I should have known it wouldn't be that simple.
...if this requires the key from Level I I'm going to be very mad at you. (Don't worry, I'm sure it can't be that!)Alright, time to pause and reflect:
1: This room is NOT electrically connected to the previous room, so the BRB will have no effect on this door.
2: There is a small "tunnel" or "hallway" in the corner of the metal plate (between the slits and the white floor on the sides) allowing for safe(ish) passage from one end to the other. This is confirmed to exist on the right side of the room (using the initial image for left/right reference). The same can be assumed to exist on the left side, but shoe-probing would be the safest way to confirm this (rather than just crawling blindly).
3: There is an easier way to get across.
4: There is presumably something on the other side of this door that will allow us to walk safely to the Stage VII door.
5: The (standard) door is locked.
6: There is "nothing of interest on or around the [locked] door".
7: The Metal Room is slowly filling up with Ozone, but here in The Hallway we are safe from it (because the Stage VI door is closed).
**: We need to find some way to open this door. The opening of the door may or may not be linked to the "easier way" to get across the room.
I'm going to do a thorough search of this side of The Hallway; floor, ceiling, walls, door. I'll tap on things with my shoe (I'll take if off again for this), listening for hollow spots or hidden panels. I'll make sure to not go over the metal panel, or the white space on either side of it, however; I've been burnt enough today.