FM Approved Water Mist System

  • The Hazard

    Beyond the typical fire protection scenarios that can be addressed with conventional sprinkler systems, there are many situations or environments that call for special fire protection. In these situations, the potential result of a fire could be catastrophic to property and life, where even a small fire could have devastating consequences.

    For instance, special situations or operations may include industrial turbine enclosures, semiconductor clean rooms and wet benches, food processing lines, industrial oil cookers, power plant turbines, raised floor spaces in data centers, and continuous wood product processing.

    In the ultra-clean world of semiconductor manufacturing, for example—where the air is 10,000 times cleaner than the average office—cleanup from even a relatively minor fire can take weeks, resulting in large financial losses, lost market share and lost orders. It’s estimated that downtime in this industry costs approximately US$1 million per hour.

    In this and other special applications, particularly environments that are sensitive to water damage, water mist fire suppression systems have long been used. Water mist has many unique properties that make it an excellent suppression and extinguishing agent for many special applications. In enclosed spaces, the atomized water droplets are quickly drawn to the base of the fire along with room air. The water instantly flashes to steam replacing the oxygen needed for combustion.

    This effective extinguishing action, along with an overall cooling and air scrubbing effects, make water mist highly effective when delivered correctly. Unlike most flooding agents water mist works in areas where a door or vent has been left open and does not pose a health risk to occupants or firefighters, and it is environmentally benign.

  • Testing Required for FM Approval

    All FM Approved water mist fire protection systems have undergone extensive testing in accordance with the requirements of Standard 5560, Approval Standard for Water Mist Systems. This standard provides the most comprehensive single source of water-mist test requirements in the world for land-based applications.

    Approval Standard 5560 provides test requirements for specific occupancies and applications that FM Approvals has tested and verified. These specific applications and occupancies are covered in appendices to the standard, including

    • Machinery spaces and special hazard machinery spaces with volumes up to or exceeding 9175 ft3 (260 m3);
    • Combustion turbines enclosures;
    • Industrial oil cookers;
    • Light-hazard occupancies such as nonstorage and nonmanufacturing areas, residential, offices, meeting rooms, hotels, museums, restaurant seating areas, institutions and schools;
    • Wet benches and similar processing equipment;
    • Local application occupancies;
    • Computer room subfloors; and
    • Continuous wood board presses

    Since each water mist system is unique in its operation and design, component testing of the water mist system is done on a case-by-case basis. The 296-page Approval Standard 5560 includes performance requirements for almost every type of water- mist system component.

    Water mist systems can be categorized as single fluid or twin fluid. A single-fluid system uses a single pipe network to supply water mist nozzles. The twin-fluid system uses two independent pipe networks to supply water and compressed air or inert gas separately to water mist nozzles. Extinguishing systems using compressed air as their atomizing medium shall be considered a twin fluid water mist system and be evaluated according to Approval Standard 5560.

    Fire extinguishing systems that use an inert gas and water, where both components are critical factors in fire control, suppression or extinguishment, are known as hybrid systems. The gases used in hybrid fire extinguishing systems may include helium, neon, argon, nitrogen, carbon dioxide or various gas blends.

    Hybrid fire extinguishing systems are evaluated in accordance with Approval Standard 5580, Hybrid (Water and Inert Gas) Fire Extinguishing Systems. Since each hybrid system is unique in its operation and design, the component testing of the system shall be performed on a case-by-case basis. Upon request for a program, and appropriate system documentation, FM Approvals will prepare a customized evaluation program for the specific hybrid system.

  • But What About...


    It is important to understand the product manufacturer’s pricing structure. It may appear that the cost of a tested and certified FM Approved water mist system is more than that of a comparable, non-certified system. Reputable testing and certification organizations such as FM Approvals will run tests and perform facility audits, which may, in fact, increase the cost of the product compared to similar, non-certified products, but not always.

    The best place to start any pricing comparison is the manufacturer’s website. The Approval Guide, an online resource of FM Approvals, provides links to the websites of most manufacturers that produce FM Approved products along with the listing for the products. That link will often go to a pricing sheet, or at least to a representative who can explain the actual cost that a manufacturer is charging his customers.

    ...Installation guidelines?

    FM Approved water mist fire control and/or extinguishing systems are complemented by the guidelines for installation, use and maintenance provided by FM Global Loss Prevention Data Sheets. Some of the Data Sheets that address water mist systems include: 4-2 Water Mist Systems, 7-79 Fire Protection for Combustion Turbine Installations, 7-7 Semiconductor Fabrication Facilities, and others in the 7 series.

    ...Local code and jurisdictional requirements?

    FM Approvals incorporates jurisdictional and code requirements into its testing Approval Standards as well as providing rigorous property loss prevention criteria. All users of FM Approved products can rely on these products to be acceptable by local jurisdictions, as well as provide the loss prevention solutions prescribed by FM Global.

  • Success Stories

    Kill the Fire—Don’t Fight It

    According to a report in the journal Professional Mariner, a water mist system put out a fire in the main machinery spaces aboard a high speed ferry operating between Helsinki, Finland, and Tallinn, Estonia, in August 2000. The fire resulted from a turbo charger failure. The ferry owners noted that the water mist system did the job it was designed for: to “kill the fire, not fight it.”