Arc flash defined by National Fire Protection Association (NFPA), is “a dangerous condition associated with the release of energy caused by an electric arc.” It occurs when electrical insulation or isolation between conductors is broken or can no longer withstand the applied voltage. Arc Flash can result from inserting a tool in the wrong place or dropping a tool into a circuit breaker or service area. In fact, an explosion 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 explosion can reach more than 5000 degrees. This 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 happen. These explosions cause 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 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 arc flash 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.
Incidents 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 the calculation and creation of a “flash protection boundary”. This imaginary boundary, which surrounds the potential arc 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 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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