Flash Protection Boundary
The Flash Protection Boundary is the approach limit from exposed live electrical parts where incident energy equals 1.2 cal/cm² (5 J/cm²), potentially causing a second-degree burn during an arc flash. For fault-clearing times ≤0.1s, the threshold is 1.5 cal/cm². This boundary is calculated using available short-circuit current and protective device interrupting time, with a default 4-foot boundary for systems ≤600V with fault current <50kA and clearing time <6 cycles.
In shop floor maintenance, the Flash Protection Boundary is critical for ensuring worker safety during tasks like examination, adjustment, or servicing of live electrical equipment. Boundaries are logged in asset records within CMMS/ServiceGrid systems to trigger PPE requirements and safety work permits when maintenance occurs within the limit. This prevents technicians from entering without arc-rated PPE, such as FR clothing and face shields, reducing the risk of second-degree burns. Proper application requires arc-flash studies, especially for equipment fed by ≥112.5kVA transformers, to define boundaries and PPE needs accurately.
How is the boundary calculated for >600V systems?
Must use engineering analysis (IEEE 1584) to find the distance where incident energy equals 1.2 cal/cm² (or 5 J/cm²).
What formula determines the boundary for <600V under engineering supervision?
D_c = [2.65 × MVAb_f × t]^0.5 or D_c = [53 × MVA × t]^0.5, where t is clearing time.
When does entry constitute crossing the boundary?
When the face, head, or trunk crosses the linear distance limit.