EE CLEANING 4' DEEP FORMS ON SLIPFORM DECK. THE 3' X 8' DOOR WAS USED TO COVER OPENINGS OF FORMS. THIS DOOR WAS RAISED TO CLEAN. ANOTHER WORKER IN AREA HAD A 6' STEPLADDER ON DOOR SIDE. THE EE KNOCKED THE LADDER OVER WHICH HIT THE FORM DOOR, THEN THE DOOR HIT EE IN FORM. THE INJURED EE LOST HARD HAT FROM THE FORCE OF IMPACT.