Jade Musto outlines the pros and cons of water mist suppression systems and emphasises the importance of pre-installation third-party testing.
Water mist systems work by spraying very fine droplets of water at relatively high pressure, propelling water through specially designed nozzles which break it up into micro droplets. They are used to suppress fires and prevent them spreading, and work by lowering the temperature and reducing the amount of oxygen in a fire, to the extent that combustion cannot be maintained and the flames are extinguished.
Water mist systems have been found to be suitable for use on ships, and are increasingly used for life safety applications in buildings. They have also been successfully deployed to protect assets such as electronic equipment, machinery and deep fat fryers. Water mist is particularly effective at supressing fires in enclosed environments, such as gas turbines or fuel storage.
As less water is used compared to sprinkler systems to suppress a fire, potential water damage is likely to be much less than is the case with sprinklers. As such, water mist systems are used in residential and domestic premises as well as in non-residential buildings such as offices, schools and leisure facilities.
Similarly, water mist systems need smaller supplies of water compared to sprinklers, and use smaller pipes and components, so take up less space. This makes them suitable for environments where it would be difficult to install larger systems, and also for retrofitting in existing buildings.
While water mist systems are effective in suppressing fires in buildings which are compartmented, they are not so effective in open or highly ventilated spaces, where the droplets of water can be dispersed by draughts or air conditioning.
One of the biggest differences between sprinkler and water mist systems is that the latter need to be designed according to the precise environment in which they are to operate, making each installation bespoke to its setting. This is because there are fewer standards or certification schemes that are appropriate to water mist installations, and components are often proprietary to specific manufacturers and might not be interchangeable. It is therefore not possible to install water mist systems solely by referring to one of the standards.
Standards for water mist systems include:
- BS 8489-1: 2016: Fixed Fire Protection Systems. Industrial and commercial water mist systems. Code of practice for design and installation
- BS 8458: 2015: Fixed fire protection systems. Residential and domestic water mist systems. Code of practice for design and installation
- BS EN 14972-1: 2020: Fixed firefighting systems. Water mist systems. Design, installation, inspection and maintenance
- NFPA 750 - Standard on Water Mist Fire Protection Systems
- IMO A800 + MSC 265 (automatic water mist nozzles)
- IMO MSC.1/Circ. 1165 (open water mist nozzles)
- FM 5560 - Approval for Water Mist Standards
- VdS Guideline 3188
Building owners and those responsible for fire safety in their premises should therefore use the services of a third party, who has the knowledge and experience to undertake a thorough pre-installation inspection, design and install an appropriate system and carry out regular maintenance.
Because the design and performance of a water mist system is so dependent on the environment in which it is to be installed, it is crucial that systems are tested prior to their installation. There are two standard tests for water mist systems, depending on the type of installation that the system is going to be in: one for domestic properties and one for commercial properties. The testing is done on that system prior to being put on the market, and the test should provide a limit for how the system can be installed (number of heads, size of room etc). The system will need to be retested if it is to be installed in a larger room or a different environment, for example a domestic system with two water mist heads couldn’t be installed in a commercial property with a larger footprint that would need more heads.
The FPA is passionate about improving fire safety standards across the built environment, and is leading the way as one of the first UKAS-accredited fire testing facilities in the UK to offer testing to BS 8458: 2015 for residential and domestic water mist systems. Testing to this standard provides system designers and installers with the assurance that their systems have been tested to the highest standard, and will perform as intended should a fire occur.
FPA test facility
The Fire Protection Association offers testing on residential and domestic water mist systems to BS 8458: 2015, one of the first UKAS-accredited fire testing facilities to offer this service.
As each water mist system is designed for the unique environment in which it is to operate, testing by a UKAS-accredited laboratory provides evidence of the effectiveness of systems using an industry and insurer-approved method. Third-party testing provides evidence of the effectiveness of systems.
This test provides residential and domestic system designers and installers the assurance their system has been tested to the highest standard, and will perform as intended should a fire occur when installed under the test conditions. The independent testing facility also provides an ideal environment in which to research and develop residential systems.
Nozzle testing
Regular testing of water mist nozzles helps to ensure that systems will continue to perform as intended in the event of fire. This should only be carried out by an independent third party to ensure that testing is impartial and unbiased. Removing the nozzles should also only be done by a trained professional, as the water pressure can be so high it could cause serious injury.
The FPA recommends as best practice that nozzles are removed and sent for testing after ten years of service and tested every five years after that. This supports the recommendation of the NFPA 25 standard for the inspection, testing and maintenance of water-based fire protection systems.
While not as well established as sprinklers, water mist suppression is a promising technology and can be especially effective in certain scenarios and building types. Despite this, they often undergo less rigorous testing than sprinklers which is a mistake, especially as systems can vary substantially from one another. Instead, building managers and those involved in the provision of fire safety should be seeking support from a certified third party, to ensure the systems can protect people and the property in the event of a fire.
Standards and certification schemes for water mist systems are continuing to emerge which should, in time, make their installation more straightforward. In addition, more testing is taking place for the approval of components, and manufacturers are developing new products to cater for a variety of scenarios.
For more on the FPA’s advice and support for water mist systems, please visit our water mist services page.
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Jade Musto is Suppression Systems Manager at the FPA.