fire flow vs. fire hydrant

[3cio]

Good day!
Iam a rookie and having difficulties on determining the location of the fire hydrant and deciding the fire flow for the building area.

I am using nfpa 1 for my reference of the needed fire flow. The scenario is that there are multiple buildings with a separation of 6m on each side for the vehicle road. all the building are dormitory building (as per nfpa 101) with 3 floors, 950sq.m each.Type II (111) construction and as per local code it doesn't require automatic sprinkler.

When computing for fire flow needed I add all the floor area (950*3) and use the table on nfpa 1 to determine the fire flow which is 2500 gpm (I used the full flow and not deducted the 75% max. as per the code because the building is not sprinklered) and equivalent to minimum of 3 hydrant with the max. spacing of 122 meters (also from table of nfpa 1).

does it means that every building i will put 3 hydrant each? or i could do space the hydrant that the 3 hydrant would cover 2 or more building?

because putting up the 3 hydrant each building is not economical.. please find attache file proposal. the max. radius per hydrant is 50m as per the local code.

also make a comment on my computation if it is valid.

**note. Is anyone has an experience using the ISO method when determining such case?



Thanks and more power

 

[chicopee]

Your fire insurance company should be able to tell you how much water in gpm and the water duration required for your classification. 2500 gpm seems high. I have guidelines at my office, however I am on the road for a while.

 

[3cio]

tnx man..

but as per the nfpa 1, that is the required fire flow needed. the fire flow is required flow rate at 20 psi used for fire fighting.

does it means it will be the capacity for my water tank and water supply? or it will be only an indication if the fire hydrant is sufficient within the building and hydraulic calculation would be the basis for the required pump capacity and water tank?

tnx again man.

 

[TravisMack]

If the water tank supplies hydrants, then it needs to meet that. If the pump supplies hydrants, then it needs to meet that demand as well. If your tank and pump only supply sprinklers, then size it based on sprinkler calculations.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[b1ueshift]

If you want to use a code to give you hydrant flows, you can use NFPA 1 or the IFC but the numbers in these standards are huge (like 2500 GPM as you've found). Not many people use these standards for urban design.

Usually in a case like this you would take your drawings to the local fire brigade (who will be the users of this system) and ask how much water they think the system should have. They might ask for 1000 gpm (which is about 4 hose streams).

 

[stookeyfpe]

Blueshift1

I disagree. The fire flow values in the IFC and NFPA 1 are commonly applied on a daily basis as these codes are adopted in about 98% of the governmental jurisdictions in the U.S. I know for a fact that questions regarding the proper application of the fire flow are answered on a weekly basis.

 

[b1ueshift]

That's interesting Stookeyfpe.

What do you mean by governmental jurisdiction? Is that a development funded by the federal government? Presumably every public utility is under some kind of government juristiction, probably the city or the county.

When I was working in the US as a sprinkler designer, most flow tests I saw tended to indicate water suppy typically around 1000-2000 gpm in the street. It could be less in a remote area with sparse development.

 

[DavidCR]

NFPA 1 asks for very high flows, I suppose that NFPA goes conservative when your design is solving the water demand by a particular system. In general local codes asks for different lower values, supposing there is a public system based on other local codes, intended to be used by fire service pumpers.

Our local authority (Costa Rica) would require in a case like this:

- One hydrant 2.5NH (most hyd. remote) of 500 gpm @ 85-100psi, or two remote close to each other hydrants 2.5NH 250 gpm @ 85-100psi.

And.
- Exterior and/or interior hose stations 1.5NH 100gpm @ 65-85 psi, with flow removable restrictors or pressure reduction valves.

 

[chicopee]

The reason for a water flow at not less than 20 psi is to not collapse the water lines when the fire engines are connected to the pumper connections of the fire hydrants.

 

[FIRESPRINK]

The fire flows are often looked at with disdain, however as previously posted they are at 20-psi!!! Also, there are a number of ways to reduce the fire flow through the IFC, again the fire flow is still only measured at 20-psi. Your building code must have adopted NFPA 1 in order to refer to it for your facility, the building and fire codes tell you what is required, the fire standards tell you how to do it. Also, the Fire Flow is an addendum to the BOCA and/or IFC, and some municipalities where I have installed systems failed to adopt the addendum. I just checked and the IBC-00 does not reference NFPA 1 in Chapter 35. I just checked another resource and my UFC-00's appendix III-A says fire flow at 20-psi and here is the exception "A reduction in required fire flow of up to 75%, as approved, is allowed when the building is provided with an approved automatic sprinkler system." My other books are in a different office, but feel certain they are all similar worded. As TM posted, there are even other exceptions when the tank is the sole supply.