What is Arc Flash

By R.W. Hurst, The Electricity Forum

What Is Arc Flash

What is Arc Flash?

Simply explained, an arc flash occurs when an electric current (usually in the form of an explosive pressure wave) suddenly leaves the equipment and travels through the air, either from one live conductor to another, or from a piece of energized electrical equipment to ground. Potential arc flash hazards include flashover and blast.


Visit Our AF Course Page:


The results of such a flashover are in most cases violent and when an electrical worker is in close proximity to the electrical equipment that is involved in a flashover and arc blast, that worker can receive a serious injury and sometimes, even death can occur.

AF is usually caused by a number of factors, including:

  • Dust inside Electrical Systems
  • The Dropping of tools
  • Accidental contact
  • Condensation on Energized Equipment
  • Equipment Material failure
  • Surface Corrosion
  • Faulty Electrical Installation

The following three factors dictate the severity of an injury:

  • Proximity of the electrical worker to the hazard
  • Temperature of the AF
  • The Duration for circuit to break

Explosions are costly. It is because of the extreme nature of an explosion that electrical workers are injured. And when they are injured, the results can be devastating, even resulting in death. Many injured electrical workers discover that their quality of future life is impaired and they can never regain their past quality of life. Extensive medical care is often needed, sometimes resulting in medical bills exceeding $1,000,000. The best way to avoid arc flash accidents is to de energize the equipment.

The National Fire Protection Association (NFPA) has developed a standard (NFPA70E) which outlines specific approach boundaries that are designed to protect electrical workers near energized electrical equipment such as a circuit breaker.

Here are the Flash Protection Boundaries:

  • Flash Protection Boundary (outer boundary)
  • Limited Approach
  • Restricted Approach
  • Prohibited Approach (inner boundary)

Flash Protection Boundary (outer boundary)

The Flash Protection Boundary is the farthest established boundary from the energized electrical equipment which contains a hazardous level of incident energy. If an AF occurs within this boundary, a worker would be exposed to a curable second degree burn (1.2 calories/cm2 ). The real issue within this boundary is the heat that is generated from the flashover, which results in a burn.

Limited Approach

The Limited Approach Boundary is defined as an approach limit at a distance from an exposed live part where a shock hazard exists.

Restricted Approach

The Restricted Approach Boundary is defined as approach limit at a distance from an exposed live part which there is an increased risk of shock.

Prohibited Approach (inner boundary)

The Prohibited Approach Boundary is defined as a distance from an exposed part which is considered the same as making contact with the live part. This distance is not common between equipment. Some equipment will have a greater flash protection boundary while other equipment will have a lesser boundary.

Ways to Protect the Workers

There are a number of important ways that workers can be protected from an electrical hazard. Some of the ways are suitable for the protection of qualified electrical workers doing work on energized electrical equipment and other ways that are intended to protect non-qualified electrical workers who work on nearby energized equipment. There are also warning labels that can be attached to electrical equipment that specify what personal protective equipment ppe is required to be worn. 

Here are our Electrical Safety Training Pages

Arc Flash Training - CSA Z462 -2021


Related Articles