A Primer on Arc Flash Boundaries

By Safeopedia Staff
Last updated: May 15, 2024
Key Takeaways

Identifying the arc flash boundaries will help you ensure that only employees with the right training and PPE work on equipment that presents an arc flash risk.

Sparks emitting from an electrical panel.
Source: YouraPechkin (Envato Elements)

There’s no such thing as a bystander during an arc flash event.


The heat, the pressure, and the explosive flash of fire are so powerful that they can injure anyone who happens to be nearby. They don’t need to be in contact with energized equipment or standing directly next to it to get hurt.

That’s why arc flash boundaries are so important. They ensure that if an arc flash event does occur, no one will be subjected to it without the right kind of protection.


What complicates matters is that there isn’t a single arc flash boundary – there are three different ones, each with their own requirements. And how big each boundary is will vary from equipment to equipment.

To sort out the details, let’s go over each of these boundaries and what is needed before anyone can set foot inside them.

What Is an Arc Flash Boundary?

Arc flashes occur when an electrical current travels through the air between two conductors.

They are a serious hazard for anyone who works on or near electrical equipment. And they literally happen in a flash, so there’s no time to think or react. It starts and stops in a matter of split seconds.



There’s no seeing it coming. There’s no time to throw on extra PPE, move out of the way, or even lift your arm to shield your face. By the time you realize it’s happening, it’s already over.

Well, the event is over – its consequences aren’t. An arc flash can cause severe burns, damage hearing, knock people off their feet, and propel shrapnel and molten metal through the air.

Workers need protection from these very serious risks. That will involve all the usual control methods: training, arc-rated PPE, and regular maintenance of electrical equipment.

But given how harmful, unpredictable, and quick these events are, one of the best ways to protect workers is to simply ensure they’re not in close proximity when an arc flash happens.

That’s the purpose of the arc flash boundaries. They demarcate arc flash danger zones, ensuring that no one crosses into them unless they have the training, certification, and equipment needed to do so safely.

The Three Arc Flash Boundaries

Arc flash boundaries are outlined in the NFPA 70E Standard for Electrical Safety in the Workplace. They are:

  • Arc Flash Protection Boundary: The outer boundary, where a person could suffer a second degree burn if an arc flash event occurred. No one should be allowed to cross this boundary without appropriate arc-rated PPE.
  • Limited Approach Boundary: Only qualified persons wearing appropriate PPE should be authorized to cross this boundary. Unqualified personnel can enter only when accompanied and supervised by a qualified person.
  • Restricted Approach Boundary: Only qualified persons with the right training and appropriate PPE can cross this boundary. Before doing so, they need a written plan for the work that will be done in this zone and how it is to be carried out. Until the plan is formally approved, no work can be done within this boundary.

Until 2015, the NFPA also included a Prohibited Approach Boundary. It was removed since it had no practical application for safety. While it did map out a zone that presented a higher risk, it required the same actions and precautions that were already laid out for entering the Restricted Approach Boundary.

Who Counts as a Qualified Person?

Only qualified persons can enter the limited and restricted approach boundaries. But the term “qualified person” is rather vague.

NFPA 70E defines a qualified person as:

“One who has demonstrated skills and knowledge related to the construction and operation of electrical equipment and installations and has received safety training to identify and avoid the hazards involved.”

On its own, that’s a bit circular. It basically tells us a person can safely cross the limited approach boundary if they are able to do it safely.

Rather than specify what it takes to become a qualified person, the standard puts the onus on employers and contractors to ensure that anyone entering an arc flash boundary has received adequate training. At a minimum, this should include:

  • Understanding of safety practices when working on live electrical equipment
  • Knowledge of PPE requirements, including arc ratings
  • The ability to execute lockout/tagout procedures
  • Awareness of the different arc flash boundaries and what they entail
  • Recognizing the presence of electrical hazards, including potential arc flash risks


Download our free AR/FR Workwear Fast Facts guide!


What Is Included on an Arc Flash Label?

Energized equipment that could pose an arc flash must be affixed with a warning label that has all the pertinent information needed to understand the level of risk associated with it.

NFPA 70E requires these labels to display:

  • The nominal system voltage
  • The distance of the arc flash boundary
  • The type of PPE required (arc flash PPE category, arc rating for protective clothing, or other requirements)

Labels can also specify the distance of the limited and restricted approach boundaries. Strictly speaking, this is optional, but including it is the prudent option.

Do Arc Flash Boundaries Need to Be Visually Demarcated?

Simply put, no. There is no strict requirement to create a clear visual indication of where an approach boundary ends or begins.

However, given the risks involved, demarcating the high-risk areas is still good practice.

One simple way to do this is by using floor marking tape, especially to mark the limited approach boundary. That way, everyone knows exactly knows which zone they’re in – if they cross over the tape, they cross over the boundary.

While signs or tapes are useful, it’s important to remember that they’re never sufficient on their own. Keeping workers from crossing the wrong boundary is primarily a matter of training them to understand the risks, creating a workflow that keeps unprotected workers away from hazardous equipment, and good old fashioned supervision to make sure no one steps foot where they shouldn’t.

Know Your Limits

The best way to protect workers from arc flashes is to keep them out of harm’s way when one takes place.

In some cases, that will be done by providing the right PPE, protective clothing, and training to minimize the likelihood that someone will get hurt.

For most employees, it will be much simpler than that. You’ll have to ensure that they don’t get close enough to get injured.

That’s why it’s essential to assess the arc flash risks in your workplace, determine the boundaries, and mark them accordingly.

Ready to learn more? Check out our free webinar on How to Build an Arc Flash PPE Program Your Workers Will Embrace!

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Written by Safeopedia Staff

Safeopedia Staff

At Safeopedia, we think safety professionals are unsung superheroes in many workplaces. We aim to support and celebrate these professionals and the work they do by providing easy access to occupational health and safety information, and by reinforcing safe work practices.

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