Forum Members,
Chapter 22 (soon to be 23) requires that you create a remote area (regardless
of walls when using the density/area method unmodified) that is equal to 1.2 x
sq rt A (1.4 for Craig's project) along the branchlines. (note the period.)
That means that the Area should be 76'8" on Craig's project. This may include
different sprinklers, different rooms and different sides of a cross main if
the branchlines are long enough to accomodate.
If you start at the single most demanding sprinkler ("most remote sprinkler"),
this would cause similar sprinklers to flow more water through the pipe which
would create more demand on the water supply in both flow and pressure
requirements. (an important point on this project) Because if you reduce the
orifice size of the sprinklers as you move back to the main, then the
originally chosen "most remote area" placement may not end up being the "most
demanding area". But there is no way to know that unless you moved a properly
sized and shaped "most remote area" to different locations on the drawing that
may include more of the sprinkler with larger k-factors. The reason there is
no way to know is because as I get closer to the water supply, there is more
pressure available (because I lose less energy through less pipe getting
there). The availability of more pressure may overcome the requirement for
more flow, if that ended up happening here.
The black and white rules of NFPA 13 call for the remote area to be laid out in
this fashion regardless of walls. If that was donew on this project, the
designer may have done things very correctly.
However, if the single room (in which all of the sprinklers would activate
before activating sprinklers in another room (probably)) is more demanding of
the calcs because all of the sprinklers are the larger k-factor, it seems
PRUDENT to calc that room and ensure that the system will indeed provide the
density over an area for the place where the fire will happen. That would
likely be more demanding. And THAT realistic situation is what we want to
defend against in the event of a fire.
But that ain't the black and white rule. So good luck with that..... :-P
In our next lesson, we'll explain why the sprinklers closest to main could be
considered more demanding......
A sprinkler geek on his 3rd day back at work in a long-long time,
Cecil Bilbo
It should be recognized that the above is my opinion as a member of the NFPA,
and has not been processed as a formal interpretation in accordance with the
NFPA Regulations Governing Committee Projects and should therefore not be
considered, nor relied upon, as the official position of the the NFPA, nor any
of their technical committees.
Sincerely,
Cecil Bilbo
Academy of Fire Sprinkler Technology
Champaign, IL
217.607.0325
www.sprinkleracademy.com
[email protected]
OUR STUDENTS SAVE LIVES!!
> From: [email protected]
> To: [email protected]
> Subject: RE: mixing densities in same calculated area
> Date: Tue, 3 Apr 2012 18:05:54 +0000
>
> I would have maintained the hydraulic area within the room and added
> additional heads on the next branch line as described in A.22.4.4.1, not gone
> to an adjacent, separate room. There are several sprinklers flowing less than
> their required flow based on their coverage area so there are other issues
> with the layout and design. Overall the total gpm flow in the calc appears to
> be within the expected flow rate based on rough numbers of a .40 over 3000
> requiring at least 1200 gpm. The calc shows a flow rate of approximately 1300
> gpm.
>
> However I cannot readily accept sprinklers 2-5 ft from the system main being
> more hydraulically remote than those which are 40-50 ft from the main.
>
> Based on the layout there are only 6 heads on the branchlines within the
> room, based on 1.4*sq rt of 3000 / 9 ft spacing (underwriter requires 1.4
> factor be applied) you should calc 8 heads per branchline so they just
> included the next two heads on the other side of the wall and system main.
>
> Craig L. Prahl, CET
> Fire Protection
> CH2MHILL
> Lockwood Greene
> 1500 International Drive
> Spartanburg, SC 29304-0491
> Direct - 864.599.4102
> Fax - 864.599.8439
> CH2MHILL Extension 74102
> [email protected]
>
>
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Roland Huggins
> Sent: Tuesday, April 03, 2012 12:35 PM
> To: [email protected]
> Subject: Re: mixing densities in same calculated area
>
> bottom line is you are required to drop a rectangle over the area that
> creates the greatest hydraulic demand. Excluding a 0.4 density area
> to include a 0.17 area (with smaller K-factors) can be safely assumed
> to present less of a demand. Show me the numbers if you want to do
> something that appears wrong to prove it is acceptable.
>
> If the area of the higher density is smaller than the minimum size,
> then you pick up sprinklers from an adjacent area with a lower
> density. The TC has gone to great pains to address this in A.11.1.2
> (as well as in 12.1). Even expanded it this cycle to address areas
> smaller than the size for the higher hazard but larger than the
> surrounding classification (ie a 1600 sf EH in an OH building which
> the current text would imply to do a 1500 sf remote area).
>
> As someone already said, seems this is a closed case of just not
> following the procedure of ch 22.4.4.1 (or lack of understanding what
> is meant by HYDRAULICALLY most demanding).
>
> Roland
>
>
> On Apr 3, 2012, at 8:50 AM, <[email protected]>
> <[email protected]> wrote:
>
> >
> > Got a submittal package where the contractor has two divided rooms.
> > One is 0.40/3000 and adjacent room is .17/2000. He is calculating
> > the .40 area and has extended his hyd remote area beyond the wall of
> > the room into the adjacent .17 area and calced about 8 heads.
> > The .40 room is plenty large enough to allow the additional
> > sprinklers to be calced from within the room.
> >
> > Off the top of your head does anyone know where this type of thing
> > is addressed within NFPA 13?
> >
> > Craig L. Prahl, CET
>
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