When an arc flash hazard exists, which boundary is defined as the distance from the arc source at which the incident energy equals 1.2 cal/cm2 (5 J/cm2)?

• A. Limited Approach Boundary
• B. Restricted Approach Boundary
• C. Arc Flash Boundary
• D. Insulation Boundary

Answer: (C)

Arc flash boundaries are energy-based limits used to protect workers from the heat of an arc. The boundary in question is the Arc Flash Boundary, defined as the distance from the arc source at which the incident energy is 1.2 cal/cm2 (about 5 J/cm2). Inside this boundary, the energy is sufficient to cause a second-degree burn, so appropriate arc-rated PPE and safety measures are required; outside, the energy level falls below that threshold and the immediate arc flash risk is reduced.

Other boundaries address shock hazards or insulation protection rather than arc energy. Limited Approach and Restricted Approach Boundaries pertain to electrical shock exposure and the required clearances and PPE for working near live parts, while the Insulation Boundary relates to avoiding shock by staying behind insulation.