Water Mist Fire Suppression Systems

The increased use of automatic fire suppression systems in the residential sector is driving developments of new systems in a quest to replace sprinklers which have been around for many years.

In the meantime, development of sprinkler systems has continued and the latest designs are low cost, use less water and are concealed from view so address the issues of older designs.

There are a number of new types of system on the market which purport to be better than sprinklers in some way or other – and this attracts our attention, as we are keen to be using the best systems available for clients.

To establish the viability of  a system, and whether it can compete with or replace the latest domestic sprinkler system, we need to give it a high degree of scrutiny and undertake a comparison.  Our guiding principles for any system we install for life saving purposes is that it must be of high quality build, fit for purpose and ideally have some identifiable life-saving history.

Through many years of operation , there’s been no better way to protect lives and property from fire than a sprinkler system – whether domestic and residential to small and large-scale commercial buildings.  In many cases legislation and the Insurance industry require sprinkler systems to be installed.    More recently, various types of Mist Systems are being marketed as an alternative to Sprinkler Systems in the domestic and residential environments to protect lives.


A Water Mist System: After 5 mins the fire brigade step in to fully quench the fire

Sprinkler System: 60 seconds and the fire is out.

The Technology comparison

There are 2 types of Mist System:  Low pressure Mist and High Pressure Mist and we compare these to a sprinkler head..

Low pressure mist systems:  have many similarities to sprinkler systems – they use very similar infrastructure, but the heads are different (mist heads emit finer water droplets).  Whilst these are low pressure mist heads, they still work at a much higher pressure than sprinkler heads and more than most water mains can supply, so a pressure pump is always needed to operate the system.  Interestingly, the specifications and tests show that mist heads require more water to operate than an equivalent low-flow sprinkler system.  There is no fully concealed version of mist head at present so possibly not as aesthetically pleasing as a concealed sprinkler head.  These ‘low pressure’ mist heads are more costly than sprinkler heads so the systems will generally be more costly to install.

When compared to sprinkler heads, the disadvantages of low-pressure mist systems are:   a) visibly less pleasing   b) greater water usage (when compared to low-flow sprinkler heads)   c) more costly   d) a proprietary product    e) always needs a pump and    f) real-world unproven in terms of fire suppression capability.   It’s difficult to see why we would use these instead of the proven sprinkler heads.

High pressure mist systems:  have many differences to standard sprinklers and little standardisation between manufacturers components.  High pressure systems use very high pressure water pumps and pipework which is fed around the fabric of a building to the mist heads.  Less water is used because the mist is very fine – similar to a fog – and shoots from the head at high pressure towards the fire.   Coverage of each head is limited when compared to sprinkler heads, so careful design and head positioning is necessary to ensure all areas are protected.  It is unknown how long a high pressure pump or indeed it’s pipework will last as the high pressure-retaining components will deteriorate over time – necessitating full replacement.  Because of the high pressures, coverage of larger buildings is a problem so multiple systems or additional booster pumps may be needed – this pushes up the complexity and cost.  Indeed, for a block of flats, a self-contained system per flat would be necessary.  This introduces multiple points of failure for a block of flats.  We think cost of ownership could be a real and costly issue for these system and once again, there they are not proven in the real-world.

When compared to sprinkler heads – it is most common for a sprinkler system to be supplied from a single water supply to the building – whether this be the mains water or a single tank and pump.  So, in the case of a block of flats this minimises the points of failure to the one installation.  Where a sprinkler system is supplied from the water mains, there are no electro-machanical components to go wrong.

There is currently no third-party certification for mist heads

The important question is, do mist systems provide an effective fire suppression alternative to Sprinklers?

Real-world evidence provides ‘proof of effectiveness’ for any fire suppression system – i.e. instances where a system has activated and saved a life and / or property from being destroyed.

There are substantial instances where sprinkler systems have saved lives and property – some of which can be found here e.g Sprinkler saves: https://www.bafsa.org.uk/bafsa-news-events/sprinkler-saves/.  

We have been unable to find instances of mist system ‘saves’ using the normal search methods and would welcome any such information from readers.

With what seems to be a lack of real-world evidence, we could simply accept the mist manufacturers specifications and controlled tests – but in a life-saving application, we have to ask if this is sufficient guarantee that it will work.

