticide chemicals ever mass-produced for peaceful purposes. Their manufacture is now banned.
While Shell estimated there were fewer than 20 grams on board, DNV said there could be up to eight kilograms - 400 times as much. PCBs may be in small capacitors fitted to each one of 250 light fittings.
DNV said that because it found out about the capacitors fairly late in its inquiry, it was not yet certain whether they did contain PCBs. But given the age of the Spar - 20 years - ''that would be the usual thing'', said DNV vice president Ole-Andreas Hafnor.
Shell said it would be going back on board next week to check. DNV pointed out that the capacitors could easily be removed for safe disposal.
Shell's assessment of the quantities of oil, radioactivity and toxic metals in the Spar were broadly correct, said DNV, one of the world's leading ship certification bodies. It slightly underestimated the levels of some and overestimated others.
The oil company estimated there was a total of 53 tonnes of oil and oily wax in the Spar. DNV said there was 74 to 103 tonnes. Greenpeace's estimate was 5,500 tonnes, but it later admitted that it took samples from the wrong place.
Both Shell and Greenpeace welcomed the DNV report and accepted its findings.
Shell said that even if it had underestimated the radioactivity and pollutants in the Spar by a factor of 10, dropping it 7,000ft on the Atlantic sea- bed would not have posed a significant environmental threat. But John Wybrew, Shell UK's corporate affairs director, confirmed Shell would not propose sea dumping for obsolete installations again.Reuse content