Performing an Arc Flash Risk Assessment: A Step-by-Step Guide

An arc flash risk assessment is a formal process required by NFPA 70E to identify arc flash hazards, estimate the likelihood and severity of injury, and determine protective measures for employees. The primary goal is to ensure worker safety by quantifying the immense thermal energy released during an arc flash event and specifying the appropriate personal protective equipment (PPE). This comprehensive evaluation involves a multi-step engineering study, including a short-circuit analysis and a calculation of the potential thermal energy, known as an incident energy analysis. The results determine the arc flash boundary and dictate the necessary level of arc-rated clothing. For any master electrician or journeyman electrician working on or near energized equipment, understanding this process is a non-negotiable part of a modern electrical safety program and is fundamental to preventing catastrophic injuries.

What is an Arc Flash Risk Assessment?

An arc flash is a dangerous condition associated with the explosive release of energy caused by an electrical fault. Temperatures can exceed 35,000°F, creating a life-threatening hazard for anyone nearby. An arc flash risk assessment is a detailed engineering study that analyzes a facility’s power system to quantify the specific level of this hazard at every point that may require energized work. Governed by NFPA 70E, Standard for Electrical Safety in the Workplace®, this assessment is a cornerstone of modern electrical safety. In fact, up to 80% of all reported electrical injuries are thermal burns caused by an arc flash.

NFPA 70E, Article 130.5 mandates that a risk assessment be performed to identify hazards, estimate the likelihood of injury, and select appropriate protective measures. This marks a shift from the old “hazard analysis” to a more comprehensive “risk assessment” that considers both the severity *and* the probability of an incident. The assessment results in detailed labels for equipment and clear directives for worker safety, including the necessary PPE. While two methods are permitted—the Incident Energy Analysis Method and the Arc Flash PPE Category Method—the incident energy analysis is the far more precise and preferred approach, as it calculates the exact energy (in cal/cm²) a worker could be exposed to.

The 7 Steps of an Arc Flash Risk Assessment

Performing a compliant and accurate arc flash risk assessment is a methodical engineering process. It requires meticulous data and specialized software to model the electrical system and calculate potential hazards. Both a master electrician and a highly trained journeyman electrician should be familiar with these steps, as their work directly intersects with the findings. The advanced skills needed for these calculations are often covered in specialized electrician training and are a key knowledge area for licensure, a topic often discussed in our master electrician exam prep study plan.

1. Data Collection and System Modeling: The first step is to gather extensive data on the electrical distribution system. This involves an on-site survey to document every component, including transformers, switchgear, protective devices, motor control centers, and every breaker panel. Key data points include transformer kVA ratings and impedance, details from every nec code book-compliant installation, conductor sizes and lengths, and protective device types and settings. This information is used to create a detailed one-line diagram in a specialized software program.
2. Short-Circuit Analysis: Once the system is modeled, a short-circuit analysis is performed. This study calculates the maximum fault current that could flow at each point in the system during a fault. This value, expressed in amperes, is a critical input for calculating the arc flash energy, as a higher fault current generally leads to a more powerful arc.
3. Protective Device Coordination Study: A protective device coordination study analyzes how fuses and circuit breakers operate in relation to each other. The goal is to ensure that the device closest to a fault opens first, isolating the problem without causing a wider outage. This study directly impacts the fault clearing time—the time it takes for a device to interrupt the current. A slower clearing time dramatically increases the arc flash incident energy.
4. Calculate Arc Flash Incident Energy: Using the data from the previous steps, the incident energy analysis is performed. This calculation determines the amount of thermal energy (in cal/cm²) that would be delivered to a surface at a specific working distance during an arc flash. The calculation, guided by the IEEE 1584 standard, considers the available fault current, the fault clearing time, and the physical characteristics of the equipment.
5. Determine Arc Flash and Shock Protection Boundaries: The calculations establish several crucial safety boundaries. The most important is the arc flash boundary, which is the distance from the source where the incident energy drops to 1.2 cal/cm²—the level that can cause a second-degree burn. In addition, shock protection boundaries are determined: the limited approach boundary and the restricted approach boundary, which define distances at which a shock hazard exists.
6. Select Personal Protective Equipment (PPE): With the incident energy known, the required personal protective equipment (PPE) can be specified. This includes arc-rated clothing and other gear with a rating equal to or greater than the calculated incident energy. This data-driven approach is a significant improvement over the older, more generic hazard/risk category (HRC) method, which assigned broad categories of PPE.
7. Create and Apply Equipment Labeling: The final step is to create and affix detailed warning labels to the equipment. As outlined in NFPA 70E and the NEC, this equipment labeling must include the nominal system voltage, the arc flash boundary, and at least one of the following: the available incident energy, the PPE category, or the minimum arc rating of clothing required. For a deeper dive into modern labeling standards, you can explore the 2023 NEC arc flash hazard warning requirements.

