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Electrical Arc-Flash Hazards

Electrical Arc-Flash Hazards

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  • 1. Electrical Arc-Flash HazardsIEEE IAS Distinguished LecturePeter E. Sutherland, IEEE Fellow, IAS Distinguished Lecturer, 2012-2013
  • 2. Discussion HighlightsThe Bigger Picture of Electrical SafetyArc-Flash Risks and EffectsArc-Flash Approach BoundariesArc-Flash Hazard CalculationsNFPA 70E TablesIEEE Standard 1584-2002Arc-Flash MitigationArc-Flash Categories & Protective ClothingArc-Flash Labels and Permits
  • 3. Worker Safety is ImportantWhy?– In addition to being the right thing to do it is intrinsicallyconnected to productivity, worker morale and liability costs– Machinery, processes & facilities usually designed with worker& machine safety as key consideration from start...– However, electrical safety often handled differently… Late, afterbase system design is finished, sometimes after equipment ispurchased . . .It should not be !– Electrical safety can best be optimized by being part of theinitially defined mission for the facility’s power distributionsystem and being considered at every decision point in thedesign, purchasing and installation process.
  • 4. Hierarchy of Hazard ControlMeasures1. Elimination of the hazard2.Substitution for less hazardous equipment,materials or process3.Engineering control for less hazardousexposure or severity4. Warnings, signs, and other communications5.Administrative controls including safe workpractices6. Personal protective equipmentFrom ANSI Z10-2005 American National Standard forOccupational Health and Safety ManagementSystemsThinking through thistable allows assigningvalue to differentpotential solutions to Arc-Flash & shock hazardsPPE is the last resort!
  • 5. Hazards Involved in Working On or NearEnergized Electrical EquipmentDangers associated with working on or around exposed energizedconductors or parts:Electrical shock - Becoming part of the circuit.Arc-Flash - The violent release of superheated gases caused byan electric arc.Arc Blast - The blast effects from the pressure wave associatedwith an Arc-Flash occurrence.Shrapnel - Ejection of projectiles or bits of metal.Noise - From initial explosive expansion of air.
  • 6. Standards for Electrical Safety and Arc-FlashHazards – Industrial and CommercialNFPA 70E -2012, “Standard forElectrical Safety in the Workplace”– AC Systems Table <240 V - 38 kV– DC Systems Table 100-600 VIEEE Std. 1584-2002, “IEEE Guidefor Performing Arc-Flash HazardCalculations”– 3-phase AC Systems 208 V-15 kV,CSA Z462-12, “Workplace ElectricalSafety”NFPA 70-2011, “National ElectricalCode”OSHA 29 CFR 1910 Subpart S -Electrical
  • 7. Standards for Electrical Safety and Arc-FlashHazards – Electric Power Generation,Transmission and DistributionIEEE Std. C2-2012, “NationalElectrical Safety Code”– 3-phase AC Systems 1 – 500 kV– Single phase-ground arc in open air.– Tables 410-1, -2, -3 for Clothing andClothing Systems.– Arc-Flash Hazard Analysis may be usedin place of tables.OSHA 29 CFR 1910 Subpart RSection 1910.269 - Electric PowerGeneration, Transmission andDistribution– No reference to Arc-Flash Standards
  • 8. NEC References to NFPA 70ENFPA 70-2011 “National Electrical Code (NEC)”– NEC Article 100, Definitions: Qualified Persons has NFPA 70Ereferenced for electrical safety training requirements.– NEC Article 110.16 requires that Electrical equipment such asswitchboards, panelboards, industrial control panels, meter socketenclosures, and motor control centers shall be field marked towarn qualified persons of potential electric Arc-Flash hazards.– NEC Article 240.87 requires that when a circuit breaker is usedwith a non-instantaneous trip one of the following means shall beprovided: zone selective interlocking, differential relaying orenergy-reducing maintenance switching with local status indicator.– NEC Article 430.102 refers to Lock-Out Tag-Out procedures forMotor Disconnecting Means.– NEC Article 490.1 Scope Statement for Equipment Over 600 Volts.
  • 9. OSHA References to NFPA 70EOSHA regulation 29 CFR 1910 Subpart S –Electrical, Appendix A: Reference Documents– NFPA 70E-2000 is the basis for most of the OSHA finalrule. However, there are some parts based upon the 2002and 2005 NEC and even some selected parts of NFPA 70E2004 Edition.– OSHA can, and has enforced lack of Arc-Flash protectionunder the "general duty clause".
