Fire Flow

[GlorifiedPlumber1984]

Wondering if anyone can help with fire flow info? We have an existing building with a sprinkler system that is getting a big renovation/tenant change. A flow test was ordered, and the numbers are not great. What is the solution IF the numbers appear to meet the fire sprinkler demand but not the fire flow demand? The flow test shows 46 static, and 974gpm @ 20psi.

I'm not sure if the water supply has degraded over time, but I'm also not sure how to approach this scenario if/when it happens.

 

[cdafd]

Is there a hydraulic calc plate for the existing system???


One trouble shoot,,, have the water dept or whatever name check valves in the area, to assure open and fully open.

Also try to get a map with main layout and size feeding the area,

As in mains good size, feed in multiple directions,,, any dead ends??

 

[UFT12]

See NFPA 1 (ed. 18)

18.4.5.4* Required Fire Flow and Automatic Sprinkler System Demand. For a building with an approved fire sprinkler system, the fire flow demand and the fire sprinkler system demand shall not be required to be added together. The water supply shall be capable of delivering the larger of the individual demands.

If the fire flow demand cannot be improved, consult your AHJ to see if the degraded performance could be thought as lesser fire flow demand, in other words to accept that the sprinkler system is the actual demand.

Edit: Don't forget the hose allowance.

 

[GlorifiedPlumber1984]

Thanks for the responses. I'm sure I'm looking at this the wrong way.....but a fire pump inside the building wouldn't solve fire flow right? Fire flow is the water available for firefighting operations at the hydrant connections serving a building? A fire pump serving the fire sprinkler system wouldn't be applicable towards that requirement? Apologies if this is common knowledge, I've never dealt with this type of issue before.

 

[SprinklerDesigner2]

Fire flows and fire sprinkler demands are two completely separate animals.

The only thing way sprinklers affect fire flows is in the fire flows are usually substantially lowered when the building is fully sprinkled.

That all said I am a fire sprinkler designer and the fire flow problems are NOT mine those should be up to the registered architect, licensed civil/professional engineer of record.

With my 46 years of experience there are two things I will NEVER do which are 1) determine if a 13R sprinkler system can be used in a residential building of any size which isn't my job and 2) determine fire flows on a project which isn't my job.

I can provide a guess on these but I do not charge money for my guesses and my guesses are worth exactly what you pay for them... nothing.

 

[UFT12]

If your system is designed not to supply fire hydrants (or there are none) then the fire flow for this system makes no sense. The other way around, if there are hydrants and supposed to be supplied by the system you design and your building code or any other official dictates fire flows to be considered, then your system must be sized to provide this flow as well.

 

[TravisMack]

This is one of the areas where fire sprinkler may have blinders on and not realize a problem exists. First off, it is not the sprinkler contractor's problem, but it is something we find and point out frequently.

In the case with the flow test mentioned, if you are to adhere to the fire flow requirements in Appendix B of the IFC, then you are in trouble. If you need pressure, you can add a pump. But, in your case you need water. The only way to get more water is to add a tank. I'm assuming this is a municipal line you are testing and finding this deficiency. At that point, you give the data to the building owner and let them fight it out.

But, you are likely looking at a minimum requirement of 1000 or 1500 gpm @ 20 psi and you don't seem to meet either.

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

http://www.mfpdesign.com

 

[MGXFP]

If you are the engineer of record, you will need to determine the minimum fire flow required. Typically NFPA 1, the International Fire Code or some other standard is used to determine this. If you in a rural setting, NFPA 1142 may be used.

If your test results are close, you can probably have a talk with the AHJ and work it out. If you need 1,500 gpm and only have 974 then that's a problem that might need a suction tank with hydrants. On a side note, NPFA 291 says one should round results to the nearest 50 gpm for flows under 1,000 gpm and to the nearest 100 gpm for flows greater than 1,000 gpm. With the vagaries of a flow test, it may be worth doing another test with more sensitive equipment.