https://www.aikenstandard.com/news/changing-colors-to-keep-first-responders-safe/article_cfabc062-d317-11e8-b9c2-cbe20a1899d0.html

Savannah River National Laboratory uses color-changing compounds to identify potential radiation risks in emergency situations.

For even the best trained emergency responders, radiation events pose a particularly daunting risk. Radiation defies a responder’s five senses; without special equipment, personnel exposure is impossible to confirm, and safety is difficult to assure.