Montag's job in Fahrenheit 451 is that of a fireman. He is charged with the task of burning books. This act is done in the hopes of calming the masses by eliminating material that may drive them to express themselves in a negative manner. At the beginning of the novel, Montag does not mind his job; he just does what he is told without question.
Then after meeting a young woman named Clarisse, he begins to change. She questions his role as firefighter which causes him to question what he does for a living. Montag soon realizes that everyone is dulled into a false sense of happiness. This is achieved through the removal of the things which could stimulate people mentally and so forth, namely the books he is burning at work.
The opening line of Fahrenheit 451 describes Montag's feelings about his job:
"It was a pleasure to burn. It was a special pleasure to see things eaten, to see things blackened, and changed" (3).
Initially, Montag is proud to be a fireman. He upholds the law by burning the houses of those who own books, and, of course, he burns the books as well.
When he meets a teenaged girl named Clarisse, he tells her that kerosene "is nothing but perfume to me" (6). This shows that Montag not only likes his job, but he fancies it to the point of loving the smell of the thing that helps to start the fires. When the girl presses him further to discuss his job, Montag proudly says that "It's fine work" (8). All he really has to do is show up to people's houses, burn books, then the house, and return to the fire station. Usually, the police arrest the owners of the home before the firemen arrive, so Montag doesn't see that he is hurting people in his line of work. It's just fun to burn things down, and he's been doing it for ten years.
After meeting Clarisse, who challenges his current state of mind about life and his job, he also sees a woman burn herself for her books. Apparently, the police didn't get to the old woman and arrest her before the firemen arrive at the scene. Montag is so mentally disturbed to witness the old woman's suicide that he goes home and throws up. Based on his experiences with Clarisse and the old woman, Montag changes and doesn't see his job as so noble anymore, and that is where the rest of the story begins.