Fire Safety in Purpose-Built Blocks of Flats

What This Requirement Covers

Purpose-built blocks of flats present unique fire safety challenges because multiple households share a single building structure and common escape routes. Approved Document B addresses these challenges through a combination of compartmentation (each flat as a fire-resistant compartment), protected common parts, and provision for firefighting access.

The stay-put strategy, where residents not directly affected by a fire remain in their flat, depends entirely on effective compartmentation and fire-stopping.

Key Requirements

Compartmentation

1. Each flat must be a separate fire compartment
2. Compartment walls and floors between flats must achieve the fire resistance periods in Approved Document B Table A1:

- Up to 5 metres building height: 30 minutes - 5-18 metres: 60 minutes - Over 18 metres: 120 minutes (walls), 60 minutes (floors)

1. The flat entrance door must be FD30S minimum (30 minutes fire resistance with smoke sealing)

Common Escape Routes

1. Common corridors and lobbies must be constructed as protected corridors with fire-resisting walls and ceilings
2. Maximum travel distance from a flat entrance to the nearest stairway: 7.5 metres (single direction) or 30 metres (where two directions of travel are available)
3. Common corridors should be ventilated for smoke clearance: natural ventilation via openable windows or AOVs (Automatic Opening Vents), or mechanical smoke ventilation
4. Emergency lighting is required in all common parts

Stairways

1. Single stairway buildings up to 11 metres: One protected stairway with natural or mechanical ventilation
2. Single stairway buildings 11-18 metres: One protected stairway accessed via a fire-fighting lobby at each level with mechanical smoke ventilation
3. Buildings over 18 metres: Minimum two stairways, each accessed via a fire-fighting lobby, with a fire-fighting shaft including a fire main, fire-fighting lift, and lobby ventilation
4. Stairways must not open directly onto the external face at ground level where this could allow fire to spread into the stairway

Firefighting Access

1. Buildings over 18 metres must provide a firefighting shaft comprising a firefighting stairway, firefighting lobby, and firefighting lift
2. A dry rising main is required in buildings over 18 metres (wet rising main over 60 metres)
3. Vehicle access for fire appliances must be provided within 45 metres of the dry riser inlet

Stay-Put vs Simultaneous Evacuation

1. The stay-put strategy is the default for purpose-built blocks: only the flat of fire origin is evacuated, and other residents remain in place
2. This relies on effective compartmentation; if compartmentation is compromised (e.g., unsafe cladding), a simultaneous evacuation strategy may be imposed by the fire service
3. Buildings with a simultaneous evacuation strategy require a communal fire alarm system and wider stairways to accommodate all occupants evacuating at once
4. The Responsible Person must review the evacuation strategy regularly and after any changes to the building

Practical Compliance Tips

1. Commission a fire strategy report for blocks over 11 metres to determine stairway provision and ventilation requirements early in design
2. Ensure flat entrance doors are FD30S and fitted with self-closing devices; test them as part of handover
3. Fire-stopping of service penetrations in compartment walls and floors is critical; use third-party certified installers
4. Install cavity barriers at all required locations, including the junction of compartment walls with external wall cavities
5. Provide clear signage for firefighting facilities (dry riser inlet, fire main outlet, firefighting lift controls)
6. Engage with the local fire service for pre-consultation on buildings over 18 metres
7. Maintain a comprehensive fire safety file for the building as required by the Regulatory Reform (Fire Safety) Order 2005 and the Building Safety Act 2022