A friend of mine welded a pigeon box on to my roof and I stood inside to put any fires out...there weren't any; the insulation melted, but there was no fire. Same for a roof patch where the flue had damaged the roof (diameter of patch bigger than the flue) and I welded a patch on to an old chimney flue hole in the engine room (smaller than the other one at about 4inches in diameter) last winter which melted the insulation but no fires.
I am not recommending not removing the insulation, I am just saying.....