  • 10. Arc-Flashover IncidentDescription: A routine voltage check at a 480Vterminal board inside the GAC resulted in an Arc-Flash burning the hand of the person checking thevoltage. The check consisting of placing one meterlead on a single phase and measuring the other 2phases with the second meter lead. The employeewas treated and released to return to work.Direct Cause: The terminal board was delivered withincorrect long terminal lugs that were also notinsulated. The terminal points of the meter wereexposed clamps too large for this small equipment.Root Cause: The equipment being used and theequipment being checked was not carefully evaluatedprior to conducting the voltage check.Contributing Factors: Terminal board delivered withincorrect terminal lugs that were also not insulated.Corrective Actions:– Use of a different style leads, the use of pointedleads instead of clip leads– Replace the terminal board with a new componentBroken Insulator and extra long terminallugsClips acrosstwo phases
  • 11. What May Happen with aSlow Protective Device
  • 12. Worker’s Flame-Resistant Shirt andInsulating Gloves
  • 13. Arc-Flash EffectsTemperature of the arc can reach 20,000°C(35,000 °F) – about 4 times the temperature ofthe sun!In US, 5-10 Arc-Flash incidents requiringhospitalization per day.1 – 2 deaths per day from electrical events,(shock, flash & blast).More than 2,000 workers treated in burncenters per year with severe Arc-Flash injuries.(This does not include injuries in other hospitalsand clinics which go unreported.)
  • 14. Examples of Activities which InvolveArc-Flash RisksRacking in or out of draw-outcircuit breakers.Removing or installing circuitbreakers or fuses.Working on control circuits withexposed energized primary parts.Applying safety grounds.Removing panel covers forinspections or other activities.Low voltage testing anddiagnostics.
  • 15. Arc-Flash StandardsSimplified Tabular method presented in:– NFPA-70E -2012, “Standard for Electrical Safety in theWorkplace”– In Canada Z462-12, “Workplace Electrical Safety”More sophisticated calculated methods suitable for lowvoltage and higher voltages developed in:– IEEE Std 1584-2002, “IEEE Guide for Performing Arc-FlashHazard Calculations.”– Amendment 1 issued in 2004 as IEEE Std 1584a-2004,(changes were relatively minor.)– Sometimes combination of these two documents referred to asStd 1584-2004.– Amendment 2: Changes to Clause 4 issued in 2011 as IEEE Std1584b-2011. Clarifications to clause on analysis process.
  • 16. NFPA 70E Approach Boundary Fig. C.1.2.4
  • 17. Shock Protection Approach BoundariesFixed LivePartProhibitedApproachDistanceRestrictedApproachDistanceLimitedApproachDistance@15,000 Volts 5 ft, 0 in2 ft, 2 in0, 7"@480 Volts 0, 1" 1 ft, 0 in 3 ft, 6 inLimited Approach Boundary – Distance from an exposed livepart within which a shock hazard exists.Restricted Approach Boundary – Distance from an exposed livepart within which there is an increased risk of shock, due to electricalarc over combined with inadvertent movement, for personnelworking in close proximity to the live part.Prohibited Approach Boundary – Distance from an exposed livepart within which work is considered the same as making contactwith the live part.
  • 18. Arc-Flash Protection ApproachBoundariesFlash Protection Boundary – Distance from an exposed live part withinwhich a person could receive a second-degree burn if an electrical Arc-Flashwere to occur. This second-degree burn results from the minimum Arc-Flashenergy of 1.2 cal/cm2, (5 joules/cm2). This boundary is determined bycalculating the distance at which an Arc-Flash energy of 1.2 cal/cm2 exists.Working Distance - Dimension between the possible arc point and the headand body of the worker positioned in place to perform the assigned task.Value selected for the application – minimum 18 in (48 cm).FlashProtectionBoundaryWorkingDistanceFixed LivePart@15,000 Volts@480 Volts 18" (Typical)36" (Typical) (Must be calculated)(Must be calculated)0.48 m (18 in.) (typical)0.96 m (36 in.) (typical)
  • 19. Combined Shock & Arc-Flash BoundariesFixed LivePart@480 Volts@15,000 VoltsLimitedApproachDistanceRestrictedApproachDistanceProhibitedApproachDistance0, 1"0, 7"1 ft, 0 in2 ft, 2 in3 ft, 6 in5 ft, 0 in(Arc Flash)WorkingDistance18" (Typical)36" (Typical)FlashProtectionBoundary(Must be calculated)(Must be calculated)Usually > than theLimited ApproachDistance but not always25 mm (0 ft 1in)0.2 m (0 ft 7 in.)0.3 m (1 ft 0in)0.7 m (2 ft 2 in.)0.48 m (18 in.) (typical)0.96 m (36 in.) (typical)1.0 m (3 ft 6in)1.5 m (5 ft 0 in.)
