Arc Flash Protective Gear Personal Safety in Performing Stray Voltage Investigations by Tom Seidl We Energies
Arc-Flash Hazard • 5-10 incidences occur every day • Burns • Hot Gases can injure lungs and impair breathing • Hot Copper/metal • Blast Pressure
General Duty Clause Section 5(a)(1) Requires an employer to provide an employee with a workplace free from recognized hazards.
OSHA 29 CFR 1910.132(d)(1) • Requires employers to evaluate hazards • Requires employers to select and require use of PPE for employees.
Details are left to Consensus Standards • NFPA 70 • NFPA 70E • ANSI • ASTM • IEEE
NFPA 70E Covers • Public and private premises • Yards, lots, carnivals, parking lots and industrial substations • Installations of conductors & equipment that connect to the supply of elecricity • Installations used by the electric utility ….that are not an integral part of a generating plant, substation, or control cntr.
NOT Covered: Installations under exclusive control of an electric utility where such: • Consist of service drops or service laterals & associated metering • Are located in …easements or rights -of-way recognized (as under jurisdiction of a utility commission) • Are on property owned by the electricity utility for the purpose of …distribution of electric energy
NESC 410 • Assessment of the system is required. • If >2 cal/cm 2 , clothing system adequate for the anticipated level of arc energy. • For voltages >1000 Volts, effective arc rating of clothing system determined from Table 410-1 & 410-2 or Arc Flash Analysis
Systems Below 1000 Volts • Engineering controls to limit exposure. • Clothing system with a minimum 4 cal/cm 2
Generally, when you go to work on a farm, even though you are a utility employee, your are governed by NFPA 70 E
Best Practice - De-energize NFPA 70E Article 130.1 : A ll equipment and circuits shall be put into an electrically safe condition before working within the Limited Approach Boundary unless: • Doing so presents a greater hazard • Infeasibility • Less than 50 Volts
FPN No. 2 Examples that might be performed w/i the Limited Approach Boundary … because of infeasibility …include performing diagnostics and testing (e.g., troubleshooting)
Arc Flash Hazard Analysis ( Required: NFPA 70E, Article 130.30) • Determine the Arc Flash Protection Boundary • Determine the personal protective equipment that people within the Arc Flash Protection Boundary shall use.
Incident Energy The amount of energy (cal/cm 2 ) impressed on a surface, a certain distance from the source, generated during an electrical arc event.
Flash Protection Boundary An approach limit at a distance from exposed live parts within which a person could receive a 2nd degree burn if an electrical fault were to occur. (1.2 cal/cm 2 )
Flash Hazard Analysis (130.3) For systems 600 Volts or less, the flash protection boundary shall be 4 feet. (Assumes 2 cycle clearing time and 50 kA ASCC or any combination not exceeding 100 kA Cycles.
The incident energy exposure level shall be based on the working distance of the employee’s face and chest areas from a prospective arc source for the specific task to be performed.
Article 130.3, Exception No. 1: An arc flash hazard analysis shall not be required where all of the following conditions exist: 1. The circuit is rated 240 Volts of less. 2. The circuit is supplied by one transformer. 3. The transformer supplying the circuit is rated less than 125 kVA
Equation of Arc in a Cubic Box • D B = distance from arc electrodes, inches (for distances 18 in. and greater) • t B = arc duration, seconds (cycles/60 cycles) • F = bolted fault short circuit current, in kA (for the range of 16 to 50 kA) -1.4738 x t A x (0.0093 x F 2 – 0.3453 x F + • E MB = 1038.7 x D B 5.9675) • E MB = maximum 20 in cubic box incident energy
Equation of Arc in Open Air • D A = Distance from arc electrodes, inches (for distances 18” and greater. • t A = arc duration, seconds (cysles/60 cycles) • F = bolted fault short circuit, in kA (for the range of 16 to 50 kA) -1.9593 x (0.0016 x F 2 – 0.0076 x F • E MA =5271 x D A + 0.8938) • E MA = maximum open arc incident energy in calories/cm 2
Arc Flash Protection (transformer) Boundary • MVA = rating of transformer • t = time of arc exposure in seconds, (cycles/60 cycles) • D C = (53 x MVA x t) 1/2 • D C = Curable Distance
Arc Flash Protection (bolted fault) Boundary • MVA bf = bolted fault MVA at point involved • V = Volts • %Z = percent impedance based on transformer MVA • T = time of arc exposure in seconds, (cycles/60 cycles) • I SC = (((MVA Base x 10 6 )/(1.732 x V)) x 100/%Z) • I SC = Short Circuit Current P = 1.732 x V x I SC 10 -6 x 0.707 2 • • P = maximum power (in MW) in a 3 phase arc • D C = (2.65 x MVA bf x t) 1/2 • D C = Curable Burn Distance
The incident energy should be calculated at the maximum and at 85 % of maximum arc fault. (A longer clearing time can result in more incident energy.
