What is a 'Cargo Tank' as defined by hazmat regulations?

A cargo tank is a bulk packaging — typically a large tanker trailer or tank truck — that holds liquid or gaseous hazardous materials. It is either permanently attached to a motor vehicle (like a gasoline tanker) or so dependent on the vehicle that it cannot be loaded or unloaded without the vehicle structure. Cargo tanks have their own subset of regulations: design specifications, periodic testing and inspection, marking requirements, and operating rules. A separate endorsement (N — tank vehicle, or X — combination of tank and hazmat) is often required for drivers operating these. Cargo tanks are responsible for some of the most catastrophic hazmat incidents in transportation history because a single failure can release a very large quantity of hazardous material.