A smoke tower is an external stairwell, of fire-resistant material, terminating at ground level, and principally intended for the use of firefighters in accessing an interior building fire. It is not intended for occupant evacuation and does not count in the building code requirements for evacuation capacity. 
More recent smoke towers pressurized to keep out smoke, but fire damage may prevent the pressurization mechanism from working.  Once the firefighters arrive at the fire location, the need to open doors into the interior, so hoses can enter, can defeat the power of the pressurizing fans. With open doors, the fans may also provide oxygen to the fire. 
A 1965 revision of the New York City building code removed a requirement for smoke towers in high-rise buildings. Evacuation of the World Trade Center buildings was slowed because emergency service personnel entering the building competed for stairwell space with civilians evacuating.
- New York Building Code (1938), quoted in "NIST NCSTAR 1-7: Occupant Behavior, Egress, and Emergency Communication", Reports of the Federal Building and Fire Investigation of the World Trade Center Disaster, p. 18
- J. Gordon Routley, Interstate Bank Building Fire, Los Angeles, California (May 4, 1988), United States Fire Administration, Federal Emergency Management Agency, Report 022 of the Major Fires Investigation Project
- Curtis S.D. Massey (July 2005), "Understanding the Core: Part 2", Firehouse Magazine