A Smattering of Sprinklers
Fire-suppression systems, like most building systems, components and construction materials, continue to take advantage of technological advancements—innovations that improve system performance, expand applications and result in cost savings or additional flexibility for building owners and users.
MICHAEL J. MADDEN, P.E., Principal, Gage Babcock Associates, La Palma, Calif.
Fire-suppression systems, like most building systems, components and construction materials, continue to take advantage of technological advancements-innovations that improve system performance, expand applications and result in cost savings or additional flexibility for building owners and users. However, the installation of fire-suppression systems in buildings is highly regulated through building codes, fire codes and fire-suppression system installation standards. Consequently, bringing new fire-suppression system technologies to the marketplace can be a costly, time-consuming process.
Most systems must be installed in accordance with standards published by the National Fire Protection Association (NFPA). Fire-suppression systems are also typically required to be listed by Underwriters Laboratories (UL), or approved by Factory Mutual (FM). This testing and approval process can take a while, and it also takes time for the installation standards to catch up with new technologies. As a result, fire suppression advancements usually do not see real-world applications for quite some time.
Nevertheless, the recent development of new sprinkler heads, the availability of water-mist systems, changes to applicable installation standards and new applications for existing system technologies-such as high-expansion foam systems-have provided members of the fire-protection engineering community with additional fire-suppression tools for their tool box.
Solid sprinkler systems
Sprinkler systems have been in use for well over 100 years, but only in the last 30 years have we seen significant changes and improvements in the technology. Large-drop sprinklers, quick-response sprinklers and early-suppression, fast-response (ESFR) sprinklers-and the new breed of extra-large-orifice sprinklers-have enabled greater installation flexibility and better protection for higher-hazard commodities. This has resulted in more protection options for storage and warehousing facilities, and in many cases has effectively reduced system installation and maintenance costs.
The way ESFR sprinklers work is by combining quick-response technology with large-orifice sprinklers, producing large droplet sizes at higher discharge velocities. Depending on the storage commodities protected and the height of storage, ESFR systems are typically designed with a dozen sprinklers at a minimum end-head pressure of 50 or 75 psi. The systems enable larger and higher-volume warehousing and distribution facilities to be protected without the use of in-rack sprinklers, and also permit greater flexibility in storage arrangements and flexibility and changing of commodities. In fact, many developers of speculative storage and industrial facilities now install ESFR sprinklers during original construction for tenant flexibility and reduced build-out costs.
The pressure requirements for ESFR sprinklers, however, often require additional fire pumps. Nevertheless, ESFR sprinklers are, and will continue to be, a very effective and flexible fire-suppression system for use in storage facilities.
Factory Mutual and Underwriters Laboratories have run numerous full-scale fire tests to validate the use of ESFR sprinkler systems for protection of various storage commodity classifications and arrangements. NFPA 13 Standard for the Installation of Sprinkler Systems identifies specific applications for which ESFR sprinklers are approved. Ongoing full-scale testing of mixed commodities and storage arrays containing higher-hazard commodities, such as plastics, flammable and combustible liquids and aerosol products, will certainly add to the list of approved ESFR applications.
A large-orifice sprinkler lesson
Large-orifice sprinklers produce larger droplet sizes at lower pressures. This effectively eliminates the extra fire pumps required by ESFR sprinklers. These sprinklers are seeing increased use, particularly in big-box retail facilities that require increased protection for their commodity mixes. Also, large retail owners are seeking the flexibility of not having to install in-rack sprinklers.
In order to classify these new large-orifice sprinklers, NFPA 13 now contains nominal K-factor designations. The K-factor for a sprinkler is the orifice coefficient, used in the equation for a flow rate of Q = KÖP. The standard 2-inch sprinkler, which has been the mainstay for 100 years and is still used in most occupancies, has a nominal K-factor of 5.6. The newer large-orifice sprinklers have K-factors of 11.2, 14.0, 16.8 and 25. In effect, a sprinkler with a K-factor of 25 provides a flow rate more than four times greater than that provided by a 5.6 K-factor sprinkler at the same discharge pressure. These higher sprinkler flow rates yield the larger discharge densities required for controlling the challenging fires found in storage and warehousing facilities.
