1. ## Determining GPMs

I was just curious as to how everyone here determines gallons-per-minute needed for a structure. I've several different ways to calculate it, but I was wondering which is the most common method. Thanks in advance for your input.

2. ## From James P. Smith's "Strategic and Tactical Considerations on the Fireground"...

Fire flow = Length x width divided by 3 x 1 for a fully involved floor. For each other fully involved floor, double it.

Figure in 25% for each exposure.

3. ## NFA Fire Flow Formula

As Captain Gonzo points out, the NFA Fire Flow Formula: (LxW)/3 is a simple way to estimate required fire flow for direct attack. However, it is often overlooked that this is the total flow capability required for both attack and backup lines, not the tactical rate of flow necessary to quickly achieve fire control. Half the flow determined by the formula is an effective flow rate for attack lines (the remaining flow should be available for backup lines).

Cheers,

4. So let's say I have a mobile home. 10 x 80/3 is 266.7 GPM Seems like that isn't enough. Doesn't one also need to consider the fire load?

5. Originally Posted by HotTrotter
So let's say I have a mobile home. 10 x 80/3 is 266.7 GPM Seems like that isn't enough. Doesn't one also need to consider the fire load?
266 gpm doesn't sound like enough for a mobile home? GPM means just that "per minute"! And what kind of trailer parks do you have with 80 ft long McMobile Homes?

I was just curious as to how everyone here determines gallons-per-minute needed for a structure. I've several different ways to calculate it, but I was wondering which is the most common method. Thanks in advance for your input.
People have mentioned the National Fire Academy formula for figuring fire flow. Thats all fine a dandy, but I have never used that, or any other formula in anything other than classroom settings.

The formula I use is Experience + Common Sense = desired line.

Its not rocket science boys.

7. Originally Posted by RFDACM02
266 gpm doesn't sound like enough for a mobile home? GPM means just that "per minute"! And what kind of trailer parks do you have with 80 ft long McMobile Homes?
You are of coarse correct, but the NFA fire flow formula is supposed to tell you what is requires to put the fire out in one, single minute. So according to the formula 266 gallon s is all that would be required "small print" if applied correctly.

Apply more faster, it will go out sooner. Apply less or take longer to do it, it will burn longer.

8. ## Hmmmmm...............

Originally Posted by RFDACM02
266 gpm doesn't sound like enough for a mobile home? GPM means just that "per minute"! And what kind of trailer parks do you have with 80 ft long McMobile Homes?
There are some Mcmansion Trailers and Trailer Parks out there. Actually, they're called "Manufactured Homes" and they are installed on a foundation, rather than just "Takin' the wheels off". My late Daughter's mother in law has one that measures 21x60 and inside you can't tell the difference between it and a "Stick Built" rancher. she has more Square feet that many Townhouse developments offer. This home also sets on a 1/8th acre lot (50x100). Trailers ain't what they used to be. To get back to GPM, 250 would seem a good estimate for a conventional "Single-wide" Trailer 60 feet long. I've tackled a Single wide with heavy fire in about half of it, with a 1.5 flowing about 125 gpm, and got a real quick knockdown.

9. I was wondering if anyone has used the Iowa ROF?

10. Originally Posted by MemphisE34a
The formula I use is Experience + Common Sense = desired line.
What formula do you use for pre-planning?

11. Originally Posted by hwoods
There are some Mcmansion Trailers and Trailer Parks out there.

I had always heard the NFA number of (length x width)/3 * height for full involvement. I hadn't heard this number assumed a single minute of flow.

I do know that I've rarely used this in the field. I don't know about everyone else but at 4am I'm lucky if I can get my left leg in left hole and the right leg in the right hole let alone do multi-ply-ca-tion.

12. Originally Posted by RFDACM02
266 gpm doesn't sound like enough for a mobile home? GPM means just that "per minute"! And what kind of trailer parks do you have with 80 ft long McMobile Homes?
So go shorter, that is even less. And as a rough estimate a 1 3/4" line takes about 125 GPM. Think about that for a minute.

13. Originally Posted by voyager9
I had always heard the NFA number of (length x width)/3 * height for full involvement. I hadn't heard this number assumed a single minute of flow.
I don't recall that either. My recollection is that the NFA formula is for pre-planning and that the minimal water supply should be at least 10 minutes at the calculated flow.

Unfortunately, any of my old NFA texts that would be likely to mention it were lost in the Great Basement Flood of '06...

Originally Posted by voyager9
... but at 4am ...
Not a problem. It's more a pre-planning calculation than a fireground calculation. If you did the pre-plan and set up your responses by it, then you'll have all the resources you need at the fire...

14. And as a rough estimate a 1 3/4" line takes about 125 GPM.
Surprisingly, you are under pumping your lines. I'd shoot for a 150gpm minimum. And if you care, we run our 1 3/4" lines at ~175gpm.

What formula do you use for pre-planning?
Pre-planning = classroom setting. And, at least here, most fires do not occur in target hazards that are pre-planned anyway.

As far as the minute of flow goes, that was told to me by an NFA instructor during strategy and tactics classes. I will see if I can get in touch with him to confirm that. I will let everyone know what he says.

