The National Institute for Occupational Safety and Health (NIOSH)
An arc flash is the sudden release of electrical energy through the air when a high-voltage gap exists and there is a breakdown between conductors. An arc flash gives off thermal radiation (heat) and bright, intense light that can cause burns. Temperatures have been recorded as high as 35,000 °F. High-voltage arcs can also produce considerable pressure waves by rapidly heating the air and creating a blast. This pressure burst can hit a worker with great force and send molten metal droplets from melted copper and aluminum electrical components great distances at extremely high velocities.
NIOSH Arc Flash Awareness, Part 1
NIOSH Arc Flash Awareness, Part 2
NIOSH Arc Flash Awareness, Part 3