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  1. #1
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    Talking Please help....fire flow formula

    What does the "3" represent in NFAs fire flow formula LXW/3 @ 100%? Thanks!


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    Forum Member MemphisE34a's Avatar
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    In 1966, Warren Y. Kimball, NFPA Fire Service Department Manager theorized that it took 3 gpm to extinguish every 100 cubic feet of space involved in fire.

    PS - Google is your friend:

    From LA SOP's:

    "The Kimball rule of thumb

    In 1966, the National Fire Protection Association published Fire Attack 1: Command Decisions and Company Operations by Warren Y. Kimball, the NFPA Fire Service Department manager. Like Laymanís book a decade earlier, Kimballís book serves a wide fire service audience. Kimball provided a rough rule of thumb in estimating required fire flow at 3 gallons per minute per 100 cubic feet. The volume of the building is determined by length multiplied by width multiplied by height.

    Using this formula, a three story building (ten feet per floor) that is 50í wide and 100í long would be a 150,000 cubic foot building. Multiplying 150,000 square feet by .03 (3 gpm for each 100 cubic feet) means that this building requires 4500 gallons per minute. That is the Los Angeles City threshold for a Category B dispatch of not less than six fire companies with not less than two truck companies. Kimballís calculations were for the entire building, a consideration reinforced by Francis Brannigan when evaluating multiple family dwellings and other Type V buildings.. Brannigan is emphatic that the company officer must assume the entire building is on fire when one room is burning."
    Last edited by MemphisE34a; 01-02-2009 at 05:43 PM.
    Robert Kramer
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    Management is making sure things are done right. Leadership is doing the right thing. The fire service needs alot more leaders and a lot less managers.

    "Everyone goes home" is the mantra for the pussification of the modern, American fire service.


    Comments made are my own. They do not represent the official position or opinion of the Fire Department or the City for which I am employed. In fact, they are normally exactly the opposite.

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    I'm not disputing the Kimball mehtod but I don't think its the same "3" as in the NFA formula. The NFA formula used on the same building Memphis used in the example in the NFA would be:

    50x100=5000 / 3 =1666.66 gpm for 100% involvement of one floor.

    Square feet vs. cubic feet. The NFA formula by most accounts is supposed to be "doable" at 0300 hrs with rough numbers. Trying to find cubic footage at the time of the incident is difficult. The Kimaball method (cubic footage) makes more sense to me for preplanning and determining box responses.

    Of course the NFA formula adds for exposures which may be another floor or one close by (25'?). Add 25% for each exposure.

  4. #4
    Forum Member MemphisE34a's Avatar
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    Quote Originally Posted by RFDACM02 View Post
    I'm not disputing the Kimball mehtod but I don't think its the same "3" as in the NFA formula. The NFA formula used on the same building Memphis used in the example in the NFA would be:

    50x100=5000 / 3 =1666.66 gpm for 100% involvement of one floor.

    Square feet vs. cubic feet. The NFA formula by most accounts is supposed to be "doable" at 0300 hrs with rough numbers. Trying to find cubic footage at the time of the incident is difficult. The Kimaball method (cubic footage) makes more sense to me for preplanning and determining box responses.

    Of course the NFA formula adds for exposures which may be another floor or one close by (25'?). Add 25% for each exposure.
    Aaahhhh. I stand corrected. I got ahead of myself and was in a hurry to get out the door and go get the kids some dinner earlier. I mistakingly put the Kimball rule and the NFA fire flow theories together. Here is the complete portion of the article partially quoted above. It explains the variances in the Kimball method, the Iowa fire flow formula, and the NFA fire flow formula:

    Determining the fire flow requirement

    The Kimball rule of thumb

    In 1966, the National Fire Protection Association published Fire Attack 1: Command Decisions and Company Operations by Warren Y. Kimball, the NFPA Fire Service Department manager. Like Laymanís book a decade earlier, Kimballís book serves a wide fire service audience. Kimball provided a rough rule of thumb in estimating required fire flow at 3 gallons per minute per 100 cubic feet. The volume of the building is determined by length multiplied by width multiplied by height.

