sprinkler design area 1

[ForeverStudent]

Hi,

I am recently joined small firm and was involved in several small projects to design fire sprinkler system. Those were designed using pipe schedule method. Now I need to perform hydraulic calculation for one project. My question is regarding area of calculation, which according to NFPA 13 is 1500 sf minimum. The example in NFPA 13 describes the procedure multiplying 1.2 by square root of 1500 (which gives 46.46’) and this should be in parallel to branch lines. In my case the building is 40’ by 70’, and branch lines are parallel to shorter side. In addition the space has a lot of partitions and the layout of the sprinkler heads is pretty irregular. Could somebody suggest how to locate design area and explain the meaning of NFPA 13 rule – 1500 sf design area minimum regardless of the size of the building? Thank you very much.

 

[TravisMack]

Design area is all about hazard classification and not about building size. You could, in theory, have a 1 million sq ft office building and size the systems based on a design area of 900 sq ft utilizing QR sprinkler reductions. Not likely that you would ever have a project like that, but it is possible.

If you read further into the calculation areas, it talks about taking extra lines on the same cross main when the branch line is not as long as the 1.2*DA^.5. You would take your 40' and go 37.5' along the cross main. You will likely have an irregular shaped remote area.

It is somewhat difficult to better describe in a written format. Don't you have some one at the office that you could sit down with and have it explained? It would only take about 5 minutes face to face.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[ForeverStudent]

Travis,

Thank you very much for the response. Unfortunately in our office now I am only who deals with this (it is really small office, but it is another story). If possible, one more clarification. What if physical area is less than 1500 sf (ex. 40'X 35')? Possibly room design method is more appropriate in this case?

Thanks a lot, I really appreciate your feedback

 

[TravisMack]

If your building area is less than the design area, you just calculate all that you have. I have done some very small buildings that only have 1-2 heads. You don't have to calculate something that doesn't exist.

Give me a call if you need to discuss it to help clarify.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[ForeverStudent]

Travis,

Thank you very much, I really appreciate that you are generously giving me an opportunity ta call you, but it looks like I need more time to delve in NFPA 13 deeper first to not ask such basic questions. Thank you again for clear and concise answer.

 

[madvb]

Travis - The Density/Area Curves in NFPA 13 that determine the flow for different Classification of Occupancies. Let's say my 6000 sf building falls under Ordinary Hazard (Group 1). So the minimum fire flow for this building would be 1500 sf * 0.15 gpm/sf = 225 gpm. Assume that it will be a wet-pipe system and no sloped ceilings.

Other than using 1500 sf * 0.15 gpm/sf, what would be the reason to sized the flow at some other points on the curve since that will result in higher flow? I guess if the client wants the sprinkler to cover more area. What if a client wants to cover the entire 6000 sf building? The curve maxed out at 4000 sf.

Thanks.

 

[TravisMack]

The benefits of going up the curve are when you have lower pressures, but a very flat water supply curve. Truthfully, the only time I ever go up the curve is in storage where I can go up the curve to get my density under 0.25 gpm / sq ft. By doing that, I get to use 130 sq ft spacing criteria instead of 100 sq ft spacing.

If you have insurer requirements, you may have to do an increased design area. Also, military projects under the UFC 3-600-1 (I think that is the reference) requires a larger design area.



Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[pipesnpumps]

UFC 3-600-01 is I think loosely based on FM highly protected risk. Design area is 3,000 sq ft.. No curve, and basically the same area increases and reductions at NFPA 13.

 

[TravisMack]

I do enough of those military jobs that you would think I could recite it verbatim by now, but I always have to look up things in there

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com