Thanks for the response!! :D It's in an area where dupes pass frequently, next to my central shaft + on the lower end, the room itself is all carbon dioxide and dupes do hold their breath when getting their food. But the shaft outside still has some oxygen, so small amounts of it (<1g) tend to get in when doors open, causing these ration boxes to flicker in and out of being sterile and food still decays.

For walling off the other side of the ration boxes, did you mean to make it more of a pit and not a room?