My favourite little intelligence site reports:
Main fuel installations of this size are routinely equipped with systems for shutting down sections to curb the spread of fire or blasts. The magnitude of the explosions that engulfed the entire installation indicate an unusual catastrophe of some kind. Witnesses reported heavy rumbles before the explosion, much as though an aircraft had crashed into the oil installations.
On Dec. 7, an Islamic website ran an excerpt of an earlier videotape in which bin Laden’s No. 2, Ayman Zawahiri called on “holy warriors” to concentrate their attacks on oil targets.
"All indications at this stage are that this was an accident. However clearly we will keep an open mind," Hertfordshire Chief Constable Frank Whiteley told a news conference after Britons, still on edge from July bomb attacks in London, awoke to images of destruction from new blasts.