Typically a shaft passes through multiple levels of a building with a damper or similar device on each level so as to control the direction in which the smoke is going to flow from the fire through into the shaft and out of the building.
Shaft systems can be designed to ventilate fire-fighting lobbies so as to assist fire-fighting operations from a fire-fighting shaft, and also to ventilate common corridors in high rise residential developments.
Types of buildings where fire-fighting stairs are required
Fire-fighting stairs are required where the building has a storey higher than 18m above the Fire Service access level or where basement levels are more than 10m below the Fire Service access level.They are also required in some classes of building when they have a storey higher than 7.5m and a footprint of greater than 900m2 . If no fire-fighting stairs are needed and it is not a residential building, then there is no requirement for shaft type systems.
Ventilating fire-fighting lobbies is an essential part of the fire-safety strategy
When fire fighters arrive at a multi-storey building, they are going to need clear access to whatever level the fire is on. The normal protocol is to take a lift to a floor somewhere below the fire floor (maybe the floor below), connect to the dry riser and then drag the hose up the stairs to the fire floor. They then open the door to the firefighting lobby and then from there go through to fight the fire.
This means that the staircase needs to fully protected, both so that the fire fighters can use the staircase to access the fire and also so that if things go wrong to allow them to retreat quickly and safely by using the stairs. The aim is to prevent, as far as possible, any smoke spreading to the staircase and, if possible, to improve conditions in the fire-fighting lobby as well, although it is protecting the stairs which is the really important issue.