EE WAS REMOVING 2X2 FT DOOR FROM NORTH DUST HOPPER ON GMD DUST COLLECTOR AT CALCINE BUILDING. WHEN LAST BOLT WAS REMOVED DUST POURED OUT DOOR & PUSHED DOOR ASIDE. EE TURNED TO MOVE OUT OF THE WAY AND HIS FOOT CAUGHT AGAINST THE PLATFORM TOEPLATE, TWISTING HIS KNEE.