Arc flash is one of the most dangerous electrical hazards on any job site. NFPA 70E defines the boundaries, PPE categories, and work permit requirements that protect workers from arc flash incidents.

What is Arc Flash?

• A violent release of energy from an electric arc — temperatures can exceed 35,000°F
• Produces intense UV/IR light, a pressure wave, sound blast, molten metal, and toxic vapor
• Can ignite clothing, cause severe burns, hearing loss, and blast injuries
• A leading cause of electrical fatalities and serious injuries in the workplace

NFPA 70E Approach Boundaries

• Arc Flash Boundary — distance where incident energy = 1.2 cal/cm² (onset of 2nd-degree burn on bare skin). Arc flash PPE required inside this line.
• Restricted Approach Boundary — only qualified persons; risk of shock same as direct contact with energized parts
• Limited Approach Boundary — unqualified workers may not cross without a qualified escort

PPE Categories (NFPA 70E Table 130.5(G))

• Category 1 — minimum 4 cal/cm²: arc-rated shirt and pants, safety glasses, face shield
• Category 2 — minimum 8 cal/cm²: add arc-rated balaclava under face shield
• Category 3 — minimum 25 cal/cm²: arc flash suit jacket and bib overalls
• Category 4 — minimum 40 cal/cm²: full arc flash suit with arc-rated hood

Energized Electrical Work Permit

• Required before any work within the arc flash boundary (NFPA 70E 130.2(B))
• Documents why equipment cannot be de-energized, the PPE selected, and the personnel involved
• Must be signed by an authorizing manager — not just the worker performing the task
• De-energizing is always preferred whenever feasible; energized work requires written justification

Key References

• NFPA 70E — Standard for Electrical Safety in the Workplace
• NFPA 70E Table 130.5(G) — Arc flash PPE categories
• OSHA 1910.333 — Selection and use of work practices