Which designation is not a standard cargo tank designation?

• A. MC 312
• B. MC 400
• C. MC 331
• D. MC 338

Answer: (B)

Understanding how cargo tanks are designated helps you recognize the type of tanker you’re dealing with and the hazards you’d expect. The “MC” numbers are standardized designations used to identify a tank’s construction and service, set by the regulatory body for hazardous materials transport. Seeing MC-312, MC-331, or MC-338 tells you the tank is a recognized, design-specified tanker with known capabilities and hazards (non-pressurized corrosive liquids, LPG/non-cryogenic gas, or cryogenic liquids, respectively).

The designation MC-400 is not a standard cargo tank designation in PHMSA's widely used list. That means it wouldn’t correspond to a recognized tank design with defined pressures, temperatures, or materials of construction. In an inspect-and-respond context, spotting MC-400 would prompt you to verify the labeling or assume nonstandard/unclear equipment, whereas MC-312, MC-331, and MC-338 indicate specific, established tank types with known hazards to plan around.