Session 2 –Explosion Protection Fundamentals

Session 2 – Explosion Protection Fundamentals

The Explosion TriangleIn order to have an explosion, all three legs of the triangle need to be present Our objective is to remove one or more of the legs of the triangle when we applyelectrical equipment in a potentially hazardous flammable atmosphere All theprotectionconcepts thatare currentlyused in theworld todayaddress oneor more legsof thistriangle

Sources of Ignition in HazardousAreasElectrical SparksTo ignite a flammable mixture of hydrogen and air requires only 20 micro Joules,the energy produced as a result of a break of 0.1 mS duration in a circuitcarrying 20mA in 10V. Flammable gases and vapors are more readily ignited athigh voltages than of low voltages, and is basically why IS circuits are seldomdesigned from use above 30V.Hot SurfacesThe flow of current through, for example the windings of an electric motorinvariably produces heat which will raise the surface temperature of the motor.If the motor is excessively overloaded and the thermal overload device isincorrectly set, the surface temperature of the motor may well exceed it’s T‐rating.BatteriesBatteries are a potential source of ignition as they will produce incendive sparksif their terminals are short‐circuited. Current of the order of 1000A can begenerated if the terminals of a car battery are short‐circuited. The certificationof portable equipment may only allow their use in hazardous areas if poweredby low‐power batteries.

Sources of Ignition in HazardousAreasFrictionThe abrasive wheels of portable grinding machines are more capable of producingincendive sparks, and hot surfaces locally at the point of contact by the abrasivewheel. Power tools unless certified shall not be used in hazardous areas.LightningLighting strikes will be readily discharged to earth by the normal metalconstruction of installation, but flammable gases or vapors can be ignited bylightning.ImpactThe combination of rusty iron or steel, aluminum and impact between the two is alikely source of ignition, known as thermite action, which can produce sparkscapable of igniting a flammable gas or vapor. Aluminum ladders are typically notused in hazardous areas due to this fact.Radio FrequencyThe energy transmitted by a mobile phone if used in a Zone 1 area, could bepicked up by the metalwork in the area, which acting as a aerial, could produce aspark of sufficient energy to ignite the petrol vapor.

Sources of Ignition in HazardousAreasStatic ElectricityTypical applications involve the transfer of fluids within a process plant. Upto 5000V can be generated at the nozzle of an aerosol canister. Similarly,1000V or more can be generated at the nozzle of high pressure cleaningequipment. Bonding and earthing of aircraft or tankers during refuelingprevents the buildup of electrostatic charges which otherwise might causethe fuel to ignite. Plastic enclosures normally carry the warning that theyshould be cleaned using a damp cloth to avoid generation of static electricity.Excerpt from Maintenance Information on Ex e GRP enclosure“Static HazardGlass Reinforced Polyester has a surface resistance of 10E9 ohms. Theycan present a hazard from static electricity and should only be cleanedwith a damp cloth.Carbon loaded glass reinforced, identified with the suffix “C” have asurface resistance of between 10E6 and 10E9 Ohms. They do notpresent a hazard from static electricity.”

Sources of Ignition in HazardousAreasOptical RadiationThe use of optical fibres in particular opensup many fields of application. This techniqueoffers in fact numerous advantages, however,the effect of the energy source "light" as apotential ignition source in explosiveatmospheres must be given consideration.Chemical ReactionMixing chemicals that have differentchemical reactions can and does createsignificant potentially explosive environments.UltrasoundChemical solvents may introduce a fire orexplosion hazard especially if exposeddirectly to ultrasound. Electrical hazards arealso present and should be consideredespecially where any liquids are involved(e.g. sonicating water baths).

