The role of fire with respect to Ralph's tribe, is associated with positive benefits, warmth, rescue signals, and cooking, yet in Ralph's it is used for more destructive purposes-he uses fire as an agent to flush his foes out into the open to slaughter.

The destructive descent of the use of fire begins with the death of the small boy, the boys were careless and inattentive to the power and force of fire, and failed to respect the power.

Finally, the fire ends with a positive fire, the destructive fire that destroys the island brings rescue, thus ending the savagery on the island.

What is the symbolic role of the fire that destroys the island in Lord of the Flies?

I think there are a number of ways you can look at the fire as a symbol.  One of them is mentioned in the previous post, the idea that Ralph was always pushing the fire as super important, as their way to be rescued.  Of course their rescuers are part of the same world that is consumed with violence and destruction, so it is ironic that Ralph's fire eventually consumes everything on the island but also brings the return of "civilization" in the form of the officer and the other men from the navy.  This is particularly brought into focus by the officer's remark about the fact that they are "all British boys" and that they would have been able to hold things together, as though they were civilized and not going to end up like these savages that he sees.

What is the symbolic role of the raging fire that kills the small boy in Lord of the Flies?

Fire is a yardstick for measuring the savagery and loss of civilization of the boys. At the beginning, the signal fire represents the wish of the boys to return to society. The forest fire they set symbolizes the distance between the boys at the beginning of the story and the boys later in the book when they are further along their path of completely abandoning society and its rules of behavior. By the end of the book, the fire they set trying to capture Ralph represents their savagery and complete abandonment of civilization.

What is the symbolic role of the fire changing between Jack's tribe and Ralph's in Lord of the Flies?

To Ralph, fire represents all the he stands for as leader: survival and rescue.  This is evident in Ralph's use of fire on top of the mountain with lots of green branches and a constant watchman in order to produce smoke that can be seen.

To Jack, fire represents all the primal urges.  Jack makes small fires along the beach to quickly cook pigs; he isn't interested in wasting man power on a large signal fire.  Of course at the end he uses an enormous fire to attempt to kill Ralph.