The IMO ISO classification of container tanks has been replaced by the "T" code system.

"The 'T' code system indicates the test pressure of each type of container tank, its shell thickness, the pressure relief valve assembly and the arrangement of the bottom and top outlet. The "T" code instructions apply to dangerous goods in Classes 1 and 3 to 9. Class 2.

The "T" code system for tanks was introduced in 2001. It identifies container tanks from T1 to T22 and the types of cargo the tank is designed to carry.

ISO container tanks have to be manufactured according to strict international codes for transporting liquids by land or water.

The following model list is not an exhaustive list of IMO types, but indicates the original classification system.

IMO type 1 - hazardous tanks. These are tanks approved for the carriage of Class 1 and Class 3 substances when the flash point of the liquids is below 0 °C. Some examples of liquid types include explosives, flammable liquids, corrosive and toxic substances.

IMO Type 2 - low-hazard tanks. These are tanks approved for the carriage of Class 3 substances with a flash point between 0 and 61 °C. Examples of flammable liquids are diesel fuel and cooking oils.

IMO type 5 - gas tanks. These are tanks approved for the carriage of Class 2 refrigerated liquefied gases.

The abbreviation IMO stands for International Maritime Dangerous Goods Code.

"T" code system for ISO container tanks and specifications:

In addition to these ISO container tank types, there are 2 more - T50 and T70.

The T50 is a gas tank with a minimum test pressure of 57.6 bar. Under the IMO system, these tanks were classified IMO5.

T70 is a cryogenic container tank for the transport of liquefied gases. Under the IMO system these tanks were classified IMO7.