On September 21, 2001, when the world was still traumatized by the attacks on the twin towers in New York, 330,000 tonnes of ammonium nitrate exploded at the AZF plant in Toulouse. This industrial catastrophe, the most serious in Western Europe since the end of the second world war, killed thirty people, injured several thousand and destroyed innumerable buildings. People lost their homes, children found themselves without schools and wage-earners were deprived of work. The site of the explosion itself resembled a devastated battlefield. When the official investigation began, observers emphasized how outrageous it was that a factory of this kind should have been located at the very heart of so densely populated an area. Thirty thousand people lived within the immediate vicinity of AZF – a plant belonging to the Total-Fina-Elf group – and its two neighbours, the Société Nationale des Poudres et Explosifs, which manufactured gunpowder and explosives, and Tolochimie. It had long been known precisely how dangerous these enterprises were. Indeed, each factory had been submitted to stringent national security standards, known as ‘Seveso 2’.