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Arc-Flash Boundary

Last updated: December 11, 2019

What Does Arc-Flash Boundary Mean?

An arc-flash boundary is a shock-hazard approach boundary that serves as a minimum safe distance from electrical equipment. An employer operating within the arc-flash boundary must use personal protective equipment (PPE) and/or other safety equipment.

The boundary reflects the distance from an electrical device at which the incident energy from an arc flash would be equal to 1.2 cal/cm2 (5 J/cm2). This amount of energy is thought to be approximately equal to the amount of energy necessary to cause a second-degree burn on a person.

Safeopedia Explains Arc-Flash Boundary

The arc-flash boundary concept is defined by the National Fire Protection Association’s 70E standard. It is an OSHA-recognized consensus standard; therefore, the arc-flash boundary has legal weight as a boundary that must be observed in workplaces in order for employers to meet their general duty obligations for workplace safety. The NFPA prescribes specific calculations for determining the arc-flash boundary under Annex D of this standard.

In lieu of calculating the point at which incident energy will equal 1.2 cal/cm2, the standard also provides a table-based solution for determining an arc-flash boundary based on the properties of the electrical equipment under consideration. Both solutions also provide specific obligations for the PPE that must be used by individuals working closer to the equipment than the arc-flash boundary.

Other standards require all equipment that necessitates an arc-flash boundary to be clearly labeled with information stating what that boundary is, thus enabling a quick understanding of the safe working distance by anyone near the equipment. Related shock-hazard approach boundaries include the limited and restricted approach boundaries, which refer to closer, more-hazardous distances from electrical equipment that require greater safety precautions in order to operate within.


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