All structures repair themselves to 50% life. All structure fires are automatically put out.
This all-in-one safety system automatically dispatches robotic drones to put out any fires and perform basic repairs on damaged structures. Although these drones are effective at doing basic repairs, they do not have a strong enough AI to perform the more delicate repairs needed to restore a structure past 50% structural integrity.
During development of StarCraft II, it was not known at first what tech buildings would be used to upgrade the terran arsenal. For the sake of having placeholder artwork, a task was given to update the armory so the building could be used in the meantime while artists waited for a design decision. The update was a simple translation of the sprite artwork of the original game to 3D. The armory was never challenged, and after the art was complete it made it all the way into the final release of the game.