The San Juanico disaster was a series of deadly fires and explosions that occurred at a Pemexliquefied petroleum gas tank farm in the settlement of San Juan Ixhuatepec, a town of Tlalnepantla de Baz, State of Mexico, Mexico, on 19 November 1984.[2] The facility and the settlement were devastated by the damage, with an estimated 500–600 people killed, and around 5000–7000 suffering severe burns.[3]
Liquefied gas Horton tanks similar to the six spherical tanks involved in the San Juanico disasterLPG bullet tanks. There were 48 tanks of this type in the Pemex plant. Note how this modern installation incorporates some of the lessons learned from San Juanico: an uncongested, well ventilated area, with the horizontal tanks in a parallel cluster configuration, which minimizes the effects of missiles arising from BLEVEs.
The incident took place at a storage and distribution terminal for liquified petroleum gas (LPG) belonging to the state-owned oil company Pemex. The terminal, locally named San Juanico, mostly stored propane and butane products,[4] and received its LPG from Pemex oil refineries across southern Mexico through three underground pipelines:
a 12-inch (305mm) pipeline from the Lazaro Cardenas Refinery in Minatitlán, Veracruz (576km; 358mi away),
a 4-inch (102mm) diameter pipeline from the Poza Rica Gas Complex in Veracruz (235km; 146mi away), and
another 4-inch (102mm) line from the Azcapotzalco Refinery in Mexico City (8km; 5mi away).[5]
The facility consisted of 54 total LPG storage tanks: six large Horton sphere tanks, of which four had a capacity of 1,600 cubic metres (57,000cuft) and two with capacity of 2,400 cubic metres (85,000cuft), as well as 48 smaller, horizontal bullet tanks of various sizes. These tanks gave the facility a total plant capacity of 16,000 cubic metres (570,000cuft),[6] representing one third of Mexico City's entire liquid petroleum gas supply.[7][8] Tanks were divided into several clusters by concrete walls about 1 metre (3.3ft) tall. There were two ground flare pits and a fire protection system including a pond, fire pumps and firewater spray distribution.[8]
Adjoining the terminal to the east was a Unigas plant with additional LPG storage and distribution capacity. Further east was a Gasomáticogas-bottling and distribution facility, where bottles distributed by truck.[8] The Pemex terminal distributed LPG to these two plants via underground pipelines. Five more gas distribution companies in the surrounding area obtained gas from the Pemex terminal using tank trucks and trucks carrying bottles.[9]
The town of San Juan Ixhuatepec surrounded the site and had a population of about 40,000 residents, with an additional 60,000 more living in nearby communities.[2][b] The closest houses were at a distance of 130 metres (430ft) from the storage tanks, and most of the houses were simple brick or wooden buildings.[9][10] The settlement of San Juan Ixhuatepec existed before the facility and disaster,[11] but housing surrounding the facility itself began only after the construction of the installation started in 1962,[9][12][13] although this is disputed.[14] At least two sphere tanks were added to the plant when it was already surrounded by the densely populated neighborhood.[5]
Previous safety concerns
The plant was said to have been built in conformance to API standards,[4] but this was later put into question.[5] In the two months leading up to the incident, local plant safety committee inspections revealed multiple issues with several of the facility’s mechanical and passive safety systems:
Between 30 and 40% of safety devices, including the firewater spray system, were being bypassed or were non-operational;
Multiple pressure gauges were physically defective and inaccurate;
a relief valve on one of the manifolds for an LPG-receiving pipe was missing; and
the support legs of the Horton sphere tanks lacked fireproofing.
It was also found that an additional relief valve would be needed for the Minatitlán pipeline, after the pipeline’s operational flow rate had been increased to 11,900 cubic meters per day (75,000 barrels/day).[15]
Accident
Site filling and initial leak
In the early hours of 19 November 1984, the facility was being filled from the Minatitlán refinery about 400 kilometres (250 miles) away, as its tanks had been nearly empty since the day prior.[16] By 5:30 a.m. CST, two of the Horton sphere tanks and all 48 of the bullet tanks were filled at 90% capacity, while the rest of the Horton sphere tanks were at 50%;[16] at this point, the plant held about 11,000–12,000 cubic metres (390,000–420,000cuft) of LPG,[10] with an energy equivalent in excess of 300 TJ,[17] roughly five times the energy released by the atomic bomb of Hiroshima.[18]
At around 5:30 a.m., a 20 cm diameter pipe between a Horton sphere tank and the bullet tanks ruptured, resulting in a release of vaporized LPG. Control room operators at both San Juanico and the pipeline pumping station40 kilometres (25 miles) upstream[6] noticed a substantial pressure drop in the pipeline. For 5 to 10 minutes after the initial pressure drop, neither set of operators could identify the cause of the leak, and the gas cloud continued to build up inside the terminal, reaching an estimated volume of 66,000 cubic metres (2,263,800 ft3).
