A NEW REGULATOR WAS BUILT TO REPLACE THE DAMAGED REGULATOR. THE EMPLOYEE STATED THAT AFTER THE DAMAGED REGULATOR WAS KNOCKED OUT HE WAS MOVING THE MATERIAL AND STACKING ON THE RIB TO CLEAR A WALKWAY. AS HE PICKED UP A BLOCK HE TURNED TO STACK ON THE RIB WHEN HE FELT A PAIN IN HIS LOWER RIGHT BACK.