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IgnitionHazardsCausedbyElectrostaticChargesinIndustrialProcessesEditionFebruary2015elektrostatik_e_feb_2015_Manual09.02.1509:32Seite12Authors:Dr.MartinGlor,SwissInstituteofSafetyandSecurityPeterThurnherr,thubaLtd.©Allrightsreserved,inparticulartherightsofreproduction,disseminationandtranslation.Nopartofthepublicationmaybereproducedinanyform(byphotocopying,microfilmingoranyotherprocess)orprocessed,copiedorpropagatedbymeansofelectronicsystemswithoutthewrittenconsentofthepublisher.®elektrostatik_e_feb_2015_Manual09.02.1509:32Seite231Introduction1.1ExplosionhazardsinindustrialprocessesProcessesinmanydifferentindustriesproduceorprocesscombustibleandexplosivesubstances,orusethemasauxiliaries.Theseincludeflam-mablegases,vapours,liquids,aerosols,dustsandtheirmixtures.Whenmixedwithair,thesesubstancescanformapotentiallyexplosiveatmos-phere.Allthatisneededtotriggeranexplosionisaneffectiveignitionsource.Thephysicallawsgoverningthesequenceofeventsleadinguptoandoccurringduringexplosionsaredescribedindetailintheliterature[1-3].Protectivemeasuresagainstexplosionscomeundertwoheadings:pre-ventiveandconstructiveprecautions.Preventiveprecautionsaredesignedtopreventexplosionsfromoccurringinthefirstplace,whileconstructiveprecautionsaimtoreducetheeffectsofexplosionstoanacceptablelevel.Amongthemeasurestakentopreventexplosionsfromoccurring,the"exclusionofeffectiveignitionsources"isaccordedveryhighpriority.Ontheonehand,itisemployedincombinationwithotherpreventivemeas-uresandinparticularwithconstructivemeasurestakentominimizeexplo-sioneffects.Evenifaplant,say,issufficientlyprotectedbyexplosionpressurerelieforexplosionsuppression,aseriouseffortismadenonethe-lesstoexcludeeffectiveignitionsourcesintheinterestofensuringplantavailability.Ontheotherhand,theexclusionofeffectiveignitionsourcesisthemostimportantprecautionofallformostoperationsinvolvingthe"open"emptying,fillingortransferofcombustibleliquidsorbulksolids.Wherevertheexclusionofeffectiveignitionsourcesisappliedasapre-caution,adetailedriskanalysismustbecarriedouttocomparetheigni-tionsensitivityofthepotentiallyexplosiveatmospheresthatmayoccurwiththeincendivityofthepossibleignitionsources.Consideringthegreatvarietyofindustrialprocessesandtheatmospheresinwhichtheytakeplace,allsortsofignitionsourcescanoccur.Thetechnicalliteraturelists13differenttypesofpossibleignitionsources.Inthisconnection,itisextremelyimportanttoassesselectrostaticchargesproperlywithregardtoincendivity.Unlikemanyothersourcesofignition,electrostaticdis-chargesoccurnotonlyasaresultofdeviationsorfaultyoperations,butfrequentlyundernormaloperatingconditionsaswell.1.2ElectrostaticchargeasignitionsourceInmanyindustrialprocesses,electrostaticchargesarequitecommon.Theycancausebreakdowns,damage,firesandexplosions.Thecrucialfactorinevaluatingthehazardsofelectrostaticchargesistheprobabilitythatapotentiallyexplosiveatmosphereandadangerouslyhighchargewilloccuratthesametimeandplace.Thisprobabilityishighest,ofcourse,wherethehandlingofagivenprod-uctcanresultinbothadangerouslyhighchargeandformationofapoten-tiallyexplosiveatmosphere.Inparticular,thiscanoccurduringthehan-dlingofnonconductive,combustibleliquidssuchashydrocarbonsoroth-ernon-polarsolventsorofnonconductive,combustiblebulksolids.Butevenconductivesubstancescanaccumulatedangerouslyhighchargesiftheyarebeingprocessedinnonconductiveequipme...