วันพุธที่ 24 กุมภาพันธ์ พ.ศ. 2553

Domino Gas BLEVE Disaster หายนะโรงก๊าซ ในเม็กซิโก เมือ 1984


Figure 1. Plot plan of the refinery LPG storage installation and the nearby installations. Domino effects zones of BLEVE accidents in the LPG handling terminal (solid line) and the refinery LPG installation (dotted line), are presented.






San Juanico Disaster


In the San Juanico Disaster 6 of these spherical type liquid petroleum gas (LPG) containers and 48 others exploded into huge fireballs killing 500–600 people and causing severe burns in 5000–7000 others.The San Juanico Disaster was an industrial disaster caused by a massive series of explosions at a liquid petroleum gas (LPG) tank farm in San Juanico, Mexico (outside of Mexico City, Mexico) on November 19, 1984. The explosions consumed 11,000 cu. meters of gas, representing one third of Mexico City's entire liquid petroleum gas supply. The explosions destroyed the facility and devastated the local town of San Juan Ixhuatepec, with 500–600 people killed, and 5000–7000 others suffering severe burns.

Facility
The incident took place at a storage and distribution facility (a "terminal") for liquid petroleum gas (LPG) belonging to the multi-state enterprise, Petroleos Mexicanos (PEMEX). The facility consisted of 54 LPG storage tanks; 6 large spherical tanks (four holding 1,600 m3 and two holding 2,400 m3) and 48 smaller horizontal bullet shaped tanks of various sizes. All together the tanks contained 11,000 m3 of a propane/butane mixture at the time of the accident.

Origin
The disaster was initiated by a gas leak on the site, likely caused by a pipe rupture during transfer operations, which caused a plume of LPG to concentrate at ground level for 10 minutes. The plume eventually grew large enough to drift on the wind towards the west end of the site, where the facility's waste-gas flare pit was located.

The fire
At 5:40 a.m., the cloud reached the flare and ignited, resulting in a vapor cloud explosion that severely damaged the tank farm and resulted in a massive conflagration fed by the LPG leaking from newly damaged tanks. Just four minutes later, at 5:44 a.m., the first tank underwent a BLEVE (Boiling Liquid/Expanding Vapor Explosion). Over the next hour, 12 separate BLEVE explosions were recorded, the two largest (from the 2,400 m3 spherical tanks) being so large as to register a 5.0 seismic reading on the Richter Scale. The fire and smaller explosions continued until 10 a.m. the next morning.

It is believed that the escalation was caused by an ineffective gas detection system.

Damage and casualties
The town of San Juan Ixhuatepec surrounded the facility and consisted of 40,000 residents, with an additional 60,000 more living in the hills. The explosions demolished houses and propelled twisted metal fragments (some measuring 30 tons) over distances ranging from a few meters to up to 1200 m. Much of the town was destroyed by the explosions and ensuing fire, with the current statistics indicating 500 to 600 deaths, and 5,000–7,000 severe injuries. Radiant heat generated by the inferno completely incinerated most corpses completely to ashes, with only 2% of the recovered remains left in recognizable condition.

References
^ "Accidente de San Juan de Ixhuatepec (México D.F., México)". www.unizar.es. http://www.unizar.es/guiar/1/Accident/San_Juan.htm. Retrieved 2008-06-11.
Universidad de Zaragoza - Reporte de Accidente de San Juan Ixhuatepec
Protección Civil Anda Lucia - Datos sobre la explosión de San Juanico
"The tragedy of San Juanico--the most severe LPG disaster in history.", Arturson, G. Burns Incl Therm Inj. 1987 Apr;13(2):87-102. PMID: 3580941

ถังก๊าซ LPG ขนาดใหญ่ 12 ถัง ถังละ 6000 ลุกบาศก์เมตร หรือทั้งหมด 72,000 ลุกบาศก์เมตร
เทียบเท่ารถก๊าซ 6500-7000 คัน จอดอยู่ใน มาบตาพุด


DOMINO EFFECTS ANALYSIS FOR THE LPG STORAGE INSTALLATION OF HELLENIC PETROLEUM ASPROPYRGOS REFINERY

P. D. Petrolekasa and I. Andreoub

a SPEC Process Services S.A., 75 Patission Str., Athens 104 34, Greece

b Safety and Hygiene Department, Aspropyrgos Industrial Complex, Hellenic Petroleum

S.A., 193 00 Aspropyrgos, Greece

Abstract

This study examines domino effects related to the LPG storage installation of Hellenic Petroleum refinery at Aspropyrgos, in accordance with the new SEVESO II Directive requirements. The analysis involves a systematic procedure for the evaluation of potential domino accident scenarios, based on a set of damage-to- equipment criteria. The results show that the main concern is for a potential BLEVE accident in the nearby LPG handling establishment, which could result to a BLEVE accident in the refinery LPG installation.

