Smoke control systems are installed to ensure stairways and communal corridors remain relatively free from smoke and heat in the event of a fire within a dwelling to enable occupants of the building to escape safely. In tall buildings (with a floor over 18m high) these systems assist firefighters in gaining access to fight the fire from inside the building.
There are 5 main systems used for smoke control
1. Stairwell ventilators
A stairwell ventilator is an automatic opening ventilator which should provide a minimum of 1.0m² of free area located at the highest point in a stairwell. Stairwell ventilators evacuate smoke in stairwells of small buildings, and provide replacement air for a lobby smoke extract system in larger buildings.
Stairwell ventilator fitted with Simon RWA folding arm actuators
They can take a number of forms including louvred, hatch type, windows and roof windows. Take a look at the advantages of hatch vs louvred vents
Smoke ventilators can be used to ventilate lobbies directly to the atmosphere. These may be a proprietary ventilator or a combination of an actuator and an existing window or roof light. They should provide a minimum free area of 1.5m².
In single staircase buildings, the ventilator should open automatically on detection of smoke in the lobby. In multiple staircase buildings the ventilator can be operated manually. In both cases, opening the AOV should also cause the stairwell ventilator to open.
Easivent sell pre-designed AOV kits to help you specify the right equipment for the job – take a look
3. BRE Shafts
Natural smoke shafts, commonly known as BRE shafts should comprise a vertical shaft with a minimum free area of 1.5m², with a ventilator into the shaft at each lobby and at the head of the shaft of 1.0m² free area. The ventilator into the shaft should have a fire resistance performance equivalent to an E30S fire door and be opened automatically on detection of smoke in the lobby.
4. Mechanical Extract Systems
Mechanical shafts are similar to BRE shafts but have additional extract fans to mechanically extract smoke from the lobbies which allow a smaller shaft and ventilators to be be employed. Shaft area typically reduces from 1.5m² to 0.6m² meaning that more space is freed for other use within the building. Extract fans are usually mounted on the roof. The automatic opening ventilator above the stairwell is used to provide replacement air for the smoke shaft.
To ensure effective smoke clearance, the extract shaft should be located as far away as practicable from the stairwell, which is the source of replacement air. This is particularly important in buildings with extended travel distance.
Mechanical extract fan skid mounted on the roof of a recent SCS Group project in London
5. Pressurisation system
Pressurisation systems protect the lobbies and staircases against the ingress of smoke by raising the pressure in these areas relative to the fire zone. In residential buildings they would commonly comprise run and standby fans to pressurise the stair and an air release path from the lobby usually via a rising duct, similar to a BRE shaft. The design procedure and equipment specifications are detailed within BS EN12101-6.
Pressurisation systems offer the highest standard of protection, however their use has declined with the rise in use of CFD modelling to design mechanical smoke shafts as these are generally simpler to install and commission.
For more information on smoke control solutions for flats, download the M&E’s contractors’ guide now
Under the Construction Products Regulations (CPR) it is a legal requirement to use only certified products for smoke ventilation. For more information see SCS Group's Technical Bulletin here.