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NFPA 13 does not clearly identify a required safety factor for hydraulically designed fire sprinkler systems. What safety factors are commonly required by jurisdictions in your area?
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6 Comments
Kristen E Nich
8/29/2017 05:47:43 am
I am not sure what is the minimum required by most AHJs, but my company standard is 10 psi. On an existing system sometimes we will allow less if most of the existing piping is to remain.
David
8/29/2017 08:16:39 am
Our state has mandated a 10 psi safety factor.
Patrick Turner, P.E.
8/29/2017 08:19:29 am
NFPA 13 does not have a specific Safety Factor requirement because NFPA 13 has numerous safety factors built into the code. For instance, a standard spray upright or pendent is required to have 7 psi minimum, and is required to be no more than 7'-6" off of a wall horizontally (except for small room rule which allows up to 9'-0" off one wall in one direction only with other stipulations as well). At Oklahoma State University, they have a Sprinkler Lab and they tested a standard spray upright at 7 psi (put a gauge on the bull head side of a tee just before the upright and throttled the control valve supplying the sprinkler until the gauge read 7 psi). They then had a circular "ruler" on the floor from the center of the sprinkler and at 7 psi, the sprinkler sprayed up to 12 feet.
Barry
12/4/2018 09:21:20 pm
Thanks for your post. I am still amazed at the result of the study. I have a light hazard job, wood truss, that I will be lucky if I can find straight shot through the truss. It' looks like they put one half of the building offset or reversed. Need to survey more thoriughly. May need to add some 90s or 45 easier on the calcs. Cant get a hold of designer, till Friday.
Pete
8/29/2017 09:19:13 am
While safety factor is not required by NFPA 13, having a 5-10 psi is a good engineering practice to account for fluctuation and deterioration of the available water supply.
Marc
8/29/2017 06:04:54 pm
The 10 PSI seems to be common. I do a lot of freelance design all over the country and I've seen quite a range of requirements. Portland, OR degrades your flow test by 80%. Colorado requires a 10% minimum up to 100 PSI then a flat 10 PSI. Montgomery County, MD requires 20 PSI. As a rule, the 10% seems to be the most prevalent. I agree that NFPA is extremely conservative in it's requirements. I have observed several fire tests and the sprinklers usually out-perform expectations. There are a lot of factors that need to be considered when performing calculations. If an area has a dense population, and is built out, I'll use more of the available flow than an area that is relatively new and still has potential impact on the water supply. Potential for field revisions, upgrades such as tenant build-outs, all weigh in for consideration in the design of a fire protection system. Leave a Reply. |
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