  • 20. Safe Approach DistancesUnqualified persons - Safe when maintaining a distance from exposedenergized parts equal to the Limited Approach Boundary or the FlashProtection Boundary, whichever is greater.Qualified persons - Appropriate Arc-Flash protection shall be utilized ifflash protection boundary crossed.To cross the Restricted Approach Boundary, the qualified person must:– Have a documented work plan approved by management.– Use appropriate protective equipment for work near exposed conductors and rated for voltageand energy level.– Be certain no part of body enters prohibited space.– Keep as much as body as possible out of restricted space.
  • 21. Safe Approach DistancesQualified personsAppropriate Arc-Flash protection shall be utilized if flash protectionboundary crossed.To cross the Prohibited Approach Boundary, which is considered the sameas making contact with exposed energized conductors or parts, thequalified person must:– Have specific training for working on energized parts– Have a documented plan justifying the need to work that close approved by management.– Perform a risk analysis approved by management.– Use appropriate protective equipment for work on exposed conductors and rated for voltage andenergy level.
  • 22. Other Key Arc-Flash DefinitionsIncident Energy – The amount of energy impressed on a surface, acertain distance from the source, generated during an electrical arc event.Measured in joules/cm2 or cal/cm2. (1 joule/cm2 = 0.24 cal/cm2).Flash Hazard Analysis – A method to determine the risk of personalinjury as a result of exposure to incident energy from an electrical Arc-Flash.Arcing Fault Current – A fault current flowing through an electrical arcplasma, also called arc fault current and arc current.Bolted Fault Current – Resulting from a short circuit or electrical contactbetween two conductors at different potentials in which the impedance orresistance between the conductors is essentially zero.Arc Duration – The total time it takes system protective devices to detectand interrupt a fault current.
  • 23. Operating Company Responsibilities1. Conduct an Arc-Flash analysis of the power system.2. Establish shock & protection boundaries and determine incident energylevels at working distances.3. Put warning labels on equipment.4. Implement qualified and general worker training.5. Provide necessary personal protective equipment, (PPE)6. Require outside engineering consulting firms involved inupgrades/expansions to provide 1, 2 and 3.7. Require outside contractors to meet 4 & 5.
  • 24. Steps in Performing an Arc-Flash HazardAnalysis1. Collect power system data.2. Determine the system modes of operation.3. Determine the bolted fault currents.4. Determine the arcing fault currents.5. Find protective device characteristics and arc durations.6. Document system voltage levels and equipment classes.7. Select the working distances.8. Determine the incident energies for all equipment9. Determine the flash protection boundary for all equipment.
  • 25. Performing an Arc-Flash Hazard AnalysisMethods– NFPA 70E-2012 Table 130.7 (C)(15)AC systemsDC systems– Power System Analysis SoftwareArc-Flash calculation modules (AC and DC) can be obtainedwith commercially available comprehensive power systemmodeling software.Steps in Arc-Flash Hazard Analysis:1. Short-Circuit Study2. Protective Device Coordination Study3. Arc-Flash Hazard Analysis (Per NFPA 70E and IEEE 1584)
  • 26. Do not do locally, on live equipment, whatcan be done remotely outside Arc-Flashboundary.Substitution and Engineering ControlsRemote Racking, Remote Controls, Remote Metering
  • 27. • “Arc Resistant Switchgear”• Common in MV systems• Moving into LV systems in US• Contains arc safely• Containment system betweenperson & arc• Must be fully assembled• Plenum needed to exhaustMay be solution for operators, but notfor maintenanceSubstitution and Engineering ControlsContainment method – passive arc resistance
