The Working Distance and Arc Flash Boundary are shown in the following illustration:Īlthough more generally used as part of the arc flash risk assessment process, the calculated Incident Energy can also be used to determine PPE requirements. Once inside the AFB, suitably-rated Arc Flash PPE should be worn to protect the worker for situations and activities where it has been determined that there is a likelihood of an arc flash occuring. This value of heat energy will cause 2nd degree burns to bare skin when it is exposed for a duration of 1 second. The AFB is the distance away from the arc at which the heat energy experienced will be 1.2 cal/cm 2. The Arc Flash Boundary (AFB) is also calculated as part of an Arc Flash Study. It is important to recognise that the Incident Energy will be greater at a distance less than the Working Distance. The IE, typically expressed in calories per square centimeter (cal/cm 2) is a quantitative evaluation of the severity of an Arc Flash and can be used in a formal risk assessment process. This is the distance from the arc to the worker's head and torso, which are the areas of the body most at risk from severe burns. The IE is determined at a specified distance away from the arc itself - this is called the Working Distance. A recognised methodology is used to calculate the thermal energy that someone working on the equipment will be subjected to during the incident – this is called the Incident Energy (IE).
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