Minimum Number of Fire Sprinkler Design Areas?

5/24/2023

What are the minimum number of design areas required for a new sprinkler system design?

It is based on hazard classification or system type?

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13 Comments

Glenn Berger

5/24/2023 08:05:27 am

Simple answer to the question is: Yes and Yes

Building configuration is another variable. The key is to prove the most hydraulically demanding area is calculated.

Jesse

5/24/2023 08:11:14 am

I always prove, and have my design staff prove multiple hydraulically remote areas. We only have to prove the most hydraulically remote area assuming a homogenous occupancy hazard class (i.e. all OH 2). However, its not necessarily intuitive. Hydraulically remote doesn't always necessarily mean most physically remote. So if I submit a set of AS plans with a single remote area to the AHJ, the reviewer may think that other area(s) are more remote. I usually only design high challenge stuff myself, but I did a fire station last week where I proved 4 different emote areas. I want to make it as easy on the reviewer as possible.

However, for the same AHJ, I also had a cold storage warehouse with 47-ft of Class-III on multirow racks. In each freezer section I only proved a single remote area of ceiling level AS balanced with in-racks.

Barry L Brainard

5/25/2023 09:47:45 am

Being an AHJ myself, I always try to understand the rationale behind the number of design areas an engineer (NICET or PFE) places onto their working plans. I know according to NFPA 13 it states the most hydraulically demanding area, but that can be very subjective.
I have always require a design area in each area of hazard classifications at each of those classifications most demanding locations. As an AHJ, I would greatly appreciate it when a design engineer explains the reasoning behind their design areas on the plans or applications.

Alex link

5/24/2023 08:17:18 am

This is all contingent on your design. If you have a basic tree system, with all branch lines sized the same, and a single occupancy classification, one would suffice.

I will always provide multiple calculations where the system design varies. My company uses SprinkCAD, making it extremally easy to calculate multiple control areas with a click of a button.

Vinnie

5/24/2023 08:22:45 am

Simply put...as many as it takes to prove that your design works

Paul Pinigis link

5/24/2023 08:30:31 am

Well, tell us a bit about the system and maybe we can guide you in the right direction. Is this an NFPA 13, 13R, or 13D system? What is the hazard classification? Is it a limited-area system?

Anthony

5/24/2023 08:32:17 am

There is no minimum number of sprinklers in a density area calculation for a full NFPA 13 system. Often in an NFPA 13D or 13R system you'll see calculations for only 1 sprinkler usually a 20x20 or 18x18 covering a largeish room.

Minimum number of sprinklers are more often in reference to room design method for corridor calculations.

There are also prescribed numbers of sprinklers such as in ESFR (12 sprinklers 4 on 3 branch lines) or CMSA heads. Also in rack sprinklers will be required to flow a particular number of heads in addition to the density area above the rack when using above CMDA heads.

System type, wet vs dry/pre-action will never call for a particular number of sprinklers with the exception of attic heads where the sprinkler calculation is per their listing and outside of the purview of NFPA 13 density area methods.

Jay

5/24/2023 03:31:05 pm

The minimum number of sprinklers using the density area method is 5.

Casey Milhorn

5/24/2023 08:41:50 am

Very subjective and ultimately up to whoever has the final say so on approval, and also on your own piece of mind. My designers probably are overkill on number of calculations. If you are an engineering technician (NICET) or a FPE, hopefully pure ethics drives those in these categories to do the right thing. Many times the reviewers could easily be fooled by the designer not calculating a more demanding area. I would estimate that I, and most other experienced designers, could probably find a more remote area on up to 50% of shop drawings being put out today. I've seen many times where a designer picks the most geographically remote area without consideration for delta flow, additional fittings, mixed K factors, elevation changes, etc... Those of us that started with HASS and doing hand calculations have the advantage of more intimate knowledge of how water flows through a system. Many designers now a days just start playing with pipe size first and stop there, and never get into the nuts and bolts. Anyway, I could go on and on about calculations. The short answer is that these are life safety systems and you should do as many calculations as it takes for you to feel like you've met the intent of NFPA 13 (or other applicable NFPA) and that you can sleep at night knowing you designed a system that will work.

Jody Aycock link

5/24/2023 08:55:29 am

The minimum for 13 is one, the minimum for 13R is two (compartment & lgt haz area), but if your 13 remote area pipe sizes are larger than other areas, if the heads are a different k-factor in another area or if there's a different density in another area, then you would need to add hyd calcs to prove those areas. Also, if the pipe does something unusual in an area, you may want to add a hyd calc. This would apply to light, ordinary, extra hazard occupancy & storage hyd calcs. Basically, if your remote area has the same pipe size, height above ff, heads & density as the other areas on the job, then one hyd calc of the most remote area is all that is needed.

JP link

5/24/2023 09:27:52 am

It is important to justify the design to the reviewer. If there are multiple hazard levels in the system, I would recommend minimally one or two design areas per hazard level depending on location within the system. Depending on building size and height, as well as the hazard level, the demand can change greatly and it is important that the level of detail provides confidence in the design.

Dan Wilder

5/24/2023 11:21:51 am

I take the approach that the area that has the calc...does it define all other areas of the building for pipe sizing, lengths, elevations, hazards and configurations?

Take a wood structure with trusses 2' on center and a sloped roof with a drop ceiling and a light hazard room below....If I calc the pendents with the intent that they are spaced further apart (greater starting pressure/GPM requirements) and have to pass through additional pipe (the 1" drops) does that prove the upright calc that is still light hazard but has a 7PSI starting pressure (due to spacing) but has 2x the sprinklers because of that reduced spacing?

Does that translate to a pendent OH calc below that I use remote area reduction on vs a light hazard increased area due to slope for uprights?

Did a reduced remote area that is physically remote also cover that adjacent room that has ceilings at 21' that is outside of the 1st remote area?

How about a large pitched roof where the high point is adjacent to the riser and the low end is physically remote?

As others have said, it depends, sometime greatly based on several factors....so to answer your question...1 calculated design area is the required minimum but unless everything is the same, that will not be the final amount.

Barry L Brainard

5/25/2023 09:46:54 am

Minimum Number of Fire Sprinkler Design Areas?

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