Balance Two Separate Foam Systems in Calc?

10/19/2022

We are designing a foam system (not a water spray) protecting an industrial facility.

Two systems are being designed, and they're located side-by-side. The two systems are not currently interconnected, but I believe they should be and balanced.

We're getting some pushback on our approach and I'm interested in other opinions here.

Do the system volumes need to be combined and compared to the available water supply, or can each system be calculated separately (but still flowing at the same time without balancing)?

Thanks in advance.

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8 Comments

Jay

10/19/2022 08:29:39 am

Are the 2 systems required to be designed to flow at the same time?

Alex

10/19/2022 08:31:17 am

Hi,

This is out of my area of expertise.

With that said, I do not believe you can simply calculate the systems independently and not balance them. Doing so will leave you short on your calculations.

Alex

Connor

10/19/2022 08:42:58 am

If the systems are not required to flow at the same time, they can be calculated separately.

If the systems flow at the same time, and if they are fed from the same water supply, they must connect together at some point upstream. Physics dictates that they will have the same pressure at the point where they converge and will therefore be "balanced."

There could be an opportunity to make both systems more efficient by balancing them further, but if the water supply can support it when you calc both systems going off at the same time, some balancing is already built in.

Dan Wilder

10/19/2022 08:43:45 am

Is the expectation that both systems will discharge together? If yes, then the calculation would be accurate for both discharging (balancing, total foam required, available water supply comparison...) however why not make them 1 system not just interconnected (unless the volume requires two valves, but you'll have to get some version of an inline flow control proportioner to help the foam ratio's)?

If the expectation is these systems are independent of each other, calc'ing both would not be required. There may be an argument for a what-if scenario, but that would be for the owner/AHJ/Insurance people to decide on a path forward. Just get it in writing for your concerns, recommendations, and their response for or against.

The last oil transformer yard retrofit I completed had a similar issue where there were a set of 5 transformers, 3 large (20'x20'x13') with 2 smaller ones (8'x8'x8') in between and due to the age of the facility, no fire separation wall was installed (circa mid-70's). We provided 5 individual deluge systems (1 for each transformer) but calculated the 3 worst-case discharging at one time (2 large, 1 small) based on the potential of the smaller one catching on fire and the radiant heat triggering the adjacent linear heat detection. While we don't expect all three to go off, the discussion was had, and all the approving authorities wanted to error on the side of caution. It might have been the fact that a new one would take 9 months to get and those control the agricultural water supply for half of a state.

In the end, document, RFI, and keep for future use.

Brad K

10/19/2022 08:46:30 am

We may be short on information here but it feels like two non-interconnected foam systems exist. It may be a scenario where a draft curtain or partition should be proposed if they are not to be interconnected and balanced. Independent systems need independent balanced foam proportioning and available water supply. Are we talking about two systems with single foam concentrate storage? Keep in mind proportioner flow minimums if there is any chance of a partial system discharge adjacent to another.

Todd E Wyatt

10/19/2022 08:47:54 am

Below are the NFPA standards related to foam systems :

NFPA 11 Standard for Low-, Medium-, and High-Expansion Foam
NFPA 11A Standard for Medium- and High-Expansion Foam Systems
NFPA 11C Standard for Mobile Foam Apparatus
NFPA 16 Standard for the Installation of Foam-Water Sprinkler and Foam-Water Spray Systems
NFPA 1145 Guide for the Use of Class A Foams in Fire Fighting
NFPA 1150 Standard on Foam Chemicals for Fires in Class A Fuels

Per 2021 NFPA 11 Standard for Low-, Medium-, and High-Expansion Foam, it references “multiple systems” as follows :

Chapter 13 — Inspection, Testing, and Maintenance
13.3 Foam-Water Sprinkler Systems.
13.3.3* Operational Tests.
13.3.3.3 Multiple Systems.
The maximum number of systems expected to operate in case of fire shall be tested simultaneously to inspect the adequacy of the water supply and concentrate pump. [25:11.3.3]

“Balanced” is referenced (31) times in 2021 NFPA 11 (e.g. 3.3.26.1.1* In-Line Balanced Pressure Proportioning) but I could not find a prescriptive requirement for the condition you described.

The Codes and Standards cannot address all (or most) fire protection design scenarios so they expect Fire Protection Engineers (and associated AHJs) to consider the Code’s and Standard’s “Design Intent” when engineering FP systems such as this.

Joe Brill

10/19/2022 09:00:55 am

Water supplies shall have the capacity and a pressure to maintain foam and/or water discharge, or both at the required design rate for the required duration over the area protected by the systems that are expected to operate simultaneously. NFPA 11, 4.2.2.2.2

Based upon this, I agree with Conner. Also remember that the foam concentrate must be able to cover the duration of both systems if there is a possibility that they both could operate at the same time.

Jesse

10/19/2022 10:20:46 am

Its hard to tell from the OP, but it sounds as if the systems are intended to flow at the same time. Is there something that would prevent them flowing at the same time? How are they actuated? Separate fire areas?

Without knowing these I'd say they need to both be calc'd and balanced.

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Balance Two Separate Foam Systems in Calc?

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