EMPLOYEE WAS INSTALLING A SCREW HOUSING TO A SCREW CONVEYOR. HE WAS WORKING OUTDOORS. THERE WAS SNOW AND ICE IN THE WORK AREA. WHEN HE WENT TO POSTION THE HOUSING INTO PLACE, HE SLIPPED ON THE ICE AND STRAINED HIS LOWER BACK. HE WAS SENT FOR MEDICAL EVALUATION ON 2/27/04. ON 3/1/04, HE BAGAN PHYSICAL THERAPY TO STRENGTHEN HIS BACK.