Smoke stacks are deceptive beasts:  They produce mainly steam, not smoke, and what you see from the outside is not the actual stack.  I did not understand that until I had the chance to take a tiny elevator up the side.  I learned that they consist of two distinct columns:  a liner and a shell.  The liner can be made of brick or fiberglass, and it carries gases into the atmosphere.  The shell is typically concrete, shielding the liner from wind and weather.  There is a small space between the two layers, with access points along the way up for monitoring and repair services.  This photo was taken at 500-feet elevation, looking straight down between the liner and the shell, with two access grates clearly visible below.