What do u do this and other details tell you about the setting of the novel? The man with the megaphone was helping them evacuate, and they thought he had authority then when ralph blew the shell they thought he was an authority figure.
The first time the fire gets out of control it is purely unintentional - they have set a signal fire. The second time the fire gets away from them, they have started it to smoke out Ralph. The boys go from using fire as a form of civility to using it as a form of savagery.
The part of the speech where it is most expressive is often stressed in iambic pentameter. The lines that make use of this format contain rhythm and are cleverly written to convey a feeling or a description. Dialogues and soliloquy appear poetic because of this meter.
