INJURED AND 2 OTHER MEN WERE TRANSFERRING A PACKAGE OF PRE-FABRICATED TRACK AIR DOOR FROM A SUPPLY CAR TO A SCOOP. ONE MAN WAS ON EACH END AND ONE IN THE MIDDLE. AS THEY WERE PLACING THE MATER IAL ONTO THE SCOOP THE MIDDLE MAN LOST HIS GRIP CAUSING THE WEIGHT TO SHIFT TO INJURED'S END. HE COULDN'T HOLD ON AND THE ACTION CAUGHT HIS HAND AGAINST SCOOP.