Upper and Lower Flammable Limits forflammable gases and vaporsJust like your automobile, the mixture needs to be in the proper range for an explosion to occur GASLEL - UELINGITION ENERGY (µJ)GAS Propane2.00%to9.50%260IIAMost gases fall in the 2%‐10% range while Acetylene andHydrogen have much larger ranges, hence one reason theyare grouped very similar

Specific Density of Flammable gasesand vaporsDensity ration gases to air:Some gases are generally denser thanair (propane) and have a tendency tocreep over long distances andpotentially ignite when exposed to anarc.Other gases have the same density asair (acetylene, ethylene) and there islittle tendency for these gases to sinkor move around.Still other gases have a density lighterthan air (methane, hydrogen) and havea tendency to disperse unlesscontained by a container or structure.

General Rules of Thumb in determininghazardous areaA continuous volume of 10 liters of explosive gases in a confined room is always considered to be ahazardous area irrespective of the size of the room A simple calculation is that if the volume of hazardous gas is 1/10,000ths of the volume of theroom or greater, a potential for explosion can occur. This does not mean that the entire roomwould be classified as a hazardous area, but possibly only a part.Where explosive pressures can rupture the vessel containing the material, much smaller volumesof gas should be considered as hazardous due to rupture from other surrounding items.Example of proper ventilation of a contained room with heavier than air mixtures.

Gas Grouping per IEC AcetoneAcetyleneAmmoniumPetrol fuelsBenzeneCyclohexanoneDiesel fuelsAcetic acidAcetic anhydrideEthaneEthyl ethanoateEthanolEthyl chlorideEthyleneEthylene oxideDiethyl etherEthyl glycolFuel oili‐Amyl acetateCarbon monixideMethaneMethanolMethyl chlorideNaphtalenen‐Butanoln‐Hexanen‐Propyl alcoholPhenolPropaneCarbon disulphideHydrogen sulphideTolueneHydrogenIgnitionTemperature BIIBIIAIIAIICIIBIIAIICExample – Ethane has anauto‐ignitiontemperature of 515 Cwhich falls into suitabilityfor equipment rated T1 orbetter and gas group IIA Is this product suitable areasin which Ethane is present forextended periods of time?Yes IIC suitability, Tidentification suitability andprotection methodsuitability

Temperature Identification NumbersExample – Product has a marking of T6 it means that at a40 C ambient, the surface temperature of the product inquestion will never exceed 85 C. Elevated ambienttemperatures can effect the T identification numberdramatically. It is best under both high and low ambientconditions to check with the manufacture to determinesuitability of the product being used or considered.Temperature ClassMax Temp limit ( C)T1450T2300T3200T4135T5100T685

Temperature Identification NumbersIn general, if you can produce a product that is rated at T3 or better,(max. surface temperature of 200 C or cooler) you will cover approx.90% of the flammable gases and vapors seen in the oil and gas industry T1The lower the ‘T’ number, the higher the temperature.Hottest is worstCoolest is bestT2T3T4T5T6

If the marking of the electrical equipment does not include an ambienttemperature range, the equipment is designed to be used within thetemperature range –20 C to 40 C.If the marking of the electrical equipment does include an ambienttemperature range, the equipment is designed to be used within this range.One thing that must never be allowed to happen is that the surface (internalor external) temperature of the equipment rise beyond the ignitiontemperature of the gas or vapour that it is located in.

