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 9
Miscellaneous dangerous substances and articles
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.
Miscellaneous, class 9
Miscellaneous
A material that is hazardous while it is being carried, but does not fit any other class. This class includes:
1. A material with an anaesthetic, noxious or similar property that could distract a flight-crew member enough to stop them doing their job; or
2. An elevated-temperature material, a hazardous substance, a hazardous waste, or a marine pollutant.
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.