What is the Process for Approving Water Mist Systems Under BS 9991:2024?
The 2024 update to BS 9991, published on November 27, 2024, no longer explicitly references water mist systems in its recommendations. However, this does not mean water mist systems are prohibited. Instead, the standard defers decisions regarding their use to BS 5306-0, which provides detailed guidance on fixed firefighting systems.
Approval Process for Water Mist Systems
The following steps outline the framework for approving water mist systems under the relevant standards:
- BS 9991:2024:
Establishes general fire safety principles and identifies the need for a fixed firefighting system as part of a building's fire safety strategy. Clause 17 states: "This British Standard does not give recommendations for any type of fixed firefighting system other than sprinklers. Guidance on the selection and key design considerations of fixed firefighting systems is given in BS 5306-0. The permitted variations summarised in Table 2 apply only to sprinkler systems."
- BS 5306-0:2020:
Provides guidance on selecting fixed firefighting systems. Table 1 confirms that water mist systems are acceptable in all domestic settings, provided they comply fully with BS 8458.
- BS 8458:
Specifies the performance and installation requirements for residential and domestic water mist systems. Compliance with this standard ensures that water mist systems are suitable for their intended application.
- Automist Compliance:
Automist Smartscan is designed and installed in accordance with BS 8458:2015, the British Standard for residential and domestic water mist systems. Its performance has been independently validated through the BSI Verification Certificate, VC 780009 (see specification on page 2).
Alternative Framework: BS 7974
Beyond the prescriptive framework, water mist systems can also be justified using BS 7974:2019, which supports a performance-based approach to fire safety engineering. This method allows for custom fire strategies that:
- Utilize probabilistic and computational methods to demonstrate fire system performance.
- Accommodate unique property layouts or circumstances where traditional prescriptive guidance may not be suitable.
Regulatory Guidance
Independent fire engineering research has demonstrated that Automist performs equivalent to or better than a domestic sprinkler system conforming to BS 9251:2021, even in open-plan, three-storey homes. This evidence also supports the use of Automist under BS 7974 for applications that deviate from standard guidance.
Disclaimer: This information is not intended to be a comprehensive guide to all of the aspects of the building regulations but rather a useful source of background information. Whilst every care has been taken to ensure that the contents of this post are correct at the time of publication, it should never be used as any form of substitution for the guidance documents. It should be noted that there may be specific additional requirements dependent upon local authority building regulations and/or fire authority.
Read more - Does Automist comply with the requirements of BS 8458?