Special Tank Vehicles and Equipment (Compressed Gas, Cargo Tanks, Portable Tanks)
Some tanks are built for pressure, cold, or portability, and the exam checks whether you can identify what the equipment is and what it demands before loading.
The common designs
- Non-pressure liquid tanks (DOT 406 / MC 306): gasoline, diesel, and similar products; elliptical shells, top-loaded through domes.
- Low-pressure tanks (DOT 407 / MC 307): mild pressure service for materials that must be kept under slight pressure.
- Corrosive tanks (DOT 412 / MC 312): lined or stainless shells for acids and similar cargo.
- High-pressure gas tanks (MC 331): pressure vessels for materials such as propane and anhydrous ammonia.
- Cryogenic tanks (MC 338): insulated vessels for refrigerated liquids that vent as they warm.
What the equipment demands
Each of these carries a specification plate stating the design and the required test and inspection dates; an expired plate means no load. Compressed-gas tanks are never filled above 80 percent by volume - the vapor space is the expansion room. Cryogenic equipment must be checked for frost, icing, and relief-valve condition. Portable tanks and intermediate bulk containers must be secured to the vehicle, marked, and current on their tests; the exam treats an expired portable tank exactly like an expired cargo tank.
Worked example
A shipper offers to load propane into a portable tank whose specification plate shows the required periodic test is a year overdue. The tank looks sound and holds pressure. The correct answer is to refuse the load: the plate, not the appearance, authorizes filling, and no carrier may fill or haul a tank past its test date.
Traps that cost marks
- Judging a tank by appearance instead of the specification plate.
- Filling a gas tank "to the top" for range; the 80 percent limit exists for expansion.
- Assuming a portable tank is exempt because it is not permanently mounted.