Arc Flash Hazard

By R.W. Hurst, The Electricity Forum

What is an Arc Flash Hazard?

The National Fire Protection Association (NFPA), defines Arc Flash Hazard as “a dangerous condition associated with the release of energy caused by an electric arc.”

Why is it hazardous?
Arc Flash Hazards occurs when electrical insulation or isolation between conductors is broken or can no longer withstand the applied voltage. An electrical safety accident can result from many different things, even something accidental as inserting a tool in the wrong place or dropping a tool into a circuit breaker or service area. In fact, an it can occur under any of the following conditions: a) if an employee is working on or near energized conductors or circuits, or b) moves near or contact the equipment, or c) a failure of the equipment occurs; any of these conditions may cause a phase-to-ground and/or a phase-to-phase electrical fault.

The thermal temperature of an arc flash explosion can reach more than 5,000 degrees. This Arc Flash Hazard energy is in the form of a blinding flash of light and a deafening noise. In this explosion, a giant amount of concentrated energy is forced outward from the electrical equipment toward the electrical worker, spreading hot gases and molten metal.

Every day in the United States, from five to 10 arc flash explosions occur. These electrical safety accident events cause arc flash injuries (from the creation of pressure waves that can damage hearing or brain function and a flash that can damage eyesight and burn exposed and covered flesh) which can range from minor burn injuries to life threatening injuries and possible death. In addition to the electrical worker being injured, the fast-moving pressure wave, or arc blast can also injure other workers in the vacinity who can be struck by loose material such as pieces of equipment, metal tools, and other projectiles.

In addition to personal injury, an electrical safety accidents can result in serious damage to electrical equipment. which can cause disruption to electrical systems in manufacturing and process industry environments,office buildings, or institutions such as hospitals, airports, schools, etc. The cost from downtime can be considerable.

Where do Arc Flash Hazards occur?
Arc Flash Hazard safety accidents typically occur in applications above 120V and can occur when electrical equipment is being serviced or inspected. In fact, some incidents occur when a worker is removing a cover or trim from a piece equipment. Many service companies recommend that electrical equipment be de-energized before any work is commenced, although this is not always possible.

NFPA 70e requires an Arc Flash Hazard calculation and creation of a “protection boundary”. This imaginary boundary, which surrounds the potential Arc Flash Hazard point, specifies what level of personal protective clothing and equipment must be used by qualified workers who enter within that boundary. NFPA 70e defines a “flash protection boundary within which a person could receive a second-degree burn if an electrical arc flash hazrd were to occur". It also defines incident energy as “the amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.”

 

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