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BS 9991: 2021 draft out for consultation

Fire Engineering By Andy Bishop, Partner, Building Services – 09 November 2021


Andy Bishop wearing a light purple shirt against a blurred park background

Andy Bishop

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Teodor stood in the atrium in front of rust red railings and interior windows

Teodor Sofroniev

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BS 9991 is the code of practice for fire safety in the design, management and use of residential buildings. It complements BS 9999 which is the code of practice for non-residential buildings.

BS 9991 gives recommendations and guidance to ensure residential buildings achieve reasonable standards of fire safety for people who are in and around them and for firefighters. This is tailored specifically to blocks of flats and houses and how they are designed, managed and occupied. It advises on the specific fire safety measures required for these buildings, such as fire detection and alarm systems, fixed firefighting systems and so on.

This document is an alternative to Approved Document B Volume 1 published by the Secretary of State and is generally preferred by fire engineers and designers due to the greater level of detail and flexibility it provides.

Following a series of tragic events that have occurred in recent years, it is now more important than ever that we build structures which place the safety of people above anything else. The suitability of current guidance and design practices has also come under scrutiny and the revision of this standard reflects this.

This long-awaited new version of BS 9991, used as the basis for fire strategies relating to blocks of flats, introduces considerable changes that will impact the design and systems of residential buildings. The full release for this standard is not expected until late 2022 but the draft includes some notable changes which are summarised below.

Applies to all residential buildings

In all developments where passenger lifts are installed, at least one lift should be an evacuation lift.

Secondary power supplies
– The previous document was suitably ambiguous when it came to the design of secondary power supplies. This caused much debate within design teams over what was and wasn’t appropriate and reasonable. This draft has taken steps to clarify the issue. The only acceptable arrangements for secondary power supplies are:

  • a generator;
  • an independent high voltage supply, provided it is fed from an independent utility primary network substation to that feeding the primary supply; or
  • an uninterruptible power supply (UPS): the standard advises on the sizing of the UPS.

Cross referencing with the new residential sprinkler standard, BS 9251:2021 (published in June 2021): the use of a modified residential sprinkler system is acceptable for some ancillary areas such as retail, café, bin stores, plan rooms, car parks, etc. subject to a limit of 100 msq. Any non-residential areas larger than this limit will require protection using a commercial BS EN 12845 system i.e. separate sprinkler tank and pumps.

Residential buildings over 11m

In line with changes to the Approved Documents, sprinklers will be required in all residential buildings with a floor over 11m. However, the standard advises that ALL areas are protected, including corridors and stairs, even if they are sterile.

Residential buildings over 18m

Single stair, high-rise buildings will only be acceptable if:

  • The stair is provided with a pressurisation system
  • Structural protection is increased from 60 minutes to 90 minutes FR
  • Timber structure is not acceptable
  • An additional lobby needs to be provided between the stair and corridor affording access to the flats (similar to current arrangements in Scotland)
  • Stairs should be wider than 1,200mm (increased from the 1,100mm width for firefighting stairs)
  • If extended corridors are present, additional mechanical smoke extract may be required in addition to the stair pressurisation

An evacuation alert system will be required to buildings over 18m with stay-put policy. Systems to BS 8629 standard provide for sounders in apartments connected to a central fire alarm panel for use by the fire service to raise an evacuation alarm in specific or all flats. This is not a change to the stay-put policy in such buildings but provides a facility to aid firefighting operations in extreme scenarios.

Buildings over 18m require two evacuation lifts, regardless of the number of staircases provided and should be arranged such that one will always be available.

Further notes on evacuation lifts

Additional lifts may be required depending on the building layout:

  • In some cases, firefighting lifts need to be separate from evacuation lifts
  • The lifts will need to be accessed from a separate lobby adjacent to the stair that does not serve the main corridors directly
  • The standard provides the first definitive guidance on the operation and programming of evacuation lifts in residential buildings. In most cases, it is likely they will need to have an automatic evacuation mode as well as the standard driver assisted mode
  • These requirements are also largely aligned with the new London D5 planning policy requirements

Residential buildings over 30m

Natural smoke shafts are no longer acceptable. Therefore, mechanical smoke extract or pressurisation systems will be the only acceptable means of smoke ventilation for buildings of this height.


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