NFPA 13 states that for hydraulically calculated sprinkler systems the fire department connection (FDC) pipe can be less than 4-inch diameter, but not less than the system riser.
What size should the fire department connection feed pipe be for a 6-inch riser, or an 8-inch riser?
Can the FDC pipe still be 4-inch for these larger risers?
I have some clients believe that 4-inch is the maximum no matter what, and some say if the riser is 6-inch or 8-inch that the FDC pipe needs to match the larger riser size.
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4/5/2021 08:11:40 am
The code in NFPA 13 states that the size for the FDC is in accordance with ONE of the following. 4" minimum for fire engine connections is the most common and somewhat serves as a "rule of thumb" in the industry. In a hydraulically calculated system that is supplied by a smaller that 4 inch riser, the code referencing the smaller size comes into play. Then it is limited to the size of the riser servicing the system.
4/5/2021 08:28:43 am
It depends.....I know right?
4/5/2021 09:07:43 am
NFPA 13, 2016 184.108.40.206 says "The size of the pipe for the fire department connection shall be in accordance with one of the following:" (which means any of the options are acceptable). 220.127.116.11(1) states "Pipe size shall be a minimum of 4" for the fire engine connections." 18.104.22.168(3) states "For hydraulically calculated system, the pipe size shall be permitted to be less than 4 in., but not less than the largest rise being served by that connection." To the best of my knowledge, the intent of this section is to require a 4" FDC for any riser size but to allow you to use a smaller FDC for smaller risers. This means22.214.171.124(3) is giving the option of making an FDC smaller when possible but not intended to require larger FDC piping. A.126.96.36.199 explains that the intent is supplemental so assuming you have a reliable water supply, there is no reason to size an FDC based on system demand.
NFPA 13, 2019
4/5/2021 09:22:20 am
It isn't as clear in earlier editions of NFPA 13, but the 2019 edition provides more guidance about the 4" minimum pipe size and two 2½" outlets.
4/5/2021 09:53:48 am
Everyone covered it pretty well. The only thing I would add is to use some common sense as well. We just had a job with one of those "surprise" fire pumps (I think we've all had one or more of these before). Well the fire pump is going to be installed at the far end of the building from the current lead-in, which meant that the FDC has to feed all the way from the discharge side of the pump back to the front wall. This is a storage type occupancy with some larger GPM requirements. Per the standard, we could have technically provided a 4" main several hundred feet back to the front, but we know the friction loss would be extreme with even just 500 gpm flowing through it. We used a little common sense and upped the size to 6". Of course many times us contractors don't have the luxury of making things "better" but fortunately this was a change order situation and we had the freedom to make a good fire protection decision with the fire fighters in mind.
4/5/2021 11:22:38 pm
No close mains you could have tied into from the front of the building? We've tied into the primary (or secondary/dead main) if it matched the size of the riser up to that point (6" riser feeding a 4" primary = 6" FDC feed tieing into a 4" primary/secondary/dead main). We still provide checks to each system, just not at the riser room.
4/6/2021 08:42:17 am
Unfortunately it's a multi-system building. We would have had to tie into 3 separate systems with checks on each one and the distances would have been more than the one bulk main. Great idea though and I've used that one before too.
4/6/2021 05:53:19 pm
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