Kerry Bell, UL Solutions Principal Engineer, Corporate Fellow - Fire Sprinkler and Pump Equipment
Brian Paoletti, UL Solutions Staff Engineer
UL Solutions recently Certified a water mist fire protection system unit intended to detect and identify the specific location of a threatening fire within a living space. This unit then directs a high-pressure water mist spray that uses a relatively small amount of water towards the specific fire location to prevent flashover and improve the opportunity for occupants to escape when installed in one- and two-family dwellings. This innovative system utilizes a combination of both smoke and flame sensing to identify the specific location of a fire. While smoke sensing is integrated into the design of the water mist system, this sensing is not to be used as a substitute for or replacement of a separate smoke alarm that is required to be provided in accordance with a building, fire or life safety code.
Installation Standards
This water mist system unit is intended to be installed in one- and two-family dwelling units in accordance with the applicable provisions of NFPA 750. Specifically, section 10.3.2 of the 2023 edition of NFPA 750 includes requirements for this end use application and information for locating the water mist fire protection system nozzles within a one- and two-family dwelling. The requirements in this section are similar to NFPA 13D and do not require protection for all areas of the home, such as garages, attics, small bathrooms, small closets and other areas where the incidence of loss of life from fires in dwellings is low. The scope of UL Solutions testing and evaluation was based upon installation in one and two-family dwellings; therefore, these units are not UL Certified for use in dwelling units located in other types of residential structures.
System Unit Equipment Scope and Relevant Requirements
The UL Certified water mist system for Plumis Ltd. integrates several pieces of equipment and incorporates sophisticated software to achieve its fire protection objective. Key equipment provided as a part of the system unit consists of the following:
- Smoke sensor
- Motorized water discharge nozzle with integral flame detection capabilities
- Motor driven positive displacement pumping unit
- Water inlet control and check valves with a strainer
- Unit controls to manage the operation of the entire system
The requirements for the system unit equipment are described in a new standard entitled Outline of Investigation for Targeting Water Mist System Units for One- and Two-Family Dwellings for Fire Protection Service, UL 2167A. The breadth and sophistication of this system unit necessitated the application of relevant requirements from many existing UL standards.
Fire Testing
A critical element associated with evaluating the ability of a fire suppression system to effectively attack a fire are the fire tests. For residential sprinklers incorporating a fixed heat responsive element to detect and discharge water in the fire area, a simulated furniture fire test package located in a corner of the room is used to evaluate this type of fire suppression technology. See Figure 1 for a photo of this fire test package.
Since this innovative water mist fire protection system unit is designed to direct the water discharge of a single nozzle towards the fire location, an extensive series of fire tests was determined to be necessary to evaluate the effectiveness of the nozzle to attack different types of fires in addition to the fire test package used to evaluate residential sprinklers. To investigate the capability of the motorized nozzle to attack a fire that could travel horizontally along the entire length of a couch, UL Solutions developed a simulated couch fire test. The simulated couch was constructed in a manner and of materials considered to be representative of commercially available couches. See Figure 2 for a photo of the simulated couch. The fire testing also includes tests to simulate a cooking oil type fire that may occur in a kitchen.
Figure 1 – Photo of simulated furniture located in room corner
Figure 2 – Photo of simulated couch
Considering that multiple nozzles may be installed within a room or space depending upon the overall room size and configuration, fire tests were considered necessary to evaluate the ability of the unit to select an appropriate nozzle to attack the fire within its coverage limitations. Tests were also conducted with external obstructions to the nozzle discharge that are permitted in the manufacturer’s installation manual in addition to fire tests conducted without obstructions. As referenced in Table 2, a total of 17 fire tests were conducted to evaluate the unit’s ability to effectively control the fires.
