What is the unit used to measure incident energy in arc flash calculations?

• A. Joules per square centimeter
• B. Cal/cm2
• C. Watts per square meter
• D. Volts per meter

Answer: (B)

Inciden energy is the amount of energy from an arc flash that would hit a surface per unit area, which is why it’s expressed as energy per area. In arc-flash calculations and PPE guidelines, this is defined in calories per square centimeter. Using cal/cm^2 lets engineers and safety professionals relate the energy delivery directly to burn injury thresholds used in standards like NFPA 70E and IEEE 1584. For context, 1 cal/cm^2 equals 41,840 J/m^2, so you can convert to SI if needed. The other options measure different physical quantities: Watts per square meter is radiant flux density (irradiance), Volts per meter is electric field strength, and joules per square centimeter would be energy per area but is not the conventional unit used in arc-flash calculations.