First and foremost, this question is purely for my curiosity only; I am not about to question what the fireman told my brother (even if I did, my brother is several hundred miles away).
My brother’s house has a chimney sticking up from the side of it (i.e. it doesn’t go through the roof, it goes up the side of the house and beside the roof). He had a chimney fire a while back requiring the services of the local fire department to put it out, but there was no house damage. The chimney is now badly cracked.
The fire department was quite definite that he must not use the chimney until it is replaced (no big deal - he just has to use only his natural gas heating for now instead of heating by wood much of the time as he likes to).
Why can’t he use the cracked chimney? Wouldn’t it just mean smoke would leak out the sides a bit rather than just come out the top? Or is the fear that it would catch fire again?