THE EMPLOYEE WAS USING A SIMPLEX RAIL JACK TO SET CONCRETE WALL FORMS ON LINE. THE JACK WAS TOO SHORT SO HE BLOCKED THE FOOT OF THE JACK WITH A 6 BY 6 TIMBER. THE JACK KICKED OFF OF THE TIMBER WHEN HE PUT IT UNDER LOAD AND STRUCK HIM IN THELEFT KNEE CAUSING A CONTUSION AND STRAIN TO HIS LEFT KNEE.