3 EE'S WERE USING A MECHANICAL SCREW JACK TO RAISE A PORTION OF THE CONE CRUSHER & SCREEN DECK FOR LEVELING PURPOSES. THE JACK FAILED RESULTING IN INJURY TO 2 OF THE EE'S. THE JACK BASE WAS N OT SUPPORTED SQUARELY ON FIRM LIFTING SURFACE. JACK FAILED USING A CHEATER BAR PUTTING PRESSUREON UNSUPPORTED BASE OF THE JACK CAUSING IT TO BREAK. THREW EE'S AGAINST CONCRETE SUPPORT BARRIER