New Feature: Estimated Fire Flow
By Dan Curran on March 15, 2017
The Estimated Fire Flow Formula was developed by NFA in the 1980's in order to estimate the flow rate in GPM required for confinement and extinguishment of a fire using an interior direct attack on a fire. This is not a scientifically proven formula, instead it was devised based on experience and observation.
The formula is:
An example would be a fire in a 30' by 40' single story structure with 25% involvement. The required flow would be 30 x 40 = 1200. 1200 divided by 3 = 400. 25% of 400 is 100 gpm required flow. Each additional story should be counted as a part of the square footage. A 30' by 40' two story structure would be 2400 square feet.
A fire in a one story 60' by 120' office building with 50% involvement is calculated exactly the same. 60 x 120 = 7200. 7200 divided by 3 is 2400. 50% of 2400 is 1200 gpm.
In the first example the 100 gpm requirement could be handled with a single inch and three quart attack line. The second example would require at least 3 alarms based on a rough estimate of each alarm being able to flow 400 gpm.
The formula changes when there are exterior exposures:
For this formula each additional story Lets re-use of first example of a fire in a 30' by 40' structure with 25% involvement and add an exposure. 30 x 40 = 1200. 1200 divided by 3 is 400. For the exposure we take 25% of 400 which is 100. We add 400 plus 100 to get 500. Then 25% of 500 is 125 gpm.
There are a number of limitations to be aware of when utilizing this formula. This formula loses effectiveness on fires with greater than 50% involvement or when required fire flow is greater than 1000 gpm. The formula is designed for use with an interior direct attack with proper ventilation. It does not work for defensive operations.
There are many other factors which can effect the flow that is required, including: heat release rate of fuel, height of ceilings, building construction, HVAC systems and ventilation. This formula is a good starting point for first arriving officer but ever changing conditions on the fire ground will ultimately dictate the tactics and resources that are required.
Estimated Fire Flow in IncidentSmart
IncidentSmart has implemented the Estimated Fire Flow as a part of the Pre-Incident Plan report. You will only need to enter the square footage of the structure and the number of exposures.
Once you have entered the square footage and the number of exposures you will see a table showing values for: 10% involvement, 25% involvement, 50% involvement and 100% involvement.
This post just scratches at the surface of the NFA estimated fire flow formula. For more information take a look at the following resources:
- Fire House Magazine Article: Calculating Fire Flow
- Fire Rescue Magazine Article: Simple Ways to Determine Your Fire Flow Requirements
If you have any questions or comments about this new feature please let us know!
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