Related: Electrical Shock and Arc Flash PPE Overview Insulated gloves, tools, and equipment are required within this boundary. Only qualified personnel wearing appropriate personal protective equipment (PPE), having specified training to work on energized conductors or components, and a documented plan justifying the need to perform this work may cross the boundary and enter the Restricted Space. The restricted approach boundary is the distance from an exposed part that is considered the same as making contact with the live part. A qualified person must use the appropriate PPE and be trained to perform the required work to cross the limited approach boundary and enter the limited space. No untrained personnel may approach energized parts any closer within this boundary unless under the supervision of a qualified worker and using proper PPE. The limited approach boundary is the minimum distance from an exposed live component where unqualified personnel may safely stand. When an energized conductor is exposed, you may not approach closer than the flash boundary without wearing appropriate personal protective clothing and personal protective equipment. In the event of an arc flash, this boundary is where an employee would be exposed to a curable second-degree burn (1.2 calories/cm2). The flash protection boundary is the farthest established boundary from the energy source.

Flash protection boundary (outer boundary) The radiant energy released by an electric arc is capable of permanently inuring or killing a human being at distances of up to ten or even twenty feet. The Prohibited Approach Boundary was removed from NFPA-70E in 2015. The shock hazard boundaries are dependent on the system voltage and can be found in Table 130.4(D).Īn update to the 2012 version of Table 130.4 includes voltages up to 800kV. NFPA 70E stipulates two approach boundaries in addition to the arc flash protection boundary that must be known and observed. Related: Electrical Power System Studies Explained NFPA 70E Arc Flash and Shock Hazard BoundariesĪs a result of workplace accidents related to arc flash, the National Fire Protection Association (NFPA) has developed specific approach boundaries designed to protect employees working on or near energized equipment. This calculation establishes various arc flash boundaries and specifies the Personal Protective Equipment (PPE) required when approaching each boundary. The massive energy released in the fault rapidly vaporizes the metal conductors involved, blasting molten metal and expanding plasma outward with extraordinary force.Īn Arc Flash Study or Analysis is a calculation performed by Professional Engineers to determine the incident energy at each location. Arc flash temperatures can reach or exceed 35,000 ☏ (19,400 ☌) at the source of the arc. This video demonstrates the devastating effects of a large arc flash. A large arc flash can easily generate incident energy in the range of 40 cal/cm2 Higher incident energy can cause third-degree (incurable) burns. If unprotected skin is exposed to an incident energy of 1.2 cal/cm2, a second-degree (curable) burn is expected. Incident energy is measured in calories/cm2. This is why its important that protective devices be properly set and coordinated in order to identify the beginnings of an arc and quickly interrupt the fault. If there is enough power available, an arc flash could last an extended period of long time. Also known as the “working distance”, this measurement is estimated to be 18 inches.ĭuration - How long the arc will last. This is calculated using the system voltage and the maximum available fault current.ĭistance - How far away a from the arc worker will be. In most cases, arc flash incident energy depends on three elements:

The radiant energy released by an electric arc is capable of permanently injuring or killing a human being at distances of up to ten or even twenty feet. If you sit right next to a campfire, you would receive more radiant (incident) energy than if you sit farther away. Incident energy of an arc flash can be best explained with a simple campfire analogy. The massive energy released in the fault rapidly vaporizes the metal conductors involved, blasting molten metal and expanding plasma outward with extraordinary force. Many of these workplace injuries result from arc flash, a type of electrical explosion that occurs due to a low-impedance connection to ground or another voltage phase in an electrical power system.Īrc flash temperatures can reach or exceed 35,000 ☏ (19,400 ☌) at the source of the arc. Numerous workers are injured or killed each year while working on energized electrical equipment. Arc Flash Hazards: NFPA 70E Working Boundaries Explained 897×550 107 KB

Arc flash restricted approach boundary