What distance was used in the incident energy calculation example?

• A. 12 inches
• B. 18 inches
• C. 24 inches
• D. 36 inches

Answer: (B)

Incident energy from an arc flash is calculated at a defined working distance—the distance from the arc source to the person exposed. The energy value you get depends strongly on this distance, since energy falls off with distance roughly as the inverse of the distance squared. In the example, eighteen inches was used as the working distance. This is a common mid-range standoff that represents a realistic clearance from the arc to the worker’s torso during a task, making the calculated energy meaningful for selecting PPE and understanding potential exposure. Using this distance shows how the energy would look at a typical, practical scenario; if the distance were shorter, the energy would be higher, and if it were longer, the energy would be lower.