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Determining Arc Flash and Shock Boundaries

Energized work equipment can be very hazardous for workers. Each year, hundreds of workers are injured or even killed as a result of accidents taking place around energized equipment. Many of these injuries and deaths follow an arc flash incident.

An arc flash is a violent type of electrical explosion, the result of an electrical current passing through the air instead of its intended path. These arc flash explosions can produce temperatures over 35,000 degrees Fahrenheit, or 19,400 degrees Celsius. Such massive amounts of energy and high temperatures can instantly vaporize, melt or burn many materials, including the surrounding equipment and workers, and produce a pressure wave that can send everything flying. Extreme burns, collapsed lungs, broken bones and ruptured eardrums are a few of the injuries workers can sustain while standing up to twenty feet from the source of the blast.

In response to the dangers associated with arc flash accidents, among other electrical hazards, the National Fire Protection Association (NFPA) developed a series of rules for companies to follow, designed to protect workers as much as possible as they work around energized equipment. Included in these rules is the implementation of approach boundaries, which limit the movement of workers so that only the most qualified and protected individuals work near the most hazardous equipment. Understanding what these NFPA boundaries are and what they mean is essential to maintaining a safe working environment.

What Is a NFPA 70E Safe Work Condition?

The NFPA 70E, also known as the Standard for Electrical Safety in the Workplace, is a regulation introduced by the National Fire Protection Association that guides workers on how to safely work around energized equipment. Though not enforced at any legal level, the NFPA 70E is often required by many businesses and their customers as way to keep workers as safe as possible while working around potentially hazardous equipment. It also works to minimize accidents, which protects both workers and equipment from harm.

The NFPA 70E is a regulation that guides workers on how to safely work around energized equipment.

The NFPA 70E describes the best ways to protect electrical workers from electrical hazards, including electrocution, arc flash and arc blast. The detailed approach describes the following:

  • Turning Off Power: When possible, equipment should be de-energized during work. At industrial plants, this is usually impossible to maintain. If the equipment has to be live during the workday, controls should be set in place to reduce the level of the hazard.
  • Developing a Plan: The company must have a written plan for the work to be done, detailing the reasons why the work has to be done live, as well as how the work will be handled safely. It should outline the requirements for qualified and unqualified workers, the requirements for safety training, and the safety procedures to follow in the event of an electrical emergency. A detailed plan is usually a requirement for work teams before they can receive a permit to proceed with their work.
  • Using PPE: Personal protective equipment, or PPE, is the last line of defense a worker has against an electrical hazard. This includes insulated tools, flame resistant clothing, face shields and flash suits, among other equipment. PPE is rated on an HRC scale, which stands for Hazard/Risk Category. There are five HRC ratings: 0, 1, 2, 3 and 4. As the rating increases, so does the level of protection provided by the PPE. Typically, an appropriate PPE HRC rating depends on the task an employee is expected to perform, and which area they are to perform it in.
  • Setting Boundaries: One of the more complex steps of the NFPA 70E requirements is setting approach boundaries for personnel working around the energized equipment. Such boundaries limit the movement of personnel so they only work in areas where they are properly equipped, both preventing personnel from causing accidents and protecting them appropriately in the event of an arc flash or electrical hazard.

Setting boundaries is one of the most important safety measures for workers in their daily routines. The boundaries themselves tend to be complex to set up, but they are some of the most important safety measures to observe.

What Are Shock Flash Boundaries?

Shock flash or arc flash boundaries are set distances measured from a piece of hazardous equipment. Only certain people can work within each boundary, provided they meet a particular set of requirements. Shock flash boundaries include the following:

  • Flash Protection Boundary: Also called the outer boundary, the flash boundary is the farthest boundary from the energized equipment. Typically, this boundary is the point at which an employee exposed to an arc flash would sustain a second-degree burn level of exposure. For example, the default flash protection boundary for a 600-volt system is set at 48 inches. Beyond this point, workers should wear PPE to protect against any potential arc flashes or blasts.
  • Limited Boundary: A limited boundary is the distance from the energized equipment at which an employee is exposed to some amount of shock hazard. Unqualified employees cannot approach any closer than this without being escorted by a qualified person. The area within the limited boundary is referred to as the limited space, and within this space, personnel must wear appropriate PPE.
  • Restricted Boundary: A restricted boundary is the distance from the energized equipment at which an employee is exposed to an even higher risk of shock. The space within this boundary is called the restricted space. Only qualified individuals are allowed to work within this area, and they must have completed appropriate training, wear appropriate PPE and have completed an approved written plan describing the work they will perform within the restricted space. Individuals working within this space must be prepared to keep all parts of their body out of the prohibited space, and have a plan to do so.
  • Prohibited Boundary: Also called the inner boundary, this is the distance from a piece of energized equipment at which standing near the equipment is considered no different from contacting the equipment directly. People within this prohibited space must be qualified and wear proper protective gear. In order to work in this space, qualified personnel must complete very specific training, submit and receive approval on a proposal for their work, and obtain a risk assessment. If completed, all of these measures can help prevent and prepare for unexpected accidents.

The boundaries vary based on the energized equipment in question — one piece of equipment will have a larger flash protection boundary than another, based largely on the nature of the equipment itself and the voltage it handles. Fixed systems handling around 50 volts have limited approach boundaries of about 3.5 feet. The same type of system handling 800 kV or more has a limited approach boundary set at 23 feet. Boundaries are set wider for systems where the conductor is not fixed in place. The reason boundaries increase with voltage is that the higher the voltage, the more incident energy a flash could produce.

