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 facility consisted of 54 LPG storage tanks: six large spherical 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-shaped tanks of various sizes, for a total plant capacity of 16,000 cubic metres (570,000cuft),[3] representing one third of Mexico City's entire liquid petroleum gas supply.[4][5] Contrary to good practice, the sphere support legs were not fireproofed. Tanks were divided into several clusters by concrete walls about 1 metre (3.3ft) tall. It received LPG through three underground pipelines from remote sites: a 12inches pipeline from Minatitlán (576km; 358mi), a 4inches pipeline from Poza Rica (235km; 146mi) and another 4inches line from the Azcapotzalcorefinery (8km; 5mi).[6]
There were two ground flare pits and a fire protection system including a pond, fire pumps and firewater spray distribution.[5] The plant was said to have been built in conformance to API standards,[7] but this was later put into question.[6] 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 11,900cubic meters/day (75,000barrels/day).[8]
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.[5] 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.[9]
The town of San Juanico surrounded the site and consisted of 40,000 residents, with an additional 60,000 more living in nearby communities.[1] The settlement of San Juan Ixhuatepec long predated the disaster,[10] but housing surrounding the facility itself began to materialize only after the construction of the installation started in 1962,[9][11][12] although this is disputed.[13] However, it is accepted that at least the two largest spheres were added to the plant only recently, when the plant was already surrounded by the densely populated neighbourhood.[6] The closest houses were at a distance of 130 metres (430ft) from the storage tanks. Most of the houses were simple brick or wooden buildings.[9][14]
The events
In the early hours of 19 November 1984, the plant was being filled from a refinery 400 kilometres (250mi) 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 (390,000–420,000cuft) 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 5:40a.m., the control room operators and those at the pipeline pumping station, sited 40 kilometres (25mi) 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 × 2metre (660 × 490 × 7ft). The cloud eventually reached one of the waste-gas flare pits at 5:45a.m, and ignited.[15]
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 7:01a.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 (980ft) in diameter, and they had a duration of some 20 seconds.[3] Smaller explosions continued until 11a.m.,[9] while the flames on the last large sphere was extinguished at 11p.m.
The four smaller spheres were completely destroyed, with fragments propelled around the plant, some at a distance of 350 metres (1,150ft) 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 (3,900ft). Missile fragments ejected weighed up to 30tons. 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 (44–88lb) 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 (4.0kW/m2) within a radius of 1,850 metres (1.15mi).[19]
Five plant workers perished, but the majority of the victims died in the housing area surrounding the plant, mostly within 300 metres (980ft) 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
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 8:00a.m. and 10:00a.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
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] However, 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 (870psi)) 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 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.[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]
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 272 of the victims.[13] 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.[26] 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 taking into account the age, family situation, or employment conditions of the deceased.[22] Indemnifications amounted to US$10,400 per each fatality.[26] The state of Mexico gave 167 families new homes in the complex of Valle de Anáhuac, each being valued at around US$8,000.[26] A park was quickly built south of the accident site, where most of the destroyed houses used to be.[22]
The disaster was detrimental to the ruling Institutional Revolutionary Party (PRI), as –official reports[25] notwithstanding– inadequately maintained Pemex infrastructure was generally seen as responsible for the explosions. However, the events would in part be overshadowed by the 1985 Mexico City earthquake.[30] In the years following the accident, the government's actions (or lack thereof) were criticized in several respects.[10] 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 12 were still in operation.[22]
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.[26][31]
Lessons learned in process safety
San Juanico had a notable impact on process safety.[19] TNO's contributions were used[6] by the American Petroleum Institute to support their standards on Design and Construction of LPG Installations[32] and fire protection of the same.[33] 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.[6][8]
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.[6] 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.[6][32][34]
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."[32]
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.[8]
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.[3][8]
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.[3]
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.[6][32]
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."[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.[6][8]
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.[3] 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.[12][34]
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.[22]
Pemex is the Mexican state-owned petroleum company managed and operated by the Mexican government. It was formed in 1938 by nationalization and expropriation of all private oil companies in Mexico at the time of its formation. Pemex had total assets worth $101.8 billion in December 2019 and as of 2009 was Latin America's second largest enterprise by annual revenue, surpassed only by Petrobras. The company is the seventh most polluting in the world according to The Guardian.
A boiling liquid expanding vapor explosion is an explosion caused by the rupture of a vessel containing a pressurized liquid that is or has reached a temperature sufficiently higher than its boiling point. Because the boiling point of a liquid rises with pressure, the contents of the pressurized vessel can remain a liquid as long as the vessel is intact. If the vessel's integrity is compromised, the loss of pressure drops the boiling point, which can cause the liquid to convert to gas expanding rapidly. BLEVEs are manifestations of explosive boiling.
The Weyauwega derailment was a railroad accident that occurred in Weyauwega, Wisconsin, United States, in the early morning hours of March 4, 1996. The derailed train was carrying a large quantity of hazardous material, which immediately caught fire. The fire, which involved the train cars and an adjacent feed mill, burned for more than two weeks after the actual derailment, resulting in the emergency evacuation of 2,300 people for 18 days, including the entire city of Weyauwega, with about 1,700 evacuees.
