Fire Pump Sizing 1

[jjmoore73]

A future project has a fire flow demand of 4000 GPM for onsite fire hydrants and sprinkler demand of 2000 GPM including hose.

An onsite fire pump will supply demand to both the onsite fire hydrants and the ESFR sprinkler system taking water from a large above ground supply tank.

We believe the fire pump should be sized for the greater of the two demands, and not sized for both demands combined.

4000 GPM fire pump vs 6000 GPM fire pump.

We are having difficulty finding code language to support either scenario.
Any idea on where we can reference a code section for this?

 

[cdafd]

So when the warehouse fire happens, and the system is flowing 4000 gallons.

Are the firefighters just going to stand around? And not flow anything.

Or if they decide to flow on top of the 4000,,, will they be robbing the system?

I guessing that there are at least two nfpa standards involved, to answer the question.

 

[mk3223]

We believe the fire pump should be sized for the greater of the two demands, and not sized for both demands combined.

The project should verify the total demanded water flow for the plant and confirm with local AHJ and per the fire protection codes. If the sprinkler system is only intended for the equipment cooling in the fire incident, it may be turned off and save the water through the hydrants as required for the fire trucks.

 

[TravisMack]

Site fire flow and fire sprinklers are independent calculations. Just as standpipes and sprinklers are independent calculations. So, you size based on the greatest demand. Typically, site fire flow will drive the fire pump capacity and sprinklers/standpipe will drive the pressure rating.

Travis Mack, SET, RME-G,
MEPCad, Inc
AutoSPRINK | AutoSPRINK FAB | AutoSPRINK RVT

 

[jjmoore73]

Thanks Travis... Agreed. Both IFC 2018 and NFPA 13 2019 appendix demonstrates this.

B105.3 Water supply for buildings equipped with an automatic
sprinkler system. For buildings equipped with an
approved automatic sprinkler system, the water supply shall
be capable of providing the greater of:
1. The automatic sprinkler system demand, including hose
stream allowance.
2. The required fire flow.

A.19.2.4.2 Appropriate area/density, other design criteria, and water supply requirements
should be based on scientifically based engineering analyses that can include submitted fire
testing, calculations, or results from appropriate computational models.
Recommended water supplies anticipate successful sprinkler operation. Because of the
small but still significant number of uncontrolled fires in sprinklered properties, which have
various causes, there should be an adequate water supply available for fire department use.
The hose stream demand required by this standard is intended to provide the fire department
with the extra flow they need to conduct mop-up operations and final extinguishment
of a fire at a sprinklered property. This is not the fire department manual fire flow, which is
determined by other codes or standards. However, it is not the intent of this standard to require
that the sprinkler demand be added to the manual fire flow demand required by other codes
and standards. While the other codes and standards can factor in the presence of a sprinkler
system in the determination of the manual fire flow requirement, the sprinkler system water
demand and manual fire flow demand are intended to be separate stand-alone calculations.
NFPA 1 emphasizes this fact by the statement in A.18.4.1 that “It is not the intent to add the
minimum fire protection water supplies, such as for a sprinkler system, to the minimum fire
flow for manual fire suppression purposes required by this section.”

 

[UFT12]

To add to this, NFPA 1 is also in alignment with the above.


18.4.4.4 * Required Fire Flow and Automatic Sprinkler System Demand.

For a building with an approved fire sprinkler system, the fire flow demand and the fire sprinkler system demand shall not be required to be added together. The water supply shall be capable of delivering the larger of the individual demands.