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Arc Flash Analysis FAQs

Arc Flash Analysis FAQs


What is an Arc Flash ?

Live Arc Flash Explosion Video

An Arc Flash is an electrical explosion due to a fault condition or short circuit when either a phase to ground or phase to phase conductor is connected and current flows through the air.

Arc flashes cause electrical equipment to explode, resulting in an arc-plasma fireball. Temperatures may exceed 35,000° F (the surface of the sun is 9000° F). These high temperatures cause rapid heating of surrounding air and extreme pressures, resulting in an arc blast. The arc flash / blast will likely vaporize all solid copper conductors which will expand up to 67,000 times its original volume when it is vaporized. The arc flash / blast produces fire, intense light, pressure waves and produces flying shrapnel.

When an arc flash happens, it does so without warning and is lightning quick. The result of this violent event is usually destruction of the equipment involved, fire, and severe injury or death to any nearby people.

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what determines the intensity of an arc flash ?

The energy released by the arc is a function of:

  • System voltage
  • Magnitude of the current
  • Duration of the arc


It is important to note that the clearing time (or duration of the arc) can significantly affect the intensity of an arc flash whereby lower amperage systems can become more dangerous than a higher amperage systems.

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i only have low voltages, should i be concerned about arc flash ?

Do not be fooled by low voltage equipment! Most arc flash accidents happen at lower voltages as a fault is created from a technician working on electrical equipment. Low voltage equipment can also have the same arc flash hazard categories as high voltage equipment. It is not uncommon to have an arc flash hazard Category 3 or Category 4 on low voltage systems due to the long clearning time of the protective devices.

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why does an arc flash happen ?

There are a variety of reasons why an Arc Flash can occur, but most of them are human error and preventable. Many arc flashes occur when maintenance workers are manipulating live electrical equipment for testing or repair and accidentally cause a fault or short circuit. Improper tools, improper electrical equipment, corrosion of electrical equipment, improper work techniques and lack of electrical safety training are just some of the events that can lead to a devastating arc flash or arc blast.

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What Type of injuries can happen from an arc flash ?

The degree of injury is directly related to the power of the arc flash, the distance the person is at the time of the arc flash and the protective equipment worn by an individual during an arc flash. Due to the force from the explosion of energy ( the blast ) and the intense heat, burns, concussions, collapsed lungs, hearing loss, shrapnel injuries, and broken bones are the common injuries. Death can and does occur from these injuries, but is mostly associated with blast.

It is estimated that 5 to 10 arc flash and blast explosions occur in electrical equipment every day in the United States with 2,000 people each year being admitted to burn centers for severe burns.

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What is my risk in being exposed to an arc flash ?

The exposure to arc flash depends on the following:

  • Number of times the workers perform a task involving exposed live electrical equipment
  • Complexity of the task performed, need to use force, available space, safety margins, reach, etc.
  • Training, skills, mental and physical agility, coordination with helper
  • Tools used
  • Condition of electrical equipment
  • The available short circuit current and the condition and rating of the overcurrent protective equipment.

 

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what are the costs of an arc flash accident ?

The average cost of medical treatment for survivors of arc flash incidents is $1.5 million.  The total costs have been estimated to be $12 - $15 million, which includes the following:

  • Medical Expenses
  • Lost productivity of worker
  • Equipment / Facility down time
  • Equipment replacement
  • Insurance complications
  • Fines and Fees
  • Litigation


OSHA has fined some facilities over $400K alone for not being compliant with electrical safety regulations, but the bigger cost in this is the 3rd party lawsuits if the employer did not properly identify the hazards and warn the workers about them / provide proper PPE / train the workers. Recently building and business owners have personally been found as negligent in some electrical accidents.

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if i'm wearing the proper ppe, I'm protected from an arc flash , right?

It is important to note that wearing the proper protective equipment is designed to limit burns to second degree burns. Those who experience an arc flash and are wearing the proper equipment can still be seriously injured or even killed from the force of the arc flash blast. An arc blast can knock people off of elevated platforms or blow doors or shrapnel across the room, to which the proper arc flash PPE provides little to no protection.

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How do you determine the correct PPE ?

In order to select the proper PPE (personal protective equipment), incident energy must be known at every point where workers may be required to perform work on electrically energized equipment.  These calculations are determined in an arc flash study and need to be performed by a qualified person such as an electrical engineer.NFPA 70E table 130.7 offers a guide to proper protection and alternative to conducting a complete arc flash study.

