The arc flash hazard analysis takes into account where in the system the fault occurs and how long the current exists before a protective device clears the fault. Therefore the protective device coordination needs to be investigated. The amount of energy liberated during a fault can then be determined. All of these factors result in a specific calories-per-square-centimeter (cal/cm2) value of incident energy that is calculated for each point in the system. This value indicates the level of personal protective equipment (PPE) that a worker must wear to safely perform any exposed energized work on the equipment. With the arc flash hazard analysis completed, it is possible to create safe work permits for specific tasks to be performed on the system. Arc flash hazard labels can also be created for each bus and specific equipment to indicate the specific hazard available at that point in the system, and the corresponding required PPE as well.
Several methods for arc flash calculations are proposed in NFPA 70E-2004. Electrical engineers typically perform the detailed engineering based calculations using IEEE 1584, with an understanding of the short circuit behavior of power systems and protective device coordination are necessary. If the available short circuit values at various equipments and the associated fault clearing times are known, then a trained person can also perform an arc flash hazard assessment by using the appropriate NFPA 70E tables. However, this approach has significant drawbacks due to gross oversimplification inherent in this simplified approach. For larger power systems with multiple sources and possible operating conditions, it is preferable to do a detailed engineering analysis using IEEE 1584 that can determine the worst-case arc flash hazard conditions that can occur. As will be seen, this will not necessarily be the conditions with the highest fault current.
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