A New Blank N^1.85 Graph [Free PDF]

By Jocelyn Sarrantonio, PE | Technical Director at MeyerFire

NEW N^1.85 GRAPH PAPER
This time of year in many parts of the US, the kids are heading back to school and parents are gleefully filling their bags with all of their required school supplies.

It seems to be an appropriate time to also publish our own “school supply” for fire protection engineers: a new clean version of the N^1.85 graph paper. You can download it here:

BLANK N^1.85 GRAPH

If you took the new course released this week, FX131: Water Supply Evaluation, you may have already seen the new tool and understand why it is valuable.

For everyone else, N^1.85 graph paper is a very specific tool that helps us evaluate water supplies for fire protection.

USE OF THE GRAPH
There is a Water Supply Analysis tool in the MeyerFire toolkit that will also display water supply data nicely, but this is a blank graph that you can use for your analysis. The graph paper is a visual and analytical tool that helps evaluate the characteristics of your water supply, extrapolate to evaluate the fire flow available, visually see if the water supply can accommodate a particular demand, and estimate safety factors.

The graph is useful if you’re in the beginning stages of a project and answering a lot of “what-if” type questions, without having to calculate exponents over and over again, and it’s also helpful in the later stages of a project, when performing and evaluating sprinkler system hydraulic calculations.

The graph is special because it’s based on the flow value in the Hazen-Williams formula, which is raised to the 1.85 exponent. I’ve never tried to do this in Excel but there are lots of forums which make it seem awkward or impossible to work with uncommon exponents. So that’s why most of us rely on a few of the online tools out there, the Toolkit, or our hard copy graph paper we have tucked away.

If you’ve been in the fire protection industry a while, or even if you just started, someone may have handed you a heavily photocopied blank N^1.85 graph that you may have stuck in a binder or folder somewhere. I still have mine from when I first started! Back then I would literally plot my water supply with a pencil and mark off the sprinkler system demand to evaluate water supplies during a project.

Graphing a Water Supply

Later, I upgraded to a cleaner PDF on my Google Drive, and I would draw nice colored lines on the graph in Bluebeam to illustrate something about a water supply for a project I was working on.

​The trouble is, I was trying to have a technical conversation about the water supply for a site with a client who was about to spend millions of dollars, and my visual aid was lines on graph paper that looked like it was photocopied forty-seven times. It didn’t present my analysis in the best way.

It's not just graph paper, I’m sure you’ve come across other engineering tools like this. The engineering hasn’t changed, so there’s really been no need to update them, and I’m sure people take pride in using the same tools they have for their whole career. I’ve seen some Mechanical Engineers proudly pull out their ductulator that they’ve probably had for 15 years.

One of my coworkers also had a little metal chain nicknamed a “hosary” that was the perfect length to measure out the 200 foot standpipe hose travel distances if you had plotted your 1/8” scale floor plans. So instead of drawing a 200 ft radius, you could use the chain to jog around furniture and go in hallways when you were layout out fire hose valves.

Using a hosary on floor plans

I’m sure I’m also not the only one who has my old graphing calculator from high school or collects cool rulers. These kinds of tools are simple, tactile, and connect us to the craft of engineering.

That’s why I was excited to develop and share the new version of the N^1.85 graph paper.

It’s still the same tool at its core, just cleaner, sharper, and designed for engineers who want professional visuals alongside reliable analysis.

​Yes, I know at the end of the day it’s still just graph paper, but it’s a small way of bridging the old school engineering and the modern world. The concepts are the same, but it’s how we share, present, and teach them to the new folks entering the field that feels new. That’s what MeyerFire is all about, and I love being part of a movement that is teaching and providing useful tools to help engineers do their jobs.

What other tools would be useful for you to do your job?

Thanks for reading, and always remember to draw the curve before you draw conclusions.
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- Jocelyn