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Electrical Arc Flash Safety and Risk Management


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Arc flash incidents can be costly in terms of personnel injury and equipment repair/replacement. This presentation provides an overview of the NFPA 70E 2012 Standard for Electrical Safety in the Workplace and the requirements of the standards, which are intended to better protect electrical workers from injury when they work on energized electrical equipment. This includes all aspects of facility and employer responsibilities for compliance to the NFPA 70E standards, as well as the current status of OSHA enforcement of these standards. Copyright AIST Reprinted with Permission.

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Electrical Arc Flash Safety and Risk Management

  1. 1. Arc Flash Protection and Mitigation Tim Cotter, P.E. Staff EngineerSchneider Electric Engineering Services
  2. 2. A Quick Look Back…“I introduced into my ears two metal rods with rounded ends and joined them to the terminals of the apparatus. At the moment the circuit was completed, I received a shock in the head – and began to hear a noise – a crackling and boiling. This disagreeable sensation, which I feared might be dangerous, has deterred me so that I have not repeated the experiment.”
  3. 3. We’ve come a long way…“I introduced into my ears two metal rods withrounded ends and joined them to the terminals ofthe apparatus.  At the moment the circuit was completed, Ireceived a shock in the head – and began to hear anoise – a crackling and boiling. This disagreeable sensation, which I feared mightbe dangerous, has deterred me so that I have notrepeated the experiment.”-Alessandro Volta, inventor of the first electricbattery, 1745-1827
  4. 4. even from … more recent times. 154. Electricians often test circuits for the presence of voltage by touching the conductors with the fingers. This method is safe where the voltage does not exceed 250 and is often very convenient for locating a blown-out fuse or for ascertaining whether or not a circuit is alive. Some men can endure the electric shock that results without discomfort whereas others cannot. Therefore, the method is not feasible in some cases. AMERICAN ELECTRICIANS’ HANDBOOK 7th Edition 1953 McGraw-Hill
  5. 5. But where are we now? NIOSH Study covering 1980-1995:  93,338 total work-related fatalities in the US  Approximately 1 in 15 were related to electrical hazards (> 1 fatality/ day in the US)  #5 hazard overall Auto accidents were #1 More recent data – # of deaths down, but proportion that is related to electrical work is about the same! Lots of work still to do!
  6. 6. Electric Arcs & Arc Flash Passage of substantial electric current through air “Short-circuit in air” May simply flow through ionized air May flow through vapor of arc-terminal material  Copper, Carbon, etc. Not necessarily harmful  Arc welding, “static electricity” Arc Flash Hazard: A dangerous condition associated with the possible release of energy caused by an electric arc. (NPFA 70E definition)
  7. 7. Severity of Arc FlashDepends on several factors, including:  Magnitude of fault current  System voltage  Duration of arcing fault  Proximity of worker to arc sourceComplex issue!Typical power distribution system – levels may be severe enough to cause serious injury or death
  8. 8. Measurements taken from atop the ladderNote melting of steel &copper
  9. 9. Relevant Codes & StandardsNational Electrical Code NFPA 70 (2011 ed.)OSHANFPA 70E (2012 ed.), Standard for Electrical Safety In the WorkplaceIEEE 1584-2002
  10. 10. National Electrical Code – NFPA 70 Best known of all electrical standards? Dates back to 1897 In general, does not address work practices Still, starting in 2002, some reference to Arc Flash NEC 110.16. Flash Protection. Electrical equipment, such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers, that are in other than dwelling occupancies, and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.
  11. 11. NEC & Arc Flash Requires equipment to be labeled, but does not specify a label format  We’ll discuss labeling in more detail later An NEC-compliant system does not necessarily do a thing to reduce, eliminate, or manage arc flash hazards
  12. 12. OSHA Occupational Safety and Health Administration Created by Occupational Safety and Health Act of 1970 Mission: “To save lives, prevent injuries, and protect the health of America’s workers.” 29.CFR 1910, Subpart S—deals with electrical systems “Law of the Land”!
