no real danger, nothing like wood-tar creosote. You can light the soot buildup on fire by creating a hot fire and opening the ashpan, the soot will ignite and burn, but, it is much lower intensity, it goes out as soon as the roaring fire below it is calmed, and is NOTHING like burning creosote from a wood fire. When I used my hand-fired stove i would wait until it was raining or the wind was blowing strongly and burn out the chimney about once/month; it is nothing like a "chimney fire". the soot would start glowing a little bit, and, after it burned down to 1/4" it would just go out. rarely if ever would I even be able to get the chimney itself to ignite, with the ashpan door wide open on a bed of glowing coals and the stove pipe temp around 900, it was almost impossible to actually get the soot inside the stack to glow, mostly any buildup was blown out from the heat and draft generated by the coalbed and what had started glowing in the stovepipe. don't worry about buildup from bit or subbit coals, it's almost completely non-flammable and even if you try to "burn the chimney" out you won't have a "chimney fire", but you will have a bunch of little soot balls down wind from your stack (do it when it's windy so they blow away or when it's raining/snowing).