To squeak:
The fireplace does not belong to you-it belongs to the building, and you have no right to put a sukkah there, especially if it endangers other people in the event of a fire. Dina Malchusa dina – the laws of the land (in this case the fire department) must be followed, even if it means you might have to walk a few blocks to use your shul’s sukkah instead. And BTW although I vehemntly disagree with your viewpoint of a sukkah on a fireplace, I don’t see what that hasanything to do with oppostion to kapparos.