  13. 13. OSHA & Arc Flash OSHA requires use of Personal Protective Equipment (PPE) Does not prescribe nature of PPE required for various tasks NFPA 70E is referenced in an appendix of OSHA 1910 Subpart S, but is not “incorporated by reference” Most serious injuries involve ignition of clothing Proper clothing must be selected based on industry standards or practices NFPA 70E: an industry consensus standard
  14. 14. OSHA General Duty Clause Each employer shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees. [OSHA’s PPE requirements] are written in general terms, requiring, for example, that personal protective equipment be provided "where necessary by reason of hazards..." (§1910.132(a)), and requiring the employer to select equipment "that will protect the affected employee from the hazards...." (§1910.132(d)(1)). Also, §1910.132(c) requires the equipment to "be of safe design and construction for the work performed." Similarly, §1910.335 contains requirements such as the provision and use of "electrical protective equipment that is appropriate for the specific parts of the body to be protected and the work to be performed (§1910.335(a)(i)). Industry consensus standards, such as NFPA 70E, can be used by employers as guides to making the assessments and equipment selections required by the standard. Similarly, in OSHA enforcement actions, they can be used as evidence of whether the employer acted reasonably. From OSHA interpretation of the General Duty Clause, 7/25/2003
  15. 15. NFPA 70E“Standard for Electrical Safety In the Workplace”Current edition published in September, 2011 Approx. 3-year revision cycle Revision process underway!Latest edition: 2012
  16. 16. NFPA 70E: Key Provisions Article 90: Scope Facilities covered include public and private buildings, parking lots, carnivals, industrial substations, service- entrance equipment, and electric utility equipment that is NOT a generating station, substation, or control center Facilities NOT covered include ships or automobiles/trucks, underground installations in mines, “3rd rail”, communications equipment under the control of communications utilities, and remaining electric utility installations Basically the same as the NEC
  17. 17. NFPA 70E: Key Provisions Qualified Employees – ones allowed to do work Knowledgeable about a piece of equipment or specific work method 70E defines specific items that should be known Can recognize and avoid electrical hazards (including arc flash) Is familiar with proper use of PPE, insulated tools, and insulating/shielding materials Not necessarily synonymous with: Master Electrician Professional Engineer CEO
  18. 18. NFPA 70E: Key Provisions “Live parts to which an employee might be exposed shall be put into an electrically safe work condition before an employee works on or near them, unless work on energized components can be justified according to 130.1”—110.8(A)(1) Basic protection strategy: de-energize the equipment! Excerpt from typical Square D instruction bulletin.
  19. 19. NFPA 70E: Key ProvisionsExceptions to the previous rule include the following: (130.1)When de-energizing introduces additional or increased hazards Deactivation of emergency alarm systems Life support system Ventilation in hazardous areaWhen de-energizing is infeasible Performing diagnostics or testing that requires energized circuit
  20. 20. NFPA 70E: Key Provisions If parts not placed in an electrically safe condition, then work to be performed shall be considered energized electrical work and shall be performed by written permit only Decision-making taken out of workers’ hands and shifted to management Why a permit?  Make you think twice before doing energized work  Create a “Paper trail” This applies to the “exemptions”  Management can’t just sign a permit and OK any energized work
  21. 21. Flash Hazard Analysis The analysis shall determine the flash protection boundary and the PPE that workers within this boundary should use Intended to protect personnel from the possibility of being injured by an arc flash How does one perform a flash hazard analysis? PPE Tables Calculations More on this later
  22. 22. Flash Protection Boundary Arc Flash Boundary (100): An approach limit at a distance from a prospective arc source within which a person could receive a second degree burn if an electric arc flash were to occur.
  23. 23. Flash Protection Boundary DDfb
  24. 24. How Much Energy is Too Much? It is generally accepted that an incident energy of 1.2 cal/cm2 is sufficient to cause 2nd-degree burns on unprotected skin  Tolerance may be higher for very short exposures Why cal/cm2? Just how hot is 1.2 cal/cm2??? Typical incident energy ranges:  0-200+ cal/cm2 Equipment that has been placed in an electrically safe work condition: energy level = zero!!
