Fire loads and GPM

[1potter1]

How do you figure GPM for fire loads.

[toutdoors]

Search this site for articles written by the late Andrew Fredericks. He wrote a two part article entitled "Little Drops of Water; 50 years later". I believe that is almost word for word the title. In it he talks about the work done at Iowa State and the Iowa Fire Flow Formula. I believe he may also mention the NFA rate of flow formula. To make your search easier type in "fire flow" or "attack lines" or "2 1/2 hose lines" also try "standpipe operations". I did some research on here a few years ago and found his articles.
For the Iowa Fire Flow Formula it is very simple though.
Length x Width x Height divided by 100 will give you the gpm needed for the fully involved area. So a 20 x 20 x 10 room or building would need 40 gpm to overcome the rate of heat release.
Some will say that this is not enough, some will say this formula still holds true and fast. The research is up to you.
Shoot me a message if you can not find the articles I have mentioned, and I will look them up in my hard copies, I still have them filed away from my research on standpipe operations I did a couple of years ago.

[slipperypete]

If I remember correctly ( and i may not ) the new formula is Length x Width divided by 3. So the above room would be 20 x 20 = 400 divided by 3 = 133 gpm. A slight increase from 40 gpm. If it was me i would rather have the 133... but that's just me.

[MemphisE34a]

If I remember correctly ( and i may not ) the new formula is Length x Width divided by 3. So the above room would be 20 x 20 = 400 divided by 3 = 133 gpm. A slight increase from 40 gpm. If it was me i would rather have the 133... but that's just me.

He gave you the Iowa formula. You came back with the NFA formula and stated your preference. If that is the case, what exactly was the purpose of this thread?

[slipperypete]

The OP wrote "How do you figure GPM for fire loads." and i answered. I am wondering what is the purpose of your reply?

[MemphisE34a]

The OP wrote "How do you figure GPM for fire loads." and i answered. I am wondering what is the purpose of your reply?

Yeah, my bad. I quoted the wrong guy! I knew what you were doing. My post was supposed to be directed to the original poster.

[toutdoors]

Slippery Pete, that was the formula I was trying to remember. Then again, at 2am, if the 1 3/4 ain't putting it out, stretch the big guy. Seriously though, thanks for reminding me pete, and I agree; I would rather have the 133 and only push water for 30 or so seconds versus getting run over using the 40 gpm. Of course we are talking theories too. lol

[DeputyChiefGonzo]

There's an easy way to figure it out that does not include mathematics at oh my God it's early hours...

big fire: big water

It's gpm vs. btu's.. it's not rocket science!

[slipperypete]

Yeah, my bad. I quoted the wrong guy! I knew what you were doing. My post was supposed to be directed to the original poster.

Thanks for the reply. I have been reading a lot of "unfriendly" posts lately and was like WTF?

[FyredUp]

There's an easy way to figure it out that does not include mathematics at oh my God it's early hours...

big fire: big water

It's gpm vs. btu's.. it's not rocket science!

The Chief is absolutely correct. Unfortunately this is one of those cases where a lack of experience OR laziness gets guys in trouble. Sadly the 1 3/4 inch hose is thought by many to be the answer to every handline need. Sorry, NO it isn't. (Those of us that are in the know will tell you 2 inch hose is the anser to every handline need, but that is another topic entirely! ) Big fire does indeed need big water and either 2 inch or 2 1/2 inch hose delivers it.

[DeputyChiefGonzo]

Originally Posted by CaptainGonzo

There's an easy way to figure it out that does not include mathematics at oh my God it's early hours...

big fire: big water

It's gpm vs. btu's.. it's not rocket science!

posted by FyredUp

The Chief is absolutely correct. Unfortunately this is one of those cases where a lack of experience OR laziness gets guys in trouble. Sadly the 1 3/4 inch hose is thought by many to be the answer to every handline need. Sorry, NO it isn't. (Those of us that are in the know will tell you 2 inch hose is the anser to every handline need, but that is another topic entirely! ) Big fire does indeed need big water and either 2 inch or 2 1/2 inch hose delivers it.

Even a stopped clock is right twice a day...


Another thing to keep in mind is that the formulas are based on area and not actual fire loads. There's a big difference between a typical 2.5 story wood frame and a 2.5 story wood frame with a collyer's mansion condition, or a 10,000 square foot warehouse containing hazmats or clothing.

It is important to know the buildings in your first due districts and the loads that can be encountered within.

[Edward Hartin]

Units of Measure

I agree with much of what has been said in concept. However, a couple of points of clarification.

Btu is an amount (i.e. the amount of energy required to raise a pound of water 1 degree F). Gallons per minute is a rate (amount per unit of time). Gallons overcome Btu, gpm overcome Btu/minute.

Heat release rate is the key in understanding the concept of required fire flow. The higher the heat release rate (big fire) the higher the flow rate (big water).

Fire Flow Estimation

The Iowa Formula (LxWxH)/100 determines the flow rate required for an indirect attack (extinguishment from outside the compartment by producing a large volume of steam to cool and displace oxygen).

The NFA Formula (LxW/3)x% Involvement determines the flow rate for attack and backup lines when making an offensive, interior direct attack (and assumes an 8'-10' ceiling height). This formula is also becomes more inaccurate for levels of involvement over 50% and is not intended for flows in excess of 1000 gpm.

It is interesting to note that the NFA formula does not address differences in heat release rate. However, it is conservative and generally provides a flow rate that is more than adequate for the task at hand.

I have never met anyone who actually does the math at 2 am. One simple way to visualize this (based on the NFA formula) is to figure that 900 square feet (30' x 30') of involved area requires a flow rate of 150 gpm (with a backup line having the same or higher flow).

More Information

My colleague Paul Grimwood has collected a substantial amount of information on the topic of fire flow which is available at http://www.fire-flows.com/.

[ffmedcbk1]

Units of Measure

I have never met anyone who actually does the math at 2 am. One simple way to visualize this (based on the NFA formula) is to figure that 900 square feet (30' x 30') of involved area requires a flow rate of 150 gpm (with a backup line having the same or higher flow).

I agree with you that it is unlikely to find someone who "does the math" at 2 am. I would venture to say that the good EC officer and crew have done it a 2 pm many times in drills and post fire reviews and therefore it is 2nd nature to them.

Our rule of thumb, interior on a residential 1 - 3 Room + Contents 1.75", interior for a residential full floor involvement or commercial = 2 1/2", everything else is 2.5" or bigger from the outside.

The basis of course is Saveable Lives and saveable property (with Risk vs. Benefit).

Our Flows are 185 and 330 gpm for those lines. We have a great amount of commercial areas and knowing the material compositions of the products today lends us to needing the greater flows. (yes, the reaction forces from the nozzles are larger but with good techinque and proper fitness they are overcome very easily.)

I am not aware of a steadfast computation for burning materials and their involvement, but DAVE DODSON's Class "THE ART OF READING SMOKE" dives into materials and release of energy during decompsition and is a great class to attend. For me, it was very eye opening after the full day event as regards to how to look and predict the fire. We all do the methods in the class but he gives discipline, scientific structure, and credance to that thought process. It is well worth your time.

I've used the rule that if the line and tactics being employed don't work withing 30 seconds of being in place (noticable change in conditions) reevaluate and reemployee. (IE: smoke not lifting enough = more ventilation, hose line flowing does not changing interior or exterior fire/smoke conditions = more lines or defensive)