All parts of the body that may be exposed to the arc flash need to be covered by the appropriate type and quality of PPE.  Proper PPE can include Flame Resistant clothing, hardhat, hood, face shield, safety glasses, gloves, shoes, etc. depending upon the magnitude of the arc energy.

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how can i prevent an arc flash from happening in the first place?

Unfortunately, there is no way to completely prevent an arc flash happening in electrical distribution systems. The best one can do is to mitigate or reduce the risk.

The Risk Control Hierarchy by NIOSH systematically reduces risk to its lowest practicable level by prioritizing ways to mitigate a given risk. Higher priority and weight are given to methods that seek to control risk by proactive means as close as possible to the root cause. Meanwhile lower priority is placed on reactive methods of controlling damage after an incident has occurred. Specifically, the Risk Control Hierarchy ranks the most effective to least effective ways to reduce risk as follows:

    1. Elimination -- remove the hazard
      1. Only work on energized electrical equipment, when absolutely necessary. De-energizing equipment removes the arc flash hazard, although there is some risk of arc flash and blast when testing to make sure that the equipment is de-energized.
    2. Substitution -- replace higher risks with lower risks. This can be done with two methods:
      1. Arc Flash Study with short circuit study and protective device coordination study can identify how to reduce an arc flash hazard category for some equipment.
      2. Technologies can be implemented to reduce risks. This includes equipment such as arc limiting fuses and remote racking technologies.
    3. Engineering Controls -- reinvent ways to limit/prevent the risk
      1. This can be done by replacing it with equipment that will lower the incident engery, including but not limited to: adjusting breaker settings and redesigning electrical distribution systems. While most of these mitigations require electrical engineering analysis, steps that don'r require engineering can be taken as well, such as implementing electrical covers with ifrared inspection ports.
    4. Awareness -- raise knowledge of risks and consequences thereof
      1. Train all workers on the hazards of arc flash Although this is #4 on the Risk Control Hierarchy, it should be the first thing done and is mandated by OSHA regulations. It is only through training that workers will understand how to eliminate, substitute or otherwise lower the risk.
      2. Conduct an arc flash study to properly identify the hazards, boundaries and required PPE
    5. Administrative Controls -- create regulations, work processes, etc.
      1. Make sure that you have a written electrical safety program AND that it is understood by everyone AND that it is enforced.
      2. Allow only Qualified Persons wearing the proper PPE and using the correct tools to work on or around electrically energized equipment.
      3. Implement a preventive maintenance plan for electrical systems based on NFPA 70B. A proper preventive maintenance program will help identify or fix electrical hazards before they become big problems.
    6. PPE -- use Personal Protective Equipment as last defense.

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What role does preventive maintenance have in reducing the potential for an arc flash ?


Preventive maintenance should be conducted on a routine basis to ensure safe operation. A preventive maintenance program not only helps the equipment work better, but it also identifies potential hazards before they cause an accident.

As part of a preventive maintenance program, electrical equipment should be thoroughly cleaned and routine inspections should be conducted by qualified personnel who understand how to uncover loose connections, overheated terminals, discoloration of nearby insulation, and pitted contacts.  A comprehensive electrical preventive maintenance plan should also include:

  • Using corrosion resistant terminals and insulate exposed metal parts if possible
  • Sealing all open areas of equipment to ensure rodents and birds cannot enter
  • Verifying that all relays and breakers are set and operate properly


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How can system design impact arc flash hazards ?


The incident energy exposure caused by an arc flash can be affected by the system configuration, system fault levels, and exposure time.  System fault levels can be reduced by changing the system configuration to reduce available fault current, and by using current limiting devices such as fuses, breakers, and reactors.  Using faster acting relays and trip devices can reduce arcing time or exposure time.  A protective device coordination study should also be conducted to ensure proper device settings.  Instantaneous relays could also improve clearing times, limiting the arc exposure time.  Fuse ratings and characteristics should also be evaluated to determine if a smaller and/or faster fuse could be used to help reduce the exposure time.

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What is a Qualified Person or an Electrical Qualified Worker ?


OSHA states that only a “Qualified Person” is permitted to work on or near exposed energized parts and that a “Qualified Person” is “one who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.”

Establishing “Qualified Person” status is mandatory for all individuals exposed to the hazards of electrical energy who are employed at US company locations including wholly-owned facilities as well as affiliate and leased facilities where the company has responsibility for facility operations through an operating (or similar) agreement.

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do i really have to do an arc flash analysis to be compliant with osha ?

