The symbolism of fire has a lot of importance in Nolan's Dark Knight trilogy - consider the flaming bat symbol, or the "the fire rises" mantra in The Dark Knight Rises - and it's never more subtly deployed than when Batman unwittingly creates Two Face in The Dark Knight When Batman is tricked into saving Harvey Dent, but fails to stop him being horribly disfigured, the flame transforms him forms the unmistakable shape of the Batman logo for a brief flash in close-up. That might seem accidental, but when you consider the imagery it becomes less so - the implication is that Batman's choice (though unintentional) created Two Face, and that the scars Dent wears are wholly because of him. In that respect it becomes a lot easier to accept Dent's psychosis.
