Calculations for Water Storage Tank in NFPA 1142?

4/19/2024

A building 2,880 sqft, 20-ft in height, Type IIB with classification of 4 for occupancy hazard.

When I calculate the gallons needed for a water storage tank, is this based off a 2-hour fire flow per NFPA 1142?

If so, where can I find that requirement?

2,880 sqft x 20-ft height = 57,600 cubic feet / 4 occupancy hazard x .75 = 10,800 gallons.

Is this 750 GPM x 120 minutes for a total of 90,000 gallons?

Huge difference between the two. Thanks.

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13 Comments

Glenn Berger

4/19/2024 08:14:38 am

There are many calculation methods that can be used to determined required fire flow. I personally have not used NFPA 1142.

There is a required fire flow rate required to be met in NFPA 1. NFPA 13 and NFPA 14 have methods to be met if those systems are installed. Various other NFPA standards are applicable when specific hazards are present.

ISO Rating Schedule (I believe that there is actually an updated title to this system) has a planning guide for water requirements.

Recommend that research is done to find out which rules, regulations, codes, and standards are applicable for your project.

Jesse

4/19/2024 08:23:16 am

I would ask your AHJ. NFPA has a couple different ways to determine fire flow, but so does IBC. If you're AHJ is operating under IBC, that may apply. Using IBC I get 1,500-gpm for a non-sprinklered IIB building for 180,000 gallons. In calculating tank size, you can factor in refill rate

And putting in a plug for the Meyer Fire Tool Kit here. We use it almost everyday!

Mike Morey

4/19/2024 08:24:49 am

Are you sure 1142 is the correct standard to determine fireflow for the project? Typically most places use IFC appendix B in my experience. If it's a non-residential structure you'd likely be at 1000gpmx120min with a full 13 system, but residential can be as low as 500 gpm for 30 minutes when equipped with a 13r sprinkler system, or the demand x duration of the sprinkler system whichever is greater.

Wright

4/23/2024 02:08:48 pm

This is NFPA 1142. I need to know if NFPA 1142 requires a 2 hour fire flow and where to find it. So far the code just states this is how much water is needed. I think for a commercial building more than 10,000 gallons is required. 10,000 divided by 500 gpm is only 20 minutes.

4/19/2024 08:44:07 am

NFPA 1142 is for rural water supply only. If you are in an "NFPA state", and there is no municipal water available, hydrant system fire flow requirements defer to NFPA 1142. You will use the calculations in NFPA 1142:4 to determine the total minimum volume required.

NFPA 1:13.5.2 Where no adequate and reliable water supply exists for firefighting purposes, the requirements of NFPA 1142 shall apply.

NFPA 1142:8.3.3* All dry hydrant systems shall be designed and constructed to provide a minimum flow of 1000 gpm (3800 L/min) at draft.

Salvatore Izzo link

4/19/2024 08:54:24 am

It needs to be clarified to which standard (purpose) the water supply storage requirement is being applied to. NFPA 1142 is applicable to "establish the minimum water supplies necessary for structural firefighting purposes in those areas where it has been determined that there is no water or inadequate water for firefighting." In these areas, it is highly likely that the water supply will be provided by FD hauled water operations. NFPA 13 requires the water supply to meet the duration requirements of the sprinkler system design and hose stream requirements only.

The ISO Fire Suppression Rating Schedule (FSRS) requires a minimum water supply for firefighting to be a water system capable of delivering 250 gpm + for a period of 2 hours plus consumption at the maximum daily rate at a fire location, or a FD supply capable of delivering 250 gpm + for a period of 2 hours at a fire location beginning within 5 minutes of arrival of the first-due engine. This equates to a minimum water supply capacity of 30,000 gallons (250 gom x 120 min.) This minimum water supply requirement and the calculated Needed Fire Flow based on the ISO formula, are used for the purposes of developing a Public Protection Classification (PPC) for insurance rating purposes. The minimum required storage capacity to be creditable for insurance rating purposes for FD response is 30,000 gallons (250 gpm for 2 hours).

The ISO Needed Fire Flow formula is different than that used in NFPA 1 for developing required fire flows. The ISO formula is more comprehensive as it considers more variables in its calculation and thus, will develop slightly higher fire flow requirements.

Therefore, the sizing of the storage tank needs to take these considerations into account.

