Arc flash is the sudden release of electrical energy through the air when a high-voltage gap exists between two conductors. The resulting explosion generates temperatures up to 35,000°F — roughly four times the surface of the sun — along with a pressure wave, intense light, and shrapnel. NFPA estimates 5 to 10 arc flash incidents occur every day in the United States. Workers exposed to energized electrical equipment across oil and gas, utilities, solar, wind power, paper and pulp, food processing, and industrial maintenance are all at risk.
The four hazardous elements of an arc flash event are intense thermal energy, a pressure wave (the arc blast), acoustic energy, and radiant light. The blast itself lasts less than a second, but ignites clothing and causes third-degree burns at distances measured in feet from the arc source. Most serious arc flash injuries come from clothing catching fire, not from direct contact with the arc — which is why arc-rated (AR) PPE is the last line of defense when energized work cannot be avoided.
The NFPA 70E-2024 Standard
NFPA 70E, Standard for Electrical Safety in the Workplace, is the authoritative reference for arc flash risk assessment and PPE selection. The current edition is NFPA 70E-2024, published April 2023. The standard requires employers to perform an arc flash risk assessment before any work on or near energized equipment operating at 50 volts or more, and to select PPE with an arc rating (in cal/cm²) at or above the calculated incident energy at the working distance.
NFPA 70E offers two methods for PPE selection: the incident energy analysis method (a detailed engineering calculation) and the PPE category method (a table-based approach for equipment that meets specific labeled parameters). The PPE category method defines four categories, each with a minimum arc rating and a required PPE ensemble. Where incident energy exceeds 40 cal/cm², NFPA 70E does not permit energized work — the equipment must be de-energized.
NFPA 70E PPE Categories
Under the PPE category method in NFPA 70E-2024 Table 130.7(C)(15)(c):
- Category 1 — minimum arc rating 4 cal/cm²: AR shirt and pants (or coverall), AR face shield or arc flash suit hood, hard hat, safety glasses, hearing protection, heavy-duty leather gloves, leather footwear.
- Category 2 — minimum arc rating 8 cal/cm²: AR shirt and pants (or coverall), AR flash suit hood or AR face shield plus AR balaclava, hard hat, safety glasses, hearing protection, heavy-duty leather gloves, leather footwear.
- Category 3 — minimum arc rating 25 cal/cm²: AR shirt, AR pants, AR coverall, AR flash suit jacket and pants, AR flash suit hood, AR or rubber insulating gloves with leather protectors, hard hat, safety glasses, hearing protection, leather footwear.
- Category 4 — minimum arc rating 40 cal/cm²: Same ensemble as Category 3, but the system arc rating must meet or exceed 40 cal/cm². A full multi-layer arc flash suit is required.
All arc-rated garments are flame-resistant, but not all flame-resistant (FR) garments are arc-rated. When layering AR clothing, the combined system arc rating must be verified — you cannot simply add the arc ratings of individual layers. Meltable synthetic fabrics (polyester, nylon, acetate, rayon) are prohibited as outer layers or under FR clothing, since they can melt into the skin during an arc event.
OSHA Requirements for Arc Flash PPE
Under OSHA 29 CFR 1910.269(l)(8), employers in electric power generation, transmission, and distribution must assess for flame and electric-arc hazards, estimate available incident heat energy in cal/cm², and ensure workers wear arc-rated PPE with an arc rating at or above the estimated heat energy. For general industry, OSHA 29 CFR 1910.335(a)(1)(ii) requires PPE appropriate for the electrical hazard, and OSHA 29 CFR 1910.132(h) requires the employer to provide the PPE at no cost to the employee. Training on proper donning, doffing, and inspection is required before the PPE is used.
Choosing PPE That Fits and Gets Worn
The best arc rating in the catalog is useless if it sits in the locker. Fit, weight, breathability, and ease of movement all affect whether the crew actually wears the gear every shift — especially in hot weather or long confined-space entries. Consider fit and wearability alongside arc rating when specifying PPE for a program: a Category 2 ensemble a worker actually wears every day protects better than a Category 4 suit that gets set aside for comfort.
