Abstract: A security door construction for a doorway in a loading dock. The door is constructed of open materials, such as expanded metal mesh, and is mounted for movement between a closed and open position on tracks which are located adjacent the sides of the doorway. A safety beam or barrier is connected to the lower portion of the door and extends across the width of the doorway when the door is in the closed position. Fixed supports are mounted on the loading dock in position to be engaged by the ends of the barrier in the event the barrier is subjected to an impact, thereby preventing lateral deflection of the door by the external force and preventing heavy objects from falling through the doorway.