An employee opened the transformer/fuse drawer and changed two medium voltage fuses while the drawer was de-energized. As the employee began to push the main power drawer (13,200 VAC./1,200 amps) back in an arc flash occurred. The arc blast energy and fire ball came out of the bottom door of the main power drawer and up. The employee was standing next to the main power drawer, on the bottom rung of a four-rung step ladder, when the fire ball engulfed his upper torso. The employee sustained second and third degree burns to his arms.