These the Blast Doors that were left out of .993b, they replace the current doors you see ingame. They add a nice touch to the structures.
This is not an official update, the download is completely optional. If you would like to see the new doors, than you can download them, if you like the current ones, then you might want to just ignore this. If you don't like the Blast Doors, just delete the w3d file from your data folder, do not post anything about them in the forums, it's up to you if you want to use them or not.
Download the Blast Doors here.
See more details here.