Arc Flash vs Shock Hazard: Boundaries, PPE, and Safe Work Logic

Regulation: NFPA 70E Articles 130, 360

Keywords: arc flash boundary NFPA 70E, shock hazard boundary, arc flash PPE category, limited approach boundary, restricted approach boundary, arc flash incident energy, PPE category 1 2 3 4, arc rated clothing requirements

Core Concepts

• Shock Hazard Boundaries: Limited Approach Boundary: unqualified persons may not cross without escort. Restricted Approach Boundary: qualified persons only; same risk as direct contact. Both based on voltage.
• Arc Flash Boundary: The distance at which incident energy equals 1.2 cal/cm² — onset of a second-degree burn. Must be calculated per IEEE 1584 or by PPE category table method.
• PPE Categories (Table Method): Category 1: min 4 cal/cm² AR rating. Category 2: min 8 cal/cm². Category 3: min 25 cal/cm². Category 4: min 40 cal/cm².
• Incident Energy Analysis vs Table Method: Incident energy analysis is more precise; table method is conservative. If analysis has been performed, PPE must match calculated value — the table cannot override it.

Exam Traps

• Arc flash PPE does NOT protect against shock — insulated gloves and tools are still required regardless of arc-rated clothing worn.
• Arc flash boundary and shock boundaries are separate and independent — you can be inside one without being inside the other.
• Leather gloves alone are not arc-rated — arc-rated gloves or leather over rubber insulating gloves are required depending on the task.
• An energized electrical work permit is required when justified energized work is performed — it is not optional.
• Switching and racking operations may require higher PPE than routine measurements on the same equipment — the task determines the hazard.

Memory Aid

SHOCK boundaries = Limited (unqualified stop) and Restricted (qualified only). ARC FLASH boundary = 1.2 cal/cm² burn onset. Separate hazards, separate PPE.