Inside a fertilizer plant, the splitting of a 15,000-ton cryogenic ammonia storage tank at the joint between the tank skirt and roof placed 9,200 tons of NH3 into contact with the atmosphere, with the rupture extending 2/3 of the way around the storage circumference. Concentrations of 150 to 400 ppm of NH3 were measured, under windy conditions, during the 6-hour period following the accident. No environmental impact was noted. The accident was caused by a defective weld between the tank shell and dome. A metallurgical expert assessment indicated that the weld displayed major penetration flaws, and these flaws would have worsened by exposure to metal fatigue effects due to pressure cycles. The analogue pressure recording at the time of the accident revealed the presence of a pressure surge (not quantified since the measurement scale had been surpassed) when rupture occurred, yet computations still showed that the pressure increase speed before the accident had a normal value. Furthermore, the weld break over 2/3 of the tank circumference induced deformation of the vertical sidewall, which could have led to tank failure below the liquid level.