Sprinkler Safety Margin

[midwestFCO]

I have seen info in other forums, but did not see anything in here.

From the best I can find, NFPA does not specify a required safety margin. In general, we have required 5% in the past but do not have anything in our ordinances that actually require it. I have seen from web searched that some jurisdictions require 10%. Just a general discussion point, not necessarily a question, what are others using as a safety margin and how have you required compliance in the past.

 

[cda]

10 psi by admendment

 

[Frank]

We require the use of Public Utilities Computer simulation that takes into account likely worst case time, tank levels, and season.

No safety factor required.

NFPA 13 "23.2.1.2 The volume and pressure of a public water supply shall be determined from waterflow test data. An adjustment to the waterflow test data to account for daily and seasonal fluctuations, possible interuption by flood or ice conditions, large simultanious industrial use, future demand on the water supply or any other condition that coudl affect the water supply shall be made as appropriate."

A simple 10% or 10 psi adjustment is not compliant particularly if you do a hydrant flow test late at night in a low use season. Engineering judgement is required.

 

[sdpaddler50]

In my area, socal, 10% is the norm. It will provide a good safety factor. I am very wary of computer generated tests. I have seen some of these that have been way off. If possible, for new construction, I always specify an actual flow test be done, preferably using a min 4 in hydrant outlet and flowing the total water demand for the project.

 

[steveray]

I believe our utilities prohibit going below 10 for fear of backsiphonage.....

 

[TheCommish]

in my area 20 psi minimum is the norm for fire engine pumping and when we do flow test the Q chart maximum available flow is at 20 psi residual

 

[Oldfieldguy]

10 PSI or 10% of the residual pressure, whichever is greater. All flow tests must be performed by our office using our equipment and we only accept our flow test results.

 

[Insurance Engineer]

10 PSI or 10% of the residual pressure, whichever is greater. All flow tests must be performed by our office using our equipment and we only accept our flow test results.

Love it, too bad not all offices take this extra step.

When you take into consideration they are designing a sprinkler system based on a gauge that is moving all over the place and picking a number. Then seeing a .98 psi safety cushion, how many jobs have you inspected that were installed exactly as the plans. All it takes a is a few extra elbows, T's and that .98 psi is no longer available.