PPE and Arc-Flash Protection (NFPA 70E)
An arc flash is a violent release of thermal energy from an arcing fault — temperatures can exceed the surface of the sun and cause severe burns. The safety hierarchy: de-energize first; if you must work energized, use the right arc-rated PPE.
1. Arc-rated (AR) clothing
Clothing worn for arc-flash protection must be arc-rated (AR) — never synthetic (polyester/ nylon melts and sticks to skin). The arc rating is measured in calories per square centimeter (cal/cm²) and represents the incident energy giving a 50% probability of a second-degree burn.
2. The arc-flash boundary
The arc-flash boundary is the distance where incident energy reaches 1.2 cal/cm² — the point at which arc-rated PPE becomes mandatory to protect against a second-degree burn.
3. NFPA 70E PPE categories (minimum arc ratings)
| Category | Minimum arc rating |
|---|---|
| 1 | 4 cal/cm² |
| 2 | 8 cal/cm² |
| 3 | 25 cal/cm² |
| 4 | 40 cal/cm² |