Smoke Ventilation and Control Systems

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

1. Natural ventilation: A minimum of 1.5 m² of openable ventilation (AOV or openable window) at the head of each common stairway
2. The AOV should be activated automatically by smoke detection in the common parts and manually from the fire service access level
3. 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
4. Mechanical smoke ventilation: Required where natural ventilation is not practical, or in buildings over 18 metres with fire-fighting lobbies
5. 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

1. Lobbies serving fire-fighting stairs must be ventilated to prevent smoke logging
2. Ventilation may be natural (via an external wall or lightwell) or mechanical
3. Mechanical lobby ventilation must achieve a minimum pressure differential to prevent smoke entering from the corridor

Non-Domestic Buildings

1. Smoke ventilation in large compartments (shopping malls, atria, warehouses) is typically designed using BS 7346 (components) and BS EN 12101 series
2. Atria require either natural or mechanical smoke ventilation designed to maintain a clear layer for evacuation
3. Car parks may rely on natural ventilation (open sides) or mechanical extraction

System Types

1. Automatic Opening Vents (AOVs): Roof or wall-mounted vents that open on fire alarm activation; suitable for stairway heads and corridors
2. Mechanical smoke extract: Powered fans that extract smoke from corridors, lobbies, or large spaces; required in basements and internal areas without natural ventilation
3. Smoke curtains: Fabric barriers that deploy to channel smoke to extraction points in large open spaces
4. Pressurisation systems: Fans that pressurise stairways or lobbies to prevent smoke ingress; used in buildings over 18 metres

Practical Compliance Tips

1. Commission smoke ventilation systems early; they require dedicated shaft routes and electrical supplies
2. AOVs must be tested under load to confirm they open against wind pressure
3. Ensure smoke ventilation controls are integrated with the fire alarm system and clearly labelled for fire service use
4. Mechanical systems require ongoing maintenance and annual testing under the fire safety order
5. In basements, provide both inlet air and extract ventilation to create an effective airflow path
6. Keep smoke ventilation design calculations as part of the fire strategy report
7. Where car parks rely on natural ventilation, demonstrate that the open area meets the minimum percentage of floor area (typically 5%)