How to "unjam" the door in the mess hall? Black Plague

[Cambium29]

I'm near the begining of the game (in the three rooms after the trusted blood door). I've looked through the kitchen and the office with the projector, put the disk in the computer, but can't find a clue as to how to open the jammed door in the mess hall. I don't have any tools. Is this the only way out of these rooms? Is there another way? The drain grate perhaps? Thanks!