WHILE EMPLOYEE WAS RUNNING GUZZLER (MACHINE THAT SUCKS UP DUST) AT #4 FINISH MILL INFEED, HE STEPPED ON A STEEL MILL BALL AND FELL DOWN ON LEFT KNEE. HE WAS ON GROUND LEVEL CONCRETE FLOOR WITH BOTH FEET ON FLOOR WHEN ACCIDENT OCCURRED. EMPLOYEE WAS EXPERIENCED AND WEARING PROPER P.P.E AT THE TIME.