Hell is not literal fire, that is a metaphor. Hell is eternal separation from God, with all that implies.
God is the source of all light, the source of all truth, the source of all life, the source of all love. Being cut off from the source of all light, truth, life and love for all eternity is what hell is. It's actually much worse than fire, if you think about it.
This is not a decision God makes. If you read the Parable of the Prodigal Son, God wants us all back, no matter how much we've done wrong, or how long we've been gone.
Atheist objections that somehow God is to blame for people's decision to reject him are illogical. The decision to reject God must be possible as a consequence of free will.
Then it's a tautology. If God permeates the universe, you can't exactly step off the universe.
Or, to look at it another way, you're separated from God right now (unless you hear someone speaking to you that no one else can hear, in which case I'd suggest that's probably not God), and you're doing just fine.
The idea that finite created beings can comprehend the intentions of That Which Created Them because of something they read in a book is...mind-boggling.
And I say this as someone raised in a fundamentalist religion.