Chapter 8 – Calculating Fire Flow

There are different calculations available to formulate the rate of flow required at a structure fire.
This program will utilize the National Fire Academy Formula (NFA) formula.

[(Length x Width)÷3 ] x percentage of involvement = GPM Required

Given the difficulty of accurately calculating the square footage, a strong recommendation is to include estimating size during training operations and including building sizes on pre-incident planning.


A 40’ x 30’ building is ¼ involved


Equation: [(40’ x 30’) ÷ 3] x .25= 100 (GPM)

The fire flow of 100 GPM is easily attainable by a single 1 ¾” handline set at 125 GPM. The Incident Commander will utilize their firefighters inside the structure to determine if there is enough water flowing for their attack. If firefighters report that the GPM is not a high enough flow rate, then the IC should consider the possibility that water is not being effectively applied to the burning material, the nozzle is set to an incorrect gallonage or a different attack strategy is required.


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Emergency Scene Management I - FIRE-1114 Copyright © by Justice Institute of British Columbia is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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