Flash Hazard Analysis (130.3) As an alternative, the PPE requirements of 130.7(C)(9) shall be permitted to be used in lieu of the detailed flash hazard analysis of 130.3A
600 Volt MCC’s
Arc Rating of a Material • Maximum incident energy resistance prior to breakopen or onset of 2nd degree burns. • cal/cm 2 • Break open - formation of 1 or more holes in the innermost layer.
Clothing made from nonmelting flammable natural materials such as cotton, wool, rayon, or silk is permitted for Hazard/Risk Category 0 if flash hazard is <1.2 cal/cm 2
Underlayers Meltable fibers are not permitted. (an incidental amount of elastic is permitted.)
Acetate, acrylic, nylon, polyester, polyethylene, polypropylene, and spandex, either alone or in blends, shall not be used.
• FR clothing is required to be work within the Flash Protection Boundary, which is generally considered to be 1.2 cal/cm 2 • FR clothing for race car drivers or pilots is not suitable for arc flash protection. Arc rated FR clothing is the only FR clothing marked with the cal/cm 2 rating.
Clothing and other apparel (hair nets, hard hat liners) made from materials that do not meet the requirements of 130.7(C)(14) regarding melting, or made from materials that do not meet the flammability requirements shall not be permitted.
Foot Protection • Shoes with an arc rating are not available. • Foot Protection. Heavy-duty leather work shoes provide some arc flash protection to the feet and shall be used in all tasks in Hazard/Risk Category 2 and higher and in all exposures greater than 4 cal/cm 2 . • An incidental amount of elastic used on nonmelting fabric underwear or socks shall be permitted.
Hands • No method exists for determining the degree of exposure for a worker’s hands. • Leather of FR gloves shall be worn where required for arc flash protection. • Where insulating rubber gloves are used for shock protection, leather protectors shall be worn over the rubber gloves.
Safety glasses must be worn under the face shield or viewing window.
Outer Layers Garments worn as outer layers over FR clothing, (jackets or rain wear) must also be FR clothing.
Exposure of more than 40 cal/cm? • task must not be performed until and electrically safe work condition exists • FR clothing with a very high incident energy rating might me needed to perform the steps necessary to establish an electrically safe condition • This is the only task that should be accomplished with the equipment energized
Care and Maintenance of FR Clothing and FR Arc Flash Suits • Inspection • Manufacturer’s Instructions. • Storage • Cleaning
Other Personal Protective Equipment • Eye protection • Head protection • Conductive Articles not worn • Face shields w/o Arc rating shall not be used. • Eye protection always be worn under face shields or hoods.
50 cal/cm2 40 cal/cm2 25 cal/cm2 15 cal/cm 2
Proper PPE • Does not guarantee the worker will remain injury free • The purpose is to reduce death • Burns to the hands and arms aren’t considered life threatening
Insulated Tools Employees shall use insulated tools and/or handling equipment when working inside the limited approach boundary. (Must be marked with a voltage rating.)
The best solution is to always do as much work as possible with the system de-energized.
Alternatives During SV Investigations • Know the maximum fault current at the farm where you are working. • Measure line voltages at receptacles • Open panels only when de-energized • Connect the “panel neutral” lead to the grounding electrode conductor externally from the panelboard • Access the panel neutral at remote panels through contact with the equipment grounding conductor at a nearby receptacle
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