What is a smoke shaft?

‘Smoke shaft’ is the common term for ventilation systems in the lobbies of tall buildings, used to maintain tenable conditions in the common escape routes in the event of a fire in the building. They are essentially a simple ventilation system designed to extract any smoke leaking into a common lobby to protect the escape stairs. Typically, a vertical builder’s work duct rising through the building would be used to extract smoke from the lobbies. Each lobby would have a damper connected to the builder’s work duct.

For natural shafts, the head of the shaft is terminated with an automatic opening ventilator (AOV). Mechanical shafts use extract fans, mounted on the roof and connected to the builder’s work duct with sheet metal ducting. An AOV would be mounted at the top of the stairwell and the complete system would be controlled by an addressable control system that provides automatic operation of the ventilation by interface with the fire alarm system or smoke detectors.

A provisional design can be achieved in minutes by selecting modular components:

  • Builder’s work shaft
  • Lobby vent
  • Roof extract unit
  • Control system

So, how does this eliminate smoke from a lobby?

  1. Smoke detector detects smoke which initiates the smoke shaft
  2. Lobby vent to the smoke extract shaft opens
  3. Folding arm actuator opens the door to the stairwell
  4. Stairwell vent opens to allow fresh air to enter
  5. On the roof, the fans in the smoke extract unit begin to remove smoke via the smoke extract shaft
  6. Fresh air is drawn into the stairwell
  7. Smoke in the lobby is removed via the smoke extract shaft
  8. The system becomes ready for firefighters


Share this post: