Brian Bell has an interesting note on as to whether or not it is real flames in Hell or just a figiure of speech:
"it seems it is a real torment, thus a real thirst, which desires real water, from a real finger, to touch his real tongue. So, I believe real flames. Is the fire spoken of literal fire? It is an accepted law of language that a figure of speech is less intense than the reality. If “fire” is merely a figurative expression, it must stand for some great reality, and if the reality is more intense than the figure, what an awful thing the punishment symbolized by fire must be."