The LWF Blog
Fire Safety Engineering for Design – Types of Water Mist System – Part 300
August 17, 2026 9:09 amLWF’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 299, LWF began to explore the types of water mist system. In part 300, we continue looking at the types of water mist system with low pressure water mist systems.
A low pressure water mist system operates at pressures of 16 bar or below. They are designed to provide an alternative approach to fire suppression where traditional sprinkler systems are not appropriate or preferred. They share many of the same design characteristics as a sprinkler system, but are engineered to produce a fine water mist rather than larger water droplets. This enables them to control or suppress instances of fire while using less water than a sprinkler system.
The heart of most low-pressure systems is a centrifugal pump, a proven technology widely used in fire protection because of its reliability and ability to deliver a steady flow of water. From a mechanical perspective, these systems often resemble traditional sprinkler installations. Pipework, valves and many other components may be approved using the same testing standards applied to sprinkler equipment, provided they also satisfy the additional fire performance tests required for water mist applications. The combination of component approval and full-scale fire testing is central to demonstrating that a complete system performs as intended under realistic fire conditions.
Not every low-pressure water mist installation relies on a pump. Some systems use a dedicated water storage tank combined with propellant gas cylinders. In such designs, compressed gas provides the energy needed to discharge the water, while pressure regulators ensure a controlled outlet pressure throughout the discharge process. Maintaining a stable pressure is important because fluctuations can affect droplet size and spray distribution, both of which influence fire suppression performance.
The defining feature of a water mist system is its nozzle technology. Unlike conventional sprinkler heads, water mist nozzles are engineered with precisely sized orifices and internal deflectors that break the water stream into very fine droplets. These droplets create a large surface area relative to their volume, allowing them to absorb heat rapidly, cool burning materials and surrounding gases, and generate steam that can help displace oxygen close to the fire. The balance between droplet size, spray pattern and discharge pressure is carefully matched to the hazards the system is designed to protect.
Because water mist systems depend heavily on nozzle performance, they are tested and approved as complete systems rather than as collections of individual components. Standards such as BS EN 14972 and NFPA 750 recognise that the interaction between pumps, pipework, valves and nozzles determines overall fire performance. A nozzle that performs well in one system may not achieve the same results in another with different hydraulic characteristics.
This system-based approach has helped establish low-pressure water mist technology as a recognised option for protecting a wide range of occupancies while reducing water consumption. Water mist systems are commonly selected for machinery spaces such as marine engine rooms and turbine enclosures, where high energy equipment presents a significant fire load. They are also used in data centres, where limiting water damage to sensitive electronic infrastructure is a key requirement. Transport environments, including tunnels and rolling stock, benefit from their rapid cooling and reduced water demand. In addition, heritage buildings, museums, archives, healthcare facilities, and certain commercial kitchens use water mist where fire control must be balanced against the need to minimise collateral water damage.
In part 301 of LWF’s series on fire engineering we will continue discussing types of water mist system by looking at single fluid systems operating at 70 bar or above. 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.