Fire and explosions
At 5:45a.m, the cloud eventually reached one of the waste-gas flare pits and ignited.[16] A flash fire ensued, which immediately transitioned to a violent vapor cloud explosion (VCE), likely due to its flame front’s acceleration being enhanced by the congested geometry of the plant. The blast was felt and recorded by a seismometer at a National Autonomous University of Mexico (UNAM) lab located some 32km (20mi) away in Mexico City.[8][10] The initial VCE created a domino effect accident,[10] as the explosion damaged more piping and storage tanks which resulted in a massive conflagration fed by multiple LPG leaks, heating and damaging other storage tanks.
About 90 seconds after the VCE blast, at 5:46a.m, the first BLEVE occurred in one of the tanks.[7] The explosion was witnessed by the pilot of a Pan Am flight on approach to Mexico City International Airport, who communicated to air traffic control that he believed a nuclear bomb may have exploded in the city.[19] Eight subsequent BLEVEs were recorded by the UNAM seismometer over the next 2 hours, with the last one at 7:01a.m. The first and sixth BLEVEs are believed to have been the most violent explosions, with both registering a peak of 0.5 on the Richter scale.[7] The BLEVE fireballs were up to 300 metres (980ft) in diameter, and had a duration of some 20 seconds.[6] Smaller explosions continued until 11a.m.,[9] when the flames on the last Horton sphere tank was extinguished.
Fatalities and damage to facility and town
The disaster resulted in 500 to 600 deaths, and 5000–7000 severe injuries,[2] although unofficial sources cite up to 2000 fatalities.[1] Five workers at the San Juanito terminal perished, but the overwhelming majority of the victims were residents living in the housing area surrounding the plant, mostly within 300 metres (980ft) of the centre of the storage area.[9] Most of the casualties were killed by the initial explosions while they slept. The heat and fire generated by explosions incinerated most of the victims’ corpses to ashes, with only 2% of the recovered remains left in recognizable condition.[2] The American Institute of Chemical Engineers (AIChE) estimated that the thermal radiation produced by the BLEVEs was in excess of the threshold of pain (4.0kW/m2) within a radius of 1,850 metres (1.15mi) of the site.[20]
The San Juanico Terminal was almost entirely destroyed. The four smaller Horton sphere tanks were completely destroyed, with fragments propelled up to 350 metres (1,150ft) away from their original location, into public areas. Only the two larger Horton sphere tanks were intact, but has collapsed onto the ground as their support legs has weakened and buckled under the intense hear of the fires. Only four of the 48 bullet tanks were found intact after the fire. 12 of the tanks that had exploded were launched from their supports and become missiles, with the furthest landing 1,200 metres (3,900ft) off-site; the total weight of the fragments of these tanks weighed up to 30 metric tons.
Several secondary gas explosions occurred inside the neighboring plant buildings and surrounding houses.[2][10] At the Gasomático site, 100 parked trucks loaded with household gas cylinders weighing 20–40 kilograms (44–88lb) each were completely burned out, with hundreds of secondary explosions taking place.[9]
An area of several square kilometers was affected, with varying degrees of damage from the fires and projectile tanks. Around 150 homes were completely destroyed, with a few hundred sustaining other levels of damage.[9]
Emergency response
The first call to the emergency services was made at 5:45, immediately after the VCE.[6] More than 200 firefighters were deployed to the affected area in the first six hours after the first explosion. Water for firefighting was provided to the site by tank trucks normally used for domestic portable water distribution.[19] After the last BLEVE at 7:01, firefighters prioritized cooling the two larger, intact Horton sphere tanks in order to avoid additional explosions.[19][21] A major rescue operation was declared, and the majority of rescue operations occured between 8:00 and 10:00a.m. Around 4,000 people, including 985 medics, 1780 paramedics, and 1332 volunteers, participated in rescue and medical activities. 363 ambulances and five helicopters were involved.[6] As many as 200,000 people were evacuated from the area.[8][5] The Mexico City Metro system and public buses were commandeered to transport the wounded to hospitals and the evacuees to evacuation centers.[22]
Investigation
Mexican government investigation
