Lawrence Webster Forrest
Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
Lawrence Webster Forrest
Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
There has been much speculation about the proposed changes to Approved Document B, since these were announced by the Government two years ago. December’s bulletin discusses the proposed revisions and the impact they will have on the design of buildings where people live (changes to buildings that are not dwellings will be covered in a future issue).
The last major revision of Part B of the Building Regulations and its supporting guidance, Approved Document B (ADB) took account of a consolidation of the Regulations . More changes in 2002 recognised the new European technical specifications and supporting fire test methods. But this did notamend any of the existing technical guidance in the 2000 edition of ADB.
In 2003 the Office of the Deputy Prime Minister (ODPM) announced its intension to revise and update the fire safety precautions of the Building Regulations; based on the Government’s desire to reduce the number and consequence of fires by moving towards a fire prevention and protection strategy. Building Regulations are of central importance to this, in terms of ‘designing-in’ fire safety to new and altered buildings.
In July this year the ODPM published three consultation documents setting out the proposed changes, including a number of deregulatory and improved regulation measures. These documents are also linked to the new Regulatory Reform (Fire Safety) Order 2005, a major deregulatory measure, which will consolidate over 100 pieces of existing fire safety legislation, as well as removing the building certification requirement by repealing the Fire Precautions Act 1971.
Currently, ADB contains guidance for all types of buildings. Under the new proposals, ADB will be split into two separate volumes ‘Dwellings’ and ‘Buildings other than Dwellings’, reflecting categories in other Approved Documents. Now that apartments are the most popular form of new housing –comprising a third of new dwellings – ADB will consider alternatives to smoke ventilation requirements for corridors and lobbies aimed at protecting common escape stairwells. The existing ADB requires automatic openable vents (AOVs), or openable vents (OVs),opening directly to the external face at each level of apartment blocks. As this has not always been either feasible or desirable, alternative fire engineering solutions have been sought. A common smoke shaft, running the full height of the apartment block, was one such option. Smoke vents at each level open directly into the shaft, where fire dampers allow the smoke to rise and vent at high level. But, because this solution did not comply with ADB 2000, building engineers had to design smoke shafts for each building, and then justify this measure to the satisfaction of the approval authorities – an exercise that often proved costly in both time and money. The revised ADB now recognises this design approach and has adopted it in the consultation documents. After an extensive research programme by the Building Research Establishment, the documents proposed the following criteria as a code-compliant design:
* The smoke shaft is to have a minimum cross-sectional area 1.2m2 (minimum dimension of 0.75m in any direction), opening at the roof level at least 0.5m above any surrounding structures with a horizontal distance of 2.0m. The shaft will be required to extend 3m above the ceiling of the highest storey served by the shaft.
* The minimum equivalent free area of the vent from the corridor/lobby into the shaft and at the head of the shaft is to be at least 0.75m2.
* On detection of smoke in the common corridor/lobby the vent(s) on the fire floor, the vent at the top of the smoke shaft and to the stairway are to all open simultaneously. The stairway vent is effectively providing an inlet air supply to the smoke shaft.
Pressure differentials, pressurisation and depressurisation may also be employed to protect stairwells from smoke. Pressurisation is based on raising the pressure in the stairwell to that of the surrounding area, thus preventing smoke and toxic gases from entering. Depressurisation extracts air and/or smoke from the fire-affected part of the building to reduce the pressure in the space to less than that in adjacent areas. The resulting pressure differential inhibits smoke from spreading further.
These methods are mentioned in the current ADB, but it directs designers to the relevant British Standard. The proposed ADB provides greater detail on the required input parameters for such systems to be acceptable in dwelling buildings. For example, in the case of singlestair buildings, it is recommended that the mechanical pressure-differential system should operate automatically when smoke is detected in the common circulation space on that storey. In buildings with more than one stair, the mechanical pressure-differential system for each stair may be operated manually, by the fire service, for example.
A fire detection and fire alarm system, although it can do nothing to reduce the incidence of fire, can help to lessen the resultant loss in terms of personal injury or property damage. The ODPM recognise this and have looked at requiring smoke detectors to be installed in the main bedroom and lounge, in addition to the current requirement for a single detector in the hall. The lounge and bedroom were considered to provide the greatest potential for reducing casualties in a fire. But it was also thought that there was an even greater possibility of the detectors being disabled by the occupants. The proposed solution is for an additional smoke detector in the main bedroom, which will serve as both detector and sounder.
The consultation documents have also noted the improvements in residential sprinkler systems in recent years. It is now generally agreed that sprinkler systems designed and installed in accordance with BS 9251 Sprinkle systems for residential and domestic occupancies – Code of practise and BS DD 252 Components for residential sprinkler systems – Specification and test methods for residentialsprinklers can reduce the risk to life and significantly reduce the damage caused by fire. For this reason, ADB acknowledge that sprinkler systems (not necessarily provided throughout the building) may be used as a compensatory feature where the prescribed standards can not be fulfilled. Approved Document B also details possible alternative approaches, for example installing residential sprinklers as an alternative means of escape from houses typically four or more storeys.
Additional proposals, based on fire incident statistics, include a complete sprinkler suppression system in high rise apartments (11 storeys or more) and residential care homes. Preliminary analysis has suggested that sprinklers in high rise apartments could save four lives and prevent 65 injuries over a 10 year period, while in residential care homes sprinklers could save one life and prevent 16 injuries.
To ensure the continuing successful development of the Building Regulations and ADB, ODPM wants all building professionals to analyse the consultation documents and give their comments. This is the last chance for professionals to make their feelings known before the proposed ADB becomes statutory. As the proposed documents are for consultation only, they are not considered to be regulatory and so ADB 2002 should be referred to until the proposals become law.
Fire engineering solutions, using the latest research and technology, have been used in many circumstances while the current ADB was in force. We believe there is always a need for prescriptive standards to set the safety benchmark with fire engineering providing alternative solutions allowing designers a greater scope of freedom with their designs.
1) ODPM. The Buildings Regulations 2000. Fire Safety. Approved Document B 2000 Edition consolidated with 2000 and 2002 amendments.
2) ODPM. Proposals for Amending Part B (Fire Safety) of the Building Regulations. Consultation Document July 2005.
3) ODPM. The Proposed New Edition of Approved Document B: Fire Safety.Volume 1 (Dwellings). Consultation Document July 2005.
4) BRE. The Forward Look Report. BD 2469.
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