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Fire safety: architectural design guidance

The fire safety requirements we must adhere to as designers, for new and existing buildings, are continually being updated. In October 2008 a new UK guidance document came into effect covering a whole range of fire related issues associated with buildings. This note informs you of the key areas which may affect your design, with particular emphasis on architectural benefits (and limitations).

There are a number of approaches which can be used to meet the Irish Building Regulations requirements for fire safety:

1. Our primary guidance Technical Guidance Document B (TGD-B) provides basic advice for most buildings; however it is limited in detail and only provides general fire guidance. If a design does not comply with TGD-B a more detailed assessment would be recommended;

2. The next tier of guidance is typically British Standards and other internationally recognised design documents. BS 9999 now supersedes the BS 5588 series (excluding part 1) and is regarded as an advanced approach. This new guidance is a consolidated document which
covers detailed design requirements and is broadly based on sound fire engineering principles.

3. Further to BS 9999, Fire Safety Engineering can be used as an alternative approach and is often the only practicable way to achieve a satisfactory standard of fire safety. BS 9999 guidance is likely to be referenced by Irish guidance documents in the future and is
particularly relevant to new building design.


BS 9999 OVERVIEW

  • Purpose Groups are related to Occupancy Characteristic & Risk Profile. The installation of sprinklers for example reduces risk and allows extended travel distance
  • Management is a key area of the new guidance. Designers should ensure that specific management requirements can be adopted within the building, which are not unduly restrictive

B1: Means of Escape

Key changes with regard to travel distance and exit width are provided.

  • Travel distances generally greater in all but two occupancies (B3 and C3)
  • Widths of escape routes are generally lower (i.e. <5mm/p), but higher in some occupancies
  • Widths of escape stairs directly related to Occupancy Type / Risk Profile. Generally small stairs are permitted, by as much as 25-30%. This may reduce the number of stairs required in a development
  • Travel distances extended when large ceiling heights, enhanced AFDS, sprinklers, etc installed
  • Escape from one fire compartment to another is now recognised
  • Automatic Fire Detection Systems to offices, assembly and other areas can be (Type M), i.e. a lower cost manual system
  • Single exits and direction of opening can now accommodate 60 persons (not 50)
  • Minimum door width regardless of numbers is 800mm clear width (taking into account door hardware, such as handles)
  • Minimum. stairs width of 1000mm for stairs above ground and 1200mm for stairs below ground, generally
  • Width of corridor shall be same as doors leading to it, or 1200mm, however may be reducedwhere no wheelchair users or maintenance areas
  • All smoke vents should be located at least 3m from an escape route
  • Crèches should be a near or located at ground level and provided with at least two exits
  • Additional precautions are relevant to mezzanines or galleries
  • Additional precautions for disabled occupants such as handrails on corridors and potentially CCTV may be needed
    Theatres, Cinemas, Shopping Centres have no significant changes

B2: Internal Fire Spread (Linings)

  • There is a new limitation on materials in small rooms (<4m²) in residential buildings.
  • There is a new classification, Class 3 / Class D-s3, d2 in non-residential rooms less than 30m² and domestic garage less than 40m²

B3: Internal Fire Spread (Structure)

  • The Fire Resistance in of structure, where ventilation can be considered for potential openings (i.e. glazing braking during fire), is reduced
  • If sprinklers are provided the Fire Resistance of structure can be reduced
  • Un-sprinklered open sided car-parks greater than 30m in height are permitted
  • All buildings greater than 30m in height are sprinklered
  • There are compartment limits dependant on single or multi-storey buildings (and height of multi-storey), but no limit on compartment volume
  • Generally, there are increased compartment limits, but some areas such as retail are smaller if multi-storey
  • Where basements are deeper than 10m, each floor would need to a compartment floor. This will affect car parks
  • Some fire doors have reduced ratings
  • Hospitals are referred back to HTM, however, atriums in hospitals are not covered (or at least won’t be after 6th April 2009)


B4: External Fire Spread

  • There is no restriction on distance between small unprotected openings (1m²) between compartment floors or walls
  • Unprotected areas for areas greater than 30m above ground in large un-compartmented buildings can be discounted (i.e. halls, or atria type entrances)
  • A 1.8m wide fire protection to external walls at angles with stairs extends to all protected escape routes, e.g. corridors, etc. The fire protection to an access corridor to a Fire Fighting shaft is increased to 5m
  • Classification of external surfaces broadened to Class 0 / 1 dependant on proximity to boundary and height

B5: Access & Facilities for the Fire Service

Generally no change from BS 5588-5: 2004

  • Extent of access related to total floor area of the building. NB. this does not exclude basements
  • Wet mains (i.e. including tanks and pumps) are needed to buildings with a top floor >50m above fire service access level
  • There is some reduction in areas of vents to stairs, but increases to lobby ventilation direct to open air to 1.5m²
  • Ventilation to Fire Fighting stairs highlights a limitation of 30m top floor

Readers' comments (2)

  • I would like to add that a similar approach is taken within England and Wales with Approved Document B Fire Safety (ADB), It should be remembered however that the guidance BS 9999 contains, whilst based on fire engineering, it is not a Fire Engineering guide and should a more advanced approach be required the client should seek professional advice from a Fire Engineer.
    The BSI were also keen to point out that adopting this risk based approach should be done by "applying the whole package of measures" contained within the document without "cherry picking" convenient sections.
    Chris Hughes BEng (Hons) CEng MIFireE GEI
    Associate
    Bodycote Warringtonfire Consultants

    Unsuitable or offensive?

  • Re: B1:
    I find it odd that there is no mention of the evacuation of people with disabilities, covered under 1.4.15 in TGD Part B (2006 Ireland).

    Unsuitable or offensive?

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