An arc flash occurs when electric current strays from the path designed for it and instead travels through air to another electrical conductor. The flash results in an uncontrolled voltage surge that can severely injure a person or persons in close proximity.
Unintended conductors include dust, tools, water, corrosion, faulty wiring to name a few. The arc flash can be responsible for fire, for burns, flying objects, extreme blast pressure, sound blast and heat. To protect against the possibility of arc flashes, the National Fire Protection Association has developed a series of four “Flash Approach Boundaries” to help limit the effects of the flash.
The Flash Protection Boundary is the farthest away from the energy source. Possible exposure from the arc flash would include the possibility of a second degree burn. The Limited Approach Boundary limits one to no closer to where a possible electric shock possibility exists from the arc flash. The Restricted Approach Boundary places one at an area where there is a definite increase in the possibility of electrical shock. The prohibited Approach Boundary puts one in an area that is considered right in the proximity of a probable arc flash. The energy measured on a surface at the specified working distance from the arc flash is known as incident energy. An arm’s length of a worker (approximately 24 inches) for low voltage equipment corresponds to the incident energy
To protect workers when the possibility of arc flash is present the following common sense rules should be followed: De-energize the circuit that is being worked on if at all possible. Use insulation to protect against arc-flash. Use guards or barricades. Use Ground Fault circuit interrupters. Simply ground the circuit. Use proper protective equipment.
The National Electrical Code states that all electrical equipment be marked to warn workers of the hazards associated with arc flash. Some of the most popular signs include: DANGER Arc Flash & Shock Hazard, No Safe PPE Exists; WARNING, Potential Arc Flash Hazard; WARNING, Arc Flash & Shock Hazard, Appropriate PPE Required. It is extremely important to follow these warnings. ArcFlash can set fire to clothing and cause severe burns in a fraction of a second, with no time to react.