Is there an established method to "prove" that we have enough fire flow for a project site?
I understand that the premise is to be sure we have the correct water supply available at the site. We do. I'm just interested in the technical 'design' portion to validate that concept.
Typically, I run a hydrant flow test at the site with nearby available hydrants. In this case, we're adding new hydrants but I understand the water supply nearby with recent testing.
Is a hydraulic graph (N^1.85) showing the available water supply at 20 psi sufficient to "prove" fire flow, or should I be conducting some type of calculation where I'm "flowing" hydrants?
We do sprinkler calculations all the time, but I'm just curious if I'm either overcomplicating things or if there's a process for fire flow that I'm not yet doing which I should be.
Trying to get things right. Thanks in advance.
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5/12/2022 06:14:09 am
5/12/2022 08:09:43 am
I have no problem conducting a flow test, but I guess my real question is if the flow test is not immediately adjacent to our site, then do I need to run a 'supply calc' to our site?
5/18/2022 01:27:04 pm
Correct answer, the proof is that the hydrant flows what is required. There are several ways of calculating the "Fire Flow" so make sure you know what method they are using before you start designing.
5/12/2022 08:07:27 am
A hydrant flow test is the only acceptable way to prove that there is sufficient flow and pressure. I have seen many projects where hydraulic modeling was not validated with a flow test.
5/12/2022 08:11:00 am
Right, and agreed. We have a flow test that is right at the location where we're going to tap the existing mains.
5/12/2022 08:09:54 am
This is the only way to test it for real: make hydrant tests as close as possible to your future connection, with possible friction loss calculations if the test is far from your connecting point.
5/12/2022 08:17:33 am
I'm so excited to write about something that Alex does not know explicitly !!!
5/12/2022 04:32:55 pm
Too funny! I absolutely agree that all new hydrants must be tested upon installation.
5/12/2022 08:28:12 am
Fire flow or available water supply is 'proven' empirically with a full flow test. Generally through either a hose monster or other contraption that relates velocity or pressure through a known orifice size into a "q" or volume per time.
5/12/2022 08:33:23 am
Run a calculation from the flow test pressure hydrant to the private hydrants onsite similarly to what you would do with a sprinkler remote area. But instead of adding a k-factor at the hydrants use a hose stream.
5/12/2022 10:07:49 am
Exactly what I was thinking. Thanks for the input Matt.
5/12/2022 10:54:44 am
Hey Matt, do you run the calculation just for internal validation or do you actually include them in your submittals for plan check?
5/12/2022 03:07:50 pm
Yes, I always verify fire flow onsite as part of the water supply verification regardless if it needs to be submitted. This helps to avoid surprises at the 11th hour.
5/12/2022 08:51:19 am
N1.85 graph. Old school and I still use it today!
Anthony C. Brown
5/12/2022 09:05:20 am
5/12/2022 10:10:01 am
Anthony, I think you're correct - but that's specific for fire sprinkler systems.
5/12/2022 10:08:50 am
Working with several AHJ's that do not allow fire hydrant flow tests, many of our designs start with the water model provided by the AHJ. In these cases, they run out the fire flows for a 2 hour duration and only ask what GPM we need (Any more I just say 2000 for anything light/ordinary and 3000 for anything storage or EH related unless a pump sizing at 150% exceeds these amounts). Their water modeling software kicks out a Static + Min/Max expected pressure for that flow duration and we use the lower value + a safety factor to do calculations. When we perform pump commissioning is about the only time we see the actual performance of the water supply and have not had any issues yet (the numbers come out better in most cases).
5/18/2022 11:40:39 am
Available water supply for fire protection system design and for calculating fire flow capability are two different things as noted in the above discussions. And as stated, there is no substitute for actual fire flow testing in the area of a subject building to determine the main capacity at 20 psi and the flow capabilities of fire hydrants and their associated piping configurations and service levels at different points in the distribution system. Part of an ISO rating evaluation measures the capabilities of the water distribution system within a community at different locations based on the Needed Fire Flow of different types of buildings whether they are receiving fire sprinkler insurance rating credit or not. Knowing this information is critical in FD preplanning and water supply operations.
5/23/2022 11:54:56 am
Typically, the required fire flow is established by local building codes. For the IFC (International Fire Code), this fire flow is based on building construction type and square footage. Or, the local AHJ may allow reductions in required fire flow if the building contains a fire sprinkler system.
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