Color-Difference Acceptance Criterion
Would PHMSA accept a quantitative colorimetric criterion as the threshold for "visible and distinct" — for example, a CIELAB color difference of ΔE*ab ≥ 30 (or another agency-preferred value) between the pre-trigger and post-trigger states, measured per ASTM D2244 or equivalent?
Patrick Shipman
shared this idea
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Andrew Leyder
commented
PHMSA has not established a specific agency-preferred quantitative colorimetric threshold for “visible and distinct” under this topic.
Offerors may propose a quantitative colorimetric criterion, such as a CIELAB color difference measured in accordance with ASTM D2244 or an equivalent method, if they believe it is appropriate. The proposal should explain and justify the selected threshold, including how it would be measured, repeated, and validated under conditions relevant to hazardous materials transportation.
Visible and distinct should be interpreted as a color change that is readily observable and meaningful to shippers, carriers, and emergency responders under realistic field conditions.