Feed Upper Level with Fire Pump, Lower Without?

1/30/2025

Is it okay to design a fire protection system for a building using street pressure for the lower garage dry-pipe system, and using a fire pump for the upper floors when required?

If so, does NFPA 13 have a diagram for this?

Also, how is the system piped to avoid starving the street pressure system when the fire pump engages?

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11 Comments

Anthony

1/30/2025 08:05:15 am

This is perfectly fine as long as the FDC is properly connected to all systems.

Anthony

1/30/2025 08:22:35 am

I'd add I've seen this approach on faster moving project where fire pump approval my take longer/ lead time issues. Also in instances where lower floors will be occupied prior to the completion of building top out.

Christopher Nelson

1/30/2025 08:07:22 am

You only account for one fire at a time.

If the upper is activated and the fire pump is running, you dont consider that you may be starving the lower system. And while design area is 1500/2500, its never between floors.

Franck

1/30/2025 08:10:43 am

Do not forget to provide backflow preventer between the areas fed by the city water supply only and the areas fed by the booster pump (to avoid too much pressure for the lower garage protection areas).

Regarding the impact on city water supply when the pump starts, this is determined on the basis of the testing of the city water supply and setting your pump so that it can not flow more water than available from the city supply.
For example, if your city water supply provides 2800 gpm @ 20 psi, it would not be a good idea to provide a 2000+ gpm fire pump. But a 1500 gpm fire pump would be fine.

James E Art Fire Protection Engineer (FPE)

1/30/2025 02:53:25 pm

Terminology and Costs. Requiring BACKFLOWs is Prohibited in Ca.

Backflows are costly, add much friction loss,
and are generally NOT required on fire sprinkler systems.

A check valve might be all that is needed, if anything,
unless there is a cross connection or other contamination present.
Some AHJ's might require if Antifreeze is used.

See link
https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HSC§ionNum=13114.7.

for Laws prohibiting requiring backflows in CA.
even where there are booster pumps, (but not prohibited IF there are tanks.)

Note that many water co's IGNORE the laws!
AND they are bigger than we are.

Do some other states require?

Jay

1/30/2025 03:23:59 pm

Is that correct? Backflow preventers are not permitted to be installed on fire sprinkler systems?
I ask because in the Illinois plumbing code, backflow preventers are required on all fire sprinkler systems because of the stagnant water in the system and probable bacteria.

Jesse

1/30/2025 04:36:15 pm

I'm not sure I'm on board with this. Indeed, NFPA 13 doesn't require a backflow preventer. This is derived from plumbing code as a means to protect the water supply from contaminant.

IF the automatic sprinkler system is fed via a dedicated fire water supply (public or private) with no tie-in to potable use, than yeah a check valve could be all that's needed. But the reality is, there really aren't a lot of public water systems out there with separate infrastructure for fire and domestic / potable use. Initial and ongoing costs are just too high.

Many AHJs have local amendments banning the use of a normal DCDA backflow device. Instead, they require a RPZ or RPDA. This generally stems from state environmental codes related to contaminants and the intersection between fire department foam systems or CAFS on their apparatus. They recognizse the surfactant nature of the Class A foam being injected into the automatic sprinkler system via the FDC as a source of contamination, and rightly so. So while they may have "banned" typical backflow devices (DCDA), a more robust backflow device is required in lieu of the DCDA - hence the RPZ RPDA. Having practiced as a loss control engineer in CA, the overwhelming majority of system are equipped with RPDA / RPZ devices, and not the typical backflow preventer DCDA style.

I looked through the codes provided, and admittedly I don't see where backflows are prohibted in CA. And I can say that if you've ever done a main drain test on a large system, you'd be pretty happy a backflow device is on the system. A check valve isn't capable of protecting the water suppl y like a backflow device.

Anthony

1/31/2025 08:23:52 am

Isn't it Cal Berkly that certifies backflow preventers?

Very curious that a state known for heavy handed government regulations would get lax is cross contamination mitigation. I'd like to see more documentation on this. These claims don't track for me.

Glenn Berger

1/30/2025 08:24:50 am

It is perfectly acceptable to provide a fire pump for upper floors and use city pressure only for lower floors.

If you are concerned about starving water when the pump is activated you might need a fire water storage tank included in the design.

Remember verify type of backflow preventor required and where the authorities require it to be placed. Remember that you might need more than 1 FDC on this applicable with proper signage.

Dan Wilder

1/30/2025 08:38:26 am

We do it, at rare times, to avoid the over-pressure issues but it has some draw backs...it is a case-by-case basis.

Most ground level or below B1 levels are not allocated enough space to have the pump room AND separate fire sprinkler risers. Having a PRV station with a secondary setup is also not on the available floor space list either so that is always a discussion.

FDC routing needs to be considered as there is now an additional point (or points) to tie it in (more check valves and piping to accommodate). Same with supply piping for shutdowns as the pump is no longer that start point of the system.

There are no issues with a system prior to the fire pump having a relation to "starve" the fire pump and there is no design provision for multiple systems to be activated simultaneously, it's a good thought but application to address.

Now, there could be an argument for the use of the standpipes downstream of the pump and the supply line have activated sprinklers taking away some of that pump supply, but that would need to be addressed during the hydraulic calculations, if needed at all as there is no requirement to consider (that I am aware of). There is a provision within 13 that if a building is considered fully sprinklered, no inside hose stream shall be added so that all falls back onto the supply anyway, but that only adds GPM not PSI.

Jack G

1/30/2025 04:08:51 pm

Agree mostly with above comments.
A consideration should be given to the fire separation between the garage level and the rest of the multi story building.
If it has the proper separation, horizontal podium design, then the two are considered separate buildings.
If not then a consideration should be given to a separate pump discharge supply to the area in question utilizing a prv.
In your scenario above I would take into account the system only demand in the hydraulics and in sizing the pump. If considered 2 separate buildings, I would not.
As for FDC s in Philadelphia a separate fdc is required for each, along with a combined.

Feed Upper Level with Fire Pump, Lower Without?

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