It is the IMO rulebook for dangerous goods on a ship: how to class them, pack them, mark them and stow them. Each substance gets a class, a UN number and packing rules that the carrier and the terminal have to follow.
Class 8
Corrosive substances
Read the divisions below as a planning note. The class name tells you the main hazard. Packing, labels and where the box may sit on the ship still come from the IMDG Code.
Corrosive substances, class 8
Corrosive material
A corrosive is a liquid or solid that destroys the full thickness of human skin at the point of contact within the time the rules set. A liquid that eats through steel or aluminium at a severe rate is a corrosive too.
If real incidents or other data show the hazard is higher or lower than the laboratory test, the authority can change the classification. That includes a finding that the material is not regulated as a corrosive.
Skin-corrosion test data produced no later than 30 September 1995, using the 49 CFR 173 Appendix A method then in force, may still be used to classify a class 8 material and to assign its packing group.
At 454 kg (1,001 lb) gross weight or more, keep acids and bases apart even though the load chart does not list that split. Many corrosives react violently if they mix, and a spill that combines them needs extra care.
Questions
What a class does not settle
The class names the main hazard. Many goods also have a second one, such as a poisonous gas that can also burn. The papers and the placards show both, and the separation rules follow whichever hazard is stricter.
It belongs to the substance, or to a small group of similar substances, in the IMDG Dangerous Goods List. It is not one number for a whole class. Two boxes in the same class can have different numbers, packing groups and separation rules.