Hola NSEU -
xxx
A severe pressure differencial inbalance between Upper Deck and Main Deck...
Would lead to a complete (structural) collapse of the floor.
xxx
I have flown 747F, 747C and 747SF. Does not matter if not 400s.
A collapse of the upper deck floor would would impede/destroy cables.
Cables linking flight deck to all tail flight controls hydraulic units.
xxx
Relief panels are installed between the
three decks.
Upper, main deck and lower lobe.
What "book" are you reading...? Only read Boeing or airline own manuals.
When I puffed my Marlboros in the flight deck, the smoke went to outflow valves...
Under the plane's belly, through each separate floor...
xxx
Happy contrails