NFPA 13 Sprinkler System Design Density Curves

NFPA 13 Sprinkler System Design Density Curves – Where Did They Come From?
By: Garner A. Palenske, P.E.

“The design criteria found today in NFPA 13 for storage occupancies can be traced mainly to fire tests conducted in the 1970s. These tests used standard 165°F (74°C), ½” (13 mm) orifice sprinklers and a test commodity intended to simulate cartoned wood and paper products.”

An interesting review on the decision-making process towards assuring the necessary water flow (via minimum required pressures) reached the hydraulically most remote area follows.  Additionally the process towards conducting the final tests on which the curves were fit is discussed.  Finally, it’s important to note that the curve from the Class II products was then fit to single tests performed on Class III and Class IV products using the assumption of “parallelism”.

“The use of automatic sprinklers to protect people and property from the consequences of fire has withstood the test of time…Conservative requirements, such as designing to a constant sprinkler pressure, inclusion of hose allowances, and reduction in water supply capacity, provide an additional factor of safety.”


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