INJURED WAS USING AN OVERHEAD HOIST AND A GRAB LIFT TO REMOVE A 2'X4'X1/2"" STEELPLATE FROM THE STORAGE RACK. HE RAISED THE PLATE APPROX 5' FROM THE FLOOR AND WAS ATTEMPTING TO ROLL THE HOIST WHEN IT REFUSED TO MOVE. HE TRIED SEVERAL TIMES TO PULL THE HOIST WHEN THE PLATE FELL OUT OF THE GRAB, STRIKING AND FRACTURING HIS LOWER RIGHT LEG