Green Roofs and Fireworks
Practically all dry organic materials are combustible at relative low temperatures. Roof shingles or many waterproofing membranes on roofs are typically petroleum-based products (including Asphalt) and there is hardly any difference to dry organic materials. Some products are equipped with chemical fire retardants that could decrease the risk of spreading fire, unfortunately not the risk of leaks cause by heat and impact.
The living vegetation of fully functional and well-engineered green roofs contains moisture and most plants (especially succulent plants on large extensive green roofs) have a fraction of the energetic potential comparing to all other components used in a building. The green roof growing media (soil for the green roof plants) is a blend of different mineral components with an organic content of typically less that 15%. It is practically impossible to set this material on fire – even when the natural moisture content is not considered.
Fires or leaks on non-vegetated roofs caused by consumer or display fireworks could have been prevented if the building would have had a fully functional green roof without mono-culture vegetation, or if conventional roofs would be well-maintained (regular removing of organic debris from the roof and gutters).
Certainly a fire is the worst-case scenario; however in most cases smoldering firework parts (and cigarettes) are only causing leaks on unprotected roofs that are discovered much later and relate to costly repair. Roof warranties typically don't cover any sort of mechanical impact and they are -again- worthless. See blog post from 2014.