Situational and dramatic irony are both present in "To Build a Fire."

Dramatic irony occurs when a reader has more information or knowledge about a character or situation than a particular character within the story does. This story is told from the third-person narrative perspective. Consequently, we know that it is much colder than the man thinks it is. The narrator even goes so far as to point out that the man was ignorant of exactly how dangerous the cold was. Even the dog is aware of the danger. We, the reader, know the man is in trouble, yet he never realizes the danger that he is in until it is too late.

The situational irony occurs when the man lights the fire under the tree, and the man (and the reader) thinks everything is going to be okay. He was in grave danger, but he managed to avoid certain death. Then the unexpected happens. Snow from the tree falls on the fire and completely extinguishes it, along with most of the man's hope for survival.