British Standard 9991

[Amatista Sheeley]

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The British Standards Institution (BSI) is the UK National Standards Body (NSB). It publishes standards and provides a range of books, self-assessment tools, conferences and training services. It also represents UK economic and social interests in European and international standards organisations.

BS 9991:2015 Fire safety in the design, management and use of residential buildings. Code of practice, complements BS 9999: Code of practice for fire safety in the design, management and use of buildings (for buildings that are not residential).

BS 9991 is intended to help people put suitable fire safety measures in place in residential buildings, such as; fire detection and alarm systems, fixed fire-fighting systems and so on. It gives recommendations and guidance on the design, management and use of residential buildings so they achieve reasonable standards of fire safety for people who are in and around them and fire-fighters.

It provides guidance on the management of fire safety during the whole lifecycle of a building. It applies to the design of new buildings, and to material alterations, extensions and material changes of use to existing buildings.

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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.

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, caf, 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.

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:

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While BS 9999 regulates fire safety in the design, management and use of non-residential constructions, BS 9991 complements it for residential buildings. It lays out specifications and practices for suitable fire safety measures, including fire detection alarm systems and fixed pre-fighting arrangements.

Luckily, a draft of the proposed 2021 revision is out, so we have taken the time to point out the recent proposed changes, as well as some glaring omissions in the new text. Note that the document is likely to be amended further, though.

The new changes spell this out and restrict the use of natural smoke ventilation to buildings up to 30 metres in height, as long as travel distances are below 7.5 metres (extended to 15 if sprinkles are installed). If the structure is taller or the distances are higher, BS 9991 states that a mechanical smoke ventilation system or pressure differential system should be used.

When it comes to rescue services, sometimes the need arises to fiddle with controls and fire systems. This is to allow firefighters to turn parts of the system on or off as the situation changes. However, some of these controls and overrides are either incredibly complex or unclearly labelled, which discourages emergency services from interacting with them for fear of worsening conditions. The new guidelines lay out how these systems should be structured to allow for maximal fire safety:

The most significant change is the regulation stating that systems should start in high-speed mode from the get-go, as well as have no overrides or manual input to change their automatic function. These amendments will completely transform the way systems are used in a fire scenario. Fire and rescue services will have to be trained to understand these controls, while designers, architects and fire engineers will need to overhaul their approach.

BS 9991 also deals with a number of smoke control products and further clarifies their correct use. Notably, this is sometimes done in a contradictory manner to previous advice, which implies it is even more important to pay attention to these changes.

The document now posits that smoke control dampers should be classified for reduced leakage S, upholding BS EN 12101-8 but departing from the SCA Guide. It also applies a minimum operations classification of C10 000. Both of these requirements ensure that the dampers are of good quality and are able to last for a long period of time, as they are used or tested weekly.

Secondary power supply methods previously included an option to use two separate intakes into the building from the same external substation. This now appears to have been removed, limiting alternatives to a life safety generator, an independent utility primary network substation to the one feeding the primary supply or an uninterruptible power supply. As of now, it is unclear why this change has been made, however, independent queries will surely clarify this.

Aerodynamic free area: There is some uncertainty between EN 120101 and Approved Document B regarding declaration of free areas versus aerodynamic free areas. BS 9991, unfortunately, does not give a standardised answer to this question in Section 3.33.

Control equipment: The document seems to be confused on when to conform with BS ISO 21927-9. The Standard is mentioned in Annex A.2.2 regarding natural smoke and heat exhaust ventilators, whereas it should be dealt with when talking about control specifications.

Mechanical smoke ventilation systems: In Annex A.3.2.1, Note 1, the document lays out parameters for a test criteria. However, these are usually applied to pressure differential systems rather than mechanical smoke ventilation systems, so it seems conspicuous.

Extract point: Section 22.3.2.3 contradicts SCA guidance when it states that a mechanical smoke ventilation system that is installed in the protected lobby or corridor can be directly adjacent to the stairwell enclosure. The previous practice asserts that the extract point should be remote from the stair core.

BS 9991 is an incredibly important update to the 2015 Standard. It has many well-needed clarifications and elucidates key concepts and practices that may have been confused before, while taking into account the changes to construction and the lessons that have been learnt since. This draft still requires some fine-tuning, though, so make sure to follow us for more information, or get in touch with us if you need professional help.

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