3 EE'S WERE USING A MECHANICAL SCREW JACK TO RAISE A PORTION OF THE CONE CRUSHER & SCREEN DECK FOR LEVELING PURPOSES. JACK BASE PLACEMENT WAS ON A PIECE OF STEEL I-BEAM 5 1/4"" WIDE. JACK BASE WAS 6 1/2"" CIRCUMFERENCE. JACK BASE NOT SUPPORTED SQUARELY ON A FIRM LIFTING SURFACE. EE'S USED 94"" CHEATER BAR TO PUT PRESSURE ON JACK BASE, CAUSING BASE TO BREAK & THROW EE'S AGAINST BARRIER