Why Royal Oak's fuel posed a different wreck problem

Why was Royal Oak's fuel drained while the scuttled German warships were treated differently?

Royal Oak was an oil-fired ship, whereas many German wrecks had carried coal, and any remaining liquid fuel had to be assessed wreck by wreck.

The comparison begins with propulsion and remaining cargo. Royal Oak was fully oil-fired, while much of the interned German fleet had been coal-fired, so the wrecks did not present identical liquid-fuel inventories. Fuel may also have escaped over time, leaving the amount still aboard as the central practical question. A later exchange says the wrecks had been studied for environmental risk and reiterates that most German ships went down with coal. Every Scapa wreck therefore requires its own assessment rather than the same fuel-removal response.