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Forums» Fire Codes» NFPA 13 vs NFPA 13R

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NFPA 13 vs NFPA 13R
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Re: NFPA 13 vs NFPA 13R By  AegisFPE

Posts: 0

10/14/2009 4:51:00 PM

The allowable building areas based on fire-flow as identified in IFC Table B105.1, which can be considered to be drawn from the ISO method, can be surprising if the only allowable areas otherwise considered are in IBC Table 503.

Health departments may require the water purveyor to determine fire flow based on a residual pressure of 20 psi throughout the entire system. Depending on system conditions, the resulting fire flow can be much different than the traditional method where the 20 psi residual is measured at the test location (as may be anticipated by most fire officials applying IFC Table B105.1 and the ISO).

Therefore, there may be some building area at stake depending on how the reported fire flow was calculated.


Re: NFPA 13 vs NFPA 13R By  rj2085

Posts: 0

10/15/2009 4:18:00 AM

AegisFPE: Your post is interesting! Could you give an example of how this would work! ie: areas at stake?


Re: NFPA 13 vs NFPA 13R By  AegisFPE

Posts: 0

10/15/2009 4:51:00 PM

From the OP, consider about 9,000 square feet of Type V-A building area. We''re all fine with IBC Table 503 and Section 506.

Then we look at the IFC, which shows a base fire flow of 1,750gpm per IFC Table B105.1. The Exception to IFC Section B105.2 allows <b>up to</b> a 75% reduction, as approved, for NFPA 13 or NFPA 13R. Some officials or local ordinances may limit the reduction to less than 75% for 13R and/or 13.

Say they allow no reduction for 13R, and allow 25% reduction for a straight 13 (these limited reductions are intended to be ultra-conservative and only for purposes of this illustration). This would mean the building needs a fire flow of 1,750gpm using 13R or 1,500gpm with a straight 13 system.

So, we need to know the fire flow.

The City water department ran a model based on the State health department requirement to maintain a minimum of 20psi throughout the distribution system during a fire flow event. They present 1,680gpm as the available fire flow at your location down in the City while maintaining 20psi for the homes up in the hills adjacent to the water tank.

Looks like they better plan on the full 13 system.

But, then you discover City field fire flow test records from last year, based on ISO and NFPA 291 test standards measured just a couple blocks away where the residual pressure was extrapolated out to 20psi at the test hydrant resulting in a fire flow of 1,780gpm.

Oh, so the project works with 13R!?

Effectively, IFC Table B105.1 is driving the project; potentially affecting either the size of the building (5,900 square feet instead of 9,000 square feet), the construction type (Type II-A instead of V-A), and/or the sprinkler system (NFPA 13 instead of 13R), dependent upon negotiations with the fire code official.

And, adding to the mix is two fire flow values for the same location, 1,680gpm and 1,780gpm, each with different implications.

The difference? One is based on a theoretical calculation for planning purposes based on estimated static and dynamic head through the distribution system while maintaining a prescribed pressure at essentially the highest point in the system, and the other is more similar to the ISO measurement, upon which the subject IFC table may arguably be based intended to ensure fire department emergency operations during which time it is doubtful the incident commander would entertain someone miles away reading a gauge at the base of a water tank and telling him to limit fire ground operations because the remote system pressure was dropping below 20psi; but that may be a topic for another thread.


Re: NFPA 13 vs NFPA 13R By  rj2085

Posts: 0

10/16/2009 2:56:00 AM

Great example! Very clear! Thanks!


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