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Fundamentals of arc flash mitigation
An arc flash is the energy release that occurs during an electrical fault when current flows through the air between two live conductors, causing a short circuit. In a residential setting, an arc flash usually produces little more than a brief flash of light before extinguishing itself harmlessly.
In a commercial or industrial setting, however, voltages and currents are significantly higher, so electrical faults typically release far more energy. As a result, an arc flash routinely produces a powerful explosion marked by searing heat, toxic fumes, blinding light, deafening noise and massive pressure waves.
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Don’t get caught off guard. Be aware of the scenarios in which an arc flash can occur.
One of the primary reasons for electrical injuries is electric arcing, commonly referred to as arc flash. Arc flash incidents are often related to human error when work is being performed on or around energized electrical equipment. Even when the work involves control equipment and the handling of small, low-voltage electrical components, the risk of arc flash still exists.
An injured worker can spend one day in the hospital for each single percent of body burned. Of the electrical injury admissions, those which had exposure from 1000 volt applications have the longest average length of stay and require the most operations. Costs could range from $10,000 to $15,000,000 USD per arc flash burn injury. In one utility, electrical injuries represented more than 2% of all accidents but 28% - 52% of injury costs.
In one study involving 40 arc flash incidents, approximately half of the workers who applied hazard analysis in selecting personal protective equipment (PPE) suffered burn injuries as a result of not wearing gloves or a face shield with hard hat. Two-thirds of the workers involved in arc flash incidents were injured when they failed to conduct an arc flash analysis for selecting personal protective equipment. More than half of the construction workers in one study were reluctant to wear personal protective equipment even when clearly necessary because they found it to be uncomfortable or did not fit properly.
In a study of more than 500 arc flash incidents, nearly half of the workers failed to recognize the hazard and even when the hazard was recognized, they still decided to engage in the specific task which resulted in the injury. Costly injuries can be prevented with proper training and protective equipment.
The hierarchy of risk controls (HoRC) for arc flash defined in NFPA 70E was transitioned from an informative section to a mandatory component in 2018. It also establishes that the first priority in the implementation of safety-related work practices is to eliminate the hazard. The processes and controls can also be viewed as ranging from immune from human error to those that just provide awareness that a hazard exists.
From an effectiveness perspective, PPE is least effective but provides the most basic protection; whereas elimination provides the highest level of protection as it eliminates the opportunity for an arc flash event. New technology for electrical equipment is available to meet all levels of this matrix.
Need help determining the best mitigation plan for your facility? Eaton can help.
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The owner of the electrical equipment is responsible for providing arc flash warning labels which are required on electrical equipment over 50V that could be accessed while energized. |
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An arc flash boundary is the distance at which the incident energy equals 1.2 cal/cm^2, and arc-rated PPE is required for any employee within the arc flash boundary. |
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The working distance is the distance from a person’s face and chest to the prospective arc source. Typical working distances, primarily based on equipment type, are published in IEEE standard 1584 and used in studies to perform the incident energy calculations. |
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While performing two sets of calculations for the load side and the line side of the main breaker on specific equipment is not specified in NFPA 70E, Eaton has made this a standard practice to enhance productivity and safety for equipment that has adequate isolation of the main protective device. |
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Calculated incident energy is the amount of thermal energy (cal/cm^2) at a distance from an electrical arc event and indicates the level of PPE required to protect workers. |
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Nominal voltage, limited and restricted approach boundaries, and PPE glove rating are also displayed on the label to help protect workers from electric shock. |
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Eaton’s labels display the arc flash study report number for easy reference and label updates. |
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The National Fire Protection Association (NFPA) Standard 70E Article 130.5 states that an arc flash assessment must be updated if a major modification or renovation takes place, and it must be reviewed periodically at intervals not to exceed 5 years. |
Tune in to Eaton's library of informative videos to find out more about resetting arc flash safety in your facility.
Incident energy, measured in calories per square centimeter (cal/cm²), quantifies the potential magnitude of an arc flash. It increases with available fault current and clearing time, making arc energy reduction crucial to minimize severity.
Reduce the incident energy = reduce the severity
Arc flash studies calculate incident energy per IEEE Std 1584-2018, considering factors like working distance, voltage, fault current, and upstream device clearing time. This data determines the required personal protective equipment (PPE) and the arc flash boundary, helping facilities protect employees and mitigate risks.
