Which Hydrants Count for Available Fire Flow?

5/20/2025

When calculating a risk score on an occupancy, a question asked is "Is fire flow available?"

My question is this: which hydrants does everyone count towards being available?

IFC 507 states that if a hydrant is not within 400-600 feet, then an on-site hydrant is required. Some of my colleagues interpret that as "Anything outside of that radius does not count as available for Fire Flow."

We carry 1000 ft of supply hose, so some say all hydrants within a 1000 ft radius contribute. However, that is really to dress a single hydrant up to 1000 ft away, not to dress multiple hydrants within 1000 ft. Ultimately, we get to decide in the end, but we want to make an informed decision and document our methods for consistency.

This question is not about calculating the needed flow and assumes the water department can provide accurate flow data for each barrel.

Any insight from the pros and other AHJ's would be fantastic. Thank you for your time.

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7 Comments

5/20/2025 08:10:13 am

We include hydrants within 1,000 feet per NFPA 1. The reference in the 2024 edition of NFPA 1 is Table 18.5.4.3.

J.H.

5/20/2025 08:24:02 am

The idea is that any single hydrant cannot be credited with delivering more fire flow than any one engine can pump. NFPA 1 sets the cap at 1500 gpm (or more, if the engine can handle more), but it will be less if the engine can't pump at 1500 gpm. For example, some of our apparatus can only pump 1250 gpm, so that could be taken into account when determining actual available fire flow for a given site.

Below is the guidance per NFPA 1, part of our JD's adopted code. IFC may have similar provisions, or they may be part of your land development code. The farther away the hydrant (see values in NFPA 1:Table 18.5.4.3), the less fire flow attributed to it.

NFPA 1(2021)

18.5.2 Detached One- and Two-Family Dwellings. Fire hydrants shall be provided for detached one- and two-family dwellings in accordance with both of the following:
(1) The maximum distance to a fire hydrant from the closest
point on the building shall not exceed 600ft (183m) .
(2) The maximum distance between fire hydrants shall not
exceed 800ft (244m).

18.5.3 Buildings Other than Detached One- and Two-Family
Dwellings. Fire hydrants shall be provided for buildings other
than detached one- and two-family dwellings in accordance with
both of the following:
(1) The maximum distance to a fire hydrant from the closest
point on the building shall not exceed 400ft (122 m).
(2) The maximum distance between fire hydrants shall not
exceed 500ft (152m).
18.5.4 Minimum Number of Fire Hydrants for Fire Flow.
18.5.4.1 The minimum number of fire hydrants needed to deliver
the required fire flow for new buildings in accordance with Section 18.4 shall be determined in accordance with Section 18.5.4.

18.5.4.2 The aggregate fire flow capacity of all fire hydrants
within 1000 ft (305m) of the building, measured in accordance
with 18.5.1.4 and 18.5.1.5, shall be not less than the required fire flow determined in accordance with Section 18.4.

18.5.4.3* The maximum fire flow capacity for which a fire hydrant shall be credited shall be as specified by Table 18.5.4.3. Capacities exceeding the values specified in Table 18.5.4.3 shall be permitted when local fire department operations have the ability to accommodate such values as determined by the fire department.

CHRIS BOYD

5/20/2025 07:03:34 pm

While its true most pumps in a ics type 1/2 engines are rated at 1500gpm, they are rated at draft. If supplied with additional volume they are capable of pumping more than they are rated for.

Robert Morgan

5/20/2025 09:27:35 am

All hydrants within 1,000' (excluding private hydrants on adjacent properties) can count. As you get further from the building the amount of GPM you can count goes down, so you cannot simply add all the hydrant flows together at max flow.

Casey Milhorn

5/20/2025 09:33:58 am

This topic fascinates me, especially on how many AHJs interpret and/or enforce it in a variety of ways. Actual fire flow capability of fire hydrants, especially "private" hydrants, can depend on the sizing and arrangement of the public or private fire line. When the fire flow demand is ran through a backflow preventer, fire meter, fire pump assembly, etc., things can start to get complicated. One of the major issues I see is that the backflow is selected based on fire sprinkler demand and/or fire pump capacity, but the fire flow demand is ignored. Many times you end up with a backflow feeding private hydrants and that backflow is not listed for the amount of fire flow demand (basically it's undersized). Another issue is when a fire pump is feeding private hydrants, you will see that fire pump and/or bypass sizing may not be adequate enough to provide the X amount of fire flow demand through it. At least by way of it's listed performance. I've seen many AHJs and design professionals base fire flow demand on the public hydrants only and are happy as long as they can meet the fire flow demand. I've also seen AHJs completely ignore the fire flow demand for rural churches, schools, etc. Basically, if they enforced the fire flow demand it would make the project untenable due to cost of water storage tanks and/or city water improvements.

sean

5/20/2025 11:58:43 am

unless you have nfpa 1 adopted then I would not use anything from that.

I would say if you can't count the hydrant for coverage then you can't include it in fire flow.

Chad

5/20/2025 12:57:03 pm

To address what you said specifically- if you carry a 1000' you cannot use a 1000' radius. rarely would a 1000' be possible in a straight line. 600' is a better conservative measure and reflected in the IFC when

Since IFC allows you to choose the fire flow method, I would use the references from NFPA 1 shown here. They leave it open to interpretation so small towns can just do nothing about it to allow for cheaper development (IMO). Although sometimes there is nothing you can do and its unrealistic to just throw money at the problem

Soapbox- On site/private hydrants are a slippery slope if you do not have progressive enforcement of NFPA 25, ensuring annual maintaince is performed and a 5 year flow test. The guys on the trucks will learn to mistrust them once you get a failure. same with public ones but less so if they are better maintained.

Which Hydrants Count for Available Fire Flow?

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