How to Calc Performance-Based Visual Coverage?

4/11/2024

Looking to learn more about NFPA 72-2019 18.5.5.7 Performance-Based Alternative for visible notification.

Currently have a single 95cd wall-mounted horn-strobe approximately centered in an club office room that is approximately 41-ft by 34-ft, ceilings at 11-ft. The is a wall on the far end that is about 10-ft and 9-ft off the back wall and full height.

Table 18.5.5.5.1(a) is based off direct line of sight is my understanding, but would give a maximum room size of 50-ft x 50-ft.

Are there any resources available to help understand how to quantify the that 0.0375 lumen/ft² of illumination is met from reflection of surfaces behind the wall?

I'm sure there are more inputs that are needed but just looking to get started at how to attack the problem. Thanks in advance

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2 Comments

Dan Wilder

4/12/2024 07:37:27 am

Asked one of our FA guys on this...paraphrased as I am not a FA expert by any means. He has not provided any design based on wall reflectivity (there were references to areas like bathrooms, grocery stores, and parts stores where taller shelving typically obstructs line of sight).

The big issue with the performance-based design is that you'll need to field test installation with a lux meter to confirm requirements, even with the initial design calculations. This does nothing to address testing prior to tenant move in vs after, wall hung items, or a wall paint changes. It was also mentioned that no one will likely be sitting close enough to that corner to avoid the wall splash from the strobe.

Putting it on the left wall (the 34' one) would avoid most of the issues to begin with if available.

Many of the light MFG's provide lumen calculators (so much easier than my old Interior Design classes with the wall of Data Books and very tiny charts), but there are sites like the below that give a decent breakdown of formulas that may be useful in your request (RBG reflectivity, Darkness adjustment) then adding in the candela ranges from the specific device being used should get you very close.

https://www.cencepower.com/calculators/lumens-calculator

Ricardo Gonzales Jr

4/17/2024 11:02:57 am

It's possible, however on new construction it's not feasible to do. What is not known is the reflectivity of the paint or texture of the surface to reflect from. Simple Gloss on a smooth surface (seldom used) has a reflectivity rage from 70-85%. Other colors and textures are a lot lower and Semi-gloss or flat are simply in the 45-10% range. A lot easier and faster to add a device.
You'd have to get finished and a Fire Inspector decides to pull a meter to check and fail. I've had that done, but fortunately already had the devices in place. Easier to up a cd than add a device after the walls are finished.
As Dan stated before me, it would help to have the data from being an Interior Designer on hand.

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How to Calc Performance-Based Visual Coverage?

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