MECHANICAL CONTRACTING | SPRINKLER SYSTEMS |
Storage sprinkler technology—unprecedented challenges for fire protection systems
DR. H.C. KUNG
the early 20th century as a means of protecting the equipment and textile goods stored in those early, multi- story spaces. Ceilings were low and goods were, for the most part, stored in wooden crates. Sprinkler technology was in its
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infancy as a science. Later, in the 1960s, the challenge became more severe. The proliferation of plastics such as Styrofoam in packing materials and the increased use of cardboard cartons created entirely new, unprecedented challenges for fire protection systems to overcome. These lightweight storage materials allowed for storage racks to be built to greater heights and changed the dynamic of how storage spaces were designed. Taller racks create a
“chimney effect” when their contents burn, creating a bigger challenge for sprinkler protection. In addition, when burned, the plastic materials now commonly used generate more heat than previous materials, increasing the fire hazard.
The scientific approach In response, scientists and
engineers at Factory Mutual began to develop a scientific approach to the evaluation of sprinkler performance in storage fire situations and to create categories of sprinklers in order to help building and fire system designers apply the proper solutions. Throughout the 1970s and 1980s,
this scientific approach yielded positive results. The prediction of a sprinkler’s response was measured in respect to the size of the fire at the time of the activation of the first sprinkler(s). The effective use of sprinkler spray was measured by its
Victaulic Innovation The FireLock®
torage and warehouse sprinkler systems were first employed in textile mills in New England in
penetration ability through the fire plume. Large-scale calorimetry was used to determine the water flux required to be delivered to the top surface of rack storages of commodities of different hazard levels to achieve fire suppression. Aided by these scientific principles,
the desired effectiveness of the sprinkler could be ensured, and the quantities of water required could be optimized, resulting in cost-effective sprinkler protection of warehouses.
Key terms and concepts Response time index (RTI): A
measurement of the sprinkler response sensitivity to the gas temperature and velocity in the vicinity of the sprinkler as the fire grows enough to activate the sprinkler Required delivery density (RDD):
The water flux required to be delivered to the top surface of a burning array to achieve fire suppression or control Actual delivery density (ADD):
The water flux delivered by the sprinkler to the top surface of a burning array that actually penetrates the fire plume to attempt fire suppression or control The application of these principles
and experimental techniques led naturally to a classification of sprinkler technologies and a deeper understanding of the performance of sprinklers for protection of hazards in storage applications.
The ESFR approach In the 1980s, Factory Mutual was
leading the development of a new technology: Early Suppression Fast Response (ESFR) sprinklers. This new technology was developed to ensure a higher ADD than RDD, while providing hazard protection
LP-46 Low Pressure Upright Storage Sprinkler from Victaulic is FM
Approved for up to 40 foot ceilings to protect up to cartoned expanded and unexpanded plastic commodities. This new proprietary design offers a significantly reduced end-head pressure as compared to traditional ESFR technology and is poised to replace ESFR as the design standard in high ceiling storage applications. Further, this new sprinkler can reduce diameters in branch lines and potentially reduce or eliminate pump size, affording significant cost savings in material and labor. The LP-46 Upright Sprinkler provides a robust conventional standard
response fusible link and a 25.2 K-Factor, distributing water in a pattern that covers 100 square feet per sprinkler. System design for the LP-46 is based upon straight forward 12-head calculations, and can result in the need for up to 20 percent fewer sprinklers in a given system, further adding to the cost savings over traditional technologies.
with storage as high as 25 feet in a 30-foot ceiling space. ESFR technology became enormously popular, protecting storage of ordinary combustibles (class 1, 2, 3 and 4 commodities and cartoned unexpanded plastic). In the 1990s, the K14 ESFR sprinkler quickly became the most popular technology for storage protection. Beyond ESFR, storage sprinkler
classification was expanded to include Control Mode (Density/Area) and Control Mode (Specific Applications). Control Mode (Density/Area) is a system design method based upon the calculation of the density of water discharged in a specified area of coverage (i.e., 0.6 gpm/sq. ft. over 3,000 sq. ft.). This approach is limited to ceiling heights of 25 feet. Control Mode (Specific
Application) sprinklers became available in a range of K11.2–K16.8 and are designed for specific water demand requirements at a pre- determined discharge pressure. Until now, this technology has been limited to 30-foot ceilings.
Recent storage sprinkler innovation Today, system designers and
contractors typically associate adequate sprinkler suppression performance of rack storage fires only with “fast response” sprinklers. Although a fast-response sprinkler responds to a fire sooner than a standard-response sprinkler, fast response alone is not the necessary and sufficient condition for a sprinkler system to achieve fire suppression. More importantly, it is the condition where ADD is greater than RDD and where superior fire suppression can be expected. A new large K-factor
standard-response sprinkler has been developed that can now achieve fire suppression of cartoned plastic commodities under a ceiling up to 40 ft high. The sprinkler model is a pendent sprinkler with a nominal one-inch diameter orifice and a K-factor of 25.2. A series of fire tests concluded
that the standard-response K 25.2 sprinkler can be as effective as ESFR sprinklers in providing protection for storages in
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phc february 2011
www.phcnews.com
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