1. INTRODUCTION

The LPG storage installation of the Hellenic Petroleum refinery at Aspropyrgos, includes four 4000 m3 LPG storage spheres, two 1600 m3 propane spheres, an 1800 m3 butane sphere, an 800 m3 LPG sphere and a truck loading station. Figure 1 shows the layout of the installation, which is located across the southern fence of the refinery establishment. Nearby installations include refinery process units, oil storage tanks, an oil truck loading station, and an LPG handling terminal. The latter establishment includes eight cylindrical LPG storage tanks, 170 m3 each, incoming pipeline from the refinery, truck loading and packaging facilities.

The Safety Study of the refinery LPG installation [1], performed according to the SEVESO I Directive requirements, examined accident scenarios resulting from failures in the installation itself, and assessed their consequences to people and the environment.

This Study, performed in accordance to the SEVESO II requirements, examines domino accident scenarios that result from failures in nearby installations and could have an impact to the refinery LPG installation. This is particularly important with respect to the identification of external hazard sources for the facility [2]. In addition, the study examines domino accident scenarios that result from failures in the refinery

LPG installation and could have secondary effects to nearby installations. This is also important with respect to a complete off-site consequences evaluation.

2. METHODOLOGY

The domino effects analysis involves identification of domino scenarios, describing a sequence of accidents, using the following procedure:

(a) Identification of the initial accident.

This involves identification of potential accidents in all installations involved, by means of systematic process hazard analyses.

(b) Assessment of domino effects zone.

This involves assessment of the initial accidents consequences and evaluation of domino effects zones according to a set of damage-to-equipment criteria.

(c) Evaluation of the secondary accident.

This involves visualisation of domino effects zones into suitable plot plans and identification of the equipment in nearby installations that could be subjected to high loads and fail, thus leading to a secondary accident.

The procedure is employed for the identification of domino scenarios resulting from accidents in nearby installations that could have an impact to the refinery LPG installation, as well as, accidents in the refinery LPG installation that could cause secondary effects to nearby installations.

2.1 Damage criteria

Thermal radiation and explosion overpressure produced during an accident can cause severe damage to nearby process equipment, and thus may initiate a secondary accident. The extent of the damage depends on radiation or overpressure intensity, the duration of exposure, the type of material, the presence of protection (e.g. water deluge) systems, etc. Practical ‘rules of thumb” found in literature, provide values of thermal radiation or overpressure corresponding to a given degree of damage. AIChE considers heat flux of 37.5 kW/m2 as the limit for severe damage to process equipment [3], while TNO identifies critical radiation intensities of 100 kW/m2 and 25 kW/m2, for rupture and deformation of structural elements, respectively [4]. In both cases, the duration of exposure is considered to be of the order of 15 - 20 minutes. Concerning explosion consequences, TNO suggests that overpressures of

0.5 -1 bar can cause cylindrical tank displacement or failure of connecting pipes, and overpressures above 1 bar can cause failure of spherical tank supports [4].

In this study, the evaluation of domino effects zones is based on a set of damage-to- equipment criteria, which were derived taking into account the literature guidelines and the specific characteristics of the various phenomena:

Fireball. A large release of superheated liquid (e.g. LPG), if immediately ignited, may burn as a fireball. The fireball grows larger and moves upward continuously because of buoyancy. The duration of the fireball is small (< style="mso-spacerun:yes"> [4]. Within the radius of the fireball there will be severe damage to process equipment and buildings. Beyond this, the danger is mainly for the people that may be affected by the radiation. Therefore, the fireball radius is defined as the domino effects radius.

Pool & tank fires. Pool fires can occur when a significant quantity of liquid is released and immediately ignited. These can be confined, e.g. in case of releases into containment dikes, or unconfined, e.g. in case of releases from LPG or gasoline road tankers. For modelling purposes, tank fires, e.g. fire in a crude tank following failure of floating roof, are considered as confined pool fires. Radiation levels are generally moderate, e.g. for an LPG pool fire the radiation at the surface of the flame is about 100 kW/m2 [4], but duration can be long. Therefore, the domino effects radius is defined as the distance from the centre of pool to a thermal radiation of 37.5 kW/m2.

