An FM Approval and a UL listing are different kinds of evidence. FM 5560, FM Approvals' Examination Standard for Water Mist Systems, certifies a complete water mist system for a named occupancy (FM 5560, January 2021). A UL 2167 listing covers a nozzle, tested to Water Mist Nozzles for Fire Protection Service (UL 2167, third edition, May 2026). NFPA 750, the US water mist standard, relies on evidence of this kind: it sets no fire performance criteria of its own and requires components to be listed for their intended use, as we explain in NFPA 750 explained.
What does an FM Approval certify?
FM 5560 sets the testing and certification requirements for water mist systems used for fire control or extinguishment. Its stated purpose is property conservation: verifying that a product meets stated conditions of performance, safety and quality. Certification rests on three things (Section 1.4):
- tests on production samples, for suitability, performance and, as far as practical, durability and reliability;
- an examination of the manufacturing facilities and an audit of quality control procedures;
- a review of the system's design, installation, operation and maintenance (DIOM) manual.
Certification lasts only while the product stays as certified. FM 5560 lists surveillance audits, re-examination of production samples and satisfactory field experience among the conditions for keeping it (Section 1.5).
The component tests are tailored. Because each water mist system works differently, FM Approvals prepares an evaluation programme for the specific system, and the component section runs from nozzles through pumps, valves, piping, hoses, control panels and detection devices to water storage tanks. The fire tests are not tailored: they are generic protocols that every system must pass for each occupancy it is certified for (Sections 1.2.1 and 4).
Which occupancies does FM 5560 test?
A system is certified for specific applications and specific protected volumes, and FM 5560 does not allow results to be extrapolated beyond the volumes tested except where it says so (Section 1.2.3). The January 2021 edition has fire test protocols for:
- machinery in enclosures up to 80 m³ (2,825 ft³), up to 260 m³ (9,175 ft³) and above 260 m³ (Appendices A, C and E);
- gas turbines in enclosures, in the same three volume bands (Appendices B, D and F), with a ½-scale option for the largest machinery and turbine enclosures (Appendix O);
- non-storage occupancies in Hazard Categories 1, 2 and 3, where Hazard Category 1 was formerly called light hazard (Appendices G and P);
- wet benches and similar processing equipment (Appendix H);
- local application (Appendix I);
- industrial oil cookers (Appendix J);
- continuous wood board presses (Appendix K);
- chemical fume hoods (Appendix L);
- data processing equipment rooms and halls, above and below a raised floor (Appendices M and N).
So the useful question is never whether a product is "FM approved" in general. It is whether a listing covers this occupancy at this volume.
Does FM 5560 cover tunnels?
No. Road and rail tunnels are not among its occupancies. Cable spreading rooms and cable tunnels appear only in Appendix Q, a list of other occupancies of interest; for those, a manufacturer applies to FM Approvals in writing and the component and fire test requirements are developed jointly (Section 1.2.3.16). UL 2167's scope does not include tunnels either.
For a tunnel, then, neither listing answers the fire performance question. That evidence comes from full-scale fire testing, and the specification should name the protocol and agree the pass/fail criteria before the test. We explain what the SOLIT tunnel fire tests showed, and why system fire tests and component certificates answer different questions.
What does UL 2167 cover?
UL 2167 sets minimum fire-protection performance, construction and marking requirements for water mist nozzles. Its scope is nozzles for systems protecting residential, light hazard and ordinary hazard areas, and shipboard machinery spaces, control spaces, service areas and public spaces. The intended use of a listed nozzle is set out in the manufacturer's design and installation instructions. The third edition was published, and ANSI-approved, on 11 May 2026, replacing the 2021 second edition.
A UL 2167 listing is evidence about a nozzle in the hazards UL 2167 tests. An FM 5560 certification is evidence about a system, with its nozzles, pumps, valves and controls, in a named occupancy at a tested volume. They answer different questions, so a submission should say which document supports which part of the design.
FM or UL: which does a project need?
NFPA 750 requires water mist system components to be listed for their intended use, with narrow exceptions, and a system to be designed and installed in accordance with its listing. NFPA defines a listing as one published by an organisation acceptable to the authority having jurisdiction, so the standard itself does not choose between FM Approvals and UL (NFPA 750, 2006 edition). Which evidence a project accepts is set by its specification and its authority having jurisdiction. Ask for the document that covers your occupancy, then read its limits.
What should a listing tell you?
FM 5560 sets out what a water mist certification listing must state (Appendix V). Check that the listing in a submission gives:
- the manufacturer's designation for the system;
- single-fluid or twin-fluid, continuous or cycled discharge, and the discharge parameters;
- nozzle operating pressure and/or flow rate;
- the hazard, with its protected volume, area or height limits;
- minimum and maximum installation temperatures;
- the DIOM manual, by title, part number, issue date and revision;
- for engineered systems, the design software and its version;
- any limitations or exceptions to the certification, and the installation provisions.
If the space in front of you falls outside the listed volume, FM 5560 does not allow the test result to be stretched to cover it.
Where Mistelix stands
FM Approval and UL listing are planned. Mistelix holds neither today, and until the certification documents exist this site will not describe any Mistelix system as FM Approved or UL Listed. We design our systems with reference to NFPA 750, and full-scale fire testing is planned. The live status of every standard we work to is in our approvals ledger.
Sources: FM Approvals, FM 5560, Examination Standard for Water Mist Systems (January 2021), Sections 1.1–1.5 and 4 and Appendices A–Q and V; UL Standards & Engagement, UL 2167, Water Mist Nozzles for Fire Protection Service (third edition, 11 May 2026), Scope; Public.Resource.Org, NFPA 750, 2006 edition, Sections 3.2.3 and 5.1.1, for the listing definition and the component listing rule.