An arc flash results from a flashover of electrical current through air in electrical equipment from one exposed live conductor to another or to ground. Electric arcs can produce temperatures of up to 35,000° F, a degree of heat that instantly vaporizes all known materials.

Sudden temperatures at this degree can cause air to suddenly expand, resulting in a blast of very strong air pressure. That air blast, in turn, can spread molten metal great distances with great force. An arc in an enclosure, such as a motor control centre or switchgear, is magnified and the energy transmitted is forced to the open side of the enclosure toward the worker, with potential for severe heating and burns.

The causes of arc flash include dust and impurities, corrosion, condensation of water on the surface of insulating material, spark discharge, accidental touching, dropping tools, improperly maintained electrical meters, over-voltages across narrow gaps, failure to insulate material, improperly designed or utilized equipment, improper work procedures, and human error.

Newfoundland and Labrador’s Department of Government Services suggests that employers conduct a hazard and risk assessment and implement control measures to protect workers against arc flash. They should develop and implement an arc flash hazard program in accordance with the NFPA 70E Standard or equivalent.

Workers, too, must protect themselves. They need training to understand the hazard of arc flash, how it is initiated, what personal protective equipment (PPE) is appropriate and how to safely use it in electrical settings. Wherever practical, workers should be discouraged from working on energized equipment.

The task should be reserved only for  qualified, competent person(s) to do after equipment is de-energized and locked out. CSA Standard Z460-2004 - Control of Hazardous Energy covers this in greater detail.

To protect workers and the public, it is vital to clearly mark electrical equipment - such as switchboards, industrial control panels and motor control centers in other-than-dwelling occupancies that are likely to require examination, servicing or maintenance while energized. Even qualified persons trained in electrical safety must always be alerted to potential electrical arc flash hazards. FSM