Flame jets. A high-pressure release of vapour or vapour/aerosol into free space, if ignited, will burn as a flame jet. Any equipment on which that flame jet impinged would be subjected to very high thermal loads, often exceeding the capacity of fixed water sprays. Outside the flame jet itself radiation hazards are very small. Therefore, the domino effects zone is defined by the length and width of the jet.

Vapour cloud fire and explosion. Release and dispersion of LPG, if ignited, could lead to a flash fire burning that part of vapour cloud within the flammability limits. Within the burning cloud, there may be ignition of equipment, but due to the short duration of the phenomenon, the risk for domino effects is small. If however, there is sufficient mass within the cloud (e.g. >1t), the ignition of a vapour cloud may result in an explosion. The effects of an explosion, defined by blast overpressure, can be significant. Overpressure 0.7 bar is considered as the domino effects limit. However, explosions are unlikely, unless the cloud is confined in a building, or semi-confined in a heavily congested process plant. In such cases, the centre of explosion may be assumed to be very near to the point of release.

3. RESULTS

3.1 Domino scenarios due to accidents in nearby installations

Accidents in nearby installations could be an important external hazard source for the refinery LPG installation. The first step in the domino effects assessment is the identification of potential accidents in nearby installations. These include:

Catastrophic failure of an LPG tank in the LPG handling establishment leading to fireball (BLEVE) or vapour cloud explosion.

Catastrophic failure of an LPG road tanker in the LPG handling establishment leading to fireball (BLEVE) or vapour cloud explosion.

Catastrophic failure of a liquid LPG pipeline in the LPG handling establishment leading to flame jet.

Fire in a refinery oil storage tank.

Failure of a gasoline road tanker in the refinery loading station leading to unconfined pool fire.

The assessment of domino effects zones leads to the identification of domino scenarios. Figure 1 presents the results for the case of a fireball due to BLEVE of an LPG tank in the nearby LPG handling establishment. It can be seen that the domino effects zone includes the refinery four 4000 m3 LPG spheres, and thus there is danger for them to BLEVE.

Similar analysis shows that BLEVE of an LPG road tanker in the nearby LPG handling establishment can also cause BLEVE of a refinery LPG 4000 m3 sphere. Conversely, accidents in the other refinery installations do not appear to involve any potential effects to the LPG installation.

3.2 Domino scenarios due to accidents in the refinery LPG installation

The identification of domino scenarios that result from accidents in the LPG installation is also performed according to the procedure described above. The results show that, BLEVE of a refinery LPG sphere will have a substantial impact to nearby installations and could cause several, though smaller, secondary accidents (Figure 1).

In addition, there is concern for a potential BLEVE of an LPG road tanker that could cause further BLEVEs in the nearby LPG establishment. Smaller accidents e.g. flame jets associated with catastrophic failures of LPG pipelines, do not appear to have an impact to nearby installations.

4. CONCLUSIONS

This study examined domino effects related with the LPG storage installation of the Hellenic Petroleum refinery at Aspropyrgos, in accordance with the SEVESO II Directive requirements. The analysis indicates that:

BLEVE accidents in the nearby LPG handling establishment could involve potential domino effects to the refinery LPG installation.

BLEVE accidents in the refinery LPG installation could cause secondary effects to nearby installations.

Due to the high safety standards of Hellenic Petroleum, the danger for a major accident, such as BLEVE, is very low. This study identified external sources of hazard related to the nearby LPG establishment. The control of such hazards could be achieved by enhancing communication on safety issues between the two companies.

REFERENCES

1. Safety study of the LPG storage installation at Hellenic Petroleum Aspropyrgos

Refinery, Hellenic Petroleum S.A. (1996).

2. G. A. Papadakis and A. Amendola (Eds), Guidance on the Preparation of a Safety Report to meet the Requirements of Council Directive 96/82/EC (SEVESO II), EUR 17690 EN, JRC (1997).

3. Guidelines for Evaluating the Characteristics of Vapour Cloud Explosions, Flash

Fires, and BLEVEs, Centre for Chemical Process Safety, AIChE (1994)

4. Methods for the determination of possible damage to people and objects resulting from releases of hazardous materials, “Green Book” CPR 16E, Labour Inspectorate, Dir. General of Labour , Voorburg, The Netherlands(1989).

5. Methods for the calculation of physical effects, “Yellow Book” CPR 14E, 2nd Ed., Director General of Labour, Voorburg, The Netherlands(1992).


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