49 CFR § 178.702 - IBC codes.
(a) Intermediate bulk container code designations consist of: two numerals specified in paragraph (a)(1) of this section; followed by the capital letter(s) specified in paragraph (a)(2) of this section; followed, when specified in an individual section, by a numeral indicating the category of intermediate bulk container.
(1) IBC code number designations are as follows:
|Type||For solids, discharged||For liquids|
|by gravity||Under pressure of more than 10 kPa (1.45 psig)|
(2) Intermediate bulk container code letter designations are as follows:
(b) For composite IBCs, two capital letters are used in sequence following the numeral indicating IBC design type. The first letter indicates the material of the IBC inner receptacle. The second letter indicates the material of the outer IBC. For example, 31HA1 is a composite IBC with a plastic inner receptacle and a steel outer packaging.