EE S SUPERVISOR HANDED A 60 JACKHAMMER DOWN TO THE EE WHO WAS STANDING ON A PLATFORM A COUPLE OF STEPS BELOW. CLINKER BALLS HAD SPILLED ONTO THE PLATFORM FROM THE FEED END OF 2 FINISH MILL. HE SLIPPED ON THE BALLS AND DROPPED THE JACKHAMMERON HIS LEFT KNEE. THIS CAUSED A CONTUISION AND SWELLING OF THE KNEE. HE WAS PUT ON RESTRICTED DUTY.