A gas explosion is the ignition of a mixture of air and flammable gas, typically from a gas leak. In household accidents, the principal explosive gases are those used for heating or cooking purposes such as natural gas, methane, propane, butane. In industrial explosions many other gases, like hydrogen, as well as evaporated (gaseous) gasoline or ethanol play an important role. Industrial gas explosions can be prevented with the use of intrinsic safety barriers to prevent ignition, or use of alternative energy.
The Waverly, Tennessee tank car explosion occurred at approximately 2:58 pm on February 24, 1978, in Waverly, Tennessee, following a train derailment incident days earlier. A tank car containing 30,161 US gallons of liquefied petroleum gas (LPG) exploded as a result of cleanup related to the derailment.
The Los Alfaques disaster was a road tanker explosion that occurred near a holiday campsite on Tuesday July 11, 1978 in Alcanar, Spain. The exploding truck, which was carrying 23 tons of highly flammable liquefied propylene, killed 215 people and severely burned 200 more. Several individuals from the company that owned the vehicle were prosecuted for criminal negligence. The accident resulted in new legislation in Spain, restricting the transit of vehicles carrying dangerous cargo through populated areas to night time only.
Fawley Refinery is an oil refinery located at Fawley, Hampshire, England. The refinery is owned by Esso Petroleum Company Limited, a subsidiary of Exxon Mobil Corporation, which acquired the site in 1925. Situated on Southampton Water, it was rebuilt and extended in 1951 and is now the largest oil refinery in the United Kingdom, and one of the most complex refineries in Europe. With a capacity of 270,000 barrels (43,000 m3) per day, Fawley provides 20 per cent of the UK's refinery capacity. Over 2,500 people are employed at the site.
The Feyzin disaster occurred in a refinery near the town of Feyzin, 10 kilometres south of Lyon, France, on 4 January 1966. An LPG spill occurred when an operator was draining water from a 1,200m³ pressurised propane tank. The resultant cloud of propane vapour spread, until it was ignited by a car on an adjoining road. The pool of propane in the bund caused the storage tank to be engulfed in flames, which produced a Boiling Liquid Expanding Vapour Explosion (BLEVE) when the tank ruptured. This resulted in a fireball which killed and injured firemen and spectators. Flying missiles broke the legs of an adjacent sphere which later BLEVE'd. Three further spheres toppled due to the collapse of support legs which were not adequately fire protected. These vessels ruptured but did not explode. A number of petrol and crude oil tanks also caught fire. The conflagration took 48 hours to bring under control. This incident resulted in the deaths of 18 people, the injury of 81 and extensive damage to the site.
The 2010 Puebla oil pipeline explosion was a large oil pipeline explosion that occurred at 5:50 am CST on December 19, 2010, in the city of San Martín Texmelucan de Labastida, Puebla, Mexico. The pipeline, running from Tabasco to Hidalgo, was owned by the Pemex petroleum company, and exploded after thieves from the Los Zetas drug cartel attempted to siphon off the oil. The gas explosion and resulting oil fire killed 29 people, including thirteen children, and injured 52. Some of the flames in the fire became ten metres high, and the smoke towered over the city. Firefighters eventually controlled the blaze, but electricity and water remained cut following the explosions, and the military was deployed to the site. Mexican President Felipe Calderón visited the explosion site on the day of the incident to offer condolences to the victims' families. The fire was one of the deadliest in Mexican history, largely destroying an area of five-kilometre radius, and some oil may have polluted the Atoyac River.
Energy resources bring with them great social and economic promise, providing financial growth for communities and energy services for local economies. However, the infrastructure which delivers energy services can break down in an energy accident, sometimes causing considerable damage. Energy fatalities can occur, and with many systems deaths will happen often, even when the systems are working as intended.
A Horton sphere, also referred to as a spherical tank or simply sphere, is a spherical pressure vessel, which is used for industrial-scale storage of liquefied gases. Example of materials that can be stored in Horton spheres are liquefied petroleum gas (LPG), liquefied natural gas (LNG), and anhydrous ammonia.
The Chala LPG tanker disaster was a road transport accident that occurred on August 27, 2012, on Indian National Highway 17 at Chala in the Kannur District of India's Kerala State. The accident occurred when an Indian Oil Corporation Limited (IOCL) LPG road tanker hit a road lane divider, overturned and exploded, starting several building fires between 9:30 p.m. and 11 p.m. The accident killed 20 people.
On August 6, 2018, the collision of a liquefied petroleum gas (LPG) road tanker with an articulated lorry carrying flammable solvents and a car transporter resulted in a huge explosion on the A14 motorway within Borgo Panigale, a neighbourhood of Bologna, Italy. It was a case of boiling-liquid expanding-vapour explosion (BLEVE), where nearly all the road tanker cargo combusted in a matter of seconds upon release, generating a tremendous amount of thermal radiation. The accident killed two people, injured 145 and caused significant damage to the surrounding commercial and residential area. One span of the viaduct where it happened collapsed and a gash opened in the motorway.
1 2 3 4 5 6 7 8 9 10 11 12 Pietersen, 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.
1 2 3 4 5 BP (2004). Integrity Management: Learning from Past Major Industrial Incidents. Process Safety Booklet 14. Sunbury-on-Thames: British Petroleum. pp.59–61.
↑ 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.
1 2 Procuraduría 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.
1 2 API (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.
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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