Fixed Roof Gas-Oil Tank Explosion.docx

ExplosionandFireinGas-OilFixedRoofStorageTank(Anoninherentlysaferdesign)YigalRieZelProcessSafetyManagement,consultantAshdod,ISRAEL77409Email：yriezeltrendline.co.ilAbstractOnNovember2nd,1997anexplosionoffixedroofgas-oiltanklocatedinthetankfarmofAshdodOilRefinerycausedlossoflifeofOneSampleMan,Fireintwoadjacenttankslocatedinthesamedike.Duringthefire,whichlastedlessthan3hours,therewasabigpublicconcernaboutnecessityforemergencyevacuationfrom2neighborhoodsettlements.Emergencyoperationsoftherefineryandexternalforceswereveryeffectiveandwithin3hoursfiresinbothtanksandthedikewereputdownwithoutanyadditionaldamagetoothertanksorequipmentinthetankfarm.Thesourcefirewasaheavytopphasepoolfire.Theinvestigationpointedoutthatthesourceofexplosivemixtureinthetankwashydrogenthatpenetratedwiththegas-oiltothetankasaresultofnon-completegas-oilstrippingwithhydrogenattheexitofgas-oilhydrotreatingunit.Thesourceofignitionwaselectrostaticsparkinitiatedbysyntheticrope(insteadofcottonone)usedwiththesamplingdeviceinordertogetsamplesoutofthetank.Aftertheaccident,unfortunatelytoolate,itwasfoundthatsimilarscenariowasreportedabout15yearsbeforebutwasnotdigestedwidelyenoughthroughaccidentdatabases.1. INTRODUCTIONThereisnodoubtthatstoragetanksofanoilrefinerybelongtoacategoryofinherentrisksystems.Theironlypurposeistostorehazardousmaterials.Butwoulditbesafeenoughtostoregas-oilordiesel-oilinanatmosphericfixedrooftankevenifthetemperatureofthestoredhydrocarbonsislowerthanitsflashpoint?Inthemorningof2ndNovember1997agas-oiltankcontaining15000cumofgas-oilexplodedandinitiatedabigfirestartingontoplayeraspoolfire.Thefirewascontainedwithinthedikeoftwoadjacenttanks.Averytallsmokeclouddispersedtowardsnortheast(thecenterofthecountry)andwithoutharminganysettlementwanderedunderverylowwindvelocityabout40kmuntilitvanished.Investigationstartedimmediatelybutalmostsametimecameinfirstquestionfromanexperiencedsafetyadviserofafamousrefiningcorporateabroad,askingforinformationinordertodigestthelessonlearnt.Themainquestionwas:',InPlatt,sOilgramNewsofNovember1997itwasindicatedthatadieseltankexplodedintheAshdodrefinery.Undernormalcircumstancesitisvirtualimpossibletohaveanexplosioninadieseltank.',.Therealityshowedthatthepossibilityforsuchexplosionisthere.Thethoroughinvestigationaimingtoidentifymainlytherootcausesfocusedonhydrogencontaminationinthegas-oil.Someweaknessesinthesystemcontributedtotheaccidentandilluminatedfewbasicsthatshouldalwaysbekeptinmindandapplied.Itisbettertobrainstormaheadthaninvestigatelater.Inherentlysaferalternativesshouldalwaysbesought.Widedistributionofaccidentdataandlessonslearntcanservemorethanmutualaidbetweenmembersofthesocietydealingwithhazardousmaterials.ComprehensiveschemesofProcessSafetyManagementsystemsapplicationsarerecommendedforuseevennotyetrequiredbyregulatorsorauthorities.Anequallyimportantlessonwasexpressedbyafamousinternationalsafetyconsultancyservicescompany:"OilRefineriesLtd.s,emergencyresponsetotheexplosionappearstohavebeenextremelygoodandfollowedtextbookprocedure'onhowtodealwithsuchasituation”.2. THEGAS-OILPRODUCTIONSYSTEMINASHDODREFINERY.TheAshdodCrudeOilRefineryisasimpletypeplantanditsgas-oilcourseofproductionfromthedistillationinthemaincrudetowertillthefinishedproductsstoragetanksisviaunitsoffairlylowcomplexityfactor.Inthemaincrudeoildistillationtowerseveraltypesofcrudeoilsormixturesofsome,areseparatedtothemainrawproductslike:gas,naphtha,kerosene,lightatmosphericgas-oil(LAGO),heavyatmosphericgas-oil(HAGO)andatmosphericbottoms(fuel-oil).TheLAGOisstripped(aswellasthekerosene)inasteamstrippingtowerinthecrudeunitinordertoreducecontentoflightmaterialsandincreaseitsflashpoint.TheLAGO,HAGOandanothervacuumgas-oilareroutedtoHydrogenCatalyticDesulfurisingunitsortodirectblendingintheproductsgas-oiltanksinthetankfarm.Theactivityisdependentonthesulfurcontentinthecrudeoilandthelevelofsulfurrequiredinthedifferentgas-oilproductsformarketing.ThereisalsoanoptiontorunthekeroseneHDS(hydrogendesulfurisingunit)withgas-oileitherinparallelorassparetothegas-oilHDS.ThetwoHDSunitsincludeastrippingsectionineachofthem.ThesesectionswerestartedasReboilingHeatersStrippersandinordertosaveenergyadaptedtosteaminjectionstripping.Asaconsequenceofturbidityprobleminthestrippedgas-oilitwasdecidedabout20yearsagotoreplacethesteamwithhydrogenasthestrippingmaterialonlyintheGas-OilHDSunitThehydrogenwasthereandcheap,theturbidityproblemdisappearedandtherewerealreadyfewexamplesforapplyingthisprocessinsomeotherindustries.IntheKeroseneHDSunitthestrippingremainedwithsteamandonlyafterabout15yearsofexperiencewithhydrogenintheGas-OilHDSandwhentherewasahigherneedtooperatethisunitalsoongas-oilthechangewasmadeandhydrogenreplacedsteamasstrippingmaterialintheKeroseneunit.Thegas-oilproductsfromthetwoHDSunitsandthosestreamsbypassingtheHDSunitsareroutedandblendedtoonspec,productsinthetankfarmwhichispartoftherefinery.Thetanksareregularatmosphericfixedconerooftankswithopenventtotheair.OnFriday02:30operationdepartmentstartedfillingtank401.