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San Juanico disaster

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), municipality of Tlalnepantla de Baz, State of Mexico, Mexico on 19 November 1984.[1] The facility and the settlement, part of Greater Mexico City, were devastated, with 500–600 victims killed, and 5000–7000 suffering severe burns.[2] It is one of the deadliest industrial disasters in world history,[1] 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.

Date

19 November 1984 (1984-11-19)

Pemex LPG storage plant in San Juan Ixhuatepec

> 500

> 5000

Fire and explosions[edit]

In the early hours of 19 November 1984, the plant was being filled from a refinery 400 kilometres (250 mi) away. At that moment, two of the spheres and the 48 cylindrical vessels were filled at 90% of their capacity and the rest of the spheres at 50%.[15] Overall, the plant held about 11,000–12,000 cubic metres (390,000–420,000 cu ft) of LPG,[14] i.e., in excess of 300 TJ of energy equivalent[16] or roughly five times the energy released by the atomic bomb of Hiroshima.[17] Shortly before 5:40 a.m., the control room operators and those at the pipeline pumping station, sited 40 kilometres (25 mi) away,[3] noticed a decrease in pressure. A pipe between a sphere and the cylinders had ruptured, resulting in a continuous release of LPG. For 5–10 minutes, with the cause of the leak not identified, the resulting gas cloud built up, reaching an estimated size of 200 × 150 × 2 metre (660 × 490 × 7 ft). The cloud eventually reached one of the waste-gas flare pits at 5:45 a.m, and ignited.[15]


A flash fire ensued, which immediately transitioned to a violent vapor cloud explosion (VCE), likely due to its flame front acceleration being enhanced by the especially congested geometry of the plant. The blast (like the ensuing boiling liquid expanding vapor explosions (BLEVEs)) was felt and recorded by a seismometer at a National Autonomous University of Mexico lab located some 32 km (20 mi) away in Mexico City.[5][14] In a textbook case of the domino effect accident,[14] the explosion damaged further piping and storage tanks, which resulted in a massive conflagration fed by multiple LPG leaks.


About 90 seconds after the VCE blast, the first tank BLEVE occurred.[4] The explosion was witnessed by the pilot of a Pan Am flight on approach to the airport, who communicated to air traffic control that he believed a nuclear bomb may have exploded in the city.[18] Eight separate BLEVEs were recorded by the seismometer, with the last one at 7:01 a.m. The first and sixth registered the highest strength, at 0.5 on the Richter scale.[4] The BLEVE fireballs were up to 300 metres (980 ft) in diameter, and they had a duration of some 20 seconds.[3] Smaller explosions continued until 11 a.m.,[9] while the flames on the last large sphere was extinguished at 11 p.m.


The four smaller spheres were completely destroyed, with fragments propelled around the plant, some at a distance of 350 metres (1,150 ft) in public areas. The larger spheres collapsed to the ground, with their legs buckled due to the heat radiation they received. Only four of the bullet tanks survived. 12 of those that failed were launched from their supports with the furthest landing at 1,200 metres (3,900 ft). Missile fragments ejected weighed up to 30 tons. Gas explosions also occurred inside the plant buildings and the surrounding houses.[1][14] At the Gasomático site, 100 parked trucks loaded with LPG household cylinders weighing 20–40 kilograms (44–88 lb) were completely burned-out and hundreds of secondary explosions took place.[9]


An area of a few square kilometers was affected, with varying degrees of damage from the fires and the missiles. Around 150 homes were estimated completely destroyed, with a few hundred sustaining lesser damage.[9] It is estimated that the thermal radiation produced by the BLEVEs was in excess of the threshold of pain (4.0 kW/m2) within a radius of 1,850 metres (1.15 mi).[19]


Five plant workers perished, but the majority of the victims died in the housing area surrounding the plant, mostly within 300 metres (980 ft) from the centre of the storage area.[9] Most of the casualties were surprised in their sleep. The disaster resulted in 500 to 600 deaths, and 5000–7000 severe injuries. Radiant heat generated by the fire incinerated most corpses to ashes, with only 2% of the recovered remains left in recognizable condition.[1]

Emergency response[edit]

The first call to the emergency services was made at 5:45.[3] More than 200 firemen were deployed to the affected area in the six hours after the first explosion. Fire-fighting water was provided to the site by tank trucks normally used for domestic potable water distribution.[18] A major rescue operation mounted, which reached its climax between 8:00 a.m. and 10:00 a.m. Around 4000 people participated in rescue and medical activities, including 985 medics, 1780 paramedics, and 1332 volunteers. 363 ambulances and five helicopters were involved.[3] After the last BLEVE, the firemen kept cooling the two larger, unexploded spheres. While this was undoubtedly an act of bravery, they were exposing themselves to further potential BLEVEs that would have surely killed them.[18][20] The metro system and public buses were commandeered to transport the wounded to hospitals and the evacuees to evacuation centers.[21] 200,000 people were evacuated from the area.[5][6]

Investigation[edit]

