Ralph first decides that a group of boys needs to watch the fire. This comes immediately after they light the first blaze, in Chapter 2. Ralph says: “We’ve got to have special people for looking after the fire." (58). But he doesn't order them at first. In fact, Jack offers his hunters to be the watchers: “Ralph, I’ll split up the choir–my hunters, that is–into groups, and we’ll be responsible for keeping the fire going–” (59). So Jack takes the first step, which the other boys see as generous.
However, in the next chapter, we see that they have already begun neglecting the fire. When Jack returns from hunting, Ralph tells him that the most important thing is to be rescued. Jack responds derisively, saying “You and your fire!” (74). the tension between the two characters is mounting, & it seems evident that it will come to a climax. This occurs when Jack and the hunters kill their first pig. Ralph has seen a ship in the meantime, and discovers that the fire is out. He is obviously upset.
“There was a ship. Out there. You said you’d keep the fire going and you let it out!” He took a step toward Jack, who turned and faced him. (99)
Jack blusters, attempting to save face based on the fact that the hunters have brought meat. none of the other boys (except perhaps Piggy) can fathom why Ralph is so upset. The true realization of what they missed hasn't hit them yet. Ralph struggles to explain in the face of this challenge to his authority.
“I was chief, and you were going to do what I said. You talk. But you can’t even build huts—then you go off hunting and let out the fire—”(99)
But Jack apologizes, and the other boys suddenly side with him. It is on Ralph to unravel the dynamics of this group, & he doesn't fully grasp the shift in power that has occurred. He does the best he can, with one weak order: “All right. Light the fire.” (102)
All of my quotes come an e-text version of the novel (see the link below). Therefore, the page numbers are quite different than a print version.