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Amuay refinery disaster: The aftermaths and challenges ahead
Kirti Bhushan Mishra a,⁎, Klaus-Dieter Wehrstedt a, Holger Krebs b
a Division 2.2 “Reactive Substances and Systems”, BAM Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205 Berlin, Germanyb Division 2.3 “Explosives”, BAM Federal Institute for Materials Research and Testing, Unter den Eichen 87, 12205 Berlin, Germany
Amuay refinery disaster (2012) is another recent example of Vapor Cloud Explosion (VCE) and fire acci-dents preceded by Buncefield (2005), Puerto-Rico (2009) and Jaipur (2009), respectively [9]. The incidenthas left many safety issues behind which must be repeatedly addressed. Unfortunately, the lessons taughtby previous similar events are just not understood carefully. It reveals that the proper safety measures forsuch facilities were either underestimated or were not accounted seriously. Consequently, the resultingoverpressures from explosion and the subsequent thermal radiation from tank fires have once again provedto be disastrous to both mankind and infrastructure. This article highlights the aftermaths of Amuay incident andaddresses the challenges put forward by it. Furthermore, a comparative study is performedbetween such incidentsto analyze the similarities and how they could have been avoided.
On the 25th of August 2012 about 1.11 AM (GMT) an explosion tookplace at Punto Fijo refinery (also known as Amuay refinery) situated inthe northwest of Venezuela and run by an state-owned companyPetróleos de Venezuela, S.A. (PDVSA) [1-6] (Fig. 1(a) and (b)). It is theworld's second largest refinery after Jamnagar in India. Themajor prod-ucts the refinery handles are crude oil, Liquefied Petroleum Gas (LPG)and Liquefied Natural Gas (LNG). The severity of shockwaves generatedby the explosion shook the nearby residential areas and the residents.According to the eyewitnesses it felt like an occurring earthquake. Theincident cost significant damage, more than 50 lives (some also report-ed up to 100), over 100 seriously injured and several suffered with lightinjuries. Apart frommore than 1600 houses that were completely dam-aged, more than 200 houses were evacuated and people were trans-ferred to safer places [2,3]. The total capital loss assessed was morethan $1 billion. The reasons behind the incident are still unclear. Somesources claim that there was a lack of maintenancewhile others consid-er poor safety practices as important reasons [1–3].Whatsoever the rea-sonswere at the end of the day it caused a huge destruction and setbackand led the safety community to review the existing plant safety normsand procedures.
49 30 81041227.ishra).
ghts reserved.
2. The incident
Fig. 1(c) is depicting the regions where the dispersion, explo-sion and fire events probably took place and the path that thevapor cloud have followed can be seen in marked arrows inFig. 1(d).
Like most of the others Amuay incident also began with a leak ofa flammable material. This time it was alkenes although some havealso reported Liquefied Natural Gas (LNG) or liquid propane (or bu-tane) [2–4]. They are all high vapor pressure fuels tending to formflammable dense-than-air (1.5 times) vapor clouds once releasedin the atmosphere [7]. Depending on the atmospheric stability andwind conditions this vapors either can be carried away or can begradually settled down on the ground and form a thick cloud. Usual-ly, in a facility like Amuay (onshore) fuel vapors resulting from aminor leak are assumed to be taken away by the strong wind.When that is not the case the chances of accumulation of the dis-persed vapor are greater and therefore the scenario can be extreme-ly hazardous when this cloud contacts an ignition source. A runningvehicle, a cigarette or pumps and motors installed nearby are suffi-cient to ignite this cloud. When a dense flammable cloud is ignitedthe flame front travels at a speed more than the speed of soundpushing the unburned mixture ahead of it and leading to detonation.The scenario gets worse when these shock waves find obstacles (build-ings, trees, congestion) on their way which help to enhance pressure.These high pressure (blast) waves and also those felt in similar in-cidents before as well ~200 kPa are sufficient to destroy a car, con-crete walls, dwellings, warehouses and nearby facilities [8–10]. Theintensity of disaster worsens when the surrounding tanks are also af-fected and join the catastrophe.
Fig. 1. Locations of: a) Amuay refinery; b) the refinery region; c) sources of explosion and multiple tank/pool fires; d) the origin and path of dispersion [5,6].
According to the media sources the plant management had laid-back attitude towards the regular maintenance and updation [2–5].Some also reasoned their negligence and ignorance even afterknowing the fact days before the incident that something wasleaking and smelling [2]. Many of them quote it as an incident thatwas just waiting to happen. However, the disaster happened andthe government has set-up a high level committee to investigate it[1].