Fixed systems handling around 50 volts have limited approach boundaries of about 3.5 feet.

Incident energy is the radiant energy released by an electric arc. Most companies have conductors with the potential to produce 2.1 cal/cm2 of incident energy, which would require a smaller set of boundaries around the equipment since second degree burns occur at 1.2 cal/cm2. However, a few potential arc flash sources can release up to 205 cal/ cm2 in incident energy. Third degree burns occur at 8 cal/cm2, and HRC 4 personal protective equipment only protects people from incident energy up to 40 cal/cm2. Equipment releasing that much incident energy would have much larger boundaries.

What Determines a Qualified vs. an Unqualified Person?

There is a distinction made between a qualified and an unqualified individual. Unqualified individuals cannot pass any further than the restricted boundary and can only pass the limited boundary if they are accompanied by a qualified individual. Qualified individuals can cross any boundary, provided they are properly equipped with the appropriate PPE and tools for the job.

What makes a person qualified as opposed to unqualified? The differences between the two are as follows:

  • Qualified Worker: OSHA defines a qualified worker or person as someone who has received training and demonstrated skills and knowledge in the electric equipment in question. Some people might be qualified for some equipment, and unqualified for others. Additionally, people undergoing on-the-job training for a certain piece of equipment may be considered provisionally qualified, as long as they are accompanied by a fully qualified individual. This distinction is important to know when considering flash boundaries, as only expressly qualified personnel are allowed to pass certain boundaries.
  • Unqualified Worker: A person with limited electrical knowledge and little or no electrical training is typically considered an unqualified worker. These individuals lack the training needed to avoid the electrical hazards of an exposed energized part, and therefore stand at a higher risk of sustaining an injury. In certain cases, unqualified workers may need to cross the limited approach boundary, but they must always be accompanied by a qualified person while doing so. This qualified person is responsible for advising the unqualified person of the possible hazards in the area and preventing them from sustaining injuries. Unqualified individuals can’t cross the restricted approach boundary even if they are escorted — the danger is too great for an unqualified person.

The most important skills necessary for a qualified worker within the limited approach boundary include the ability to distinguish potential hazards, approximate their danger and recognize appropriate approach distances for potential hazard sources. It’s also important that qualified individuals demonstrate an ability to use special precautionary techniques, PPE and appropriate tools. Such skills are imperative to making sure that accidents are kept to a minimum within the limited space.

With proper training, workers can observe boundaries more safely & completely.

Many companies will require workers both qualified and unqualified to undergo training to help them recognize the unique responsibilities and dangers associated with each of their designations. With such training, workers can observe boundaries more safely and completely.

How Do You Determine an Arc Flash Boundary?

There are several methods available to determine the appropriate set of boundaries for a piece of hazardous electrical equipment. The most popular of these methods include

  • NFPA Tables: NFPA 70E provides several tables, which determine proper boundary lines based on current and flash time. Since this method uses tables instead of precise measurements and calculations, it is very easy but generally inaccurate.
  • Formula Method: Both NFPA 70 E and IEEE Standard 1584 provide formulas for calculating appropriate boundaries for a piece of equipment, but are used in different situations. The NFPA 70 E equation for an “arc in a box” or “contained arc” event is the most commonly used equation since it most accurately accounts for an arc flash’s behavior within a fuse box or switchgear. The only problem is that it’s only useable for certain conditions within a narrow range of currents. The IEEE 1584 set of equations models a broader range of currents, though it is less accurate. The problem with the formula method is that it takes significantly longer than other methods and takes an engineer’s expertise to handle appropriately. It also leaves more room for error.
  • Automated Calculator: The IEEE has a spreadsheet that can be used as a calculator, which helps assist arc flash assessment teams in determining appropriate approach boundaries. The spreadsheet is easy to use and requires detailed information about the equipment in question, as well as the circuit to which it is connected. All of this information usually requires an electrical engineer to get an accurate reading.
  • Software: There are several software products available on the market today, any of which can help to simplify approach boundary calculations, making them faster and easier to determine. This software is usually also able to create warning labels and diagrams as required by NFPA 70E.

In addition to setting boundaries, the calculation methods can also help determine the proper PPE HRC rating at each boundary.

Learn More About Arc Flash Events and Boundaries

Arc flashes and other electrical hazards are not minor incidents. The immense danger associated with electrical hazards place people in mortal danger on a daily basis, which is why understanding them and how to prevent them is so important.

Technical Skills Development provides a wealth of free resources on the topic of arc flashes, including everything from equipment guides to arc flash terms. Discover more on our blog, like our basic training guide for OSHA compliance.

If you want help training your people on arc flash boundaries and safety training, Technical Skills Development Services can help.

If you want help training your people on arc flash boundaries and safety training, Technical Skills Development Services can help. For over 13 years, we’ve been providing on-site training to companies across the country. Our training, provided by experienced instructors, is guaranteed to help you and your team get up to speed on the latest in OSHA and NAFP 70E regulations. Minimize your risk and improve your OSHA compliance with an efficient electrical safety training course customized to the needs of your organization and your employees.

To learn more, contact us or visit our website today.