San Juanico DisasterNovember 19, 1984 — San Juan Ixhuatepec, Mexico

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On the northern edge of Mexico City, in the town of San Juan Ixhuatepec in the State of Mexico, stood one of the largest liquefied petroleum gas terminals in the world. The San Juanico terminal, owned and operated by the state oil company Pemex, stored and distributed the propane and butane on which the capital cooked and heated. It held 54 pressure vessels in all — six spherical Horton tanks, four of 1,600 cubic metres and two of 2,400, and 48 smaller horizontal “bullet” tanks — with a total capacity of 16,000 cubic metres, about one third of Mexico City’s entire LPG supply, delivered by three underground pipelines from refineries across Mexico. The terminal had been built from 1962 onward, and it did not stand in open country: the town grew up around it until some 40,000 people lived alongside the plant, in simple brick and wooden houses built as close as 130 metres from the storage tanks.

In the early hours of Monday, November 19, 1984, the terminal was being refilled from the Minatitlán pipeline after standing nearly empty the day before. By 5:30 a.m. its spheres and bullets held between 11,000 and 12,000 cubic metres of LPG. At about that time, a pipe 20 centimetres (8 inches) across, running between a sphere and the row of bullet tanks, ruptured. Operators at the plant, and at a pumping station 40 kilometres away, saw the pressure fall — but for five to ten minutes nobody could find where the gas was escaping, and the plant had no gas detection system. The escaping LPG, heavier than air, spread at ground level as a cloud some 200 metres by 150 and about two metres deep, and drifted towards one of the terminal’s waste-gas flare pits.

At 5:45 a.m. the cloud reached the flare pit and ignited. The flash fire raced back through the congested plant and became a violent vapour cloud explosion, felt across the city and registered on a seismograph at the National University 32 kilometres away. About ninety seconds later the first vessel burst in a BLEVE — a boiling liquid expanding vapour explosion — throwing up a fireball up to 300 metres across. Eight more BLEVEs followed as the fire took hold of vessel after vessel, the last of them recorded at 7:01 a.m. Tanks weighing up to 30 tons were torn from their mountings and hurled as far as 1,200 metres into the town. Only four of the 48 bullet tanks survived intact; the four smaller spheres were destroyed outright, and the two large spheres escaped only by collapsing as their unprotected support legs buckled in the heat. Around 150 houses were destroyed and hundreds more damaged. Smaller explosions went on until late morning while firefighters concentrated on cooling the two surviving spheres, and as many as 200,000 people were evacuated from the surrounding districts.

Most of those who died were townspeople, killed in their sleep in the houses within a few hundred metres of the tanks; only five of the dead were plant workers. The Mexican government put the official death toll at 503; most accounts place the dead between 500 and 600, though unofficial estimates ran far higher, and the exact figure will never be known — of the remains recovered, only 16 could be identified, and the rest were buried in a common grave in the Caracoles cemetery. Between 5,000 and 7,000 people were injured, most of them burned. It remains the most severe LPG disaster in history.

Pemex officials at first tried to shift the blame onto the neighbouring gas distribution companies, and onto the residents themselves for living beside the plant. No results of any public inquiry — or of Pemex’s own investigation — have ever been published, and there is no official report for this page to link to. The only official finding ever released was a declaration by Mexico’s Attorney General on December 22, 1984, which held Pemex responsible for the disaster and ordered the company to fund compensation to the victims. Payments began some six weeks later at a flat rate, about US$10,400 for each person killed, and 167 families were given new homes. An informal review later carried out by the United States pipeline safety agency pointed to maintenance problems, and to relief valves that should have prevented the fatal overpressure but had never been installed on the receiving pipelines.

The fullest technical account of San Juanico was written not in Mexico but in the Netherlands. A team from TNO, the Dutch national research organisation, reached the site two weeks after the disaster: a scientific mission, undertaken without Pemex’s assistance, to test the explosion and damage models used in safety studies. Its report, R 85/0222, issued in May 1985, concluded that the fires, more than the blasts, had caused the destruction; it criticised the terminal’s crowded layout, which had let the accident escalate from vessel to vessel, and the land-use planning that had allowed housing inside the plant’s damage radius. The analysis became a standard reference for LPG storage worldwide and fed directly into the American Petroleum Institute’s Standard 2510 for LPG installations. The terminal was demolished; its site is now Cri Cri Park, and in Hidalgo Park nearby a large metal cross stands in memory of the victims. The lesson the industry took from San Juanico is written into modern practice: a separation of 300 metres between such a plant and housing was proposed in the forensic reviews that followed — storage on this scale belongs at a distance, and never in the middle of a town.