NFPA 22 - Fire Water Storage Tanks (Suction Tank Appurtenances)

[stn-cadams]

Hi all,

My company (municipal engineering firm) have been engaged to design a factory coated bolted-steel water tank for fire protection service. The tank feeds a NFPA 20 compliant fire pump and NFPA 13 compliant sprinkler system. Sizing has been performed by a fire protection engineer, we are required to design the tank complete with drains, fill and discharge lines in accordance with NFPA 22.

We frequently design these in accordance with AWWA D103 for municipal water supply but are new to aligning to the NFPA 22 code. I am looking for clarity on some nuances in NFPA 22 outlined below.

Below Grade Piping:
NFPA 22 12.6.4 and 12.6.4.1: This project is located in Canada, our typical design for factory coated bolted-steel reservoirs (constructed at grade) is to have pipes come below the tank foundation (typical design shown below). Does this design conflict with 12.6.4 or since the bottom of the foundation is below grade are pipes below the foundation permitted? Would the pipes need to be encased in the concrete foundation to adhere to this?


Anti-Votex Plate:
Per NFPA 22 14.2.13 every suction tank is required to include an anti-vortex plate. Typical installation has the suction piping leave the tank above grade with a minimum clearance from the floor. Ideally, I would like to provide a tank drain and outlet on the bottom of the floor (with below grade piping). Based on my understanding of the code, there is no specific outline of how to do this other than the schematic shown for concrete lined embankment supported suction tanks. It seems fair to me to use this installation for my proposed purpose. Any thoughts on this would be appreciated. Is anyone aware of a standard product (floor mounted vortex plate assembly) for this purpose?




Thank you in advance for your help,

 

[JStephen]

I think the paragraph above is just saying you can't build a tank on top of existing pipelines, not that you can't use bottom connections.

The tank supplier should be able to come up with a vortex plate detail and bottom connections without any problem.

Normally, municipal tanks are prevented from freezing by the circulation of warmer water through the tank. For tanks with no circulation, such as a fire protection tank, you will normally need heaters and/or insulation. There is some information on heat loss in NFPA 22.

In southern climates, shell nozzles are preferred due to easier access and inspection. Farther north, undertank connections are more commonly used for freeze protection. If you have to insulate and heat the tank anyway, there may be minimal advantages to using undertank connections.

There are a number of minor differences in appurtenances, etc. for fire protection tanks, so go through NFPA 22 paragraph by paragraph to ferret all those out.

 

[stn-cadams]

I think the paragraph above is just saying you can't build a tank on top of existing pipelines, not that you can't use bottom connections.

The tank supplier should be able to come up with a vortex plate detail and bottom connections without any problem.

Normally, municipal tanks are prevented from freezing by the circulation of warmer water through the tank. For tanks with no circulation, such as a fire protection tank, you will normally need heaters and/or insulation. There is some information on heat loss in NFPA 22.

In southern climates, shell nozzles are preferred due to easier access and inspection. Farther north, undertank connections are more commonly used for freeze protection. If you have to insulate and heat the tank anyway, there may be minimal advantages to using undertank connections.

There are a number of minor differences in appurtenances, etc. for fire protection tanks, so go through NFPA 22 paragraph by paragraph to ferret all those out.

Thank you for the clarification.

As the lowest one day mean temperature of my project site is greater than -15°C (5°F) per the National Building Code, I won't be including a heating system for this tank, assuming I understand Chapter 16 correctly.

 

[JStephen]

I was thinking the cutoff line for requiring heating was quite a bit farther south, but don't have a copy of NFPA 22 here handy to check.