The LWF Blog

Fire Safety Engineering for Design – Water Mist Maintenance – Part 309

October 19, 2026 8:38 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 308, LWF discussed the approvals system for water mist systems. In part 309, we will look at the maintenance requirements for water mist systems.

The maintenance of a watermist fire suppression system is not an optional afterthought. A system may remain unused for years, but when a fire occurs, pumps, cylinders, valves, pipework and nozzles all need to perform as designed. Regular inspection and testing provide assurance that the system remains capable of doing so.

Maintenance requirements for industrial and commercial watermist systems are addressed through relevant standards, including the BS 8489 series and NFPA 750. BS 8489-1:2016  provides recommendations for the design and installation of industrial and commercial watermist systems, while the wider series covers specific applications and performance testing.

NFPA 750 also places responsibility for inspection, testing and maintenance on the property owner or occupant. Its maintenance provisions require periodic inspection and testing to establish whether equipment remains in good operating condition or whether defects and impairments are present. Work should follow the standard and the manufacturer’s instructions and be carried out by personnel with appropriate training and experience.

Pump-based watermist systems supplied from a dedicated water tank have maintenance requirements that share many characteristics with sprinkler installations. The water supply, pump equipment, valves, pipework and nozzles all need to remain serviceable and available for operation.

Inspection should not focus solely on the pump. The complete system needs to be considered, including the condition of the water supply, the accessibility and condition of components, control equipment and any detection or activation arrangements. NFPA documentation (PDF download) also emphasises the need to correct deficiencies and impairments promptly and to consider changes to occupancy, processes, building layout or other conditions that could affect the system’s ability to protect the original hazard.

Cylinder-based watermist systems require particular attention to their pressure vessels. Periodic hydrostatic testing and internal examination may be required, with the applicable interval determined by the governing standard, jurisdiction, cylinder specification and manufacturer’s requirements.

For maritime installations, the International Maritime Organization’s MSC.1/Circ.1432 (PDF download) specifies ten-year servicing provisions for watermist, water spray and sprinkler systems, including hydrostatic testing and internal examination of gas and water pressure cylinders in accordance with applicable requirements or EN 1968:2002+A1.

The ten-year interval should therefore not be treated as a universal rule for every cylinder-based watermist installation. The system’s certification, manufacturer documentation and applicable regulations should be checked before testing is scheduled.

Effective maintenance is ultimately about verifying the complete fire protection system, not ticking off individual components. A well-maintained watermist installation should be inspected against its original design intent, tested according to the applicable requirements and returned to full operational readiness whenever maintenance or repair work has been completed.

In part 310 of LWF’s series on fire engineering we will begin to discuss gaseous fixed fire extinguishing systems. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.