What This Requirement Covers
Smoke ventilation systems remove smoke from escape routes, enabling occupants to see and breathe while evacuating. Approved Document B requires smoke ventilation in the common parts of residential buildings and in certain non-domestic buildings to maintain tenable conditions on escape routes.
Key Requirements
Residential Common Parts
- Natural ventilation: A minimum of 1.5 m² of openable ventilation (AOV or openable window) at the head of each common stairway
- The AOV should be activated automatically by smoke detection in the common parts and manually from the fire service access level
- Cross-ventilation corridors: Corridors longer than 12 metres with a stairway at one end should have an openable vent at the far end to allow cross-ventilation
- Mechanical smoke ventilation: Required where natural ventilation is not practical, or in buildings over 18 metres with fire-fighting lobbies
- Mechanical systems must be designed to BS EN 12101-6 and provide a minimum extraction rate to maintain the smoke layer above head height
Fire-Fighting Lobbies and Shafts
- Lobbies serving fire-fighting stairs must be ventilated to prevent smoke logging
- Ventilation may be natural (via an external wall or lightwell) or mechanical
- Mechanical lobby ventilation must achieve a minimum pressure differential to prevent smoke entering from the corridor
Non-Domestic Buildings
- Smoke ventilation in large compartments (shopping malls, atria, warehouses) is typically designed using BS 7346 (components) and BS EN 12101 series
- Atria require either natural or mechanical smoke ventilation designed to maintain a clear layer for evacuation
- Car parks may rely on natural ventilation (open sides) or mechanical extraction
System Types
- Automatic Opening Vents (AOVs): Roof or wall-mounted vents that open on fire alarm activation; suitable for stairway heads and corridors
- Mechanical smoke extract: Powered fans that extract smoke from corridors, lobbies, or large spaces; required in basements and internal areas without natural ventilation
- Smoke curtains: Fabric barriers that deploy to channel smoke to extraction points in large open spaces
- Pressurisation systems: Fans that pressurise stairways or lobbies to prevent smoke ingress; used in buildings over 18 metres
Practical Compliance Tips
- Commission smoke ventilation systems early; they require dedicated shaft routes and electrical supplies
- AOVs must be tested under load to confirm they open against wind pressure
- Ensure smoke ventilation controls are integrated with the fire alarm system and clearly labelled for fire service use
- Mechanical systems require ongoing maintenance and annual testing under the fire safety order
- In basements, provide both inlet air and extract ventilation to create an effective airflow path
- Keep smoke ventilation design calculations as part of the fire strategy report
- Where car parks rely on natural ventilation, demonstrate that the open area meets the minimum percentage of floor area (typically 5%)