Arc Flash PPE Categories, Shock Boundaries & Safety Resources
This page provides general educational reference information only. Always refer to the current editions of NFPA 70E, OSHA regulations, and your site-specific electrical safety program for compliance requirements. Conduct a proper arc flash risk assessment for your specific equipment. When in doubt, consult a qualified electrical safety professional.
Arc-rated (AR) PPE is categorized based on the minimum arc rating required to protect against thermal hazards from an arc flash. The arc rating indicates the level of incident energy (measured in cal/cm²) that the PPE can withstand while still providing protection against second-degree burns. Higher categories require more protection.
Reading panel meters, IR thermography (with doors open, outside restricted boundary), operating normally enclosed energized equipment with covers on.
Working on energized parts (voltage testing), removing/installing CBs or starters, opening hinged covers to expose energized parts, work on control circuits with exposed parts.
CAT 3 typically involves work such as inserting/removing starters from MCC buckets, racking breakers into/out of cubicles. Full arc flash suit system required.
When incident energy calculations exceed 40 cal/cm², NO PPE provides adequate protection. The equipment MUST be de-energized before work can proceed. The pressure wave and blast from such an arc flash can cause severe injury regardless of thermal protection.
| Category | Min Arc Rating | Clothing | Face/Head | Hands | Typical Tasks |
|---|---|---|---|---|---|
| CAT 1 | 4 cal/cm² | AR shirt & pants or coverall | Face shield or hood | Heavy leather gloves | Meter reading, IR thermography |
| CAT 2 | 8 cal/cm² | AR shirt & pants or coverall | Hood or face shield + balaclava | Heavy leather gloves | Voltage testing, CB removal |
| CAT 3 | 25 cal/cm² | Multi-layer AR flash suit | AR flash suit hood | AR gloves or rubber + protectors | MCC bucket work, racking breakers |
| CAT 4 | 40 cal/cm² | Full multi-layer AR flash suit | AR flash suit hood | AR gloves | High-energy switching operations |
Approach boundaries define safe distances from exposed energized electrical conductors and circuit parts. There are two types of hazards with different boundaries: Shock Hazard Boundaries (based on voltage) and the Arc Flash Boundary (based on incident energy). Always use the GREATER of the two distances when setting up barricades.
Based on system voltage - distances to exposed fixed circuit parts
| Voltage (Phase-Phase) | Limited Approach | Restricted Approach |
|---|---|---|
| 50V - 300V | 3 ft 6 in (1.0 m) | Avoid Contact |
| 301V - 750V | 3 ft 6 in (1.0 m) | 1 ft 0 in (0.3 m) |
| 751V - 15kV | 5 ft 0 in (1.5 m) | 2 ft 2 in (0.7 m) |
| 15.1kV - 36kV | 6 ft 0 in (1.8 m) | 2 ft 7 in (0.8 m) |
| 36.1kV - 46kV | 8 ft 0 in (2.4 m) | 2 ft 9 in (0.8 m) |
| 46.1kV - 72.5kV | 8 ft 0 in (2.4 m) | 3 ft 3 in (1.0 m) |
The Arc Flash Boundary (AFB) is the distance from exposed energized parts where incident energy equals 1.2 cal/cm² — the threshold for onset of second-degree burns on unprotected skin.
The AFB is determined by:
Lockout/Tagout (LOTO) procedures are required by OSHA (29 CFR 1910.147 and 1910.333) to protect workers from hazardous energy during service and maintenance. The goal is to establish an Electrically Safe Work Condition.
Identify all energy sources, understand equipment operation, notify affected employees, gather LOTO devices.
Shut down equipment using normal stopping procedures. Never pull disconnects under load unless rated.
Operate all energy isolating devices to disconnect equipment from energy sources (disconnects, valves, etc.).
Apply locks and tags to each energy isolating device. Each authorized employee applies their own lock.
Release, restrain, or dissipate all stored/residual energy (capacitors, springs, elevated parts, pressure, heat).
