Hybrid Fire Extinguishing Systems utilize a combination of atomized water and inert gas, to extinguish fires. Hybrid fire extinguishing systems are a technology that is becoming an established solution in Information Technology (IT), Power as well as Industrial applications and is gaining acceptance as a solution for protecting other high value assets.
These systems provide the fire protection engineer with an option to address concerns with life safety, limited water supply, room integrity, costly clean up and potentially damaging water run-off. Hybrid Fire Extinguishing Systems are effective in applications such as combustion turbines, machinery spaces, data centers, control rooms, clean rooms, semiconductor processing equipment, engine test cells and for the protection of other specialized equipment. (Figure 1)
Hybrid media is a combination of inert gas, typically nitrogen, and atomized water that creates an atmosphere that does not support combustion. The inert gas dilutes oxygen, and is used to atomize the water into small (10 micron) droplets. The atomized water droplets provide a large available surface area for heat absorption, and are easily converted to steam to provide cooling and oxygen dilution.
Hybrid Fire Extinguishing Systems may be used as total flooding or local application systems. “Total Flooding” is a fire protection system designed to discharge an extinguishant into an enclosure to achieve a uniform distribution of that extinguishant, at or above the concentration required to extinguish fire throughout the enclosure. “Local-application” is a method where fire extinguishant is discharged directly onto a burning surface or article, or within a non-retentive volume.
Hybrid media discharge is regulated, with the nozzles operating at a controlled nitrogen pressure of 25 – 140 pounds per square inch (psi) (1.7 bar – 2.8 bar). The discharge is at a controlled rate of typically 150 – 250 standard cubic feet per minute (scfm) (255 m3/hr – 425 m3/hr). The result is reduced stress on the enclosure and the need for room pressure relief vents is reduced or eliminated entirely. In occupied spaces, the controlled discharge rate allows time for egress while providing cooling and extinguishing the fire.
Water is delivered to each nozzle at a controlled flow rate of approximately 0.25 – 1.1 gallon per minute (gpm) (1 liter per minute (LPM) – 4 LPM), mixed with the nitrogen, and atomized into small droplets. (Figure 2) The 10-micron water droplet size allows water droplets to stay in suspension longer, minimizing the amount of water that settles on equipment and surfaces, while still providing sufficient cooling to prevent re-ignition. Comparative to other fire suppression systems, the droplet size is 10 – 100x smaller than a water mist system, and 1000x smaller than the droplets discharged by many sprinklers. As droplet size decreases, the time suspended in air increases exponentially, which allows the system to function like a total flooding system. The longer suspension time, and the nitrogen, make Hybrid Fire Extinguishing Systems effective on concealed or shielded fires. In many instances, these fires would not be reached by larger droplets that tend to fall directly to the ground.
Hybrid Fire Extinguishing System Standards Development
As a relatively new technology, standards for Hybrid Fire Extinguishing Systems have been developed, and additional development is currently underway. In 2012, FM Research established FM 5580, Approval Standard for Hybrid Fire Extinguishing Systems. Currently systems from 2 manufacturers are approved under FM 5580. FM 5580 contains approval tests for protection of machinery in enclosures, combustion turbines in enclosures, and test protocol for protecting computer room raised floors. One Hybrid Fire Extinguishing System has also been approved for protection of wet benches and semiconductor processing equipment.
Hybrid Fire Extinguishing Systems have unique design, installation, and maintenance requirements when compared to other fire extinguishing systems. In October 2013 the NFPA Fire Protection Research Foundation initiated a literature review to determine the need for a new NFPA standard providing guidance for the installation and use of this new hybrid technology. As a result of this literature review, the NFPA Standards Council approved the development of NFPA 770, Hybrid (Water and Inert Gas) Fire Extinguishing Systems. NFPA 770 will be a new standard that specifically covers Hybrid Fire Extinguishing systems. Currently, NFPA 770 is in development and defines what a Hybrid Fire Extinguishing System is, and provides design and installation guidance for the industry. When approved, the standard will be published as a 2021 edition.
