Three Simple Ways to Create Arc Flash Boundaries That Protect Workers

By James Strohecker, Contributer

In an arc flash, the most common and most severe injuries are burns. These burns are caused by the extreme heat given off by the runaway arc; the radiant heat that spreads out in all directions.

As a result, NFPA 70E includes a “stay-back” distance intended to limit these burns. The Arc Flash Boundary marks the distance from the equipment at which the Incident Energy of an arc flash would be.

What Is the Arc Flash Boundary?

The Arc Flash Boundary determines the distance from the equipment at which the Incident Energy of an arc flash would be 1.2 cal/cm².

The Arc Flash Boundary was developed at OSHA’s request by the NFPA to help companies, electrical workers, and employees avoid workplace injuries and fatalities due to shock, electrocution, arc flash, and arc blast, when working in proximity to energized electrical equipment.

The electrical worker has to be able to determine his relative risk, according to the distance from the equipment. The Arc Flash Boundary helps him to determine a safe distance.

Staying outside the Arc Flash Boundary is a way to reduce or eliminate injuries from an arc flash.

1. Require Arc Flash Protection

Staying away from the equipment is an easy way to keep safe, but sometimes a worker must get closer to do their work. In this case, the Arc Flash Boundary offers another related benefit; it tells workers when they need specific gear. If workers must cross this boundary to work on the equipment while it is still powered, they need specific personal protective equipment (PPE) to protect them from burns. Failure to use the right PPE can lead to injuries.

The type of required PPE will depend on the work being done, the nature of the equipment, and the available power. Qualified workers, who have the training to safely perform the task in question, should use the information on the equipment’s arc flash label to identify the PPE they need. Unqualified workers, who may not be prepared to protect themselves to the same degree, should stay away; they should not cross the Arc Flash Boundary.

2. Protect Workers from Electric Shock

If workers must cross this boundary to work on the equipment while it is still powered, they need specific personal protective equipment (PPE) to protect them from burns. Failure to use the right PPE can lead to injuries.

Most equipment that poses an arc flash hazard also presents a risk of electric shock. However, the two hazards need to be addressed separately. Two shock protection boundaries are intended to protect workers from this second hazard.

Limited Approach Boundary is the normal “stay-back” distance for unqualified persons (that is, people without any special training or equipment).

  • Qualified persons, who have been trained and equipped for the task at hand, may cross this boundary, if needed.
  • Qualified persons may also escort unqualified persons through the area, if appropriate protective equipment is provided for the visitor, as well.

Restricted Approach Boundary is closer and may only be crossed by qualified persons.

  • Crossing this boundary to perform work while the equipment is still powered also requires an energized electrical work permit.
  • The permit includes a specific plan of action, a list of protective steps to be taken, and supervisory approval.

3. Calculate Protection Boundaries

The two shock protection boundaries are based exclusively on the voltage of the equipment and can be found in a set of tables in NFPA 70E. AC systems are covered in Table 130.4(D)(a), and DC systems are covered in Table 130.4(D)(b).

Calculating the Arc Flash Boundary is more complex, partly because the phenomenon of arc flash is still being researched.

  • NFPA 70E provides a simplified formula for calculating incident energy.
  • IEEE 1584 provides an alternative, empirically based formula, which was developed through laboratory testing and was substantially updated in late 2018.
  • For common equipment types and installations, NFPA 70E includes tables that assign Arc Flash PPE Categories and Arc Flash Boundaries. Table 130.7(C)(15)(A)(b) covers AC systems, and Table 130.7(C)(15)(B) covers DC systems.
  • All three of the NFPA 70E boundaries are described in this Electrical Safety Boundaries infographic.
  • Arc Flash software, such as Arc Advisor or EasyPower, can calculate Arc Flash Boundaries and perform many of the other tasks associated with electrical system analysis.
  • Under NFPA 70E, arc flash warning labels must inform workers about the equipment’s power level, potential for arc flash, and appropriate personal protective equipment (PPE).
  • To provide effective protection from a hazard, perform a risk assessment. NFPA 70E describes a basic risk assessment as having three broad steps: 1. Identify a hazard (a potential source of injury); 2. Estimate the likelihood and potential severity of injuries caused by that hazard; and 3. Determine what protective measures are needed.

Whatever approach you take in your facility, be sure to post these boundaries and train your workers to understand and respect them. And keep your workplace safe with arc flash labeling. Implementing each of these strategies will help to reduce downtime and injuries, and can help improve morale, productivity, and revenue through more efficient worksite operations. ESW

James Strohecker is the Director of Marketing Innovation at Graphic Products + DuraLabel ( Graphic Products is a leader in delivering innovative design software, industrial sign and label printers, all-purpose floor marking, multi-language signs and labels, and colored pipe markers for any facility’s compliance and safety requirements. Learn how to create safety signs that meet OSHA requirements with the Best Practice Guide to Arc Flash Labeling: What You Need to Know. This helpful guide from Graphic Products breaks down all the requirements. The Guide’s Do’s and Don’ts of Arc Flash hazard equipment labeling list the requirements from the NEC, NFPA, and OSHA, that will help make your operation safe and compliant (

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