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Fire Safety in the Design, Management and Use of Residential Buildings - Code of Practice
The new code of practice for fire safety in the design, management and use of residential buildings BS9991 is published by BSI and came into effect on 31 December 2011. This British Standard supersedes BS 5588-1: 1990 which is withdrawn. The intention of this document is to complement BS 9999, which excludes individual dwelling houses from its scope. The following bulletin discusses the new standpoint of fire safety provision in residential buildings and highlights the significant changes from the previous BS 5588-1.
Variation of Guidance
One of the major changes from the previous BS 5588-1 is that the latest guidance adopts an advanced approach which gives a more transparent and flexible approach to fire safety design through the provision of additional fire protection measures. Such measures include:
- The provision of an active fire-fighting system (e.g. sprinklers);
- The provision of an enhanced smoke management system;
- The provision of an additional level of automatic fire detection.
Designers, occupiers and approving authorities are thus able to allow a degree of flexibility in the provision of fire safety measures as part of the overall design package. However, there are limits on the extent of variation permitted within the scope of BS 9991. While much of the guidance in the British Standard is based on fire safety engineering principles and research it is not intended to be used as a guide to fire safety engineering.
The following outlines the permitted variations of guidance:
Open-plan flat design
In accordance with BS 9991, it is now permitted to design open-plan flats incorporating inner bedroom arrangements without the provision of an escape route using a traditional protected entrance hallway or alternative exit such as an external staircase or secondary escape stair. In order to compensate for the risk of the escape route being impassable if a fire starts in the access room of open-plan flats, it is recommended in BS 9991 that open-plan flats be fitted throughout with a sprinkler system designed and installed in accordance with BS EN 12845 or BS 9251 and a fire alarm system in accordance with BS 5839-6, Grade D, LD1. However, the limitations that apply when designing open-plan flats using the guidance are:
- The size of the open-plan flat should not exceed 16m x 12m;
- Open-plan flats should be situated on a single level only (single level flats exclude flats with galleries);
- The ceilings within the open-plan flat should have a minimum height of 2.25m;
- The kitchen should be enclosed in open-plan flats having an area exceeding 10m x 8m. Cooking appliances in open-plan flats having an area smaller than 10m x 8m should not be adjacent to the entrance of the flat;
- An open-plan flat design is not compatible with small, single staircase building reliant upon internal protected entrance halls for lobby protection to the staircase enclosure.
Sprinkler and watermist systems
Since its introduction in the UK sprinkler protection to residential occupancies is occasionally adopted as part of an alternative solution to standard building regulation guidance. The types of variations that have been allowed in BS 9991 as a result of residential sprinklers are:
- Where a sprinkler system is fitted throughout a three storey house in conjunction with a fire-resisting partition and fire-resisting door to enable occupants on the upper floors to access an escape window at first floor level, the internal layout of the ground floor may be open plan.
- Where a sprinkler is fitted throughout a house having four or more storeys in conjunction with a protected stairway, a second stairway is not required.
- Where sprinklers are fitted throughout a house or blocks of flats, the minimum distance between the side of the building and the relevant boundary may be halved.
- Where attendance time of the local fire and rescue service is expected to be no more than 10 minutes (subject to variation and consultation with the fire and rescue service):
a. the distance between the fire appliances and any point within the house (in house having no floor more than 4.5m above ground level and having a sprinkler system throughout) may be up to 90m;
b. the distance between the fire appliances and any point within the house or flat (in house or flats having one floor more than 4.5m above ground level and a sprinkler system installed throughout) may be up to 75m.
- Where a block of flats is fitted with a sprinkler system, the maximum travel distance for escape in common corridors in one direction only may be increased from 7.5m to 15m and for escape in more than one direction it may be increased from 30m to 60m.
There are restrictions in certain sprinklered residential buildings. For example, it is not permitted that sprinkler systems be used as a compensatory measure in sheltered housing and extra care housing to allow extended travel distances in the common areas.
Watermist systems may be considered as an alternative to sprinkler systems where agreed with the relevant enforcing authority. The acceptance of watermist application in residential buildings is usually subject to water mist systems being designed using suitable standards, fire demonstrations and performance tests to ensure the system is fit for purpose.
Minimum levels of fire resistance for elements of structure
BS 9991 introduces a new method to be used to specify the required fire resistance for element of structure in residential buildings. This has been developed based on the fundamental fire safety engineering principles which use a combination of deterministic analysis combined with a risk and consequence evaluation to reflect the severity of a real fire and threat to life safety in residential buildings. Based on Table 4 of BS 9991, the fire resistance specification for elements of structure may be reduced depending on the provision of sprinkler protection and ventilation conditions for residential buildings.
Guidance on different atrium design options can be found in BS 9991 to ensure that the incorporation of an atrium into a new or existing residential building does not present an increased risk to life as a result of fire and smoke. It must be noted that the wide range of design possible in atrium buildings make it impossible for this British Standard to cover every conceivable scheme and its associated fire risk, therefore it deals only with atria up to a height of 18m. Design solutions and exemplars for atria in residential buildings that do not fall within the scope of BS 9991 are given in Annex C of BS 9999.
Additional Considerations for Property and Business Continuity Protection
The recommendations given in the previous BS 5588-1 mainly concentrate on the protection of life. It must be noted that the provision of fire safety systems for life safety do not necessarily give adequate protection to property or the business carried out in the residential buildings. In this case it is considered that in communal dwellings a fire which is contained to the dwelling of origin may not present a significant life risk but it can very easily cause damage which will affect the habitability of other dwellings, for example through the damage of shared services. Therefore, a new guidance has been added to BS 9991 to ensure that the potential for property and business loss is assessed so that risks are understood and acceptable.
The published new guidelines for residential buildings have been discussed where they provide a baseline standard for life safety using advanced approach and makes further recommendations for enhanced property and business continuity protection. It now gives more flexibility to homebuilders, e.g. open-plan layouts with inner rooms. It must however be noted that all building layouts are unique and have different compartment geometries, risk level and fire load. Therefore, each case should be assessed individually. Further care needs to be taken when using a ‘pick and mix’ approach as it is essential that accessible means of escape and the associated fire safety strategy be considered as an integral part of the design process, and not as a separate issue.
This bulletin was written by Ken Seow MSc Fire Engineer
Peter J Gyere