A qualified person must be trained in the use of PPE in a dry run to make him familiar. For a person to be deemed qualified he must have training in the construction and operation of the equipment. He is trained to recognize the hazard and ways of avoiding the hazard. A qualified person is also aware of the limitations of PPE and can relate the hazards to the type of work performed. A qualified person is a person who has a knowledge of electrical hazards associated with working with electrical equipment. In various shock hazard analyses, the qualified person has been authorized to enter the various shock hazard boundaries. Please refer to the table for more voltages. Another example is for a voltage between 751 V to 15 KV the distance for the limited approach boundary for a circuit with fixed exposed circuit part is 5 feet 0 inch, whereas the restricted approach boundary is 2 feet 2 inches, and the prohibited approach boundary is 0 feet 7 inches. the limited approach boundary with an exposed movable conductor is 10 feet. For example, referring to NFPA 70 E Table 130.2 ( c) for a voltage between 50 to 300 Volts. NFPA 70E calculates electrical shock hazard boundaries depending upon the voltage and then specifies the distance for the various approaches. How Shock Hazard Boundaries are Calculated Working within this limit is considered as the same as working on an energized live part. Within this limit there is an increased risk of shock due to electric arching and movement of the personnel while working.Ī Prohibitive Approach Boundary can only be crossed by qualified persons and is considered the same as having contact with a live part. Any unqualified person cannot cross this boundary, even with an escort or PPE. It is the limit within which a shock hazard exists.Ī Restrictive Approach Boundary is shock protection boundary that can be crossed only by qualified persons with knowledge of shock protection techniques and wearing PPE. This boundary depends on the voltage of the equipment. It is the minimum distance from the energized part any unqualified person can come. No untrained person can approach closer than this boundary and a trained person must use PPE or personal protective equipment to cross this boundary. There are three electrical shock hazard boundaries depending on the voltage of the appliance and termed the limited approach boundary, the restricted approach boundary, and the prohibited approach boundary.Īs per NFPA 70, the Limited Approach Boundary is a shock protection boundary that can only be crossed by qualified persons and unqualified persons under escort by qualified persons. In view of all these hazards the NFPA 70E has stated regulations to reduce the risk of injury to workers due to shock and arc flash hazards Electric Shock Hazard Boundaries The electric arc generated by switch gears while loading and unloading equipment can cause deep tissue burns, and the pressure from an arc blast can make a household wall fall due to the impact. Electric current passing through the heart can cause fibrillation of the heart resulting in a cardiac arrest. Apart from these an electric shock can also kill or injure people working at heights through falls. The hazards of electricity are of three kinds: electrocution, electric arc flash, and electric arc blast. People fail to realize that even our domestic supply of 120 Volts is a potential hazard that can be deadly if certain conditions are met. Our proximity to electrical appliances throughout our home and work environment make us take them for granted and we forget that if these are not handled properly they can kill. Electricity is a silent killer because it cannot be seen or heard.
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