Arc flash boundaries definitions3/7/2024 Section 1910 Subpart S-Electrical Standard number 1910.333 specifically addresses Standards for Work Practices. OSHA, Subpart S-Electrical: Occupational Safety and Health Standards. OSHA: Occupational Safety and Health Administration. NFPA 70E Standard: Standard that provides guidance on implementing appropriate work practices that are required to safeguard workers from injury while working on or near exposed electrical conductors or circuit parts that could become energized. NFPA: The National Fire Protection Association. ![]() Limited Approach Boundary: An approach limit at a distance from an exposed live part within which a shock hazard exists. One of the units used to measure incident energy is calories per centimeter squared (cal/cm2). Incident Energy: The amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. ATPV rated PPE is required for categories 1 through 4 as follows: Hazard Risk Category (HRC): Categories defined by NFPA 70E to explain protection levels needed when performing tasks. This includes pants, jacket, and bee-keeper-type hood fitted with a face shield. One calorie per centimeter squared per second can be equal to holding your finger over the tip of the flame of a cigarette lighter for one second.ĭe-energized: Free from any electrical connection to a source of potential difference and from electrical charge not having a potential different from that of the earth.Įlectrical Hazard: A dangerous condition such that contact or equipment failure can result in electric shock, arc flash burn, thermal burn, or blast.Įlectrical Safety: Recognizing hazards associated with the use of electrical energy and taking precautions so that hazards do not cause injury or death.Įlectrically Safe Work Condition: A state in which the conductor or circuit part to be worked on or near has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.Įnergy Breakopen Threshold (EBT): Primarily, this addresses the physical strength of the fabric with respect to thermal energy and at what arc-flash value the fabric will fail.įlame-Resistant (FR): The property of a material whereby combustion is prevented, terminated, or inhibited following the application of a flaming or non-flaming source of ignition, with or without subsequent removal of the ignition source.įlash Hazard: A dangerous condition associated with the release of energy caused by an electric arc.įlash Hazard Analysis: appropriate levels of PPE.įlash Protection Boundary: An approach limit at a distance from exposed live parts within which a person could receive a second degree burn if an electrical arc flash were to occur.įlash Suit: A complete FR clothing and equipment system that covers the entire body, except for the hands and feet. The onset of second-degree burns may occur at 1.2 calories per centimeter squared per second. ![]() See ATPV.Ĭalorie: A calorie is the energy required to raise one gram of water one degree Celsius at one atmosphere. ![]() Once this value is known, the ATPV rating of the flash clothing required for work at that distance from the potential flash hazard is also known. The calories per square centimeter rating of most arc flash protection suits, coveralls, and coats is commonly sewn into the fabric in large letters on the outside of the garment.Ĭalories per Centimeter Squared (cal/cm2): This is a number identifying the amount of energy that can be delivered to a point at a particular distance from an arc flash. This rating also applies to fabrics, however, a garment made from more than one layer of arc flash rated fabric will have a calorie per square centimeter rating greater than the sum of the ATPV ratings of the original fabrics. An arcing fault can release tremendous amounts of concentrated radiant energy at the point of the arcing in a small fraction of a second resulting in extremely high temperatures, a tremendous pressure blast, and shrapnel hurling at high velocity.ĪSTM: American Society for Testing and MaterialsĪrc Thermal Performance Value (ATPV): This value is presented in calories per square centimeter and represents the maximum capability for arc flash protection of a particular garment. Arc Flash: An arcing fault is the flow of current through the air between phase conductors or phase conductors and neutral or ground.
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