NFPA 70E provides a simplified formula for calculating incident energy.AC systems are covered in Table 130.4(D)(a), and DC systems are covered in Table 130.4(D)(b).Ĭalculating the Arc Flash Boundary is more complex, partly because the phenomenon of arc flash is still being researched. The two shock protection boundaries are based exclusively on the voltage of the equipment and can be found in a set of tables in NFPA 70E. The permit includes a specific plan of action, a list of protective steps to be taken, and supervisory approval.Crossing this boundary to perform work while the equipment is still powered also requires an energized electrical work permit.Restricted Approach Boundary is closer and may only be crossed by qualified persons. Qualified persons may also escort unqualified persons through the area, if appropriate protective equipment is provided for the visitor, as well.Qualified persons, who have been trained and equipped for the task at hand, may cross this boundary, if needed.Limited Approach Boundary is the normal “stay-back” distance for unqualified persons (that is, people without any special training or equipment). Two shock protection boundaries are intended to protect workers from this second hazard. However, the two hazards need to be addressed separately. Most equipment that poses an arc flash hazard also presents a risk of electric shock. Failure to use the right PPE can lead to injuries. If workers must cross this boundary to work on the equipment while it is still powered, they need specific personal protective equipment (PPE) to protect them from burns. Unqualified workers, who may not be prepared to protect themselves to the same degree, should stay away they should not cross the Arc Flash Boundary. Qualified workers, who have the training to safely perform the task in question, should use the information on the equipment’s arc flash label to identify the PPE they need. The type of required PPE will depend on the work being done, the nature of the equipment, and the available power. If workers must cross this boundary to work on the equipment while it is still powered, they need specific personal protective equipment (PPE) to protect them from burns. In this case, the Arc Flash Boundary offers another related benefit it tells workers when they need specific gear. Staying away from the equipment is an easy way to keep safe, but sometimes a worker must get closer to do their work. Staying outside the Arc Flash Boundary is a way to reduce or eliminate injuries from an arc flash. The Arc Flash Boundary helps him to determine a safe distance. The electrical worker has to be able to determine his relative risk, according to the distance from the equipment. The Arc Flash Boundary was developed at OSHA’s request by the NFPA to help companies, electrical workers, and employees avoid workplace injuries and fatalities due to shock, electrocution, arc flash, and arc blast, when working in proximity to energized electrical equipment. The Arc Flash Boundary determines the distance from the equipment at which the Incident Energy of an arc flash would be 1.2 cal/cm². The Arc Flash Boundary marks the distance from the equipment at which the Incident Energy of an arc flash would be. These burns are caused by the extreme heat given off by the runaway arc the radiant heat that spreads out in all directions.Īs a result, NFPA 70E includes a “stay-back” distance intended to limit these burns. In an arc flash, the most common and most severe injuries are burns.
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