Tank Size, Options for Sprinkler System Supply?

8/3/2021

We have a fire sprinkler system with a 550 gpm total sprinkler demand (including hose allowances). The supply duration is 60 minutes. There is no city water supply and we are only utilizing a storage tank.

Is the tank required to have a minimum capacity of 33,000 gallons?

Or, could we rely on fire department response, potentially reduce the tank size, and have a manual fire department connection for tank refill?

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12 Comments

Pete

8/3/2021 06:47:32 am

I might be out of my depth here, but I'm seeing nothing in NFPA 22 even suggesting the idea of a manual refill or fdc connection to a tank. I can't imagine the FDC would be considered listed for such an application.

So yeah, I'm inclined to say you're getting a 33,000 gallon tank (or 40,000 based on standard sizing.)

Glenn Berger

8/3/2021 08:19:19 am

Your question said that there is no city water supply. To me this implies that the project is located remotely from any municipality that has any type of reliable water supply.

I would strongly recommend to provide at least the minimum, if not something more robust. I would not recommend decreasing the water supply.

Michael Newell

8/3/2021 08:21:12 am

It would be based in my opinion on worst case scenario. If you do not have a water supply you could in theory be required to have fire fighting water storage as well. But this would potentially increase tank size depending on system and demand instead of reducing it. I wouldn't think the AHJ would allow you to reduce the system demand below what is required for your system duration.

Roland lopez

8/3/2021 08:21:57 am

Based on NFPA 13 & 20. It is required for your safety. You can reduce the tank size if proximity of Fire department is very near and will not take a longer time to response… say within 10 minutes arrival of fire department. Immediate source of water is essential in supressing fire.

schulman

8/3/2021 08:24:26 am

with no "city water supply" you'd get approximately one minutes worth of water from a pumper truck ... FYI ...

"... Key components of a fire engine include: Water tank (usually 500-750 gallons)..."

MattC

8/3/2021 08:49:36 am

If you can prove that the fire department response is really fast, and the department has tanker/shuttle accreditation then this may warrant or justify the reduction in tank sizing. Of course you're at the mercy of the AHJ and they likely want as much water on-site as possible.

The reality is that if you're excavating for an existing building or building a brand new building anyway, then the cost of increased tank sizes or even additional tanks is negligible, in my opinion. You should still have a fill port or at least a hatch either way if the tanks are below-grade.

Typically the fire dept does not fill the tanks at all during fireground operations. They would simply shuttle water in from a filling station using a water tanker (this is not the same as an engine, as it carries substantially more water) but are typically already filled in the station. At the fire scene, suppression staff would set up what is essentially a pool which they draft water out of. In instances where a large quantity of water is needed, multiple of these can be connected together for increased storage capacity. The tankers then simply go out, fill, return and dump into the pools, while the pumper or engine on-scene would draft from here and use this water for firefighting operations.

Also, most jurisdictions should allow you to omit the outside hose allowance, assuming there's no draft hydrant connected to the tanks. Make sure if your building doesn't have standpipe that you're also not including inside hose allowance. This will help reduce your demand and therefore reduce tank sizes.

Anonymous

8/5/2021 07:33:56 pm

That last part was very helpful, thank you

CJ Bonczyk

8/3/2021 08:50:54 am

We have ran into this before. If no supply connection is available for the refill rate to be reduced then the tank is required to be sized for total demand at the duration required. If the refill rate cannot be refilled within 8 hours per NFPA 22 a variance from the fire department can be requested to where they will connect their mobile tank truck (if the department has one) to help with supply refill once on scene.

Casey Milhorn

8/3/2021 09:19:59 am

Yes, full amount with no reduction. Also as someone else mentioned there should probably be the conversation about IFC fire flow if any draft hydrant or private hydrants are to be fed from the tank. A good compromise would be to add a draft hydrant on the tank, size up to 40,000 gallons, and the fire department at least has a little extra in there for drafting from the tank. From the sound of the demand, you might be ordinary hazard group 1 or 2. Make sure the building has offsite monitoring of fire alarm so that you can truly use the 60 minute duration. Also, if there is no draft hydrant or private hydrants, you could argue that the hose allowance is not needed but again a draft hydrant would probably be a good idea anyway.

Franck

8/3/2021 04:37:01 pm

Insurance point of view : not acceptable (as many other point of views above)
There is no reliability if you do not have the required volume for the required period. There is no warranty that the outside fire department (outside company) would fill the tank.
If it was an automatic refill with sufficient flow, that would be acceptable, but in no way a manual refill from a fire department would be considered acceptable.
As already said by other above, the fd has already other many “much more important” duties.

Alex

8/4/2021 06:59:25 am

Anonymous,

NFPA 22 (2018) 4.1.6 states that a “tank shall be sized so that the stored supply plus reliable automatic refill shall meet the system demand for the design duration”. It is my interpolation of the code that a reliable automatic refill is referring to a city/town water system, not the fire department.

In my town, each engine has roughly 1,000 gallons of water onboard. This water is used for handlines or the deck gun and would not be used to refill the tank. As mentioned in previous responses, for a rural area with no hydrants, a shuttle system would need to be set up. This takes valuable time when initial suppression of the fire is required. In addition, many rural departments have on-call firefighters, which already decreases response time.

In the end, it would be up to AHJ to make the final call. I would recommend calling the fire department to determine their SOP (standard operating procedure) for structures similar to yours.
Best of luck with your design.

Alex

jim williams link

10/4/2025 11:58:21 am

the architect shows two 20,000 gal fire and combination domestic water tanks, the domestic water demand can average around 12 thousand gallons in the morning. my second question is can the same tanks be used for domestic and fire supply???

Tank Size, Options for Sprinkler System Supply?

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