Staircases

Stair cores below 18m means of escape.

The escaping occupants rely on having a relatively short escape route if they are to escape from their apartment to a place of safety. However the primary focus for “means of escape” is the protection of the stair core. This is normally served by an Openable Vent (OV) to the roof over both stairs cores, this OV is normally 1m² (Free Area).

When there is only one stair core to the building this must become an Automatically Opening Vent (AOV) controlled from a fire signal. The AOV must be a size of at least 1.5m² (Free Area).

Roof vents can not be a single opening flap unless it opens past 120º. Double flaps can be used or Louvre type blades. These units are normally insulated and “failsafe open” on power loss.

Stair cores over 18m Fire Service assistance.

At over 18m in height the stair core must be ventilated to each storey by a 1m² free area openable vent, OV. If vents are not on each level a 1.5m² (Free Area) roof vent must open automatically over the stair and have overrides available at access level and close to the vent itself.

Corridors and lobbies attached to stair cores with external elevations.

Once a lobby or corridor is longer than 4m or only has one direction of escape leading off the stair core, up to 7.5m long, an AOV measuring 1.5m² (Free Area) must be installed. This will provide some relief in the corridor, as well as adding protection to the stairs.

AOV’s to elevations (walls), are windows really but, should always open to 90º if side hung or hinged at the bottom of the window if they drop away from the frame. We can use chain drive actuators or pneumatics to open and close the vents.

Internal Corridors and lobbies requiring AOV’s.

If no external elevation is available an internal smoke shaft is used, or chimney to you and I, as an AOV replacement a shaft is required to have the same cross sectional area, i.e. 1.5m² (Free Area).

This is generally a builders work shaft constructed from block work and has smoke or fire dampers at each floor level (except ground generally). The vent/AOV/damper could take the form of a door opening into the shaft. At the head of the shaft is a roof vent, as is the case above the stair cores, and this opens with the fire floor damper. Unless this shaft extends at least one storey above the fire floor it will not serve that top floor effectively.

To save space on a 1.5m² (Free Area) naturally ventilating smoke shaft a mechanical solution can be offered, this is often 0.6m² (Free Area) and extracts of between 2.5m³/s for means of escape and no more than 5m³/s for fire service use.