    Using this formula, a three story building (ten feet per floor) that is 50í wide and 100í long would be a 150,000 cubic foot building. Multiplying 150,000 square feet by .03 (3 gpm for each 100 cubic feet) means that this building requires 4500 gallons per minute. That is the Los Angeles City threshold for a Category B dispatch of not less than six fire companies with not less than two truck companies. Kimballís calculations were for the entire building, a consideration reinforced by Francis Brannigan when evaluating multiple family dwellings and other Type V buildings.. Brannigan is emphatic that the company officer must assume the entire building is on fire when one room is burning.

    Iowa State University Rate of Flow Formula

    The Iowa State University Rate-of-Flow Formula was developed to determine the fire flow needed to knock down a fully involved structure or compartment in a structure. The knockdown flow is determined by dividing the cubic size of the compartment or building by 100. Using Kimballís 150,000 cubic foot building, the Iowa Rate-of-Flow formula would require a thirty second flow of 1500 gallons per minute to achieve knockdown.

    National Fire Academy Fire Flow Formula

    The National Fire Academy Fire Flow Formula is used in the strategy and tactics classes. It is a more complex version of the Iowa Rate-of-Flow formula. It requires a three-part calculation:

    * For each floor, estimate the length and width of the building and divide by three. NFF = (Length x Width)/3 Using Kimballís example, one floor is 50 Ď by 100í. The equation will be (50 x 100)/3 or 1700 gpm for one floor. The answer is rounded to the nearest 100. If all three floors are fully involved, you will need 5000 gallons per minute.

    * Determine the percentage of fire involvement on the floor. If one fourth of the floor is involved, reduce the fire flow by 75%. NFF = [(Length x Width)/3] x % involvement.

    * Exposures come in two flavors, interior and exterior. For interior exposures, add 25% of your fire flow to each floor above the fire, not to exceed five floors. Using the Kimball example, letís assume the first floor is fully involved. That requires a 1700 gpm flow. The second floor exposure requires 25% of that flow, or 400 gpm. So does the third floor.

    The fire flow for the Kimball example, with the first floor fully involved,

    will be 1700 + 400 + 400 = 2500 gpm.

    o For exterior exposures, you will add 25% of the required fire flow for each side of a building that has another building exposed to the fire. In the Kimball example, there are exposed buildings on the B and D sides of the building. The original fire flow for the 50í by 100í by three story (30í) building was determined to by 1700 gpm if the first floor was fully involved. Each exposure will require 25% of that flow, or 400 gpm, to cover the exposure. So, the final fire flow for the Kimball example, with a fully involved first floor and exposures on sides B and D is:

    + First floor = 1700 gpm

    + Second floor exposure = 400 gpm

    + Third floor exposure = 400 gpm

    + Side B exposure = 400 gpm

    + Side D exposure = 400 gpm

    + The exposures total 1600 gpm, and are called EC in the NFA equation

    + Total required fire flow is 3300 gpm.

    * Final NFA formula is NFF gallons per minute = ([(length x width)/3] + EC) x % involvement

    For grins, lets see what you need if the entire Kimball building is involved on your arrival:

    * First floor = 1700 gpm

    * Second floor = 1700 gpm

    * Third floor = 1700 gpm

    * Fire building requires 5100 gpm fire flow. Remember that the Kimball rule of thumb said you needed 4500 gpm.

    * No interior exposures, but Side B requires 25% of 5100 gpm, or 1300 gpm. So does the Side D exposure.

    So, if the Kimball building is fully involved with two exposures you will need 7700 gpm to handle the event.
    Last edited by MemphisE34a; 01-05-2009 at 03:17 PM.
    Robert Kramer
    cell #901-494-9437

    Management is making sure things are done right. Leadership is doing the right thing. The fire service needs alot more leaders and a lot less managers.

    "Everyone goes home" is the mantra for the pussification of the modern, American fire service.


    Comments made are my own. They do not represent the official position or opinion of the Fire Department or the City for which I am employed. In fact, they are normally exactly the opposite.

