NFPA 13-2016 - In-Rack Sprinkler Water Demand

[sl3656]

NFPA 13-2016 has the following statements on how to treat water demand between the ceiling sprinkler system and the in-rack system:

17.1.2.9.6 The in-rack sprinkler demand shall not be required to be hydraulically balanced with the ceiling-level sprinkler system.
23.4.5.2 Water demand of sprinklers installed in racks shall be added to ceiling sprinkler water demand over the same protected area at the point of connection.
23.4.5.3 The demand shall be balanced to the higher pressure.

My reading of 17.1.2.9.6 is that there is no interaction between the ceiling system and the in-rack system, as though the rack itself is its own compartment. The ceiling system would then only protect the area beyond rack, including the top tier of the rack which may have exposed commodities.

23.4.5.2 and 23.4.5.3 appear to contradict my interpretation.

Any thoughts on reconciling this apparent contradiction is appreciated!

 

[SprinklerDesigner2]

With ESFR sprinklers it's been a long, long time since I did any in-racks.

17.1.2.9.6 tells me the in-rack sprinklers don't have to be balanced with the overhead but 23.4.5.3 says it does?

Doesn't make sense to me unless they are saying I don't have to layout the rack sprinklers to "match" the sprinkler pressure to the overhead.

 

[sl3656]

Thanks SprinklerDesigner2. This is a retrofit project due to occupancy class change and we have no fire pump with around 60 psi at the riser base.

Looking to protect Class A Plastic Unexpanded in Cartons up to 20 feet. ESFRs would require at least K-14.0 with 50 psi end pressure. Don't think our riser base can support that. Which is why I went for the in-rack option, assuming 17.1.2.9.6 is valid and I don't have to consider any interaction between the ceiling and in-rack system.

 

[SprinklerDesigner2]

"The in-rack sprinkler demand shall not be required to be hydraulically balanced with the ceiling-level sprinkler system"

I think all that means is the rack doesn't need to be balanced with the overhead which would really be impossible to do.

But make no mistake about it that the rack demand MUST be added to the overhead.

So your rack requires 386 gpm @ 43 psi at the point of connection to the rack.

The overhead requires 1,358 gpm @ 52 psi at the point of connection to the rack.

How you add them and how you do that is:

K=385/43^.5 so K=58.72.

The actual amount water to the racks will be Q=K*p^.5 or 58.72*52^.5 for Q=423.4 gpm.

Total demand will be 1,358+423.4=1,781.4 gpm

If all you got at your riser is 60 psi I really don't see that happening unless your curve is very, very flat and even then your pipe sizes will be huge.

Just curious, how high is the building?

PS I have been working all day and my brain is tired so maybe I missed a number but you get the idea.

 

[aaron johnson llc]

Chapter 17 applies specifically to rack storage of plastic and rubber commodities. Whereas, 23.4.5 applies to hydraulic calculations for other in-rack systems.

 

[TravisMack]

Location has meaning when reading NFPA 13. The part where it talks about not balancing is specific to a specific scenario. You can't just pick and choose lines from the standard to apply.

Travis Mack, SET, RME-G,
Ferguson Fire & Fab, dba MFP Design

http://www.mfpdesign.com