Testing and Research on Hybrid Fire Extinguishing Systems
In addition to NFPA and FM standards, there is a substantial amount of research and testing available on Hybrid Fire Extinguishing Systems. Variables recently identified as requiring more research are the effects of altitude, enclosure integrity and fire size on extinguishing time and hybrid media requirements. In 2016, the NFPA Fire Protection Research Foundation established a Project Technical Panel (PTP) to provide oversight for Hybrid Fire Extinguishing System testing.
Upon commissioning of this testing, limited data was available regarding fire extinguishing testing at high elevations. In order to eliminate external variables in relation to room geometry and size, a mobile fire laboratory was constructed using a 40-foot (12.2 meter) cargo container as the enclosure. (Figure 3). A Victaulic Vortex™ fire extinguishing system was installed in the container, and the laboratory included allowances for adjusting nozzle placement and the quantity of openings in the enclosure. Tests were conducted by Victaulic at locations with elevations of 500 feet (152 meter) above sea level (ASL), 6500 feet (1981 meter) ASL and 10,000 feet (3048 meter) ASL. Fire tests were conducted using similar test protocol as Underwriters Laboratories UL 2127, Inert Gas Clean Agent Extinguishing System Units, with fuels including heptane and polymers, polypropylene (PP), acryonitril butadiene styrene (ABS) and polymethyl methacrylate (PMMA). Additional tests were performed at a lower elevation, including extinguishment of wood crib fires, variations to opening size and fire size, and the ability to prevent re-ignition.
Data collected from the mobile laboratory demonstrated that the required amount of hybrid media for extinguishment decreases with elevation. The new data provided a basis for using the Atmospheric Correction Factors (ACF) determined in NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems to adjust the required amount of hybrid media based on the local atmospheric pressure.
Testing has also demonstrated that designing a total flooding Hybrid Fire Extinguishing System for a smaller 68kW heptane fire (Figure 4) resulted in a conservative design when larger fires are considered. In total flooding applications, as fire size increased (utilizing a larger fuel source), extinguishment occurred sooner, based on increased oxygen consumption from the fire and increased oxygen dilution from conversion of water to steam.
An important design consideration for fire suppression systems is preventing re-ignition of fuel after a system discharge, particularly in hazards such as machinery and combustion turbines where there are rotating parts that need to come to a stop, lube oil that needs to continue flowing, and other large heated surfaces that can become sources of re-ignition.
The project included tests to evaluate the extinguishment and protection times for Hybrid Fire Extinguishing Systems using different sized openings in the enclosure. Testing of the Victaulic Vortex Hybrid system, in an enclosure with varied opening sizes, demonstrated that a total flooding Hybrid Fire Extinguishing System will provide protection from re-ignition after the fire has been extinguished and the discharge has stopped.
To test protection time of a hybrid system, re-ignition of the fuel was attempted after extinguishment. The ignition source was a spark provided by an oil burner ignition transformer that was used for ignition and re-ignition of the fuel. For the Victaulic Vortex System used for this test series, the maximum recommended opening size of 1.25 square feet (0.12 square meter) per nozzle provided 10 minutes of protection time. Smaller opening sizes were capable of providing substantially longer protection times, in some cases exceeding 1 hour of protection.
Outside of this work with the NFPA Fire Protection Research Foundation, research has been conducted on combustion turbines used for power generation. FM 5580, Approval Standard for Hybrid Fire Extinguishing Systems, allows for the approval of Hybrid Fire Protection Systems for the protection of combustion turbines. Combustion turbines operate at very close internal clearances and there is concern that discharging water onto the case can cause rapid cooling and failure. Victaulic, manufacturer of the Victaulic Vortex™ Hybrid Fire Extinguishing System, has worked with owners and operators of Frame 7 combustion turbine and FT4 Aero-derivative turbines to conduct discharge testing on operating units deployed at power generation facilities. Testing included bringing the unit up to temperature by connecting to the grid and generating electricity, followed by a shutdown and discharge of the Victaulic Vortex Hybrid Fire Extinguishing System. Testing demonstrated that the minimal water discharge of a Hybrid Fire Extinguishing system allowed these systems to be discharged on combustion turbines without damage.
