Within a fertilizer plant, a cylindrical horizontal tank containing 50 tons of ammonia under pressure (6.2 bar) failed during unloading, releasing 30 tons of NH3, with 8 tons escaping from the tanker truck. A cloud measuring 150 m in diameter and 20 m high immediately formed and extended a total of 450 m. An employee standing 45 m from the tank at the time of the explosion was killed instantly. In all, 18 people died, 6 of whom were located outside the plant and 65 intoxicated to a point of requiring hospitalisation. The burst tank bottom was composed of two metal panels (one wide and one narrow) assembled by welding before the forming operation undertaken for the tank bottom. The rupture occurred transversally to this bottom weld, with a quarter of the bottom surface separating, practically without any deformation, and being projected. The point of failure surrounded a zone where 2 years prior metal rolling flaws had been detected during an ultrasound inspection; these flaws were subsequently repaired with welds. The investigation performed indicated various causes of rupture, including: failure to release tension on the device following construction, a tank bottom metal plate warped and deteriorated due to the cold forming operation applied to the large tank radius, and the introduction of additional stresses from hydraulic testing performed a few days prior.