How to Determine the Reserve Amount of Foam?

8/25/2023

What is the correct procedure for determining the quantity of the reserve amount of foam, such as FP 3%, for a plant?

I've looked specifically through NFPA 11 and NFPA 16, and can't determine it.

Thanks in advance.

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6 Comments

Jonathan Griffin

8/25/2023 08:13:55 am

Look in the 2016 edition of NFPA 11 (printed in 2019) Section 4.3.2.5.2 -- Reserve Supply of Foam Concentrate.

You are required to have a reserve supply equal to the amount delivered by the system as designed; either onsite or available for delivery to the system within 24 Hrs.

i.e.: Your system is a 1200-Gal. Bladder Tank, have at least 1200 gallons of listed foam concentrate available for refill post-discharge.

Pete H

8/25/2023 08:18:15 am

Take with grain of salt, only briefly looked at this:

From NFPA 11 (2021) 8.3.5.1 - A reserve supply of foam concentrate sufficient to meet system design requirements shall be provided in order to put the system back into service after operation.

8.3.5.2 - The reserve supply shall be in separate tanks or compartments, in drums or cans on the premises, or available from an approved outside source within 24 hours.

----

I'm pretty sure the "3%" is just the level of foam concentrate in proportion to the water.

So I'd say figure out how many gallons of fully mixed foamy water your system needs to put out to meet the demand of your system design requirements.

And then 3% of that total number is the amount of concentrate you need in a reserve tank.

Once again, take with a grain of salt, this is not something I look at very often.

Todd E Wyatt

8/25/2023 08:32:17 am

The prior references to NFPA 11 & NFPA 16 are correct but I recommend you verify the editions of these standards based on the scoping Code(s) (e.g. IBC & IFC).

For instance, if your jurisdiction has adopted the 2021 IBC, the referenced editions of these standards are as follows :

NFPA 11 = 2016 edition
NFPA 16 = 2019 edition

REFERENCES
2012 IBC

Chapter 9 Fire Protection and Life Safety Systems
904.7 Foam Systems
Foam-extinguishing systems shall be installed, maintained, periodically inspected and tested in accordance with NFPA 11 and NFPA 16 and their listing. Records of inspections and testing shall be maintained.

Chapter 35 Referenced Standards
NFPA 11 (2016) Standard for Low-, Medium, and High Expansion Foam (904.7)
NFPA 16 (2019) Standard for the Installation of Foam-water Sprinkler and Foam-water Spray Systems (904.7, 904.13)

Dan Wilder

8/25/2023 08:38:48 am

In both 11-21' & 16 - 19' and specific of low-expansion foams for NFPA 11

11-6.5.10.2.2

16-7.10.2.2

2 sets of calculations for the most demanding and the least demanding...

This is where things get a little divergent
-NFPA references a demand calculation (with hose stream) and supply calculation (with no hose stream) - Typically performed on the same remote area (at least that what I have done for previous systems)
-The last seminar I attended with a foam supplier made note that the calcs needed to include the demand calc from the hydraulically remote part of the system (with hose allowance) and the supply calc from the closest available remote area to the riser (physically, like the first sprinklers closest to the riser and no hose allowance)

So that means the same 2 calcs processes, just on two separate areas to make sure the pipe sizing is correct and the foam duration will last for a fire that would pull the most water.

In both cases, sprinkler water demand (no hose) * foam contrate % * duration.

There is also the allowance to reduce the duration to 7 minutes per 11-6.5.2.3.2 & 16-7.2.3.2.

In all cases - verify with the listing of the sprinklers/foam MFG for discharge requirements because they all do not follow the densities listed within NFPA.

There is also the 4 sprinkler calc to determine the low proportioner rate to make sure the equipment will provide the correct mix across the low and high flows per 16-19'-7.2.4

Dan Wilder

8/25/2023 08:51:04 am

I put all that in there so that the tank sizing is correct, but hit send prior to the reserve sizing...

11-21'-4.3.2.5.2 - [.1] Enough to put the system back into service after operation and [.2] within 24 hours

16-19'-6.3.3 - Enough to put the system back into service after operation and within 24 hours

The AHJ typically has a say in this as well.

Glenn Berger

8/25/2023 08:48:06 am

I have always just determined my required primary supply and then provided a reserved supply of the same quantity.

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How to Determine the Reserve Amount of Foam?

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