Initially, director-general of Pemex Mario Ramón Beteta and other government officials attempted to shift responsibility for the accident onto the gas-distributing businesses adjoining the terminal,[14][23][24] as well as blaming the people of San Juan Ixhuatepec for settling next to the gas plant.[1] No results from a public inquiry or a Pemex investigation have ever been made available, except for a declaration of the Attorney General[5] released on 22 December 1984, which identified the origin of the initial gas release as having occurred in the row of bullet tanks next to the Horton sphere tanks. In this press release, it was also stated that the responsibilities were not to be sought in the lack of plant maintenance.[25][26][27] The Attorney General ultimately found Pemex responsible for the disaster, and ordered the company to provide the funds necessary for the Mexican Government to pay for indemnifications.[11][28] The Mexican Petroleum Institute (IMP),[8] who provides training for Pemex employees, stated that the cause of the accident was a disgruntled employee that had allegedly sabotaged the plant. The IMP also added that further investigation would not necessarily be useful.[5]
TNO investigation
Through an internal initiative and mediation of the local Dutch embassy, a team of the Netherlands Organisation for Applied Scientific Research (TNO) reached the former terminal site two weeks after the accident. This investigation was not to determine the cause of the accident and was not assisted by Mexican authorities or Pemex, rather it was a scientific mission whose purpose was to test physical models used in safety studies for the prediction of damage from industrial explosions and examining the emergency response to the accident. The investigation was accompanied by the IMP.[8]
The TNO report was issued in May of 1985. Although the Dutch team did not primarily focus on the cause of the accident, the final report hypothesizes that the initial leak may have been caused by an overpressure of a pipe to one of the bullet tanks, possibly due to the high discharge pressure (>60 bars (870psi)) of a booster pump in one of the underground pipelines. This overpressure, likely combined with the tank overfilling and the opening of its relief valve, ruptured the pipe and discharged LPG vapor to atmosphere.
The report iterated that the majority of the destruction in the disaster was caused by the fires that engulfed the terminal, with overpressure from the explosions only playing a secondary role. TNO criticized the dense, congested plant layout as a factor that greatly contributed to the rapid escalation of the accident, as well as poor land-use planning which led to housing built within the credible damage radius for the plant. It also commends the work of the emergency services.[9]
USDOT/PHMSA investigation
An informal investigation was conducted by the Pipeline and Hazardous Materials Safety Administration (PHMSA) of the United States Department of Transportation (USDOT), which corroborated the findings from the TNO report on the cause of the accident, additionally pointing out that the overpressure event should have been prevented by relief valves placed on the receiving pipelines, which had not been installed.[25]
Their report also called attention to an earlier statement made by Pemex, in which they claimed that the pipelines refilling the terminal were not shut down or isolated during the accident, with LPG being pumped into the terminal at the usual rate until 6:40 a.m., the accident. This further aggravated the fire, with an estimated additional fuel inventory of roughly 500cubic meters (18,000cuft). The USDOT concluded that the main causal factors were "the human element, maintenance problems, and inadequate relief capacity and pressure control." They also identified two more contributing factors: multiple tanks being lined up (i.e., not isolated from) a common header, which increased the effectiveness of the chain reaction; and the failure of piping underneath the spheres as a consequence of the initial vapor cloud explosion, which meant that the consequent tank heating ultimately escalated to the BLEVEs.[25]
A team from KAMEDO (Katastrofmedicinska organisationskommittén, or Disaster Medicine Organization Committee) of the Swedish National Defence Research Institute were sent to Mexico for an ex-post evaluation of the medical emergency management.[2] Members of the team were experienced in BLEVE accidents, having already conducted a similar onsite inquiry in the aftermath of the Los Alfaques disaster of 1978.[29] They found that the response in treating the burns of the injured from San Juanico had been effective and supported by considerable local medical resources and experience.[29][30]
