Arc Flash Risk Assessment: What It Is and How to Do It

An arc flash risk assessment is the formal process NFPA 70E requires before any worker approaches energized electrical equipment. It is not a label on the side of a panel. It is a documented evaluation that identifies the hazard, estimates how severe an arc flash event could be, and determines what protection a worker needs before the work begins.

Most facilities satisfy this requirement through an engineering study under IEEE 1584. That study produces incident energy values, arc flash boundaries, and PPE requirements for each piece of equipment. Those results get recorded, labeled, and reviewed on a schedule. The assessment is the process. The arc flash analysis is the engineering calculation inside it.

What NFPA 70E requires

NFPA 70E 130.5(A) states that an arc flash risk assessment must be performed for three specific purposes:

All three purposes must be addressed. A label that states a PPE category satisfies purpose three. It does not automatically satisfy purposes one and two unless the underlying assessment documented the hazard and estimated severity. The standard is clear on this. All three steps must happen.

When an arc flash risk assessment is required

The requirement triggers at 50 volts. Any qualified worker who may be exposed to arc flash hazards during work on or near energized electrical equipment needs an assessment in place before the work starts.

This covers more situations than most facilities realize. Visual inspections near open panels. Measuring voltage on energized equipment. Operating a disconnect switch. Racking a circuit breaker. All of these can expose a worker to an arc flash hazard. The assessment tells that worker what PPE to wear and how close they can safely get.

NFPA 70E applies at workplaces where employees interact with energized electrical equipment. It does not cover utility infrastructure or installations under the exclusive control of an electric utility on utility property.

The three required purposes

Identifying arc flash hazards

The first step is identifying where arc flash hazards exist. Not every piece of electrical equipment presents the same risk. A 120V panelboard poses a lower hazard than a 480V motor control center fed by a large transformer. The assessment must document which equipment creates arc flash exposure and under what conditions.

For most facilities, this means surveying all switchgear, MCCs, panelboards, transformers, and the connections between them. Any equipment where a qualified worker might open the door, operate a device, or perform maintenance falls within the scope of the assessment.

Estimating likelihood and severity

The second purpose requires estimating both how likely an arc flash event is and how severe the consequences could be. Severity is quantified as incident energy, measured in calories per centimeter squared (cal/cm²). That number determines whether an arc event would cause a burn and how serious.

The calculation method most facilities use is IEEE 1584, an empirical model that takes system parameters and produces incident energy values. The likelihood component considers factors like the frequency of the task, the condition of the equipment, and the proximity to energized parts.

Determining required protective measures

The third purpose is where PPE requirements get established. But PPE is the last resort, not the first. NFPA 70E aligns with the standard hierarchy of risk controls. The assessment must consider whether the hazard can be eliminated first before specifying what arc-rated gear workers must wear.

Hierarchy of risk controls

NFPA 70E follows the same control hierarchy used across occupational safety. The most effective control eliminates the hazard. PPE is listed last because it does not reduce the hazard itself. It only protects the worker if something goes wrong.

The assessment must document why higher-level controls are not practical before defaulting to PPE. Most facilities cannot eliminate energized work entirely. But they can often apply engineering controls that reduce incident energy levels and lower the PPE requirement over time.

The arc flash boundary

The arc flash boundary is one of the core outputs of an arc flash risk assessment. NFPA 70E 130.5(E)(1) defines it precisely:

At 1.2 cal/cm², a worker without arc-rated PPE could sustain a second-degree burn from an arc flash event. The arc flash boundary marks the distance at which that threshold is reached. Workers inside the boundary must wear arc-rated PPE. Workers outside it can observe without special protection, assuming they are not exposed to other electrical hazards.

The boundary distance varies by equipment. A well-coordinated system with fast-clearing protective devices may have a short boundary. Equipment fed by a large transformer with a slow upstream breaker can have a boundary extending several feet or more.

Two methods for selecting PPE

Once the arc flash boundary is established, the assessment must specify what PPE workers need inside that boundary. NFPA 70E provides two methods for making that determination.

Incident energy analysis method

The incident energy analysis method uses IEEE 1584 engineering calculations to determine the actual incident energy level at a specific piece of equipment. The worker's PPE must have an arc rating equal to or greater than the calculated incident energy. This method is more precise and can justify lower PPE requirements where the system supports it.

This method requires an arc flash analysis performed by a licensed engineer using power system modeling software. The analysis feeds data about fault current levels, clearing times, and working distances into the IEEE 1584 model and produces incident energy values in cal/cm².

PPE category method

The PPE category method uses tables in NFPA 70E to assign PPE based on the type of task being performed. No engineering study is required. The tables specify PPE categories for common tasks at common equipment types.

This approach is faster but conservative. The tables assume worst-case conditions that may not apply to a well-designed, properly coordinated system. For equipment where the actual incident energy is low, the table may require heavier PPE than the hazard actually warrants. Large industrial facilities typically use the incident energy analysis method. The accuracy pays for itself in lower PPE costs and better worker compliance with gear that is right-sized for the actual hazard.

See our arc flash study overview for more on how the engineering analysis is structured.

Data required for the assessment

An arc flash risk assessment based on incident energy analysis requires accurate field data. The quality of the calculations depends directly on what goes into the model.

Required data: a current one-line diagram, available fault current from the utility, transformer kVA ratings and percent impedance, protective device types and settings for every breaker and fuse in the system, cable sizes and lengths, and working distances for each equipment type. This data comes from a field walkdown before any engineering analysis begins.

Getting this data right matters. A wrong impedance value on a transformer changes fault current calculations. A missed breaker setting changes clearing times. Either error shifts the incident energy result and can produce labels that understate the actual hazard.

Download the free arc flash field data collection checklist covering every data point by equipment type, formatted for field use. 70Ez speeds up the data collection process: technicians photograph equipment nameplates in the field, AI reads the data and populates project records, and the result exports directly to your analysis software. See how modern arc flash data collection works.

Equipment labeling requirements

The arc flash risk assessment must produce labels for each piece of equipment covered by the assessment. NFPA 70E 130.5(H)(1) specifies what those labels must show.

Required label information: nominal system voltage, arc flash boundary, and at least one of the following: available incident energy with the corresponding working distance; arc flash PPE category from NFPA 70E tables; minimum arc rating of required PPE; or site-specific PPE level.

Labels that only show a PPE category satisfy the minimum requirement. But they do not give workers the full picture of the hazard level. Facilities that commission a full incident energy analysis can put the actual cal/cm² value on the label. That is more useful information for workers and makes the hazard level visible to anyone who reads the label.

Five-year review requirement

The arc flash risk assessment is not a one-time event. NFPA 70E 130.5(G)(1)(d) states that the incident energy analysis shall be reviewed for accuracy at intervals not to exceed five years. NFPA 70E 130.5(H)(3) states that label data must be reviewed on the same schedule.

The five-year clock resets with each review. But the review can conclude that the existing assessment is still valid. If nothing significant has changed in the electrical system, the engineer documents that and the existing labels remain current.

Any significant system change should trigger an immediate review regardless of where you are in the five-year cycle. Adding a transformer changes available fault current. Replacing a breaker with a different model or settings changes clearing time. Either type of change can shift incident energy values enough to invalidate existing labels. See our arc flash study software guide for information on the platforms used to manage ongoing study data.