What energy threshold defines the Arc Flash Boundary expressed in cal/cm2 (and its SI equivalent)?

• A. 1.2 cal/cm2 (5 J/cm2)
• B. 2.0 cal/cm2 (10 J/cm2)
• C. 0.5 cal/cm2 (2.5 J/cm2)
• D. 3.0 cal/cm2 (15 J/cm2)

Answer: (A)

The Arc Flash Boundary is the distance from an arc fault at which the incident energy is high enough to cause a potential burn on unprotected skin. The standard value used to define this boundary is 1.2 cal/cm^2, which is about 5 J/cm^2. This threshold is chosen because it corresponds to the energy level at which a second-degree burn can occur with a brief exposure, so it marks the point where PPE and safety measures become necessary. Therefore, the boundary is defined by 1.2 cal/cm^2 (5 J/cm^2). The other options represent different energy levels, not the widely adopted boundary value.