What is an Arc Flash?

An arc flash is the light and heat produced from an electric arc.

When an uncontrolled electric arc forms at high voltages, and especially where large supply-wires or high-amperage conductors are used, arc flashes can produce deafening noises, supersonic concussive-forces, super-heated shrapnel, temperatures far greater than the Sun's surface, and intense, high-energy radiation capable of vaporizing nearby materials.

Arc flash temperatures can reach or exceed 19,400 °C at the arc terminals. The massive energy released in the fault rapidly vaporizes the metal conductors involved, blasting molten metal and expanding plasma outward with extraordinary force. A typical arc flash incident can be inconsequential but could conceivably easily produce a more severe explosion. The result of the violent event can cause destruction of equipment, fire, and injury not only to an electrical worker but also to bystanders. During an arc flash, electrical energy vaporizes the metal, which changes from solid state to gas vapour, expanding it with explosive force.

In addition to the explosive blast, called the arc blast, destruction also arises from the intense radiant heat produced by the arc. The metal plasma arc produces tremendous amounts of light energy from far infrared to ultraviolet. Surfaces of nearby objects, including people, absorb this energy and are instantly heated to vaporizing temperatures. The effects of this can be seen on adjacent walls and equipment - they are often ablated and eroded from the radiant effects.

There are many methods of protecting personnel from arc flash hazards. This can include personnel wearing arc flash personal protective equipment (PPE) or modifying the design and configuration of electrical equipment. The best way to remove the hazards of an arc flash is to de-energize electrical equipment when interacting with it, however de-energizing electrical equipment is in and of itself an arc flash hazard. In this case, one of the newest solutions is to allow the operator to stand far back from the electrical equipment by operating equipment remotely, this is called remote racking.

 

Arc flash protection equipment

The materials used in Arc Flash PPE are tested for their arc rating. The arc rating is the maximum incident energy resistance demonstrated by a material prior to break open (a hole in the material) or necessary to pass through and cause with 50% probability the onset of a second degree burn. Arc rating is normally expressed in cal/cm² (or small calories of heat energy per square centimetre).

PPE provides protection after an arc flash incident has occurred and should be viewed as the last line of protection. Reducing the frequency and severity of incidents should be the first option and this can be achieved through a complete arc flash hazard assessment and through the application of technology such as high-resistance grounding which has been proven to reduce the frequency and severity of incidents