  25. 25. Working Inside the FPB Employer shall determine and document the incident energy exposure of the worker (cal/cm2)  Based on a working distance from source of arc to employee’s face and chest Use FR clothing and PPE appropriate for hazard level  Use additional PPE for parts of the body closer than the distance at which the incident energy was determined (Alt.) Select PPE from tables
  26. 26. Equipment Labeling Now required in the 2012 edition of NFPA 70E 130.5 (C) – Several options listed for identifying the arc flash hazard along with nominal voltage and arc flash boundary.  Field marked – can’t determine at factory  Minimal information actually required  Most labels contain significantly more information
  27. 27. IEEE Standard 1584 “IEEE Guide for Performing Arc-Flash Hazard Calculations” Incorporates results of extensive testing performed by several parties Provides method for calculating incident arc-flash energy Does not replace NEC or NFPA 70E—instead, it works with and alongside of them More on this when we talk about calculations
  28. 28. NFPA 70E PPE RequirementsPPE should:  Cover all ignitable clothing (130.7(C)(2))  Allow for movement and visibility (130.7(C)(2))  Include head, face, neck, and chin protection (130.7(C)(3))  Include eye protection (safety glasses) (130.7(C)(4))  Include FR clothing for body (130.7(C)(6)) for all exposures over 1.2 cal/cm2  Include hand and arm protection (130.7(C)(7))  Include foot protection (130.7(C)(8))  Conform to relevant ANSI and/or ASTM standards (130.7(C)(14))
  29. 29. Additional PPE Requirements Outer layers over FR clothing also must be FR Avoid tight-fitting clothes Choose PPE that poses minimal interference while still providing adequate protection Wear safety glasses under face shields/hoods Visor in flash suit should protect as well as the rest of the suit Non-FR synthetic fabrics not permitted*
  30. 30. Selection of PPE Based on Hazard/Risk Analysis NFPA 70E Tables  List common work tasks for several types of equipment  Each task assigned a HRC  PPE defined for these HRCs Calculations  Calculations define AFIE for a given location  Select protective clothing that will protect against that AFIE  Technically, HRCs don’t apply to calculated results, but in practice, most still correlate calculated AFIE levels to clothing systems listed in NFPA 70E Table 130.7.C.15
  31. 31. Protective Clothing Classes Min Arc RatingClass Description (cal/cm2) 0 Nonmelting, flammable materials N/A 1 FR shirt + FR pants or FR coverall 4 2 FR shirt + FR pants or FR coverall 8 3 (2) + additional PPE to reach 25 cal/cm2 25 4 (2) + additional PPE to reach 40 cal/cm2 40 Category 0 Clothing OK for up to 1.2 cal/cm2
  32. 32. H/R Category 0 (Non-FR)Untreated, long-sleeve shirtUntreated, long pantsHearing protectionSafety Glasses Good for up to 1.2 cal/cm2 Photos courtesy of Oberon
  33. 33. H/R Category 1 (one FR layer) FR pants with ATPV of at least 4 cal/cm2  No more untreated denim! FR long-sleeve shirt Optional FR coverall in lieu of FR shirt/pants FR jacket/parka/rainwear (as needed) Hard hat Safety Glasses Hearing protection Arc Rated Face Shield Leather gloves & leather work shoes (as needed) Good for up to 4.0 cal/cm2
  34. 34. H/R Category 2 (one FR layer + cotton)  FR long-sleeve shirt (minimum arc rating of 8)  Pants: FR with min arc rating of 8  FR Coverall (Arc Rating 8 or more) permissible in lieu of other FR clothing  FR jacket/parka/rainwear (as needed)  Hard Hat  Safety glasses or Safety Goggles  Leather gloves & leather work shoes  Hearing protection  Face Shield & Arc Rated Balaclava or Arc Rated HoodPhotos courtesy of Oberon Good for up to 8.0 cal/cm2
  35. 35. H/R Category 3 (two FR layers) Option 1:  FR shirt/pants  FR coverall Option 2:  FR clothing system w/arc rating of 25 FR jacket/parka/rainwear (as needed) Hard hat Safety glasses or safety goggles Double-layer switching hood Photos courtesy of Oberon Hearing protection Arc rated gloves or rubber gloves w/leather protectors Good for up to 25 cal/cm2 Leather work shoes
  36. 36. H/R Category 4  FR clothing with arc rating of 40  Flash suit  Shirt/pants/coverall combination providing equivalent protection  FR jacket/parka/rainwear (as needed)  Hard hat w/FR liner  Safety glasses or safety goggles  Double-layer switching hood  Hearing protection  Arc rated gloves or rubber insulating gloves w/leather protectors  Leather work shoes Photos courtesy of OberonGood for up to 40 cal/cm2
  37. 37. Beyond 40 cal/cm2… PPE vendors: 100 calorie suits NFPA 70E: defines no clothing class higher than 40 cal/cm2 Does not explicitly prohibit work at such locations 70E Handbook: appears to have backed off a statement in the earlier editions that allowing work at such locations was never the intent of 70E Other issues to consider Blast effects Equipment integrity Is PPE rated against shrapnel? No “ballistics rated” flash suit or face shield Hearing damage
  38. 38. Why is PPE Important? Has major impact on burn survival rates  Major factor: total % of body burned Burn of 75% of body (easily possible if clothing ignites) results in:  < 50% survival rate for males aged 30-39  < 20% survival rate for males aged 50-59 Rule of thumb: one day in hospital for each 1% of body burned Photos courtesy of Oberon
  39. 39. Clothing Performance BenchmarksEase of ignitionTendency to continue burning after heat source removedDegree/ease of flame spreadAmount of heat transmittedTendency to meltStrength—does arc flash tear it apart, or does it hold together?
