Why Doesn't Plastic Catch Fire Easily?Watch
Is that even true. Many plastics have been removed from certain applications or are required to be treated with protecting agent before being used in consumer product because of their flammability. Expanded polystyrene, polyurethane foam, nylon textiles even pvc cable insulation all have fire risk issues.
These are hydrocarbon polymers, we use hydrocarbons as fuels essentially... Polymers are only dangerous once a temperature is reached that allows decomposition and ignition of the respective monomer (over simplification).