1. #1
    Firehouse.com Guest

    Question Fireground Formulas

    What equations do you tend to use the most, or should use more often, on the fire scene? (Please include the actual formula since there are multiple ways figure GPM, etc.)

    Hope I haven't made anybody dig out the ol NFSTA book.

    Kevin Sink
    Fair Grove Fire Dept.
    Thomasville, NC USA

    [This message has been edited by FGFD43 (edited 05-14-2001).]

  2. #2
    Firehouse.com Guest


    I have relied on two basic formulas. Friction loss and Pump discharge pressure. I have rarely had to use some of the more exotic formulas available. Here they are--
    FL= C Q2 L. c=given coeficient for your hose size-- Q= quantity of water flowing squared (GPM ) L= hose length.
    The other and ( I think ) the most important, PDP= FL+NP----friction loss formula added to your nozzle pressure--50psi for smooth bore, 100psi for fog.
    Stay safe----

  3. #3
    Jolly Roger
    Firehouse.com Guest


    I agree with Smokeetr4, and would add on that somewhat.

    For needed fire flow, I use the N.F.A. formula: L x W / 3 = GPM. The Iowa Formula is ok, but I find it to be unrealistic. I find that the NFA formula makes it easier to do a "jump seat fast figuring" as to how much flow will be needed, and what line I should strech.

    Hope it helps.

    Let us never, ever forget those of us that have gone before us in the line of duty. Because those brave souls have given all, it is up to us to always keep them alive in our hearts and our memories.


  4. #4
    Firehouse.com Guest


    Rules of thumbs

    1 3/4" 1 gpm per psi engine pressure

    FL for 4" hose 2 psi per 100 gpm flowing per 100 feet

    FL for 5" hose 1 psi per 100 gpm flowing per 100 feet

    FL for 7 1/4" hose 1 psi per 1000 gpm flowing per 100 feet

  5. #5
    Firehouse.com Guest

    Thumbs up

    We have adopted NYC's 180gpm rule for our interior firefighting. This eliminates the need to use dimension calculations for square footage when determining GPM. It works since the square footage calcs tend to end up light in the GPM's. This way when figuring PDP we already know Q2 (GPM) is 180. Quickens the process in the chaos. Stay safe..

  6. #6
    Firehouse.com Guest


    formulas don't belong on the fireground. In the heat of the battle it's to hard calculate. There are easier ways to do things.

  7. #7
    Plug Ugly
    Firehouse.com Guest


    I like rule of thumbs like LHS* pointed out and I also agree with you BIG PAULIE!
    The best fireground formula = K.I.S.S.

  8. #8
    Firehouse.com Guest


    I agree and disagree. In most cases the rigs hosebed configurations will remain the same. The chauffeur knows what pressures he or she will need based on prior use. So, yes, I agree that the chauffeur should not have to use formulas on the fire scene on a regular basis. They should however have a working knowledge of them in order to adapt to those unforeseen circumstances that do happen. Knowledge is power and flexibility is necessity! Stay safe--

  9. #9
    Firehouse.com Guest


    smokeetr4 I agree but what about the unknowns such as gpm and amount of hose. preconects are easy, its the muliple line fires that involve different types evolutions that can be tough using formulas.Example: A hose pack being used in a school fire that is several hundred feet from the engine. The pack is brought in followed by supply hose to make the conection. The amount of supply hose is unknown. Formulas will not work here.

  10. #10
    Firehouse.com Guest


    Paulie, I have had to deal with similar scenarios like the one you stated. Using multiple lines and different size hose does present a challenge but like I said in a previous post, having a good working knowledge of the basic flow formulas saved my butt.These are rare examples though and involved high rise applications and long stretches. the flow calculations are nor rocket science. They are repetitive and for the most part can be done in your head.

    Bob--stay safe--

  11. #11
    Firehouse.com Guest


    I vote for pretested hose charts.

    Test your hose to determine FL. In most cases the published charts are OK but testing will show you how close your equipment is. I'm also a fan of labeling the pump panel for the preconnects.

  12. #12
    Firehouse.com Guest


    There is only one equation you have to remember:

    The tips of your fingers are even numbers (2,4,6,8, and 10) and the knuckles are odd numbers (3,5,7,9, and 11). I haven't been working pumps for a while so I forgot how it works. I will update as soon as I remember it.

  13. #13
    Firehouse.com Guest


    There are a lot of good ideas on this post. Most of the rules of thumbs are just extimates and aren't always that accurate. We have a chart in our engines that lets the chauffer know what engine pressure is required for each give gpm on all our preconnected hose lines, including our 3" to gate valve apartment leader line. We also leave the manufactures cheater cards in the pump panel for extended operations or when flow is critical, and the operator needs to make adjustments. More often than not though the preconnects do most of the work.

    For our pre plans we also use the NFA flow equation (LxW)/3= gpm. On our pre plans we give four numbers, 1/4, 1/2, 3/4, and total involvement.

    The best place for the formulas is back at the station, when you have time to work them out properly. Either carry the cards or stick to some of the quick estimated rules of thumbs to get you started on the fire ground.

  14. #14
    Junior Member

    Join Date
    Jan 1999
    Howell, Mi. U.S.A.


    Kevin-contrary to what you said I hope people are still pulling out the good ol' IFSTA manual, we still need it every now and then! Although I believe hands on is the best teacher. Just remember 50, 80, 100 psi rule of thumb and we'll figure it out-the officer inside should let you know up or down on psi, if needed.
    "Stay Safe, Stay Low and lets Rock-n-Roll"

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