Smoke control systems for multi-storey residential buildings
Smoke control systems are required in multi-storey residential buildings, principally to protect the stairs to assist escape in the event of a fire, in compliance with the recommendations of Approved Document B and BS 9991:2011.
Aims and principles
In multi-storey residential buildings, the main escape route is always via common corridors and/or lobbies into the stairs. The aim is to keep stairs reasonably free of smoke and to improve conditions in corridors and lobbies opening onto the stairs.
When the door to the apartment which is on fire is open (typically for occupants to escape), a significant amount of smoke can quickly fill a corridor or lobby, making escape difficult for occupants. So legislation limits the distance between fire doors in corridors to 30m and the length of dead-end corridors to 7.5m to limit the distance people may have to travel through smoke. (BS 9991 permits 15m if the apartments are sprinklered).
If this smoke enters the stairs it can also make escape difficult for occupants of other storeys and hamper fire service entry and deployment. Smoke control systems are provided for each stair and for the lobbies or corridors opening onto each stair in order to stop smoke from spreading to the stairs. Ventilation may be either natural or mechanical, or alternatively a pressurisation system may be used.
Tall and deep buildings
Furthermore, there is a requirement for buildings with a floor more than 18m above fire service access level or with a basement more than 10m below it to have a protected fire-fighting core with a firefighting lift. Certain other buildings just require a fire-fighting core. The requirements are set out in ADB and BS 9999. However in residential buildings ADB does not require a firefighting lobby or the higher performance ventilation such a lobby would require.
Protection for the stairs
Stairs are generally ventilated by a 1.5 m2 automatic stairwell ventilator (AOV) at the head of the stairs.
For corridors with external walls – use OVs and AOVs
Natural ventilation is the simplest and most cost effective choice where a ventilated corridor or lobby extends to an external wall.
In this instance a 1.5 m2 Corridor AOV (Automatic Opening Ventilator) or Corridor OV (Opening Ventilator) may be used at each level. AOVs are required when there is only access to a single stair. OVs are permitted when there is access to multiple stairs, but as the AOV at the head of the stair needs to open automatically whenever an OV is opened, it is common practice to use an AOV in any case. Typical AOVs include Coltlite louvred ventilators and Kameleon casement ventilators.
For corridors which are enclosed – use ventilation shafts
If there is no external wall adjacent to the corridor, a single vertical smoke shaft may be installed through the building serving each level, with a natural ventilator (such as the Colt Seefire ventilator) at the top of the shaft.
Smoke enters the shaft from the corridor either through a smoke damper with a decorative grille, or through an actuated fire rated door.
Shafts can be either natural or mechanical
Shaft systems can be either a Standard Smoke Shaft as described in Approved Document B or a Colt Mechanical Shaft.
A Standard Shaft (natural ventilation shaft) requires a 1.0m² OV (openable ventilator) at each lobby opening into a 1.5m² shaft which is open at the top. The shaft is fully automatic in operation.
Mechanical shafts can reduce costs and increase reliability
A mechanical shaft is often used to reduce the required shaft cross section, trading the additional costs for the space saving. The Colt Mechanical Shaft uses a fan system to draw smoke out of the fire fighting lobby (fire ventilation) and requires a smaller shaft, which can be as small as only 0.6m².
In addition the Colt Mechanical Shaft can perform better than a Standard Shaft since it extracts at a defined rate - this means that it is unaffected by external wind pressures. It is also less susceptible to obstructions to the airflow within the duct.
We offer a Colt Shaft Variable or a Colt Shaft Constant.
In addition, if it is desirable to extend the travel distance from the apartment door to the staircase, then the Colt Shaft Extended Corridor system may be used.
All shaft systems extract from the lobby or corridor opening onto the stairs and require a stairwell vent at the head of the stairs.
A pressurisation system may be used in place of natural ventilators or shaft systems and generally provides better protection. An air supply system maintains a positive air pressure in the staircase, which prevents smoke from entering it from the fire location. Excess air pressure needs to be avoided, either by fan speed control or by pressure relief from the staircase. An air leakage path from the non-pressurised area to outside needs to be provided to prevent the area from becoming pressurised if a door is kept open. This can be either by natural ventilators to outside, or by a common natural shaft through the building, or by a mechanical shaft system.
Such systems are generally relatively expensive, so they are normally only used where demanded by regulations or standards or by Building Control, usually as a trade off.
Please refer to the Smoke Control in Apartments leaflet (3 MB) for details on the alternative design approaches.
Further guidance is available in the SCA “Guidance on smoke control to common escape routes in apartment buildings”, available as a free download from www.FETA.co.uk
Environmental ventilation systems – providing added value to a shaft system
The quest for energy efficiency has led to very good insulation in residential buildings. While this is very good for the environment and electricity bills, it is having unintended consequences stair lobbies, corridors and entrance halls, which tend to overheat.
Using the equipment specified to provide smoke control of the common areas, it is possible to provide a simple and effective cross flow ventilation system to extract warm, stale air from these spaces and their ceiling voids.
View our Ventilation solutions for overheated corridors in multi-storey residential buildings white paper and our CoolShaft page for further info.