Had one ONCE, I always have two 2’ft tall fire extinguishers in shop at all times. Heard the rumbling looked out side yup chimney fire ripped clean out door off chimney and discharged both extinguishers up flue. Fire out except crap below clean out door poured water on that. Flue liner was fubar, rebuilding a chimney in January not fun. Most of it is inside but you know shingles, flashing, hording and heating. Lesson learned don’t go by time line use a mirror, look up clean out regularly