I agree with the NFPA response, but one thing I question is, why did the 
contractor assume 20 sq. ft. of coverage area for the sprinklers in that pocket?

By the S x L rule, from NFPA 13-2016, Section 8.5.2, using the dimensions that 
you've reported:

-  S = 11'-5½", which is the distance between the sprinklers along the line ; 
-  L = 4'-0", which is two times the 2'-0" distance of the line from the wall 
(which is greater than the distance of 1'-2" from the beam).

So by my math, A = S x L = 11.46 ft x 4.0 ft = 45.84 sq. ft.

Larry Keeping

-----Original Message-----
From: Sprinklerforum [mailto:sprinklerforum-boun...@lists.firesprinkler.org] On 
Behalf Of Chris Born
Sent: March-13-18 11:43 AM
To: sprinklerforum@lists.firesprinkler.org
Subject: Fwd: NFPA Technical Question Response [ 
ref:_00D5077Vx._5005013DQXS:ref ]

Here is the response I received from NFPA concerning my “area of coverage” 
question last week. Subsequent conversation confirmed other replies on the 
forum to this question that if the sprinkler can’t spray past the obstruction 
you only have to measure to the obstruction.

Sent from my iPad

Christopher H. Born, P.E.
Director, Fire Protection Engineering|Principal Clark Nexsen
4525 Main Street, Suite 1400
Virginia Beach, VA 23462
(757) 455-5800
(757) 961-7933 (direct)
(757) 644-8581(mobile)

Begin forwarded message:

> From: NFPA Systems <techquessyst...@nfpa.org>
> Date: March 13, 2018 at 9:18:17 AM EDT
> To: "fireph...@cox.net" <fireph...@cox.net>
> Subject: NFPA Technical Question Response    [ 
> ref:_00D5077Vx._5005013DQXS:ref ]
> I apologize I’m not sure I fully understand your question but if you are 
> asking do you space your sprinkler coverage between beams when sprinklering 
> beam pockets vs trying to use the obstruction rules to spray past the beams 
> then the answer is yes you space to the beams as if they were walls.   
> Important Notice: This correspondence is not a Formal Interpretation issued 
> pursuant to NFPA Regulations. Any opinion expressed is the personal opinion 
> of the author and does not necessarily represent the official position of the 
> NFPA or its Technical Committees. In addition, this correspondence is neither 
> intended, nor should it be relied upon, to provide professional consultation 
> or services.
> Regards,
> Chad Duffy, PE
> Senior Fire Protection Engineer
> If you have a follow-up question directly related to this inquiry, please 
> reply to this email.  If you have another question on either a separate topic 
> or different document please return to the document information pages and 
> submit your new question by clicking on the “Technical Questions” tab.
> ----------------------------------------------------------------------
> -----------------------------
> Create Date: 3/9/2018
> Contact: Christopher Born
> Subject: Protection area of coverage when spacing is impacted by 
> obstructions
> Question for NFPA: We have a building with exposed structure and some of 
> these beams are deep enough to be obstructions. For both spacing along and 
> between branch lines, the standard states to measure the distance between 
> sprinklers (or to wall or obstruction in the case of the last sprinkler or 
> branch line). The reference to "last sprinkler" in the reference to measuring 
> to an obstruction seems incorrect for both of these sections. Please confirm 
> that the intent is that if there is an obstruction, regardless of location, 
> it is acceptable to use twice the distance to the obstruction for determining 
> the coverage area for a particular sprinkler. 
> We have two review comments from the insurer, one regarding the sprinkler 
> area used in hydraulic calculations and the other concerning the maximum 
> allowable coverage area. In the case of the hydraulic calculation comment, 
> two sprinklers are located within a beam pocket, 11'-5.5" apart, less than 2' 
> from a wall and approximately 1'-2" from a 27" deep beam. The contractor has 
> assumed 20 square feet of coverage area. 
> In the other case, branch lines are located on either side of a 36" deep 
> beam. Sprinklers are spaced a maximum of 12' apart on a line that is 3'-10" 
> from the beam. The other line is 7'-5.5" from the beam and sprinklers are 
> spaced 8' apart. 
> In both of these cases, we believe that the intent of NFPA 13 is to determine 
> area of coverage by measuring to the obstruction and not the next line. 
> Please confirm our interpretation.
> ref:_00D5077Vx._5005013DQXS:ref
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