THREE EMPLOYEES WERE REBUILDING THE UNDERCARRIAGE ON A HITACHI BACKHOE. TWO WERE UNLOADING THE NEW UNDERCARRIAGE PARTS AND THE THIRD TURNED AND WAS WALKING AWAY FROM THEM. ONE OF THE CARRIAGE ROLLERS ROLLED OFF THE TRUCK AND STRUCK ANOTHER ROLLER THAT WAS LAYING ON THE GROUND. WHEN THE 2 ROLLERS HIT, A SMALL SLIVER OF METAL SHOT OFF & HIT THE THIRD EE WHO WAS ABOUT 20' AWAY.