Into the mist

ALTHOUGH WATERMIST systems have been in use for fire suppression for more than 20 years there are still significant issues around where watermist is an appropriate choice and more significantly to what standards mist systems should be specified and installed. 

The Design of Watermist Systems and Standards

At the outset it should be accepted that all fire suppression systems should meet three tests:

1. The system should be designed in accordance with an appropriate national or international standard.

2. The system components should have been tested and listed in accordance with a specific test standard.

3. The installer should be in possession of third-party certification for the work undertaken.

The publication of BS 8458 and the BS 8489¹ series should have resolved some of the issues which prior to their publication meant that the only broadly acceptable internationally - available watermist standard was NFPA 750². Quite often reference is made to this standard as if it were a design standard - which it is not. 

The wider problems are demonstrated by the somewhat flexible attitude adopted by some companies active in the watermist market towards the question of standards and compliance. Misleading claims are not unusual - for example in quoting approvals for components related to tests under design standards. 

Systems design compliance

In the UK, watermist systems should be designed and installed in accordance with one of the two referenced standards. The standards require that the system application complies with the Scope laid down in the standard. For example, in BS 8489 Part 1, Table 1, a number of suitable occupancies for mist systems are specified. Watermist systems, complying with the three tests outlined above, can therefore being installed in any or all of these with some degree of confidence.

Table 1: BS 8489 Part 1

This list of permitted applications is not without its problems. Note for example, that Table 1 includes ‘hotel bed rooms and their access (only)’. Thus, to fit a watermist system to protect all parts of a hotel, this could not be done under BS 8489 Part 1. This means that the system specifier for the hotel must require the designer and installer to produce other evidence that the proposed system is fit for purpose. This should include one or more of each of the following:

• Fire testing undertaken in a reputable fire laboratory

• Reference to tests already undertaken elsewhere for such an application

• Reference to an identical, existing installation using the same system components whose design was supported by testing

Care should be taken by manufacturers and installers to avoid claims appearing to fulfil these criteria but which on closer inspection do not. 

Systems product compliance

A compliant design is only part of the issue. The equipment to be installed must also comply with fire test protocols (which prove that the system will perform as required) and an appropriate equipment or product standard (which include a variety of tests concerning through-life reliability and durability). At the time of writing, full compliance with this is impaired by the lack of any widely acceptable equipment standards other than for watermist nozzles. It simply is not enough for a manufacturer or installer to claim that a nozzle has been 'tested'. The problem should be resolved with the recent publication of a specific British Standard for testing watermist nozzles, BS 8663-1 (2019) “Fixed fire protection systems – Components for watermist systems – Part 1: Specification and test methods for watermist nozzles ). 

While BS 8458 and BS 8489 set out the essential features of watermist fire suppression systems and include some limited fire test protocols, they are not component test standards. As far as the UK is concerned, the only appropriate watermist nozzle standard should be BS 8663-1 (2019). Where other test standards are quoted these should be no less rigorous.

In the UK, traditionally it has been the LPCB which has tested, certificated and listed active fire system components. In the Watermist section of RedBookLive there is a strong caveat printed in bold (which appears often to be ignored) which relates to the approval of individual components – ‘Watermist component approval does not mean LPCB watermist system approval’. It should therefore be absolutely clear that systems and components must each be certificated

In Section 1.2 of Part 5 of the Red Book we find confirmation that watermist nozzles from three manufacturers have so far been successfully tested by LPCB but there is no reference to any systems being tested and approved.In fact, the only approved system so-far listed is a single, stand-alone “personal protection system’ to LPS 1666.

The following UK-based TPC schemes for watermist systems and equipment are active:

BRE/LPCB Certification

LPS 1283: Requirements and test methods for the approval of watermist systems for use in commercial low hazard occupancies:

No approved companies

LPS 1285: Requirements and test methods for the approval of watermist systems for use in domestic and residential occupancies: 

No approved companies

Watermist nozzles to SD0231 Appendix 4

Three companies' products are listed: Ceasefire Industries PvT Ltd; Prevent Systems AS; Telsto Sp zo.o

FIRAS Certification

Watermist Installers: Three companies listed: Fireworks Fire Protection Ltd, Marioff Limited; Ultra Surefire Ltd

IFC Certification Ltd

Watermist installers: Three companies listed: Premier Mist UK Ltd; Cambrian Electrical; Nationwide Fire Sprinklers Ltd

To summarise and for the avoidance of doubt, it should be understood from that for any company to be able to make an authentic claim of full third-party certification for a particular watermist system, the body undertaking the test must be nationally accredited for that purpose and the standard against which the test has been run must be for the type of equipment and the relevant application. In the UK this means listed by the United Kingdom Accreditation Service (UKAS).

System design 

One of the principle problems which inevitably arise in respect of watermist system design results from the fact that there is no universality of design (as there is with sprinkler systems) and this situation is exacerbated by the fact that watermist nozzle design is unique to each manufacturer. The ‘normal’ approach to managing mist system design is for the system manufacturer (usually the nozzle manufacturer) to issue a Design, Installation, Operation and Maintenance manual (DIOM) which allows the generation of a detailed design for the system in respect of a specific fire risk in a identifiable property. The critical components in watermist systems are the nozzles and the pumps and even a superficial assessment will reveal that there is no commonality of design or interchangeability in respect of the nozzles (in contrast with sprinkler heads). By contrast, the pumps used in low pressure watermist systems tend to be drawn from manufacturers’ available ranges. However, high pressure watermist pumps tend, like the nozzles, to be manufacturer-specific as are compressed gas systems. 

Table 1 (above) makes it clear that there are few ‘low hazard’ occupancies where watermist cannot be used for automatic fire suppression – the Notes making it clear where either the fire load or the size of the compartment is limited may makes watermist less useful.

Other locations where watermist can be used without reservation are those where there is an approved test protocol. – the Table below summarises the applications for which reliable test protocols exist.

Test Protocol	Occupancy/Application	Observations
BS 8458	Residential and domestic premises	As defined stated in Table 1
BS 8489-4	Local applications involving flammable liquid
BS 8489-5	Protection of combustion turbines and machinery spaces up to 80m3	See also FM 5560-A/B
BS 8489-6	Industrial oil cookers	See also FM 5560-J
BS 8489-7	Low hazard occupancies	As defined in BS 8489-1 from Category I – III and limited by table 1 and associate notes

Table 2: Acceptable Test Protocols and Hazard Classifications

Conclusions

Water mist is a promising technology with many physical characteristics that make it effective and attractive in some fire protection scenarios but, with misunderstandings regarding specification. Supporting standards and certification schemes are still emerging with many significant issues still not adequately dealt with. There are low levels of system and component interoperability and this has the potential to cause significant through-life issues. For would-be buyers and specifiers, watermist may be a good option in specific occupancies, however, end-users and their advisers are urged to exercise caution and recognise the problems which still exist. Authorities having jurisdiction including the fire and rescue service and building control officials should also exercise caution when recommending or proposing the use of watermist without ensuring that the systems which will be installed are fully compliant with British Standards, by installers who are fully competent using tested equipment. The views of insurers should always be sought before committing to any significant expenditure on fire suppression systems.

References

^{1 } BS 8458:2015 Fixed fire protection systems. Residential and domestic watermist systems. Code of practice for design and installation; BS 8489-1 (2016): Fixed fire protection systems – Industrial and commercial watermist Systems Part 1: Code of practice for design and installation

^2  NFPA 750 – 2019: Standard on Water Mist Fire Protection Systems

Stewart Kidd is managing director at Loss Prevention Consultancy. For more information, visit www.risk-consultant.com