Looking at the two answers above I cast my vote for the second: Since there is no actual fire involved, it is a metaphor - the 'fire' stands here for something else. What that is we can't know without knowing the context, but I would agree that it could be something like intense energy or intense anger or some other kind of strong emotion. (In contrast, we call personification any kind of figurative speech that assigns human qualities to non-human beings or inanimate things but the phrase you provided didn't include any context like that).