Versatility of Hybrid Fire Extinguishing Systems
For total flooding Hybrid Fire Extinguishing Systems, the amount of hybrid media required is based on the fuels present and the enclosure volume. A typical system for protecting a machinery space would have one nozzle for every 1500 – 2500 cubic feet (cu ft) (43 cubic meters (cu m) – 72 cu m) of enclosure volume, and discharge for 3 – 5 minutes, with longer discharge times used when additional cooling of hot surfaces is required. A typical hybrid nozzle will discharge 0.25 – 1.1 GPM (1.0 LPM – 4.0 LPM) of water. This results in reduced water storage requirements and reduced cleanup requirements. The low water usage allows Hybrid Fire Extinguishing Systems to be installed with their own dedicated water tank next to the nitrogen supply, and pressurized from the nitrogen supply. In a total flooding application, Hybrid Fire Extinguishing Systems are capable of extinguishing concealed or shielded fires where the nozzle does not directly impinge on the fuel source.
A Hybrid Fire Extinguishing System has recently been approved for use in protection of wet benches and other similar processing equipment. Wet benches are used in the fabrication of semiconductors, and are constructed with significant amounts of polymers and significant ventilation to accommodate the chemicals used in the process. Testing, witnessed by FM Approvals, in Victaulic’s laboratory demonstrated the suitability of the system for the protection of wet bench equipment. In these applications, the small amount of water and nitrogen required also permits the use of in house reagent grade water and nitrogen supplies, minimizing cleanup requirements in the event of a system discharge.
When an enclosure is not available, Hybrid Fire Extinguishing Systems may be designed as local application systems. Local application system designs are performance based, and testing includes fire tests using a mock-up of the protected equipment and samples of the fuels present. The Victaulic Vortex Hybrid Fire Extinguishing system has been applied to steel mill pickling lines, where the corrosive chemicals present require substantial amounts of non-metallic materials. These facilities have traditionally been protected by deluge fire sprinkler systems. The combination of appropriate detection and a Hybrid Fire Extinguishing System reduces the amount of water that needs to be contained. The low pressures at which hybrid nozzles operate permit the use of non-metallic piping and nozzles, reducing maintenance to equipment installed in corrosive environments. The design is based on testing conducted with a full-scale mockup of the protected equipment in a controlled laboratory setting.
Hybrid Fire Extinguishing Systems are interfaced to an agent releasing fire alarm control panel. A 24-volt signal routed to a solenoid valve is used to release nitrogen and initiate system discharge. The fire alarm control panel will also monitor the system for trouble and supervisory conditions, using low pressure switches and water level switches to verify that sufficient hybrid media will be available. The use of a 24-volt release signal allows compatibility with panels from a range of manufacturers and provides the fire protection engineer greater flexibility in choosing a method of detection that is suitable for the application.
Conclusion
Hybrid Fire Extinguishing Systems meet the need for an extinguishing system that is effective, safe, uses no toxic components or by-products, and has minimal cleanup requirements. Hybrid Fire Extinguishing Systems have been successfully deployed and accepted as part of the overall fire protection design for a variety of applications, as both a supplemental and the primary fire protection system. In business occupancies, a Hybrid Fire Extinguishing System may be specified as the protection for a data center within a building, while the remainder of the building is protected by sprinklers. In industrial applications, Hybrid Fire Extinguishing Systems have been an FM-Approved solution for protecting Combustion turbines and machinery. Other applications for Hybrid Fire Extinguishing Systems that benefit from the minimal wetting, non-toxic components, and reduced enclosure integrity requirements include switch rooms, control rooms, clean rooms, wet benches, ducts, engine test cells, archives, libraries and museums. Hybrid Fire Extinguishing Systems provide a solution for difficult challenges when protecting high value assets.
For more information, go to www.victaulic.com/systems/victaulic-vortex-hybrid-fire-extinguishing-system
About the Author
Larry Carmen is a Senior Project engineer with Victaulic’s Fire Suppression Technology department.
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