In-Rack sprinkler effects on Required Density of Ceiling Sprinklers

In-Rack sprinkler effects on Required Density of Ceiling Sprinklers

Where the installation of in-rack sprinklers is not mandatory and is an option, designer can choose it and take the benefit.

For the following example, NFPA13 permits designing the system with or without in-rack sprinklers:

Double Row Rack Storage, Open Rack Type, Non-encapsulated Class I commodity, Storage height 12 to 20 ft., 4 ft. Aisle width, Using CMDA Ordinary temperature.

If  the user selects “With in-rack Sprinkler option”, Curve D of Figure 16.2.1.3.2(a)-2016 Edition shall be used:

And if the user selects “Without in-rack Sprinkler option”, Curve H of Figure 16.2.1.3.2(a)-2016 Edition shall be used:

(In-Rack sprinkler effects on Required Density of Ceiling Sprinklers)

Assume the storage height is equal to 20 ft. and the lower points of the curves are selected for design, so the estimated flow rate of ceiling sprinklers will be:

1) With in-Rack Sprinklers: (0.255 gpm/ft.²) x (2000 ft.²) = 510 gpm

2) Without in-Rack Sprinklers: (0.355 gpm/ft.²) x (2000 ft.²) = 710 gpm

Although the flow rate of ceiling sprinkler where in-rack sprinklers are installed is 200 gpm less than without sprinkler option,

we should remember the demand of the in-rack sprinklers should be added to the ceiling flow rate in accordance with the balancing method. Estimated flow rate of  the In-rack sprinkler is:

(Number of design sprinklers) x (K factor) x (Square root of pressure) =

6 x 5.6 x √15 = 130.1 gpm

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Written by: Hesam Tavoosi, CFPS, CWBSP, CSITMS