Arc Flash Boundary
What physical quantity defines the arc flash boundary?
Incident energy at the skin level of 1.2 cal/cm² (5 J/cm²), the threshold for second-degree burns on unprotected skin.
Does the arc flash boundary depend on voltage only?
No. It depends on arc-flash incident energy, influenced by voltage, fault current, arcing current, clearing time, equipment geometry, and working distance.
Can the arc flash boundary be inside the limited approach boundary?
Yes. The arc flash boundary is independent of shock boundaries and may be inside or outside them depending on system characteristics.
The arc flash boundary is the calculated distance from exposed energized conductors where a worker's unprotected skin could receive a second-degree burn (1.2 cal/cm² or 5 J/cm²) during an arc flash. It determines who may enter, required PPE, and work controls, as per CSA Z462/NFPA 70E. This boundary is distinct from shock approach boundaries and varies based on system parameters.
On a shop floor, the arc flash boundary is posted on equipment labels and used to control access and PPE. Workers must stay outside unless entry is justified, then they use arc-rated PPE and follow work controls from the arc-flash study. It is part of a hazard control system to prevent thermal burns, distinct from shock boundaries. In Canada, CSA Z462 defines it at 5 J/cm², calculated via IEEE 1584 or tabulated values. Compliance requires that unqualified workers only cross with proper PPE and supervision.
Treating the boundary as a fixed distance for all equipment; it varies with system parameters like fault current and clearing time.
Confusing arc-flash protection with shock boundaries; the arc flash boundary does not replace limited or restricted approach boundaries.
Entering the boundary without required arc-rated PPE and work controls; unqualified workers need proper PPE and supervision.