Relevant International standards forHazardous LocationsConceptGeneral requirementsIncreased SafetyNon‐arcingFlameproofPowder fillingProtected facilities and componentsIntrinsic Safety (IS)Energy‐limited apparatusPressurized enclosureRestricted breathingEncapsulationOil immersionDesignationExEx ebEx ecEx nAEx dEx qEx nCEx iaEx ibEx icEx nLEx pxEx pyEx pzEx nREx maEx mbEx mcEx oZone suitabilityZone 0, 1 & 2Zone 1 & 2Zone 2Zone 2Zone 1 & 2Zone 1 & 2Zone 2Zone 0, 1 & 2Zone 1 & 2Zone 2Zone 2Zone 1 & 2Zone 1 & 2Zone 2Zone 2Zone 0, 1 & 2Zone 1 & 2Zone 2Zone 1 & 2EuropeanEN 60079‐0EN 60079‐7EN 60079‐7EN 60079‐15EN 60079‐1EN 60079‐5EN 60079‐15EN 60079‐11EN 60079‐11EN 60079‐11EN 60079‐15EN 60079‐2EN 60079‐2EN 60079‐2EN 60079‐15EN 60079‐18EN 60079‐18EN 60079‐18EN 60079‐6InternationalIEC 60079‐0IEC 60079‐7IEC 60079‐7IEC 60079‐15IEC 60079‐1IEC 60079‐5IEC 60079‐15IEC 60079‐11IEC 60079‐11IEC 60079‐11IEC 60079‐15IEC 60079‐2IEC 60079‐2IEC 60079‐2IEC 60079‐15IEC 60079‐18IEC 60079‐18IEC 60079‐18IEC 60079‐6

Hazardous Area Classification .Category ConceptDefinition explosiveatmosphere is present:Continously or long term orfrequentlyGases, Vapours, MistsDustsZone 0 ‐ Category 1GZone 20 ‐ Category 1DZone 1 ‐ Category 2GZone 21 ‐ Category 2DOccansionallyZone 2 ‐ Category 3GZone 22 ‐ Category 3DInfrequently or short periodG Gases, D Dusts

Gas Grouping for Ex ‘d’ enclosuresExplosion groupsMaximum experimental safe gapMinimum ignition current ratiorelative to methaneIIA 0.9 mm 0.8 mmIIB0.5 mm to 0.9 mm0.45 to 0.8IIC 0.5mm 0.45mm

Relevant International standards for DustHazardous LocationsIEC StandardEN StandardIEC 60079‐31EN 60079‐31IEC 61241‐14EN 60069‐14ISO/IEC 80079‐20‐2IEC 61241‐10EN 60079‐10‐2DescriptionElectrical apparatus for use in the presence ofcombustible dust ‐ Part 1: Protection by enclosures"tD"Electrical apparatus for use in the presence ofcombustible dust ‐ Part 1‐2: Electrical apparatusprotected by enclosures and surface temperaturelimitation ‐ Selection, installation and maintenanceElectrical apparatus for use in the presence ofcombustible dust ‐ Part 2: Test methods ‐ Section 1:Methods for determining the minimum ignitiontemperatures of dustElectrical apparatus for use in the presence ofcombustible dust ‐ Part 3: Classification of areaswhere combustible dust are or may be present

Harmonization of ATEX& IECEx update (as of April 2015)Protection ConceptGas/Vapour GeneralRequirementsGas/Vapour and DustsGeneral RequirementsStandardEN50014:1997EN 60079‐0:2004(IEC 60079‐0:2004 Ed. 4Harmonization StatusWithdrawnUse for ATEXNoUse for IECExNoNever harmonizedNoNoEN 60079‐0:2006(IEC 60079‐0:2004 Ed4 modified)Contains non‐technical amendmentsto fit the IEC standard for ATEXpurposes, particularly relating toNomarking and instructions.Harmonisation expired June 2012NoEN 60079‐0:2009(IEC 60079‐0:2007Edition 5)Harmonisation expired April 2015PossibleIEC 60079‐0:2011Edition 6EN 60079‐0:2012(Minor corrigendumissued June 13)EN 60079‐0:2012/A11:2013NoThe EN version omits the clauses onfans (where thereis a separateharmonised standard EN14986:2007) Harmonisation hasbeen delayed because of issues onNothe status (Normative orInformative) for some of the text inAnnex ZY and information in AnnexZZ. For most purposes, it can beused as if it is harmonisedHarmonised version of IEC 60079‐0:2011 Edition 6 with all the ATEXaspects now agreed. Note that theOJ lists the 2012 edition and theYes2013 amendment separately but theintention is that only the versionincorporatinYesYes (except inrelation tofans)