Hazard Class 4 Dangerous When Wet 4-Digit Placards are required by 49 CFR 172.500 for highway, rail and water shipments of hazardous gases. Designed to meet DOT specifications for color and size, these 273mm x 273mm Dangerous When Wet Hazard Class 4 Placards may be used domestically as well as internationally. Our DOT placards are printed with durable UV inks that retard peeling, chipping and fading. Sold in packages of 25.