In this article the incident has been technically analyzed and probablecauses of the incident are looked in. Care must be exercised whiletreating certain specifications taken from the internet pages which maynot be fully correct.
2.1. Failure of equipments
The story of hazard most often begins when an installed compo-nent fails to function. Such failures can be in the valves, pumps andpipings. The reasons for these failures could be the lack of mainte-nance, corrosion, and poor safety know-hows and can be even inten-tional. The investigation reports published on previous incidentsthat took place in Buncefield (UK) and Sitapura (India) [8,9] revealedthat the failure of a valve led the gasoline tank to overflow for manyhours. However, in Amuay the leak of a liquefied gaseous fuel (basedon the tellings of eyewitnesses) was reported [2–4]. Improper func-tioning of pump, piping and valve connected to the olefin tankswas also published on some sites [2,3]. On the basis of these factorsit was believed that in Amuay incident the failure was somewherein the valve and pipings.
2.2. Dispersion of fuel
As a result of the failure of a valve the accumulating high vaporpressure fuel (olefins) started to disperse in the atmosphere. Thevapors of olefins are about 50% denser than air [4]. This dense-than-air cloud has a tendency to stick to the ground and formwhite irregular pattern like fog under stable wind conditions. Itdoes not smell as such unless it contains some additives like hydro-gen sulfide [2]. The reported smell in the surroundings may be be-cause of the same [2]. The fuel continued to disperse but was notharmful as long as strong winds flew it off. Soon the wind speedslowed down and the accumulation of dispersed fuel began. It al-most spread out to a radius of 0.6 km (see Fig. 2). Based on the vi-sual observation of witnesses, employees of lube oil plant and thedevastated cars (road adjacent to guard's residence) support theextent of this dispersion radius.
2.3. Vapor Cloud Explosion
The spread of the dense-than-air cloud continued to get wideruntil 1.11 AM of 25th when it came into contact of a potential sourceof ignition and exploded. There were no evidences of second andsubsequent explosions. The damages inside and outside the plantfavor the idea that the ignition source was probably not inside the pre-mises as what was also felt and told by the residents. The vehicles pass-ing by are the most likely source of ignition [3]. Also the self-ignition ofsuch clouds could be possible under certain conditions [8]. The Amuayrefinery and surroundings cannot be considered fully unconfined toprove the deflagration to detonation transitions. In the past in the
Fig. 2. Extent of the possible dispersion radius and location of potential source of ignition.
sites of similar nature the partial confinements were always consideredto be present. The overpressures generated due to the explosion wavesare of such high magnitude that they crushed vehicles, bent concreteand steel fences, blown away the roofs and demolished structure(Fig. 6(a), (b), (c) and (d)). For such destruction previous analyseshave shown that overpressures in such explosions can be in the rangeof a minimum of 150 kPa (1.5 bar) to a maximum of even up to2000 kPa (20 bar) (Fig. 3). In Fig. 3 the overpressure values vs. scaleddistance (TNT method [11]) and effects thereof are shown [9]. Thewidely used overpressure calculation methods [8–14] are discussed asfollows:
2.3.1. Baker and Strehlow methodThis method is based on the Mach number MW (flame veloci-
ty), reactivity of fuel and level of congestion and confinement[11,12]. Eqs. (1), (2) and (3) for maximum overpressure Pmax,
Fig. 3. Explosion overpressure versus scaled distance.
dimensionless average side on pressure PS and the scaled distanceR are
Pmax ¼ 2:4M2
W
1þMWð Þ ð1Þ
PS ¼Pmax
Pað2Þ
R ¼ RPa
E1
� �1=3: ð3Þ
When a medium reactivity, a Mach number MW of 0.55, a totalavailable energy E1 (J) and a high level of congestion are assumedan overpressure of 50 kPa results. The PS is plotted against R inFig. 4.
2.3.2. TNO (multi energy method)In multi-energy method the following equation describes the maxi-
mum overpressure caused by a VCE:
Pmax ¼ 0:84 VBRL f
D
� �2:75S2:7L D0:7
=84: ð4Þ
Where Pmax: Maximum overpressure in kPa; VBR: Volume blockageratio (%); Lf: Flame path length (m); D: Average obstacle diameter (m);SL: Laminar burning velocity of flammable mixture (m/s).
