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Fundamentals of arc flash mitigation

If you haven't taken the proper steps to mitigate the risks of arc flash, you're compromising worker safety, and you could be breaking the law. Eaton offers solutions in the form of protective gear, trainings, and product components. Use these Eaton resources to reset arc flash safety in your facility. 

What is arc flash?

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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Temperatures of arc blasts can reach 35,000°F (more than three times hotter than the sun) causing severe burns, hearing loss, eye injuries, lung damage, and blast injuries. Maintaining a heightened sense of awareness can help to save lives and protect equipment. 

Want to learn more?

View the new eBook series on Arc Flash Mitigation.

What are the common causes of arc flash incidents?

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. 

Arc flash statistics

What is the cost of an arc flash electrical injury?

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.

Why is proper personal protective equipment (PPE) important?

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.

Why are training and awareness of arc flash safety key for electrical workers?

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.

Estimated number of arc flash explosions in the U.S. per day
5-10
Estimated number of arc flash explosions in the U.S. per day
The distance at which arc flash blasts can kill
10 ft
The distance at which arc flash blasts can kill
Number of people in U.S. admitted for arc flash burns each year
2000
Number of people in U.S. admitted for arc flash burns each year

What is the Hierarchy of Risk Control (HoRC)?

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.

What information is provided on an arc flash label?

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Learn what each piece of information on an arc flash label means so you can be certain you're taking the right steps to enhance safety in your facility. To help you get started, we've provided a sample label with descriptions.

Arc flash label key

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.
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.
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.
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.
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.
Nominal voltage, limited and restricted approach boundaries, and PPE glove rating are also displayed on the label to help protect workers from electric shock.
Eaton’s labels display the arc flash study report number for easy reference and label updates.
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.

Understanding and reducing incident energy in arc flash events

What is incident energy?

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 and calculating incident energy

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.

What are the NEC code requirements for reducing incident energy?

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.

NEC compliance tips

How does NFPA 70B impact arc flash safety? 

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. 

What are arc flash and coordination studies?

What is a coordination study?

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. 

What is included in an arc flash study?

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.

  1. Executive summary

    A synopsis of the key findings and recommendations to improve the safety and operation of the power system

  2. One-line diagram

    A model of the entire electrical system which forms the basis for the study

  3. Short circuit analysis

    Calculates available fault current for each piece of electrical distribution equipment in your facility

  4. Protective device coordination study

    Modeling each protective device and its recommended set points

  5. Settings table

    A list of recommended settings for circuit breakers and relays

  6. 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

  7. Input data used in the analysis

    A reference to the data upon which the study was based

What are the steps to scale an arc flash study?

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.

Focus on the most important things first when scaling an arc flash study. Use these questions to help identify the best place to start.

Assess your operations to identify critical equipment that may be difficult to shut down, that is necessary to run critical processes or that provides power to other equipment that may mitigate another hazard. Prioritizing these critical locations for arc flash analysis may help you avoid costly and unplanned shutdowns in the future.
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Working on energized equipment should be avoided, but there are some instances when it is simply unavoidable. Energized work can cause arc flash incidents to occur and it should be a priority to inform personnel of the associated hazards. There may be overlap between the critical equipment listed above and the equipment listed here, but it’s important to further characterize equipment that must remain energized.
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It’s important to identify which buildings house equipment key to the core function of your business, and then prioritize them in the first phase of an arc flash analysis. For example, a university would likely consider a utility plant to be a more critical load than dormitory lighting.
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Older equipment tends to have a greater potential for hazards due to unresponsive protection which could slip out of tolerance as the years pass. Depending on how often equipment has been maintained, relays and breakers may not respond to a fault as quickly as expected. Understanding when the age of the equipment represents a greater potential for an arc flash incident helps prioritize which part of your system should take precedence in an arc flash study.
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Knowing what resources you have available will assist in the development of a schedule for your buildings. Begin to quantify resources in terms of what may be required for an arc flash study including budget, internal trained resources to support on-site data collection and required PPE to support the data collection effort.
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Electrical and arc flash safety training

A top-notch safety culture incorporates comprehensive training for employees focusing on the specific hazards associated with electrical energy. Per NFPA 70E, Article 110 , employees shall be trained in safety-related work practices and procedural requirements, as necessary, to provide protection from the electrical hazards associated with their respective job or task assignments.​
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Training to enhance arc flash safety

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

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Are you ready to Reset Safety?

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.