Fire Pump Flow for Manual Standpipes, Sprinkler?

7/3/2024

We have a low-rise building with a manual wet standpipe and a sprinkler system. One combination riser is 6-inch and the other is 4-inch. Standpipes will be Class I.

The calculated sprinkler demand is 195 gpm (Light Hazard).

My total manual wet standpipe system demand will be 750 gpm (500 gpm first riser + 250 gpm second riser).

Does my fire pump need to accommodate the 750 gpm of the manual standpipe system, since they're interconnected?

I know the fire department will handle the standpipe demand, but does the flow rating for the fire pump need to accommodate 750 gpm?

I've searched but haven't found specific code references in NFPA 13 or 20 to address this sizing. Thanks in advance.

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9 Comments

Brett

7/3/2024 06:55:15 am

The idea behind a manual standpipe is that the fire department will provide the pressure required to operate the hose valves inside. You do not need to include any standpipe demand in your pump calculation. The pump is required to be tied into a manual standpipe, but it is not required to be sized to NFPA 14 design requirements.

Brian

7/3/2024 08:06:06 am

No, the fire pump is only for the sprinkler system. The fire truck is for the manual standpipe.

Josh

7/3/2024 08:10:05 am

On a manual standpipe system, the intent is for the fire department to use their pumper to boost the pressures at the FDC. What I do when I have a manual system is tell the FM what pressure is available in the standpipe after calculations so they know what they need to boost. You still have to account for 750 gpm in your manual calculations if you have 2 standpipes.

Example - I say: you will have 36 psi at the hydraulically most remote standpipe, or 64 psi short of the 14 code of 100 psi. I assume a boost to be 150 psi typically so they know.

Check out the language in 2019 NFPA 14 A.7.8.1.2:

"It is not the intent of this standard to provide an automatic water supply for manual standpipe systems. Manual standpipe systems are designed (sized) to provide 100 psi (6.9 bar) at the topmost hose connection using a fire department pumper as the source of flow and pressure."

Pete H

7/3/2024 09:51:44 am

Yeah, that annex section hits the nail on the head.

Casey Milhorn

7/3/2024 08:17:52 am

As others have responded, no, the fire pump is sized to your sprinkler demand only, HOWEVER, you need to consider the path from your FDC to your standpipes independently, and size the feed main and standpipes by way of hydraulic calculation. You will use the responding fire departments pumper truck as your water source. Many designers will just plug in 165 to 175 psi static, with residual a pound or two less, and a supply at 750 gpm.
Once you consider the path for the standpipe flow, all other systems piping can be sized to the sprinkler demand. I have designed systems with a 250 gpm fire pump, 4" incoming line, then upsizing to 6" at the bypass and standpipe feed main. It happens.

Glenn Berger

7/3/2024 08:26:25 am

I agree with the responses provided above.

The question does not state if the standpipe system in question is a Class I, II, or III. The question also does not mention the reliability of the water supply system. I would like to know if the responding fire fighting group is an on-site brigade, local volunteer group, or a paid professional team.

Josh

7/3/2024 08:39:49 am

The OP does state it's class 1 just FYI.

Dan Wilder

7/3/2024 08:41:00 am

As it's always nice to see the backup

NFPA 14, 2019 - Removes the requirement for the pump to supply the standpipes.
7.7.3 Where a manual system is permitted by Section 5.4 and an attached water supply is provided to supply an automatic sprinkler system or to maintain water in a wet system, the attached water supply shall not be required to satisfy the standpipe system demand.

7.7.4 When the system demand to be supplied by the fire department at the fire department connection is being determined, the local fire department shall be consulted regarding the water supply available from a fire department pumper.

Manual standpipe calculations should be using NFPA 1901 in parallel with information from the local AHJ & responding agencies. These aren't numbers that are made on the fly, NFPA 1901 Chapter 16 has the needed info (2016 referenced below)

16.2.3 Pumping System Capability.

16.2.3.1 If the pumping system is rated at less than 3000 gpm (12,000 L/min), it shall be capable of delivering the following:
(1) One hundred percent of rated capacity at 150 psi (1000 kPa) net pump pressure

(2) Seventy percent of rated capacity at 200 psi (1400 kPa) net pump pressure

(3) Fifty percent of rated capacity at 250 psi (1700 kPa) net pump pressure

16.2.3.2*
If the pumping system is rated at 3000 gpm (12,000 L/min) or greater, it shall be capable of delivering the following:
(1) One hundred percent of rated capacity at 100 psi (700 kPa) net pump pressure

(2) Seventy percent of rated capacity at 150 psi (1000 kPa) net pump pressure

(3) Fifty percent of rated capacity at 200 psi (1400 kPa) net pump pressure

Then, using the above info and after calculations, using signage at the FDC to tell the responding Fire Department what pressure and flow is required is the final step. Just remember, there will be the sprinkler calculations for each system using the available water supply and fire pump, then a separate standpipe calculation with a supply at the FDC proving the standpipe (the remote standpipe may not be the combination sprinkler/standpipe FYI).

Final note, in the rare occasion, I have had the AHJ require that the signage show loss through the FDC and attached wye fittings & hoses, back to the actual fire pumper apparatus itself....just be clear with your discussions that the calc is from the FDC inlets and no further. The type of FDC (Siamese, Storz, Header) makes no difference (or shouldn't anyway), it's a supply point.

Jack G

7/3/2024 11:01:04 am

Dan nails it.
Be sure to provide “ Standpipe hydraulic calculation places” as shown in NFPA 14.
I provide one at each fdc, one for/ on each standpipe at ground level, and stick one at the pump identifying manual wet standpipe, their flow rate and pressure and max pressure of the standpipe system.
I have metal signs made up, and stick ones for the pump room.

Fire Pump Flow for Manual Standpipes, Sprinkler?

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