  • 28. Transfer energy to alternate current pathCrowbar method• Remove arcing fault via bolted fault• Energy goes to lowest impedance path• Protection provided even if equipmentdoors are open• Not reusableMain LVBreakerFeeders. . . . .XFMR52MVBreakerBCASubstitution and Engineering ControlsArc Fault Diversion – Crowbar Method
  • 29. Containment method• Triggered fault in containment vessel• Lower resistance arcing fault• Lower energy than bolted fault• < 8 ms transfer• Reusable, maintainableSubstitution and Engineering ControlsArc Fault Diversion – Containment MethodProtectedZoneContainmentVesselArcDiversionRelay
  • 30. Arc-Flash Categories & ProtectiveClothingArcRatingHazard/RiskCategoryDescription of Required Clothingcal/cm2(HRC) and Personal Protective Equipment (PPE)-- 0 Nonmelting or Untreated Natural Fiber (Weight ≥≥≥≥ 4.5 Oz/yd2) Pants andShirt + Safety glasses or goggles + Hearing protection + Heavyduty leather gloves (AN)4 1 AR Shirt & AR Pants or AR Coverall + AR AF Suit Hood or AR FaceShield & Balaclava + AR jacket, parka, rainwear or hard hat liner(AN) + Hard Hat + Safety glasses or goggles + Hearing protection +Heavy-duty leather gloves + Leather work shoes (AN)8 2 AR Shirt & AR Pants or AR Coverall + AR AF Suit Hood or AR FaceShield & Balaclava + AR jacket, parka, rainwear or hard hat liner(AN) + Hard Hat + Safety glasses or goggles + Hearing protection +Heavy-duty leather gloves + Leather work shoes25 3 AR Shirt & AR Pants + AR Coverall + AR AF Suit Jacket, Pants and Hood+ AR Gloves + AR jacket, parka, rainwear or hard hat liner (AN) +AR = Arc-Rated, AF = Arc-Flash, AN = As NeededSource NFPA 70E-2012 Table 130.7(C)(16) and Clause130.7(C)(10)(b)
  • 31. Arc-Flash PPE by HRCHRC 28 cal/cm2HRC 14 cal/cm2HRC 3 = 25 cal/cm2HRC 4 = 40 cal/cm2HRC 01.2 cal/cm2
  • 32. AF Hazard Analysis & ProtectiveClothingLocationIncidentEnergyDescription of Required Clothing*Arc-FlashBoundarycal/cm2and Personal Protective Equipment (PPE)Outside ≤≤≤≤1.2 Nonmelting or Untreated Natural Fiber (Weight ≥≥≥≥ 4.5 Oz/yd2) Pantsand Shirt + Safety glasses or goggles + Hearing protection +Face shield for projectile motion (AN) + Heavy-duty leathergloves or rubber insulating gloves with leather protectors(AN)Inside >1.2 to 12 AR Shirt & AR Pants or AR Coverall or AF Suit + AR Face Shield &AR Balaclava or AR AF Suit Hood + AR jacket, parka orrainwear (AN) + Hard Hat + AR hard hat liner (AN) + Safetyglasses or goggles + Hearing protection + Heavy-duty leathergloves or rubber insulating gloves with leather protectors +Leather work shoesInside >12 AR Shirt & AR Pants or AR Coverall and/or AF Suit + AR AF SuitHood + AR gloves or rubber insulating gloves with leatherprotectors + AR jacket, parka or rainwear (AN) + Hard Hat +*Arc-Rating must be ≥≥≥≥ Incident Energy from AF Hazard Analysis.AR = Arc-Rated, AF = Arc-Flash, AN = As NeededSource NFPA 70E-2012 Table H.3(b)
  • 33. Arc-Flash PPE by Incident Energy>1.2 to 12 cal/cm2>12 cal/cm2Arc Rating must be ≥≥≥≥ Incident Energy from AF Hazard Analysis.
  • 34. Notes on AF Hazards & ProtectiveClothingSource: NFPA70E-1012 130.7 (A) Informational Notes (IN) 1 – 3,130.7(C)(15) IN2 and 130.7(C)(16) IN 21. PPE Requirements of NFPA 70E-2012 130.7 do not protectagainst effects of explosions such as physical trauma injuries.2. Normal operation of enclosed electrical equipment is “not likely”to present an electrical hazard when it isa) 600 volts or lessb) Properly installed by qualified persons.c) Properly maintained by qualified persons.3. However, closed equipment doors do not remove therequirement to wear PPE.4. These tasks are Category 0 in Table 130.7(C)(15)(a).5. For Incident Energy > 40 cal/cm2 it is recommended to de-energize the equipment before working on energized parts orequipment. There is no HRC greater than 4.
  • 35. Typical Arc-Flash & Shock EquipmentLabel
  • 36. Typical Shock & Arc-Flash Work Permit(1)
  • 37. Typical Shock & Arc-Flash Work Permit(2)
  • 38. Thank you!Any questions?