An arc flash can be spontaneous or result from inadvertently bridging electrical contacts with a conducting object. Other causes may include dropped tools or the buildup of conductive dust or corrosion. An electric arc flash can occur if a conductive object gets too close to a high-amp current source or by equipment failure (for instance, while opening or closing disconnects).
Conditions under which arc flash can occur:
Human Error, which is considered the most common cause:
A worker was injured while laying block for a surface electrical installation. He was cleaning the mortar joints with a piece of metal conduit when the conduit fell through the top of a 660 VAC panel, causing a short. The ensuing arc burned through the panel access door (Figure 1), the flash inflicting 1st and 2nd degree burns to the worker's arm, face and neck.
Figure 1: Arc Blast Damage in Electrical Cabinet Door