What This Requirement Covers
While BS 9251 sprinkler systems are the standard residential fire suppression technology, water mist systems and other suppression technologies are increasingly used in dwellings, particularly in retrofit situations where water supply limitations or space constraints make conventional sprinklers impractical.
Key Requirements
Water Mist Systems
- Operate at higher pressures than conventional sprinklers, producing a fine mist that suppresses fire through cooling and oxygen displacement
- Require less water than conventional sprinklers (potentially suitable where mains water pressure or flow is limited)
- Must be designed and installed to a recognised standard; BS 8458 covers residential and domestic watermist systems
- Some Building Control Bodies accept water mist as an alternative to BS 9251 sprinklers; acceptance varies by authority
When Suppression Is Required or Beneficial
- Mandatory: Buildings over 30 metres (Approved Document B Table A5); buildings over 11 metres (Government announcement for new blocks of flats); all new dwellings in Wales
- As an alternative compliance measure: Loft conversions where a full protected stairway is impractical; open-plan layouts that exceed travel distance limits; single-staircase buildings where a second staircase would otherwise be required
- Risk reduction: HMOs with complex escape routes; care homes; buildings with vulnerable occupants
System Components
- Sprinkler heads or mist nozzles rated to activate at specified temperatures (typically 57 or 68 degrees C)
- Water supply (mains, tank, or pump-fed)
- Flow switch connected to the fire alarm system to alert occupants and the fire service
- Control valve and drain valve for maintenance
Practical Compliance Tips
- Discuss suppression system options with Building Control and the fire service early in the design process
- Confirm that the local Building Control Body accepts the proposed suppression technology (water mist acceptance is not universal)
- For BS 9251 sprinkler systems, confirm mains water pressure and flow rate with the water company
- Concealable sprinkler heads are available that are virtually invisible once installed; they minimise aesthetic impact
- Plan pipework routes during the design phase to avoid clashes with other services
- Commission the system on completion and arrange annual servicing
- Keep the installation certificate and maintenance records for Building Control and the building safety file