Arc Flash Hazard Explained

By R.W. Hurst, The Electricity Forum

Arc flash hazard, as defined by the National Fire Protection Association (NFPA), is "a dangerous condition associated with the release of energy caused by an electric arc.”

The primary risk created by an arcing fault is the risk of severe burn injuries due to the intense heat created by the arc. Therefore, protective devices are needed. Fatal burns can occur when the victim is several feet from the explosion. Serious burns are common at a distance of 10 feet.

Staged tests have shown temperatures greater than 437°F on the neck area and hands for a person standing close to a blast.Ordinary clothing can be ignited several feet away. Clothed areas on the body can be burned more severely than exposed skin, depending on the garment’s fabric.

Additional hazards that can occur include:

• Damage to Eyes: Infrared and ultraviolet radiation can damage unprotected eyes.

• Molten Metal: Arcs can spray droplets of molten metal at high-speed onto unprotected parts of the body.

• Shrapnel: Metal shrapnel created by an arcing fault can injure the body.

• Metal Vapor: Vaporized metal can be created, causing severe injury if inhaled.

• Air Pressure: Extreme events can create air pressure waves similar to chemical explosions. These have thrown workers across rooms and knocked them off ladders.

• Hearing damage: The sound magnitude is more than 140 dB within 2 to 3 meters of an arc.


Why is it hazardous?
Electrical explosions occur when electrical insulation or isolation between conductors is broken or can no longer withstand the applied voltage. An electrical safety incident can result from many different things, even something inconsequential as inserting a tool in the wrong place or dropping a tool into a circuit breaker or service area. 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 a phase-to-phase electrical fault.

The thermal temperature can reach more than 5,000 degrees. This is as hot as the surface of the sun. 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, occurs five to 10 times. These electrical safety incidents 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 for electricians who are not wearing personal protective equipment PPE. In addition to the electrical worker being injured, the fast-moving pressure wave or blast can injure other workers in the vicinity who can be struck by loose material such as equipment, metal tools, and other projectiles.

In addition to personal injury, electrical safety incidents can severely damage electrical equipment, disrupting electrical systems in manufacturing and process industry environments, office buildings, or institutions such as hospitals, airports, schools, etc. Furthermore, the cost of downtime can be considerable. Therefore, a proper risk assessment must be performed.


Where does it occur?
AF safety incidents typically occur in applications above 120V and can occur when electrical equipment is serviced or inspected. For example, some incidents occur when a worker removes a cover or trim from a piece of equipment. As a result, many service companies recommend that electrical equipment be de-energized before any work is commenced, although this is only sometimes possible.

NFPA requires a calculation to determine a hazard assessment and create a “protection boundary.” This imaginary boundary, which surrounds the potential risk point, specifies what level of personal protective clothing and equipment must be used by qualified workers who enter within that boundary. NFPA defines a “flash protection boundary within which a person could receive a second-degree burn if an electrical risk occurs." 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.”