I destroyed one of the walls on the staircase and walked above the ceiling of the bunker, turns out, the undergound isn't filled with anything, its just an empty void where basements are the only constructions and hitboxes.
On another note, generators power things 2 levels up and 2 levels down, so:
POWER
POWER
GENERATOR
POWER
POWER
Fumes only go upwards, and they do disipate. It takes a day or two. So
FUMES / NO POWER
FUMES / POWER
FUMES / POWER
GENERATOR
POWER
POWER
-X-
Think of it as hot gases going upwards untill reaching open air
I think you're missing out on the greater philosophical implications of it all. It isn't too too difficult to make a self sufficient base far away from any zombies, but it isn't very exciting. Then, if you make a base near the cities were it's more dangerous, it becomes, well, much more dangerous, while still being more exciting. The sort of Last Man on Earth, Night Eats the World sense of ennui that comes with a good end game base isn't something you see many zombie games explore.
I get your point, but it is important to remember, you are playing an unfinished product. It is unreasonable to expect it to answer all your wants, needs or desires. How many complete games have done that for you? That's a unicorn Pegasus.
Enjoy your opportunity to play it as is. Offer constructive feedback to make it better. Get bored and chase zeds. Get dead and start over or get over the boredom.
Or don't. But your comments are not shedding any light on anything new and they are therefore not constructive.
What I don't understand is why, when you have an easy answer for your own problem (and I'm not talking about installing mods), why don't you just apply the solution?