I have never heard of a chimney fire in a coal burning system either, clogging up and suffocating the people in the house but never burning it down. The creosote is a gooey mix that once started burns very hot, like the above poster says try burning the soot and see what happens.
I have burned all types of wood in my house, and built a rumsford fireplace/insert, burned for over thirty years and have never once cleaned the chimney. I check it with a mirror and it is always clean. IT is not air tight by any means or that efficient and the chimney goes right up the center of the house which is insulated and open in the attic. The chimney heats the second floor. So if any creosote is there is doesn't condense on the liner apparently. hope this isn't too off topic. kevin