FIRE SAFETY | BS 9991 FIRE ALERT A new version of BS 9991, the fire safety standard for residential buildings, is expected later in 2022 and contains changes that will impact the design of all flats, not just high-rise buildings, says Cundalls Teodor Sofroniev and Andy Bishop T his 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 notable changes. BS 9991 is a code of practice for fire safety, which complements BS 9999, the standard covering non-residential buildings. BS 9991 gives guidance on the design, management and use of residential buildings so they achieve compliance with Part B of the Building Regulations covering fire safety of people 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 and is generally preferred by fire engineers and designers because of the greater level of detail and flexibility it provides. Note, Building Regulation requirements can leapfrog standards (and vice versa). For example, changes to Approved Document B reduced the trigger height for sprinklers in flats to 11 metres. Designers should be aware of the latest guidance changes and refer to the more recent and onerous. It is important that we build structures that place safety of people above all else. The suitability of current guidance and design practices has come under scrutiny and the to 100m2. Any non-residential areas larger than this will require protection using a commercial BS EN 12845 system. Residential buildings over 11m In line with changes to the Approved Documents, sprinklers will be required in all residential buildings with a floor over 11 metres. However, the standard advises that all areas are protected, including corridors and stairs, even if fire sterile (where a person can be considered to be safe from immediate danger from flame and smoke). Residential buildings over 18m Andy Bishop Teodor Sofroniev standard reflects this. The most significant changes are listed for each of the following: all residential buildings; over 11m high; over 18m high; and over 30m high. All residential buildings In all developments where passenger lifts are installed, at least one lift should be an evacuation lift. The previous document was ambiguous when it came to the design of secondary power supplies. This draft clarifies the issue. The only acceptable arrangements for secondary power supplies are: n a generator n an independent high voltage supply provided it is fed from an independent utility primary network substation to that of the primary supply n an uninterruptible power supply (UPS). A single electrical intake with diverse routes and life-safety distribution board is no longer acceptable. Cross referencing with the new residential sprinkler standard, BS 9251:2021: the use of a modified residential sprinkler system is acceptable for some ancillary areas such as retail, bin stores and plantrooms subject up WHEN BS 9991 SAYS SINGLE STAIRS ARE ACCEPTABLE In high-rises over 18m, compliance with Part B1, reasonable means of escape, may be able to be shown where: n The stair is provided with a pressurisation system n Structural protection is increased from 60 minutes to 90 minutes fire rating n Timber structure is not acceptable n An additional lobby needs to be provided between the stair and corridor affording access to the flats (similar to current arrangements in Scotland) n Stairs should be wider than 1,200 mm (increased from the 1,100 mm width for firefighting stairs) n If extended corridors are present, additional mechanical smoke extraction may be required in addition to the stair pressurisation. Single stair, high-rise buildings will only be acceptable in some circumstances (see panel). An evacuation alert system that complies with BS 8629 will be required for buildings over 18m with a stay-put policy that keeps people safe, and in place, when they are not in an area affected by fire. BS 8629 is evacuation alert system code of practice for use by fire and rescue services in buildings containing flats. Systems designed to BS 8629 provide sounders in flats connected to a central fire alarm panel for use by the fire service to raise an evacuation alarm in specific, or all, flats. The alert system in BS 8629 is not a change to the stay-put policy but is an aid to firefighting operations in extreme scenarios. Buildings over 18m require two evacuation lifts, regardless of the number of staircases provided and one should always be available. Additional lifts may be required depending on the building layout. In some cases, firefighting lifts need to be separate to evacuation lifts. Firefighting lifts will need to be accessed from a separate lobby adjacent to the stair that does not serve the main corridors directly Residential buildings over 30m The revision to BS 9991 provides the first definitive guidance on the operation and programming of evacuation lifts in residential buildings. It is likely that most lifts will need to have an automatic evacuation mode as well as the standard driver-assisted mode. For flats over 30m, natural smoke shafts are no longer acceptable and mechanical smoke extract or pressurisation systems will be the only acceptable means of smoke ventilation. Please note our comments relate only to the draft revision of BS 9991. CJ ANDY BISHOP is a partner and TEODOR SOFRONIEV is a principal engineer at Cundall 46 July 2022 www.cibsejournal.com CIBSE July 22 pp46 Building safety code.indd 46 24/06/2022 17:37