The dead were hastily buried on 20 and 21 November. Only sixteen bodies could be identified, with the rest buried in a common grave in the cemetery of the Caracoles neighborhood of Tlalnepantla.[1] President of Mexico Miguel de la Madrid and other high-ranking government officials drew criticism for not attending either the funeral ceremony or the mass burial of the victims.[14] Some sources point to Pemex officials and public authorities potentially hampering the relief and investigation efforts. The parish priest of San Juan Ixhuatepec may have been removed to elsewhere in the State of Mexico by church authorities, after complaining that much of the financial aid allocated to the affected families was quickly disappearing. In a speech in Guadalajara, head of Pemex Mario Ramón Beteta likened criticism directed at the company to cannibalism, declaring that Pemex's tax money was key in keeping Mexico afloat.[27] Barely six weeks after the events, with no official investigation results, the government started payment of indemnifications to those affected by the disaster. Loss of life was indemnified "at a flat rate", without considering the different ages, family situations and employment conditions.[23] Indemnification amounted to US$10,400 per fatality.[27] The state of Mexico gave 167 families new homes in the complex of Valle de Anáhuac, each being valued at around US$8,000.[27] A park was quickly built south of the accident site, where most of the destroyed houses used to be.[23]
The disaster was detrimental to the ruling Institutional Revolutionary Party (PRI), as – official reports notwithstanding[26] – inadequately maintained Pemex infrastructure was generally seen as responsible for the explosions, which were soon overshadowed by the 1985 Mexico City earthquake.[31] In the years following the accident, the government's actions (or lack thereof) were criticized in several respects.[11] For example, concerns were raised on the uncontrolled growth of the housing areas immediately adjoining the LPG terminal, which was against the Ley del petróleo (Petroleum Act), establishing minimum safety distances and mandating approvals from the Secretariat of Health and Assistance. While the government made an official communication to the effect that all gas plants in San Juan Ixhuatepec should be shut down, as of 2020 six out of twelve were still in operation.[23]
Although the accident became well known worldwide in the technical domain of process safety, it had relatively little mainstream resonance outside of Mexico (e.g., as opposed to the Bhopal tragedy, which followed it by merely two weeks), likely due to the fact that no non-Mexican companies were involved.[27][32]
Legacy in process safety
San Juanico had a notable impact on process safety.[20] TNO's contributions were used[5] by the American Petroleum Institute to support their standards on Design and Construction of LPG Installations[33] and fire protection of the same.[34] Some of the lessons learned, or in certain cases re-learned, were:
It appears that the San Juanico plant was not formally reviewed by hazard and operability analysis (HAZOP). Failure to HAZOP the design probably caused the design flaw that, upon tank overfilling, allowed the booster pump to pressurize the tanks being filled, which was not fitted with a relief capacity able to cope with the incoming liquid pressure. Additionally, and for the same lack of design safety analysis, an automatic tank overfill protection was probably lacking, which meant the incoming flow was not automatically stopped upon the level reaching a preset high value. These arrangements, as well as a thorough plant HAZOP and a functional safety review to allocate sufficient safety integrity levels (SIL) to critical instrumentation and actuated valves, are a must nowadays.[5][15]
Gas plant layout design should be based on inherent safety principles to minimize escalation effects:
A significant factor was the tight clustering of the tanks, especially the horizontal ones. This contributed to concentrate the gas cloud and, once ignition took place, to accelerate the flame front of the initial flash fire, resulting in a violent vapor cloud explosion that caused multiple pipes to fail, which ultimately led to the conflagration that heated the tanks until they BLEVE'd.[5] API 2510 now incorporates a requirement to limit the grouping of tanks to six per cluster. Further, in order to minimize the chance of escalation due to fragments, the horizontal tanks longitudinal axis should not be in the way of sensitive targets (such as other tanks). In San Juanico, the horizontal tanks were grouped in such a way that, upon BLEVE, fragments hit other tanks placed directly in the line of fire.[5][33][35]
The layout congestion, caused by tight tank clustering, was exacerbated by the relatively high (1meter; 3.3ft) bund walls, which also contributed to limiting the dispersion of the gas cloud and the acceleration of the flame front. This lesson was implemented in the API Standard 2510, which states that an open area around the tanks is required, with a slope away from the tanks. Dikes and bunds are still permitted in the standard, but there is an explicit requirement for the diking "to permit [...] free ventilation."[33]
Nowadays, certain companies prefer to place LPG tanks underground, in order to prevent any chance of BLEVE.
