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NFPA 704-2017 hazard rating reading (legibility) distances

Question asked by mstromme on Apr 25, 2019

Our question deals with NFPA 704-2017, Standard System for the Identification of the Hazards of Materials for Emergency Response. We plotted the NFPA 704-2017 hazard rating reading (legibility) distances and hazard rating inches from Figure 9.1(c) on a line chart. We put hazard rating inches along the horizontal axis (or x axis), and we put reading distance feet along the vertical axis (or y axis). Then we proceeded to plot the line on the chart using the NFPA 704 inches and feet from Figure 9.1(c)………………………………..You would expect to see a straight line, meaning as you go up in inches, the reading distance (legibility) would go up proportionally. However, that’s not what you get when you plot the inches and feet from figure 9.1(c). For example, the figure says a 2 inch rating is readable (legible) at 75 feet, and you’d expect a 4 inch rating to be double that (or 150 feet), but the Figure says it is more readable than that and a 4 inch rating is readable at 200 feet. Likewise the figure says a 6 inch rating is readable at 300 feet, so you’d think a 3 inch rating would have a reading distance half that (or 150 feet), but the figure says it is not that readable, and a 3 inch rating is only readable (legible) up to 100 feet………………………………..QUESTION 1: How can we calculate the readability (legibility) in feet for hazard ratings that are between or greater than or less than the inches given in the figure? ………………………………..QUESTION 2: How do we calculate the reading (legibility) distance of a rating that is the following in height: (a) ¾ inch, (b) 1 and 7/16 inches, (c) 3 and 13/16 inches, (d) 4 and 11/16 inches, and (e) 7 and 1/16 inches. Each of these rating heights are between or outside of the inches listed in Figure 9.1(c).………………………………..QUESTION 3: Using our line chart, we see and can determine the slope of the line between the 1, 2, 3, 4, and 6 inch dimensions. Are we to use that slope to calculate the reading (legibility) distance for the rating heights in examples (a) to (e) above? ………………………………..QUESTION 4: What is the original source of the reading (legibility) distances in Figure 9.1(c)? ………………………………..QUESTION 5: Why do the legibility distances not form a straight line, based on the hazard rating inches, on our line chart? ………………………………..QUESTION 6: Why is a 4 inch rating (with a 200 feet legibility) twice as legible as a 3 inch rating (with 100 feet legibility)? Thank you so much for your time and expertise........................Chart attachment: The attached line chart shows the NFPA reading (legibility) distances and other trajectories. The dark blue line is the NFPA reading distances. The gray, orange, yellow, and light blue lines show other possible trajectories that we formulated.

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