Storage Sprinkler Technology — Unprecedented Challenges for Fire Protection Systems


By Dr. H.C. Kung S


torage and warehouse sprinkler systems were first employed in textile mills in New England in 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 infancy as a science.


Later, in the 1960s, the challenge became more severe. The proliferation of plastics such as Styrofoam in pack- ing materials and the increased use of cardboard cartons created entirely new, unprecedented challenges for fire protection systems to overcome. These lightweight stor- age 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 chal- lenge 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 sprin- kler(s). The effective use of sprinkler spray was mea- sured by its 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 effec-


tiveness of the sprinkler could be ensured, and the quan- tities 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


Page 36/Plumbing Engineer


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 deliv-


ered by the sprinkler to the top surface of a burning array that actually penetrates the fire plume to attempt fire sup- pression or control The application of these principles and experimental


techniques led naturally to a classification of sprinkler technologies and a deeper understanding of the perfor- mance of sprinklers for protection of hazards in storage applications.


The ESFR approach In the 1980s, Factory Mutual was leading the develop-


ment of a new technology: Early Suppression Fast Response (ESFR) sprinklers. This new technology was developed to ensure a higher ADD than RDD, while pro- viding hazard protection with storage as high as 25 feet in a 30-foot ceiling space. ESFR technology became enormously popular, protecting storage of ordinary com- bustibles (class 1, 2, 3 and 4 commodities and cartoned unexpanded plastic). In the 1990s, the K14 ESFR sprin- kler 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 speci- fied 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 tech- nology 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


February 2011


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40