EE was working in hopper & noticed the breaker had slipped. Went into electrical building & opened electrical box & noticed a fuse that was loose. EE smacked it w/hand & fire came out of box. EE thought EE had turned breaker off before EE touched it. EE also thought EE was fine, but looked down & saw blood dripping from arm. Had to go to ER & received 6 stitches in L arm.