Fire Line for Sprinkler 1

[cenc]

An existing building, that is approximately 5,000 SF, is being furnished with a fire sprinkler. NFPA 13. There is a 6" main along the roadway with an existing hydrant approximately 300 feet to the east and west.

The new line will only service the sprinkler system. I'm not sure where to begin on what calc's are needed. I've ordered the NC Fire Code and have a copy of the IPC. I've contacted the plumber to see what criteria he is going to list in the bid documents, since the actual design of the system will be done after award. I've got a call into the Fire Marshal as well.

Figured I put a question out to get some feedback on what things I should be looking for and asking for, so as to get what I need from the appropriate parties.

A representative with the utility department felt a 2" line would be sufficient. How do I confirm?

Thanks in advance.

 

[sam74]

You'll need a fire flow test on the hydrants in order to get a static pressure and a residual pressure at the max flow rate. This process is explained at the following link

http://www.firehydrant.org/info/ftest2.html

The tests are usually performed by the local fire dept., the local utility, or an independent contractor. This data can be used to model the existing lines flow and pressure characteristics using a pump and reservoir in either EPAnet or waterCAD.

Who ever is desinging the sprinkler system should be able to provide you with the necessary demand and pressures that will be required for the proposed sprinkler system based on code requirements.

Look at this book online for more in-depth info

http://www.haestad.com/books/pdf/awdm.pdf

 

[TravisMack]

The size of the fire line is determined by what is in the building. You calculate fire sprinkler systems to a given density over a given area. In theory, you could have a 1 million sq ft building of only office space and need just about 100 gallons/minute for the sprinkler system, or you could have a 2000 sq ft building storing plastics to 20 in racks and need about 1200 gpm.

I have had many jobs where the water utility says a 2" line should work and we ended up need an 8" line. Again, it all depends on what the fire sprinkler design criteria is for the building.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[cenc]

Thank you for the feedback. I'll take a look at the provided links.

 

[cenc]

Received the flow of 2532 gpm @ 20 psi for one hydrant to the west of where we are tapping. Do I need the numbers for the hydrant to the east? The hydrant to the east has not been tested for a number of years due to ongoing construction. Was reading a post earlier that had a question about determining which way the water was coming from.

 

[cenc]

Received this feedback from the plumber: "I will be providing the criteria only which will be the density the actual flow and pressures will have to come from the sprinkler designer. It will be a 4" line but the actual volume will come from the FP contractor."

The FP contractor won't get going until the project is awarded. I'm supposed to have materials needed to the Architect by Wednesday.

Doesn't seem that the needed information is available at this time?

 

[TravisMack]

Is it an office building, a factory, residential or storage building? This would help you in determining the criteria. You can view NFPA 13 standards online for free at nfpa.org.



Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[cenc]

It is a historic house converted to office.

I've scanned the document, though wasn't looking for this in particular at the time. Will take another look.

 

[sam74]

Tell the architect "no" then. They seem to like that.

But on a more serious note you could determine the likely linear footage but explain that this is best case because you don't know where the connection to the mechanical room will be located.

You could also explain that you can't determine the size until the fire protection calculations have been performed by the FP engineer. If you want to guess the size at least guess big so the projects cost will decrease instead of increase in case of changes.

That is the general rule of thumb if someone wants some impossible to obtain number prior to project design. Guess big preliminarily so construction cost will decrease not increase in the long run.

 

[cenc]

Thanks again. Utility guy said 2". Plumber in quoted comment above I assume is figuring on 4". Figuring I should be safe stating a 4".

 

[TravisMack]

If this is now an office space with full protection by a fire sprinkler system in compliance with NFPA 13, it is not unheard of for the dry system in the attic to have a demand of 500 gallons. Assuming wood structure <36" on center, roof pitch of >=4:12 then you have a line at the peak, and then sprinklers at 8' on center going through the trusses with max distance between lines of 15' along the slope. The average area per head in these applications is about 90 sq ft / sprinkler. When you figure the over-discharge inherent in a dry system and the design area 2535 sq ft minimum (1500 sq ft + 30% for dry + 30% for slope), you get a big flow. You are also limited to 5.6k sprinklers unless you use galvanized piping in the attic.

4" may or may not be enough depending on what pressures you have available. Recently did a large dry attic that required a 6" lead-in. The calc area was still 2535 sq ft.

There are other sprinklers and other options that may allow for smaller flows, but this just goes to show that the size of the building has little to do with the required flow. It is more about commodity, system type and the over-discharge of the system (dry systems have relatively high over-discharges)

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[jgailla]

Going from nothing, I would use a 6" line in this situation with a note that the size is preliminary pending sprinkler data.
A 4" pipe hits 8 ft/sec at about 350 gpm, which isn't much for a sprinkler system.
Also, your feed has to be at least the size of the riser.

 

[cenc]

Once again, I appreciate the feedback. Though I don't know all the appropriate ranges for velocity in pipes, I do recall that 8 fps is getting towards the upper range of what would be desired. I didn't think of checking that.

 

[MGXFP]

Velocities in sprinkler piping is less important than plumbing pipes given that hopefully for the vast majority of their lifespans, sprinkler systems are static.

Also a size smaller than 6" may be permitted if the ug line is used for nothing else and calculations prove it is sufficient.

However you should wait until your FP contractor verifies the size.