What does it means for "NFPA 13: Sprinklers under the obstruction shall not be required to be i

[Corey Rao]

What does it means for "NFPA 13: Sprinklers under the obstruction shall not be required to be included in the hydraulic calculation of the ceiling sprinklers", so I can just add some sprinklers under obstructions from branch without sizing change? if now I need to add some sprinklers under some obstruction(if width larger than 1.2m) from branch main, should I change the sizes of all the branch due to more hydraulic needs?

 

[UFT12]

It means if you have obstruction sprinklers inside your design area, these need not be incorporated into the calculations. Its sizing can be made with a separate calculation. If the dimensioning scheme is the same as above, separate caclulations are typically not needed (see 27.2.4.7.3.2 of edition 19).

If your system feeding obstruction sprinklers is substucially large and complicated (complexity that is typically found in industrial occupancies), a calculation should be made anyway.

 

[Corey Rao]

@UFT12 thanks a lot for your reply, but should I change the size of upstream confluent pipes due to added obstruction sprinklers?

 

[UFT12]

As said, assuming the same dimensioning scheme, these sprinklers are typically not included in the calculations. If they are not flowing and running lower why increasing the system piping? It is assumed that either the lower or the higher sprinklers are going to discharge.

 

[Corey Rao]

thank you very much!

 

[TravisMack]

You calculate the worst case demand. Either the ones above or below. Unless you have a deluge system, it is assumed only one level will flow.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, a Ferguson Enterprise

http://www.mfpdesign.com