Protection Area (SxL) for Each Sprinkler - NFPA 13 (2013) - 8.5.2

[Haldorson]

Good day,

All scenarios shown in NFPA 13 for design area are of single, rectangular, rooms. What about oddly shaped rooms? Take for instance Figure A in the attached PDF. Would each sprinkler cover 120 sq.ft. (15 ft. x 8 ft.), or would it be 172.5 sq. ft. (15 ft. x 11.5 ft.)?

Exhibit 8.7 of NFPA 13 2013 states that you take the larger distance between the wall and the sprinkler as your dimension, which would indicate that the calculated area is 172.5 sq. ft. However, exhibit 23.11, showing sprinklers of multiple orifices, indicates that when determining the protection area of a sprinkler, you do not always take half the distance between two sprinklers. Furthermore, if a wall were placed between the two sprinklers, as shown in Figure B of the attached PDF, each sprinkler would definitively cover 120 sq. ft., so why would the lack of a wall impact the coverage of the sprinklers?

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1553547537/tips/Sprinkler_Spacing_Inquiry_v3syak.pdf[/url]

 

[cdafd]

Not an engineer or into design, so not sure what the question is,

But in the 2016 edition there is what I call the triangle rule 8.6.2.3, which talks about irregular walls.

 

[UFT12]

The standard is clear and although the exhibits you refer talk mostly for a repetitive pattern of sprinklers, I don't see a reason why it shouldn't apply for this case too. Therefore strictly speaking, the sprinkler to the left will have to cover 15 x 11.5 ft2 as it has to throw water up to halfway between the two heads. And that's the larger of the two distances (btw heads and 2x against the wall) as defined for S & L. One thing you have not mentioned though is the classification of hazard. Depending on that, two heads may or may not be enough.

 

[Haldorson]

Assume this is ordinary hazard occupancy, 130 SF coverage.

The question is: based on the two scenarios in the link, is the scenario with the wall removed acceptable?

 

[TravisMack]

I would say it is not, as you have exceeded 130 sq ft spacing. I get where you are going. But, the standard is pretty clear on how to determine As and in one example, you are 15x8 and in the other example you are 15x11.5 following the procedures outlined in NFPA 13.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

 

[Jon.M]

to confuse things even more, you could put an 8" lintel at the wall position in figure b, and your head coverage would be 120ft2. as the 8" lintel would then define those two areas as compartments according to 3.3.6.