OSHA mandates that employers identify electrical hazards, warn employees about the hazards and provide them proper protection and training related to the hazards. Compliance with OSHA is mandatory for all US companies.

While OSHA mandates that you warn workers of the arc flash hazards, they do not mandate "how" you must do this, so in theory, each company can implement their own way to identify the hazards and protect their workers form them. In reality, however, there isn't much choice on other ways to properly identify the flash hazards. See NFPA 130.7 Table and Full Arc Flash Protection for other options.

The definitive line in this decision becomes very clear if an accident occurs. If a person is injured or killed and the employer knew there were potential electrical hazards and either chose to do nothing about it or chose not to follow industry standards and best practices, the company is subject to a lawsuit that can exceed $10 million and individual managers can be found negligent.

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What regulations govern arc flash analysis ?

OSHA mandates that employers identify electrical hazards, warn their workers about them and provide the proper protective equipment and training related to working around the hazards. These are the only official regulations. OSHA provides the employer "what" to do, but does not define "how" to do it. The role of NFPA 70E, IEEE and NEC is to provide guidance on "how" to properly implement the OSHA regulations.

The regulations that govern arc flash are:

1.  OSHA Standards 29-CFR, Part 1910. Occupational Safety and Health Standards. 1910 sub part S (electrical) Standard number 1910.333 specifically addresses Standards for Work Practices and references NFPA 70E.  OSHA 29CFR 1910.335 (a) (1)(i) requires the use of protective equipment when working where a potential electrical hazard exists and 29CFR 1910.132(d)(1) which requires the employer assess the workplace for hazards and the need for personal protective equipment.

2.  NFPA 70E provides guidance on implementing appropriate work practices that are required to safeguard workers from injury while working on or near exposed electrical conductors or circuit parts that could become energized. Part II 2-1.3.3 regarding Arc Flash Study / Analysis states that an " Arc Flash Hazard Analysis shall be done before a person approaches any exposed electrical conductor or circuit part that has not been placed in an electrical safe work condition". This Arc Flash Hazard Analysis must be done to determine the level of Personal Protection Equipment PPE that a worker must use, and the Arc Flash Boundary in inches along with the incident energy found at each location. Each electrical panel must be marked with an ANSI z535 approved Arc Flash Warning Label.

3.  The National Fire Protection Association (NFPA) Standard 70 - “The National Electrical Code” (NEC) contains requirements for warning labels, including ANSI compliance.

4.  The Institute of Electronics and Electrical Engineers ( IEEE ) 1584 – Provides the Guide to Performing Arc Flash Hazard Study Calculations.

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what does osha look for in arc flash compliance ?

Compliance with OSHA involves adherence to a six-point plan:

A facility must provide, and be able to demonstrate, a safety program with defined responsibilities.

    1. Calculations for the degree of arc flash hazard.
    2. Correct personal protective equipment (PPE) for workers
    3. Electrical Safety Training for workers on the hazards of arc flash.
    4. Appropriate tools for safe working.
    5. Warning labels on equipment. Note that the labels are provided by the equipment owners, not the manufacturers.
    6. Companies will be cited and fined for not complying with these standards.

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What is an electrically safe work condition ?


An electrically safe work condition is defined as a state in which the conductor or circuit part to be worked on or near has been disconnected from energized parts, locked / tagged out in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.

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what is nfpa and nfpa 70e ?


The National Fire Protection Association is a non-profit organization and is the world's leading advocate of fire prevention and an authoritative source on public safety, NFPA develops, publishes, and disseminates more than 300 consensus codes and standards intended to minimize the possibility and effects of fire and other risks.

NFPA 70E is a comprehensive standard that establishes best electrical safety practices standards on how to protect electricians from electric arc flash and arc blast exposure and resulting potential injury and death. OSHA has referenced this electrical safety standard in numerous cases. Many organizations have now designed an NFPA 70E Compliance Guide to help protect their electrical personnel from the hazards associated with arc flash.

OSHA adopted regulations on safe electrical work practices in 1990 based on NFPA 70E, and is proposing a revised standard that conforms to the most recent editions of NFPA 70E. Given that the NEC (National Electrical Code) and OSHA have both started referring to it in their documents, citations are now being written based on NFPA 70E.

NFPA 70e applies to employees who work on or near exposed energized electrical conductors or circuit parts. This includes electrical maintenance personnel, operators, troubleshooters, electricians, linemen, engineers, supervisors, site safety personnel or anyone exposed to energized equipment of 50 volts or more.

