I’ve never experienced a chimney fire, so what is the danger in leaving it alone till it runs out of fuel? Can it spread to the rest of the house somehow?
Simple answer is it certainly can. Chimney fires can be slow burners or the type where flames are shooting three or four feet out of the chimney which might look spectacular but there is an awful lot of heat produced which can damage the chimney inners, create cracks and then the heat can cause fires internally. The slow burning fire in a chimney may not be so alarming as the first but there is still a considerable amount of heat built up. Different materials in a house have different combustion ranges, depending on the heat given off, materials will first start to smoke, known as Pyrolysis, this smoke is a gas and will ignite. Its the build up of this in house fires that suddenly turns a small fire in a corner into a huge ignition known as Flashover when the whole room becomes engulfed, extremely frightening to watch. In chimneys its the build up of not soot but Creosote, this is caused by the hot fire gases cooling during the upward draft of the chimney during every day use. Regular cleaning removes this but if its left and a chimney fire begins then its the Creosote that catches and depending on the amount burning to what is seen from outside. When I first started at Tyne and Wear Fire Training Centre we used 40ft containers as Fire Behaviour training exercises. They would have the bottom end of the container walled with sheets of Chipboard, set alight by using two small wigwam style fires until the boards were all burning well. Then the fire crews would go in and carry out hose techniques to quell the fire just as they would in a building. The walls of the containers were all covered in this black sticky Creosote which had to be avoided with bare skin and I was also told it contained traces of Formaldehyde, so nasty stuff. I have to say guys I done a lot of stuff with fires during my time as a Fireground Supervisor there and fire still scares the life out of me, have a look at your local Fire Service Facebook site they have lots of safety info, not only on fires but other hazards, everyone should have a fire escape plan for their home. Anyway hope that helped answer the chimney fire thing, fortunately coal fires are rare these days and burning chimney’s not so common. Franky.