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I have a project right now that the sprinkler system is being supplied from a tank and pump because the only water available is 25 gpm from a well. The AHJ refuses to allow NFPA 1142 for mobile apparatus to supply fire flow, saying it has to be a "fixed" system. However, he does let me use NFPA 1142 for fire flow rate.
I've added an additional 30,000 gallons to the tank for the 250 gpm fire flow for 2 hours. The AHJ just says to add a connection to the tank so the fire department can pull directly from the tank. The problem I'm running into is how can I be sure the fire department only uses 250 gpm so they don't rob the sprinkler system of any water? I don't have any experience doing this. Any advice or guidance you could provide would be greatly appreciated. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
8 Comments
anthony
8/12/2026 08:12:25 am
At the point the FD is there its on them to understand and use the systems they've approved for instillation. If the AHJ has aligned and signed off on a design then they own the implications of response. Note there may be other 'fire' uses for the water. there may be a car accident or a wild fire that needs response and they will avail themselves of the tank to stop an on going fire. All that is to say the 250gpm is a good faith engineering judgment not a guarantee of use in a dynamic fire situation.
Glenn Berger
8/12/2026 08:19:02 am
I would not be concerned with exceeding the 250 gpm flow rate. I would be concerned with low level in the tank, You can get alarms based upon low level supervisory switches.
Mike
8/12/2026 08:21:45 am
The sprinkler will be discharging from the time of activation until the FD starts to put water on the fire. At that point it depends on the size of fire and the department. Most will stretch a 1.75 or 2.5 inch line that will flow at 250 or below. If it is a defensive fire that is not contained and they use a master stream or a ladder truck that flow rate may jump to 1,000+ gpm. At that point it is not the requirement of the design to account for that flow rate. The FD will have to utilize a mobile water supply.
Pete D
8/12/2026 11:35:42 am
I concur. This is especially true if your overhead design is CMDA, the function of the sprinklers is to control the fire. FD may elect to connect a pumper to the system to supplement overhead flow and pressure. Alternately, I've had them tell me to close the overhead control valve during the fire or to shut the fire pumps off.
James Sills
8/12/2026 08:48:49 am
The water supply is designed in accordance with the requirements of NFPA 13, 13R, and 13D. The fire department connection serves as a valuable bonus for two key reasons: it can be used as an additional water source for various incidents, especially in areas where hydrants and water sources are limited, and it allows the fire department to supplement the water supply if needed.
Dan Wilder
8/12/2026 08:52:33 am
You don't and they will take what they need. No truck engineer ever (that I have talked to) will restrict the ability to put the wet stuff on the red stuff just to keep a 2-hour duration...they will attack it fast to knock it down. Remember fire growth is exponential so more early will always be better than less with consistency for an active fire.
Jack G
8/12/2026 10:24:43 am
The departments priority is speed and volume. Goal is getting an uninterrupted high volume supply of water to the fire lines. ( not tracking exact gallons )
Jack G
8/12/2026 10:27:41 am
Vacuum gauges ( not calcium) Leave a Reply. |
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