Verify zero energy state by attempting to operate controls and testing with appropriate meters. Test before you touch!
Per NFPA 70E principles, an electrically safe work condition requires verification that equipment cannot be re-energized:
All sources of electrical supply to equipment
Open disconnecting means for each source
Visually verify all blades open (where possible)
Apply lockout/tagout devices
Release stored electrical energy (capacitors)
Test each conductor with rated meter
Apply grounding devices where required
Always use a properly rated voltage tester to verify absence of voltage. Use the Live-Dead-Live method: verify tester works on known live source, test the circuit, verify tester still works on known live source. Never assume power is off!
Electrical equipment must be field-marked with a label containing information to assist in determining appropriate PPE. Labels result from an arc flash risk assessment or incident energy analysis.
Labels should include information to help workers select appropriate PPE:
Labels are based on system conditions at time of study. Changes to available fault current, protective device settings, or equipment configuration may invalidate the label. Re-evaluate after significant system changes.
Measured in cal/cm² at a specific working distance (typically 18"). This is the amount of thermal energy that would be released during an arc flash. Your PPE's arc rating must meet or exceed this value.
The distance from the arc source used in calculations. Typically 18 inches for low voltage equipment. Incident energy increases significantly as distance decreases — stay back when possible!
Distance where incident energy drops to 1.2 cal/cm². Anyone closer must wear appropriate arc-rated PPE. Set barricades at this distance (or limited approach, whichever is greater).
If using the table method, the category (1-4) tells you the minimum PPE required. If incident energy is provided, select PPE with arc rating ≥ incident energy regardless of category.
Federal regulations for electrical safety in the workplace. Includes 1910 Subpart S (General Industry) and 1926 Subpart K (Construction).
osha.gov/electrical →Control of Hazardous Energy (29 CFR 1910.147). Requirements for LOTO procedures, training, and devices.
osha.gov/control-hazardous-energy →OSHA publication on protecting employees from arc flash hazards. Free PDF download.
OSHA Publication 4472 (PDF) →Standard for Electrical Safety in the Workplace. The primary consensus standard for arc flash and shock protection. (Purchase required)
nfpa.org/70e →Standard for Electrical Equipment Maintenance. Now a standard (not recommended practice). Covers maintenance requirements.
nfpa.org/70b →Guide for Performing Arc Flash Hazard Calculations. The basis for most arc flash studies and incident energy calculations.
standards.ieee.org →Mine Safety and Health Administration electrical safety requirements for mining operations.
msha.gov/electrical →Workplace Electrical Safety (Canadian standard). Harmonized with NFPA 70E for Canadian workplaces.
csagroup.org →National Institute for Occupational Safety and Health. Research and recommendations on electrical hazards.
cdc.gov/niosh →Electrical Safety Foundation International. Non-profit dedicated to electrical safety education and awareness.
esfi.org →DOE-sponsored program for compressed air system efficiency. Free resources and training.
compressedairchallenge.org →Department of Energy industrial best practices for motor systems, compressed air, steam, and process heating.
energy.gov/amo →| Regulation | Title |
|---|---|
| 29 CFR 1910.147 | Control of Hazardous Energy (LOTO) |
| 29 CFR 1910.331-335 | Electrical Safety-Related Work Practices |
| 29 CFR 1910.333 | Selection and Use of Work Practices |
| 29 CFR 1910.269 | Electric Power Generation, Transmission, Distribution |
| 29 CFR 1910.132 | Personal Protective Equipment (General) |
| 29 CFR 1926.405 | Electrical - Wiring Methods (Construction) |
Electrical safety training is required for anyone who faces a risk of electrical hazard:
One who has demonstrated skills and knowledge related to construction and operation of electrical equipment and installations and has received safety training to identify and avoid hazards involved.
One with little or no training in avoiding electrical hazards. May only enter limited approach boundary when escorted by qualified person and wearing appropriate PPE.
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