  40. 40. Relative Performance – non-FR Clothing Natural fibers are fairly good, at least if they don’t ignite  Cotton may continue to burn after heat removed  Wool does not normally sustain a fire Non-FR Synthetics particularly bad either when alone or when blended w/cotton  Easily ignited  Melt  Increase chance of infection  Exception?
  41. 41. PPE Selection Principles Heavier fabrics provide more protection Multiple layers more effective than single layer of equivalent weight No non-FR synthetics next to skin  “Performance underwear” may contain polyester or nylon/spandex blend—good for a ski trip, but bad for electrical work!!
  42. 42. Head and Face Protection Face shields provide some protection against molten splatter Non-FR face shields provide little or no protection against burns Tinted face shield with ATPV rating—better Protective shield inside FR hood—best  Beware old FR hoods with non-FR shields! If visibility is a concern, provide lighting! Safety glasses always required
  43. 43. Arc Rating Values Based on testing Shown on equipment label Some PPE—no tests performed, so no official arc rating assigned  Leather work gloves (unofficially 12 cal/cm2)  Leather glove protectors  Rubber insulating gloves Class 0 yellow gloves: limited testing indicated ignition 10% of the time at 25 cal/cm2; 50% of the time at 31 cal/ cm2  Shoes (limited testing indicates resistance of 50-60 cal/cm2)
  44. 44. PPE Innovations – Arc Hood Cooling Systems
  45. 45. PPE Innovations – Improved VisibilityWarning: older clear faceshields may not be FR. In thepresence of a high energy arc, they can melt. The pressurewave will tend to push the molten plastic into your face.
  46. 46. PPE “Gotchas” Not all FR rainwear is “arc resistant” – i.e., may have elements that can melt EVERYTHING needs to be arc resistant (or at least made out of something that won’t melt or burst into flame) during energized work  Underwear  Safety vests  Hair nets  Employee ID cards  Logos / names sewn on to FR clothing  Paper towels stuffed in hard hat to catch sweat Maintain the PPE Carefully observe laundering instructions
  47. 47. Use Your Head Use PPE correctly…no rolled-up sleeves or unzipped coveralls Body positioning when operating devices But: don’t make face shield an “arc scoop” No more workers than necessary in vicinity of energized work Remove yourself from the source when possible Hot stick Remote operations
  48. 48. Disclaimers NFPA 70E, 130.7.C.16, Informational Note #2:  The PPE requirements of this section are intended to protect a person from arc flash and shock hazards. While some situations could result in burns to the skin, even with the protection described in Table 130.7.C.16, burn injury should be reduced and survivable. Due to the explosive effect of some arc events, physical trauma injuries could occur. The PPE requirements of this section do not address protection against physical trauma other an exposure to the thermal effects of an arc flash. PPE is supposed to be your last line of defense. How do you feel about sustaining a “survivable” injury?
  49. 49. Thank You Tim Cotter, P.E. Staff EngineerSchneider Electric Engineering Services, LLC