In addition to the development of large-orifice sprinklers, other sprinkler designs address specific installation configurations to reduce costs and improve aesthetics. Extended-coverage sprinklers , in both pendant and sidewall-sprinkler configurations, have provided great installation flexibility in light-hazard occupancies, particularly in residential and institutional occupancies. Attic sprinklers have been developed which allow a single row of sprinklers installed in the peak of an attic to protect the entire attic space. Window sprinklers and cornice sprinklers are additional examples of sprinklers developed for specific applications.
In response to these new sprinkler designs, the latest edition of NFPA 13 has mandated that a new six-character identification number be marked on all sprinklers. Each change in orifice size, response characteristics or deflector design requires a change in model number. This model number allows for quick reference to manufacturer data on performance characteristics and listings.
The merits of mist
Water-mist systems continue to gain popularity for specific hazard applications. The apparatus is a water-extinguishing system that disperses water in fine droplet sizes to put out a fire through cooling, oxygen depletion and radiation attenuation. Water-mist systems have been shown to be effective on Class A-ordinary combustibles-and Class B-flammable/combustible liquid fires. The reduced water-supply requirements for water-mist systems-and the reduction in water-damage potential-make it attractive for a wide variety of hazard types, from turbines and marine-engine compartments to data-processing facilities and hotel rooms.
Because various manufacturers involved in the development of water-mist systems utilize different nozzle designs and different technologies to generate the fine droplet sprays, NFPA 750 Standard for Water Mist Fire Protection Systems requires that water-mist systems be specifically tested and approved for each application. Testing usually involves full-scale performance testing with listing limitations based upon the specific tests performed. Therefore, if a water-mist system is not tested and listed for a specific hazard, it would generally not be accepted by code authorities.
As a result, it will be a while before sufficient information on water-mist systems can be transferred to engineered installations without full-scale testing of actual end-use conditions. At the same time, the benefits of these systems will continue to drive the development of this technology.
Fighting fires with foam
High-expansion foam is an aggregation of bubbles mechanically generated by the passage of air or other gases through a fine mesh screen or other porous medium that is wetted from an aqueous solution of foaming agents. Under the proper conditions, foams with expansion ratios of 20:1 up to 1,000:1 can be produced. Originally developed to fight fires in coal mines, high-expansion foam provided a method of transporting water to a fire that could not be reached by typical hose streams. The three-dimensional state of the high-expansion foam allows for water transport to inaccessible spaces, and also prevents the movement of air within the protected space, which is necessary for continued combustion. It is also beneficial for the total flooding of confined spaces, and the displacement of vapor, heat and other products of combustion. Testing also shows that high-expansion foam, in conjunction with water sprinklers, provides better fire-control and extinguishment capabilities than either system by itself.
Over the years, however, high-expansion foam systems have only been utilized for specialized hazards and confined-space fire protection. Today, high-expansion foam systems are receiving more interest for the protection of high-piled storage facilities, flammable- and combustible-liquid storage facilities and aircraft hangars. Storage facilities that handle products such as roll paper or rubber tires can benefit from the use of high-expansion foam systems.
While Halon fire-suppression systems used to be specified for data-processing facilities and telecommunications spaces, the Montreal Protocol has essentially eliminated Halon for general fire-protection system uses. Although available Halon supplies are being used for some fire-extinguishing system applications such as onboard aircraft systems, typical Halon applications such as computer, data-processing and telecommunications facilities are now being protected by other gaseous agents or automatic-sprinkler systems. Although the development of alternative agents has slowed since the days when manufacturers were rushing to fill the Halon gap, the development of various gas agents should continue, especially for high-value computer and telecommunications equipment spaces, art collections and similar hazards.
Another promising agent type currently under development is the technology of aerosol-generator fire-extinguishing systems , which involve chemically produced aerosols dispersed within an enclosure to provide fire extinguishment.
Future fire suppression
Fire-suppression systems will continue to take advantage of new technologies. At the same time, existing technologies will be applied to new applications and new hazards. The days of fire-suppression system selection not involving realistic system choices are behind us. Now fire-protection engineers can, and must, select and specify fire-suppression systems based upon an engineering assessment of the hazard, the needs of the client, the life-safety and property-protection goals established for the facility and the environmental characteristics of the extinguishing agent.