Appropriate PPE should be worn by qualified workers in the limited space (space between the limited approach boundary and the restricted boundary). Within this boundary, it is still possible to be exposed to a shock hazard. Moving toward the energized and exposed equipment, you’ll find the limited approach boundary. If the limited approach boundary is further out, then that should be treated as the line no one should pass without training and PPE.

When the arc flash boundary is the furthest away, it becomes the line no one should pass without training and PPE. Sometimes this boundary is the furthest one from the exposed equipment, other times the limited approach boundary is the furthest out.

That’s the distance where a worker without appropriate PPE would receive second-degree burns. The arc flash boundary is calculated to 1.2 calories/cm2 of incident energy. The arc flash boundary, or restricted approach boundary, changes depending on the potential arc flash hazard. Arc Flash Levels of Protection are best understood as layers or boundaries of protection around and away from hazardous electrical equipment.