The San Juanico disaster involved a series of fires and explosions at a liquefied petroleum gas (LPG) tank farm in the settlement of San Juan Ixhuatepec (popularly known as San Juanico), a municipality of Tlalnepantla de Baz, State of Mexico, Mexico, on 19 November 1984. The facility and the settlement, part of Greater Mexico City, were devastated, with 500–600 victims killed, and 5000–7000 suffering severe burns. It is one of the deadliest industrial disasters in world history, and the deadliest industrial accident involving fires and/or explosions from hazardous materials in a process or storage plant since the Oppau explosion in 1921.
Background
The incident took place at a storage and distribution terminal for liquified petroleum gas (LPG) belonging to the state-owned oil company Pemex. The facility consisted of 54 LPG storage tanks: six large spherical tanks, of which four had a capacity of 1,600 cubic metres (57,000 cu ft) and two with capacity of 2,400 cubic metres (85,000 cu ft), as well as 48 smaller horizontal bullet-shaped tanks of various sizes, for a total plant capacity of 16,000 cubic metres (570,000 cu ft), representing one third of Mexico City's entire liquid petroleum gas supply. Contrary to good practice, the sphere support legs were not fireproofed. Tanks were divided into several clusters by concrete walls about 1 metre (3.3 ft) tall. It received LPG through three underground pipelines from remote sites: a 12-inch (305 mm) pipeline from Minatitlán (576 km; 358 mi), a 4-inch (102 mm) pipeline from Poza Rica (235 km; 146 mi) and another 4-inch (102 mm) line from the Azcapotzalco refinery (8 km; 5 mi). There were two ground flare pits and a fire protection system including a pond, fire pumps and firewater spray distribution. The plant was said to have been built in conformance to API standards, but this was later put into question. In the two months leading up to the incident, local plant safety committee inspections revealed that: 30–40% of safety devices (including firewater spray) were bypassed or non-operational; housekeeping was substandard; pressure gauges were in bad shape and inaccurate; a relief valve on an LPG-receiving manifold was missing; an additional relief valve was needed for the Minatitlán pipeline, after operational flowrate had been increased to 11,900 cubic meters/day (75,000 barrels/day). Adjoining the terminal to the east, there was a Unigas plant with further LPG storage and distribution capacity. Immediately further east was a Gasomático facility for bottling the LPG and dispatch it by truck. The Pemex terminal distributed LPG to these two plants via underground pipelines. Further away from this cluster, five more gas distribution companies imported gas from the Pemex terminal using tank trucks and bottles. The town of San Juanico surrounded the site and consisted of 40,000 residents, with an additional 60,000 more living in nearby communities. The settlement of San Juan Ixhuatepec long predated the disaster, but housing surrounding the facility itself began to materialize only after the construction of the installation started in 1962, although this is disputed. However, at least the two largest spheres were added to the plant only recently, when the plant was already surrounded by the densely populated neighborhood. The closest houses were at a distance of 130 metres (430 ft) from the storage tanks. Most of the houses were simple brick or wooden buildings.
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