Exclusive: Water mist system design and review

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Luciano Nigro, Jensen Hughes Italy and Member of the IWMA Board evaluates the tools assisting fire engineers and authorities in system selection and approval

Water mist technology can now be considered a mature fire suppression technology as it has entered the third decade of installation both in marine and in land-based applications. Initiated more than 30 years ago to support the Halon replacement on board of ships, the technology grew rapidly achieving almost 100% of the marine fire protection market on board passenger ships, protecting all the hazards from the machinery spaces to the accommodation and public spaces.

By the end of millennium, water mist applications for land-based occupancies were developed, based on several fire test protocols published by international organisations including Factory Mutual Approvals, UL, VdS, LPCB and others. Nevertheless, in the land based market the technology has not yet achieved the diffusion that could reach, for various reasons one of which, it is the opinion of the writer, remains the difficulties that fire engineers, designing and/or reviewing water mist system for acceptance, find in the process of selecting the system appropriate for each application and in verifying the adequacy of the design parameters that have been used per each system.

To support the fire engineers in this commitment, the IWMA (International Water Mist Association) has developed, in recent years, a descriptive document called the “Project Water Mist – an Alternate Solution to Sprinkler Protection in Building Fire Protection” published in 2014 and a working tool called THE MATRIX – both available on the IWMA website.

The document is a complete list of all the fire test protocols available on the market at the date of its publication with the description of the occupancies to which they apply and the indication of the organisations that developed and published them.

The MATRIX was then studied and developed by the IWMA Scientific Council, with advice from association members, to become a real working tool for the fire engineers, having a structure more attuned to the design and review activity a fire engineer undertakes, and being updated on a constant basis to be representative of what is state-of-the-art – this is a key focus when designing and installing an advanced technology fire suppression system.

A partial view of the summary of the MATRIX outcome for the Land Based Applications is summarised by the table here below; The complete MATRIX is published both for Marine and Land Based applications which can be accessed at: https://iwma.net/the-matrix/land-based-applications.  


The MATRIX for Land Based Applications serves as a guideline for fire engineers to understand the complexity and nuances involved in water mist fire suppression systems across various business segments and contains five columns of information.

The first column refers to the business segment of the case under consideration, divided into Residential, Commercial and Industrial. The second column is the most important for the fire engineer – it is the column dedicated to the Applications and is the key point for the correct interpretation of the MATRIX. The selection of the application that more accurately represents the fire hazard related to the “formal” applications for which a test protocol exists, requires considerable judgment from the fire engineer.

Of course, the real world is not so simple, because the applications listed in the Application column of the MATRIX are not easily related to the actual application under consideration; paragraph of the EN 14972-1 states: “Test protocols: one of the greatest challenges to engineering of water mist fire suppression systems lies in determining whether the conditions of a particular and recognised test protocol are representative of the actual conditions in a given application based on an understanding of the dynamics of the interaction of water mist with fire.”

Upon closer examination, certain applications have clear and well-defined relationships, for example the “car garages/parking garages”, but there are also several applications that are not so well defined as for example “residential occupancies” or “data halls”. In all these cases additional information is needed to relate the applications listed in the MATRIX and the real world.

The third column of the MATRIX is the Test Protocol column; third and fourth columns fully identify the test protocol(s) existing for a given application. The list is updated regularly by the Association therefore it can be considered as the most updated list of water mist fire test protocols presently available worldwide.

As mentioned, there are many applications for which more than one protocol is available; how to select the protocol that best fit the actual application under consideration remains with the responsibility of the fire engineer.

The last column identifies the type approval that can be obtained by ‘positively passing’ each test protocol mentioned in the previous columns. This column differentiates between test protocols that result in a formal approval, indicating the organization granting the approval, and protocols that are not intended for formal approval but are instead provided to the market as reference protocols. These reference protocols are intended for use by authorities having jurisdiction, laboratories, verification agencies, manufacturers, and other relevant entities.

