Fire! A synopsis of Approved Document B

Architects and developers can now choose to include sprinklers as a compensatory fire safety feature in the design of dwellinghouses, but for flats in buildings over 30 m high, sprinklers are mandatory. Meanwhile, a central plank of the government's fire safety media strategy seems to be to educate us to close our bedroom doors.

In this exclusive extract from Shortcuts: Book 2 by Austin Williams, we give an overview of the requirements of Approved Document B: Fire Safety.

The current Approved Document B – Fire Safety (AD B) was published on 22 January 2007 and has been split into two substantial volumes: Volume 1: Dwellinghouses and Volume 2: Buildings other than dwellinghouses. Notwithstanding the repetition of introductory blurbs, the two documents are significantly larger than the 2002 edition, but, helpfully, they have most of the changes to the previous edition displayed in the front, and a workable index at the back. A dwellinghouse is defined as a "unit of residential occupation" occupied by an individual, a family or a single household (the latter comprising not more than six persons). Also included are sheltered housing and adult placement homes, etc., but not flats, common areas or buildings containing flats, which are dealt with under AD B2.

AD B affects new-build projects, but will also have significant repercussions on change of use and refurbishment schemes. AD B2, Section 0.13 states that even though "Building Regulations do not impose any requirements on the management of a building ... (a) design which relies on an unrealistic or unsustainable management regime cannot be considered to have met the requirements of the Regulations."

The Regulatory Reform (Fire Safety) Order: 2005 (RRO) is the guide to providing the requisite realistic and sustainable management regime to satisfy the Building Regulations, and with beautiful symmetry, compliance with the new AD B will be deemed to satisfy the physical fire protection requirements of the RRO. Obviously, it's not as simple as that. The RRO imposes a duty on a "competent person" to provide fire safety information to the fire service or local authority prior to them issuing a completion certificate. As part of the ongoing strategy, an operational risk assessment will still need to be carried out and maintained to show that buildings (other than dwellinghouses) continue to comply. Fire certificates, however, are now worthless, but provided that they are not too old, they can still provide a useful guide – but a guide only – to assessing the risk levels in a given building. Additional practical assistance can be found in the Fire Protection Association's guide to AD B2 that spells out loss prevention advice to designers of industrial and commercial buildings. Following its guidance will "add resilience" to a project to ensure compliance with insurers' needs. It also provides alternative sets of design targets that comply with the statutory requirements.

As with the RRO, the new AD B tends to rely to a considerable degree on risk assessments as opposed to prescriptive design rules, and therefore it places a greater responsibility on the building designer (or "competent person", i.e. someone with proven competency who may be delegated by the "responsible person") to provide detailed risk management information on the maintenance and operation of the building. There is, however, plenty of proscriptive detail and complexity for those that like that sort of thing.

Sprinklers and hoses

In AD B1, sprinklers (and other automatic fire suppression systems) will be acceptable as part of the overall fire safety strategy in domestic situations, subject to a risk assessment. Therefore, they may be used in lieu of alternative means of escape in certain circumstances (e.g. incorporating domestic sprinklers as an alternative to a secondary escape from houses with a storey over 4.5 m above ground level). Smoke alarms must have standby power sources, and smoke detectors should be provided in circulation spaces.

AD B2 does not require sprinklers in common areas, e.g. corridors and stairwells, but they may be included in flats. Sprinklers are now mandatory in flats in buildings over 30 m high (current guidance in BS 9251: 2005 about buildings below 20 m in height "can be ignored") but this increased specification does not result in a consequent relaxation in compartmentation criteria. In flats, each storey (and within residential and institutional buildings, including healthcare buildings, each floor) must be a compartment floor. It has been assessed that, for some tall city centre developments, compliance may necessitate increased floor to ceiling heights, additional risers for buildings over 45 m high to equalise the water pressure, and extra plant space for storage and pump capacity; the additional costs could be in the region of £1,000–£2,000 per apartment.

Unsprinklered buildings should have fire main outlets within 45 m of all parts of every storey over 18 m. The 45 m distance must be measured in three dimensions, not just on plan, and measured to the end of the nozzle, not to the end of the jet. If a firefighting shaft has been provided – and buildings over 900 m² with a floor level above 7.5 m must have firefighting shafts – this can extend to 60 m. Large storage buildings that contain a floor level below 18 m no longer need firefighting shafts, neither do retail units, provided that each level is provided with a rising main and ventilated lobbies.

Fire tenders need access to within 45 m of all points "within" a dwellinghouse. In buildings other than dwellinghouses, with compartments over 280 m² and with fire mains, hydrants should be provided within 90 m of the dry fire riser. Buildings without fire mains should have hydrants provided within 90 m of the entrance and additional hydrants at 90 m centres, each clearly marked. Where hydrants are impracticable, water may be drawn from substantial water supplies (storage tanks, rivers or other approved sources) all of which may add significant costs to a project.

Dead ends, doors and stairwells

Designers may now omit door closers in dwellinghouses (save for those separating the dwelling from integral garages) as well as omitting them within flats (save for those separating multiple occupancy premises). This is not a licence to remove fire doors and create open plan internal areas, and the maze of lobby doors common to most flat entrances are still required. Even with sprinklers and automatic detection, fire doors need to be specified as before. Recognising that, in real life situations, fire doors get wedged open and closing devices disconnected, the government orchestrated a media campaign to train us to shut doors ourselves.

In single direction (dead-end) corridors off flats leading only to a stair lobby, it is the stair lobby rather than the corridor that has to be ventilated. The maximum travel distance of 7.5 m from the external flat door to the vented stair lobby remains unchanged, but some fire engineers have expressed concern that people fleeing flaming flats may cause the dead-end portion of the corridor to fill with smoke. A careful risk assessment of this situation is advisable.

As in the past, in AD B2 the number and width of stairs is dependent on the occupant load. Because firefighters are sometimes going up while large numbers of occupants are coming down, the new AD B recommends that, in buildings over 45 m in height, this potential bottleneck situation be alleviated by proposing that a greater width and/ or increased number of staircases be included in the design. This has a serious impact on the plan layout and should be discussed with the relevant building control and fire and rescue service authority. Costs for an additional 1100 mm wide stair within a generic Central London office building are reputed to be in the region of £35,000–£45,000 per storey, notwithstanding a significant loss of rental income.

In conclusion, the basic Building Regulations enforcement powers are unchanged, although there are greater requirements for transparent post-occupancy management procedures. A more holistic fire strategy is required that considers the building, the user and the firefighter. Some changes will have cost implications for the scheme build as well as post-occupancy management, and these should be raised early in design discussions with the client.

Thanks to Miller Hannah of Hoare Lea Fire.

Shortcuts provide an eclectic mix of at-a-glance guides to the minefield of regulations, new materials, and technologies that confront building designers today. Comprising hand-drawn sketches, technical drawings, and punchy articles, each Shortcut takes you right to the heart of a key topic in architecture and construction, presenting a wealth of invaluable information in an accessible and lively way.

Shortcuts: Sustainability and Practice by Austin Williams explores the issues that affect the way building designers work. The shortcuts range from zero carbon energy sources to green roofs, and from drawing conventions to contracts and case law.

To order a copy of this book, please visit RIBA Bookshops.

Copyright RIBA Publishing March 2009.

Additional publications and services

Available to buy now from RIBA Bookshops:

Shortcuts: Structure and Fabric

Approved Document B: Fire Safety (Volume 2) - Buildings Other Than Dwellinghouses. Incorporating Insurers' Requirements for Property Protection

Also available:

NBS Building Regulations

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