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what is an arc flash hazard study or analysis ?


An Arc Flash Study or Analysis is a calculation performed by Professional Engineer to determine the incident energy found at each location which determines the various arc flash boundaries and what personal protective equipment (PPE) must be used in approaching each boundary. 

As part of the study, the engineer should also provide recommendations to reduce the incident engery / arc flash hazard category, which requires a short circuit study and a protective device coordination study.

An Arc Flash Study / Analysis should only be performed by experienced and qualified electrical engineers knowledgeable in power system engineering, IEEE 1584, NFPA 70E and arc flash studies.

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can we do a study / analysis ourselves ?


Yes, you may conduct your own arc flash study, however, there are many issues to consider.

Conducting an arc flash study / analysis is a complex process and requires engineers familiar with conducting power analysis studies and arc flash analysis in particular. Properly collecting all the data is the first phase of the project, which is difficult for anyone to do if they are not first familiar with all the potential outcomes and pitfalls of conducting an arc flash analysis. The engineer that conducts the study needs to proficient in conducting short circuit studies, protective device coordination studies and have a strong understanding of NFPA 70E and IEEE 1584.

Beyond technical qualifications, in-house assessments are something that plant managers or engineers have little time for, often resulting in the project not getting completed or conditions of the electrical equipment changing before completion, making the results void.

The biggest reason not to do the study internally is the cost of getting it wrong. If someone is injured or killed due to an arc flash and the analysis was incorrect and done by someone who is not considered qualifed to conduct the study, the liability will rest with the person or group that performed the study.

For some larger organizations that have multiple and large facilities and are willing to invest in developing a team to perform the analysis and are comfortable with the liability, conducting the studies internally can help save money. For all other organizations, conducting an arc flash analysis internally typically has little or no upside compared to any cost savings.

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Can't we just use NFPA Table 130.7 (C) (9)


NFPA Table 130.7 (C) (9) identifies arc flash hazard risk categories based on tasks being performed and the equipment which its being performed on. On the surface, this table appears to be an easy and low-cost solution, however, it has many conditions and potential problems.

Using the NFPA Table 130.7 is acceptable if you know your short circuit current and fault clearing time AND these results fall within the parameters of using the table. If you do not know your short circuit current and fault clearing time of each piece of the equipment or the short circuit current or clearing times exceed the parameters of using the table, then the table can not be used and an arc flash study / analysis must be conducted.

The problem here is that very few facilities have up-to-date electrical one-line drawings, let alone any knowledge as to what their short circuit current or fault clearing times are.  In order to determine the short circuit current and the fault clearing times, an electrical engineering analysis must be completed, which is comprised primarily of the same work process and costs in doing an arc flash analysis, so unless this information is already known and accurate, an engineering analysis will need to be done anyways. Even once the engineering study is completed, most  facilities and plants will find that they have equipment that falls outside of the table, which will require them to do a full arc flash analysis anyways.

Independent of having the right information to use the charts, the recommendations of the table have some gaps and are, in general, widely contested. In particular, the table has the following deficiencies:

    1. The NFPA 70E Table does not address or have any ratings for the highest arc flash hazard category; Greater than Category 4.
    2. The NFPA 70E Table does not address all tasks. If the task one is performing is not listed on the table, the table can not be used.
    3. Actual engineering studies have found that the NFPA 70E table can suggest using far more protective equipment than is actually necessary. Working in Cat 3 or Cat 4 PPE can be hot, difficult and result in loss of dexterity and vision. If the work does not require this for safety purposes, the worker should not be exposed to this. Further, those experienced in working on electrical equipment may realize that the table recommendations are over-protective and therefore, the table gets devalued or ignored because of lack of accuracy.
    4. Labeling: Labels are still required to warn workers of the hazards and must included specific information. Using the table alone does not satisfy the label requirements. Further, providing just the information from the charts requires a worker to read and self-determine the hazard category, adding room for error.
    5. No ability to mitigate hazards. Without doing an arc flash study, there is no ability to identify and mitigate the hazards down to a lower level.

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can i use the NFPA 130.7 table as a guide until my arc flash is completed ?


According to OSHA experts, using the NFPA 70E Table as guide when an arc flash analysis has not yet been completed or when your short circuit current and fault clearing time is known is significantly better than doing nothing at all, but is not a substitute for doing an arc flash study and is only a short-term solution.

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can't i just have all my employees dress in category 4 PPE when working on energized equipment ?


