NFPA 13 - Residential fire sprinklers in bedrooms 2

[Derik Brooks]

Good Morning everyone,
Within a apartment building unit, is it allowed with a 4 head calculation @ 16'x16' (256ft²) in a bedroom space the single fire sprinkler head to a "area room design" and space the fire sprinkler at 14'x18' (252ft²)?
I have used this method in the past without being questioned but now the field inspector is saying it is not allowed. I am digging through NFPA 13 right now, but if somebody could point me in the right direction I would really appreciate it!

 

[cdafd]

Are you asking if the same 16 x 16 sprinkler can be used for the 14x18 spacing?


Did the inspector give you a section out of 13 where he is making the call? If not you might ask for it.

 

[Derik Brooks]

@cdafd - yes, to use the 16'x16' used for the 14'x18' spacing

 

[Derik Brooks]

I am a little torn on two different ideas.
With NFPA 13 11.3.1.3 (3)
-room size is 11'-0" x 14'-6" = 159.5ft²
-one (1) fire sprinkler x .10 = 15.95
-so calculate the room within the design area @ 15.95gpm

or

The fire sprinkler in the bedroom is spaced @ 14'x18' (252ft²) is less square footage than the design are calculations, 8 fire sprinklers spaced @ 16'x16' (256ft²) the flow would be the same due to the less square footage coverage from the spacing.

 

[SprinklerDesigner2]

If I understand your question correctly the inspector is correct.

You mentioned NFPA 13 so it is a 13 and not 13R?

If the standard is NFPA 13R then you must use the discharge requirements of the residential sprinkler for 18'x18' spacing.

If the standard is NFPA #13 and you are using residential sprinklers then you must use the discharge requirement for the 18'x18' sprinkler in addition to doing a second calculation demonstrating you can achieve a discharge of 25.2 gpm which would be a density of .10 gpm over the room.

Let assume you are using the Viking FREEDOM® RESIDENTIAL PENDENT SPRINKLER VK466 (K5.2) [URL unfurl="true"]https://www.vikinggroupinc.com/sites/default/files/documents/091406_0.pdf[/url]

For a NFPA #13R system in a room measuring 16'x18' with the sprinkler no more than 9'-0" from any wall your minimum discharge would be 17.0 gpm. Even if the room measured 18'x4' your minimum discharge would still be 17.0 gpm.

However if your system is a NFPA #13 system then you must discharge 17.0 gpm AND 28.8 GPM showing compliance with a density of .10 gpm as stipulated in NFPA #13. And yes, if your room measured 18'x4' you would still need a minimum discharge of 17.0 gpm or 18x4x0.10=7.2 gpm whichever is greater.

 

[TravisMack]

I believe I know what you are looking for:

1 - Can you use the sprinkler at 14'x18' spacing? Yes, if it is listed for 18' spacing.

2 - What is the required minimum discharge for the sprinkler?

Assumptions:
The room meets the requirements for a small room.

So, if you have something like a Tyco LFII 4.9k sprinkler, you must look at both the minimum from the data sheet and the minimum flow with a 0.10 density. At 18' spacing, the minimum flow is 17 gpm. In your room example, you are covering a space that is ±160 sq ft. Since the criteria in 13 allows you to apply the "small room rule" for area of coverage (Room area / # of sprinklers per room), this requires a minimum of 16 gpm. However, the listing of the sprinkler requires 17 gpm so you calculate for 17 gpm.

If you are arbitrarily calculating your residential sprinklers at 25.6 gpm since you are spaced at 16', you may be doing way above the minimum requirements - which is perfectly acceptable. So, you can get up to 256 sq ft of coverage per sprinkler. Since a 4.9k residential pendent at 20' spacing requires 20 gpm, you can space your sprinklers as much as 20' between sprinklers and no more than 10' off walls and still be in compliance, provided that the rooms/compartments you are calculating meet the requirements of a small room.



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

http://www.mfpdesign.com

 

[Danefre]

Sorry to derail the thread but I wanted to clarify something Travis Mack mentioned. I was under the impression that NFPA 13 (2013) 8.6.2.1.2.1 only applies to Standard Spray heads - so most commonly in LH applications - QR heads. I'm not sure why but the NFSA article agrees with that.

NFSA Article

Can anyone shed some light on this? Can you apply 8.6.2.1.2.1 with residential heads? What about extended coverage? I think i've been too conservative with my interpretation.

 

[TravisMack]

Read through the standard very carefully. It was also clarified in the 2016 and newer editions so people wouldn't get confused on this. In Chap 11 of the 2007-2013 editions, the residential section refers you to do either the SxL or sends you back to the section in Chap 8 for small room rules. So, because Chap 11 directs you to that section specifically, you can apply the room area / # of sprinklers. 2016 and 2019 don't redirect you back there any longer, it just re-states the information right in the section on residential sprinklers. I assume the committee found too many AHJs not correctly applying this, so they just clarified the language to make it crystal clear.

No, you can't apply that same rule to EC sprinklers. Location in the standard has meaning. That section referenced above is specific to standard spray. You can use it with residential because the residential calc section directs you specifically to that section. The EC stuff doesn't direct you there. Now, there are some special listings that come into play. For the Tyco CC3 sprinklers, they can cover up to 16x16. But, you can calculate them based on actual spacing. So, I can space at 15X12 and calc for 180 sq ft vs 256 sq ft. If I were using a regular EC sprinkler like a Tyco EC-11, then I would have to calculate something spaced at 15x12 at the criteria for 16x16. Also, the Tyco EC-25 sprinklers have similar listings. You can calculate at the actual spacing. So if you are 12x14, you calc at 168 sq ft, not at 14x14 spacing or 196 sq ft. Understand though, these are very specifically listed sprinklers.

Edited to add: I just skimmed the NFSA article. Since it was written in 2020, the article is correct. You can't apply the section in Chap 8 of the 2016 edition of NFPA 13 to residential because you are no longer directed back there. 2016 tells you to basically do the room area / # of sprinklers right in Chap 11. If the article was written based on the 2007 - 2013 editions of NFPA 13 then it would have an incorrect statement there.

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

http://www.mfpdesign.com

 

[Danefre]

Thanks, Travis - great explanation. The 2016 edition does make it crystal clear.