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skdesigner (Mechanical) (OP)
23 Jan 13 10:27
I recall seeing an explanation in an issue of Sprinkler Quarterly, however I have since misplaced the issue and the intent of the section.

NFPA 13-2010 22.4.4.6.2 Where the design area is equal to or greater than the area in Table 22.4.4.6.2 for the hazard being protected by the sprinkler system, the discharge for sprinklers protecting small rooms such as closets, washrooms and similar small compartments that are in the design area shall be permitted to be omitted from the hydraulic calculations.

To me, this seems pretty straightforward. Don't reduce your design area and you can omit all the sprinklers in small rooms.

What has me unsure is the 13-2010 handbook explanation, specifically "the intent of this provision is to prevent designers from falsely minimizing system demands by omitting sprinkler discharge from compartments addressed by this rule".

Where does the line between falsely minimizing system demands and correctly minimizing system demands get drawn?

Thanks in advance!

cdafd (Specifier/Regulator)
23 Jan 13 14:30
does the first line in the commentary paragraph answer your question, where it says that " the comparment are to be of such size that only one sprinkler is required to protect them"?????????


and also comply with table 22.4.4.6.2
FIRESPRINK (Mechanical)
28 Jan 13 22:37
I am not sitting with my NFPA 13 tonight but have reviewed this with designers. As you indicate, I recall that the approach is an RA of the minimum required size (1500 SF in an LH or OH occupancy) or larger, you may omit the rooms protected with a single head from WITHIN the RA. Provided one uses the NFPA 13 listed method for reducing the RA size to less than X,XXX SF (to as little as 900 SF) then a room protected by a single head within the 900 SF area is to be calculated. I presume that you may also elect to use a third method, the area of greatest fire demand in certain occupancies, and be less than 900 SF in the RA. I don't feel that these methods are provided to minimize the sprinkler protection, perhaps the NFPA recognizes that most LH and OH fires are put out by 3 heads or less and are attempting to apply what has been gathered via fire statistics. Also, as you know the Handbook is a guide and provides non-enforceable insight and commentary to those in the industry and in the enforcement side. To my knowledge an AHJ has never adopted the Handbook, I interpret that the statement is intended to guide designers to the correct RA.
fpst (Computer)
29 Jan 13 6:18
The line gets drawn in accordance with TABLE 23.4.4.6.2



The line also gets drawn if the small room has more than one sprinkler protecting it in accordance with the following commentary from the NFPA 13 2013 handbook:

"The intent of 23.4.4.6.2 is to permit sprinklers in a small space (compartment) to be considered as not open (closed) during a fire in the area around the compartment. In order to use this rule, the area of operation for calculations must be at least 1500 ft2 (139 m2) for wet pipe systems in light and ordinary hazard occupancies and at least 2500 ft2 (232 m2) for wet pipe systems in extra hazard occupancies. For dry pipe systems, the area of operation for calculations must be at least 1950 ft2 (181 m2) for light and ordinary hazard occupancies and at least 3250 ft2 (302 m2) for extra hazard occupancies. This provision resulted in considerable confusion to the point that the committee added Table 23.4.4.6.2 to the 2010 edition to clarify what has always been the intent of this requirement. If quick-response sprinklers are used in a wet pipe system in a light or ordinary hazard occupancy, and the design area is decreased below 1500 ft2 (139 m2), the sprinklers in the small compartments are not permitted to be considered closed. In other words, this rule is not permitted to be applied, because the design/density area falls below the minimum required in Figure 11.2.3.1.1. In most cases, when the room design method is utilized, the area of operation is usually below 1500 ft2 (139 m2). Since the area is less than the minimum, this rule cannot be applied when using the room design option. In order to use this rule, these spaces (compartments) are to be of such a size that only one sprinkler is required to protect them. The sprinkler within the small compartment must be verified as capable of producing the appropriate discharge density, as specified in Figure 11.2.3.1.1. The intent of this provision is to prevent designers from falsely minimizing system demands by omitting sprinkler discharge from the compartments addressed by this rule."

The line also gets drawn by the types of areas described in 23.4.4.6.2 in accordance with the following commentary from the NFPA 13 2013 handbook:

"It is compelling to note the types of areas described in 23.4.4.6.2. Small compartments are intended not only to be physically small but also to contain a relatively small fuel load. For example, a small office, because of its size, can require only one sprinkler. However, this rule is not intended to apply to small offices, because the anticipated fuel load is greater than that expected in closets and washrooms."


The line also gets drawn by common sense in accordance to the following commentary from the NFPA 13 2013 handbook:

"In compartmented areas, such as the small spaces previously described, the simultaneous operation of all of the sprinklers in the design area is unlikely. On the other hand, the sprinklers in the foyer, closet, and bathroom of a hotel room could all operate in response to a fire in the bedroom."


fpst (Computer)
29 Jan 13 6:34
So, after digesting all of that information, we can now analyze your interpretation:
"To me, this seems pretty straightforward. Don't reduce your design area and you can omit all the sprinklers in small rooms."

I disagree with this interpretation because of the following emphasized words:

"23.4.4.6.2* Where the design area is equal to or greater than the area in Table 23.4.4.6.2 for
the hazard being protected by the sprinkler system, the discharge for sprinklers protecting
small rooms such as closets, washrooms, and similar small compartments that are in the design
area shall be permitted to be omitted from the hydraulic calculations."

The fuel load of some small rooms, such as small offices, which fit NFPA 13's definition of small rooms, may contain a higher fuel load than closets, washrooms, and other small compartments of equal fuel load as closets and washrooms as 23.4.4.6.2 implies. Furthermore, in some buildings such as hotels, small rooms may surround the primary occupancy on multiple sides. Therefore it doesn't make sense to me to omit "all" of the sprinklers in "all" small rooms.

This is my personal analysis, YMMV.
fpst (Computer)
29 Jan 13 6:46
The Sprinkler Quarterly feature you are thinking of is from the January-February 2010 release, page 27 "Non-Uniform Hydraulic Calculation Areas: Part 2"

Attached is the extracted article in a .pdf

I have yet to read it to see if it agrees with my interpretation, yours, or neither, but I thought you might want to solve the mystery of what/where that article was as those things drive me crazy.
Helpful Member!  fpst (Computer)
29 Jan 13 6:57
I just realized there was another article in SQ magazine that addressed the same thing, and that could be the one you're thinking of. This one is called "Hydraulic Calculations for Small Rooms."
skdesigner (Mechanical) (OP)
29 Jan 13 9:16
That was it, thanks for your help!

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