More protection is not always better and this solution does not address the six points OSHA will consider.

Working in Cat 3 or Cat 4 PPE can be hot, difficult and result in loss of dexterity and vision. Some workers argue that while working in Cat 4 PPE provides them more protection in the event of an accident, they are more likely to make a mistake and cause and accident when wearing Cat 4 PPE. If the work does not require this for safety purposes, the worker should not be exposed to this.

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arc flash boundary

what is incident energy and incident energy exposure ?


This is the amount of thermal incident energy to which the worker's face and chest could be exposed at working distance during an electrical arc event. Incident energy is measured in joules per centimeter squared (J/cm2) or calories per centimeter squared (cal/cm2).

Holding your hand over the hottest part of the lighter flame for one second is equivalent to one calorie.

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arc flash boundary

what is an arc flash boundary ?


NFPA 70e defines a “flash protection boundary within which a person could receive a second-degree burn if an electrical arc flash were to occur". It also defines incident energy as “the amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.”  NFPA 70e requires the calculation and creation of a “flash protection boundary”. This imaginary boundary, which surrounds the potential arc point, specifies what level of personal protective clothing and equipment must be used by qualified workers who enter within that boundary.

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what is a short circuit study and must this be performed in conjuction with an arc flash ?


The short-circuit study is based on a review of one-line drawings by a professional engineer.  Maximum available fault current is calculated at each significant point in system. Each interrupting protective device is then analyzed to determine whether it is appropriately designed and sized to interrupt the circuit in the event of a bolted type of short circuit. Next, the associated equipment must be reviewed to insure that the bus bar is adequately braced to handle the available fault current. Finally, the bolted fault currents are converted into arc fault currents for additional analysis.

A short circuit study is not required to complete an arc flash study, however, short circuit information is required in order to analize an electrical distribution system to determine if changes can be made to mitigate arc flash hazards. A minor change in an adjustable breaker may make the difference in the result of an arc flash hazard category "4" or a "2". The availability of the short circuit information is a standard output of an arc flash study calculation, however, there is a big difference between having the information available and doing a report. Arc flash mitigations can be completed with short circuit information, but with out doing a study. A study is value added information to help a plant run more efficiently.

Most companies that complete an arc flash study / analysis also choose to get the short circuit study as well in order to take adavantage of the information at a reduced cost compared to doing just an short circuit study. Future standards for conducting an arc flash will most likely include a short circuit study in order to help standardize the expected results of an arc flash program.

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what is a protective device coordination study / analysis and must this be performed in conjuntion with an arc flash study ?


A coordination analysis is the examination of the electrical system and available documentation with the goal of ensuring that over-current protection devices are properly designed and coordinated. Over-current protective devices are rated, selected and adjusted so only the fault current carrying device nearest the fault opens to isolate a faulted circuit from the system. This permits the rest of the system to remain in operation, providing maximum service continuity. The study consists of time-current coordination curves that illustrate coordination among the devices shown on the one-line diagram. Note that protective devices are set or adjusted so that pickup currents and operating times are short but sufficient to override system transient overloads such as inrush currents experienced when energizing transformers or starting motors.

A protective device coordination study is not required as part of an arc flash study, however, doing this analysis one can determine if minor revisions in breaker settings or equipment can lead to major reductions of arc flash hazards.  No arc flash analysis should be completed without first doing a protective device coordination analysis in order to save money and to remove potential hazards.

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What are arc flash hazard categories ?

The hazard / risk category is specified as a number representing the level of danger, which depends upon the incident energy.  The category ratings range from 0 to 4 where category 0 represents little or no risk, and category 4 signifies the greatest risk.  Above category 4 (>40 calories/cm2) all equipment is considered too dangerous to work on energized because of the tremendous pressure blast.

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what is an arc flash label ?

The NEC® and NFPA 70E require labeling of equipment to warn of potential arc flash hazards. Each panel must be marked with an ANSI approved Arc Flash Warning Label to warn and instruct workers of the arc flash hazard, voltage, arc flash boundary and required PPE (Personal Protective Equipment). Subject to the requirements of the facility and arc flash analysis, labels are attached for each analyzed point of concern.

arc flash hazard label

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Where can I find more information about arc flash regulations and codes ?

Martin Technical free electrical safety resources and information page provide additional information on electrical safety and codes.

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Where can I find more information about arc flash & electrcial accidents ?

Electrical Accidents Blog containing information on electrical accidents.

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