NFPA 70E uses the measurement of ___ in determining the arc flash boundary.

• A. 1.0 cal/cm²
• B. 1.2 cal/cm²
• C. 2.5 cal/cm²
• D. 3.0 cal/cm²

Answer: (B)

Arc flash boundaries are defined by the distance from the arc source at which the incident energy equals a specific threshold. In NFPA 70E, that boundary is set where the incident energy is 1.2 cal/cm^2, because this level corresponds to the energy that can cause a second‑degree burn on bare skin. So, the arc flash boundary is the distance at which E = 1.2 cal/cm^2. This value is used because it provides a practical, safety-based cutoff for requiring arc-rated PPE and protective measures. The other energy values aren’t used to define the boundary, though they may relate to other PPE categories or hazard levels.