PK Safety carries arc-rated kits, coveralls, hoods, and accessories across all four NFPA 70E categories, plus arc-flash-rated fall protection (harnesses and lanyards) for elevated electrical work. Browse the full lineup at our Arc Flash Kits collection and Arc Flash Coveralls collection. For example, the Enespro 40 Cal ArcGuard Performance Arc Flash Kit with Fan Hood is a Category 4 ensemble built on GORE PYRAD fabric, made in the USA, with a 41 cal/cm² arc rating.
Not sure which category your work requires? Call PK Safety at 800.829.9580 — our team can walk you through the risk assessment and match the right ensemble to your incident energy analysis.
Frequently Asked Questions
What is the difference between arc flash and arc blast?
Arc flash refers to the intense thermal energy and light released when electrical current jumps a gap in the air, generating temperatures up to 35,000°F. Arc blast is the pressure wave produced by the same event, caused by the rapid expansion of superheated air and vaporized conductor material. Both hazards occur together during an arc fault. Arc flash is the primary burn hazard; arc blast can cause blunt trauma, hearing damage, and can propel workers or debris.
What does cal/cm² mean and how do I know what arc rating my PPE needs?
Calories per square centimeter (cal/cm²) is a measure of incident thermal energy — how much heat energy strikes a surface at a defined working distance during an arc event. It is the standard unit for both arc flash hazard assessment and PPE arc ratings. Your PPE arc rating must equal or exceed the incident energy calculated for the task at your working distance. Under NFPA 70E-2024 you determine the required arc rating one of two ways: an incident energy analysis (engineering calculation, often on the equipment's arc flash label), or the PPE category method (Table 130.7(C)(15)(c) matching equipment type to a category). Where incident energy exceeds 40 cal/cm², energized work is prohibited and the equipment must be de-energized.
What are the four NFPA 70E PPE categories?
NFPA 70E-2024 defines four PPE categories by minimum arc rating: Category 1 (4 cal/cm²), Category 2 (8 cal/cm²), Category 3 (25 cal/cm²), and Category 4 (40 cal/cm²). Each category specifies a required ensemble of arc-rated shirt and pants or coverall, arc-rated face and head protection (face shield with balaclava at Category 2, arc flash hood at Categories 3 and 4), hard hat, safety glasses, hearing protection, gloves, and leather footwear. The former Category 0 (natural-fiber non-arc-rated clothing) was eliminated in the 2015 edition and does not exist in current NFPA 70E.
What is an arc flash risk assessment and when is it required?
An arc flash risk assessment identifies arc flash hazards, estimates the likelihood and severity of an incident, and determines the appropriate protective measures. NFPA 70E-2024 requires an arc flash risk assessment before any work on or near energized equipment operating at 50 volts or more, and any time equipment is modified, replaced, or the electrical distribution system changes. The assessment produces an arc flash label showing incident energy at the working distance, required PPE, and the arc flash boundary. Assessments must be reviewed at least every five years.
Is flame-resistant (FR) clothing the same as arc-rated (AR) clothing?
All arc-rated clothing is flame-resistant, but not all flame-resistant clothing is arc-rated. FR clothing self-extinguishes when the ignition source is removed and resists melting. AR clothing is FR clothing that has additionally been tested and rated for arc thermal performance, with a specified arc rating in cal/cm² per ASTM F1959 (arc thermal performance value, ATPV) or ASTM F2178 (energy of breakopen threshold). For arc flash protection, always specify AR clothing with a rating that meets or exceeds your incident energy — plain FR clothing without an arc rating does not qualify.
What is the arc flash boundary and who must wear PPE inside it?
The arc flash boundary is the distance from a potential arc source at which the incident energy equals 1.2 cal/cm² — the level at which a person wearing standard non-arc-rated clothing would receive a second-degree burn. NFPA 70E-2024 requires anyone crossing the arc flash boundary during energized work to wear arc-rated PPE with an arc rating at or above the incident energy calculated at their working distance. The boundary distance appears on the equipment's arc flash label and depends on the available fault current, clearing time, and equipment geometry.
Related resources:
- Differences Between FR and Arc Flash Clothing
- How to Read an Arc Flash Label
- When to Wash, Repair, or Replace Your Arc Flash & FR PPE
For guidance on selecting arc flash PPE for your workplace, contact PK Safety at 800.829.9580 or visit our Arc Flash Kits collection.