Cryogenic liquid tank trucks are designated as which cargo tank type?

• A. MC 331
• B. MC 312
• C. MC 307 / DOT 407
• D. MC 338

Answer: (D)

Cryogenic liquids must be kept at extremely low temperatures during transport, so the tank used for this service is specially built with double-wall insulation and a vacuum jacket to minimize heat transfer. It also includes a venting system to safely release boil-off gas as the liquid warms. This combination of insulation and controlled venting is what makes a cryogenic cargo tank distinct. In DOT/PHMSA terminology, that specific cargo-tank designation is MC 338, and it is used for transporting liquefied gases such as LNG, LOX, and LN2.

The other tank types are designed for liquids at higher or ambient temperatures and handle different pressure regimes, so they don’t provide the required insulation and cryogenic features.