Not only are the placards color coded, the numbers at the bottom mean something too. What do these numbers indicate?

The material's hazard class is specified with the number at the bottom of the placard. For example, class 1 is for explosives, class 2 is for gases, class 3 is for liquids, and class 4 is for flammable solids or dangerous when wet materials. There are nine classes in total.

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