Hydraulic Calculation Safety Cushion

[DennisR4]

Ok, so I recently had an engineer and an uncertified sprinkler "designer" tell me that NFPA states when performing hydraulic calculations, you need to end up with a cushion of 7 psi below your water source? I have scoured my copy of NFPA 13, and I do not see where this is stated? I think they have the "minimum operating pressure" requirement confused with the safety cushion. Anyone have any ideas where I can find this requirement?

Before everyone puts me on blast, I usually shoot for 10 psi or 10%. This is not in regards to any calculations I performed.

 

[TravisMack]

There is no set requirement in NFPA 13 for a safety margin. Simply ask them to provide the code/standard reference.

Many local jurisdictions may incorporate that requirement into local amendments. That may come in to play.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

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[UFT12]

This requirement is typically found in Europe where the EN 12845 is normally employed. However, this is not always the case as the insurers' association sprinkler standard VdS CEA 4001 (similar to FM) does not mandate such thing. For me, a safety factor is always prudent to consider.

 

[LCREP]

Check with the insurance carrier loss prevention/engineering department they often have the 10 psi or 10% you mentioned.