PLANT MAN STEPPED UP ONTO MIDDLE OF HANDRAIL TO LOOK INTO LOG WASHER. AS HE WAS ATTEMPTING TO STEP BACK DOWN HIS FOOT SLIPPED OFF THE MIDDLE ANGLE OF HANDRAIL AND FELL BACKWARDS ONTO HIS BACK. MIDDLE ANGLE WAS SLIPPERY DUE TO WATER SPRAY IN AREA. FELL ONTO PLATFORM NEXT TO LOG WASHER.