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The fireball sets fire to combustibles and damages objects in the area. It can melt metals with low melting points, such as lead, gold, copper, silver, and bronze.
However, on perusing the DMG we find this under The Environment section:
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Characters exposed to burning oil, bonfires, and noninstantaneous magic fires might find their clothes, hair, or equipment on fire. Spells with an instantaneous duration don’t normally set a character on fire, since the heat and flame from these come and go in a flash.