Is a Mist Fire Suppression System fit-for-purpose in your home?

We often see the terms – Sprinklers and Mist –  being used interchangeably.  But they are very different systems and each has it’s own specifications and standards.

There is now – more than ever – an increased focus and scrutiny on the effectiveness of fire protection strategies in commercial and residential buildings. Negligence or simply being unable to prove that the proper precautions have been taken means risking legal action.

As a starting point, we refer to the the Fire Safety Regulations Approved Document B.  This key regulation document clearly refers to the use of Sprinklers and the Sprinkler Standard BS9251 – but makes no reference to Mist Systems or BS8458 as an option or otherwise.

And to be very clear, BS8458 is most definitely not equivalent to BS9251.

In some circumstanses under BS9991, watermist systems can be deemed as an appropriate fire suppression solution so long as agreement can be sought with the relevant Authority Having Jurisdiction (AHJ) such as a Building Control Officer.  But (and this is the big one),  specific scenario testing is required as evidence to prove that the system is fit for purpose.

If an AHJ (or anyone else for that matter) recommends a mist system, they become equally responsible for evaluating and confirming that the system has passed all the installation and operational checks to be fully effective in the proposed building! (see below: The Mist system installation checklist)

But recommending or specifying a sprinkler system under BS9251 passes no responsibility onto the AHJ – other than receiving from the installer a FIRAS endorsed certificate!

In test cases, a mist system can put out certain fires – but it has to be said they take considerably longer than a sprinkler.  Furthermore, a mist system can be effected by the immediate environment – which has a habit of changing (doors & windows open/closed, furniture gets moved around).

And whilst it’s easy to find many examples where a Sprinkler system has saved lives – the same cannot be said of Mist Systems.


The current fire safety landscape…

The Grenfell tragedy has become a defining moment in the history of Fire Safety in the UK.  The enquiries and reports conclude that it’s not, and should never be, just about meeting regulations.

Regulations are defined at a moment in time and the industry is good at finding different ways to conform (legitimately in most cases) – especially to save costs.

But the building industry also has a DUTY OF CARE – which goes beyond meeting regulations – to ensure that materials and systems installed are appropriate and Fit-for-Purpose.

Public anger aborted the first Grenfell inquiry hearings which started on Monday 2nd March 2020 ….

Grenfell survivors will ‘not settle for anything less’ than prosecutions  – So tensions are running high and responsibilities are being tested!

Faced with a probable increase in LIABILITY and PROSECUTIONS if things go wrong, we need to pause before simply accepting the marketing hype from suppliers and base ‘critical decisions’ on real-world empirical evidence.

Indeed, the Grenfell enquiry has highlighted possible cases of misleading marketing/sales tactics with respect to materials used for critical elements of construction – and in a similar vein, we have come across a considerable amount of misleading and downright incorrect information relating to mist systems – so caution is strongly advised.


What are the key deciding factors…

Given that sprinklers are a proven technology, it then become a simple case of examining whether Mist systems are capable of equaling or improving on a Sprinkler system.

The environmental factors

Mist systems can be affected by various environmental conditions.  Open doors or windows or furniture obstructing the mist spray or open spaces etc can all impact the effectiveness of a mist system.   An example is the movement of furniture.  Many Mist heads are typically set at a low height of around 1.4 – 1.5m up from the floor – how many people will always respect the full direction and span of spray from a mist head in a room when they are moving and replacing furniture?  and what about new owners – will this knowledge be transferred?

These impacting factors are the reason why the Mist stsndard BS8458 is ‘Application Specific’.  Each and every Mist installation should be tested as-installed to confirm it works as intended (and how is this accomplished?) – but even this installation test can not guarantee it will work in the future.

System complexity (the devil is in the detail)

Fact… there are many more potential points of failure in a Mist system!   A sprinkler system with mains fed water supply has no electrical components (other than a simple flow switch) and no moving parts and everything is working stress free.  But a mist system has a tank and a very high pressure pump, high pressure seals and high pressure pipework running around a building.  There are minute orifices in the mist heads which could get clogged, and some mist heads have scanning/moving parts.  And many mist systems need an additional fire detector in the ceiling – which can look ugly.  All these components can and do fail.

Indeed certain higher stressed component will have a limited life span and will need to be replaced at considerable cost – and annual servicing is a must.  In comparison, a mains fed sprinkler system can easily operate over tens of years without being touched.

  • Mist system have many points of failure – mains fed sprinkler systems have very few by comparison

  • Mist systems are affected by environmental factors such as open spaces and drafts –  sprinklers are not.

  • Mist systems installers have no third party accreditation.  Sprinkler installers can be FIRAS accredited.

  • Mist systems from different manufacturers are incompatible.  All sprinkler system conforming to BS9251 are compatible.

  • Since mist systems are incompatable, installation companies are typically single supplier trained.

Sprinklers have a clear advantage – A sprinkler system fed from a mains water supply will be cheaper and more reliable than any mist system – both in the short and longer term.


Installation considerations of mist system

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.

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.

3. 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 of the environmental factors 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.  Another could be that the resident has put something in the way of the mist head.

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.

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.

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