# fire flow problem

• 05-11-2010, 10:56 AM
wmanseau
fire flow problem
Looking for a way to calculate sq if I have 3500gpm@25% involvement. I know that fire flow= lxw/3 trying to find a way to see what the square footage would be to narrow the search of all the buildings in town?
• 05-13-2010, 07:37 AM
fire49
which book are you getting the formula from??
• 05-13-2010, 09:17 AM
fire49
http://www.melbourneflorida.org/form...s/ENG-1107.pdf

http://www.amwater.com/files/Fire Flow Calculator Worksheet.xls - 715.0KB

http://hcpid.org/permits/docs/FC_fir..._calcultor.pdf

found what you are using:::

http://www.firehouse.com/forums/arch...p/t-30682.html

The NFA quick-calculation formula is:
L x W/3 = fire flow for one floor at 100% involvement. Then as you determine the % of involvement upon arrival you can adjust what is needed at that point. For example if 100% involvement of the structure needs 1000 gpm then if the structure is 25% involved you would need 250 gpm. Or if two floors were 100% involved then it would be 2000 gpm.

Don't forget the NFA formula is not based upon fact or scientific evidence. It is based upon a survey of NFA students.

I know this about 8 years too late, but I stumbled upon your forum here and noticed some errors. It is a common misconception that the NFA fire flow formula is lxw/3 for 100% involvement. This is not correct. There are several parameters that go with the formula. The correct formula is lxw/3 for the size of the FIRE, not the size of the room. The formula was only designed for 50% involvement. Any more than 50% involvement, the formula degrades and is not accurate. In addition to this, the formula is for a non-accelerated fire (ordinary fire growth) with ordinary combustibles. This also means you need to be hitting the base of the fire. If you are doing all of this, your fire should go out within 1-2 min. So, if your pre-connect flows 200gpm, you should be able to put out 600 sq ft of ordinary combustibles, in a structure with less than 50% involvement in less than 2 min(Usually less than a minute). If you can't, you might not be hitting the base, or could be dealing with an accelerated fire.