The National Electrical Code (NEC) Sections 240.67 (fusible equipment) and 240.87 (circuit breaker equipment) mandate methods to reduce arc energy by shortening clearing times. These requirements apply to devices rated 1200 A and above. Compliance involves understanding arcing current levels and their relation to incident energy, then taking steps to reduce risks. High incident energy levels are hazardous, so incorporating reduction methods into equipment design and installation is essential for safety.
Arc energy is directly proportional to clearing time – the longer it takes to clear, the more intense the energy can become and the more devastating the incident energy can be. So, a clearing time of 67 milliseconds (about four cycles in the case of power circuit breakers) can be enough time to allow a significant arc flash event to occur. Learn about the compliant solution that clears in 4 milliseconds or less.
The 2023 edition of NFPA 70B has transitioned from a “recommended practice” to a “standard” and contains mandatory language for the development, implementation and operation of an electrical maintenance program (EMP). It provides a framework to safeguard people, equipment and processes from electrical system failures.
In order to complete an arc flash study, you must first model the entire power system using software such as SKM, CYME, Easypower, or ETAP. A coordination study generally refers to a broad power system study – which includes short circuit analysis, protective device coordination and arc flash incident energy analysis.
These studies are generally required on a new construction project per the project specifications, but are often generalized as a “coordination study” by electrical contractors (and others) tasked with installing new equipment on the project. Simply said, the short circuit analysis is done to ensure each piece of electrical equipment is rated to handle the available fault current at the location.
A protective device coordination study refers to a process that engineers use to ensure adjustable protective devices, such as circuit breakers and relays, are set so that only the affected portion of the system is isolated during a fault condition. Lastly, an arc flash incident energy analysis calculates the incident energy—the effective heat produced in cal/cm2—at each equipment location and is used for arc flash labeling and to determine the proper personal protective equipment (PPE) when working on that equipment while it is energized.
To gauge the quality of a study, first, verify that the study will be performed by experienced engineers. Inquire about their education, licenses and experience.
Then ask about their ability to offer a turnkey solution after the study, including offering training, PPE identification, maintenance program guidance as well as products and solutions to help reduce high incident energy.
And finally, ask to see a sample of the final report and compare against the information below. There are seven components to an arc flash study.
Executive summary
A synopsis of the key findings and recommendations to improve the safety and operation of the power system
One-line diagram
A model of the entire electrical system which forms the basis for the study
Short circuit analysis
Calculates available fault current for each piece of electrical distribution equipment in your facility
Protective device coordination study
Modeling each protective device and its recommended set points
Settings table
A list of recommended settings for circuit breakers and relays
Arc flash incident energy analysis
Used to generate arc flash warning labels showing nominal system voltage and arc flash boundaries, available incident energy, or PPE category
Input data used in the analysis
A reference to the data upon which the study was based
Managing the risks of arc flash safety in a large facilty or campus may seem overwhelming due to the significant scope and resources required. Yet, continually postponing a project of this magnitude can leave the facility and its employees at increased risk for an arc flash incident.
You can get started with an arc flash study now while working within the constraints of your available resources. Not only will you begin to improve arc flash safety for your business, but you will gain the valuable experience you need to plan for arc flash studies across your entire facility or campus.
It is the employer’s responsibility to see that this training occurs and is documented, and it may be conducted in the classroom, on-the-job or a combination of both, determined by the risk to the employee. They must ensure employees are qualified workers and maintain records on which equipment they are qualified to service.
Arc flash is just one training aspect of an electrical safety program. Be sure to train employees on lockout/tagout (LOTO), workspace and barriers, and shock hazard. For expert training, turn to Eaton’s trainers, the same electrical engineers who not only perform arc flash analyses, but also install, commission, troubleshoot and maintain electrical equipment every day.
Best practice is to ensure your trainer has experience with equipment from various manufacturers, is familiar with electrical standards and regulations, has helped companies develop safe work practices and is knowledgeable with up-to-date tools and equipment used in electrical work
Now that you have an understanding of the fundamentals of arc flash, it's time to take the next step to reset safety in your facility with an arc flash study.
