The most common sense of inferno in English, when used as a common noun rather than with reference to Dante’s poem, is “large conflagration.” But why? Because of the traditional (and biblical) image of hell-fire, of course — but why is the Italian word inferno, which entered English through Dante, used this way when hell so rarely is? Those who have read Dante’s Inferno know that fire hardly figures in it at all; and of course etymologically inferno simply means “underworld” (related to inferior and infra-). No one would dream of calling a conflagration a “towering underworld.”
Nevertheless, the word inferno is inextricably linked with the idea of a conflagration — so much so that some publishers simply must have a fire on the cover of Dante and aren’t too picky about what kind of fire it is. Here’s the Collins Classics edition:
Notice anything strange about that picture? Why is a horse burning in hell? Because this wasn’t originally meant to be a picture of hell at all. It’s Johann Georg Trautmann’s painting View of the Burning Troy. You will search Dante in vain for anything resembling this scene. But it shows “an inferno” — a conflagration — and was thus deemed appropriate.
My theory is that English-speakers are subconsciously influenced by the phonetic resemblance of inferno to furnace, with perhaps echoes of fire, burn, and incinerate as well.