For those that are not so much familiar with the type approval process, it is possible to say that the fire test protocols are the procedures issued by the organisations involved in the water mist fire suppression technology to run each of the mentioned test. They list the materials to be used, the procedure to run the tests, and the pass-fail criteria to determine the outcome of the tests.

Approval and Standardisation

To complete these considerations, it should be noted that the organisations issuing fire test protocols for water mist applications are few and can be divided in two groups: the Approval Bodies and the Standardisation Bodies.

Approval Bodies for water mist applications include FM Approvals1, UL2 and VdS3; the Standardisation Bodies include the CEN4 committee on water mist system and the BSI5. As it is possible to see on the MATRIX table, the Approval Bodies always grant a type-approval for the system passing the test protocol for the specific application; the Standardisation Bodies normally do not, except for the residential applications tested according to BS standard 8458 that are approved by the LPCB6.

The approval issued by an Approval Body is a very useful information document also for the above-mentioned matter concerning the correlation between the test protocol and the actual application under consideration. An example is the chapter 1.2 of the FM standard 55607 where all the 16 applications for which FM Approvals has issued a test protocol are described in detail with all the applicable limitations and/or extensions.

The same does not apply to the test protocols issued by the Standardisation Bodies that also include a paragraph per each protocol describing the scenarios to which the protocol can be applied, but this information is “embedded” in the test protocol text and is not easily available to the fire engineer.

The above is a complete description of the MATRIX content. All the information included in the MATRIX is carefully verified and checked by the IWMA Scientific Council that includes some of the most relevant professionals dealing with water mist technology world widely.

However, there are some comments and recommendations that need to be considered in order to improve the content and make it even more useful for fire engineers.

Considerations for fire engineers

The correlation between the fire test protocol and the actual application under consideration poses challenges for fire engineers. Test protocols issued by Approval Bodies are expected to provide all the necessary information for their correct use and hold liability for their indications. However, achieving a clear correlation is less straightforward when dealing with Standardisation Body protocols.

The second and most important comment is related to the real availability of the system on the market. With the MATRIX it is only possible to say that, for a given application, one or more test protocols exist and whether they lead to a type approval or not, but no information is given about the availability of one or more manufacturers that can provide a water mist system designed and installed in accordance to the test protocol under consideration.

The identification of the manufacturer(s) holding an approval or having carried out a fire test according to one of the test procedures issued by the Standardisation bodies remains a responsibility of the fire engineer in charge for the design of the system.

Future steps

Ensuring the continuous update and maintenance of the MATRIX is of utmost importance for both the tool itself and the IWMA. This commitment aims to provide tangible support to fire engineers engaged in the design, installation, or verification of water mist systems in land-based applications. By keeping the MATRIX up to date, it serves as a valuable resource for professionals in this field.

Two possible enhancements could significantly aid in selecting the correct protocol for a given application. Firstly, adding a new column alongside the existing ones to provide a detailed description of the specific application to which the protocol is applicable would offer valuable assistance. Alternatively, introducing a supplementary page in the summary section where each protocol line is accompanied by a comprehensive description of the applicable scenarios mentioned within the protocol itself would also prove beneficial in facilitating protocol selection.

Finally, the availability of water mist systems on the market: this is an issue going above the scope of the Association.

The MATRIX provides the list of occupancies and protocols, but the demonstration that a company has successfully passed a protocol remains with the fire engineer responsibility to ascertain. As stated in the last sentence of the introduction to EN 14972-1: Water mist is a specific application solution which needs to be proven for each individual application and/or occupancy.


This article was informed by a range of resources, including the SFPE Handbook of Fire Protection Engineering, FM Approvals, UL’s water mist system testing, VdS’s fire protection content, and CEN/TC191/WG10’s material on Water Mist Fire Fighting Systems. Also referenced are the EN 14972 series, standards by BS, the LPCB’s Red Book, and the FM Class Number 5560’s January 2021 edition on Water Mist Systems.

This exclusive article was originally published in the June 2023 issue of International Fire & Safety Journal. To read your FREE digital copy, click here.

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