One of the more recent systems to be introduced to the special hazards world of fire protection are hybrid fire extinguishing systems. These systems utilize a combination of atomized water and inert gas to extinguish fires. The inert gas, typically nitrogen, is used to deluge the oxygen content in order to protect the space, as well as to atomize the water into small (>200 micron) droplets. This way, the system efficiently cools the fire while lowering the oxygen level below the level needed to sustain a fire. Typical oxygen levels after discharge are between 12.5 and 15 percent, which is safer than standalone inert gas clean agent or CO2 systems. The atomized water droplets provide a large surface area for heat absorption and are easily converted to steam to provide cooling and oxygen for further dilution. The combination is more efficient at extinguishing fires than standalone mist or clean agent systems.
Hybrid fire extinguishing systems, such as the Victaulic Vortex™ System, can be used as total flooding or local application systems. Total flooding systems are designed to discharge the hybrid media into an enclosure to achieve a uniform distribution of extinguishant at, or above, the concentration required to extinguish fire throughout the enclosure. Local-application systems are used to protect a piece of equipment or a specific area. The hybrid media is discharged directly onto a burning surface or equipment.
Hybrid fire extinguishing systems are used to extinguish Class A, Class B, and Class C fires in accordance with the listing or fire test data that is acceptable to the authority having jurisdiction. They 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.
The discharge of the hybrid system is typically between three and five minutes. The inert gas enters the protected space through nozzles, which operate at a controlled pressure of 25 – 140 pounds psi (1.7 bar – 2.8 bar) and a flow rate of 150 – 250 scfm (255 m3/hr – 425 m3/hr). This controlled discharge is less stressful 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 flow rate of approximately 0.25 – 1.1 gpm (1 LPM – 4 LPM) and is atomized by the nitrogen into small droplets. 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. Compared to other system types, the droplet size of hybrid systems is 10 – 100 times smaller than water mist system droplets and 1,000 times smaller than the droplets discharged by many sprinklers. As droplet size decreases, the time suspended in air increases exponentially. The longer suspension time of the water droplets and the addition of 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.
In 2012, FM Approvals established FM 5580, Approval Standard for Hybrid Fire Extinguishing Systems. There are currently two manufacturers’ systems that are approved under FM 5580. This standard contains approval tests for protection of machinery and combustion turbines housed within enclosures, as well as a 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.
Despite the growing adoption of hybrid fire extinguishing Systems and the introduction of FM’s approval standard, the National Fire Protection Association (NFPA) did not have any guidance for these systems. In October 2013, the NFPA Fire Protection Research Foundation initiated a literature review to determine if a new NFPA standard was needed to provide guidance for the installation and use of this hybrid technology. What they found was that hybrid systems fell between two standards – NFPA 750, Standard on Water Mist Fire Protection Systems, and NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems. Each of these standards only cover one aspect of a hybrid system and do not provide any guidance for the two components used together. As a result, the NFPA Standards Council approved the development of the now released NFPA 770, Hybrid Fire Extinguishing Systems. The 2021 Edition of NFPA 770 defines Hybrid Fire Extinguishing Systems and provides design and installation guidance for the industry.
Per NFPA 770, a hybrid fire extinguishing system needs to be able to deliver, “the hybrid media a design rate and proportion.” That proportion is known as the hybrid factor and is used in the design calculations for the system. The standard also indicates that hybrid media is, “created by the simultaneous discharge of water mist and an inert gas agent in a controlled proportion from a common discharge device that results in an oxygen concentration less than 16 percent.” The standard also defines the use of hybrid system for total flooding (Chapter 8), where there is a permanent enclosure around the hazard area, as well as local applications (Chapter 9) to protect an unenclosed or partially enclosed hazard that is located indoors. In Chapter 12, the standard details that the person responsible for designing, installing, servicing, or maintaining hybrid extinguishing system must be trained and certified for the service they are performing – either by the manufacture or by an organization that is acceptable to the AHJ.
Hybrid fire extinguishing systems meet the need for an extinguishing system that is effective, safe, non-toxic, has no effect on the ozone or the environment, has no by-products, and has minimal cleanup requirements. They are ideal in locations with reduced enclosure integrity or limited access to water. Hybrid systems have been used in data centers, turbine enclosures, 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.
