An arc flash is a short circuit through the air. In an arc flash incident, an enormous amount of concentrated radiant energy explodes outward from electrical equipment, creating:

• Pressure waves that can damage hearing, fracture ribs, collapse lungs, and knock a person off a ladder or blow a worker across a room  
• Pressure waves that can send loose material like pieces of damaged equipment, tools, and other objects flying through the air at speeds in excess of 700 miles per hour  
• A high-intensity flash that can damage eyesight and leave a worker blind  
• A superheated ball of gas with temperatures in excess of 35,000° Fahrenheit that can ignite clothing and cause serious burns over much of the body

Five to 10 arc flash explosions occur in electrical equipment every day in the United States. Exposure to an arc flash frequently results in multiple injuries of a very serious nature and, in some cases, immediate or eventual death.

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Employees can be injured by an arc flash even if they don’t touch anything. Workers have been injured even when they were 10 feet away from the arc center.

What’s more, electrical arc flash hazards are not found only where high-voltage sources are present. In fact, locations consisting of many low voltage equipment sources account for the most arc flash incidents.

Safety Standards

Because of the serious risks associated with arc flash, safety standards have been established to protect workers. These include:

• OSHA regulations require the use of safety signs, symbols, or accident prevention tags to warn employees about electrical hazards that may place them in danger.
• National Fire Protection Association (NFPA) standards recommend that employers perform an arc flash hazard analysis before allowing employees to work on energized equipment.  
• NFPA standards also recommend personal protective equipment (PPE) and protective clothing to keep workers safe.
• NFPA standards address the issue of safe flash protection boundaries designed to restrict entry into areas where flash hazards exist.
• Standard 1584, Guide for Performing Arc Flash Hazard Calculations, published by the Institute of Electrical and Electronic Engineers (IEEE), helps you calculate the hazards of arc flash in different types of equipment in various power systems.

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Flash Protection Boundary

The flash protection boundary is the distance from the source within which the potential heat energy generated by an arc flash could cause a second-degree burn.

According to NFPA standards:

• The limited approach boundary may not be crossed by “unqualified” people unless accompanied by a “qualified” employee.
• The restricted approach boundary is the area near the exposed live parts and may be crossed only by “qualified” personnel using appropriate shock prevention techniques and equipment.
• The prohibited approach boundary is the area near exposed live parts that may be crossed only by “qualified” personnel using the same protection as if direct contact with live parts is planned.

Tomorrow, we’ll review causes of arc flash, prevention strategies, and essential protective measures for employees at risk.

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