The dependence of dimensionless overpressure Eq. (2) on distanceEq. (3) is shown in Fig. 5. When this method is applied with VBR of4%, Lf = 60 m,D = 0.3 m and SL = 0.52 m/s for butane [9] it estimatesthe overpressure to be N2000 kPa [9].
Considering the damaged vehicle at the source and the destructedhouse (Fig. 6) at about 0.2 km from the source a conservative estima-tion of overpressure predicted by Baker–Strehlow–Tang and Game cor-relation (TNOmethod) [11,12] can be in the range of 120–300 kPa (1.2to 3 bar). This estimation considered the flame path length of morethan 30 m which is likely that the flame traveled from road towardsthe tank which is at about 200 m and volume blockage ratio of 4%
although considering the vegetation (trees) and buildings it can be upto 6% [10]. Also medium confinement and reactivity of the fuel are con-sidered. Moreover, the vapor cloud must have been ignited at the pe-riphery (at the road) which made the overpressure significantly lowerthan those recorded in Buncefield [8]. The destructions seen in the near-by region, e.g., in the entire residential area of national guards which isabout 0.4 km in radius from the probable source of explosion (Fig. 2)are clearly from within the unsafe region considering the presentedrange of overpressures [11]. However, comparing the previous inci-dents with Amuay can be onlyworthywhen a detailed investigation re-port has been performed.
2.4. Multiple tank fires
The heavier and medium vapor pressure hydrocarbon (naptha)tanks that were installed just across the olefin tanks also got ignitedafter the explosion occurred. Three of the four tanks shown in Figs. 1(c)and 7(d) were observed to be firing (Fig. 7). Very large and thick fireswith a great amount of smoke obscured the sky. Sometimes the fireswere also seen to be highly influenced by the crosswind (Fig. 7(b) and(c)) and approaching other tanks. Fortunately, none of the gas tankswere further exploded although the scenario could not have beenimpossible.
There are variousmodels available to estimate the thermal radiationemitted by the single or multiple fires. Here only two methods are con-sidered and are discussed as follows:
2.4.1. Solid flame modelSolidflamemodel basically considers theflame as a solid body (3D cy-
lindrical or 2D rectangular) and if the average radiation from the surfaceof such an assumed body is defined one can estimate the safety distanceby using the equation for view factor φF,R as written below [9,12,13].
WhereE is irradiance (kW/m2);SEP: average surface emissive power(kW/m2); τ: Transmissivity (−); b: averageflamewidth (m); andH: av-erage flame length (m).
The measured irradiance and relative safety distance for largescale pool/tank fire experiments are shown in Fig. 8. The largestsize of the pool used was 25 m. Nonetheless, it forms a basis for fur-ther approximations.
In Amuay one tank was of size of about 64 m and considering amulti-fire scenario with 3 tanks a safety distance for thermal radiationexposure (a limiting value 1.5 kW/m2) of about 0.5 km from the bound-ary of tank farms can be established [9]. Fortunately, the tanks were notseen to be engulfed to form a large single pool reducing the chance ofmore catastrophic consequences.
2.4.2. CFD (Computational Fluid Dynamics) modelComputer based simulation can also be used to assess the reliable
safety distances from large pool/tank fires. The detailed methodologiesare described in [9,15–17]. The time averaged flame surface tempera-tures can be obtained by solving reactive Navier–Stokes equations.This average flame surface temperature can be further utilized to ob-tain a Surface Emissive Power SEP with appropriate emissivity. Afterobtaining the SEP the discussed solid flamemodel above can be used topredict the average irradiance and relative safety distances (Δy/d). Sucha prediction togetherwith experimental data [17] for large hydrocarbonfuel (diesel, gasoline, JP-4) pool fires is shown in Fig. 8. Considering thelarge diameter d of fires at Amuay site the safety distances Δy~ 3d (EN1413: 1.5 kW/m2 [9,16]) can be established.
3. Challenges ahead
Avoiding future refinery disaster requires a number of reviews of safe-ty guidelines/regulations that were targeted and finally achieved. In caseswhere the favorable conditions for such catastrophes are majorly con-trolled by the surrounding weather e.g. onshore facilities like in Amuayit is expected to bemore cautious while performing routinemaintenanceor transferring the fuels for transportation purposes. Above all, specialcare must be given to high vapor pressure fuels like LNG which have en-tirely different dispersion behavior. The storage tanks of LNG and fuelsalike should be separated by a reasonable distance from medium vapor
Fig. 6. Aftermaths of the incident: a) crushed car; b) bent column and destructed boundary wall; c) collapsed steel frames; d) severe cracks on the walls [5].
pressure fuels e.g. crude oil as there could be an engulfment scenario ofother fuel tanks leading to more devastation.
