What is an Arc Flash Boundary?

An arc flash is a dangerous electrical explosion that can severely injure, or kill anyone in the vicinity. An arc flash is created when a fault in an electrical system allows an arc of electricity to escape and pass through ionized air. Arc flashes can be caused by accidental contact with the electrical system and things like dust, rust, corrosion, moisture, dropped tools, and human contact.

When an arc flash occurs it explodes creating intense heat and light. Temperatures in an arc flash can be approximately 35,000 degrees Fahrenheit, which is four times hotter than the surface of the Sun. Clouds of plasma and ionized particles will fill the room, which will severely burn airways and lungs if inhaled. An arc flash is often followed by an arc blast, which is a supersonic shock wave that breaks nearby material and launches shrapnel and often molten metal throughout the area.

An arc flash may sound like an uncommon occurrence, but unfortunately, the Bureau of Labor Statistics estimates that between 5 and 10 arc flashes occur in the United States each day. This is why arc flash safety, and creating an arc-flash boundary in particular, are so important when working with energized electrical systems.

To minimize risk in work spaces where an arc flash could occur, the arc-flash boundary was created. Arc-flash boundaries were developed through cooperation between OSHA (Occupational Safety and Health Administration) and the NFPA (National Fire Protection Association) to prevent worker injuries.


What is an Arc-Flash Boundary?

An arc-flash boundary is the minimum safe distance from energized equipment that has the potential to cause an arc flash. In the event that an arc flash occurs, anyone outside of the arc-flash boundary will likely be unharmed. Individuals working inside the arc flash boundary will be extensively trained on the dangers, and wearing enough personal protective equipment that harm will be mitigated.

When working with exposed energized equipment, such as electrical maintenance, there is always a potential for an arc flash to occur. Because of this, an arc-flash boundary is established to prevent individuals without protective gear from getting close enough to equipment that could result in them being hit by an arc-flash. After the arc-flash boundary is determined, a physical barrier or clearly marked border is set up along the perimeter to prevent accidental entry.

Arc-flash boundaries are not a fixed distance, because they have to be calculated based on the system voltage, available fault current and associated protective devices being used. Some arc-flash boundaries will be larger than others, and the distance of the arc-flash boundary needs to be determined on a case-by-case basis.

The furthest edge of the arc-flash boundary represents the minimum safe distance for someone who isn’t wearing personal protective equipment. Bear in mind, because an arc-flash explosion is so loud and bright, an individual could still be injured and receive second degree burns while standing at the edge of this radius, so extreme precaution should be taken at all times.

Because the arc-flash boundary is an OSHA-recognized standard, the safety procedures associated with it must be observed in the workplace.


What’s the Difference Between an Arc Flash and an Arc Blast?

An arc flash is the primary explosion that occurs when a fault occurs in an electrical circuit. The arc blast is a supersonic shock wave that occurs after the arc flash. The arc blast is strong enough to throw anyone nearby across the room, along with launching super-hot metal, shrapnel, and nearby objects in every direction.


Areas Within an Arc-Flash Boundary

Under ideal circumstances, maintenance on electrified systems would occur when a facility is empty; but in reality, there will be other employees working alongside or in the vicinity of the electrical engineer when an arc-flash risk is present.

As such, there are three defined areas that exist within the arc-flash boundary. These include the arc-flash boundary, the limited-approach boundary, and the restricted boundary. The further a person progresses through these areas, the more training and arc-rated personal protective equipment (PPE) they will need.

Arc-flash boundary - An employee wearing no PPE and with no training should remain outside of the arc-flash boundary. It’s important to remember that it’s still possible to be injured by an arc flash from this distance.

Limited-approach boundary - An individual that needs to enter the limited approach boundary should be wearing some PPE and have some training.

Restricted boundary - For the restricted boundary the employee is directly in front of the potential arc flash and would need to be wearing full PPE and have full training. This is the most dangerous of the three boundaries and untrained employees without the appropriate PPE should never enter this boundary.


How are Arc Flash Boundaries Calculated?

Calculating the arc-flash boundary correctly is critical; if the arc-flash boundary is incorrectly calculated, it could result in serious injury or death. The arc-flash boundary can be calculated manually using a complex mathematical formula, but for better accuracy; using digital arc-flash software is recommended. To correctly calculate the arc-flash boundary using either method, you’ll need to perform a detailed analysis of the electrical system and when and where faults could occur.

MTA Electrical Engineers can advise you on arc-flash safety and calculate the correct arc-flash boundary required for your system. Because of the extreme risk of harm that an arc flash can cause, taking appropriate safety measures is essential.


NFPA Guidelines for Calculating an Arc-Flash Boundary

The NFPA 70E and CSA Z462 standards provide guidance on how to calculate the arc-flash boundary using several different methods, including the incident energy analysis method and the arc-flash PPE category method.


Arc-Flash Personal Protective Equipment (PPE)

When an arc flash hazard is present, workers need to wear the appropriate arc-rated PPE that will protect them in the event of an arc flash. These items can vary depending on the severity of the risk, these include:

  • Hard hat with arc-rated face shield (or protective hood)
  • Safety goggles/protective glasses
  • Arc-rated long-sleeve jacket
  • Arc-rated pants
  • Protective balaclava (face and neck covering)
  • Rubber insulating gloves (with leather protectors)
  • Non-conducting leather footwear
  • Protective ear plug inserts

It’s an employer’s responsibility to provide arc-flash resistant personal protective equipment to employees, make sure the PPE is inspected regularly, and provide employee training on when and how PPE needs to be used. After performing an arc-flash risk assessment, the employer will know what types of PPE is required.


Keep Your Teams Safe from Arc Flashes

MTA Electrical Engineering can help your business by providing expert advice on arc-flash safety, employee training, PPE recommendations, and regulatory compliance. Contact us today for an arc-flash analysis and risk assessment for your California facility.

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