HYDRO CHEM EMPLOYEE WAS ATTEMPTING TO MOVE A HIGH PRESSURE HYDROBLASTING ""ROTOJET"" BY HANDLING A 15' 1"" PIPE ATTACHED TO THE ROTOJET. THE ROTOJET WAS UNDER PRESSURE WHEN EMPLOYEE WAS ATTEMPTIN G TO DISLODGE THE ROTOR ARMS INSIDE THE DIGESTER BY MOVING THE PIPING OUTSIDE THE DIGESTER. THE ROTOR ARMS DISLODGED CAUSING HIGH PRESSURE WATER AND BAUXITE MATERIAL TO SPRAY OUT OF A MANWAY