Unlike sprinklers, water mist is not designed from generic tables. Each application follows a manufacturer's system that has been approved through full-scale fire tests, and stays within the limits of those tests. We assess the hazard and operating conditions, select a suitably approved system, and take on the stainless steel pipework, pump unit and commissioning tests.
ATypes and components
High pressure systems
NFPA 750 classes systems operating at 34.5 bar or more as high pressure; in practice they mostly run at 100 bar or above. Droplets are very fine, pipe sizes are small and stainless steel tube is used.
Intermediate pressure systems
Operating between 12.1 and 34.5 bar. They produce larger droplets than high pressure systems and are used in some machinery space and industrial applications.
Low pressure systems
Operating below 12.1 bar, with pipework conditions close to those of sprinklers. Droplets are coarser, but the special nozzles still use markedly less water than conventional sprinklers.
Automatic (closed) nozzle systems
Each nozzle has its own glass bulb and only those exposed to heat open. Used in hotels, residential buildings, offices and heritage buildings, where the sprinkler principle applies.
Open nozzle (deluge) systems
All nozzles are open; when the section valve is opened by the detection system, every nozzle in the section discharges together. Used for volume or object protection in machinery spaces, turbine enclosures and industrial fryers.
Pump and cylinder units
Large systems are supplied by an electric or diesel-driven positive displacement pump unit. Small, standalone hazards can be covered by compact units of water and nitrogen cylinders that need no electrical power.
BHow it works
- A nozzle bulb breaks, or the detection system opens the section valve.
- The pressure drop starts the pump unit, which delivers water to the nozzles at design pressure.
- Fine droplets evaporate in the flame zone, absorbing heat and diluting oxygen locally.
- The mist cools the surrounding surfaces and air, limiting fire spread and re-ignition.
CAdvantages
- Far less water use and water damage than sprinklers
- Small-bore pipework, easy to route in tight spaces
- Safe for use in occupied areas
- No chemical agents involved
- Strong cooling keeps re-ignition risk low
DApplications
- Hotels and heritage buildings
- Data centres and electrical rooms
- Gas and steam turbine enclosures
- Machinery spaces and generator rooms
- Industrial fryers and cooking lines
- Tunnels and rail systems
- Ship and yacht engine rooms
EFrequently asked questions
Can water mist replace a sprinkler system?
It can, but only where the chosen system has been fire-tested and approved for that hazard and the authority having jurisdiction accepts it. A design based on sprinkler tables cannot be turned into a mist system by swapping nozzles. Hazard, approval documents and local regulatory requirements need to be reviewed together at the start of the project.
Can water mist be used on electrical equipment?
Because there are gaps between the droplets, a mist conducts far less than a solid water jet, and many systems have been tested for use near live equipment. The application still has to fall within the manufacturer's approval and test scope. In data centres, water mist is considered as an alternative to gaseous systems, particularly in large halls.
What does water mist maintenance involve?
With very small nozzle orifices, water quality and filters are at the centre of maintenance. Pump unit run tests, filter cleaning, visual nozzle checks and functional tests of section valves are carried out regularly. Intervals follow NFPA 750 and the manufacturer's manual, and stainless pipework means internal corrosion is rarely an issue.