While this guide covers the essential steps, mastering the nuances of incident energy analysis and protective device coordination requires advanced electrician training. Go beyond the basics with our Advanced Arc Flash Safety course.

Key Considerations for a Compliant Assessment

Beyond the core steps, several principles are essential for an effective electrical safety program that incorporates arc flash safety. These considerations ensure compliance and, more importantly, maximize worker protection.

• Hierarchy of Risk Controls: The most effective safety measure is to eliminate the hazard. This means establishing an electrically safe work condition through robust lockout/tagout (LOTO) procedures whenever possible. PPE is the last line of defense, not the first choice.
• Energized Work Permit: An energized work permit is a formal document required by NFPA 70E for most work performed on live circuits. It justifies why the work must be done energized and outlines the specific safety precautions that will be taken.
• Normal Operating Conditions: Interacting with energized equipment, like opening a panel door, is permitted without PPE only if “Normal Operating Conditions” are met. This includes ensuring the equipment is properly installed, maintained, and used as intended. You can learn more about how to determine normal operating conditions for electrical equipment in our detailed lesson.
• Regular Review: An arc flash risk assessment is not a one-time event. NFPA 70E requires that it be reviewed at least every five years or whenever there is a major modification to the electrical system that could affect the results.
• Qualified Persons: Only qualified persons—those with the skills and knowledge related to the construction and operation of electrical equipment and installations and who have received safety training—should work on or near exposed energized parts.

Arc Fault Breakers vs. Arc Flash Events

It is critical to distinguish between an arc fault circuit breaker (AFCI) and protection against an arc flash event. An arc fault breaker is a device required by the NEC in residential dwelling units to protect against low-level series or parallel arcing that can cause fires (e.g., from a damaged lamp cord). These devices are not designed to mitigate the massive energy release from a high voltage phase-to-ground or phase-to-phase fault, which is the cause of a dangerous arc flash. While both involve “arcing,” the scale and protective strategy are completely different.

Primary Sources

• NFPA 70E®, Standard for Electrical Safety in the Workplace®
• IEEE 1584™, Guide for Performing Arc-Flash Hazard Calculations
• NFPA 70®, National Electrical Code® (NEC®)

Frequently Asked Questions (FAQ)

How often does an arc flash risk assessment need to be performed?

According to NFPA 70E, an arc flash risk assessment must be reviewed at intervals not to exceed five years. It must also be updated sooner if there is a major modification or renovation of the electrical system that could change the results of the initial study.

What is the difference between an arc flash risk assessment and an incident energy analysis?

An incident energy analysis is a component *of* an arc flash risk assessment. The risk assessment is the overall process that identifies hazards and determines protective measures, while the incident energy analysis is the specific engineering calculation that quantifies the thermal energy hazard at a specific point.

Does an arc fault circuit breaker (AFCI) protect against arc flash?

No. An arc fault circuit breaker is designed to detect and interrupt low-level, fire-starting arcs in residential-style wiring. It does not have the capability to mitigate a high-energy arc flash event, which involves thousands of amperes and is typically seen in commercial and industrial settings.

What is the arc flash boundary?

The arc flash boundary is the minimum safe distance from an energized component within which a person could receive a second-degree burn if an arc flash were to occur. It is the distance where the incident energy is calculated to be 1.2 cal/cm². Only qualified personnel wearing appropriate personal protective equipment (PPE) should cross this boundary.