Fire is a prominent allegory in a book about book burning. In the beginning of the book, fire is quite destructive. It is used to destroy physical books yes, but book burning represents so much more. With the destruction of the books comes a destruction of historical knowledge, ideas, concepts, teachings, philosophies, etc. Beatty loves burning the books, because in his opinion they represent a whole host of contradictory meanings. Beatty does not like that. Other fire references come in the form of anger. Anger has a tendency to make people "burn with rage."
Later in the novel though, Montag learns that fire is not only destructive, but can be beneficial. After he escapes from the hound, Montag is warmed by the fire. It's not used to hurt, maim, and destroy, but to illuminate and heal. What's great about this realization is that it brings fire back to what Beatty hates so much about books. Beatty can't stand that books don't give a clear cut answer and are so full of contradiction. Fire, being both constructive and destructive, shows that it (like books) are open for interpretation and multiple uses. Think Yin and Yang.
Another allegorical reference are the animal-like machines. Stomach pumping machine like a snake, helicopters like insects, etc. In each case, it's a man made machine trying to mimic nature. Perhaps it's a comment on how destructive technologies are upsetting the natural balance of things. Maybe another Yin and Yang concept?
Fire can also be an allegory for not only death, but rebirth. In the beginning of Fahrenheit 451, fire is what Montag and other firemen use to destroy books and the ideas and concepts that they bring. Towards the end, Montag realizes that fire can also represent strength and warmth. The chapter is also called "Burning Bright", giving a more positive connotation to a symbol that was seen as destructive in previous chapters. When Montag escapes the Mechanical Hound, he finds a fire. He realizes that this fire, unlike previous ones, was used to warm people, not to burn things down. This eventually leads him to Granger and the former intellectuals to rebuild the city.