Initially, director-general of Pemex Mario Ramón Beteta and government officials attempted to shift the responsibility for the accident onto the gas-distributing businesses adjoining the terminal.[13][22][23] No results from a public inquiry or a Pemex investigation have ever been made available, except for a declaration of the Attorney General[6] released on 22 December 1984, which pointed to the gas escape having occurred at the row of bullet tanks next to the spheres. In this press release, it was also stated that the responsibilities were not to be sought in the lack of plant maintenance.[24][25][26] The Attorney found Pemex ultimately responsible for the disaster and summoned the company to provide to the government funds necessary for the indemnifications.[10][27]


On TNO's initiative and through mediation of the local Netherlands embassy, a Dutch team reached the accident site two weeks after the facts. This investigation was not instigated by the Mexican authorities or Pemex, but rather was a scientific mission whose purpose was testing 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 also participated by the Mexican Petroleum Institute (IMP).[5] IMP stated that the cause of the accident was already known, pointing to a disgruntled employee that had allegedly sabotaged the plant. They also added that further investigation would not necessarily be useful.[6]


The TNO report was issued in May 1985. Although the Dutch team did not primarily focus on the causes of the accident, the final report hypothesizes that the initial leak may have been caused by overpressure and rupture of a pipe to one of the cylindrical vessels (possibly due to the high discharge pressure (> 60 bars (870 psi)) of a booster pump in one of the underground pipelines), likely combined with a tank overfill and the consequent opening of a tank relief valve discharging to atmosphere. The report also stresses how it was the fires that brought about most of the destruction, with blast overpressures playing only a secondary role. It further calls attention to the congested plant layout as a factor that greatly contributed to the rapid escalation of the accident, and to the fact that poor land-use planning led to housing built within the credible damage radius from accidents originating from the plant. It also commends the work of the emergency services.[9]


An informal investigation was conducted by the U.S. Department of Transportation, which corroborated the TNO's findings on the cause of the accident, additionally pointing out that the overpressure should have been prevented by relief valves placed on the receiving pipelines, but these had not been installed. Their report also called attention to an earlier statement by Pemex that the pipelines were not isolated, with LPG being pumped into the terminal at the usual rate until 6:40 a.m., long after the onset of the accident. This further aggravated the fire, with an estimated additional fuel inventory of roughly 500 cubic meters (18,000 cu ft). 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.[24]


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.[1] 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.[28] 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.[28][29]

It appears that the San Juanico plant was not formally reviewed by . 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.[6][8]

hazard and operability analysis (HAZOP)

accelerate the flame front

Key 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.[8]

change management

The plant did not have an effective 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.[3][8]

gas detection

Another 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.[3]

barrier

The lack of 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.[6][32]

fireproofing

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 10 liter/minute/square meter (0.25 gal/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."

[33]

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.[8]

[6]

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.

[3]

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. Based on models that did in part benefit from validation provided by the accident itself, safety distances of 300 metres (980 ft) have been proposed between an LPG plant the size of San Juanico's and the nearest houses.[12][34]

[3]

(France, 1966)

Feyzin disaster

(Arizona, 1973)

Kingman explosion

(Spain, 1978)

Los Alfaques disaster

(Tennessee, 1978)

Waverly tank car explosion

(Tennessee, 1978)

Memphis tanker truck disaster

Other notable BLEVE accidents:

. Health and Safety Executive. Archived from the original on 27 March 2023. Retrieved 13 August 2023.

"PEMEX LPG Terminal, Mexico City, Mexico. 19th November 1984"

Aparicio Florido, José Antonio (2004). [The Gas Explosion at San Juanico]. Protección Civil en Andalucía (in Spanish). Archived from the original on 6 April 2008. Retrieved 12 August 2023.

"La explosión de gases de San Juanico"

Carrión Velázquez, Alejandra (2002). [San Juan Ixhuatepec: A History of Violence and Impunity. How Many More Have to Die for Them to Realize We Are in Danger?]. El Cotidiano (in Spanish). 18 (111): 58–63.

"San Juan Ixhuatepec: una historia de violencia e impunidad. ¿Cuántos más debemos morir para que se den cuenta que estamos en peligro?"

(2014). "Thirty Years Ago – An LPG Tragedy" (PDF). Process Safety Beacon (November 2014). Archived (PDF) from the original on 19 August 2023.

CCPS

(1985). San Juan Ixhuatepec: memoria de una emergencia [San Juan Ixhuatepec: Memory of an Emergency] (in Spanish). Toluca de Lerdo: Gobierno del Estado de México. Archived from the original on 17 March 2008.

Gobierno del Estado de México

Marsh, Peter (2022). Learning Lessons from Major Incidents: Improving Process Safety by Sharing Experience. Rugby: . p. 32. ISBN 978-1-911446-77-4.

Institution of Chemical Engineers

Ortega Celene, Íñiguez (2006). [San Juan Ixhuatepec: The Two Visions. Photographic Analysis of Images from La Prensa and Uno Más Uno] (PDF). Graduate dissertation (in Spanish). San Juan de Aragón: Universidad Nacional Autónoma de México. Archived (PDF) from the original on 19 August 2023. Retrieved 20 August 2023.

San Juan Ixhuatepec: las dos visiones. Análisis fotográfico de las imágenes de La Prensa y del Uno Más Uno

: podcast

Disaster Area – Episode 202: The San Juanico Disaster

: YouTube video (in Spanish)

Explosiones en San Juanico