Rack Sprinklers

[bmlxd40]

We have a project where we have encapsulated storage of class IV commodities on racks, and the FPE has specified the criteria to be in accordance with NFPA 13, 16.2.1.3.2(g). I am trying to make sure we have the correct K Factor for the rack sprinklers, but I seem to be overlooking it. 16.2.4.4 gives the minimum operating pressure , but I have missed the K factor requierment and could use to be pointed in the right direction. Also, We are using standard response sprinklers at the ceiling, and I am thinking we need standard response in the racks also, but I could use a little help in confirming that too.

 

[stookeyfpe]

See Section 8.13 of the 2013 edition of NFPA 13.

 

[bmlxd40]

Thanks. I reviewed that section, but it lists multiple K factor choices. Maybe I am over thinking things, but since rack sprinklers are almost always designed to discharge at a specific pressure, wouldn't the sprinkler designer always default to the smaller K sprinkler? I guess I am a bit confused on why 8.13 lists multiple choices for K factors when the other sections of the standards specify operating pressures. It seems to me that both of them would need to be specified. Like I said, sorry if I am overthinking things and missing the forest for the trees as the saying goes.

 

[skdesigner]

The 13 handbook does a pretty good job of explaining:

"The user of NFPA 13 is allowed to select from a wide range of orifice sizes for the in-rack sprinklers. For the protection of Class I through Class IV commodities stored up to 25 ft (7.6 m) in
height, NFPA 13 specifies the minimum pressure at which the sprinkler needs to operate rather than the minimum flow. This means that the smaller orifice sizes are going to be the most efficient ones to select. For example, the standard requires a minimum pressure of 15 psi (1 bar). A K-5.6 sprinkler will discharge 21.7 gpm at 15 psi (80 L/min at 1 bar). A K-8.0 sprinkler would
discharge 31 gpm (115 L/min) at the same pressure. If the goal is to use less water, using a K-5.6 instead of a K-8.0 sprinkler would be the better approach. Note that the smallest orifice
size in-rack sprinkler that Section 8.13 allows is a K-5.6"

When storage exceeds 25' in height, In rack sprinklers are designed based on a minimum flow rate, as opposed to a minimum starting pressure, which is where larger orifices come into play.

R M Arsenault Engineering Inc.

http://www.rmae.ca