No need to do the calculations for a collision with the walls of smoke inside the building, it is necessary to gradually fill the cose room with smoke, and the smoke from the windows, above the smoke out of the room did not go through walls, don't foget wind inside the rooms = 0!, make it transparent outside and plus gradually fill the room with smoke, and the smoke sources from the windows and open! doors. Smoke outside shall not penetrate into buildings, make it transparent inside part.