The tragedy of San Juanico--the most severe LPG disaster in history

During the early morning of Monday, 19 November 1984, one of the largest disasters in industrial history occurred in the Mexico City Area, causing the greatest rescue effort to assist population in an emergency ever undertaken. The tragic catastrophe started in a large LPG (Liquid Petroleum Gas) storage and distribution centre in San Juan Ixhuatepec, 20 km north of Mexico City. The facilities, owned by the Pemex State Oil Company, consisted of six spherical storage tanks (four with a volume of 1600 m3 and two with a volume of 2400 m3) and 48 horizontal cylindrical bullet tanks of different sizes. At the time of the disaster the storage tanks contained 11,000 m3 of a mixture of propane and butane. The inhabitants of San Juan Ixhuatepec numbered about 40,000, and a further 60,000 lived in the hills surrounding the village. The majority were poor country people living in one-story houses constructed of concrete pillars filled in with bricks and with roofs of iron sheets. The disaster started due to LPG leakage, probably a pipe leakage or rupture due to excess pressure. A vapour cloud built up and was slowly moved by the north-east wind towards the ground-placed flare pit located in the western part of the plant. The vapour cloud was ignited around 5:40 a.m. and was followed by an extensive fire at the plant area. The first explosion was registered on the seismograph at the University of Mexico at 05 h 44 min 52 s and was followed by a dozen explosions within the next hour, some of them of BLEVE type (Boiling Liquid Expanding Vapour Explosion) due to rupture of one or more storage tanks. Two of the explosions had an intensity of 0.5 on the Richter scale. Unburned and burning gas entered the houses south of the plant area and set fire to everything. Blast waves from the explosions not only destroyed a number of houses but also shifted several cylindrical tanks from their supports and added more gas to the fire. The smaller spheres and some of the cylinders exploded and fragments and even whole cylinders weighing around 30 tons, were scattered over distances ranging from a few to up to 1200 m.