Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Hydraulically most demanding area shape, regarding walls

Hydraulically most demanding area shape, regarding walls

Hydraulically most demanding area shape, regarding walls

NFPA 13 says to use 1.2 * sqrt(min remote area) to find the L dimension of the remote area rectangle. I need to know if this means we just ignore walls and assume the fire teleports through them, or if we use them as barriers and can then make square or "tall rectangle" remote areas, see the pdf for graphical representation.

RE: Hydraulically most demanding area shape, regarding walls

fpst, I am not a sprinkler designer, but I dust off my hydraulic program a few times per year to run calcs, more for verification purposes in consulting, not final design. If i had a one hour, floor to ceiling wall, i would stop the most remote area at that point. The 1.2 rule (1.4 for FM i believe) is just to ensure designers dont calc unreasonable demand areas. The 1.2 dimension assures we calc the area most representative of the expected fire growth area. If the area is bounded by rated walls, then using those boundries is allowable. But, i will let the people who design for a living correct me if I am off base here.

RE: Hydraulically most demanding area shape, regarding walls

It depends on what calculation method you have elected to use. NFPA 13 does not say multiply 1.2 by the square root of the design area to determine the length of the design area, NFPA 13-2010 does (i.e only one part of the standard). does not tell you to stop at a wall, it says "the design area shall be a rectangular area having a dimension parallel to the branch lines AT LEAST 1.2 times the square root of the area of sprinkler operation used." Room design method states "Where the design is based on the room design method, the calculation shall be based on the room and communicating space, if any, that is hydraulically most demanding".

In this case, you would stop at the walls. All depends on which method best suits your particular design.

RE: Hydraulically most demanding area shape, regarding walls

So skdesigner, are you saying that if I wasn't doing the room design method, I would not stop at the walls? I'm having trouble interpreting your message

RE: Hydraulically most demanding area shape, regarding walls

I'm saying that if you're using the density/area method, your design area length must be at least 1.2 times the square root of the design area, regardless of building features.

Keep in mind that NFPA 13-2010 states "In systems having branch lines with an insufficient number of sprinklers to fulfill the 1.2 requirement, the design area shall be extended to include sprinklers on adjacent branch lines supplied by the same cross main." Meaning, the only time your design area is permitted to be shorter than 1.2*sqrt(DA) is when the branch lines are not physically long enough to fulfill the requirement.

RE: Hydraulically most demanding area shape, regarding walls

Thank you skdesigner, was right there in the standard, I just didn't want it to be that way so I guess I was blind to it *facepalm*
Can anyone put forward a probable theory as to why it's this way, when clearly a fire is going to be hindered by a wall, especially one without a door or a CMU fire wall. NFPA, I want to understand you!

RE: Hydraulically most demanding area shape, regarding walls

It's a factor of safety in anticipation that an opening protective such as a fire door does not close. If the fire occurs at the room adjacent to the opening, we may see flame rollover out of the opening until water is discharged. The 20% increase compensates for the door not closing, or not being closed if a fire-resistance rated door assembly is not required (which is generally the case).

RE: Hydraulically most demanding area shape, regarding walls

""""""""""" How you treat walls when the design basis is the same, though, depends on whether you're designing a new system or modifying an existing system. In designing new systems, you can ignore walls in the portion of the building with the same design basis and select the remote area simply based on the most demanding adjacent fire sprinklers. For existing systems, however, you must treat walls as boundaries. The ease of placement is no longer the driving factor, and you should consider the impact walls will have on a fire's heat flow. Is it possible to create a more demanding remote area by ignoring walls? Certainly. Since this is another gray issue, however, the AHJ must again define what he or she will allow."""""""""""""


RE: Hydraulically most demanding area shape, regarding walls

Hmm, interesting link cdafd, just goes to show how easily one can get confused in all of these rules!
I can't follow that article as I'm new to sprinkler design and haven't even seen the circa 2003 nfpa 13, and all of the sections he refers to for that quote are missing/different now in nfpa 13 2013. From what I gathered, however, he is saying to sometimes treat walls as boundaries as a safety factor, because it could cause elongated remote area shapes along branch lines and make the hazard more demanding, which is the opposite of my case. Treating walls as barriers in my case would mean more of a square shape for a remote area.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


White Paper - Strategies to Secure Connected Cars with Firewalls
White-hat hackers have demonstrated gaining remote access to dashboard functions and transmissions of connected vehicles. That makes a firewall a vital component of a multilayered approach to vehicle security as well as overall vehicle safety and reliability. Learn strategies to secure with firewalls. Download Now
White Paper - Model Based Engineering for Wire Harness Manufacturing
As complexity rises, current harness manufacturing methods are struggling to keep pace due to manual data exchanges and the inability to capture tribal knowledge. A model-based wire harness manufacturing engineering flow automates data exchange and captures tribal knowledge through design rules to help harness manufacturers improve harness quality and boost efficiency. Download Now
White Paper - What is Generative Design and Why Do You Need It?
Engineers are being asked to produce more sophisticated designs under a perfect storm of complexity, cost, and change management pressures. Generative design empowers automotive design teams to navigate this storm by employing automation, data re-use and synchronization, and framing design in the context of a full vehicle platform. Download Now
eBook - Simulation-Driven Design with SOLIDWORKS
Simulation-driven design can reduce the time and cost of product development. In this engineering.com eBook, we’ll explore how SOLIDWORKS users can access simulation-driven design through the SOLIDWORKS Simulation suite of analysis tools. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close