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In the absence of a code-mandated requirement, what safety factor should we apply when evaluating fire flow, if you apply one at all? I am currently working on a building that has a code-required fire flow of 2,000 gpm at 20 psi. Using the MeyerFire Toolkit to evaluate the water supply, I found that the available fire flow is 2,004 gpm at 20 psi. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe 
12 Comments
Dan Wilder
1/7/2026 07:28:40 am
I may be off on this, but I have never heard of a safety factor requirement (mandated or self-imposed) as it relates to Fire Flow vs water supply. You just need to achieve that minimum flow at 20 PSI.
Anthony
1/7/2026 08:05:36 am
Is a safety factor required, no. But I'd be more worried about an additional flow test that charts out lower then your 2000@20. If you have a slow project and the FP designer needs a new test within 12 months of design and you don't have that then you'll have to figure it out. If you're in the planning stages now I would preceded as if you don't need to update the water flow and leave a contingency budget item and document the risk with your client - assuming you're on the consulting side.
Franck
1/7/2026 08:14:26 am
Normally, no safety margin requested.
Glenn Berger
1/7/2026 08:26:20 am
As others have said no safety factor is required. However I would ask for additional hydrant flow test to be conducted at various times of the time and then come back to check seasonal variances (ss Franck indicated). Be on watch for aging of the existing system which will lower the available conditions.
Craig Prahl
1/7/2026 08:37:41 am
One big thing I'd recommend is to verify that the 2000 gpm flow rate is actually attainable and available from the water supply. You can calculate anything but reality versus theoretical may vary. To your original question, there is no need to apply any kind of safety factor. There is no code or other requirement to do so. Also, for fire flow, there is a duration, be sure the water supply has adequate volume to provide for the required duration and that the local water purveyor is agreeable to that amount being depleted. In some jurisdictions water consumption is limited and large volume fire flows are expected to be provided via an owner provided water tank.
Jesse
1/7/2026 08:57:58 am
I'm generally not concerned about a safety factor for fire-flow. We want to ensure that the residual pressure is >20-psi, or higher if required by the AHJ
Mark Harris
1/7/2026 08:58:16 am
All great comments. Note Dan's comment that the sprinkler system calculations will need a safety margin (Reduce curve by 20% of static pressure in my area but that is up to your AHJ). So that supply may be fine for code fire flow it still could require a pump and possibly water tank some sprinkler systems. Depends on hazard and height of building. 60 PSI not much to start with.
Jay
1/7/2026 09:08:05 am
Appears you have a system demand of 1500gpm with a 500gpm outside hose allowance.
James Art, FPE
2/4/2026 02:58:08 pm
Good Point!
Jack G
1/7/2026 09:19:58 am
I m a believer in supply calcs. Because it’s “ real” based on the flows and pressures at the time of system ( entire MRA) activating .
David Kendrick
1/7/2026 10:15:43 am
Before any data is published it has been tested as sufficient and included with that is a built in safety factor.
Brett
1/7/2026 11:02:11 am
Others have already answered your question. If you don't mind some unsolicited advice I recommend getting another flow test done. That is a pretty steep drop off. See if they can do a two outlet test or open up another hydrant to get a higher flow from the test so you're not depending on such a big extrapolation. Leave a Reply. |
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