The rising action in the book starts when Montag meets Clarisse for the first time, and it continues at a steady pace until the moment when Montag reads poetry to the visiting women. Until the final climax, the action between the poetry scene and Montag's confrontation with Beatty is held at a roughly level plane; Montag knows that he is going to be discovered but he can't do anything to avoid it. Essentially, Montag's personal journey of self-discovery provides most of the rising action, and as he comes to terms with his own individualism, the action levels and starts to fall.
Of course I'm happy. What does she think? I'm not? he asked the quiet rooms. He stood looking up at the ventilator grille in the hall and suddenly remembered that something lay hidden behind the grille, something that seemed to peer down at him now. He moved his eyes quickly away.
(Bradbury, Fahrenheit 451, Google Books)
This moment, which foreshadows Montag's revelation that he has been stealing books for years, is the start of the rising action. His unease in the society, which has informed and shaped his opinions all his life, allows the reader to feel equally uncomfortable, and each revelation adds to this discomfort. The rising action of Montag's mind is echoed by the events in his life: the old woman who will not leave her books, his sadness at Clarisse's death, his sudden understanding of what the firemen actually do. Each moment is part of Montag's personal journey, and so the rising action follows his individual development.