Minor leakages should not be ignored prior to routine maintenanceschedule. It should be reported to higher authorities and causes of leakshould be tried to identify. The semi-skilled workers performing suchmaintenance should be trained to not ignore such leakages even when
Fig. 7. a) Tank fire and other approximate tanks. b) Crosswind pushes the fire to the other taincident.
they have done the same and did not face ugly consequences in thepast. Sometimes, it is neglected by the higher officials of the safetyunit as they believe that the small/minor leakage can be carried awayby the strong wind (onshore facilities). If that is not the case the vaporcloud will spread and accumulate depending on the extremities of thebund. When a small maintenance activity like welding work is started
nks/facilities. c) Thermal radiation from fire influencing the olefin tanks. d) Site after the
within the lower flammability limits of themixture vapor cloud will ig-nite and explode with overpressure values leading to severe conse-quence like those faced in Amuay. Additionally, the congestion in theform of residential buildings and vegetation in the blast and radiationradius should be avoided as much as possible. Obstacle free path willlower the probability of DDT (deflagration to detonation transitions).
Top management responsible for the safety of the plant shouldkeep on reviewing and inspecting safety measures on regular basisclose to the places where probably a leak might begin. Such placesare fittings, joints, valves and pipings. The properties of materialsfor these equipment's should also be checked with great care toavoid any material failure due to corrosion.
To deal with post incident scenario proper mitigation plan has to bemade beforehand. Obviously, suchmitigationmeasures will rely largelyon the reliable estimation of major hazards else it would be too conser-vative and may overestimate the consequences and put unnecessary fi-nancial burden on the plant. Therefore, a proper coordination betweenplant safety personnel and management is also necessary to assurethe economical safety measures.
On top of the abovementioned suggestions the safety experts of theplant should rathermotivate and aware the subordinates to follow safe-ty practices at the maximum possible limits.
The following points summarize the challenges ahead.
1. Appropriate estimation of the overpressures and learning fromBuncefield, Sitapura and Perto Rico incidents.
2. Appropriate estimation of thermal radiation hazards from multiplefire tanks.
3. Reducing the poor management policies towards maintenance andmotivating employee awareness towards safety.
4. Strict procedures/rules for negligence and ignorance on minorleakages.
5. Minimizing the congestion in the safety region (blast radius).
4. Conclusions
Amuay incident has added onemore questionmark in process safetyknow-hows and serious implementations thereof. The residents and
daily lives should be in no way affected by the incidents. Similar inci-dents in the past have occurred more or less due to similar reasons.The predictions of safety distances from theblast overpressure and ther-mal radiation from multi-tank fires were carried out in the presentstudy. These conservative estimations are symbolic in nature howeverdetailed investigation by the safety community and government shouldperhaps indicate the causes and remedies to avoid such disastrousevents worldwide in the future.
[8] The Buncefield Incident, The final report of the Major Incident Investigation BoardVolume 1 and 2, Health and Safety Executive, UK, 11 December 2005. ISBN 978 07176 6270 8.
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[10] J. Taveau, The Buncefield explosion: were the resulting overpressures really unfore-seeable? Process Safety Progress 31 (1) (2012) 55–71.
[12] A.C. Van den Berg, The multi-energy method: a framework for vapor cloud explo-sion blast prediction, Journal of Hazardous Materials 12 (1989) 1–10.
[13] http://www2.gexcon.com/calculators/new/TNTMethod.php.[14] O.R. Hansen, P. Hinze, D. Engel, S. Davis, Using computational fluid dynamics (CFD)
for blast wave predictions, Journal of Loss Prevention in the Process Industries 23(2010) 885–906.
[15] P.K. Raj, A review of the criteria for people exposure to radiant heat flux from fires,Journal of Hazardous Materials 159 (2008) 61–71.
[16] K.B. Mishra, Experimental investigation and CFD simulation of organic peroxidepool fires (TBPB and TBPEH), BAM-Dissertation Series 63, Berlin, Germany, 2010,ISBN 978-3-9813550-6-2.
[17] I. Vela, CFD Prediction of Thermal Radiation of Large, Sooty, Hydrocarbon Pool Fires,PhD Thesis University of Duisburg-Essen, Germany, 2009.
