1. Two permitted assessment methods

Method A: Table-based simplified method

Use NFPA 70E task/equipment tables (Table 130.7(C)(15) AC / DC task tables):

1. Identify the equipment type, voltage, available fault current, fault clearing time, and task (e.g., remove panel cover, rack breaker).
2. Look up the corresponding arc flash PPE category and arc flash boundary.
3. Select full PPE from Table 130.7(C)(16) for that category.

Limitation: Only valid when system parameters stay within the table’s stated limits. If fault current or clearing time exceeds table bounds, you must use incident energy calculation.

Method B: Incident energy calculation (analytical method, preferred for accuracy)

1. Collect system data: one-line diagram, available short-circuit current, overcurrent protective device (OCPD) time-current curves, working distance for the task, equipment configuration.
2. Run short-circuit and protective-device coordination study.
3. Calculate incident energy (cal/cm²) at the worker’s working distance and calculate the arc flash boundary (distance where incident energy = 1.2 cal/cm²). IEEE 1584 formulas are commonly used for this calculation, referenced by NFPA 70E Annex K.
4. Select arc-rated clothing/PPE whose ATPV or EBT arc rating ≥ calculated incident energy at the working distance.

2. Key outputs required from the assessment

• Whether an arc flash hazard exists for the task.
• Arc Flash Boundary: the approach limit; workers crossing this boundary must use the specified arc-flash PPE.
• Required safe work procedures (energized work permit, qualified persons only, barriers, remote operation where possible).
• The minimum arc rating and full set of PPE for the task.
• Equipment arc flash warning labels: label energized equipment with boundary, incident energy or PPE category, working distance, shock hazard information (required by both NFPA 70E and NEC 110.16).

3. Hierarchy of risk controls (before relying on PPE)

NFPA 70E requires applying controls in this priority order; PPE is the last line of defense:

1. Eliminate hazard: De-energize equipment and apply LOTO (Lockout/Tagout) — the preferred method. Avoid energized work whenever practicable.
2. Substitution / Engineering controls: Use arc-resistant switchgear, remote racking, remote operation, barriers, current-limiting devices, or reduce clearing time to lower incident energy.
3. Administrative controls: Limit work to qualified electrical workers, energized work permits, job briefings, restricted access, training.
4. PPE: Arc-rated clothing and associated protective gear, selected from assessment results.

4. Rules for selecting adequate arc flash PPE

• Clothing must be arc-rated (AR), not just ordinary flame-resistant (FR) clothing. Rating is ATPV or EBT, measured in cal/cm².
• The arc rating must be greater than or equal to the calculated incident energy at the worker’s working distance.
• PPE ensemble includes: arc-rated coverall/shirt + pants, arc-rated hood/face shield, hard hat, safety eyewear, hearing protection, leather gloves over insulating rubber gloves, leather footwear, and additional layers as needed per category.
• PPE categories 1–4 each have defined minimum arc ratings and ensemble requirements (Table 130.7(C)(16)).

5. Mandatory review & reassessment rules

• Reassess when: system changes (new transformers, breakers, cable changes), equipment modifications, new fault data, incidents/near misses, or periodic scheduled review.
• The assessment applies per specific task, not just per piece of equipment; different tasks on the same panel can have different incident energy and PPE requirements.
• Only qualified electrical persons may perform energized work within the arc flash boundary, after completing a job briefing covering arc flash and shock hazards.

6. Shock hazard is separate

Arc flash assessment does not replace electric shock hazard assessment. NFPA 70E also requires evaluating shock boundaries (limited, restricted, prohibited approach boundaries) and shock PPE (insulating gloves, sleeves) for live work.