"To Build a Fire" is written in the Naturalist and Realist styles, where events and prose are detailed realistically. This means that there are not many metaphors; there are no need for them, as the reader is presented with exactly what is on the page, without comment or interpretation. For example, in the introductory paragraph, the omniscient narrator states:
It was a clear day, and yet there seemed an intangible pall over the face of things, a subtle gloom that made the day dark, and that was due to the absence of sun.
This is in contrast to a metaphorical reading of the dark-yet-clear day, which might compare it to, for example, a clear pond which is still opaque in its deeper areas.
One good example, one of the very few that exist in this story, refers to the customary tone that men use to talk to their sled-dogs. Since the dogs are working animals, the men do not speak to it as a pet, but as an employee or slave, and the dog has associated the sounds of human voices with punishment.
His erect position in itself started to drive the webs of suspicion from the dog's mind; and when he spoke peremptorily, with the sound of whip-lashes in his voice, the dog rendered its customary allegiance and came to him.
(London, "To Build a Fire," jacklondons.net)
The man's voice is not literally built of whip-lashes, nor does it sound like one. However, since it symbolizes the sting and sound of the whip to the dog, it is likened to that consequence. The man's voice is one of the things that make him an unsympathetic protagonist; since he doesn't care about the dog, or about anything but the "Real," it is hard to empathize with his situation. When he thinks about killing the dog to use its warmth, the reader sees the ultimate pragmatism of his position; his voice, equated with whips, is not comforting to the dog, and so both the reader and the dog understand that his intent is entirely selfish.
In his article "To Build a Fire" a Physical Fiction and Metaphysical Critics Charles E. May comments and disagrees with a statement that "To Build a Fire" is "a masterpiece of a short fiction"(20). Literary critics claimed that London used many metaphors in this work such as "sun-fire-life" or "cold-darkness-depression-death"(20), but May argues that this story should be read and interpreted literally and does not contain deep, dual or metaphorical meaning. He says: "For Jack London and consequently for the reader, the man in the story is simply a living body, the cold is simply a physical fact"(22). What is more article's author strongly disagrees with the critic, who compares the theme of the story to a theme of a classical tragedy. May sarcastically states that the only visible similarity in terms of theme would be the issue of protagonist's death(22).
I think that "To Build a Fire" story relates to many issues hidden behind a superficial plot. The story takes place in a very severe winter; the man under appreciates the dangers of nature forces and struggles to return to camp. He is warned about possible dangers, but he is also too pride and too self-confident to take the advice into consideration. The protagonist is accompanied by a dog. The man tries to survive, but forces of nature are stronger and he dies.