A hyperbole is a type of rhetorical device or figure of speech that describes something by exaggerating it. The main reason why an author might employ such a device is because he wants a word or a certain description to be dramatic and have a lot of impact. In this case, the author says that his father fought "a couple of million fires." This is an example of hyperbole, as the number is certainly an exaggeration, and is instead intended to create a dramatic effect.
