Class 4 Dangerous When Wet placards are required by law to be attached to hazardous materials shipment containers. Transporting Class 4 Dangerous When Wet hazardous materials by highway, railroad car, or cargo ship all necessitate proper identification on the containers and FlipPlacards.com provides a seamless solution for your placards needs. P.O.P. 49CFR part 172.500 regulations dictate that Class 4 Dangerous When Wet placards have a blue background, and bare a Class 4 numeral code in white text. Domestic and international shipments must be identified, and our placards are available in heavy duty polycoatedtagboard, which is water resistant. In addition, our self-adhesive vinyl placards mount easily on the surface, and peel off cleanly without having to remove any extra mess.