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    Forum Member len1582's Avatar
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    And you have to cut the roof

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    MembersZone Subscriber Edward Hartin's Avatar
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    Default NFA Fire Flow Formula

    The 3 in the NFA formula has nothing to do with the Iowa Formula or the Kimble Rule of Thumb. The NFA formula was developed as part of the Preparing for Incident Command (PIC) Commanding the Initial Response (CIR) courses (late 1980s) based on experienced fire officers opinions about the flow rate required for attack lines and backup lines for hypothetical fire scenarios. The flow rates estimated by these officers was divided by the area of involvement for each scenario with the resulting constant being 3.

    This formula is intended for offensive direct attack and it becomes increasingly inaccurate for levels of involvement above 50% and flows in excess of 1000 gpm.

    Unfortunately, the original intent and assumptions related to this useful fire flow estimation method have been forgotten and it is frequently used inappropriately.

    Information on the NFA formula was provided by AC Ed Burns, LA City Fire Department (ret) and DC Burt Phelps, Anne Arundel County Fire Department (ret) who were members of the course development team for PIC and CIR.

    The Iowa Fire Flow Formula on the other hand is intended for determining the flow rate for fire control using indirect attack from outside the involved compartment (cooling and displacement of oxygen by production of a large volume of steam). This formula is not appropriate for determining the flow rate required for direct attack.

    Cheers,
    Ed Hartin, MS, EFO, MIFireE

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    Gentlemen: Thanks very much for your responses!! Stay Safe!!

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    Quote Originally Posted by len1582 View Post
    And you have to cut the roof

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    all most every time I hear this formula given one thing every one leaves out is, after you take LXH and divide by 3 you spray that number for 30 seconds and than close the compartment (shut the door to the room) so you are not realy putting the number you get after your math but only 1/2 that much, (that is why it is such a bigger number than the Iowa one)

    Its not math you want to do at a fire, but during your preplan, you can get a number for the whole building (or floor) than divide by say 4 if its one room and 1/4 of the building or 2 if its 1/2 the building when you pull up and its on fire.

    I took "FIRE GROUND OPS" at NFA in 1989 that is what they taught at the time

  10. #10
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    Question Not the same as the NFA formula

    Quote Originally Posted by fireflymedic View Post
    all most every time I hear this formula given one thing every one leaves out is, after you take LXH and divide by 3 you spray that number for 30 seconds and than close the compartment (shut the door to the room) so you are not realy putting the number you get after your math but only 1/2 that much, (that is why it is such a bigger number than the Iowa one)
    I'd like to see that in print as it's clearly not the same thing we've been taught for many moons. Sounds like some fog nozzle enthusiast's modified formula.

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    Since I don't carry a slide rule and calculator with me on the rig I tend to use these slightly simpler formulas as taught by the University of Firefighting in Anytown U.S.A.:
    Big fire = Big water
    Small fire = Less water
    No fire = No water
    or:
    GPMs absorb BTUs, so keep adding GPMs in the right place until there are no more BTUs anyplace

    Whatever the formula always remember the surest way to solve the problem is to put the fire out. The sooner you do that the sooner everything else falls in line.

    Cogs

    Oh yeah almost forgot...
    Smoothbore = interior firefighting
    Fog nozzle = lawn sprinkler
    Last edited by FFPCogs08; 03-23-2009 at 10:48 AM.

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    Quote Originally Posted by FFPCogs08 View Post
    Since I don't carry a slide rule and calculator with me on the rig I tend to use these slightly simpler formulas as taught by the University of Firefighting in Anytown U.S.A.:
    Big fire = Big water
    Small fire = Less water
    No fire = No water
    or:
    GPMs absorb BTUs, so keep adding GPMs in the right place until there are no more BTUs anyplace

    Whatever the formula always remember the surest way to solve the problem is to put the fire out. The sooner you do that the sooner everything else falls in line.

    Cogs

    Oh yeah almost forgot...
    Smoothbore = interior firefighting
    Fog nozzle = lawn sprinkler
    Or you can use a manueverable sized attack line that will give you both big water and less water controlled by the nozzle choice and operator.

    We use 2 inch hose with a combo nozzle that flows to 200 gpm and it is backed by a slug tip that we flow at 300 gpm.

    But back to the topic. Fire flow formulas are great for pre-incident planning. OR for secondary lines. The truth is closer to what Cogs says for first lines pulled. It counts on the firefighter or officer having experience and fireground savy.

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