Mulitiple Pipes, Continous Obstruction

[jjmoore73]

I am 3D Model/BIM coordinating a military OH-2 mechanical room. Upright sprinkler coverage is provided and there is no ceiling. There are multiple 24" (+ insulation) round rigid duct within the room. In a few areas, 2, 3 or 4 ducts run side by side at the same elevation creating an obstruction over 4' wide. Without much room to work with, the though is to put some space between the ducts so they are not a continuious object over 4' wide. I am trying to keep the duct more than 18" below the sprinkler deflector, but I cannot find guidance on how far they need to be spaced apart to be considered seperate. I realize the further apart they are the better, but what should the mimumim clear distance be?

There is a similar scenario for the electrical raceway. Multiple conduits side by side eventually creating an obstruction over 4' wide. What distance should the conduit be apart so a continous obstruction over 4 feet wide is a non issue?

If you know of code or handbook guidance, it would be greatly appreciated.

 

[cdafd]

may not answer your question but look at the page 13/14, no code references

http://www.nfpa.org/assets/files//2011 FLSC/2011FLSCChaseSprinklerObstruction.pdf

As an ahj If it looks like the pattern may not develop, water not get to the floor, then I require additional heads under the obstrucion. not sure of any rule as far as opening, except 50%?

 

[Sdpaddler50]

For someone who can barely draw straight lines in CAd in a 2D format, i think this BIM modeling is amazing. The fact that you are able to see these obstructions from other trades, before they are even installed is an example of how powerfull this tool is. For people who dont know much about BIM (me included) there is a nice article in the most recent edition of Sprinkler Age that describes how it works in the sprinkler industry.

You have some good questions. FM has specific criteria regarding how far obstructions need to be spaced, to consider them isolated, not continuous. I believe those are in DS 2-0. This is especially crtitical for high rack/ESFR because just one obstructed head can cause the fire to overwhelm the system - yup just one head.

I did a quick search through NFPA 13 (2010 version), and I would direct you to sections 8.5.5 and 8.6.5. I could not find minimum separation distances noted, that would define isolated, verses continuous. I would suggest you take the approach of 50% open. I know it's in 13 somewhere, so you can check it out. If i remember correctly, you can consider a open grated mezzanine open, if you have at least 50% openings. Applying that same logic to your pipes/conduit: If you have a 2 in. diameter conduit, then you should have a gap of 2 in. horizontally to the next 2 in conduit, and so on to consider it open, ie isolated, not continuous obstructions. But, i will let the sprinkler contractors out there correct me if i am off base here.

Lastly, I am confused by your statement "there is no ceiling".

 

[cdafd]

http://www.fmglobal.com/fmglobalregistration/Vshared/FMDS0200.pdf

check page 37

 

[jjmoore73]

I know it is a gray area; I hate gray areas. I see some good information here, but nothing really answers the question. Initially, 50% seems like the best fit, however, If the ducts are 24" diameter, then having 24" clear space between the duct seems to be much more than needed. If the raceway conduit is 2" diameter, then having 2" of clear space between each conduit seems reasonable, but I know I have seen them closer with no worries from the inspector. I am sure to get laughed out of the coordination room if I tell the mechanical guy he has to keep his 24" ducts 24" apart from each other. I remember years ago as a newbie being told... "if there is separation, then it isn't continuous." I see page 13 of CDAFD's NFPA slide show and it shows a horizontal obstruction example. A bunch of pipes side by side, and most all appear to have separation. Water isn't going to pool on the pipes and water will make its way down to the floor. It will not be a nice even pattern of drops, but water will flow between the pipes. I wonder what an informal interpretation would result from this picture.

FM Global page 37 is what I'm trying to avoid. If I can provide separation of "x" distance, then I should not have to put protection under the continuous object that is no longer greater than 4' wide.

By no ceiling, I only meant this large mechanical room had a roof deck only with upright sprinkler protection. There was no dropped ceiling with pendent sprinkler heads.