The speaker is looking at a house slowly filling up with books, stacked wherever there's room. The title, "Fire hazard," suggests the clutter might be a real danger, and the poem seems to admit that. But the speaker isn't apologetic. "I will get more," he says, flatly, as if the matter is already settled.
The middle lines explain why. Books are "sweepstakes," a chance at winning something unexpected, and "infinite ships," ways of travelling anywhere. Both images treat a book as an open possibility rather than an object taking up space.
The ending turns the title around. Books "might be the best fire / with which to see." Fire is the danger, but it is also light. Here the books become a source of illumination, a way of seeing more clearly. The mood is playful and quietly stubborn, a small defense of a habit that looks messy from the outside but feels essential from within.