Key change management processes were not applied: The recently increased flowrate from the Minatitlán pipeline would have warranted improved pressure relief arrangements; and additional tankage was added without assessing the need for correct tank spacing. Management of change is nowadays a key element of process safety management systems, like the one promulgated by OSHA in 1992, which recognize that changes that are not thoroughly risk-assessed and communicated can and do lead to serious accidents.[15]
The plant did not have an effective gas detection system. This prevented early detection of the leak and safe isolation of the plant, thus contributing to a much greater inventory being available to the raging fires.[6][15]
Another barrier that failed was the means for emergency isolation. This greatly contributed to the escalation of the accident due to the contiguity of inventories that should have become segregated by isolation valves, as well as the failure to stop the incoming pipeline flow, which continued to feed the fire.[6]
The lack of fireproofing on the spherical tank legs may have contributed to the BLEVEs of the smaller spheres, since tank wall failure may have been triggered by the tanks collapse as a consequence of the weakening of the structural steel supporting them. API 2510 mandates application of suitable passive fire protection means on the aboveground portions of LPG tanks' supporting structures.[5][33]
The fire extinguishing/cooling system was inadequate. Apart from likely being partially not operational, it had a cooling spray rate much lower than the minimum of 10liter/minute/square meter (0.25gal/min/ft2) advised in API 2510A for LPG tanks where "there is concern or risk of a vessel being fully engulfed by flame because of its location, piping configuration, or impounding or drainage design."[34]
On the same note, the firewater distribution at San Juanico failed due to the effects of the initial explosion. In particular the firewater main line was installed aboveground, which made it liable to rupture when exposed to blast. Means to apply firewater should be designed to survive the effects of credible explosion scenarios.[5][15]
Firemen exposed themselves futilely and at great risk to BLEVEs when trying to cool the unexploded sphere. It is important that emergency services be aware of the dangers of liquefied gas vessels exposed to impinging fires.[6]
The fundamental role of land-use planning and its rigorous enforcement became all too apparent after the disaster. Planning must be supported by robust risk assessment and accident models.[6] Based on models that did in part benefit from validation provided by the accident itself, safety distances of 300 metres (980ft) have been proposed between an LPG plant the size of San Juanico's and the nearest houses.[13][35]
The San Juanico tragedy, which followed other destructive BLEVE events such as those of Feyzin and Los Alfaques, resulted in higher awareness of the destructive potential of BLEVEs and the necessity to manage effectively the risk associated to these phenomena.
Later accident
In 1996 another Pemex site in San Juan Ixhuatepec suffered a serious accident, this time involving a petrol tank, which led to the death of a fireman and the evacuation of around 5000 people from their homes.[23]
12345Pérez, Ana Lilia (October 2017). Pemex RIP: Vida y asesinato de la principal empresa mexicana[Pemex RIP: The Life and Murder of Mexico's Largest Company] (in Spanish). Ciudad de México, Mexico: Grijalbo. pp.198–202, 250. ISBN978-607-315-991-3.
123456789101112Pietersen, C.M. (2013). 25 Years Later: The Two Largest Industrial Disasters with Hazardous Material. Nieuwerkerk aan den Ijssel: Gelling Publishing. ISBN978-90-78440-42-0.
12345BP (2004). Integrity Management: Learning from Past Major Industrial Incidents. Process Safety Booklet 14. Sunbury-on-Thames: British Petroleum. pp.59–61.
123Marmo, Luca; Fiorentini, Luca (2019). Principles of Forensic Engineering Applied to Industrial Accidents. Hoboken, N.J. and Chichester: Wiley. pp.60–64. ISBN9781118962817. LCCN2018034915.
↑Skandia International Insurance Corporation (1985). BLEVE! The Tragedy of San Juanico. Stockholm: Skandia International. If a BLEVE had occurred during the later morning, a large number of those 3000 people who were engaged in rescue and guarding would have been killed.
↑"It Was as if an Atomic Bomb Had Dropped". The Citizen. 20 November 1984. pp.A6.
12Procuraduría General de la República (1984). Boletín de prensa[Press Release]. 488/84 (in Spanish). Ciudad de México: Procuraduría General de la República (published 22 December 1984). Petróleos Mexicanos hizo entrega de la documentación en la que se analizan los problemas de mantenimiento ordinario de esta planta, y se concluye que aquéllos no pudieron causar por sí mismos los hechos sujetos a examen [Petróleos Mexicanos handed over the documentation in which the ordinary maintenance problems of this plant are analyzed, and it is concluded that they could not have caused the events under examination by themselves]
↑Arturson, Gösta; Brandsjö, Kaare (1986). Katastrofmedicinska studier i Mexico: Explosions- och brandkatastrofen i San Juanico Ixhuatepec den 19 november 1984[Disaster Medicine Studies in Mexico: The Explosion and Fire Disaster in San Juanico Ixhuatepec, 19 November 1984]. Kamedorapport 51 (in Swedish). Ursvik and Sorunda: Försvarets forskningsanstalt.
12API (1996). Fire-Protection Considerations for the Design and Operation of Liquefied Petroleum Gas (LPG) Storage Facilities. API Publication 2510A (2nded.). Washington, D.C.: American Petroleum Institute.
↑Official data report 503 deaths. Unofficial sources cite up to 2000 fatalities[1]
↑According to another source, the official census recorded 45,000 residents in San Juanico, with an additional floating population of 25,000; however, figures published in 1984 were in disagreement, with some stating 50,000 residents and others as many as 500,000.[1]
Aparicio Florido, José Antonio (2004). "La explosión de gases de San Juanico"[The Gas Explosion at San Juanico]. Protección Civil en Andalucía (in Spanish). Archived from the original on 6 April 2008. Retrieved 12 August 2023.
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