[Jordan Baker]

This sums it up well. Basically pyrolysis is the conversion and off gassing of and item to a gas due to application of heat and results in charring. It’s like a piece of wood doesn’t actually burn when in a fire. Heat converts the wood to a gas and that is what is actually burning. The same for tires when the rim is heated to whatever temps needed for the rubber to start the off gassing process. Except when a tire is mounted to a rim that gas has no where to go and builds up until something fails. Think of car tyres exploding during a car fire. This is the fire fighter in me coming out.