A diagram explaining the layout of an arc flash boundary, showing the boundary, the limited approach boundary and restricted approach boundary.

Understanding Arc Flash Boundaries

Also known as a flash protection boundary, an arc flash boundary specifies the minimum safe distance from exposed energised conductors or circuit parts that have the potential for an arc flash event. It is important to take the proper steps to ensure worker safety before taking any measurements, especially on energised equipment. Workers should know exactly where the arc flash boundary is and keep this safety measure in mind at all times.

What are Arc Flash Boundaries?

An arc flash boundary depends on the potential arc flash hazard and is calculated to 1.2 calories/cm2 of incident energy. That is the distance where a worker without wearing the appropriate level of personal protective equipment (PPE) would receive second degree burns.

No workers should pass an arc flash boundary without having first undertaken the necessary training and donning the required PPE. 

How are Arc Flash and Electric Shock Protection Boundaries determined?

The National Fire Protection Association (NFPA) 70E states that there are three boundaries to observe. These are the shock protection boundaries - limited approach and restricted approach - and an arc flash boundary. Each boundary triggers different requirements in NFPA 70E, including determining the type and level of PPE that workers must wear and the qualifications required to cross into each level.

These boundaries are put in place to minimise worker’s risk to harm through avoidance or the use of PPE.

How do you find Arc Flash Boundaries?

Whilst there are differing methods available for finding out an arc flash boundary (NFPA 70E or IEEE 1584), the main variables to consider is the voltage, the level of local grounding versus high resistance, the time available for arching before the protective equipment of the equipment activates, the type of equipment, conductivity gaps, and the size of the three phase fault. Armed with all of that vital information, workers are able to accurately find what the arc flash boundary is.

It is important to note that he exact method of calculation is different for DC and AC systems, so it is critical to have the above information available.

What is the default Arc Flash Boundary?

Sometimes the arc flash boundary is the furthest of the three boundaries from the exposed equipment, and other times it is the limited approach boundary that is the furthest away. When the arc flash boundary is the furthest one away, it becomes the default boundary that no worker should pass without the correct training and the suitable PPE.

If, for instance, the limited approach boundary is further out, then that should be treated as the boundary that no worker should pass without the necessary training and the correct PPE to keep them safe.

Who determines the Arc Flash Boundary?

Most companies use software programs where they can enter information, such as in the voltage of a piece of equipment, and it will automatically calculate the arc flash boundary.

It is important that this is performed by a worker who has the correct training and can use the software program proficiently. This is because, if the information is entered incorrectly, the arc flash boundary will be incorrect also, and workers will be put at great risk of harm..

Who can enter the Arc Flash Boundary?

In order to pass an arc flash boundary, workers must be a qualified with the correct training and PPE. Any worker who needs to perform a job on the energised equipment, may also be required to have a work permit and other similar documentation.

Those workers who do not have the necessary training are strictly prohibited from crossing an arc flash boundary.

No matter what the arc flash boundary is, our arc flash and fire retardant workwear will keep workers safe from harm – view the full arc flash collection here. To find out more about our clothing and PPE, and how they keep workers safe, visit our Arc Flash Information Hub

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