Allow a Tank Fill Tee'd off the Building Fire Main?

2/4/2025

I'm working on an interesting scenario in which the client would like one main line into the building for fire and to tee off that line inside the building, with one line going to a giant indoor tank that holds 350,000 gallons.

It would be filled just one time per year. Assume 1,000 gpm for 6 hours that one time per year.

First - do you all see this as a possibility right off the bat?

We were talking about putting motorized valves wired back to FACP that shut off if the fire protection activates flow as a potential solution if it could work.

Initially I asked about a water tank for that until I learned it was 350,000 gallons.

Second - is it even possible to calculate out in that scenario?

One thing I love about FPE is the unique, always challenging scenarios that come up regularly. I'm looking forward to figuring out how we're going to handle this facility. Thanks in advance for any input.

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11 Comments

Anthony

2/4/2025 07:34:50 am

It sounds like the tank isn't for fire protection. If that's the case, you'll need to meter the water coming into the building. So if you have a metered service, sure no problem, use a manual valve though so you know its closed when you're not filling it. In this case your system will be under impairment during the fill, a fire watch will be needed. This would be a combined service instance you may need 2 backflow preventers?

If there is no meter this probably won't be legal as you're not paying for the water. Also note the water won't be considered potable.

If the tank is for fire protection, then get a solenoid fill valve and a fill sensor (high/low/ fill line) as you would for any FP tank.

Josh

2/4/2025 10:12:21 am

It is not a tank for fire protection. It's a big enclosed tank for testing aquatic equipment. A very big tank.

I want to avoid multiple BFPs. All of this water is non-potable usage, thankfully.

As I mentioned in a reply further down in the comments, I'm told it's like 1/4th of a mile away from the town's large water tank and outbound pumping station and to expect "very high pressures and flows" at that location.

These are the feathers in the ol' cap at the end of the day. It's these different/unique questions and scenarios that keep me in this field. Lots of other engineers, even some I work with, just do the similar stuff with nothing at all unusual or very challenging on a regular basis.

Chad

2/4/2025 08:17:14 am

I am wondering what that tank is for too. Sounds like its not FP?

More and more water departments are not permitting combination FP/Non-FP services so they need to confirm they are not going to run afoul with the water authority as well.

Glenn Berger

2/4/2025 08:23:00 am

I agree that your scenario is interesting, but I have some questions that I need to ask to fully understand the situation.

Where does the FP portion of the system begin?

What is the purpose of this 350K storage tank?

Are there going to be procedures in place to terminate the filling of the tank, if a fire emergency happens?

One can interpret your question of can you use one tap from a water supply for two different purposes. If that is the case then yes it is possible.

2/4/2025 09:34:04 am

The tank is not for FP. It's for testing certain aquatic equipment. Think of them as enclosed raceways. I'm kind of in a spot here because the principal has proposed a solution then came to me and needs me to make it work, essentially. I have the same concerns the rest of you have but I'm also, like you all, a solutions guy and love a good challenge.

The solution to terminate filling the tank in a fire emergency, at this point in time, would have to be a logic controller that shuts the valve if the flow switch detects flow through the fire line.

The last sentence in your reply is one that typically I would say, sure this is kind of standard, but when you talk about the volume of water that needs to come through the non-FP line...now we are not talking about typical things I've seen happen before. This isn't your bathroom groups or something super run of the mill.

Jack G

2/4/2025 09:09:08 am

I m on board with questioning what the water is to be used for as it sounds like it’s not fire protection.
With this extremely large quantity ( not being fire protection) is it to be used for irrigation— hot climate?
Yes, connected to your fire system— non potable— then all the rules for non potable water supply in NFPA 13 apply— like return bend loops on pendent sprinklers.
The tank is too large I would think to be lined like used on fiberglass tanks used for domestic water.
Only opened for filling once a year is strange.
Agree this should have a water meter— and the pump incoming a turbo detector check valve as there usually a charge when water to the pump is used—- so a meter pit may be in order.

2/4/2025 09:37:24 am

Correct - it is not for fire protection. It's for testing marine equipment in an enclosure. It's one of those "oh, that's interesting" new things that comes up throughout one's career.

One of the rather interesting bits is the air relief of some sort to keep buildup from happening in this large enclosure. I'm either going to have to air gap it or put a proper relief on. Second interesting tidbit is I'm told it's like 1/4th mile away from the city's massive water tank and outbound pumping station and to expect "very high pressures and flows" from there.

It's going to be a neat one in the portfolio when all is said and done.

2/4/2025 09:56:02 am

If used the way described above, the tank, with or without a pump for the testing of marine equipment—- the tank itself should be atmospheric and/ or have a vent( like in a fire tank) so a vacuum is not formed.
I would also use an appropriate clay valve vent ( for underground ) so that any trapped air in the underground is properly vented .

2/4/2025 10:03:25 am

Atmospheric tank vent. Clay valve vents for underground piping systems. Additional venting as required when pumps are operating. I m concerned about vacuums being formed on both systems .

Franck

2/4/2025 10:33:48 am

Just a comment: what if the tank was located at a neighbour's place and he would fill it once per year from the city water supply?
You would not even know...
This is what could happen with city water supplies as they may supply other facilities/industries and deplete seasonally your available water flow and pressure.

The good thing in your case, is that you know when your system is not fully operational.
And you can react as for any impairment for the same water supply.

Providing some kind of "motorized valves wired back to FACP that shut off if the fire protection activates flow" could also be a solution. But if there are people attending on site when the water is used to refill the tank, you can also consider that those people could stop manually the filling operations (with some delays compared to an automatic interlock).

It is a potential threat. But only for a very limited period of time.
If I were the AHJ, I would probably accept it. But require a dedicated impairment procedure during this operation.

Jesse

2/5/2025 07:45:32 am

Yep, can be done. I've actually seen this before in LA or MS at a place supplying off-shore oil prorjects. The tank was a training dive tanak.

Allow a Tank Fill Tee'd off the Building Fire Main?

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