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Rated Fire Flow
Just a little something for you die hard fire hounds out there like myself. How about some equations on how you figure rated fire flow for a structure in your districts or whatever your apart of???
For intance ours is Length X Width
_______________ (Divided)
3
Now for us this gets you a 100% involvement and in the case only a 1/4% is involved we multiple the number of 100% you come up with on the above equation by .25 or so on with how ever much is being eaten and that gives us a pretty close figure of how many lines we need on the ground to supply the wet stuff on the hot stuff, make since?
In layman's terms or whatever terms you use lets say the fire is calling for 800 gpm for fire suppression (You know put the wet stuff on the hot stuff and your useing 2-1/2" hose and 2-1/2" adjustable gallonage nozzles which most nozzles and not all are capable of 250 gpm and not exlude friction loss of lets say we have 200' (foot) down on the ground per connection of 2-1/2" hose, with that being said approximately 10 psi per a 100' of hose of friction loss then we would need how many lines on the ground to handle this fire????
The answeer is approximately Four (4) preconnects of 200' of 2-1/2" hose with a nozzle capable of 250gpm on each preconnect with one heck of a water load feeding that truck....
Now this is just a short version we use and is very quick with that handy-dandy cell phone everyone has in there pocket that has a calculator in the tools part...
Now its your turn to give everyone food for thought and lets learn something new today!!!!!!
Replies to This Discussion
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Permalink Reply by FETC on
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Question? Because I would live to learn something new today... What if it is a multi-story home, like a 2 story or 3 story Victorian. How do you calculate when your formula is missing the height factor. Your formula is per floor in a one story dwelling only.
Something new would be that formula is not consistant with newer higher BTU producing synthetic fuels. It was designed off a 6000 BTU per lb formula (natural wood) verse todays fire seeing nearly 18,000 BTU per lb of fuel plastics and synthetics per NIST.
These have changed to size-up formula "unofficially" of course.
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Permalink Reply by CHIEF NORMAN on
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Well FETC we always figure on a 100% involvement and with your question you ask if it is a two or three story build you still do the same equations as above X 2 or 3 and in the case lets say you have the whole bottom floor on fire and that is calling for 800 gpm and only a 1/4% is on fire on the next sector then we would need 1050 gpm to produce enough water suppression for this fire. What is being done is the next floor is cut in 1/4's or 1/2's. But like I said if both floors are being eaten then your looking at 1600 gpm...When doing these kind of equations in your pre fire plans for your largest buildings in your district its very important to know how much water your going to need for 100% involvement and how much apparatus your going to need at that scene to extinguish that fire or keep it under control. And never forget to add in your friction loss you may have...
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Permalink Reply by Norm Tindell on
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Here's a link to a FIRE ENGINEERING article on the "Iowa Formula," a formula that gives you a quick flow estimate based on the cubic footage of the involved room alone...
http://www.firedistrict7.com/tpdffiles/nozleproject/FSeptembe1995IO...
The formula is cubic footage(involved) divided by 100 = GPM. The article goes into detail and cites variables.
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Permalink Reply by Ben Waller on
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The National Fire Academy formula (essentially what is posted above) was developed as a way to be more accurate and easier to calculate on scene than the Iowa formula.
The required fire flow for extinguishing 100% involvement is going to be a rare need.
The fire development curve helps explain why - either we kill the fire before the fire curve peaks or we won't generally have the water power and manpower on scene to extinguish the fire until after it consumes more than 50% of the fuel and becomes less exothermic.
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Now this is very interesting Ben!!!!
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Two additional options to help with this...
1) Get your local community to legislate automatic fire sprinklers for every new commercial building and every new multi-residential building larger than a duplex. Include any renovation that adds square footage or that renovates more than 50% of the structure to this and have the building codes and/or fire codes folks enforce it.
We did that, and it dramatically reduced the number of major fires we had over time. We simply don't have fires in large, unsprinklered buildings unless the sprinklers are out of service.
2) Consider that if you have that kind of major involvement, unless you have a very good hydrant system with all hydrants operational and a tremendous amount of apparatus and manpower, this structure is already lost with that much infolvement. It might be time to calculate the fire flow for nearby exposures, not counting the street on Side A and the empty parking lot on Side C. (hypothetically speaking)
Fire flow calculations are fine, but they are generally overkill for incipient fires and inadequate for the really big ones.
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Permalink Reply by Paul Montpetit on
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OK...Here's a little something that I learned during Fire Officer 1 class....If you are using CAFS then you take your Fire flow and reduce it by 25%....The studies indicate that CAFS will allow you to do that and still be correct in your assessment.....Thanks for bringing this back to an old dog....LOL
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Brother Ben Sorry I have to disagree with you on rated fire flow being over kill or inadequate. What I have found is if the right amount of water is supplied at the right time and convection occurs and operations is done to its up most potential then you as a fire chief have everything in your power to control that fire and extinguish it...Sprinkled buildings are great but remember not everyone lives by certain codes or ordinances and so on. So what we need to do is teach and all learn on the same principle. That way no matter where we go we can put what we know into action.
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Permalink Reply by Engineer k7 on
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One could also get the new calculater put out by Akron Brass to figure that out.
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Kudos K7!!!!!! And allot of companies out there provide a cheat sheet to carry in your pre fire plans or on your engines...Thank you sir....
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Pre-planning GPM for fully involved is seldom obtained and thus you catch it on the decay side as Ben mentioned.
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Pre-planning GPM for fully involved is seldom obtained. Do you mind explaining in-depth detail on (Y)? The reason (Y) I ask is because in so many cases when arson is transpired and comes out after or during your fire investigation and an accelerant was used what do you have? A fully involved fire which in some cases a back draft is formed and we all know what that does to firefighters. Now I don’t speak for everyone but my time is just as important at a scene as anyone else’s and the longer I'm there the higher my overhead and the more resources I’m using. If you pre plan for 100% involvement even thou we may or may not need it when we get on that scene don’t you thank its better to have those resources at your disposal as an officer then not planning ahead and get caught with you pants down so to speak and end up in court because this was not done. Does this make since?
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