During the fire testing, the unit was required to limit temperatures within the room as follows, which is similar to the criteria applied to residential sprinklers:
a) The maximum temperature 3 in. (76 mm) below the ceiling at the center of the room shall not exceed 600 °F (316 °C);
b) The maximum temperature at the location 63 in. (1.6 m) above the floor at one of two specified locations is not to exceed 200 °F (93 °C);
c) The temperature at the location described in (b) is not to exceed 130 °F (54 °C) for more than any continuous 2-minute period during the test at one of two specified locations; and
d) The maximum ceiling material temperature 0.25 in. (6 mm) behind the finished ceiling surface directly over ignition shall not exceed 500 °F (260 °C).
Table 2 – Description of Fire Tests
| Test No. | Fuel Package | Location of Fire In Regard to the Nozzle | Nozzle Obstructed? | Room Size |
|---|---|---|---|---|
| 1 | Fabricated sofa with combustible wall | Far wall | No | Based upon maximum nozzle coverage |
| 2 | Fabricated sofa with combustible wall | Near wall | No | Based upon maximum nozzle coverage |
| 3 | Fabricated sofa near center of room | Near wall | No | Based upon maximum nozzle coverage |
| 4 | UL 2167 Residential Dwelling Units Fire Test | Far corner | No | Based upon maximum nozzle coverage |
| 5 | UL 2167 Residential Dwelling Units Fire Test | Near corner | No | Based upon maximum nozzle coverage |
| 6 | Same as Test No. 4 with drapes in lieu plywood walls | Far corner | No | Based upon maximum nozzle coverage |
| 7 | Same as Test No. 5 with drapes in lieu plywood walls | Near corner | No | Based upon maximum nozzle coverage |
| 8 | Cooking oil | Near wall | No | Based upon maximum nozzle coverage |
| 9 | Cooking oil | Far wall | No | Based upon maximum nozzle coverage |
| 10 | Fire considered most challenging from Test Nos 1 – 7 | Far wall or corner – obstruction near nozzle | Yes | Based upon maximum nozzle coverage |
| 11 | Fire considered most challenging from Test Nos 1 – 7 | Near wall or corner - obstruction near nozzle | Yes | Based upon maximum nozzle coverage |
| 12 | Fire considered most challenging from Test Nos 1 – 7 | Far wall or corner – obstruction near fuel package | Yes | Based upon maximum nozzle coverage |
| 13 | Fire considered most challenging from Test Nos 1 – 7 | Near wall or corner – obstruction near package | Yes | Based upon maximum nozzle coverage |
| 14 | Fabricated sofa with combustible wall | Unobstructed | No | Large room requiring at least 4 nozzles |
| 15 | UL 2167 Residential Dwelling Units Fire Test | Unobstructed | No | Large room requiring at least 4 nozzles |
| 16 | Fabricated sofa with combustible wall | Obstruction | Yes | Large room requiring at least 4 nozzles |
| 17 | UL 2167 Residential Dwelling Units Fire Test | Obstruction | Yes | Large room requiring at least 4 nozzles |
Installation and maintenance of water mist fire protection system
Compliance with the manufacturer’s instructions for system design, installation, operation and maintenance is critical for the system to perform as intended. The instruction manual includes important information related to limitations of the equipment and specifies that the installation, commissioning and annual maintenance are only to be conducted only those qualified by the manufacturer to perform these tasks. As previously indicated, this system unit has been evaluated by UL Solutions for use in one- and two-family dwellings only, specifically with ceiling heights not exceeding 8 ft (2.4 m). This unit has not been investigated by UL Solutions for use in dwellings units located in other types of residential structures.
Summary
Consistent with the built environment in which we live, new technology is being integrated into fire suppression systems at a rapid pace. The UL Certification of the Plumis Ltd water mist system unit is an example of this on-going integration. General information on the UL Certification of this equipment can be found on UL Product iQ under the UL category entitled “Water Mist Residential System Units - Targeted Discharge,” UL category code “ZDSE.” Product iQ is free to use but requires a one-time registration.