It's been too long since our last cheatsheet! Happy to bring about a new one to the table today.
One number that I seem to always need to crunch when laying out or reviewing fire sprinkler systems is the remote area adjustments, and the minimum width of a remote area. This applies specifically to the Density/Area method of Hydraulic Calculations in NFPA 13.
The formula is simple enough, w = 1.2 x sqrt(remote area size), where w is the minimum remote area width, and the remote area size is our final adjusted remote area that we're using.
Now for a routine calculation with a remote area of 1,500 sqft, I pretty much have the 46.5-foot area width memorized. Why is it important? The minimum width dimension tells us how wide our remote area needs to be. It's the dimension parallel to the branch lines, that captures as many sprinklers as it can along the branch line.
We take this minimum area, see how many sprinklers this area covers, and round up to the next whole sprinkler. It's our minimum width dimension that we're not allowed to reduce.
The 46.5-foot dimension might be easy enough to remember, but what about when a remote area is reduced using the quick-response reduction? What if the ceiling is also sloped?
Adjustments to the remote area are a process on their own, and each have implications for the minimum remote area width.
If you're using our Toolkit you already know we have tools that will compound the calculations for you. Our Quick-Response Reduction tool will adjust the remote area size based on the ceiling height, and our System Estimator tool will adjust for quick-response, sloped ceilings, dry and pre-action systems, high-temperature sprinklers, and more:
But, there are still times where I just want to quickly glance at my remote area size and translate that into a minimum width. That's what today's cheatsheet is all about.
This quick reference PDF helps address a few things:
I hope this one is helpful for you as conduct or review hydraulic calculations on your projects. Any tips, feedback or improvement ideas, be sure to let me know.
Thanks & have a great rest of your week!
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Joe Meyer, PE, is a Fire Protection Engineer out of St. Louis, Missouri who writes & develops resources for Fire Protection Professionals. See bio here: About