Defining arc flash boundaries is the crucial part of the Arc Flash Analysis. Depending on the potential arc flash hazard, this boundary is calculated separately based on specific system information. There are different types of boundaries as shown in the figure below.

Let’s look at what the mentioned terms mean –

Boundary Arc Flash:

When an arc Flash hazard exists, an approach limit from an arc source at which incident energy equals 1.2 cal/cm2 (5 J/cm2 ). The flash boundary is the farthest established boundary from the energy source. If an arc flash occurred, this boundary is where an employee would be exposed to a curable second-degree burn (1.2 calories/cm2 ). The issue here is the heat generated from a flash that results in burns.

Limited Approach Boundary: 

An approach limit at a distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists

Restricted Approach Boundary:

An approach limit at a distance from an exposed energized electrical conductor or circuit part within which there is an increased likelihood of electric shock due to electrical arc-over.

Restricted Space: 

Restricted space is the area within the restricted approach boundary where chances of electric shock due to arc flash is high.

Prohibited Approach Boundary:

As the distance from an exposed energized component where the effects of an electric arc would be the same as actually touching the live part. No one should be within this boundary while equipment is energized, except the engineers who meet the following mentioned criteria.

• A responsible and trained person who has carried out a full risk assessment.
• The electrical work has been documented through an energized work permit.
• The qualified electrical worker has been trained and is authorized to conduct work on live electrical equipment.
• The electrical work has been properly trained and equipped with appropriate Arc Flash PPE.
• It is ensured that electrical workers use the correct equipment and follow precise procedures when in proximity of live electrical equipment.

Prohibited Space: 

The area within the prohibited approach boundary where no one is permitted to be as there is a high risk of serious injury/fatality.

Need of defining Arc Flash Boundaries

• Defines the area where the chances of arc flash hazards are high.
• Sets criteria for the trained engineer to work on the live networks.
• Avoid untrained people working on it as it will be more harmful.
• Helps label the equipment with stickers containing the necessary information.
• Helps engineers to decide on the appropriate PPE to be used based on the incident energy.