Mission 10 in Regret is map 16-19. The level you indicate specifically is on map 18 (pretty much by itself, with a square empty room way off on the right).
Map 18 has 1022 objects on it. Since it's a non-dead object it can't be in one of the gumps (precompiled object sets that have no place for IDs to link objects), so that leaves 870.
The wall you're next to is shape 287 frame 0, or 808 frame 0 (wider). There are 6 instances of that exact wall on the map. But, doors are typically modeled separately from the walls that look identical, so the door is probably separate. The door model is 893 for the one on a top-left wall (but we're looking for the top right wall). The top-right one is 1244.
That's this line from the file:
00003070 7f 15 0f 6c 00 dd 04 00 00 00 11 00 00 00 01 04 |...l............|
This indicates the count value for that item is 0x11. That usually links up objects, so let's find the others with the same ID and see what objects we get. I've filtered on the ones with an id of 0x11 (or that might match), and drawn them below.
Hope this helps! Let me know if you figure it out. If I have to guess, it's the pressure plate behind the door... but that implies something else is the entry into that room.
The squares with setp in it - I have no idea what those are.
The two guns, the generator at the bottom, and the three squares in the middle match the 0x11 but not exactly. The rest matches exactly.