Casey Milhorn

4/19/2024 09:25:10 am

I am no expert on fire flow demand to be clear. But from my experience typically private water storage tanks aren't required to meet fire flow demand. Even when dealing with a subpar rural water supply, many times the AHJ overlooks this. There would be many small country churches in our area with huge water tanks if this got enforced as code is written. Again, no expert but this has been my experience.

Salvatore Izzo

4/19/2024 09:37:55 am

Casey,

The minimum size of a storage tank would depend on what the purpose of the storage tank is being used for. If it is a water supply for a fire pump to meet the demand and duration requirements for a fire sprinkler system, then yes, it would be sized per NFPA 13 and does not have to include capacity for fire flow requirements for firefighting purposes. However, for insurance rating consideration, if the storage tank is solely being used as a water supply source for FD suppresion operations only, then for it to be creditable for the building under consideration, it needs to be located within 1000 ft of the building and have a minimum storage capacity of 30,000 gallons. It would also be considered a creditable water supply source for hauled water operations in the general area.

Jack G

4/19/2024 04:21:02 pm

I love fire protection But:
The cost of a code fire system would far exceed the cost of the building.
Tank, pump, diesel enclosure , proper insulation or buried water tank, 400 k. Building 300 k.
If in a ‘ Cal- Fire- wilderness area, the site should have available water for the fire department per 1142.
Response time of the fire department?
AHJ ma allow the tank and pump sized per the response time.
If so,
1. Full fire alarm system.
2. Qr heads with reduced area of operation.
3. Pump and tank sized per the density, I.e. if oh2, 1125 sq ft,
About 250 (vertical pump, buried tank with sump, if 30 minute response 7500 gallons x 1.05)
4 . Pumper - fdc- at street for the pumper/ tank fire truck.
Like I supposed above— the owner may not want a fire sprinkler system.

Jim

4/25/2024 03:12:43 pm

It is all up to the ADJ. He or she can increase or reduce the required fire flows. See the Codes.

IFC Appendix B says:
The provisions contained in this appendix are not mandatory unless specifically referenced in the adopting ordinance or legislation of the jurisdiction.
User note:
About this appendix: Appendix B provides a tool for the use of jurisdictions in establishing a policy for determining fire-flow requirements in accordance with Section 507.3. The determination of required fire flow is not an exact science, but having some level of information provides a consistent way of choosing the appropriate fire flow for buildings throughout a jurisdiction. The primary tool used in this appendix is a table that presents fire flow based on construction type and building area based on the correlation of the Insurance Services Office (ISO) method and the construction types used in the International Building Code®.

Q. ALSO.
Can someone let me know where I can access the International Wildland-Urban Interface Code?
That is another code that may provide guidance.

IF buildings are sprinklered it does recommend flows
25% of the value in Table B105.1(2)a, (with minimum flows) for the same durations.

JIM

4/25/2024 03:13:49 pm

AHJ

Mesbah Redouane

4/28/2024 06:19:37 am

I AM AGREE AHJ

Fritz Descovich

4/29/2024 09:16:03 am

Just throwing in some thoughts. I and the sprinkler contracting company where I work have been doing system designs for multi-level office and residential buildings in Northern CA for the past 40+ years.

Many of the systems for these types of buildings need fire pumps. And for high-rise buildings, sprinkler systems need the secondary water supply in seismic zone locations per the CBC and CFC which are based upon the IBC and IFC model codes.

We also have a few clients that are FM Global insured.

The sizing or the minimum capacity required for the (fire water) storage tank is one topic that gets most of the attention. And meeting all of the required codes and standards, including any additional requirements by the local AHJs must be addressed. And sometimes the property owner's insurance company requirements must also be added to the mix.

If ever there was a topic that would benefit from a MeyerFire Cheatsheet, this topic certainly qualifies.

For all water-based fire protection sprinkler, standpipe and fire pump systems, the CBC/IBC and CFC/IFC provide code sections for each system as well as chapters that adopt the applicable NFPA 13, 14 and 20 standards.

And each of these standards includes criteria for a fire water storage tank to be used as the sole/primary water supply for each system. In this case NFPA 22 must also be used for the design of such tanks for private fire protection.

The CBC/IBC and CFC/IFC also has a section whereby an on-site secondary water supply is required for sprinkler systems in seismic zones in high-rise buildings.

Over the years we have come to understand that sizing a fire water storage tank requires understanding all of the requirements outlined above.

And to make sure to separate what criteria comes from building and fire codes, NFPA standards, local AHJ requirements and insurance companies/underwriters. All this criteria may not be applicable in all cases or for all projects.

Calculations for Water Storage Tank in NFPA 1142?

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