16. I was being slightly "tongue in cheek" about the McTrailer's as I've yet to see a mobile home that was 80 ft. and mobile. But Harve does bring up the point that many manufatured homes come in multiple peices on trailers and can be quite large. No doubt that you can use a 2.5" on a mobile home and it should go out quicker.

I've found mobile homes to be worse than "normal" stick built due to the 2x3 studs the melting aluminum siding, faux wood veneer wall coverings, and the fact that the overall cubic footage is quite small allow heat to travel quite rapidly from one end to the other. Unlike a house the small room and contents fire is usually a full blown job on arrival as the hollow core doors don't hold any fire back for long and the fire spreads rapidly. An 1 3/4" line can fight a decent amount of fire room to room, but when it's one wide open floor? Another story. And as Bones said, we shoot for 150 to 180 gpm on our 1.75" lines.

I've not heard of the NFA formula being used to snuff the fire in one minute, yet more of a guide as to determining the need for water supply additional companies to operate hoselines. There is a huge difference between 1500 sq. ft. of compartmented residential space and a 1500 sq.ft. wide open commercial space when in comes to fighting a fire.

17. Originally Posted by Bones42
Surprisingly, you are under pumping your lines. I'd shoot for a 150gpm minimum. And if you care, we run our 1 3/4" lines at ~175gpm.
Sorry, went back and checked the thread I started on that topic. The answers ranged from 100 to 200 GPM. I'm guessing 150 is a better number. Which takes me back to the 266 number I derived earlier for a 10 x 80 trailer. That formula doesn't give you nearly enough water.

18. Originally Posted by MemphisE34a
The formula I use is Experience + Common Sense = desired line.
Bingo.

Thumb up, more, thumb down, too much.

19. ## Experience

The observations about the NFA formula being applied to preplanning is right on track. I have not found anyone yet who uses this formula on the fireground. However, developing a sense of what flow rate is adequate on the basis of experience is tough when most firefighters don't go to a large number of fires. This formula was developed by distilling the experience of quite a few highly experienced fire officers. Using it in the training environment can help develop a sense of what will be adequate on the fireground.

In field tests that we ran using an acquired structure and applying the NFA formula we found that an application of 50% of the required flow rate (saving half for the backup line) achieved knockdown in 30 to 45 seconds of direct attack.

Learning about required fire flow simply from experience rather than in training (think about this as learning from the experience of others) may result lots of parking lots. Good judgment results from experience. Experience results from bad judgment. The guys who developed the NFA fire flow formula burned down lots of buildings (by their own admission) learning about fire flow. Take what they learned and integrate this with your own experience!

Cheers,

20. Originally Posted by HotTrotter
Which takes me back to the 266 number I derived earlier for a 10 x 80 trailer. That formula doesn't give you nearly enough water.
Again, I think someone else here may have been mistaken. It's gallons per minute. Meaning the rate of flow not the total amount of water needed. If you still think 266 gpm is not nearly enough I think the TSA is looking for help.

21. Originally Posted by RFDACM02
Again, I think someone else here may have been mistaken. It's gallons per minute. Meaning the rate of flow not the total amount of water needed. If you still think 266 gpm is not nearly enough I think the TSA is looking for help.
Yea, I was thinking the same thing. I can't imagine "wetting" more than one 1.75 line.

I might pull another, but it would probably be dry. Unless the thing was fully involved and then who cares what the flow says, just open up whatever you got handy they burn up pretty quick at that point.

22. Originally Posted by RFDACM02
Again, I think someone else here may have been mistaken. It's gallons per minute. Meaning the rate of flow not the total amount of water needed. If you still think 266 gpm is not nearly enough I think the TSA is looking for help.
A single 1 3/4 will use about 150 to 175 GPM (thanks Bones). On your typical trailer fire we will 2, 3, or 4 lines. 2 lines will require 300 GPM. It should be noted that the calculation of 266 GPM is wrong, the correct number is 533. And this makes sense. I believe the ISO states you need 1000 gpm for a two story residential.

23. Ohio fire flow formula

'nuff gpm till it becomes dark.....

24. Originally Posted by HotTrotter
A single 1 3/4 will use about 150 to 175 GPM (thanks Bones). On your typical trailer fire we will 2, 3, or 4 lines. 2 lines will require 300 GPM. It should be noted that the calculation of 266 GPM is wrong, the correct number is 533. And this makes sense. I believe the ISO states you need 1000 gpm for a two story residential.
Your trailers must be a lot bigger then ours.. I can't see having more then 1 line in service for a typical 15x80 trailer. Maybe having a 2nd on the ground as backup. Certainly can't see the need for 500+ gpm.

25. Originally Posted by voyager9
I can't see having more then 1 line in service ...
And you'd probably be right although I'd tend to use two lines just to apply water in two locations because the fire is so "long". IMHO, 266 gpm for a fully involved trailer already borders on excessive.

Claiming that a trailer requires over 500 gpm and needs 4 lines only serves to demonstrate, once again, that Trotts isn't a firefighter...

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