Indeed, as described below, the mist standard for domestic / residential BS8458 is far from being as comprehensive and specific as the Sprinkler standard BS9251, and the onus is on the Authority Having Jurisdiction (AHJ) and certified installers to go through a detailed test and confirmation regime to confirm if the proposed system and it’s installation design will be fit-for-purpose in each and every building.  This introduces a significant degree of subjectivity and requires an AHJ to hold specific knowledge of the system in order to quantify and validate the results.  We believe this is quite risky in a critical fire safety application.

Since companies such as ours are relied on to provide a fire suppression system which is always fit for purpose, the issues with mist systems weigh heavily on our choice for any given application.

Comparing the sprinkler standard BS9251 to the mist standard BS8458

The following should be noted…

1. The mist standard  BS8458 is ‘Application Specific’.    It is the ‘Application Specific’ nature of BS8458 amongst other aspects which differentiates it from the sprinkler standard BS9251: 2014 which is not application specific.  Any suggestion they are equivalent is misleading.

2. Currently Mist system components have no certification.  But for most life-critical applications, the third-party certification gives an important stamp of approval.

To install a mist system an installation checklist should be followed and the affects of the surrounding environmental conditions taken into account.   The ‘Mist system installation checklist’ differentiates the installation from sprinkler systems which have no need for such a requirement.

The Mist system installation checklist* as recommended by the British Automatic Fire Sprinkler Association (BAFSA):

  • Has the system been tested and approved by a third party approval body such as LPCB, VdS, UL or FM for the specific application intended?
  • Has all testing been carried out by a capable laboratory such as BRE, FM, UL, SINTEF, VdS, SP, VTT or CNPP?
  • Are products and components specific to the system approved for such use by a qualified third party approval body?
  • Can all claims made by the system supplier be verified?
  • Is there a formal agreement between manufacturer and installer?
  • Has the installer received training from the manufacturer?
  • Does the testing and approval data correspond to the intended use of the system?
  • Does the geometry of the space to be protected, including ceiling height, correspond to the testing and approval data?
  • Where insurers are the AHJ, ensure compliance with the insurer’s requirements /questionnaire / checklist.

*Extracted from British Automatic Fire Sprinkler Association – Information leaflet

Why are Mist systems application specific – it’s not possible to establish the fire suppression performance of a mist system until it is tested and/or analysed as an installed system in the particular building.   This is because there are factors – such as the immediate environment – which can affect the correct operation.  An simple example would be a significant draft (perhaps caused by open windows or doors) occurring in the vicinity of the mist head which could affect the mist jet and whether the fire is in a larger open area where the mist could dissipate too quickly away from the fire.  After all, mist is made up of very small and light particles of water (similar to a fog).

A closed environment (such as a plant & Machinery room) will likely remain closed during a fire outbreak so a mist system should work well – but is a room with people – doors and windows will get opened.   See the demo videos on this page of a sprinkler system and a mist system in operation and make your own mind up.

Currently, the opinion from BAFSA and others (including insurers) is that this unproven technology should be used with considerable caution.

Mist Systems generally fall short of the industry standards of sprinkler systems in the following ways:

  • A mist system cannot be FIRAS certified at present
  • No standardisation of components between manufacturers
  • Manufacturers going out of business and unavailability of proprietary spares for servicing
  • A lack of examples of actual lives saved as a result of a mist system activation.  (There are many thousands of sprinkler life saves)
  • No significant in-service life history of components (and especially the high pressure components which can be more fragile)
  • Can easily be affected by the environment – operation in open areas and areas where drafts occur is likely to be problematical
  • Poor installation record and components malfunction after installation (possible high degree of maintenance over the working life)

As a last note, the importance of using manufacturers and certified installers who have been in business for a good while, with sound knowledge and capability is crucial – very few companies will take over responsibility of installation by suppliers who may come and go.  So you could be left with a system that no-one wants to maintain or service.

A well known review website has this to say about a particular mist system..  https://uk.trustpilot.com/review/www.mistsafetyuk.co.uk

So, whist there are applications where a mist system can be considered, we are of the opinion that there is a very big question mark over the use of a mist system in a life-saving application – especially where vulnerable people may be present. 

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Domestic Sprinklers Cornwall Limited

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